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8 <title>D-Bus Specification</title>
9 <releaseinfo>Version 0.22</releaseinfo>
10 <date>(not yet released)</date>
13 <firstname>Havoc</firstname>
14 <surname>Pennington</surname>
16 <orgname>Red Hat, Inc.</orgname>
18 <email>hp@pobox.com</email>
23 <firstname>Anders</firstname>
24 <surname>Carlsson</surname>
26 <orgname>CodeFactory AB</orgname>
28 <email>andersca@codefactory.se</email>
33 <firstname>Alexander</firstname>
34 <surname>Larsson</surname>
36 <orgname>Red Hat, Inc.</orgname>
38 <email>alexl@redhat.com</email>
43 <firstname>Sven</firstname>
44 <surname>Herzberg</surname>
46 <orgname>Imendio AB</orgname>
48 <email>sven@imendio.com</email>
53 <firstname>Simon</firstname>
54 <surname>McVittie</surname>
56 <orgname>Collabora Ltd.</orgname>
58 <email>simon.mcvittie@collabora.co.uk</email>
63 <firstname>David</firstname>
64 <surname>Zeuthen</surname>
66 <orgname>Red Hat, Inc.</orgname>
68 <email>davidz@redhat.com</email>
75 <revnumber>0.22</revnumber>
76 <date>not yet released (<ulink url='http://cgit.freedesktop.org/dbus/dbus/log/doc/dbus-specification.xml'>commit log</ulink>)</date>
77 <authorinitials></authorinitials>
78 <revremark></revremark>
81 <revnumber>0.21</revnumber>
82 <date>2013-04-25</date>
83 <authorinitials>smcv</authorinitials>
84 <revremark>allow Unicode noncharacters in UTF-8 (Unicode
85 Corrigendum #9)</revremark>
88 <revnumber>0.20</revnumber>
89 <date>22 February 2013</date>
90 <authorinitials>smcv, walters</authorinitials>
91 <revremark>reorganise for clarity, remove false claims about
92 basic types, mention /o/fd/DBus</revremark>
95 <revnumber>0.19</revnumber>
96 <date>20 February 2012</date>
97 <authorinitials>smcv/lp</authorinitials>
98 <revremark>formally define unique connection names and well-known
99 bus names; document best practices for interface, bus, member and
100 error names, and object paths; document the search path for session
101 and system services on Unix; document the systemd transport</revremark>
104 <revnumber>0.18</revnumber>
105 <date>29 July 2011</date>
106 <authorinitials>smcv</authorinitials>
107 <revremark>define eavesdropping, unicast, broadcast; add eavesdrop
108 match keyword; promote type system to a top-level section</revremark>
111 <revnumber>0.17</revnumber>
112 <date>1 June 2011</date>
113 <authorinitials>smcv/davidz</authorinitials>
114 <revremark>define ObjectManager; reserve extra pseudo-type-codes used
115 by GVariant</revremark>
118 <revnumber>0.16</revnumber>
119 <date>11 April 2011</date>
120 <authorinitials></authorinitials>
121 <revremark>add path_namespace, arg0namespace; argNpath matches object
125 <revnumber>0.15</revnumber>
126 <date>3 November 2010</date>
127 <authorinitials></authorinitials>
128 <revremark></revremark>
131 <revnumber>0.14</revnumber>
132 <date>12 May 2010</date>
133 <authorinitials></authorinitials>
134 <revremark></revremark>
137 <revnumber>0.13</revnumber>
138 <date>23 Dezember 2009</date>
139 <authorinitials></authorinitials>
140 <revremark></revremark>
143 <revnumber>0.12</revnumber>
144 <date>7 November, 2006</date>
145 <authorinitials></authorinitials>
146 <revremark></revremark>
149 <revnumber>0.11</revnumber>
150 <date>6 February 2005</date>
151 <authorinitials></authorinitials>
152 <revremark></revremark>
155 <revnumber>0.10</revnumber>
156 <date>28 January 2005</date>
157 <authorinitials></authorinitials>
158 <revremark></revremark>
161 <revnumber>0.9</revnumber>
162 <date>7 Januar 2005</date>
163 <authorinitials></authorinitials>
164 <revremark></revremark>
167 <revnumber>0.8</revnumber>
168 <date>06 September 2003</date>
169 <authorinitials></authorinitials>
170 <revremark>First released document.</revremark>
175 <sect1 id="introduction">
176 <title>Introduction</title>
178 D-Bus is a system for low-overhead, easy to use
179 interprocess communication (IPC). In more detail:
183 D-Bus is <emphasis>low-overhead</emphasis> because it uses a
184 binary protocol, and does not have to convert to and from a text
185 format such as XML. Because D-Bus is intended for potentially
186 high-resolution same-machine IPC, not primarily for Internet IPC,
187 this is an interesting optimization. D-Bus is also designed to
188 avoid round trips and allow asynchronous operation, much like
194 D-Bus is <emphasis>easy to use</emphasis> because it works in terms
195 of <firstterm>messages</firstterm> rather than byte streams, and
196 automatically handles a lot of the hard IPC issues. Also, the D-Bus
197 library is designed to be wrapped in a way that lets developers use
198 their framework's existing object/type system, rather than learning
199 a new one specifically for IPC.
206 The base D-Bus protocol is a one-to-one (peer-to-peer or client-server)
207 protocol, specified in <xref linkend="message-protocol"/>. That is, it is
208 a system for one application to talk to a single other
209 application. However, the primary intended application of the protocol is the
210 D-Bus <firstterm>message bus</firstterm>, specified in <xref
211 linkend="message-bus"/>. The message bus is a special application that
212 accepts connections from multiple other applications, and forwards
217 Uses of D-Bus include notification of system changes (notification of when
218 a camera is plugged in to a computer, or a new version of some software
219 has been installed), or desktop interoperability, for example a file
220 monitoring service or a configuration service.
224 D-Bus is designed for two specific use cases:
228 A "system bus" for notifications from the system to user sessions,
229 and to allow the system to request input from user sessions.
234 A "session bus" used to implement desktop environments such as
239 D-Bus is not intended to be a generic IPC system for any possible
240 application, and intentionally omits many features found in other
241 IPC systems for this reason.
245 At the same time, the bus daemons offer a number of features not found in
246 other IPC systems, such as single-owner "bus names" (similar to X
247 selections), on-demand startup of services, and security policies.
248 In many ways, these features are the primary motivation for developing
249 D-Bus; other systems would have sufficed if IPC were the only goal.
253 D-Bus may turn out to be useful in unanticipated applications, but future
254 versions of this spec and the reference implementation probably will not
255 incorporate features that interfere with the core use cases.
259 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
260 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
261 document are to be interpreted as described in RFC 2119. However, the
262 document could use a serious audit to be sure it makes sense to do
263 so. Also, they are not capitalized.
266 <sect2 id="stability">
267 <title>Protocol and Specification Stability</title>
269 The D-Bus protocol is frozen (only compatible extensions are allowed) as
270 of November 8, 2006. However, this specification could still use a fair
271 bit of work to make interoperable reimplementation possible without
272 reference to the D-Bus reference implementation. Thus, this
273 specification is not marked 1.0. To mark it 1.0, we'd like to see
274 someone invest significant effort in clarifying the specification
275 language, and growing the specification to cover more aspects of the
276 reference implementation's behavior.
279 Until this work is complete, any attempt to reimplement D-Bus will
280 probably require looking at the reference implementation and/or asking
281 questions on the D-Bus mailing list about intended behavior.
282 Questions on the list are very welcome.
285 Nonetheless, this document should be a useful starting point and is
286 to our knowledge accurate, though incomplete.
292 <sect1 id="type-system">
293 <title>Type System</title>
296 D-Bus has a type system, in which values of various types can be
297 serialized into a sequence of bytes referred to as the
298 <firstterm>wire format</firstterm> in a standard way.
299 Converting a value from some other representation into the wire
300 format is called <firstterm>marshaling</firstterm> and converting
301 it back from the wire format is <firstterm>unmarshaling</firstterm>.
305 The D-Bus protocol does not include type tags in the marshaled data; a
306 block of marshaled values must have a known <firstterm>type
307 signature</firstterm>. The type signature is made up of zero or more
308 <firstterm id="term-single-complete-type">single complete
309 types</firstterm>, each made up of one or more
310 <firstterm>type codes</firstterm>.
314 A type code is an ASCII character representing the
315 type of a value. Because ASCII characters are used, the type signature
316 will always form a valid ASCII string. A simple string compare
317 determines whether two type signatures are equivalent.
321 A single complete type is a sequence of type codes that fully describes
322 one type: either a basic type, or a single fully-described container type.
323 A single complete type is a basic type code, a variant type code,
324 an array with its element type, or a struct with its fields (all of which
325 are defined below). So the following signatures are not single complete
336 And the following signatures contain multiple complete types:
346 Note however that a single complete type may <emphasis>contain</emphasis>
347 multiple other single complete types, by containing a struct or dict
351 <sect2 id="basic-types">
352 <title>Basic types</title>
355 The simplest type codes are the <firstterm id="term-basic-type">basic
356 types</firstterm>, which are the types whose structure is entirely
357 defined by their 1-character type code. Basic types consist of
358 fixed types and string-like types.
362 The <firstterm id="term-fixed-type">fixed types</firstterm>
363 are basic types whose values have a fixed length, namely BYTE,
364 BOOLEAN, DOUBLE, UNIX_FD, and signed or unsigned integers of length
369 As a simple example, the type code for 32-bit integer (<literal>INT32</literal>) is
370 the ASCII character 'i'. So the signature for a block of values
371 containing a single <literal>INT32</literal> would be:
375 A block of values containing two <literal>INT32</literal> would have this signature:
382 The characteristics of the fixed types are listed in this table.
388 <entry>Conventional name</entry>
389 <entry>ASCII type-code</entry>
390 <entry>Encoding</entry>
395 <entry><literal>BYTE</literal></entry>
396 <entry><literal>y</literal> (121)</entry>
397 <entry>Unsigned 8-bit integer</entry>
400 <entry><literal>BOOLEAN</literal></entry>
401 <entry><literal>b</literal> (98)</entry>
402 <entry>Boolean value: 0 is false, 1 is true, any other value
403 allowed by the marshalling format is invalid</entry>
406 <entry><literal>INT16</literal></entry>
407 <entry><literal>n</literal> (110)</entry>
408 <entry>Signed (two's complement) 16-bit integer</entry>
411 <entry><literal>UINT16</literal></entry>
412 <entry><literal>q</literal> (113)</entry>
413 <entry>Unsigned 16-bit integer</entry>
416 <entry><literal>INT32</literal></entry>
417 <entry><literal>i</literal> (105)</entry>
418 <entry>Signed (two's complement) 32-bit integer</entry>
421 <entry><literal>UINT32</literal></entry>
422 <entry><literal>u</literal> (117)</entry>
423 <entry>Unsigned 32-bit integer</entry>
426 <entry><literal>INT64</literal></entry>
427 <entry><literal>x</literal> (120)</entry>
428 <entry>Signed (two's complement) 64-bit integer
429 (mnemonic: x and t are the first characters in "sixty" not
430 already used for something more common)</entry>
433 <entry><literal>UINT64</literal></entry>
434 <entry><literal>t</literal> (116)</entry>
435 <entry>Unsigned 64-bit integer</entry>
438 <entry><literal>DOUBLE</literal></entry>
439 <entry><literal>d</literal> (100)</entry>
440 <entry>IEEE 754 double-precision floating point</entry>
443 <entry><literal>UNIX_FD</literal></entry>
444 <entry><literal>h</literal> (104)</entry>
445 <entry>Unsigned 32-bit integer representing an index into an
446 out-of-band array of file descriptors, transferred via some
447 platform-specific mechanism (mnemonic: h for handle)</entry>
455 The <firstterm id="term-string-like-type">string-like types</firstterm>
456 are basic types with a variable length. The value of any string-like
457 type is conceptually 0 or more Unicode codepoints encoded in UTF-8,
458 none of which may be U+0000. The UTF-8 text must be validated
459 strictly: in particular, it must not contain overlong sequences
460 or codepoints above U+10FFFF.
464 Since D-Bus Specification version 0.21, in accordance with Unicode
465 Corrigendum #9, the "noncharacters" U+FDD0..U+FDEF, U+nFFFE and
466 U+nFFFF are allowed in UTF-8 strings (but note that older versions of
467 D-Bus rejected these noncharacters).
471 The marshalling formats for the string-like types all end with a
472 single zero (NUL) byte, but that byte is not considered to be part of
477 The characteristics of the string-like types are listed in this table.
483 <entry>Conventional name</entry>
484 <entry>ASCII type-code</entry>
485 <entry>Validity constraints</entry>
490 <entry><literal>STRING</literal></entry>
491 <entry><literal>s</literal> (115)</entry>
492 <entry>No extra constraints</entry>
495 <entry><literal>OBJECT_PATH</literal></entry>
496 <entry><literal>o</literal> (111)</entry>
498 <link linkend="message-protocol-marshaling-object-path">a
499 syntactically valid object path</link></entry>
502 <entry><literal>SIGNATURE</literal></entry>
503 <entry><literal>g</literal> (103)</entry>
505 <firstterm linkend="term-single-complete-type">single
506 complete types</firstterm></entry>
513 <sect3 id="message-protocol-marshaling-object-path">
514 <title>Valid Object Paths</title>
517 An object path is a name used to refer to an object instance.
518 Conceptually, each participant in a D-Bus message exchange may have
519 any number of object instances (think of C++ or Java objects) and each
520 such instance will have a path. Like a filesystem, the object
521 instances in an application form a hierarchical tree.
525 Object paths are often namespaced by starting with a reversed
526 domain name and containing an interface version number, in the
528 <link linkend="message-protocol-names-interface">interface
530 <link linkend="message-protocol-names-bus">well-known
532 This makes it possible to implement more than one service, or
533 more than one version of a service, in the same process,
534 even if the services share a connection but cannot otherwise
535 co-operate (for instance, if they are implemented by different
540 For instance, if the owner of <literal>example.com</literal> is
541 developing a D-Bus API for a music player, they might use the
542 hierarchy of object paths that start with
543 <literal>/com/example/MusicPlayer1</literal> for its objects.
547 The following rules define a valid object path. Implementations must
548 not send or accept messages with invalid object paths.
552 The path may be of any length.
557 The path must begin with an ASCII '/' (integer 47) character,
558 and must consist of elements separated by slash characters.
563 Each element must only contain the ASCII characters
569 No element may be the empty string.
574 Multiple '/' characters cannot occur in sequence.
579 A trailing '/' character is not allowed unless the
580 path is the root path (a single '/' character).
588 <sect3 id="message-protocol-marshaling-signature">
589 <title>Valid Signatures</title>
591 An implementation must not send or accept invalid signatures.
592 Valid signatures will conform to the following rules:
596 The signature is a list of single complete types.
597 Arrays must have element types, and structs must
598 have both open and close parentheses.
603 Only type codes, open and close parentheses, and open and
604 close curly brackets are allowed in the signature. The
605 <literal>STRUCT</literal> type code
606 is not allowed in signatures, because parentheses
607 are used instead. Similarly, the
608 <literal>DICT_ENTRY</literal> type code is not allowed in
609 signatures, because curly brackets are used instead.
614 The maximum depth of container type nesting is 32 array type
615 codes and 32 open parentheses. This implies that the maximum
616 total depth of recursion is 64, for an "array of array of array
617 of ... struct of struct of struct of ..." where there are 32
623 The maximum length of a signature is 255.
630 When signatures appear in messages, the marshalling format
631 guarantees that they will be followed by a nul byte (which can
632 be interpreted as either C-style string termination or the INVALID
633 type-code), but this is not conceptually part of the signature.
639 <sect2 id="container-types">
640 <title>Container types</title>
643 In addition to basic types, there are four <firstterm>container</firstterm>
644 types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, <literal>VARIANT</literal>,
645 and <literal>DICT_ENTRY</literal>.
649 <literal>STRUCT</literal> has a type code, ASCII character 'r', but this type
650 code does not appear in signatures. Instead, ASCII characters
651 '(' and ')' are used to mark the beginning and end of the struct.
652 So for example, a struct containing two integers would have this
657 Structs can be nested, so for example a struct containing
658 an integer and another struct:
662 The value block storing that struct would contain three integers; the
663 type signature allows you to distinguish "(i(ii))" from "((ii)i)" or
668 The <literal>STRUCT</literal> type code 'r' is not currently used in the D-Bus protocol,
669 but is useful in code that implements the protocol. This type code
670 is specified to allow such code to interoperate in non-protocol contexts.
674 Empty structures are not allowed; there must be at least one
675 type code between the parentheses.
679 <literal>ARRAY</literal> has ASCII character 'a' as type code. The array type code must be
680 followed by a <firstterm>single complete type</firstterm>. The single
681 complete type following the array is the type of each array element. So
682 the simple example is:
686 which is an array of 32-bit integers. But an array can be of any type,
687 such as this array-of-struct-with-two-int32-fields:
691 Or this array of array of integer:
698 <literal>VARIANT</literal> has ASCII character 'v' as its type code. A marshaled value of
699 type <literal>VARIANT</literal> will have the signature of a single complete type as part
700 of the <emphasis>value</emphasis>. This signature will be followed by a
701 marshaled value of that type.
705 Unlike a message signature, the variant signature can
706 contain only a single complete type. So "i", "ai"
707 or "(ii)" is OK, but "ii" is not. Use of variants may not
708 cause a total message depth to be larger than 64, including
709 other container types such as structures.
713 A <literal>DICT_ENTRY</literal> works exactly like a struct, but rather
714 than parentheses it uses curly braces, and it has more restrictions.
715 The restrictions are: it occurs only as an array element type; it has
716 exactly two single complete types inside the curly braces; the first
717 single complete type (the "key") must be a basic type rather than a
718 container type. Implementations must not accept dict entries outside of
719 arrays, must not accept dict entries with zero, one, or more than two
720 fields, and must not accept dict entries with non-basic-typed keys. A
721 dict entry is always a key-value pair.
725 The first field in the <literal>DICT_ENTRY</literal> is always the key.
726 A message is considered corrupt if the same key occurs twice in the same
727 array of <literal>DICT_ENTRY</literal>. However, for performance reasons
728 implementations are not required to reject dicts with duplicate keys.
732 In most languages, an array of dict entry would be represented as a
733 map, hash table, or dict object.
738 <title>Summary of types</title>
741 The following table summarizes the D-Bus types.
746 <entry>Conventional Name</entry>
748 <entry>Description</entry>
753 <entry><literal>INVALID</literal></entry>
754 <entry>0 (ASCII NUL)</entry>
755 <entry>Not a valid type code, used to terminate signatures</entry>
757 <entry><literal>BYTE</literal></entry>
758 <entry>121 (ASCII 'y')</entry>
759 <entry>8-bit unsigned integer</entry>
761 <entry><literal>BOOLEAN</literal></entry>
762 <entry>98 (ASCII 'b')</entry>
763 <entry>Boolean value, 0 is <literal>FALSE</literal> and 1 is <literal>TRUE</literal>. Everything else is invalid.</entry>
765 <entry><literal>INT16</literal></entry>
766 <entry>110 (ASCII 'n')</entry>
767 <entry>16-bit signed integer</entry>
769 <entry><literal>UINT16</literal></entry>
770 <entry>113 (ASCII 'q')</entry>
771 <entry>16-bit unsigned integer</entry>
773 <entry><literal>INT32</literal></entry>
774 <entry>105 (ASCII 'i')</entry>
775 <entry>32-bit signed integer</entry>
777 <entry><literal>UINT32</literal></entry>
778 <entry>117 (ASCII 'u')</entry>
779 <entry>32-bit unsigned integer</entry>
781 <entry><literal>INT64</literal></entry>
782 <entry>120 (ASCII 'x')</entry>
783 <entry>64-bit signed integer</entry>
785 <entry><literal>UINT64</literal></entry>
786 <entry>116 (ASCII 't')</entry>
787 <entry>64-bit unsigned integer</entry>
789 <entry><literal>DOUBLE</literal></entry>
790 <entry>100 (ASCII 'd')</entry>
791 <entry>IEEE 754 double</entry>
793 <entry><literal>STRING</literal></entry>
794 <entry>115 (ASCII 's')</entry>
795 <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated and contain no other nul bytes.</entry>
797 <entry><literal>OBJECT_PATH</literal></entry>
798 <entry>111 (ASCII 'o')</entry>
799 <entry>Name of an object instance</entry>
801 <entry><literal>SIGNATURE</literal></entry>
802 <entry>103 (ASCII 'g')</entry>
803 <entry>A type signature</entry>
805 <entry><literal>ARRAY</literal></entry>
806 <entry>97 (ASCII 'a')</entry>
809 <entry><literal>STRUCT</literal></entry>
810 <entry>114 (ASCII 'r'), 40 (ASCII '('), 41 (ASCII ')')</entry>
811 <entry>Struct; type code 114 'r' is reserved for use in
812 bindings and implementations to represent the general
813 concept of a struct, and must not appear in signatures
814 used on D-Bus.</entry>
816 <entry><literal>VARIANT</literal></entry>
817 <entry>118 (ASCII 'v') </entry>
818 <entry>Variant type (the type of the value is part of the value itself)</entry>
820 <entry><literal>DICT_ENTRY</literal></entry>
821 <entry>101 (ASCII 'e'), 123 (ASCII '{'), 125 (ASCII '}') </entry>
822 <entry>Entry in a dict or map (array of key-value pairs).
823 Type code 101 'e' is reserved for use in bindings and
824 implementations to represent the general concept of a
825 dict or dict-entry, and must not appear in signatures
826 used on D-Bus.</entry>
828 <entry><literal>UNIX_FD</literal></entry>
829 <entry>104 (ASCII 'h')</entry>
830 <entry>Unix file descriptor</entry>
833 <entry>(reserved)</entry>
834 <entry>109 (ASCII 'm')</entry>
835 <entry>Reserved for <ulink
836 url="https://bugs.freedesktop.org/show_bug.cgi?id=27857">a
837 'maybe' type compatible with the one in GVariant</ulink>,
838 and must not appear in signatures used on D-Bus until
839 specified here</entry>
842 <entry>(reserved)</entry>
843 <entry>42 (ASCII '*')</entry>
844 <entry>Reserved for use in bindings/implementations to
845 represent any <firstterm>single complete type</firstterm>,
846 and must not appear in signatures used on D-Bus.</entry>
849 <entry>(reserved)</entry>
850 <entry>63 (ASCII '?')</entry>
851 <entry>Reserved for use in bindings/implementations to
852 represent any <firstterm>basic type</firstterm>, and must
853 not appear in signatures used on D-Bus.</entry>
856 <entry>(reserved)</entry>
857 <entry>64 (ASCII '@'), 38 (ASCII '&'),
858 94 (ASCII '^')</entry>
859 <entry>Reserved for internal use by bindings/implementations,
860 and must not appear in signatures used on D-Bus.
861 GVariant uses these type-codes to encode calling
872 <sect1 id="message-protocol-marshaling">
873 <title>Marshaling (Wire Format)</title>
876 D-Bus defines a marshalling format for its type system, which is
877 used in D-Bus messages. This is not the only possible marshalling
878 format for the type system: for instance, GVariant (part of GLib)
879 re-uses the D-Bus type system but implements an alternative marshalling
884 <title>Byte order and alignment</title>
887 Given a type signature, a block of bytes can be converted into typed
888 values. This section describes the format of the block of bytes. Byte
889 order and alignment issues are handled uniformly for all D-Bus types.
893 A block of bytes has an associated byte order. The byte order
894 has to be discovered in some way; for D-Bus messages, the
895 byte order is part of the message header as described in
896 <xref linkend="message-protocol-messages"/>. For now, assume
897 that the byte order is known to be either little endian or big
902 Each value in a block of bytes is aligned "naturally," for example
903 4-byte values are aligned to a 4-byte boundary, and 8-byte values to an
904 8-byte boundary. To properly align a value, <firstterm>alignment
905 padding</firstterm> may be necessary. The alignment padding must always
906 be the minimum required padding to properly align the following value;
907 and it must always be made up of nul bytes. The alignment padding must
908 not be left uninitialized (it can't contain garbage), and more padding
909 than required must not be used.
913 As an exception to natural alignment, <literal>STRUCT</literal> and
914 <literal>DICT_ENTRY</literal> values are always aligned to an 8-byte
915 boundary, regardless of the alignments of their contents.
920 <title>Marshalling basic types</title>
923 To marshal and unmarshal fixed types, you simply read one value
924 from the data block corresponding to each type code in the signature.
925 All signed integer values are encoded in two's complement, DOUBLE
926 values are IEEE 754 double-precision floating-point, and BOOLEAN
927 values are encoded in 32 bits (of which only the least significant
932 The string-like types are all marshalled as a
933 fixed-length unsigned integer <varname>n</varname> giving the
934 length of the variable part, followed by <varname>n</varname>
935 nonzero bytes of UTF-8 text, followed by a single zero (nul) byte
936 which is not considered to be part of the text. The alignment
937 of the string-like type is the same as the alignment of
938 <varname>n</varname>.
942 For the STRING and OBJECT_PATH types, <varname>n</varname> is
943 encoded in 4 bytes, leading to 4-byte alignment.
944 For the SIGNATURE type, <varname>n</varname> is encoded as a single
945 byte. As a result, alignment padding is never required before a
951 <title>Marshalling containers</title>
954 Arrays are marshalled as a <literal>UINT32</literal>
955 <varname>n</varname> giving the length of the array data in bytes,
956 followed by alignment padding to the alignment boundary of the array
957 element type, followed by the <varname>n</varname> bytes of the
958 array elements marshalled in sequence. <varname>n</varname> does not
959 include the padding after the length, or any padding after the
964 For instance, if the current position in the message is a multiple
965 of 8 bytes and the byte-order is big-endian, an array containing only
966 the 64-bit integer 5 would be marshalled as:
969 00 00 00 08 <lineannotation>8 bytes of data</lineannotation>
970 00 00 00 00 <lineannotation>padding to 8-byte boundary</lineannotation>
971 00 00 00 00 00 00 00 05 <lineannotation>first element = 5</lineannotation>
976 Arrays have a maximum length defined to be 2 to the 26th power or
977 67108864. Implementations must not send or accept arrays exceeding this
982 Structs and dict entries are marshalled in the same way as their
983 contents, but their alignment is always to an 8-byte boundary,
984 even if their contents would normally be less strictly aligned.
988 Variants are marshalled as the <literal>SIGNATURE</literal> of
989 the contents (which must be a single complete type), followed by a
990 marshalled value with the type given by that signature. The
991 variant has the same 1-byte alignment as the signature, which means
992 that alignment padding before a variant is never needed.
993 Use of variants may not cause a total message depth to be larger
994 than 64, including other container types such as structures.
999 <title>Summary of D-Bus marshalling</title>
1002 Given all this, the types are marshaled on the wire as follows:
1007 <entry>Conventional Name</entry>
1008 <entry>Encoding</entry>
1009 <entry>Alignment</entry>
1014 <entry><literal>INVALID</literal></entry>
1015 <entry>Not applicable; cannot be marshaled.</entry>
1018 <entry><literal>BYTE</literal></entry>
1019 <entry>A single 8-bit byte.</entry>
1022 <entry><literal>BOOLEAN</literal></entry>
1023 <entry>As for <literal>UINT32</literal>, but only 0 and 1 are valid values.</entry>
1026 <entry><literal>INT16</literal></entry>
1027 <entry>16-bit signed integer in the message's byte order.</entry>
1030 <entry><literal>UINT16</literal></entry>
1031 <entry>16-bit unsigned integer in the message's byte order.</entry>
1034 <entry><literal>INT32</literal></entry>
1035 <entry>32-bit signed integer in the message's byte order.</entry>
1038 <entry><literal>UINT32</literal></entry>
1039 <entry>32-bit unsigned integer in the message's byte order.</entry>
1042 <entry><literal>INT64</literal></entry>
1043 <entry>64-bit signed integer in the message's byte order.</entry>
1046 <entry><literal>UINT64</literal></entry>
1047 <entry>64-bit unsigned integer in the message's byte order.</entry>
1050 <entry><literal>DOUBLE</literal></entry>
1051 <entry>64-bit IEEE 754 double in the message's byte order.</entry>
1054 <entry><literal>STRING</literal></entry>
1055 <entry>A <literal>UINT32</literal> indicating the string's
1056 length in bytes excluding its terminating nul, followed by
1057 non-nul string data of the given length, followed by a terminating nul
1064 <entry><literal>OBJECT_PATH</literal></entry>
1065 <entry>Exactly the same as <literal>STRING</literal> except the
1066 content must be a valid object path (see above).
1072 <entry><literal>SIGNATURE</literal></entry>
1073 <entry>The same as <literal>STRING</literal> except the length is a single
1074 byte (thus signatures have a maximum length of 255)
1075 and the content must be a valid signature (see above).
1081 <entry><literal>ARRAY</literal></entry>
1083 A <literal>UINT32</literal> giving the length of the array data in bytes, followed by
1084 alignment padding to the alignment boundary of the array element type,
1085 followed by each array element.
1091 <entry><literal>STRUCT</literal></entry>
1093 A struct must start on an 8-byte boundary regardless of the
1094 type of the struct fields. The struct value consists of each
1095 field marshaled in sequence starting from that 8-byte
1102 <entry><literal>VARIANT</literal></entry>
1104 The marshaled <literal>SIGNATURE</literal> of a single
1105 complete type, followed by a marshaled value with the type
1106 given in the signature.
1109 1 (alignment of the signature)
1112 <entry><literal>DICT_ENTRY</literal></entry>
1114 Identical to STRUCT.
1120 <entry><literal>UNIX_FD</literal></entry>
1121 <entry>32-bit unsigned integer in the message's byte
1122 order. The actual file descriptors need to be
1123 transferred out-of-band via some platform specific
1124 mechanism. On the wire, values of this type store the index to the
1125 file descriptor in the array of file descriptors that
1126 accompany the message.</entry>
1138 <sect1 id="message-protocol">
1139 <title>Message Protocol</title>
1142 A <firstterm>message</firstterm> consists of a
1143 <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you
1144 think of a message as a package, the header is the address, and the body
1145 contains the package contents. The message delivery system uses the header
1146 information to figure out where to send the message and how to interpret
1147 it; the recipient interprets the body of the message.
1151 The body of the message is made up of zero or more
1152 <firstterm>arguments</firstterm>, which are typed values, such as an
1153 integer or a byte array.
1157 Both header and body use the D-Bus <link linkend="type-system">type
1158 system</link> and format for serializing data.
1161 <sect2 id="message-protocol-messages">
1162 <title>Message Format</title>
1165 A message consists of a header and a body. The header is a block of
1166 values with a fixed signature and meaning. The body is a separate block
1167 of values, with a signature specified in the header.
1171 The length of the header must be a multiple of 8, allowing the body to
1172 begin on an 8-byte boundary when storing the entire message in a single
1173 buffer. If the header does not naturally end on an 8-byte boundary
1174 up to 7 bytes of nul-initialized alignment padding must be added.
1178 The message body need not end on an 8-byte boundary.
1182 The maximum length of a message, including header, header alignment padding,
1183 and body is 2 to the 27th power or 134217728. Implementations must not
1184 send or accept messages exceeding this size.
1188 The signature of the header is:
1192 Written out more readably, this is:
1194 BYTE, BYTE, BYTE, BYTE, UINT32, UINT32, ARRAY of STRUCT of (BYTE,VARIANT)
1199 These values have the following meanings:
1204 <entry>Value</entry>
1205 <entry>Description</entry>
1210 <entry>1st <literal>BYTE</literal></entry>
1211 <entry>Endianness flag; ASCII 'l' for little-endian
1212 or ASCII 'B' for big-endian. Both header and body are
1213 in this endianness.</entry>
1216 <entry>2nd <literal>BYTE</literal></entry>
1217 <entry><firstterm>Message type</firstterm>. Unknown types must be ignored.
1218 Currently-defined types are described below.
1222 <entry>3rd <literal>BYTE</literal></entry>
1223 <entry>Bitwise OR of flags. Unknown flags
1224 must be ignored. Currently-defined flags are described below.
1228 <entry>4th <literal>BYTE</literal></entry>
1229 <entry>Major protocol version of the sending application. If
1230 the major protocol version of the receiving application does not
1231 match, the applications will not be able to communicate and the
1232 D-Bus connection must be disconnected. The major protocol
1233 version for this version of the specification is 1.
1237 <entry>1st <literal>UINT32</literal></entry>
1238 <entry>Length in bytes of the message body, starting
1239 from the end of the header. The header ends after
1240 its alignment padding to an 8-boundary.
1244 <entry>2nd <literal>UINT32</literal></entry>
1245 <entry>The serial of this message, used as a cookie
1246 by the sender to identify the reply corresponding
1247 to this request. This must not be zero.
1251 <entry><literal>ARRAY</literal> of <literal>STRUCT</literal> of (<literal>BYTE</literal>,<literal>VARIANT</literal>)</entry>
1252 <entry>An array of zero or more <firstterm>header
1253 fields</firstterm> where the byte is the field code, and the
1254 variant is the field value. The message type determines
1255 which fields are required.
1263 <firstterm>Message types</firstterm> that can appear in the second byte
1269 <entry>Conventional name</entry>
1270 <entry>Decimal value</entry>
1271 <entry>Description</entry>
1276 <entry><literal>INVALID</literal></entry>
1278 <entry>This is an invalid type.</entry>
1281 <entry><literal>METHOD_CALL</literal></entry>
1283 <entry>Method call.</entry>
1286 <entry><literal>METHOD_RETURN</literal></entry>
1288 <entry>Method reply with returned data.</entry>
1291 <entry><literal>ERROR</literal></entry>
1293 <entry>Error reply. If the first argument exists and is a
1294 string, it is an error message.</entry>
1297 <entry><literal>SIGNAL</literal></entry>
1299 <entry>Signal emission.</entry>
1306 Flags that can appear in the third byte of the header:
1311 <entry>Conventional name</entry>
1312 <entry>Hex value</entry>
1313 <entry>Description</entry>
1318 <entry><literal>NO_REPLY_EXPECTED</literal></entry>
1320 <entry>This message does not expect method return replies or
1321 error replies; the reply can be omitted as an
1322 optimization. However, it is compliant with this specification
1323 to return the reply despite this flag and the only harm
1324 from doing so is extra network traffic.
1328 <entry><literal>NO_AUTO_START</literal></entry>
1330 <entry>The bus must not launch an owner
1331 for the destination name in response to this message.
1339 <sect3 id="message-protocol-header-fields">
1340 <title>Header Fields</title>
1343 The array at the end of the header contains <firstterm>header
1344 fields</firstterm>, where each field is a 1-byte field code followed
1345 by a field value. A header must contain the required header fields for
1346 its message type, and zero or more of any optional header
1347 fields. Future versions of this protocol specification may add new
1348 fields. Implementations must ignore fields they do not
1349 understand. Implementations must not invent their own header fields;
1350 only changes to this specification may introduce new header fields.
1354 Again, if an implementation sees a header field code that it does not
1355 expect, it must ignore that field, as it will be part of a new
1356 (but compatible) version of this specification. This also applies
1357 to known header fields appearing in unexpected messages, for
1358 example: if a signal has a reply serial it must be ignored
1359 even though it has no meaning as of this version of the spec.
1363 However, implementations must not send or accept known header fields
1364 with the wrong type stored in the field value. So for example a
1365 message with an <literal>INTERFACE</literal> field of type
1366 <literal>UINT32</literal> would be considered corrupt.
1370 Here are the currently-defined header fields:
1375 <entry>Conventional Name</entry>
1376 <entry>Decimal Code</entry>
1378 <entry>Required In</entry>
1379 <entry>Description</entry>
1384 <entry><literal>INVALID</literal></entry>
1387 <entry>not allowed</entry>
1388 <entry>Not a valid field name (error if it appears in a message)</entry>
1391 <entry><literal>PATH</literal></entry>
1393 <entry><literal>OBJECT_PATH</literal></entry>
1394 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1395 <entry>The object to send a call to,
1396 or the object a signal is emitted from.
1398 <literal>/org/freedesktop/DBus/Local</literal> is reserved;
1399 implementations should not send messages with this path,
1400 and the reference implementation of the bus daemon will
1401 disconnect any application that attempts to do so.
1405 <entry><literal>INTERFACE</literal></entry>
1407 <entry><literal>STRING</literal></entry>
1408 <entry><literal>SIGNAL</literal></entry>
1410 The interface to invoke a method call on, or
1411 that a signal is emitted from. Optional for
1412 method calls, required for signals.
1413 The special interface
1414 <literal>org.freedesktop.DBus.Local</literal> is reserved;
1415 implementations should not send messages with this
1416 interface, and the reference implementation of the bus
1417 daemon will disconnect any application that attempts to
1422 <entry><literal>MEMBER</literal></entry>
1424 <entry><literal>STRING</literal></entry>
1425 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1426 <entry>The member, either the method name or signal name.</entry>
1429 <entry><literal>ERROR_NAME</literal></entry>
1431 <entry><literal>STRING</literal></entry>
1432 <entry><literal>ERROR</literal></entry>
1433 <entry>The name of the error that occurred, for errors</entry>
1436 <entry><literal>REPLY_SERIAL</literal></entry>
1438 <entry><literal>UINT32</literal></entry>
1439 <entry><literal>ERROR</literal>, <literal>METHOD_RETURN</literal></entry>
1440 <entry>The serial number of the message this message is a reply
1441 to. (The serial number is the second <literal>UINT32</literal> in the header.)</entry>
1444 <entry><literal>DESTINATION</literal></entry>
1446 <entry><literal>STRING</literal></entry>
1447 <entry>optional</entry>
1448 <entry>The name of the connection this message is intended for.
1449 Only used in combination with the message bus, see
1450 <xref linkend="message-bus"/>.</entry>
1453 <entry><literal>SENDER</literal></entry>
1455 <entry><literal>STRING</literal></entry>
1456 <entry>optional</entry>
1457 <entry>Unique name of the sending connection.
1458 The message bus fills in this field so it is reliable; the field is
1459 only meaningful in combination with the message bus.</entry>
1462 <entry><literal>SIGNATURE</literal></entry>
1464 <entry><literal>SIGNATURE</literal></entry>
1465 <entry>optional</entry>
1466 <entry>The signature of the message body.
1467 If omitted, it is assumed to be the
1468 empty signature "" (i.e. the body must be 0-length).</entry>
1471 <entry><literal>UNIX_FDS</literal></entry>
1473 <entry><literal>UINT32</literal></entry>
1474 <entry>optional</entry>
1475 <entry>The number of Unix file descriptors that
1476 accompany the message. If omitted, it is assumed
1477 that no Unix file descriptors accompany the
1478 message. The actual file descriptors need to be
1479 transferred via platform specific mechanism
1480 out-of-band. They must be sent at the same time as
1481 part of the message itself. They may not be sent
1482 before the first byte of the message itself is
1483 transferred or after the last byte of the message
1493 <sect2 id="message-protocol-names">
1494 <title>Valid Names</title>
1496 The various names in D-Bus messages have some restrictions.
1499 There is a <firstterm>maximum name length</firstterm>
1500 of 255 which applies to bus names, interfaces, and members.
1502 <sect3 id="message-protocol-names-interface">
1503 <title>Interface names</title>
1505 Interfaces have names with type <literal>STRING</literal>, meaning that
1506 they must be valid UTF-8. However, there are also some
1507 additional restrictions that apply to interface names
1510 <listitem><para>Interface names are composed of 1 or more elements separated by
1511 a period ('.') character. All elements must contain at least
1515 <listitem><para>Each element must only contain the ASCII characters
1516 "[A-Z][a-z][0-9]_" and must not begin with a digit.
1520 <listitem><para>Interface names must contain at least one '.' (period)
1521 character (and thus at least two elements).
1524 <listitem><para>Interface names must not begin with a '.' (period) character.</para></listitem>
1525 <listitem><para>Interface names must not exceed the maximum name length.</para></listitem>
1530 Interface names should start with the reversed DNS domain name of
1531 the author of the interface (in lower-case), like interface names
1532 in Java. It is conventional for the rest of the interface name
1533 to consist of words run together, with initial capital letters
1534 on all words ("CamelCase"). Several levels of hierarchy can be used.
1535 It is also a good idea to include the major version of the interface
1536 in the name, and increment it if incompatible changes are made;
1537 this way, a single object can implement several versions of an
1538 interface in parallel, if necessary.
1542 For instance, if the owner of <literal>example.com</literal> is
1543 developing a D-Bus API for a music player, they might define
1544 interfaces called <literal>com.example.MusicPlayer1</literal>,
1545 <literal>com.example.MusicPlayer1.Track</literal> and
1546 <literal>com.example.MusicPlayer1.Seekable</literal>.
1550 D-Bus does not distinguish between the concepts that would be
1551 called classes and interfaces in Java: either can be identified on
1552 D-Bus by an interface name.
1555 <sect3 id="message-protocol-names-bus">
1556 <title>Bus names</title>
1558 Connections have one or more bus names associated with them.
1559 A connection has exactly one bus name that is a <firstterm>unique
1560 connection name</firstterm>. The unique connection name remains
1561 with the connection for its entire lifetime.
1562 A bus name is of type <literal>STRING</literal>,
1563 meaning that it must be valid UTF-8. However, there are also
1564 some additional restrictions that apply to bus names
1567 <listitem><para>Bus names that start with a colon (':')
1568 character are unique connection names. Other bus names
1569 are called <firstterm>well-known bus names</firstterm>.
1572 <listitem><para>Bus names are composed of 1 or more elements separated by
1573 a period ('.') character. All elements must contain at least
1577 <listitem><para>Each element must only contain the ASCII characters
1578 "[A-Z][a-z][0-9]_-". Only elements that are part of a unique
1579 connection name may begin with a digit, elements in
1580 other bus names must not begin with a digit.
1584 <listitem><para>Bus names must contain at least one '.' (period)
1585 character (and thus at least two elements).
1588 <listitem><para>Bus names must not begin with a '.' (period) character.</para></listitem>
1589 <listitem><para>Bus names must not exceed the maximum name length.</para></listitem>
1593 Note that the hyphen ('-') character is allowed in bus names but
1594 not in interface names.
1598 Like <link linkend="message-protocol-names-interface">interface
1599 names</link>, well-known bus names should start with the
1600 reversed DNS domain name of the author of the interface (in
1601 lower-case), and it is conventional for the rest of the well-known
1602 bus name to consist of words run together, with initial
1603 capital letters. As with interface names, including a version
1604 number in well-known bus names is a good idea; it's possible to
1605 have the well-known bus name for more than one version
1606 simultaneously if backwards compatibility is required.
1610 If a well-known bus name implies the presence of a "main" interface,
1611 that "main" interface is often given the same name as
1612 the well-known bus name, and situated at the corresponding object
1613 path. For instance, if the owner of <literal>example.com</literal>
1614 is developing a D-Bus API for a music player, they might define
1615 that any application that takes the well-known name
1616 <literal>com.example.MusicPlayer1</literal> should have an object
1617 at the object path <literal>/com/example/MusicPlayer1</literal>
1618 which implements the interface
1619 <literal>com.example.MusicPlayer1</literal>.
1622 <sect3 id="message-protocol-names-member">
1623 <title>Member names</title>
1625 Member (i.e. method or signal) names:
1627 <listitem><para>Must only contain the ASCII characters
1628 "[A-Z][a-z][0-9]_" and may not begin with a
1629 digit.</para></listitem>
1630 <listitem><para>Must not contain the '.' (period) character.</para></listitem>
1631 <listitem><para>Must not exceed the maximum name length.</para></listitem>
1632 <listitem><para>Must be at least 1 byte in length.</para></listitem>
1637 It is conventional for member names on D-Bus to consist of
1638 capitalized words with no punctuation ("camel-case").
1639 Method names should usually be verbs, such as
1640 <literal>GetItems</literal>, and signal names should usually be
1641 a description of an event, such as <literal>ItemsChanged</literal>.
1644 <sect3 id="message-protocol-names-error">
1645 <title>Error names</title>
1647 Error names have the same restrictions as interface names.
1651 Error names have the same naming conventions as interface
1652 names, and often contain <literal>.Error.</literal>; for instance,
1653 the owner of <literal>example.com</literal> might define the
1654 errors <literal>com.example.MusicPlayer.Error.FileNotFound</literal>
1655 and <literal>com.example.MusicPlayer.Error.OutOfMemory</literal>.
1656 The errors defined by D-Bus itself, such as
1657 <literal>org.freedesktop.DBus.Error.Failed</literal>, follow a
1663 <sect2 id="message-protocol-types">
1664 <title>Message Types</title>
1666 Each of the message types (<literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, <literal>ERROR</literal>, and
1667 <literal>SIGNAL</literal>) has its own expected usage conventions and header fields.
1668 This section describes these conventions.
1670 <sect3 id="message-protocol-types-method">
1671 <title>Method Calls</title>
1673 Some messages invoke an operation on a remote object. These are
1674 called method call messages and have the type tag <literal>METHOD_CALL</literal>. Such
1675 messages map naturally to methods on objects in a typical program.
1678 A method call message is required to have a <literal>MEMBER</literal> header field
1679 indicating the name of the method. Optionally, the message has an
1680 <literal>INTERFACE</literal> field giving the interface the method is a part of. In the
1681 absence of an <literal>INTERFACE</literal> field, if two interfaces on the same object have
1682 a method with the same name, it is undefined which of the two methods
1683 will be invoked. Implementations may also choose to return an error in
1684 this ambiguous case. However, if a method name is unique
1685 implementations must not require an interface field.
1688 Method call messages also include a <literal>PATH</literal> field
1689 indicating the object to invoke the method on. If the call is passing
1690 through a message bus, the message will also have a
1691 <literal>DESTINATION</literal> field giving the name of the connection
1692 to receive the message.
1695 When an application handles a method call message, it is required to
1696 return a reply. The reply is identified by a <literal>REPLY_SERIAL</literal> header field
1697 indicating the serial number of the <literal>METHOD_CALL</literal> being replied to. The
1698 reply can have one of two types; either <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>.
1701 If the reply has type <literal>METHOD_RETURN</literal>, the arguments to the reply message
1702 are the return value(s) or "out parameters" of the method call.
1703 If the reply has type <literal>ERROR</literal>, then an "exception" has been thrown,
1704 and the call fails; no return value will be provided. It makes
1705 no sense to send multiple replies to the same method call.
1708 Even if a method call has no return values, a <literal>METHOD_RETURN</literal>
1709 reply is required, so the caller will know the method
1710 was successfully processed.
1713 The <literal>METHOD_RETURN</literal> or <literal>ERROR</literal> reply message must have the <literal>REPLY_SERIAL</literal>
1717 If a <literal>METHOD_CALL</literal> message has the flag <literal>NO_REPLY_EXPECTED</literal>,
1718 then as an optimization the application receiving the method
1719 call may choose to omit the reply message (regardless of
1720 whether the reply would have been <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>).
1721 However, it is also acceptable to ignore the <literal>NO_REPLY_EXPECTED</literal>
1722 flag and reply anyway.
1725 Unless a message has the flag <literal>NO_AUTO_START</literal>, if the
1726 destination name does not exist then a program to own the destination
1727 name will be started before the message is delivered. The message
1728 will be held until the new program is successfully started or has
1729 failed to start; in case of failure, an error will be returned. This
1730 flag is only relevant in the context of a message bus, it is ignored
1731 during one-to-one communication with no intermediate bus.
1733 <sect4 id="message-protocol-types-method-apis">
1734 <title>Mapping method calls to native APIs</title>
1736 APIs for D-Bus may map method calls to a method call in a specific
1737 programming language, such as C++, or may map a method call written
1738 in an IDL to a D-Bus message.
1741 In APIs of this nature, arguments to a method are often termed "in"
1742 (which implies sent in the <literal>METHOD_CALL</literal>), or "out" (which implies
1743 returned in the <literal>METHOD_RETURN</literal>). Some APIs such as CORBA also have
1744 "inout" arguments, which are both sent and received, i.e. the caller
1745 passes in a value which is modified. Mapped to D-Bus, an "inout"
1746 argument is equivalent to an "in" argument, followed by an "out"
1747 argument. You can't pass things "by reference" over the wire, so
1748 "inout" is purely an illusion of the in-process API.
1751 Given a method with zero or one return values, followed by zero or more
1752 arguments, where each argument may be "in", "out", or "inout", the
1753 caller constructs a message by appending each "in" or "inout" argument,
1754 in order. "out" arguments are not represented in the caller's message.
1757 The recipient constructs a reply by appending first the return value
1758 if any, then each "out" or "inout" argument, in order.
1759 "in" arguments are not represented in the reply message.
1762 Error replies are normally mapped to exceptions in languages that have
1766 In converting from native APIs to D-Bus, it is perhaps nice to
1767 map D-Bus naming conventions ("FooBar") to native conventions
1768 such as "fooBar" or "foo_bar" automatically. This is OK
1769 as long as you can say that the native API is one that
1770 was specifically written for D-Bus. It makes the most sense
1771 when writing object implementations that will be exported
1772 over the bus. Object proxies used to invoke remote D-Bus
1773 objects probably need the ability to call any D-Bus method,
1774 and thus a magic name mapping like this could be a problem.
1777 This specification doesn't require anything of native API bindings;
1778 the preceding is only a suggested convention for consistency
1784 <sect3 id="message-protocol-types-signal">
1785 <title>Signal Emission</title>
1787 Unlike method calls, signal emissions have no replies.
1788 A signal emission is simply a single message of type <literal>SIGNAL</literal>.
1789 It must have three header fields: <literal>PATH</literal> giving the object
1790 the signal was emitted from, plus <literal>INTERFACE</literal> and <literal>MEMBER</literal> giving
1791 the fully-qualified name of the signal. The <literal>INTERFACE</literal> header is required
1792 for signals, though it is optional for method calls.
1796 <sect3 id="message-protocol-types-errors">
1797 <title>Errors</title>
1799 Messages of type <literal>ERROR</literal> are most commonly replies
1800 to a <literal>METHOD_CALL</literal>, but may be returned in reply
1801 to any kind of message. The message bus for example
1802 will return an <literal>ERROR</literal> in reply to a signal emission if
1803 the bus does not have enough memory to send the signal.
1806 An <literal>ERROR</literal> may have any arguments, but if the first
1807 argument is a <literal>STRING</literal>, it must be an error message.
1808 The error message may be logged or shown to the user
1813 <sect3 id="message-protocol-types-notation">
1814 <title>Notation in this document</title>
1816 This document uses a simple pseudo-IDL to describe particular method
1817 calls and signals. Here is an example of a method call:
1819 org.freedesktop.DBus.StartServiceByName (in STRING name, in UINT32 flags,
1820 out UINT32 resultcode)
1822 This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = StartServiceByName,
1823 <literal>METHOD_CALL</literal> arguments are <literal>STRING</literal> and <literal>UINT32</literal>, <literal>METHOD_RETURN</literal> argument
1824 is <literal>UINT32</literal>. Remember that the <literal>MEMBER</literal> field can't contain any '.' (period)
1825 characters so it's known that the last part of the name in
1826 the "IDL" is the member name.
1829 In C++ that might end up looking like this:
1831 unsigned int org::freedesktop::DBus::StartServiceByName (const char *name,
1832 unsigned int flags);
1834 or equally valid, the return value could be done as an argument:
1836 void org::freedesktop::DBus::StartServiceByName (const char *name,
1838 unsigned int *resultcode);
1840 It's really up to the API designer how they want to make
1841 this look. You could design an API where the namespace wasn't used
1842 in C++, using STL or Qt, using varargs, or whatever you wanted.
1845 Signals are written as follows:
1847 org.freedesktop.DBus.NameLost (STRING name)
1849 Signals don't specify "in" vs. "out" because only
1850 a single direction is possible.
1853 It isn't especially encouraged to use this lame pseudo-IDL in actual
1854 API implementations; you might use the native notation for the
1855 language you're using, or you might use COM or CORBA IDL, for example.
1860 <sect2 id="message-protocol-handling-invalid">
1861 <title>Invalid Protocol and Spec Extensions</title>
1864 For security reasons, the D-Bus protocol should be strictly parsed and
1865 validated, with the exception of defined extension points. Any invalid
1866 protocol or spec violations should result in immediately dropping the
1867 connection without notice to the other end. Exceptions should be
1868 carefully considered, e.g. an exception may be warranted for a
1869 well-understood idiosyncrasy of a widely-deployed implementation. In
1870 cases where the other end of a connection is 100% trusted and known to
1871 be friendly, skipping validation for performance reasons could also make
1872 sense in certain cases.
1876 Generally speaking violations of the "must" requirements in this spec
1877 should be considered possible attempts to exploit security, and violations
1878 of the "should" suggestions should be considered legitimate (though perhaps
1879 they should generate an error in some cases).
1883 The following extension points are built in to D-Bus on purpose and must
1884 not be treated as invalid protocol. The extension points are intended
1885 for use by future versions of this spec, they are not intended for third
1886 parties. At the moment, the only way a third party could extend D-Bus
1887 without breaking interoperability would be to introduce a way to negotiate new
1888 feature support as part of the auth protocol, using EXTENSION_-prefixed
1889 commands. There is not yet a standard way to negotiate features.
1893 In the authentication protocol (see <xref linkend="auth-protocol"/>) unknown
1894 commands result in an ERROR rather than a disconnect. This enables
1895 future extensions to the protocol. Commands starting with EXTENSION_ are
1896 reserved for third parties.
1901 The authentication protocol supports pluggable auth mechanisms.
1906 The address format (see <xref linkend="addresses"/>) supports new
1912 Messages with an unknown type (something other than
1913 <literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>,
1914 <literal>ERROR</literal>, <literal>SIGNAL</literal>) are ignored.
1915 Unknown-type messages must still be well-formed in the same way
1916 as the known messages, however. They still have the normal
1922 Header fields with an unknown or unexpected field code must be ignored,
1923 though again they must still be well-formed.
1928 New standard interfaces (with new methods and signals) can of course be added.
1938 <sect1 id="auth-protocol">
1939 <title>Authentication Protocol</title>
1941 Before the flow of messages begins, two applications must
1942 authenticate. A simple plain-text protocol is used for
1943 authentication; this protocol is a SASL profile, and maps fairly
1944 directly from the SASL specification. The message encoding is
1945 NOT used here, only plain text messages.
1948 In examples, "C:" and "S:" indicate lines sent by the client and
1949 server respectively.
1951 <sect2 id="auth-protocol-overview">
1952 <title>Protocol Overview</title>
1954 The protocol is a line-based protocol, where each line ends with
1955 \r\n. Each line begins with an all-caps ASCII command name containing
1956 only the character range [A-Z_], a space, then any arguments for the
1957 command, then the \r\n ending the line. The protocol is
1958 case-sensitive. All bytes must be in the ASCII character set.
1960 Commands from the client to the server are as follows:
1963 <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
1964 <listitem><para>CANCEL</para></listitem>
1965 <listitem><para>BEGIN</para></listitem>
1966 <listitem><para>DATA <data in hex encoding></para></listitem>
1967 <listitem><para>ERROR [human-readable error explanation]</para></listitem>
1968 <listitem><para>NEGOTIATE_UNIX_FD</para></listitem>
1971 From server to client are as follows:
1974 <listitem><para>REJECTED <space-separated list of mechanism names></para></listitem>
1975 <listitem><para>OK <GUID in hex></para></listitem>
1976 <listitem><para>DATA <data in hex encoding></para></listitem>
1977 <listitem><para>ERROR</para></listitem>
1978 <listitem><para>AGREE_UNIX_FD</para></listitem>
1982 Unofficial extensions to the command set must begin with the letters
1983 "EXTENSION_", to avoid conflicts with future official commands.
1984 For example, "EXTENSION_COM_MYDOMAIN_DO_STUFF".
1987 <sect2 id="auth-nul-byte">
1988 <title>Special credentials-passing nul byte</title>
1990 Immediately after connecting to the server, the client must send a
1991 single nul byte. This byte may be accompanied by credentials
1992 information on some operating systems that use sendmsg() with
1993 SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain
1994 sockets. However, the nul byte must be sent even on other kinds of
1995 socket, and even on operating systems that do not require a byte to be
1996 sent in order to transmit credentials. The text protocol described in
1997 this document begins after the single nul byte. If the first byte
1998 received from the client is not a nul byte, the server may disconnect
2002 A nul byte in any context other than the initial byte is an error;
2003 the protocol is ASCII-only.
2006 The credentials sent along with the nul byte may be used with the
2007 SASL mechanism EXTERNAL.
2010 <sect2 id="auth-command-auth">
2011 <title>AUTH command</title>
2013 If an AUTH command has no arguments, it is a request to list
2014 available mechanisms. The server must respond with a REJECTED
2015 command listing the mechanisms it understands, or with an error.
2018 If an AUTH command specifies a mechanism, and the server supports
2019 said mechanism, the server should begin exchanging SASL
2020 challenge-response data with the client using DATA commands.
2023 If the server does not support the mechanism given in the AUTH
2024 command, it must send either a REJECTED command listing the mechanisms
2025 it does support, or an error.
2028 If the [initial-response] argument is provided, it is intended for use
2029 with mechanisms that have no initial challenge (or an empty initial
2030 challenge), as if it were the argument to an initial DATA command. If
2031 the selected mechanism has an initial challenge and [initial-response]
2032 was provided, the server should reject authentication by sending
2036 If authentication succeeds after exchanging DATA commands,
2037 an OK command must be sent to the client.
2040 The first octet received by the server after the \r\n of the BEGIN
2041 command from the client must be the first octet of the
2042 authenticated/encrypted stream of D-Bus messages.
2045 If BEGIN is received by the server, the first octet received
2046 by the client after the \r\n of the OK command must be the
2047 first octet of the authenticated/encrypted stream of D-Bus
2051 <sect2 id="auth-command-cancel">
2052 <title>CANCEL Command</title>
2054 At any time up to sending the BEGIN command, the client may send a
2055 CANCEL command. On receiving the CANCEL command, the server must
2056 send a REJECTED command and abort the current authentication
2060 <sect2 id="auth-command-data">
2061 <title>DATA Command</title>
2063 The DATA command may come from either client or server, and simply
2064 contains a hex-encoded block of data to be interpreted
2065 according to the SASL mechanism in use.
2068 Some SASL mechanisms support sending an "empty string";
2069 FIXME we need some way to do this.
2072 <sect2 id="auth-command-begin">
2073 <title>BEGIN Command</title>
2075 The BEGIN command acknowledges that the client has received an
2076 OK command from the server, and that the stream of messages
2080 The first octet received by the server after the \r\n of the BEGIN
2081 command from the client must be the first octet of the
2082 authenticated/encrypted stream of D-Bus messages.
2085 <sect2 id="auth-command-rejected">
2086 <title>REJECTED Command</title>
2088 The REJECTED command indicates that the current authentication
2089 exchange has failed, and further exchange of DATA is inappropriate.
2090 The client would normally try another mechanism, or try providing
2091 different responses to challenges.
2093 Optionally, the REJECTED command has a space-separated list of
2094 available auth mechanisms as arguments. If a server ever provides
2095 a list of supported mechanisms, it must provide the same list
2096 each time it sends a REJECTED message. Clients are free to
2097 ignore all lists received after the first.
2100 <sect2 id="auth-command-ok">
2101 <title>OK Command</title>
2103 The OK command indicates that the client has been
2104 authenticated. The client may now proceed with negotiating
2105 Unix file descriptor passing. To do that it shall send
2106 NEGOTIATE_UNIX_FD to the server.
2109 Otherwise, the client must respond to the OK command by
2110 sending a BEGIN command, followed by its stream of messages,
2111 or by disconnecting. The server must not accept additional
2112 commands using this protocol after the BEGIN command has been
2113 received. Further communication will be a stream of D-Bus
2114 messages (optionally encrypted, as negotiated) rather than
2118 If a client sends BEGIN the first octet received by the client
2119 after the \r\n of the OK command must be the first octet of
2120 the authenticated/encrypted stream of D-Bus messages.
2123 The OK command has one argument, which is the GUID of the server.
2124 See <xref linkend="addresses"/> for more on server GUIDs.
2127 <sect2 id="auth-command-error">
2128 <title>ERROR Command</title>
2130 The ERROR command indicates that either server or client did not
2131 know a command, does not accept the given command in the current
2132 context, or did not understand the arguments to the command. This
2133 allows the protocol to be extended; a client or server can send a
2134 command present or permitted only in new protocol versions, and if
2135 an ERROR is received instead of an appropriate response, fall back
2136 to using some other technique.
2139 If an ERROR is sent, the server or client that sent the
2140 error must continue as if the command causing the ERROR had never been
2141 received. However, the the server or client receiving the error
2142 should try something other than whatever caused the error;
2143 if only canceling/rejecting the authentication.
2146 If the D-Bus protocol changes incompatibly at some future time,
2147 applications implementing the new protocol would probably be able to
2148 check for support of the new protocol by sending a new command and
2149 receiving an ERROR from applications that don't understand it. Thus the
2150 ERROR feature of the auth protocol is an escape hatch that lets us
2151 negotiate extensions or changes to the D-Bus protocol in the future.
2154 <sect2 id="auth-command-negotiate-unix-fd">
2155 <title>NEGOTIATE_UNIX_FD Command</title>
2157 The NEGOTIATE_UNIX_FD command indicates that the client
2158 supports Unix file descriptor passing. This command may only
2159 be sent after the connection is authenticated, i.e. after OK
2160 was received by the client. This command may only be sent on
2161 transports that support Unix file descriptor passing.
2164 On receiving NEGOTIATE_UNIX_FD the server must respond with
2165 either AGREE_UNIX_FD or ERROR. It shall respond the former if
2166 the transport chosen supports Unix file descriptor passing and
2167 the server supports this feature. It shall respond the latter
2168 if the transport does not support Unix file descriptor
2169 passing, the server does not support this feature, or the
2170 server decides not to enable file descriptor passing due to
2171 security or other reasons.
2174 <sect2 id="auth-command-agree-unix-fd">
2175 <title>AGREE_UNIX_FD Command</title>
2177 The AGREE_UNIX_FD command indicates that the server supports
2178 Unix file descriptor passing. This command may only be sent
2179 after the connection is authenticated, and the client sent
2180 NEGOTIATE_UNIX_FD to enable Unix file descriptor passing. This
2181 command may only be sent on transports that support Unix file
2185 On receiving AGREE_UNIX_FD the client must respond with BEGIN,
2186 followed by its stream of messages, or by disconnecting. The
2187 server must not accept additional commands using this protocol
2188 after the BEGIN command has been received. Further
2189 communication will be a stream of D-Bus messages (optionally
2190 encrypted, as negotiated) rather than this protocol.
2193 <sect2 id="auth-command-future">
2194 <title>Future Extensions</title>
2196 Future extensions to the authentication and negotiation
2197 protocol are possible. For that new commands may be
2198 introduced. If a client or server receives an unknown command
2199 it shall respond with ERROR and not consider this fatal. New
2200 commands may be introduced both before, and after
2201 authentication, i.e. both before and after the OK command.
2204 <sect2 id="auth-examples">
2205 <title>Authentication examples</title>
2209 <title>Example of successful magic cookie authentication</title>
2211 (MAGIC_COOKIE is a made up mechanism)
2213 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2219 <title>Example of finding out mechanisms then picking one</title>
2222 S: REJECTED KERBEROS_V4 SKEY
2223 C: AUTH SKEY 7ab83f32ee
2224 S: DATA 8799cabb2ea93e
2225 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2231 <title>Example of client sends unknown command then falls back to regular auth</title>
2235 C: AUTH MAGIC_COOKIE 3736343435313230333039
2241 <title>Example of server doesn't support initial auth mechanism</title>
2243 C: AUTH MAGIC_COOKIE 3736343435313230333039
2244 S: REJECTED KERBEROS_V4 SKEY
2245 C: AUTH SKEY 7ab83f32ee
2246 S: DATA 8799cabb2ea93e
2247 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2253 <title>Example of wrong password or the like followed by successful retry</title>
2255 C: AUTH MAGIC_COOKIE 3736343435313230333039
2256 S: REJECTED KERBEROS_V4 SKEY
2257 C: AUTH SKEY 7ab83f32ee
2258 S: DATA 8799cabb2ea93e
2259 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2261 C: AUTH SKEY 7ab83f32ee
2262 S: DATA 8799cabb2ea93e
2263 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2269 <title>Example of skey cancelled and restarted</title>
2271 C: AUTH MAGIC_COOKIE 3736343435313230333039
2272 S: REJECTED KERBEROS_V4 SKEY
2273 C: AUTH SKEY 7ab83f32ee
2274 S: DATA 8799cabb2ea93e
2277 C: AUTH SKEY 7ab83f32ee
2278 S: DATA 8799cabb2ea93e
2279 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2285 <title>Example of successful magic cookie authentication with successful negotiation of Unix FD passing</title>
2287 (MAGIC_COOKIE is a made up mechanism)
2289 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2291 C: NEGOTIATE_UNIX_FD
2297 <title>Example of successful magic cookie authentication with unsuccessful negotiation of Unix FD passing</title>
2299 (MAGIC_COOKIE is a made up mechanism)
2301 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2303 C: NEGOTIATE_UNIX_FD
2310 <sect2 id="auth-states">
2311 <title>Authentication state diagrams</title>
2314 This section documents the auth protocol in terms of
2315 a state machine for the client and the server. This is
2316 probably the most robust way to implement the protocol.
2319 <sect3 id="auth-states-client">
2320 <title>Client states</title>
2323 To more precisely describe the interaction between the
2324 protocol state machine and the authentication mechanisms the
2325 following notation is used: MECH(CHALL) means that the
2326 server challenge CHALL was fed to the mechanism MECH, which
2332 CONTINUE(RESP) means continue the auth conversation
2333 and send RESP as the response to the server;
2339 OK(RESP) means that after sending RESP to the server
2340 the client side of the auth conversation is finished
2341 and the server should return "OK";
2347 ERROR means that CHALL was invalid and could not be
2353 Both RESP and CHALL may be empty.
2357 The Client starts by getting an initial response from the
2358 default mechanism and sends AUTH MECH RESP, or AUTH MECH if
2359 the mechanism did not provide an initial response. If the
2360 mechanism returns CONTINUE, the client starts in state
2361 <emphasis>WaitingForData</emphasis>, if the mechanism
2362 returns OK the client starts in state
2363 <emphasis>WaitingForOK</emphasis>.
2367 The client should keep track of available mechanisms and
2368 which it mechanisms it has already attempted. This list is
2369 used to decide which AUTH command to send. When the list is
2370 exhausted, the client should give up and close the
2375 <title><emphasis>WaitingForData</emphasis></title>
2383 MECH(CHALL) returns CONTINUE(RESP) → send
2385 <emphasis>WaitingForData</emphasis>
2389 MECH(CHALL) returns OK(RESP) → send DATA
2390 RESP, goto <emphasis>WaitingForOK</emphasis>
2394 MECH(CHALL) returns ERROR → send ERROR
2395 [msg], goto <emphasis>WaitingForData</emphasis>
2403 Receive REJECTED [mechs] →
2404 send AUTH [next mech], goto
2405 WaitingForData or <emphasis>WaitingForOK</emphasis>
2410 Receive ERROR → send
2412 <emphasis>WaitingForReject</emphasis>
2417 Receive OK → send
2418 BEGIN, terminate auth
2419 conversation, authenticated
2424 Receive anything else → send
2426 <emphasis>WaitingForData</emphasis>
2434 <title><emphasis>WaitingForOK</emphasis></title>
2439 Receive OK → send BEGIN, terminate auth
2440 conversation, <emphasis>authenticated</emphasis>
2445 Receive REJECTED [mechs] → send AUTH [next mech],
2446 goto <emphasis>WaitingForData</emphasis> or
2447 <emphasis>WaitingForOK</emphasis>
2453 Receive DATA → send CANCEL, goto
2454 <emphasis>WaitingForReject</emphasis>
2460 Receive ERROR → send CANCEL, goto
2461 <emphasis>WaitingForReject</emphasis>
2467 Receive anything else → send ERROR, goto
2468 <emphasis>WaitingForOK</emphasis>
2476 <title><emphasis>WaitingForReject</emphasis></title>
2481 Receive REJECTED [mechs] → send AUTH [next mech],
2482 goto <emphasis>WaitingForData</emphasis> or
2483 <emphasis>WaitingForOK</emphasis>
2489 Receive anything else → terminate auth
2490 conversation, disconnect
2499 <sect3 id="auth-states-server">
2500 <title>Server states</title>
2503 For the server MECH(RESP) means that the client response
2504 RESP was fed to the the mechanism MECH, which returns one of
2509 CONTINUE(CHALL) means continue the auth conversation and
2510 send CHALL as the challenge to the client;
2516 OK means that the client has been successfully
2523 REJECTED means that the client failed to authenticate or
2524 there was an error in RESP.
2529 The server starts out in state
2530 <emphasis>WaitingForAuth</emphasis>. If the client is
2531 rejected too many times the server must disconnect the
2536 <title><emphasis>WaitingForAuth</emphasis></title>
2542 Receive AUTH → send REJECTED [mechs], goto
2543 <emphasis>WaitingForAuth</emphasis>
2549 Receive AUTH MECH RESP
2553 MECH not valid mechanism → send REJECTED
2555 <emphasis>WaitingForAuth</emphasis>
2559 MECH(RESP) returns CONTINUE(CHALL) → send
2561 <emphasis>WaitingForData</emphasis>
2565 MECH(RESP) returns OK → send OK, goto
2566 <emphasis>WaitingForBegin</emphasis>
2570 MECH(RESP) returns REJECTED → send REJECTED
2572 <emphasis>WaitingForAuth</emphasis>
2580 Receive BEGIN → terminate
2581 auth conversation, disconnect
2587 Receive ERROR → send REJECTED [mechs], goto
2588 <emphasis>WaitingForAuth</emphasis>
2594 Receive anything else → send
2596 <emphasis>WaitingForAuth</emphasis>
2605 <title><emphasis>WaitingForData</emphasis></title>
2613 MECH(RESP) returns CONTINUE(CHALL) → send
2615 <emphasis>WaitingForData</emphasis>
2619 MECH(RESP) returns OK → send OK, goto
2620 <emphasis>WaitingForBegin</emphasis>
2624 MECH(RESP) returns REJECTED → send REJECTED
2626 <emphasis>WaitingForAuth</emphasis>
2634 Receive BEGIN → terminate auth conversation,
2641 Receive CANCEL → send REJECTED [mechs], goto
2642 <emphasis>WaitingForAuth</emphasis>
2648 Receive ERROR → send REJECTED [mechs], goto
2649 <emphasis>WaitingForAuth</emphasis>
2655 Receive anything else → send ERROR, goto
2656 <emphasis>WaitingForData</emphasis>
2664 <title><emphasis>WaitingForBegin</emphasis></title>
2669 Receive BEGIN → terminate auth conversation,
2670 client authenticated
2676 Receive CANCEL → send REJECTED [mechs], goto
2677 <emphasis>WaitingForAuth</emphasis>
2683 Receive ERROR → send REJECTED [mechs], goto
2684 <emphasis>WaitingForAuth</emphasis>
2690 Receive anything else → send ERROR, goto
2691 <emphasis>WaitingForBegin</emphasis>
2701 <sect2 id="auth-mechanisms">
2702 <title>Authentication mechanisms</title>
2704 This section describes some new authentication mechanisms.
2705 D-Bus also allows any standard SASL mechanism of course.
2707 <sect3 id="auth-mechanisms-sha">
2708 <title>DBUS_COOKIE_SHA1</title>
2710 The DBUS_COOKIE_SHA1 mechanism is designed to establish that a client
2711 has the ability to read a private file owned by the user being
2712 authenticated. If the client can prove that it has access to a secret
2713 cookie stored in this file, then the client is authenticated.
2714 Thus the security of DBUS_COOKIE_SHA1 depends on a secure home
2718 Throughout this description, "hex encoding" must output the digits
2719 from a to f in lower-case; the digits A to F must not be used
2720 in the DBUS_COOKIE_SHA1 mechanism.
2723 Authentication proceeds as follows:
2727 The client sends the username it would like to authenticate
2733 The server sends the name of its "cookie context" (see below); a
2734 space character; the integer ID of the secret cookie the client
2735 must demonstrate knowledge of; a space character; then a
2736 randomly-generated challenge string, all of this hex-encoded into
2742 The client locates the cookie and generates its own
2743 randomly-generated challenge string. The client then concatenates
2744 the server's decoded challenge, a ":" character, its own challenge,
2745 another ":" character, and the cookie. It computes the SHA-1 hash
2746 of this composite string as a hex digest. It concatenates the
2747 client's challenge string, a space character, and the SHA-1 hex
2748 digest, hex-encodes the result and sends it back to the server.
2753 The server generates the same concatenated string used by the
2754 client and computes its SHA-1 hash. It compares the hash with
2755 the hash received from the client; if the two hashes match, the
2756 client is authenticated.
2762 Each server has a "cookie context," which is a name that identifies a
2763 set of cookies that apply to that server. A sample context might be
2764 "org_freedesktop_session_bus". Context names must be valid ASCII,
2765 nonzero length, and may not contain the characters slash ("/"),
2766 backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"),
2767 tab ("\t"), or period ("."). There is a default context,
2768 "org_freedesktop_general" that's used by servers that do not specify
2772 Cookies are stored in a user's home directory, in the directory
2773 <filename>~/.dbus-keyrings/</filename>. This directory must
2774 not be readable or writable by other users. If it is,
2775 clients and servers must ignore it. The directory
2776 contains cookie files named after the cookie context.
2779 A cookie file contains one cookie per line. Each line
2780 has three space-separated fields:
2784 The cookie ID number, which must be a non-negative integer and
2785 may not be used twice in the same file.
2790 The cookie's creation time, in UNIX seconds-since-the-epoch
2796 The cookie itself, a hex-encoded random block of bytes. The cookie
2797 may be of any length, though obviously security increases
2798 as the length increases.
2804 Only server processes modify the cookie file.
2805 They must do so with this procedure:
2809 Create a lockfile name by appending ".lock" to the name of the
2810 cookie file. The server should attempt to create this file
2811 using <literal>O_CREAT | O_EXCL</literal>. If file creation
2812 fails, the lock fails. Servers should retry for a reasonable
2813 period of time, then they may choose to delete an existing lock
2814 to keep users from having to manually delete a stale
2815 lock. <footnote><para>Lockfiles are used instead of real file
2816 locking <literal>fcntl()</literal> because real locking
2817 implementations are still flaky on network
2818 filesystems.</para></footnote>
2823 Once the lockfile has been created, the server loads the cookie
2824 file. It should then delete any cookies that are old (the
2825 timeout can be fairly short), or more than a reasonable
2826 time in the future (so that cookies never accidentally
2827 become permanent, if the clock was set far into the future
2828 at some point). If no recent keys remain, the
2829 server may generate a new key.
2834 The pruned and possibly added-to cookie file
2835 must be resaved atomically (using a temporary
2836 file which is rename()'d).
2841 The lock must be dropped by deleting the lockfile.
2847 Clients need not lock the file in order to load it,
2848 because servers are required to save the file atomically.
2853 <sect1 id="addresses">
2854 <title>Server Addresses</title>
2856 Server addresses consist of a transport name followed by a colon, and
2857 then an optional, comma-separated list of keys and values in the form key=value.
2858 Each value is escaped.
2862 <programlisting>unix:path=/tmp/dbus-test</programlisting>
2863 Which is the address to a unix socket with the path /tmp/dbus-test.
2866 Value escaping is similar to URI escaping but simpler.
2870 The set of optionally-escaped bytes is:
2871 <literal>[0-9A-Za-z_-/.\]</literal>. To escape, each
2872 <emphasis>byte</emphasis> (note, not character) which is not in the
2873 set of optionally-escaped bytes must be replaced with an ASCII
2874 percent (<literal>%</literal>) and the value of the byte in hex.
2875 The hex value must always be two digits, even if the first digit is
2876 zero. The optionally-escaped bytes may be escaped if desired.
2881 To unescape, append each byte in the value; if a byte is an ASCII
2882 percent (<literal>%</literal>) character then append the following
2883 hex value instead. It is an error if a <literal>%</literal> byte
2884 does not have two hex digits following. It is an error if a
2885 non-optionally-escaped byte is seen unescaped.
2889 The set of optionally-escaped bytes is intended to preserve address
2890 readability and convenience.
2894 A server may specify a key-value pair with the key <literal>guid</literal>
2895 and the value a hex-encoded 16-byte sequence. <xref linkend="uuids"/>
2896 describes the format of the <literal>guid</literal> field. If present,
2897 this UUID may be used to distinguish one server address from another. A
2898 server should use a different UUID for each address it listens on. For
2899 example, if a message bus daemon offers both UNIX domain socket and TCP
2900 connections, but treats clients the same regardless of how they connect,
2901 those two connections are equivalent post-connection but should have
2902 distinct UUIDs to distinguish the kinds of connection.
2906 The intent of the address UUID feature is to allow a client to avoid
2907 opening multiple identical connections to the same server, by allowing the
2908 client to check whether an address corresponds to an already-existing
2909 connection. Comparing two addresses is insufficient, because addresses
2910 can be recycled by distinct servers, and equivalent addresses may look
2911 different if simply compared as strings (for example, the host in a TCP
2912 address can be given as an IP address or as a hostname).
2916 Note that the address key is <literal>guid</literal> even though the
2917 rest of the API and documentation says "UUID," for historical reasons.
2921 [FIXME clarify if attempting to connect to each is a requirement
2922 or just a suggestion]
2923 When connecting to a server, multiple server addresses can be
2924 separated by a semi-colon. The library will then try to connect
2925 to the first address and if that fails, it'll try to connect to
2926 the next one specified, and so forth. For example
2927 <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
2932 <sect1 id="transports">
2933 <title>Transports</title>
2935 [FIXME we need to specify in detail each transport and its possible arguments]
2937 Current transports include: unix domain sockets (including
2938 abstract namespace on linux), launchd, systemd, TCP/IP, an executed subprocess and a debug/testing transport
2939 using in-process pipes. Future possible transports include one that
2940 tunnels over X11 protocol.
2943 <sect2 id="transports-unix-domain-sockets">
2944 <title>Unix Domain Sockets</title>
2946 Unix domain sockets can be either paths in the file system or on Linux
2947 kernels, they can be abstract which are similar to paths but
2948 do not show up in the file system.
2952 When a socket is opened by the D-Bus library it truncates the path
2953 name right before the first trailing Nul byte. This is true for both
2954 normal paths and abstract paths. Note that this is a departure from
2955 previous versions of D-Bus that would create sockets with a fixed
2956 length path name. Names which were shorter than the fixed length
2957 would be padded by Nul bytes.
2960 Unix domain sockets are not available on Windows.
2962 <sect3 id="transports-unix-domain-sockets-addresses">
2963 <title>Server Address Format</title>
2965 Unix domain socket addresses are identified by the "unix:" prefix
2966 and support the following key/value pairs:
2973 <entry>Values</entry>
2974 <entry>Description</entry>
2980 <entry>(path)</entry>
2981 <entry>path of the unix domain socket. If set, the "tmpdir" and "abstract" key must not be set.</entry>
2984 <entry>tmpdir</entry>
2985 <entry>(path)</entry>
2986 <entry>temporary directory in which a socket file with a random file name starting with 'dbus-' will be created by the server. This key can only be used in server addresses, not in client addresses. If set, the "path" and "abstract" key must not be set.</entry>
2989 <entry>abstract</entry>
2990 <entry>(string)</entry>
2991 <entry>unique string (path) in the abstract namespace. If set, the "path" or "tempdir" key must not be set.</entry>
2998 <sect2 id="transports-launchd">
2999 <title>launchd</title>
3001 launchd is an open-source server management system that replaces init, inetd
3002 and cron on Apple Mac OS X versions 10.4 and above. It provides a common session
3003 bus address for each user and deprecates the X11-enabled D-Bus launcher on OSX.
3007 launchd allocates a socket and provides it with the unix path through the
3008 DBUS_LAUNCHD_SESSION_BUS_SOCKET variable in launchd's environment. Every process
3009 spawned by launchd (or dbus-daemon, if it was started by launchd) can access
3010 it through its environment.
3011 Other processes can query for the launchd socket by executing:
3012 $ launchctl getenv DBUS_LAUNCHD_SESSION_BUS_SOCKET
3013 This is normally done by the D-Bus client library so doesn't have to be done
3017 launchd is not available on Microsoft Windows.
3019 <sect3 id="transports-launchd-addresses">
3020 <title>Server Address Format</title>
3022 launchd addresses are identified by the "launchd:" prefix
3023 and support the following key/value pairs:
3030 <entry>Values</entry>
3031 <entry>Description</entry>
3037 <entry>(environment variable)</entry>
3038 <entry>path of the unix domain socket for the launchd created dbus-daemon.</entry>
3045 <sect2 id="transports-systemd">
3046 <title>systemd</title>
3048 systemd is an open-source server management system that
3049 replaces init and inetd on newer Linux systems. It supports
3050 socket activation. The D-Bus systemd transport is used to acquire
3051 socket activation file descriptors from systemd and use them
3052 as D-Bus transport when the current process is spawned by
3053 socket activation from it.
3056 The systemd transport accepts only one or more Unix domain or
3057 TCP streams sockets passed in via socket activation.
3060 The systemd transport is not available on non-Linux operating systems.
3063 The systemd transport defines no parameter keys.
3066 <sect2 id="transports-tcp-sockets">
3067 <title>TCP Sockets</title>
3069 The tcp transport provides TCP/IP based connections between clients
3070 located on the same or different hosts.
3073 Using tcp transport without any additional secure authentification mechanismus
3074 over a network is unsecure.
3077 Windows notes: Because of the tcp stack on Windows does not provide sending
3078 credentials over a tcp connection, the EXTERNAL authentification
3079 mechanismus does not work.
3081 <sect3 id="transports-tcp-sockets-addresses">
3082 <title>Server Address Format</title>
3084 TCP/IP socket addresses are identified by the "tcp:" prefix
3085 and support the following key/value pairs:
3092 <entry>Values</entry>
3093 <entry>Description</entry>
3099 <entry>(string)</entry>
3100 <entry>dns name or ip address</entry>
3104 <entry>(number)</entry>
3105 <entry>The tcp port the server will open. A zero value let the server
3106 choose a free port provided from the underlaying operating system.
3107 libdbus is able to retrieve the real used port from the server.
3111 <entry>family</entry>
3112 <entry>(string)</entry>
3113 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
3120 <sect2 id="transports-nonce-tcp-sockets">
3121 <title>Nonce-secured TCP Sockets</title>
3123 The nonce-tcp transport provides a secured TCP transport, using a
3124 simple authentication mechanism to ensure that only clients with read
3125 access to a certain location in the filesystem can connect to the server.
3126 The server writes a secret, the nonce, to a file and an incoming client
3127 connection is only accepted if the client sends the nonce right after
3128 the connect. The nonce mechanism requires no setup and is orthogonal to
3129 the higher-level authentication mechanisms described in the
3130 Authentication section.
3134 On start, the server generates a random 16 byte nonce and writes it
3135 to a file in the user's temporary directory. The nonce file location
3136 is published as part of the server's D-Bus address using the
3137 "noncefile" key-value pair.
3139 After an accept, the server reads 16 bytes from the socket. If the
3140 read bytes do not match the nonce stored in the nonce file, the
3141 server MUST immediately drop the connection.
3142 If the nonce match the received byte sequence, the client is accepted
3143 and the transport behaves like an unsecured tcp transport.
3146 After a successful connect to the server socket, the client MUST read
3147 the nonce from the file published by the server via the noncefile=
3148 key-value pair and send it over the socket. After that, the
3149 transport behaves like an unsecured tcp transport.
3151 <sect3 id="transports-nonce-tcp-sockets-addresses">
3152 <title>Server Address Format</title>
3154 Nonce TCP/IP socket addresses uses the "nonce-tcp:" prefix
3155 and support the following key/value pairs:
3162 <entry>Values</entry>
3163 <entry>Description</entry>
3169 <entry>(string)</entry>
3170 <entry>dns name or ip address</entry>
3174 <entry>(number)</entry>
3175 <entry>The tcp port the server will open. A zero value let the server
3176 choose a free port provided from the underlaying operating system.
3177 libdbus is able to retrieve the real used port from the server.
3181 <entry>family</entry>
3182 <entry>(string)</entry>
3183 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
3186 <entry>noncefile</entry>
3187 <entry>(path)</entry>
3188 <entry>file location containing the secret</entry>
3195 <sect2 id="transports-exec">
3196 <title>Executed Subprocesses on Unix</title>
3198 This transport forks off a process and connects its standard
3199 input and standard output with an anonymous Unix domain
3200 socket. This socket is then used for communication by the
3201 transport. This transport may be used to use out-of-process
3202 forwarder programs as basis for the D-Bus protocol.
3205 The forked process will inherit the standard error output and
3206 process group from the parent process.
3209 Executed subprocesses are not available on Windows.
3211 <sect3 id="transports-exec-addresses">
3212 <title>Server Address Format</title>
3214 Executed subprocess addresses are identified by the "unixexec:" prefix
3215 and support the following key/value pairs:
3222 <entry>Values</entry>
3223 <entry>Description</entry>
3229 <entry>(path)</entry>
3230 <entry>Path of the binary to execute, either an absolute
3231 path or a binary name that is searched for in the default
3232 search path of the OS. This corresponds to the first
3233 argument of execlp(). This key is mandatory.</entry>
3236 <entry>argv0</entry>
3237 <entry>(string)</entry>
3238 <entry>The program name to use when executing the
3239 binary. If omitted the same value as specified for path=
3240 will be used. This corresponds to the second argument of
3244 <entry>argv1, argv2, ...</entry>
3245 <entry>(string)</entry>
3246 <entry>Arguments to pass to the binary. This corresponds
3247 to the third and later arguments of execlp(). If a
3248 specific argvX is not specified no further argvY for Y > X
3249 are taken into account.</entry>
3257 <sect1 id="meta-transports">
3258 <title>Meta Transports</title>
3260 Meta transports are a kind of transport with special enhancements or
3261 behavior. Currently available meta transports include: autolaunch
3264 <sect2 id="meta-transports-autolaunch">
3265 <title>Autolaunch</title>
3266 <para>The autolaunch transport provides a way for dbus clients to autodetect
3267 a running dbus session bus and to autolaunch a session bus if not present.
3269 <sect3 id="meta-transports-autolaunch-addresses">
3270 <title>Server Address Format</title>
3272 Autolaunch addresses uses the "autolaunch:" prefix and support the
3273 following key/value pairs:
3280 <entry>Values</entry>
3281 <entry>Description</entry>
3286 <entry>scope</entry>
3287 <entry>(string)</entry>
3288 <entry>scope of autolaunch (Windows only)
3292 "*install-path" - limit session bus to dbus installation path.
3293 The dbus installation path is determined from the location of
3294 the shared dbus library. If the library is located in a 'bin'
3295 subdirectory the installation root is the directory above,
3296 otherwise the directory where the library lives is taken as
3299 <install-root>/bin/[lib]dbus-1.dll
3300 <install-root>/[lib]dbus-1.dll
3306 "*user" - limit session bus to the recent user.
3311 other values - specify dedicated session bus like "release",
3323 <sect3 id="meta-transports-autolaunch-windows-implementation">
3324 <title>Windows implementation</title>
3326 On start, the server opens a platform specific transport, creates a mutex
3327 and a shared memory section containing the related session bus address.
3328 This mutex will be inspected by the dbus client library to detect a
3329 running dbus session bus. The access to the mutex and the shared memory
3330 section are protected by global locks.
3333 In the recent implementation the autolaunch transport uses a tcp transport
3334 on localhost with a port choosen from the operating system. This detail may
3335 change in the future.
3338 Disclaimer: The recent implementation is in an early state and may not
3339 work in all cirumstances and/or may have security issues. Because of this
3340 the implementation is not documentated yet.
3347 <title>UUIDs</title>
3349 A working D-Bus implementation uses universally-unique IDs in two places.
3350 First, each server address has a UUID identifying the address,
3351 as described in <xref linkend="addresses"/>. Second, each operating
3352 system kernel instance running a D-Bus client or server has a UUID
3353 identifying that kernel, retrieved by invoking the method
3354 org.freedesktop.DBus.Peer.GetMachineId() (see <xref
3355 linkend="standard-interfaces-peer"/>).
3358 The term "UUID" in this document is intended literally, i.e. an
3359 identifier that is universally unique. It is not intended to refer to
3360 RFC4122, and in fact the D-Bus UUID is not compatible with that RFC.
3363 The UUID must contain 128 bits of data and be hex-encoded. The
3364 hex-encoded string may not contain hyphens or other non-hex-digit
3365 characters, and it must be exactly 32 characters long. To generate a
3366 UUID, the current reference implementation concatenates 96 bits of random
3367 data followed by the 32-bit time in seconds since the UNIX epoch (in big
3371 It would also be acceptable and probably better to simply generate 128
3372 bits of random data, as long as the random number generator is of high
3373 quality. The timestamp could conceivably help if the random bits are not
3374 very random. With a quality random number generator, collisions are
3375 extremely unlikely even with only 96 bits, so it's somewhat academic.
3378 Implementations should, however, stick to random data for the first 96 bits
3383 <sect1 id="standard-interfaces">
3384 <title>Standard Interfaces</title>
3386 See <xref linkend="message-protocol-types-notation"/> for details on
3387 the notation used in this section. There are some standard interfaces
3388 that may be useful across various D-Bus applications.
3390 <sect2 id="standard-interfaces-peer">
3391 <title><literal>org.freedesktop.DBus.Peer</literal></title>
3393 The <literal>org.freedesktop.DBus.Peer</literal> interface
3396 org.freedesktop.DBus.Peer.Ping ()
3397 org.freedesktop.DBus.Peer.GetMachineId (out STRING machine_uuid)
3401 On receipt of the <literal>METHOD_CALL</literal> message
3402 <literal>org.freedesktop.DBus.Peer.Ping</literal>, an application should do
3403 nothing other than reply with a <literal>METHOD_RETURN</literal> as
3404 usual. It does not matter which object path a ping is sent to. The
3405 reference implementation handles this method automatically.
3408 On receipt of the <literal>METHOD_CALL</literal> message
3409 <literal>org.freedesktop.DBus.Peer.GetMachineId</literal>, an application should
3410 reply with a <literal>METHOD_RETURN</literal> containing a hex-encoded
3411 UUID representing the identity of the machine the process is running on.
3412 This UUID must be the same for all processes on a single system at least
3413 until that system next reboots. It should be the same across reboots
3414 if possible, but this is not always possible to implement and is not
3416 It does not matter which object path a GetMachineId is sent to. The
3417 reference implementation handles this method automatically.
3420 The UUID is intended to be per-instance-of-the-operating-system, so may represent
3421 a virtual machine running on a hypervisor, rather than a physical machine.
3422 Basically if two processes see the same UUID, they should also see the same
3423 shared memory, UNIX domain sockets, process IDs, and other features that require
3424 a running OS kernel in common between the processes.
3427 The UUID is often used where other programs might use a hostname. Hostnames
3428 can change without rebooting, however, or just be "localhost" - so the UUID
3432 <xref linkend="uuids"/> explains the format of the UUID.
3436 <sect2 id="standard-interfaces-introspectable">
3437 <title><literal>org.freedesktop.DBus.Introspectable</literal></title>
3439 This interface has one method:
3441 org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data)
3445 Objects instances may implement
3446 <literal>Introspect</literal> which returns an XML description of
3447 the object, including its interfaces (with signals and methods), objects
3448 below it in the object path tree, and its properties.
3451 <xref linkend="introspection-format"/> describes the format of this XML string.
3454 <sect2 id="standard-interfaces-properties">
3455 <title><literal>org.freedesktop.DBus.Properties</literal></title>
3457 Many native APIs will have a concept of object <firstterm>properties</firstterm>
3458 or <firstterm>attributes</firstterm>. These can be exposed via the
3459 <literal>org.freedesktop.DBus.Properties</literal> interface.
3463 org.freedesktop.DBus.Properties.Get (in STRING interface_name,
3464 in STRING property_name,
3466 org.freedesktop.DBus.Properties.Set (in STRING interface_name,
3467 in STRING property_name,
3469 org.freedesktop.DBus.Properties.GetAll (in STRING interface_name,
3470 out DICT<STRING,VARIANT> props);
3474 It is conventional to give D-Bus properties names consisting of
3475 capitalized words without punctuation ("CamelCase"), like
3476 <link linkend="message-protocol-names-member">member names</link>.
3477 For instance, the GObject property
3478 <literal>connection-status</literal> or the Qt property
3479 <literal>connectionStatus</literal> could be represented on D-Bus
3480 as <literal>ConnectionStatus</literal>.
3483 Strictly speaking, D-Bus property names are not required to follow
3484 the same naming restrictions as member names, but D-Bus property
3485 names that would not be valid member names (in particular,
3486 GObject-style dash-separated property names) can cause interoperability
3487 problems and should be avoided.
3490 The available properties and whether they are writable can be determined
3491 by calling <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>,
3492 see <xref linkend="standard-interfaces-introspectable"/>.
3495 An empty string may be provided for the interface name; in this case,
3496 if there are multiple properties on an object with the same name,
3497 the results are undefined (picking one by according to an arbitrary
3498 deterministic rule, or returning an error, are the reasonable
3502 If one or more properties change on an object, the
3503 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3504 signal may be emitted (this signal was added in 0.14):
3508 org.freedesktop.DBus.Properties.PropertiesChanged (STRING interface_name,
3509 DICT<STRING,VARIANT> changed_properties,
3510 ARRAY<STRING> invalidated_properties);
3514 where <literal>changed_properties</literal> is a dictionary
3515 containing the changed properties with the new values and
3516 <literal>invalidated_properties</literal> is an array of
3517 properties that changed but the value is not conveyed.
3520 Whether the <literal>PropertiesChanged</literal> signal is
3521 supported can be determined by calling
3522 <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>. Note
3523 that the signal may be supported for an object but it may
3524 differ how whether and how it is used on a per-property basis
3525 (for e.g. performance or security reasons). Each property (or
3526 the parent interface) must be annotated with the
3527 <literal>org.freedesktop.DBus.Property.EmitsChangedSignal</literal>
3528 annotation to convey this (usually the default value
3529 <literal>true</literal> is sufficient meaning that the
3530 annotation does not need to be used). See <xref
3531 linkend="introspection-format"/> for details on this
3536 <sect2 id="standard-interfaces-objectmanager">
3537 <title><literal>org.freedesktop.DBus.ObjectManager</literal></title>
3539 An API can optionally make use of this interface for one or
3540 more sub-trees of objects. The root of each sub-tree implements
3541 this interface so other applications can get all objects,
3542 interfaces and properties in a single method call. It is
3543 appropriate to use this interface if users of the tree of
3544 objects are expected to be interested in all interfaces of all
3545 objects in the tree; a more granular API should be used if
3546 users of the objects are expected to be interested in a small
3547 subset of the objects, a small subset of their interfaces, or
3551 The method that applications can use to get all objects and
3552 properties is <literal>GetManagedObjects</literal>:
3556 org.freedesktop.DBus.ObjectManager.GetManagedObjects (out DICT<OBJPATH,DICT<STRING,DICT<STRING,VARIANT>>> objpath_interfaces_and_properties);
3560 The return value of this method is a dict whose keys are
3561 object paths. All returned object paths are children of the
3562 object path implementing this interface, i.e. their object
3563 paths start with the ObjectManager's object path plus '/'.
3566 Each value is a dict whose keys are interfaces names. Each
3567 value in this inner dict is the same dict that would be
3568 returned by the <link
3569 linkend="standard-interfaces-properties">org.freedesktop.DBus.Properties.GetAll()</link>
3570 method for that combination of object path and interface. If
3571 an interface has no properties, the empty dict is returned.
3574 Changes are emitted using the following two signals:
3578 org.freedesktop.DBus.ObjectManager.InterfacesAdded (OBJPATH object_path,
3579 DICT<STRING,DICT<STRING,VARIANT>> interfaces_and_properties);
3580 org.freedesktop.DBus.ObjectManager.InterfacesRemoved (OBJPATH object_path,
3581 ARRAY<STRING> interfaces);
3585 The <literal>InterfacesAdded</literal> signal is emitted when
3586 either a new object is added or when an existing object gains
3587 one or more interfaces. The
3588 <literal>InterfacesRemoved</literal> signal is emitted
3589 whenever an object is removed or it loses one or more
3590 interfaces. The second parameter of the
3591 <literal>InterfacesAdded</literal> signal contains a dict with
3592 the interfaces and properties (if any) that have been added to
3593 the given object path. Similarly, the second parameter of the
3594 <literal>InterfacesRemoved</literal> signal contains an array
3595 of the interfaces that were removed. Note that changes on
3596 properties on existing interfaces are not reported using this
3597 interface - an application should also monitor the existing <link
3598 linkend="standard-interfaces-properties">PropertiesChanged</link>
3599 signal on each object.
3602 Applications SHOULD NOT export objects that are children of an
3603 object (directly or otherwise) implementing this interface but
3604 which are not returned in the reply from the
3605 <literal>GetManagedObjects()</literal> method of this
3606 interface on the given object.
3609 The intent of the <literal>ObjectManager</literal> interface
3610 is to make it easy to write a robust client
3611 implementation. The trivial client implementation only needs
3612 to make two method calls:
3616 org.freedesktop.DBus.AddMatch (bus_proxy,
3617 "type='signal',name='org.example.App',path_namespace='/org/example/App'");
3618 objects = org.freedesktop.DBus.ObjectManager.GetManagedObjects (app_proxy);
3622 on the message bus and the remote application's
3623 <literal>ObjectManager</literal>, respectively. Whenever a new
3624 remote object is created (or an existing object gains a new
3625 interface), the <literal>InterfacesAdded</literal> signal is
3626 emitted, and since this signal contains all properties for the
3627 interfaces, no calls to the
3628 <literal>org.freedesktop.Properties</literal> interface on the
3629 remote object are needed. Additionally, since the initial
3630 <literal>AddMatch()</literal> rule already includes signal
3631 messages from the newly created child object, no new
3632 <literal>AddMatch()</literal> call is needed.
3637 The <literal>org.freedesktop.DBus.ObjectManager</literal>
3638 interface was added in version 0.17 of the D-Bus
3645 <sect1 id="introspection-format">
3646 <title>Introspection Data Format</title>
3648 As described in <xref linkend="standard-interfaces-introspectable"/>,
3649 objects may be introspected at runtime, returning an XML string
3650 that describes the object. The same XML format may be used in
3651 other contexts as well, for example as an "IDL" for generating
3652 static language bindings.
3655 Here is an example of introspection data:
3657 <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
3658 "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
3659 <node name="/com/example/sample_object">
3660 <interface name="com.example.SampleInterface">
3661 <method name="Frobate">
3662 <arg name="foo" type="i" direction="in"/>
3663 <arg name="bar" type="s" direction="out"/>
3664 <arg name="baz" type="a{us}" direction="out"/>
3665 <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
3667 <method name="Bazify">
3668 <arg name="bar" type="(iiu)" direction="in"/>
3669 <arg name="bar" type="v" direction="out"/>
3671 <method name="Mogrify">
3672 <arg name="bar" type="(iiav)" direction="in"/>
3674 <signal name="Changed">
3675 <arg name="new_value" type="b"/>
3677 <property name="Bar" type="y" access="readwrite"/>
3679 <node name="child_of_sample_object"/>
3680 <node name="another_child_of_sample_object"/>
3685 A more formal DTD and spec needs writing, but here are some quick notes.
3689 Only the root <node> element can omit the node name, as it's
3690 known to be the object that was introspected. If the root
3691 <node> does have a name attribute, it must be an absolute
3692 object path. If child <node> have object paths, they must be
3698 If a child <node> has any sub-elements, then they
3699 must represent a complete introspection of the child.
3700 If a child <node> is empty, then it may or may
3701 not have sub-elements; the child must be introspected
3702 in order to find out. The intent is that if an object
3703 knows that its children are "fast" to introspect
3704 it can go ahead and return their information, but
3705 otherwise it can omit it.
3710 The direction element on <arg> may be omitted,
3711 in which case it defaults to "in" for method calls
3712 and "out" for signals. Signals only allow "out"
3713 so while direction may be specified, it's pointless.
3718 The possible directions are "in" and "out",
3719 unlike CORBA there is no "inout"
3724 The possible property access flags are
3725 "readwrite", "read", and "write"
3730 Multiple interfaces can of course be listed for
3736 The "name" attribute on arguments is optional.
3742 Method, interface, property, and signal elements may have
3743 "annotations", which are generic key/value pairs of metadata.
3744 They are similar conceptually to Java's annotations and C# attributes.
3745 Well-known annotations:
3752 <entry>Values (separated by ,)</entry>
3753 <entry>Description</entry>
3758 <entry>org.freedesktop.DBus.Deprecated</entry>
3759 <entry>true,false</entry>
3760 <entry>Whether or not the entity is deprecated; defaults to false</entry>
3763 <entry>org.freedesktop.DBus.GLib.CSymbol</entry>
3764 <entry>(string)</entry>
3765 <entry>The C symbol; may be used for methods and interfaces</entry>
3768 <entry>org.freedesktop.DBus.Method.NoReply</entry>
3769 <entry>true,false</entry>
3770 <entry>If set, don't expect a reply to the method call; defaults to false.</entry>
3773 <entry>org.freedesktop.DBus.Property.EmitsChangedSignal</entry>
3774 <entry>true,invalidates,false</entry>
3777 If set to <literal>false</literal>, the
3778 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3780 linkend="standard-interfaces-properties"/> is not
3781 guaranteed to be emitted if the property changes.
3784 If set to <literal>invalidates</literal> the signal
3785 is emitted but the value is not included in the
3789 If set to <literal>true</literal> the signal is
3790 emitted with the value included.
3793 The value for the annotation defaults to
3794 <literal>true</literal> if the enclosing interface
3795 element does not specify the annotation. Otherwise it
3796 defaults to the value specified in the enclosing
3805 <sect1 id="message-bus">
3806 <title>Message Bus Specification</title>
3807 <sect2 id="message-bus-overview">
3808 <title>Message Bus Overview</title>
3810 The message bus accepts connections from one or more applications.
3811 Once connected, applications can exchange messages with other
3812 applications that are also connected to the bus.
3815 In order to route messages among connections, the message bus keeps a
3816 mapping from names to connections. Each connection has one
3817 unique-for-the-lifetime-of-the-bus name automatically assigned.
3818 Applications may request additional names for a connection. Additional
3819 names are usually "well-known names" such as
3820 "com.example.TextEditor". When a name is bound to a connection,
3821 that connection is said to <firstterm>own</firstterm> the name.
3824 The bus itself owns a special name,
3825 <literal>org.freedesktop.DBus</literal>, with an object
3826 located at <literal>/org/freedesktop/DBus</literal> that
3827 implements the <literal>org.freedesktop.DBus</literal>
3828 interface. This service allows applications to make
3829 administrative requests of the bus itself. For example,
3830 applications can ask the bus to assign a name to a connection.
3833 Each name may have <firstterm>queued owners</firstterm>. When an
3834 application requests a name for a connection and the name is already in
3835 use, the bus will optionally add the connection to a queue waiting for
3836 the name. If the current owner of the name disconnects or releases
3837 the name, the next connection in the queue will become the new owner.
3841 This feature causes the right thing to happen if you start two text
3842 editors for example; the first one may request "com.example.TextEditor",
3843 and the second will be queued as a possible owner of that name. When
3844 the first exits, the second will take over.
3848 Applications may send <firstterm>unicast messages</firstterm> to
3849 a specific recipient or to the message bus itself, or
3850 <firstterm>broadcast messages</firstterm> to all interested recipients.
3851 See <xref linkend="message-bus-routing"/> for details.
3855 <sect2 id="message-bus-names">
3856 <title>Message Bus Names</title>
3858 Each connection has at least one name, assigned at connection time and
3859 returned in response to the
3860 <literal>org.freedesktop.DBus.Hello</literal> method call. This
3861 automatically-assigned name is called the connection's <firstterm>unique
3862 name</firstterm>. Unique names are never reused for two different
3863 connections to the same bus.
3866 Ownership of a unique name is a prerequisite for interaction with
3867 the message bus. It logically follows that the unique name is always
3868 the first name that an application comes to own, and the last
3869 one that it loses ownership of.
3872 Unique connection names must begin with the character ':' (ASCII colon
3873 character); bus names that are not unique names must not begin
3874 with this character. (The bus must reject any attempt by an application
3875 to manually request a name beginning with ':'.) This restriction
3876 categorically prevents "spoofing"; messages sent to a unique name
3877 will always go to the expected connection.
3880 When a connection is closed, all the names that it owns are deleted (or
3881 transferred to the next connection in the queue if any).
3884 A connection can request additional names to be associated with it using
3885 the <literal>org.freedesktop.DBus.RequestName</literal> message. <xref
3886 linkend="message-protocol-names-bus"/> describes the format of a valid
3887 name. These names can be released again using the
3888 <literal>org.freedesktop.DBus.ReleaseName</literal> message.
3891 <sect3 id="bus-messages-request-name">
3892 <title><literal>org.freedesktop.DBus.RequestName</literal></title>
3896 UINT32 RequestName (in STRING name, in UINT32 flags)
3903 <entry>Argument</entry>
3905 <entry>Description</entry>
3911 <entry>STRING</entry>
3912 <entry>Name to request</entry>
3916 <entry>UINT32</entry>
3917 <entry>Flags</entry>
3927 <entry>Argument</entry>
3929 <entry>Description</entry>
3935 <entry>UINT32</entry>
3936 <entry>Return value</entry>
3943 This method call should be sent to
3944 <literal>org.freedesktop.DBus</literal> and asks the message bus to
3945 assign the given name to the method caller. Each name maintains a
3946 queue of possible owners, where the head of the queue is the primary
3947 or current owner of the name. Each potential owner in the queue
3948 maintains the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and
3949 DBUS_NAME_FLAG_DO_NOT_QUEUE settings from its latest RequestName
3950 call. When RequestName is invoked the following occurs:
3954 If the method caller is currently the primary owner of the name,
3955 the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and DBUS_NAME_FLAG_DO_NOT_QUEUE
3956 values are updated with the values from the new RequestName call,
3957 and nothing further happens.
3963 If the current primary owner (head of the queue) has
3964 DBUS_NAME_FLAG_ALLOW_REPLACEMENT set, and the RequestName
3965 invocation has the DBUS_NAME_FLAG_REPLACE_EXISTING flag, then
3966 the caller of RequestName replaces the current primary owner at
3967 the head of the queue and the current primary owner moves to the
3968 second position in the queue. If the caller of RequestName was
3969 in the queue previously its flags are updated with the values from
3970 the new RequestName in addition to moving it to the head of the queue.
3976 If replacement is not possible, and the method caller is
3977 currently in the queue but not the primary owner, its flags are
3978 updated with the values from the new RequestName call.
3984 If replacement is not possible, and the method caller is
3985 currently not in the queue, the method caller is appended to the
3992 If any connection in the queue has DBUS_NAME_FLAG_DO_NOT_QUEUE
3993 set and is not the primary owner, it is removed from the
3994 queue. This can apply to the previous primary owner (if it
3995 was replaced) or the method caller (if it updated the
3996 DBUS_NAME_FLAG_DO_NOT_QUEUE flag while still stuck in the
3997 queue, or if it was just added to the queue with that flag set).
4003 Note that DBUS_NAME_FLAG_REPLACE_EXISTING results in "jumping the
4004 queue," even if another application already in the queue had specified
4005 DBUS_NAME_FLAG_REPLACE_EXISTING. This comes up if a primary owner
4006 that does not allow replacement goes away, and the next primary owner
4007 does allow replacement. In this case, queued items that specified
4008 DBUS_NAME_FLAG_REPLACE_EXISTING <emphasis>do not</emphasis>
4009 automatically replace the new primary owner. In other words,
4010 DBUS_NAME_FLAG_REPLACE_EXISTING is not saved, it is only used at the
4011 time RequestName is called. This is deliberate to avoid an infinite loop
4012 anytime two applications are both DBUS_NAME_FLAG_ALLOW_REPLACEMENT
4013 and DBUS_NAME_FLAG_REPLACE_EXISTING.
4016 The flags argument contains any of the following values logically ORed
4023 <entry>Conventional Name</entry>
4024 <entry>Value</entry>
4025 <entry>Description</entry>
4030 <entry>DBUS_NAME_FLAG_ALLOW_REPLACEMENT</entry>
4034 If an application A specifies this flag and succeeds in
4035 becoming the owner of the name, and another application B
4036 later calls RequestName with the
4037 DBUS_NAME_FLAG_REPLACE_EXISTING flag, then application A
4038 will lose ownership and receive a
4039 <literal>org.freedesktop.DBus.NameLost</literal> signal, and
4040 application B will become the new owner. If DBUS_NAME_FLAG_ALLOW_REPLACEMENT
4041 is not specified by application A, or DBUS_NAME_FLAG_REPLACE_EXISTING
4042 is not specified by application B, then application B will not replace
4043 application A as the owner.
4048 <entry>DBUS_NAME_FLAG_REPLACE_EXISTING</entry>
4052 Try to replace the current owner if there is one. If this
4053 flag is not set the application will only become the owner of
4054 the name if there is no current owner. If this flag is set,
4055 the application will replace the current owner if
4056 the current owner specified DBUS_NAME_FLAG_ALLOW_REPLACEMENT.
4061 <entry>DBUS_NAME_FLAG_DO_NOT_QUEUE</entry>
4065 Without this flag, if an application requests a name that is
4066 already owned, the application will be placed in a queue to
4067 own the name when the current owner gives it up. If this
4068 flag is given, the application will not be placed in the
4069 queue, the request for the name will simply fail. This flag
4070 also affects behavior when an application is replaced as
4071 name owner; by default the application moves back into the
4072 waiting queue, unless this flag was provided when the application
4073 became the name owner.
4081 The return code can be one of the following values:
4087 <entry>Conventional Name</entry>
4088 <entry>Value</entry>
4089 <entry>Description</entry>
4094 <entry>DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER</entry>
4095 <entry>1</entry> <entry>The caller is now the primary owner of
4096 the name, replacing any previous owner. Either the name had no
4097 owner before, or the caller specified
4098 DBUS_NAME_FLAG_REPLACE_EXISTING and the current owner specified
4099 DBUS_NAME_FLAG_ALLOW_REPLACEMENT.</entry>
4102 <entry>DBUS_REQUEST_NAME_REPLY_IN_QUEUE</entry>
4105 <entry>The name already had an owner,
4106 DBUS_NAME_FLAG_DO_NOT_QUEUE was not specified, and either
4107 the current owner did not specify
4108 DBUS_NAME_FLAG_ALLOW_REPLACEMENT or the requesting
4109 application did not specify DBUS_NAME_FLAG_REPLACE_EXISTING.
4113 <entry>DBUS_REQUEST_NAME_REPLY_EXISTS</entry> <entry>3</entry>
4114 <entry>The name already has an owner,
4115 DBUS_NAME_FLAG_DO_NOT_QUEUE was specified, and either
4116 DBUS_NAME_FLAG_ALLOW_REPLACEMENT was not specified by the
4117 current owner, or DBUS_NAME_FLAG_REPLACE_EXISTING was not
4118 specified by the requesting application.</entry>
4121 <entry>DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER</entry>
4123 <entry>The application trying to request ownership of a name is already the owner of it.</entry>
4131 <sect3 id="bus-messages-release-name">
4132 <title><literal>org.freedesktop.DBus.ReleaseName</literal></title>
4136 UINT32 ReleaseName (in STRING name)
4143 <entry>Argument</entry>
4145 <entry>Description</entry>
4151 <entry>STRING</entry>
4152 <entry>Name to release</entry>
4162 <entry>Argument</entry>
4164 <entry>Description</entry>
4170 <entry>UINT32</entry>
4171 <entry>Return value</entry>
4178 This method call should be sent to
4179 <literal>org.freedesktop.DBus</literal> and asks the message bus to
4180 release the method caller's claim to the given name. If the caller is
4181 the primary owner, a new primary owner will be selected from the
4182 queue if any other owners are waiting. If the caller is waiting in
4183 the queue for the name, the caller will removed from the queue and
4184 will not be made an owner of the name if it later becomes available.
4185 If there are no other owners in the queue for the name, it will be
4186 removed from the bus entirely.
4188 The return code can be one of the following values:
4194 <entry>Conventional Name</entry>
4195 <entry>Value</entry>
4196 <entry>Description</entry>
4201 <entry>DBUS_RELEASE_NAME_REPLY_RELEASED</entry>
4202 <entry>1</entry> <entry>The caller has released his claim on
4203 the given name. Either the caller was the primary owner of
4204 the name, and the name is now unused or taken by somebody
4205 waiting in the queue for the name, or the caller was waiting
4206 in the queue for the name and has now been removed from the
4210 <entry>DBUS_RELEASE_NAME_REPLY_NON_EXISTENT</entry>
4212 <entry>The given name does not exist on this bus.</entry>
4215 <entry>DBUS_RELEASE_NAME_REPLY_NOT_OWNER</entry>
4217 <entry>The caller was not the primary owner of this name,
4218 and was also not waiting in the queue to own this name.</entry>
4226 <sect3 id="bus-messages-list-queued-owners">
4227 <title><literal>org.freedesktop.DBus.ListQueuedOwners</literal></title>
4231 ARRAY of STRING ListQueuedOwners (in STRING name)
4238 <entry>Argument</entry>
4240 <entry>Description</entry>
4246 <entry>STRING</entry>
4247 <entry>The well-known bus name to query, such as
4248 <literal>com.example.cappuccino</literal></entry>
4258 <entry>Argument</entry>
4260 <entry>Description</entry>
4266 <entry>ARRAY of STRING</entry>
4267 <entry>The unique bus names of connections currently queued
4268 for the name</entry>
4275 This method call should be sent to
4276 <literal>org.freedesktop.DBus</literal> and lists the connections
4277 currently queued for a bus name (see
4278 <xref linkend="term-queued-owner"/>).
4283 <sect2 id="message-bus-routing">
4284 <title>Message Bus Message Routing</title>
4287 Messages may have a <literal>DESTINATION</literal> field (see <xref
4288 linkend="message-protocol-header-fields"/>), resulting in a
4289 <firstterm>unicast message</firstterm>. If the
4290 <literal>DESTINATION</literal> field is present, it specifies a message
4291 recipient by name. Method calls and replies normally specify this field.
4292 The message bus must send messages (of any type) with the
4293 <literal>DESTINATION</literal> field set to the specified recipient,
4294 regardless of whether the recipient has set up a match rule matching
4299 When the message bus receives a signal, if the
4300 <literal>DESTINATION</literal> field is absent, it is considered to
4301 be a <firstterm>broadcast signal</firstterm>, and is sent to all
4302 applications with <firstterm>message matching rules</firstterm> that
4303 match the message. Most signal messages are broadcasts.
4307 Unicast signal messages (those with a <literal>DESTINATION</literal>
4308 field) are not commonly used, but they are treated like any unicast
4309 message: they are delivered to the specified receipient,
4310 regardless of its match rules. One use for unicast signals is to
4311 avoid a race condition in which a signal is emitted before the intended
4312 recipient can call <xref linkend="bus-messages-add-match"/> to
4313 receive that signal: if the signal is sent directly to that recipient
4314 using a unicast message, it does not need to add a match rule at all,
4315 and there is no race condition. Another use for unicast signals,
4316 on message buses whose security policy prevents eavesdropping, is to
4317 send sensitive information which should only be visible to one
4322 When the message bus receives a method call, if the
4323 <literal>DESTINATION</literal> field is absent, the call is taken to be
4324 a standard one-to-one message and interpreted by the message bus
4325 itself. For example, sending an
4326 <literal>org.freedesktop.DBus.Peer.Ping</literal> message with no
4327 <literal>DESTINATION</literal> will cause the message bus itself to
4328 reply to the ping immediately; the message bus will not make this
4329 message visible to other applications.
4333 Continuing the <literal>org.freedesktop.DBus.Peer.Ping</literal> example, if
4334 the ping message were sent with a <literal>DESTINATION</literal> name of
4335 <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
4336 forwarded, and the Yoyodyne Corporation screensaver application would be
4337 expected to reply to the ping.
4341 Message bus implementations may impose a security policy which
4342 prevents certain messages from being sent or received.
4343 When a message cannot be sent or received due to a security
4344 policy, the message bus should send an error reply, unless the
4345 original message had the <literal>NO_REPLY</literal> flag.
4348 <sect3 id="message-bus-routing-eavesdropping">
4349 <title>Eavesdropping</title>
4351 Receiving a unicast message whose <literal>DESTINATION</literal>
4352 indicates a different recipient is called
4353 <firstterm>eavesdropping</firstterm>. On a message bus which acts as
4354 a security boundary (like the standard system bus), the security
4355 policy should usually prevent eavesdropping, since unicast messages
4356 are normally kept private and may contain security-sensitive
4361 Eavesdropping is mainly useful for debugging tools, such as
4362 the <literal>dbus-monitor</literal> tool in the reference
4363 implementation of D-Bus. Tools which eavesdrop on the message bus
4364 should be careful to avoid sending a reply or error in response to
4365 messages intended for a different client.
4369 Clients may attempt to eavesdrop by adding match rules
4370 (see <xref linkend="message-bus-routing-match-rules"/>) containing
4371 the <literal>eavesdrop='true'</literal> match. If the message bus'
4372 security policy does not allow eavesdropping, the match rule can
4373 still be added, but will not have any practical effect. For
4374 compatibility with older message bus implementations, if adding such
4375 a match rule results in an error reply, the client may fall back to
4376 adding the same rule with the <literal>eavesdrop</literal> match
4381 <sect3 id="message-bus-routing-match-rules">
4382 <title>Match Rules</title>
4384 An important part of the message bus routing protocol is match
4385 rules. Match rules describe the messages that should be sent to a
4386 client, based on the contents of the message. Broadcast signals
4387 are only sent to clients which have a suitable match rule: this
4388 avoids waking up client processes to deal with signals that are
4389 not relevant to that client.
4392 Messages that list a client as their <literal>DESTINATION</literal>
4393 do not need to match the client's match rules, and are sent to that
4394 client regardless. As a result, match rules are mainly used to
4395 receive a subset of broadcast signals.
4398 Match rules can also be used for eavesdropping
4399 (see <xref linkend="message-bus-routing-eavesdropping"/>),
4400 if the security policy of the message bus allows it.
4403 Match rules are added using the AddMatch bus method
4404 (see <xref linkend="bus-messages-add-match"/>). Rules are
4405 specified as a string of comma separated key/value pairs.
4406 Excluding a key from the rule indicates a wildcard match.
4407 For instance excluding the the member from a match rule but
4408 adding a sender would let all messages from that sender through.
4409 An example of a complete rule would be
4410 "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='Foo',path='/bar/foo',destination=':452345.34',arg2='bar'"
4413 The following table describes the keys that can be used to create
4420 <entry>Possible Values</entry>
4421 <entry>Description</entry>
4426 <entry><literal>type</literal></entry>
4427 <entry>'signal', 'method_call', 'method_return', 'error'</entry>
4428 <entry>Match on the message type. An example of a type match is type='signal'</entry>
4431 <entry><literal>sender</literal></entry>
4432 <entry>A bus or unique name (see <xref linkend="term-bus-name"/>
4433 and <xref linkend="term-unique-name"/> respectively)
4435 <entry>Match messages sent by a particular sender. An example of a sender match
4436 is sender='org.freedesktop.Hal'</entry>
4439 <entry><literal>interface</literal></entry>
4440 <entry>An interface name (see <xref linkend="message-protocol-names-interface"/>)</entry>
4441 <entry>Match messages sent over or to a particular interface. An example of an
4442 interface match is interface='org.freedesktop.Hal.Manager'.
4443 If a message omits the interface header, it must not match any rule
4444 that specifies this key.</entry>
4447 <entry><literal>member</literal></entry>
4448 <entry>Any valid method or signal name</entry>
4449 <entry>Matches messages which have the give method or signal name. An example of
4450 a member match is member='NameOwnerChanged'</entry>
4453 <entry><literal>path</literal></entry>
4454 <entry>An object path (see <xref linkend="message-protocol-marshaling-object-path"/>)</entry>
4455 <entry>Matches messages which are sent from or to the given object. An example of a
4456 path match is path='/org/freedesktop/Hal/Manager'</entry>
4459 <entry><literal>path_namespace</literal></entry>
4460 <entry>An object path</entry>
4463 Matches messages which are sent from or to an
4464 object for which the object path is either the
4465 given value, or that value followed by one or
4466 more path components.
4471 <literal>path_namespace='/com/example/foo'</literal>
4472 would match signals sent by
4473 <literal>/com/example/foo</literal>
4475 <literal>/com/example/foo/bar</literal>,
4477 <literal>/com/example/foobar</literal>.
4481 Using both <literal>path</literal> and
4482 <literal>path_namespace</literal> in the same match
4483 rule is not allowed.
4488 This match key was added in version 0.16 of the
4489 D-Bus specification and implemented by the bus
4490 daemon in dbus 1.5.0 and later.
4496 <entry><literal>destination</literal></entry>
4497 <entry>A unique name (see <xref linkend="term-unique-name"/>)</entry>
4498 <entry>Matches messages which are being sent to the given unique name. An
4499 example of a destination match is destination=':1.0'</entry>
4502 <entry><literal>arg[0, 1, 2, 3, ...]</literal></entry>
4503 <entry>Any string</entry>
4504 <entry>Arg matches are special and are used for further restricting the
4505 match based on the arguments in the body of a message. Only arguments of type
4506 STRING can be matched in this way. An example of an argument match
4507 would be arg3='Foo'. Only argument indexes from 0 to 63 should be
4511 <entry><literal>arg[0, 1, 2, 3, ...]path</literal></entry>
4512 <entry>Any string</entry>
4514 <para>Argument path matches provide a specialised form of wildcard matching for
4515 path-like namespaces. They can match arguments whose type is either STRING or
4516 OBJECT_PATH. As with normal argument matches,
4517 if the argument is exactly equal to the string given in the match
4518 rule then the rule is satisfied. Additionally, there is also a
4519 match when either the string given in the match rule or the
4520 appropriate message argument ends with '/' and is a prefix of the
4521 other. An example argument path match is arg0path='/aa/bb/'. This
4522 would match messages with first arguments of '/', '/aa/',
4523 '/aa/bb/', '/aa/bb/cc/' and '/aa/bb/cc'. It would not match
4524 messages with first arguments of '/aa/b', '/aa' or even '/aa/bb'.</para>
4526 <para>This is intended for monitoring “directories” in file system-like
4527 hierarchies, as used in the <citetitle>dconf</citetitle> configuration
4528 system. An application interested in all nodes in a particular hierarchy would
4529 monitor <literal>arg0path='/ca/example/foo/'</literal>. Then the service could
4530 emit a signal with zeroth argument <literal>"/ca/example/foo/bar"</literal> to
4531 represent a modification to the “bar” property, or a signal with zeroth
4532 argument <literal>"/ca/example/"</literal> to represent atomic modification of
4533 many properties within that directory, and the interested application would be
4534 notified in both cases.</para>
4537 This match key was added in version 0.12 of the
4538 D-Bus specification, implemented for STRING
4539 arguments by the bus daemon in dbus 1.2.0 and later,
4540 and implemented for OBJECT_PATH arguments in dbus 1.5.0
4547 <entry><literal>arg0namespace</literal></entry>
4548 <entry>Like a bus name, except that the string is not
4549 required to contain a '.' (period)</entry>
4551 <para>Match messages whose first argument is of type STRING, and is a bus name
4552 or interface name within the specified namespace. This is primarily intended
4553 for watching name owner changes for a group of related bus names, rather than
4554 for a single name or all name changes.</para>
4556 <para>Because every valid interface name is also a valid
4557 bus name, this can also be used for messages whose
4558 first argument is an interface name.</para>
4560 <para>For example, the match rule
4561 <literal>member='NameOwnerChanged',arg0namespace='com.example.backend'</literal>
4562 matches name owner changes for bus names such as
4563 <literal>com.example.backend.foo</literal>,
4564 <literal>com.example.backend.foo.bar</literal>, and
4565 <literal>com.example.backend</literal> itself.</para>
4567 <para>See also <xref linkend='bus-messages-name-owner-changed'/>.</para>
4570 This match key was added in version 0.16 of the
4571 D-Bus specification and implemented by the bus
4572 daemon in dbus 1.5.0 and later.
4578 <entry><literal>eavesdrop</literal></entry>
4579 <entry><literal>'true'</literal>, <literal>'false'</literal></entry>
4580 <entry>Since D-Bus 1.5.6, match rules do not
4581 match messages which have a <literal>DESTINATION</literal>
4582 field unless the match rule specifically
4584 (see <xref linkend="message-bus-routing-eavesdropping"/>)
4585 by specifying <literal>eavesdrop='true'</literal>
4586 in the match rule. <literal>eavesdrop='false'</literal>
4587 restores the default behaviour. Messages are
4588 delivered to their <literal>DESTINATION</literal>
4589 regardless of match rules, so this match does not
4590 affect normal delivery of unicast messages.
4591 If the message bus has a security policy which forbids
4592 eavesdropping, this match may still be used without error,
4593 but will not have any practical effect.
4594 In older versions of D-Bus, this match was not allowed
4595 in match rules, and all match rules behaved as if
4596 <literal>eavesdrop='true'</literal> had been used.
4605 <sect2 id="message-bus-starting-services">
4606 <title>Message Bus Starting Services</title>
4608 The message bus can start applications on behalf of other applications.
4609 In CORBA terms, this would be called <firstterm>activation</firstterm>.
4610 An application that can be started in this way is called a
4611 <firstterm>service</firstterm>.
4614 With D-Bus, starting a service is normally done by name. That is,
4615 applications ask the message bus to start some program that will own a
4616 well-known name, such as <literal>com.example.TextEditor</literal>.
4617 This implies a contract documented along with the name
4618 <literal>com.example.TextEditor</literal> for which object
4619 the owner of that name will provide, and what interfaces those
4623 To find an executable corresponding to a particular name, the bus daemon
4624 looks for <firstterm>service description files</firstterm>. Service
4625 description files define a mapping from names to executables. Different
4626 kinds of message bus will look for these files in different places, see
4627 <xref linkend="message-bus-types"/>.
4630 Service description files have the ".service" file
4631 extension. The message bus will only load service description files
4632 ending with .service; all other files will be ignored. The file format
4633 is similar to that of <ulink
4634 url="http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html">desktop
4635 entries</ulink>. All service description files must be in UTF-8
4636 encoding. To ensure that there will be no name collisions, service files
4637 must be namespaced using the same mechanism as messages and service
4642 On the well-known system bus, the name of a service description file
4643 must be its well-known name plus <literal>.service</literal>,
4645 <literal>com.example.ConfigurationDatabase.service</literal>.
4649 On the well-known session bus, services should follow the same
4650 service description file naming convention as on the system bus,
4651 but for backwards compatibility they are not required to do so.
4655 [FIXME the file format should be much better specified than "similar to
4656 .desktop entries" esp. since desktop entries are already
4657 badly-specified. ;-)]
4658 These sections from the specification apply to service files as well:
4661 <listitem><para>General syntax</para></listitem>
4662 <listitem><para>Comment format</para></listitem>
4665 Service description files must contain a
4666 <literal>D-BUS Service</literal> group with at least the keys
4667 <literal>Name</literal> (the well-known name of the service)
4668 and <literal>Exec</literal> (the command to be executed).
4671 <title>Example service description file</title>
4673 # Sample service description file
4675 Name=com.example.ConfigurationDatabase
4676 Exec=/usr/bin/sample-configd
4682 Additionally, service description files for the well-known system
4683 bus on Unix must contain a <literal>User</literal> key, whose value
4684 is the name of a user account (e.g. <literal>root</literal>).
4685 The system service will be run as that user.
4689 When an application asks to start a service by name, the bus daemon tries to
4690 find a service that will own that name. It then tries to spawn the
4691 executable associated with it. If this fails, it will report an
4692 error. [FIXME what happens if two .service files offer the same service;
4693 what kind of error is reported, should we have a way for the client to
4697 The executable launched will have the environment variable
4698 <literal>DBUS_STARTER_ADDRESS</literal> set to the address of the
4699 message bus so it can connect and request the appropriate names.
4702 The executable being launched may want to know whether the message bus
4703 starting it is one of the well-known message buses (see <xref
4704 linkend="message-bus-types"/>). To facilitate this, the bus must also set
4705 the <literal>DBUS_STARTER_BUS_TYPE</literal> environment variable if it is one
4706 of the well-known buses. The currently-defined values for this variable
4707 are <literal>system</literal> for the systemwide message bus,
4708 and <literal>session</literal> for the per-login-session message
4709 bus. The new executable must still connect to the address given
4710 in <literal>DBUS_STARTER_ADDRESS</literal>, but may assume that the
4711 resulting connection is to the well-known bus.
4714 [FIXME there should be a timeout somewhere, either specified
4715 in the .service file, by the client, or just a global value
4716 and if the client being activated fails to connect within that
4717 timeout, an error should be sent back.]
4720 <sect3 id="message-bus-starting-services-scope">
4721 <title>Message Bus Service Scope</title>
4723 The "scope" of a service is its "per-", such as per-session,
4724 per-machine, per-home-directory, or per-display. The reference
4725 implementation doesn't yet support starting services in a different
4726 scope from the message bus itself. So e.g. if you start a service
4727 on the session bus its scope is per-session.
4730 We could add an optional scope to a bus name. For example, for
4731 per-(display,session pair), we could have a unique ID for each display
4732 generated automatically at login and set on screen 0 by executing a
4733 special "set display ID" binary. The ID would be stored in a
4734 <literal>_DBUS_DISPLAY_ID</literal> property and would be a string of
4735 random bytes. This ID would then be used to scope names.
4736 Starting/locating a service could be done by ID-name pair rather than
4740 Contrast this with a per-display scope. To achieve that, we would
4741 want a single bus spanning all sessions using a given display.
4742 So we might set a <literal>_DBUS_DISPLAY_BUS_ADDRESS</literal>
4743 property on screen 0 of the display, pointing to this bus.
4748 <sect2 id="message-bus-types">
4749 <title>Well-known Message Bus Instances</title>
4751 Two standard message bus instances are defined here, along with how
4752 to locate them and where their service files live.
4754 <sect3 id="message-bus-types-login">
4755 <title>Login session message bus</title>
4757 Each time a user logs in, a <firstterm>login session message
4758 bus</firstterm> may be started. All applications in the user's login
4759 session may interact with one another using this message bus.
4762 The address of the login session message bus is given
4763 in the <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment
4764 variable. If that variable is not set, applications may
4765 also try to read the address from the X Window System root
4766 window property <literal>_DBUS_SESSION_BUS_ADDRESS</literal>.
4767 The root window property must have type <literal>STRING</literal>.
4768 The environment variable should have precedence over the
4769 root window property.
4771 <para>The address of the login session message bus is given in the
4772 <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment variable. If
4773 DBUS_SESSION_BUS_ADDRESS is not set, or if it's set to the string
4774 "autolaunch:", the system should use platform-specific methods of
4775 locating a running D-Bus session server, or starting one if a running
4776 instance cannot be found. Note that this mechanism is not recommended
4777 for attempting to determine if a daemon is running. It is inherently
4778 racy to attempt to make this determination, since the bus daemon may
4779 be started just before or just after the determination is made.
4780 Therefore, it is recommended that applications do not try to make this
4781 determination for their functionality purposes, and instead they
4782 should attempt to start the server.</para>
4784 <sect4 id="message-bus-types-login-x-windows">
4785 <title>X Windowing System</title>
4787 For the X Windowing System, the application must locate the
4788 window owner of the selection represented by the atom formed by
4792 <para>the literal string "_DBUS_SESSION_BUS_SELECTION_"</para>
4796 <para>the current user's username</para>
4800 <para>the literal character '_' (underscore)</para>
4804 <para>the machine's ID</para>
4810 The following properties are defined for the window that owns
4812 <informaltable frame="all">
4821 <para>meaning</para>
4827 <para>_DBUS_SESSION_BUS_ADDRESS</para>
4831 <para>the actual address of the server socket</para>
4837 <para>_DBUS_SESSION_BUS_PID</para>
4841 <para>the PID of the server process</para>
4850 At least the _DBUS_SESSION_BUS_ADDRESS property MUST be
4851 present in this window.
4855 If the X selection cannot be located or if reading the
4856 properties from the window fails, the implementation MUST conclude
4857 that there is no D-Bus server running and proceed to start a new
4858 server. (See below on concurrency issues)
4862 Failure to connect to the D-Bus server address thus obtained
4863 MUST be treated as a fatal connection error and should be reported
4868 As an alternative, an implementation MAY find the information
4869 in the following file located in the current user's home directory,
4870 in subdirectory .dbus/session-bus/:
4873 <para>the machine's ID</para>
4877 <para>the literal character '-' (dash)</para>
4881 <para>the X display without the screen number, with the
4882 following prefixes removed, if present: ":", "localhost:"
4883 ."localhost.localdomain:". That is, a display of
4884 "localhost:10.0" produces just the number "10"</para>
4890 The contents of this file NAME=value assignment pairs and
4891 lines starting with # are comments (no comments are allowed
4892 otherwise). The following variable names are defined:
4899 <para>Variable</para>
4903 <para>meaning</para>
4909 <para>DBUS_SESSION_BUS_ADDRESS</para>
4913 <para>the actual address of the server socket</para>
4919 <para>DBUS_SESSION_BUS_PID</para>
4923 <para>the PID of the server process</para>
4929 <para>DBUS_SESSION_BUS_WINDOWID</para>
4933 <para>the window ID</para>
4942 At least the DBUS_SESSION_BUS_ADDRESS variable MUST be present
4947 Failure to open this file MUST be interpreted as absence of a
4948 running server. Therefore, the implementation MUST proceed to
4949 attempting to launch a new bus server if the file cannot be
4954 However, success in opening this file MUST NOT lead to the
4955 conclusion that the server is running. Thus, a failure to connect to
4956 the bus address obtained by the alternative method MUST NOT be
4957 considered a fatal error. If the connection cannot be established,
4958 the implementation MUST proceed to check the X selection settings or
4959 to start the server on its own.
4963 If the implementation concludes that the D-Bus server is not
4964 running it MUST attempt to start a new server and it MUST also
4965 ensure that the daemon started as an effect of the "autolaunch"
4966 mechanism provides the lookup mechanisms described above, so
4967 subsequent calls can locate the newly started server. The
4968 implementation MUST also ensure that if two or more concurrent
4969 initiations happen, only one server remains running and all other
4970 initiations are able to obtain the address of this server and
4971 connect to it. In other words, the implementation MUST ensure that
4972 the X selection is not present when it attempts to set it, without
4973 allowing another process to set the selection between the
4974 verification and the setting (e.g., by using XGrabServer /
4981 On Unix systems, the session bus should search for .service files
4982 in <literal>$XDG_DATA_DIRS/dbus-1/services</literal> as defined
4984 <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG Base Directory Specification</ulink>.
4985 Implementations may also search additional locations, which
4986 should be searched with lower priority than anything in
4987 XDG_DATA_HOME, XDG_DATA_DIRS or their respective defaults;
4988 for example, the reference implementation also
4989 looks in <literal>${datadir}/dbus-1/services</literal> as
4990 set at compile time.
4993 As described in the XDG Base Directory Specification, software
4994 packages should install their session .service files to their
4995 configured <literal>${datadir}/dbus-1/services</literal>,
4996 where <literal>${datadir}</literal> is as defined by the GNU
4997 coding standards. System administrators or users can arrange
4998 for these service files to be read by setting XDG_DATA_DIRS or by
4999 symlinking them into the default locations.
5003 <sect3 id="message-bus-types-system">
5004 <title>System message bus</title>
5006 A computer may have a <firstterm>system message bus</firstterm>,
5007 accessible to all applications on the system. This message bus may be
5008 used to broadcast system events, such as adding new hardware devices,
5009 changes in the printer queue, and so forth.
5012 The address of the system message bus is given
5013 in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment
5014 variable. If that variable is not set, applications should try
5015 to connect to the well-known address
5016 <literal>unix:path=/var/run/dbus/system_bus_socket</literal>.
5019 The D-Bus reference implementation actually honors the
5020 <literal>$(localstatedir)</literal> configure option
5021 for this address, on both client and server side.
5026 On Unix systems, the system bus should default to searching
5027 for .service files in
5028 <literal>/usr/local/share/dbus-1/system-services</literal>,
5029 <literal>/usr/share/dbus-1/system-services</literal> and
5030 <literal>/lib/dbus-1/system-services</literal>, with that order
5031 of precedence. It may also search other implementation-specific
5032 locations, but should not vary these locations based on environment
5036 The system bus is security-sensitive and is typically executed
5037 by an init system with a clean environment. Its launch helper
5038 process is particularly security-sensitive, and specifically
5039 clears its own environment.
5044 Software packages should install their system .service
5045 files to their configured
5046 <literal>${datadir}/dbus-1/system-services</literal>,
5047 where <literal>${datadir}</literal> is as defined by the GNU
5048 coding standards. System administrators can arrange
5049 for these service files to be read by editing the system bus'
5050 configuration file or by symlinking them into the default
5056 <sect2 id="message-bus-messages">
5057 <title>Message Bus Messages</title>
5059 The special message bus name <literal>org.freedesktop.DBus</literal>
5060 responds to a number of additional messages.
5063 <sect3 id="bus-messages-hello">
5064 <title><literal>org.freedesktop.DBus.Hello</literal></title>
5075 <entry>Argument</entry>
5077 <entry>Description</entry>
5083 <entry>STRING</entry>
5084 <entry>Unique name assigned to the connection</entry>
5091 Before an application is able to send messages to other applications
5092 it must send the <literal>org.freedesktop.DBus.Hello</literal> message
5093 to the message bus to obtain a unique name. If an application without
5094 a unique name tries to send a message to another application, or a
5095 message to the message bus itself that isn't the
5096 <literal>org.freedesktop.DBus.Hello</literal> message, it will be
5097 disconnected from the bus.
5100 There is no corresponding "disconnect" request; if a client wishes to
5101 disconnect from the bus, it simply closes the socket (or other
5102 communication channel).
5105 <sect3 id="bus-messages-list-names">
5106 <title><literal>org.freedesktop.DBus.ListNames</literal></title>
5110 ARRAY of STRING ListNames ()
5117 <entry>Argument</entry>
5119 <entry>Description</entry>
5125 <entry>ARRAY of STRING</entry>
5126 <entry>Array of strings where each string is a bus name</entry>
5133 Returns a list of all currently-owned names on the bus.
5136 <sect3 id="bus-messages-list-activatable-names">
5137 <title><literal>org.freedesktop.DBus.ListActivatableNames</literal></title>
5141 ARRAY of STRING ListActivatableNames ()
5148 <entry>Argument</entry>
5150 <entry>Description</entry>
5156 <entry>ARRAY of STRING</entry>
5157 <entry>Array of strings where each string is a bus name</entry>
5164 Returns a list of all names that can be activated on the bus.
5167 <sect3 id="bus-messages-name-exists">
5168 <title><literal>org.freedesktop.DBus.NameHasOwner</literal></title>
5172 BOOLEAN NameHasOwner (in STRING name)
5179 <entry>Argument</entry>
5181 <entry>Description</entry>
5187 <entry>STRING</entry>
5188 <entry>Name to check</entry>
5198 <entry>Argument</entry>
5200 <entry>Description</entry>
5206 <entry>BOOLEAN</entry>
5207 <entry>Return value, true if the name exists</entry>
5214 Checks if the specified name exists (currently has an owner).
5218 <sect3 id="bus-messages-name-owner-changed">
5219 <title><literal>org.freedesktop.DBus.NameOwnerChanged</literal></title>
5223 NameOwnerChanged (STRING name, STRING old_owner, STRING new_owner)
5230 <entry>Argument</entry>
5232 <entry>Description</entry>
5238 <entry>STRING</entry>
5239 <entry>Name with a new owner</entry>
5243 <entry>STRING</entry>
5244 <entry>Old owner or empty string if none</entry>
5248 <entry>STRING</entry>
5249 <entry>New owner or empty string if none</entry>
5256 This signal indicates that the owner of a name has changed.
5257 It's also the signal to use to detect the appearance of
5258 new names on the bus.
5261 <sect3 id="bus-messages-name-lost">
5262 <title><literal>org.freedesktop.DBus.NameLost</literal></title>
5266 NameLost (STRING name)
5273 <entry>Argument</entry>
5275 <entry>Description</entry>
5281 <entry>STRING</entry>
5282 <entry>Name which was lost</entry>
5289 This signal is sent to a specific application when it loses
5290 ownership of a name.
5294 <sect3 id="bus-messages-name-acquired">
5295 <title><literal>org.freedesktop.DBus.NameAcquired</literal></title>
5299 NameAcquired (STRING name)
5306 <entry>Argument</entry>
5308 <entry>Description</entry>
5314 <entry>STRING</entry>
5315 <entry>Name which was acquired</entry>
5322 This signal is sent to a specific application when it gains
5323 ownership of a name.
5327 <sect3 id="bus-messages-start-service-by-name">
5328 <title><literal>org.freedesktop.DBus.StartServiceByName</literal></title>
5332 UINT32 StartServiceByName (in STRING name, in UINT32 flags)
5339 <entry>Argument</entry>
5341 <entry>Description</entry>
5347 <entry>STRING</entry>
5348 <entry>Name of the service to start</entry>
5352 <entry>UINT32</entry>
5353 <entry>Flags (currently not used)</entry>
5363 <entry>Argument</entry>
5365 <entry>Description</entry>
5371 <entry>UINT32</entry>
5372 <entry>Return value</entry>
5377 Tries to launch the executable associated with a name. For more information, see <xref linkend="message-bus-starting-services"/>.
5381 The return value can be one of the following values:
5386 <entry>Identifier</entry>
5387 <entry>Value</entry>
5388 <entry>Description</entry>
5393 <entry>DBUS_START_REPLY_SUCCESS</entry>
5395 <entry>The service was successfully started.</entry>
5398 <entry>DBUS_START_REPLY_ALREADY_RUNNING</entry>
5400 <entry>A connection already owns the given name.</entry>
5409 <sect3 id="bus-messages-update-activation-environment">
5410 <title><literal>org.freedesktop.DBus.UpdateActivationEnvironment</literal></title>
5414 UpdateActivationEnvironment (in ARRAY of DICT<STRING,STRING> environment)
5421 <entry>Argument</entry>
5423 <entry>Description</entry>
5429 <entry>ARRAY of DICT<STRING,STRING></entry>
5430 <entry>Environment to add or update</entry>
5435 Normally, session bus activated services inherit the environment of the bus daemon. This method adds to or modifies that environment when activating services.
5438 Some bus instances, such as the standard system bus, may disable access to this method for some or all callers.
5441 Note, both the environment variable names and values must be valid UTF-8. There's no way to update the activation environment with data that is invalid UTF-8.
5446 <sect3 id="bus-messages-get-name-owner">
5447 <title><literal>org.freedesktop.DBus.GetNameOwner</literal></title>
5451 STRING GetNameOwner (in STRING name)
5458 <entry>Argument</entry>
5460 <entry>Description</entry>
5466 <entry>STRING</entry>
5467 <entry>Name to get the owner of</entry>
5477 <entry>Argument</entry>
5479 <entry>Description</entry>
5485 <entry>STRING</entry>
5486 <entry>Return value, a unique connection name</entry>
5491 Returns the unique connection name of the primary owner of the name
5492 given. If the requested name doesn't have an owner, returns a
5493 <literal>org.freedesktop.DBus.Error.NameHasNoOwner</literal> error.
5497 <sect3 id="bus-messages-get-connection-unix-user">
5498 <title><literal>org.freedesktop.DBus.GetConnectionUnixUser</literal></title>
5502 UINT32 GetConnectionUnixUser (in STRING bus_name)
5509 <entry>Argument</entry>
5511 <entry>Description</entry>
5517 <entry>STRING</entry>
5518 <entry>Unique or well-known bus name of the connection to
5519 query, such as <literal>:12.34</literal> or
5520 <literal>com.example.tea</literal></entry>
5530 <entry>Argument</entry>
5532 <entry>Description</entry>
5538 <entry>UINT32</entry>
5539 <entry>Unix user ID</entry>
5544 Returns the Unix user ID of the process connected to the server. If
5545 unable to determine it (for instance, because the process is not on the
5546 same machine as the bus daemon), an error is returned.
5550 <sect3 id="bus-messages-get-connection-unix-process-id">
5551 <title><literal>org.freedesktop.DBus.GetConnectionUnixProcessID</literal></title>
5555 UINT32 GetConnectionUnixProcessID (in STRING bus_name)
5562 <entry>Argument</entry>
5564 <entry>Description</entry>
5570 <entry>STRING</entry>
5571 <entry>Unique or well-known bus name of the connection to
5572 query, such as <literal>:12.34</literal> or
5573 <literal>com.example.tea</literal></entry>
5583 <entry>Argument</entry>
5585 <entry>Description</entry>
5591 <entry>UINT32</entry>
5592 <entry>Unix process id</entry>
5597 Returns the Unix process ID of the process connected to the server. If
5598 unable to determine it (for instance, because the process is not on the
5599 same machine as the bus daemon), an error is returned.
5603 <sect3 id="bus-messages-get-connection-credentials">
5604 <title><literal>org.freedesktop.DBus.GetConnectionCredentials</literal></title>
5608 DICT<STRING,VARIANT> GetConnectionCredentials (in STRING bus_name)
5615 <entry>Argument</entry>
5617 <entry>Description</entry>
5623 <entry>STRING</entry>
5624 <entry>Unique or well-known bus name of the connection to
5625 query, such as <literal>:12.34</literal> or
5626 <literal>com.example.tea</literal></entry>
5636 <entry>Argument</entry>
5638 <entry>Description</entry>
5644 <entry>DICT<STRING,VARIANT></entry>
5645 <entry>Credentials</entry>
5653 Returns as many credentials as possible for the process connected to
5654 the server. If unable to determine certain credentials (for instance,
5655 because the process is not on the same machine as the bus daemon,
5656 or because this version of the bus daemon does not support a
5657 particular security framework), or if the values of those credentials
5658 cannot be represented as documented here, then those credentials
5663 Keys in the returned dictionary not containing "." are defined
5664 by this specification. Bus daemon implementors supporting
5665 credentials frameworks not mentioned in this document should either
5666 contribute patches to this specification, or use keys containing
5667 "." and starting with a reversed domain name.
5673 <entry>Value type</entry>
5674 <entry>Value</entry>
5679 <entry>UnixUserID</entry>
5680 <entry>UINT32</entry>
5681 <entry>The numeric Unix user ID, as defined by POSIX</entry>
5684 <entry>ProcessID</entry>
5685 <entry>UINT32</entry>
5686 <entry>The numeric process ID, on platforms that have
5687 this concept. On Unix, this is the process ID defined by
5696 This method was added in D-Bus 1.7 to reduce the round-trips
5697 required to list a process's credentials. In older versions, calling
5698 this method will fail: applications should recover by using the
5699 separate methods such as
5700 <xref linkend="bus-messages-get-connection-unix-user"/>
5705 <sect3 id="bus-messages-get-adt-audit-session-data">
5706 <title><literal>org.freedesktop.DBus.GetAdtAuditSessionData</literal></title>
5710 ARRAY of BYTE GetAdtAuditSessionData (in STRING bus_name)
5717 <entry>Argument</entry>
5719 <entry>Description</entry>
5725 <entry>STRING</entry>
5726 <entry>Unique or well-known bus name of the connection to
5727 query, such as <literal>:12.34</literal> or
5728 <literal>com.example.tea</literal></entry>
5738 <entry>Argument</entry>
5740 <entry>Description</entry>
5746 <entry>ARRAY of BYTE</entry>
5747 <entry>auditing data as returned by
5748 adt_export_session_data()</entry>
5753 Returns auditing data used by Solaris ADT, in an unspecified
5754 binary format. If you know what this means, please contribute
5755 documentation via the D-Bus bug tracking system.
5756 This method is on the core DBus interface for historical reasons;
5757 the same information should be made available via
5758 <xref linkend="bus-messages-get-connection-credentials"/>
5763 <sect3 id="bus-messages-get-connection-selinux-security-context">
5764 <title><literal>org.freedesktop.DBus.GetConnectionSELinuxSecurityContext</literal></title>
5768 ARRAY of BYTE GetConnectionSELinuxSecurityContext (in STRING bus_name)
5775 <entry>Argument</entry>
5777 <entry>Description</entry>
5783 <entry>STRING</entry>
5784 <entry>Unique or well-known bus name of the connection to
5785 query, such as <literal>:12.34</literal> or
5786 <literal>com.example.tea</literal></entry>
5796 <entry>Argument</entry>
5798 <entry>Description</entry>
5804 <entry>ARRAY of BYTE</entry>
5805 <entry>some sort of string of bytes, not necessarily UTF-8,
5806 not including '\0'</entry>
5811 Returns the security context used by SELinux, in an unspecified
5812 format. If you know what this means, please contribute
5813 documentation via the D-Bus bug tracking system.
5814 This method is on the core DBus interface for historical reasons;
5815 the same information should be made available via
5816 <xref linkend="bus-messages-get-connection-credentials"/>
5822 <sect3 id="bus-messages-add-match">
5823 <title><literal>org.freedesktop.DBus.AddMatch</literal></title>
5827 AddMatch (in STRING rule)
5834 <entry>Argument</entry>
5836 <entry>Description</entry>
5842 <entry>STRING</entry>
5843 <entry>Match rule to add to the connection</entry>
5848 Adds a match rule to match messages going through the message bus (see <xref linkend='message-bus-routing-match-rules'/>).
5849 If the bus does not have enough resources the <literal>org.freedesktop.DBus.Error.OOM</literal>
5853 <sect3 id="bus-messages-remove-match">
5854 <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title>
5858 RemoveMatch (in STRING rule)
5865 <entry>Argument</entry>
5867 <entry>Description</entry>
5873 <entry>STRING</entry>
5874 <entry>Match rule to remove from the connection</entry>
5879 Removes the first rule that matches (see <xref linkend='message-bus-routing-match-rules'/>).
5880 If the rule is not found the <literal>org.freedesktop.DBus.Error.MatchRuleNotFound</literal>
5885 <sect3 id="bus-messages-get-id">
5886 <title><literal>org.freedesktop.DBus.GetId</literal></title>
5890 GetId (out STRING id)
5897 <entry>Argument</entry>
5899 <entry>Description</entry>
5905 <entry>STRING</entry>
5906 <entry>Unique ID identifying the bus daemon</entry>
5911 Gets the unique ID of the bus. The unique ID here is shared among all addresses the
5912 bus daemon is listening on (TCP, UNIX domain socket, etc.) and its format is described in
5913 <xref linkend="uuids"/>. Each address the bus is listening on also has its own unique
5914 ID, as described in <xref linkend="addresses"/>. The per-bus and per-address IDs are not related.
5915 There is also a per-machine ID, described in <xref linkend="standard-interfaces-peer"/> and returned
5916 by org.freedesktop.DBus.Peer.GetMachineId().
5917 For a desktop session bus, the bus ID can be used as a way to uniquely identify a user's session.
5925 <appendix id="implementation-notes">
5926 <title>Implementation notes</title>
5927 <sect1 id="implementation-notes-subsection">
5935 <glossary><title>Glossary</title>
5937 This glossary defines some of the terms used in this specification.
5940 <glossentry id="term-bus-name"><glossterm>Bus Name</glossterm>
5943 The message bus maintains an association between names and
5944 connections. (Normally, there's one connection per application.) A
5945 bus name is simply an identifier used to locate connections. For
5946 example, the hypothetical <literal>com.yoyodyne.Screensaver</literal>
5947 name might be used to send a message to a screensaver from Yoyodyne
5948 Corporation. An application is said to <firstterm>own</firstterm> a
5949 name if the message bus has associated the application's connection
5950 with the name. Names may also have <firstterm>queued
5951 owners</firstterm> (see <xref linkend="term-queued-owner"/>).
5952 The bus assigns a unique name to each connection,
5953 see <xref linkend="term-unique-name"/>. Other names
5954 can be thought of as "well-known names" and are
5955 used to find applications that offer specific functionality.
5959 See <xref linkend="message-protocol-names-bus"/> for details of
5960 the syntax and naming conventions for bus names.
5965 <glossentry id="term-message"><glossterm>Message</glossterm>
5968 A message is the atomic unit of communication via the D-Bus
5969 protocol. It consists of a <firstterm>header</firstterm> and a
5970 <firstterm>body</firstterm>; the body is made up of
5971 <firstterm>arguments</firstterm>.
5976 <glossentry id="term-message-bus"><glossterm>Message Bus</glossterm>
5979 The message bus is a special application that forwards
5980 or routes messages between a group of applications
5981 connected to the message bus. It also manages
5982 <firstterm>names</firstterm> used for routing
5988 <glossentry id="term-name"><glossterm>Name</glossterm>
5991 See <xref linkend="term-bus-name"/>. "Name" may
5992 also be used to refer to some of the other names
5993 in D-Bus, such as interface names.
5998 <glossentry id="namespace"><glossterm>Namespace</glossterm>
6001 Used to prevent collisions when defining new interfaces, bus names
6002 etc. The convention used is the same one Java uses for defining
6003 classes: a reversed domain name.
6004 See <xref linkend="message-protocol-names-bus"/>,
6005 <xref linkend="message-protocol-names-interface"/>,
6006 <xref linkend="message-protocol-names-error"/>,
6007 <xref linkend="message-protocol-marshaling-object-path"/>.
6012 <glossentry id="term-object"><glossterm>Object</glossterm>
6015 Each application contains <firstterm>objects</firstterm>, which have
6016 <firstterm>interfaces</firstterm> and
6017 <firstterm>methods</firstterm>. Objects are referred to by a name,
6018 called a <firstterm>path</firstterm>.
6023 <glossentry id="one-to-one"><glossterm>One-to-One</glossterm>
6026 An application talking directly to another application, without going
6027 through a message bus. One-to-one connections may be "peer to peer" or
6028 "client to server." The D-Bus protocol has no concept of client
6029 vs. server after a connection has authenticated; the flow of messages
6030 is symmetrical (full duplex).
6035 <glossentry id="term-path"><glossterm>Path</glossterm>
6038 Object references (object names) in D-Bus are organized into a
6039 filesystem-style hierarchy, so each object is named by a path. As in
6040 LDAP, there's no difference between "files" and "directories"; a path
6041 can refer to an object, while still having child objects below it.
6046 <glossentry id="term-queued-owner"><glossterm>Queued Name Owner</glossterm>
6049 Each bus name has a primary owner; messages sent to the name go to the
6050 primary owner. However, certain names also maintain a queue of
6051 secondary owners "waiting in the wings." If the primary owner releases
6052 the name, then the first secondary owner in the queue automatically
6053 becomes the new owner of the name.
6058 <glossentry id="term-service"><glossterm>Service</glossterm>
6061 A service is an executable that can be launched by the bus daemon.
6062 Services normally guarantee some particular features, for example they
6063 may guarantee that they will request a specific name such as
6064 "com.example.Screensaver", have a singleton object
6065 "/com/example/Application", and that object will implement the
6066 interface "com.example.Screensaver.Control".
6071 <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
6074 ".service files" tell the bus about service applications that can be
6075 launched (see <xref linkend="term-service"/>). Most importantly they
6076 provide a mapping from bus names to services that will request those
6077 names when they start up.
6082 <glossentry id="term-unique-name"><glossterm>Unique Connection Name</glossterm>
6085 The special name automatically assigned to each connection by the
6086 message bus. This name will never change owner, and will be unique
6087 (never reused during the lifetime of the message bus).
6088 It will begin with a ':' character.
projects / platform / upstream / dbus.git / blob