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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-latency, low-overhead, easy to use
179 interprocess communication (IPC). In more detail:
183 D-Bus is <emphasis>low-latency</emphasis> because it is designed
184 to avoid round trips and allow asynchronous operation, much like
190 D-Bus is <emphasis>low-overhead</emphasis> because it uses a
191 binary protocol, and does not have to convert to and from a text
192 format such as XML. Because D-Bus is intended for potentially
193 high-resolution same-machine IPC, not primarily for Internet IPC,
194 this is an interesting optimization.
199 D-Bus is <emphasis>easy to use</emphasis> because it works in terms
200 of <firstterm>messages</firstterm> rather than byte streams, and
201 automatically handles a lot of the hard IPC issues. Also, the D-Bus
202 library is designed to be wrapped in a way that lets developers use
203 their framework's existing object/type system, rather than learning
204 a new one specifically for IPC.
211 The base D-Bus protocol is a one-to-one (peer-to-peer or client-server)
212 protocol, specified in <xref linkend="message-protocol"/>. That is, it is
213 a system for one application to talk to a single other
214 application. However, the primary intended application of the protocol is the
215 D-Bus <firstterm>message bus</firstterm>, specified in <xref
216 linkend="message-bus"/>. The message bus is a special application that
217 accepts connections from multiple other applications, and forwards
222 Uses of D-Bus include notification of system changes (notification of when
223 a camera is plugged in to a computer, or a new version of some software
224 has been installed), or desktop interoperability, for example a file
225 monitoring service or a configuration service.
229 D-Bus is designed for two specific use cases:
233 A "system bus" for notifications from the system to user sessions,
234 and to allow the system to request input from user sessions.
239 A "session bus" used to implement desktop environments such as
244 D-Bus is not intended to be a generic IPC system for any possible
245 application, and intentionally omits many features found in other
246 IPC systems for this reason.
250 At the same time, the bus daemons offer a number of features not found in
251 other IPC systems, such as single-owner "bus names" (similar to X
252 selections), on-demand startup of services, and security policies.
253 In many ways, these features are the primary motivation for developing
254 D-Bus; other systems would have sufficed if IPC were the only goal.
258 D-Bus may turn out to be useful in unanticipated applications, but future
259 versions of this spec and the reference implementation probably will not
260 incorporate features that interfere with the core use cases.
264 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
265 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
266 document are to be interpreted as described in RFC 2119. However, the
267 document could use a serious audit to be sure it makes sense to do
268 so. Also, they are not capitalized.
271 <sect2 id="stability">
272 <title>Protocol and Specification Stability</title>
274 The D-Bus protocol is frozen (only compatible extensions are allowed) as
275 of November 8, 2006. However, this specification could still use a fair
276 bit of work to make interoperable reimplementation possible without
277 reference to the D-Bus reference implementation. Thus, this
278 specification is not marked 1.0. To mark it 1.0, we'd like to see
279 someone invest significant effort in clarifying the specification
280 language, and growing the specification to cover more aspects of the
281 reference implementation's behavior.
284 Until this work is complete, any attempt to reimplement D-Bus will
285 probably require looking at the reference implementation and/or asking
286 questions on the D-Bus mailing list about intended behavior.
287 Questions on the list are very welcome.
290 Nonetheless, this document should be a useful starting point and is
291 to our knowledge accurate, though incomplete.
297 <sect1 id="type-system">
298 <title>Type System</title>
301 D-Bus has a type system, in which values of various types can be
302 serialized into a sequence of bytes referred to as the
303 <firstterm>wire format</firstterm> in a standard way.
304 Converting a value from some other representation into the wire
305 format is called <firstterm>marshaling</firstterm> and converting
306 it back from the wire format is <firstterm>unmarshaling</firstterm>.
310 The D-Bus protocol does not include type tags in the marshaled data; a
311 block of marshaled values must have a known <firstterm>type
312 signature</firstterm>. The type signature is made up of zero or more
313 <firstterm id="term-single-complete-type">single complete
314 types</firstterm>, each made up of one or more
315 <firstterm>type codes</firstterm>.
319 A type code is an ASCII character representing the
320 type of a value. Because ASCII characters are used, the type signature
321 will always form a valid ASCII string. A simple string compare
322 determines whether two type signatures are equivalent.
326 A single complete type is a sequence of type codes that fully describes
327 one type: either a basic type, or a single fully-described container type.
328 A single complete type is a basic type code, a variant type code,
329 an array with its element type, or a struct with its fields (all of which
330 are defined below). So the following signatures are not single complete
341 And the following signatures contain multiple complete types:
351 Note however that a single complete type may <emphasis>contain</emphasis>
352 multiple other single complete types, by containing a struct or dict
356 <sect2 id="basic-types">
357 <title>Basic types</title>
360 The simplest type codes are the <firstterm id="term-basic-type">basic
361 types</firstterm>, which are the types whose structure is entirely
362 defined by their 1-character type code. Basic types consist of
363 fixed types and string-like types.
367 The <firstterm id="term-fixed-type">fixed types</firstterm>
368 are basic types whose values have a fixed length, namely BYTE,
369 BOOLEAN, DOUBLE, UNIX_FD, and signed or unsigned integers of length
374 As a simple example, the type code for 32-bit integer (<literal>INT32</literal>) is
375 the ASCII character 'i'. So the signature for a block of values
376 containing a single <literal>INT32</literal> would be:
380 A block of values containing two <literal>INT32</literal> would have this signature:
387 The characteristics of the fixed types are listed in this table.
393 <entry>Conventional name</entry>
394 <entry>ASCII type-code</entry>
395 <entry>Encoding</entry>
400 <entry><literal>BYTE</literal></entry>
401 <entry><literal>y</literal> (121)</entry>
402 <entry>Unsigned 8-bit integer</entry>
405 <entry><literal>BOOLEAN</literal></entry>
406 <entry><literal>b</literal> (98)</entry>
407 <entry>Boolean value: 0 is false, 1 is true, any other value
408 allowed by the marshalling format is invalid</entry>
411 <entry><literal>INT16</literal></entry>
412 <entry><literal>n</literal> (110)</entry>
413 <entry>Signed (two's complement) 16-bit integer</entry>
416 <entry><literal>UINT16</literal></entry>
417 <entry><literal>q</literal> (113)</entry>
418 <entry>Unsigned 16-bit integer</entry>
421 <entry><literal>INT32</literal></entry>
422 <entry><literal>i</literal> (105)</entry>
423 <entry>Signed (two's complement) 32-bit integer</entry>
426 <entry><literal>UINT32</literal></entry>
427 <entry><literal>u</literal> (117)</entry>
428 <entry>Unsigned 32-bit integer</entry>
431 <entry><literal>INT64</literal></entry>
432 <entry><literal>x</literal> (120)</entry>
433 <entry>Signed (two's complement) 64-bit integer
434 (mnemonic: x and t are the first characters in "sixty" not
435 already used for something more common)</entry>
438 <entry><literal>UINT64</literal></entry>
439 <entry><literal>t</literal> (116)</entry>
440 <entry>Unsigned 64-bit integer</entry>
443 <entry><literal>DOUBLE</literal></entry>
444 <entry><literal>d</literal> (100)</entry>
445 <entry>IEEE 754 double-precision floating point</entry>
448 <entry><literal>UNIX_FD</literal></entry>
449 <entry><literal>h</literal> (104)</entry>
450 <entry>Unsigned 32-bit integer representing an index into an
451 out-of-band array of file descriptors, transferred via some
452 platform-specific mechanism (mnemonic: h for handle)</entry>
460 The <firstterm id="term-string-like-type">string-like types</firstterm>
461 are basic types with a variable length. The value of any string-like
462 type is conceptually 0 or more Unicode codepoints encoded in UTF-8,
463 none of which may be U+0000. The UTF-8 text must be validated
464 strictly: in particular, it must not contain overlong sequences
465 or codepoints above U+10FFFF.
469 Since D-Bus Specification version 0.21, in accordance with Unicode
470 Corrigendum #9, the "noncharacters" U+FDD0..U+FDEF, U+nFFFE and
471 U+nFFFF are allowed in UTF-8 strings (but note that older versions of
472 D-Bus rejected these noncharacters).
476 The marshalling formats for the string-like types all end with a
477 single zero (NUL) byte, but that byte is not considered to be part of
482 The characteristics of the string-like types are listed in this table.
488 <entry>Conventional name</entry>
489 <entry>ASCII type-code</entry>
490 <entry>Validity constraints</entry>
495 <entry><literal>STRING</literal></entry>
496 <entry><literal>s</literal> (115)</entry>
497 <entry>No extra constraints</entry>
500 <entry><literal>OBJECT_PATH</literal></entry>
501 <entry><literal>o</literal> (111)</entry>
503 <link linkend="message-protocol-marshaling-object-path">a
504 syntactically valid object path</link></entry>
507 <entry><literal>SIGNATURE</literal></entry>
508 <entry><literal>g</literal> (103)</entry>
510 <firstterm linkend="term-single-complete-type">single
511 complete types</firstterm></entry>
518 <sect3 id="message-protocol-marshaling-object-path">
519 <title>Valid Object Paths</title>
522 An object path is a name used to refer to an object instance.
523 Conceptually, each participant in a D-Bus message exchange may have
524 any number of object instances (think of C++ or Java objects) and each
525 such instance will have a path. Like a filesystem, the object
526 instances in an application form a hierarchical tree.
530 Object paths are often namespaced by starting with a reversed
531 domain name and containing an interface version number, in the
533 <link linkend="message-protocol-names-interface">interface
535 <link linkend="message-protocol-names-bus">well-known
537 This makes it possible to implement more than one service, or
538 more than one version of a service, in the same process,
539 even if the services share a connection but cannot otherwise
540 co-operate (for instance, if they are implemented by different
545 For instance, if the owner of <literal>example.com</literal> is
546 developing a D-Bus API for a music player, they might use the
547 hierarchy of object paths that start with
548 <literal>/com/example/MusicPlayer1</literal> for its objects.
552 The following rules define a valid object path. Implementations must
553 not send or accept messages with invalid object paths.
557 The path may be of any length.
562 The path must begin with an ASCII '/' (integer 47) character,
563 and must consist of elements separated by slash characters.
568 Each element must only contain the ASCII characters
574 No element may be the empty string.
579 Multiple '/' characters cannot occur in sequence.
584 A trailing '/' character is not allowed unless the
585 path is the root path (a single '/' character).
593 <sect3 id="message-protocol-marshaling-signature">
594 <title>Valid Signatures</title>
596 An implementation must not send or accept invalid signatures.
597 Valid signatures will conform to the following rules:
601 The signature is a list of single complete types.
602 Arrays must have element types, and structs must
603 have both open and close parentheses.
608 Only type codes, open and close parentheses, and open and
609 close curly brackets are allowed in the signature. The
610 <literal>STRUCT</literal> type code
611 is not allowed in signatures, because parentheses
612 are used instead. Similarly, the
613 <literal>DICT_ENTRY</literal> type code is not allowed in
614 signatures, because curly brackets are used instead.
619 The maximum depth of container type nesting is 32 array type
620 codes and 32 open parentheses. This implies that the maximum
621 total depth of recursion is 64, for an "array of array of array
622 of ... struct of struct of struct of ..." where there are 32
628 The maximum length of a signature is 255.
635 When signatures appear in messages, the marshalling format
636 guarantees that they will be followed by a nul byte (which can
637 be interpreted as either C-style string termination or the INVALID
638 type-code), but this is not conceptually part of the signature.
644 <sect2 id="container-types">
645 <title>Container types</title>
648 In addition to basic types, there are four <firstterm>container</firstterm>
649 types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, <literal>VARIANT</literal>,
650 and <literal>DICT_ENTRY</literal>.
654 <literal>STRUCT</literal> has a type code, ASCII character 'r', but this type
655 code does not appear in signatures. Instead, ASCII characters
656 '(' and ')' are used to mark the beginning and end of the struct.
657 So for example, a struct containing two integers would have this
662 Structs can be nested, so for example a struct containing
663 an integer and another struct:
667 The value block storing that struct would contain three integers; the
668 type signature allows you to distinguish "(i(ii))" from "((ii)i)" or
673 The <literal>STRUCT</literal> type code 'r' is not currently used in the D-Bus protocol,
674 but is useful in code that implements the protocol. This type code
675 is specified to allow such code to interoperate in non-protocol contexts.
679 Empty structures are not allowed; there must be at least one
680 type code between the parentheses.
684 <literal>ARRAY</literal> has ASCII character 'a' as type code. The array type code must be
685 followed by a <firstterm>single complete type</firstterm>. The single
686 complete type following the array is the type of each array element. So
687 the simple example is:
691 which is an array of 32-bit integers. But an array can be of any type,
692 such as this array-of-struct-with-two-int32-fields:
696 Or this array of array of integer:
703 <literal>VARIANT</literal> has ASCII character 'v' as its type code. A marshaled value of
704 type <literal>VARIANT</literal> will have the signature of a single complete type as part
705 of the <emphasis>value</emphasis>. This signature will be followed by a
706 marshaled value of that type.
710 Unlike a message signature, the variant signature can
711 contain only a single complete type. So "i", "ai"
712 or "(ii)" is OK, but "ii" is not. Use of variants may not
713 cause a total message depth to be larger than 64, including
714 other container types such as structures.
718 A <literal>DICT_ENTRY</literal> works exactly like a struct, but rather
719 than parentheses it uses curly braces, and it has more restrictions.
720 The restrictions are: it occurs only as an array element type; it has
721 exactly two single complete types inside the curly braces; the first
722 single complete type (the "key") must be a basic type rather than a
723 container type. Implementations must not accept dict entries outside of
724 arrays, must not accept dict entries with zero, one, or more than two
725 fields, and must not accept dict entries with non-basic-typed keys. A
726 dict entry is always a key-value pair.
730 The first field in the <literal>DICT_ENTRY</literal> is always the key.
731 A message is considered corrupt if the same key occurs twice in the same
732 array of <literal>DICT_ENTRY</literal>. However, for performance reasons
733 implementations are not required to reject dicts with duplicate keys.
737 In most languages, an array of dict entry would be represented as a
738 map, hash table, or dict object.
743 <title>Summary of types</title>
746 The following table summarizes the D-Bus types.
751 <entry>Conventional Name</entry>
753 <entry>Description</entry>
758 <entry><literal>INVALID</literal></entry>
759 <entry>0 (ASCII NUL)</entry>
760 <entry>Not a valid type code, used to terminate signatures</entry>
762 <entry><literal>BYTE</literal></entry>
763 <entry>121 (ASCII 'y')</entry>
764 <entry>8-bit unsigned integer</entry>
766 <entry><literal>BOOLEAN</literal></entry>
767 <entry>98 (ASCII 'b')</entry>
768 <entry>Boolean value, 0 is <literal>FALSE</literal> and 1 is <literal>TRUE</literal>. Everything else is invalid.</entry>
770 <entry><literal>INT16</literal></entry>
771 <entry>110 (ASCII 'n')</entry>
772 <entry>16-bit signed integer</entry>
774 <entry><literal>UINT16</literal></entry>
775 <entry>113 (ASCII 'q')</entry>
776 <entry>16-bit unsigned integer</entry>
778 <entry><literal>INT32</literal></entry>
779 <entry>105 (ASCII 'i')</entry>
780 <entry>32-bit signed integer</entry>
782 <entry><literal>UINT32</literal></entry>
783 <entry>117 (ASCII 'u')</entry>
784 <entry>32-bit unsigned integer</entry>
786 <entry><literal>INT64</literal></entry>
787 <entry>120 (ASCII 'x')</entry>
788 <entry>64-bit signed integer</entry>
790 <entry><literal>UINT64</literal></entry>
791 <entry>116 (ASCII 't')</entry>
792 <entry>64-bit unsigned integer</entry>
794 <entry><literal>DOUBLE</literal></entry>
795 <entry>100 (ASCII 'd')</entry>
796 <entry>IEEE 754 double</entry>
798 <entry><literal>STRING</literal></entry>
799 <entry>115 (ASCII 's')</entry>
800 <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated and contain no other nul bytes.</entry>
802 <entry><literal>OBJECT_PATH</literal></entry>
803 <entry>111 (ASCII 'o')</entry>
804 <entry>Name of an object instance</entry>
806 <entry><literal>SIGNATURE</literal></entry>
807 <entry>103 (ASCII 'g')</entry>
808 <entry>A type signature</entry>
810 <entry><literal>ARRAY</literal></entry>
811 <entry>97 (ASCII 'a')</entry>
814 <entry><literal>STRUCT</literal></entry>
815 <entry>114 (ASCII 'r'), 40 (ASCII '('), 41 (ASCII ')')</entry>
816 <entry>Struct; type code 114 'r' is reserved for use in
817 bindings and implementations to represent the general
818 concept of a struct, and must not appear in signatures
819 used on D-Bus.</entry>
821 <entry><literal>VARIANT</literal></entry>
822 <entry>118 (ASCII 'v') </entry>
823 <entry>Variant type (the type of the value is part of the value itself)</entry>
825 <entry><literal>DICT_ENTRY</literal></entry>
826 <entry>101 (ASCII 'e'), 123 (ASCII '{'), 125 (ASCII '}') </entry>
827 <entry>Entry in a dict or map (array of key-value pairs).
828 Type code 101 'e' is reserved for use in bindings and
829 implementations to represent the general concept of a
830 dict or dict-entry, and must not appear in signatures
831 used on D-Bus.</entry>
833 <entry><literal>UNIX_FD</literal></entry>
834 <entry>104 (ASCII 'h')</entry>
835 <entry>Unix file descriptor</entry>
838 <entry>(reserved)</entry>
839 <entry>109 (ASCII 'm')</entry>
840 <entry>Reserved for <ulink
841 url="https://bugs.freedesktop.org/show_bug.cgi?id=27857">a
842 'maybe' type compatible with the one in GVariant</ulink>,
843 and must not appear in signatures used on D-Bus until
844 specified here</entry>
847 <entry>(reserved)</entry>
848 <entry>42 (ASCII '*')</entry>
849 <entry>Reserved for use in bindings/implementations to
850 represent any <firstterm>single complete type</firstterm>,
851 and must not appear in signatures used on D-Bus.</entry>
854 <entry>(reserved)</entry>
855 <entry>63 (ASCII '?')</entry>
856 <entry>Reserved for use in bindings/implementations to
857 represent any <firstterm>basic type</firstterm>, and must
858 not appear in signatures used on D-Bus.</entry>
861 <entry>(reserved)</entry>
862 <entry>64 (ASCII '@'), 38 (ASCII '&'),
863 94 (ASCII '^')</entry>
864 <entry>Reserved for internal use by bindings/implementations,
865 and must not appear in signatures used on D-Bus.
866 GVariant uses these type-codes to encode calling
877 <sect1 id="message-protocol-marshaling">
878 <title>Marshaling (Wire Format)</title>
881 D-Bus defines a marshalling format for its type system, which is
882 used in D-Bus messages. This is not the only possible marshalling
883 format for the type system: for instance, GVariant (part of GLib)
884 re-uses the D-Bus type system but implements an alternative marshalling
889 <title>Byte order and alignment</title>
892 Given a type signature, a block of bytes can be converted into typed
893 values. This section describes the format of the block of bytes. Byte
894 order and alignment issues are handled uniformly for all D-Bus types.
898 A block of bytes has an associated byte order. The byte order
899 has to be discovered in some way; for D-Bus messages, the
900 byte order is part of the message header as described in
901 <xref linkend="message-protocol-messages"/>. For now, assume
902 that the byte order is known to be either little endian or big
907 Each value in a block of bytes is aligned "naturally," for example
908 4-byte values are aligned to a 4-byte boundary, and 8-byte values to an
909 8-byte boundary. To properly align a value, <firstterm>alignment
910 padding</firstterm> may be necessary. The alignment padding must always
911 be the minimum required padding to properly align the following value;
912 and it must always be made up of nul bytes. The alignment padding must
913 not be left uninitialized (it can't contain garbage), and more padding
914 than required must not be used.
918 As an exception to natural alignment, <literal>STRUCT</literal> and
919 <literal>DICT_ENTRY</literal> values are always aligned to an 8-byte
920 boundary, regardless of the alignments of their contents.
925 <title>Marshalling basic types</title>
928 To marshal and unmarshal fixed types, you simply read one value
929 from the data block corresponding to each type code in the signature.
930 All signed integer values are encoded in two's complement, DOUBLE
931 values are IEEE 754 double-precision floating-point, and BOOLEAN
932 values are encoded in 32 bits (of which only the least significant
937 The string-like types are all marshalled as a
938 fixed-length unsigned integer <varname>n</varname> giving the
939 length of the variable part, followed by <varname>n</varname>
940 nonzero bytes of UTF-8 text, followed by a single zero (nul) byte
941 which is not considered to be part of the text. The alignment
942 of the string-like type is the same as the alignment of
943 <varname>n</varname>.
947 For the STRING and OBJECT_PATH types, <varname>n</varname> is
948 encoded in 4 bytes, leading to 4-byte alignment.
949 For the SIGNATURE type, <varname>n</varname> is encoded as a single
950 byte. As a result, alignment padding is never required before a
956 <title>Marshalling containers</title>
959 Arrays are marshalled as a <literal>UINT32</literal>
960 <varname>n</varname> giving the length of the array data in bytes,
961 followed by alignment padding to the alignment boundary of the array
962 element type, followed by the <varname>n</varname> bytes of the
963 array elements marshalled in sequence. <varname>n</varname> does not
964 include the padding after the length, or any padding after the
969 For instance, if the current position in the message is a multiple
970 of 8 bytes and the byte-order is big-endian, an array containing only
971 the 64-bit integer 5 would be marshalled as:
974 00 00 00 08 <lineannotation>8 bytes of data</lineannotation>
975 00 00 00 00 <lineannotation>padding to 8-byte boundary</lineannotation>
976 00 00 00 00 00 00 00 05 <lineannotation>first element = 5</lineannotation>
981 Arrays have a maximum length defined to be 2 to the 26th power or
982 67108864. Implementations must not send or accept arrays exceeding this
987 Structs and dict entries are marshalled in the same way as their
988 contents, but their alignment is always to an 8-byte boundary,
989 even if their contents would normally be less strictly aligned.
993 Variants are marshalled as the <literal>SIGNATURE</literal> of
994 the contents (which must be a single complete type), followed by a
995 marshalled value with the type given by that signature. The
996 variant has the same 1-byte alignment as the signature, which means
997 that alignment padding before a variant is never needed.
998 Use of variants may not cause a total message depth to be larger
999 than 64, including other container types such as structures.
1004 <title>Summary of D-Bus marshalling</title>
1007 Given all this, the types are marshaled on the wire as follows:
1012 <entry>Conventional Name</entry>
1013 <entry>Encoding</entry>
1014 <entry>Alignment</entry>
1019 <entry><literal>INVALID</literal></entry>
1020 <entry>Not applicable; cannot be marshaled.</entry>
1023 <entry><literal>BYTE</literal></entry>
1024 <entry>A single 8-bit byte.</entry>
1027 <entry><literal>BOOLEAN</literal></entry>
1028 <entry>As for <literal>UINT32</literal>, but only 0 and 1 are valid values.</entry>
1031 <entry><literal>INT16</literal></entry>
1032 <entry>16-bit signed integer in the message's byte order.</entry>
1035 <entry><literal>UINT16</literal></entry>
1036 <entry>16-bit unsigned integer in the message's byte order.</entry>
1039 <entry><literal>INT32</literal></entry>
1040 <entry>32-bit signed integer in the message's byte order.</entry>
1043 <entry><literal>UINT32</literal></entry>
1044 <entry>32-bit unsigned integer in the message's byte order.</entry>
1047 <entry><literal>INT64</literal></entry>
1048 <entry>64-bit signed integer in the message's byte order.</entry>
1051 <entry><literal>UINT64</literal></entry>
1052 <entry>64-bit unsigned integer in the message's byte order.</entry>
1055 <entry><literal>DOUBLE</literal></entry>
1056 <entry>64-bit IEEE 754 double in the message's byte order.</entry>
1059 <entry><literal>STRING</literal></entry>
1060 <entry>A <literal>UINT32</literal> indicating the string's
1061 length in bytes excluding its terminating nul, followed by
1062 non-nul string data of the given length, followed by a terminating nul
1069 <entry><literal>OBJECT_PATH</literal></entry>
1070 <entry>Exactly the same as <literal>STRING</literal> except the
1071 content must be a valid object path (see above).
1077 <entry><literal>SIGNATURE</literal></entry>
1078 <entry>The same as <literal>STRING</literal> except the length is a single
1079 byte (thus signatures have a maximum length of 255)
1080 and the content must be a valid signature (see above).
1086 <entry><literal>ARRAY</literal></entry>
1088 A <literal>UINT32</literal> giving the length of the array data in bytes, followed by
1089 alignment padding to the alignment boundary of the array element type,
1090 followed by each array element.
1096 <entry><literal>STRUCT</literal></entry>
1098 A struct must start on an 8-byte boundary regardless of the
1099 type of the struct fields. The struct value consists of each
1100 field marshaled in sequence starting from that 8-byte
1107 <entry><literal>VARIANT</literal></entry>
1109 The marshaled <literal>SIGNATURE</literal> of a single
1110 complete type, followed by a marshaled value with the type
1111 given in the signature.
1114 1 (alignment of the signature)
1117 <entry><literal>DICT_ENTRY</literal></entry>
1119 Identical to STRUCT.
1125 <entry><literal>UNIX_FD</literal></entry>
1126 <entry>32-bit unsigned integer in the message's byte
1127 order. The actual file descriptors need to be
1128 transferred out-of-band via some platform specific
1129 mechanism. On the wire, values of this type store the index to the
1130 file descriptor in the array of file descriptors that
1131 accompany the message.</entry>
1143 <sect1 id="message-protocol">
1144 <title>Message Protocol</title>
1147 A <firstterm>message</firstterm> consists of a
1148 <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you
1149 think of a message as a package, the header is the address, and the body
1150 contains the package contents. The message delivery system uses the header
1151 information to figure out where to send the message and how to interpret
1152 it; the recipient interprets the body of the message.
1156 The body of the message is made up of zero or more
1157 <firstterm>arguments</firstterm>, which are typed values, such as an
1158 integer or a byte array.
1162 Both header and body use the D-Bus <link linkend="type-system">type
1163 system</link> and format for serializing data.
1166 <sect2 id="message-protocol-messages">
1167 <title>Message Format</title>
1170 A message consists of a header and a body. The header is a block of
1171 values with a fixed signature and meaning. The body is a separate block
1172 of values, with a signature specified in the header.
1176 The length of the header must be a multiple of 8, allowing the body to
1177 begin on an 8-byte boundary when storing the entire message in a single
1178 buffer. If the header does not naturally end on an 8-byte boundary
1179 up to 7 bytes of nul-initialized alignment padding must be added.
1183 The message body need not end on an 8-byte boundary.
1187 The maximum length of a message, including header, header alignment padding,
1188 and body is 2 to the 27th power or 134217728. Implementations must not
1189 send or accept messages exceeding this size.
1193 The signature of the header is:
1197 Written out more readably, this is:
1199 BYTE, BYTE, BYTE, BYTE, UINT32, UINT32, ARRAY of STRUCT of (BYTE,VARIANT)
1204 These values have the following meanings:
1209 <entry>Value</entry>
1210 <entry>Description</entry>
1215 <entry>1st <literal>BYTE</literal></entry>
1216 <entry>Endianness flag; ASCII 'l' for little-endian
1217 or ASCII 'B' for big-endian. Both header and body are
1218 in this endianness.</entry>
1221 <entry>2nd <literal>BYTE</literal></entry>
1222 <entry><firstterm>Message type</firstterm>. Unknown types must be ignored.
1223 Currently-defined types are described below.
1227 <entry>3rd <literal>BYTE</literal></entry>
1228 <entry>Bitwise OR of flags. Unknown flags
1229 must be ignored. Currently-defined flags are described below.
1233 <entry>4th <literal>BYTE</literal></entry>
1234 <entry>Major protocol version of the sending application. If
1235 the major protocol version of the receiving application does not
1236 match, the applications will not be able to communicate and the
1237 D-Bus connection must be disconnected. The major protocol
1238 version for this version of the specification is 1.
1242 <entry>1st <literal>UINT32</literal></entry>
1243 <entry>Length in bytes of the message body, starting
1244 from the end of the header. The header ends after
1245 its alignment padding to an 8-boundary.
1249 <entry>2nd <literal>UINT32</literal></entry>
1250 <entry>The serial of this message, used as a cookie
1251 by the sender to identify the reply corresponding
1252 to this request. This must not be zero.
1256 <entry><literal>ARRAY</literal> of <literal>STRUCT</literal> of (<literal>BYTE</literal>,<literal>VARIANT</literal>)</entry>
1257 <entry>An array of zero or more <firstterm>header
1258 fields</firstterm> where the byte is the field code, and the
1259 variant is the field value. The message type determines
1260 which fields are required.
1268 <firstterm>Message types</firstterm> that can appear in the second byte
1274 <entry>Conventional name</entry>
1275 <entry>Decimal value</entry>
1276 <entry>Description</entry>
1281 <entry><literal>INVALID</literal></entry>
1283 <entry>This is an invalid type.</entry>
1286 <entry><literal>METHOD_CALL</literal></entry>
1288 <entry>Method call.</entry>
1291 <entry><literal>METHOD_RETURN</literal></entry>
1293 <entry>Method reply with returned data.</entry>
1296 <entry><literal>ERROR</literal></entry>
1298 <entry>Error reply. If the first argument exists and is a
1299 string, it is an error message.</entry>
1302 <entry><literal>SIGNAL</literal></entry>
1304 <entry>Signal emission.</entry>
1311 Flags that can appear in the third byte of the header:
1316 <entry>Conventional name</entry>
1317 <entry>Hex value</entry>
1318 <entry>Description</entry>
1323 <entry><literal>NO_REPLY_EXPECTED</literal></entry>
1325 <entry>This message does not expect method return replies or
1326 error replies; the reply can be omitted as an
1327 optimization. However, it is compliant with this specification
1328 to return the reply despite this flag and the only harm
1329 from doing so is extra network traffic.
1333 <entry><literal>NO_AUTO_START</literal></entry>
1335 <entry>The bus must not launch an owner
1336 for the destination name in response to this message.
1344 <sect3 id="message-protocol-header-fields">
1345 <title>Header Fields</title>
1348 The array at the end of the header contains <firstterm>header
1349 fields</firstterm>, where each field is a 1-byte field code followed
1350 by a field value. A header must contain the required header fields for
1351 its message type, and zero or more of any optional header
1352 fields. Future versions of this protocol specification may add new
1353 fields. Implementations must ignore fields they do not
1354 understand. Implementations must not invent their own header fields;
1355 only changes to this specification may introduce new header fields.
1359 Again, if an implementation sees a header field code that it does not
1360 expect, it must ignore that field, as it will be part of a new
1361 (but compatible) version of this specification. This also applies
1362 to known header fields appearing in unexpected messages, for
1363 example: if a signal has a reply serial it must be ignored
1364 even though it has no meaning as of this version of the spec.
1368 However, implementations must not send or accept known header fields
1369 with the wrong type stored in the field value. So for example a
1370 message with an <literal>INTERFACE</literal> field of type
1371 <literal>UINT32</literal> would be considered corrupt.
1375 Here are the currently-defined header fields:
1380 <entry>Conventional Name</entry>
1381 <entry>Decimal Code</entry>
1383 <entry>Required In</entry>
1384 <entry>Description</entry>
1389 <entry><literal>INVALID</literal></entry>
1392 <entry>not allowed</entry>
1393 <entry>Not a valid field name (error if it appears in a message)</entry>
1396 <entry><literal>PATH</literal></entry>
1398 <entry><literal>OBJECT_PATH</literal></entry>
1399 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1400 <entry>The object to send a call to,
1401 or the object a signal is emitted from.
1403 <literal>/org/freedesktop/DBus/Local</literal> is reserved;
1404 implementations should not send messages with this path,
1405 and the reference implementation of the bus daemon will
1406 disconnect any application that attempts to do so.
1410 <entry><literal>INTERFACE</literal></entry>
1412 <entry><literal>STRING</literal></entry>
1413 <entry><literal>SIGNAL</literal></entry>
1415 The interface to invoke a method call on, or
1416 that a signal is emitted from. Optional for
1417 method calls, required for signals.
1418 The special interface
1419 <literal>org.freedesktop.DBus.Local</literal> is reserved;
1420 implementations should not send messages with this
1421 interface, and the reference implementation of the bus
1422 daemon will disconnect any application that attempts to
1427 <entry><literal>MEMBER</literal></entry>
1429 <entry><literal>STRING</literal></entry>
1430 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1431 <entry>The member, either the method name or signal name.</entry>
1434 <entry><literal>ERROR_NAME</literal></entry>
1436 <entry><literal>STRING</literal></entry>
1437 <entry><literal>ERROR</literal></entry>
1438 <entry>The name of the error that occurred, for errors</entry>
1441 <entry><literal>REPLY_SERIAL</literal></entry>
1443 <entry><literal>UINT32</literal></entry>
1444 <entry><literal>ERROR</literal>, <literal>METHOD_RETURN</literal></entry>
1445 <entry>The serial number of the message this message is a reply
1446 to. (The serial number is the second <literal>UINT32</literal> in the header.)</entry>
1449 <entry><literal>DESTINATION</literal></entry>
1451 <entry><literal>STRING</literal></entry>
1452 <entry>optional</entry>
1453 <entry>The name of the connection this message is intended for.
1454 Only used in combination with the message bus, see
1455 <xref linkend="message-bus"/>.</entry>
1458 <entry><literal>SENDER</literal></entry>
1460 <entry><literal>STRING</literal></entry>
1461 <entry>optional</entry>
1462 <entry>Unique name of the sending connection.
1463 The message bus fills in this field so it is reliable; the field is
1464 only meaningful in combination with the message bus.</entry>
1467 <entry><literal>SIGNATURE</literal></entry>
1469 <entry><literal>SIGNATURE</literal></entry>
1470 <entry>optional</entry>
1471 <entry>The signature of the message body.
1472 If omitted, it is assumed to be the
1473 empty signature "" (i.e. the body must be 0-length).</entry>
1476 <entry><literal>UNIX_FDS</literal></entry>
1478 <entry><literal>UINT32</literal></entry>
1479 <entry>optional</entry>
1480 <entry>The number of Unix file descriptors that
1481 accompany the message. If omitted, it is assumed
1482 that no Unix file descriptors accompany the
1483 message. The actual file descriptors need to be
1484 transferred via platform specific mechanism
1485 out-of-band. They must be sent at the same time as
1486 part of the message itself. They may not be sent
1487 before the first byte of the message itself is
1488 transferred or after the last byte of the message
1498 <sect2 id="message-protocol-names">
1499 <title>Valid Names</title>
1501 The various names in D-Bus messages have some restrictions.
1504 There is a <firstterm>maximum name length</firstterm>
1505 of 255 which applies to bus names, interfaces, and members.
1507 <sect3 id="message-protocol-names-interface">
1508 <title>Interface names</title>
1510 Interfaces have names with type <literal>STRING</literal>, meaning that
1511 they must be valid UTF-8. However, there are also some
1512 additional restrictions that apply to interface names
1515 <listitem><para>Interface names are composed of 1 or more elements separated by
1516 a period ('.') character. All elements must contain at least
1520 <listitem><para>Each element must only contain the ASCII characters
1521 "[A-Z][a-z][0-9]_" and must not begin with a digit.
1525 <listitem><para>Interface names must contain at least one '.' (period)
1526 character (and thus at least two elements).
1529 <listitem><para>Interface names must not begin with a '.' (period) character.</para></listitem>
1530 <listitem><para>Interface names must not exceed the maximum name length.</para></listitem>
1535 Interface names should start with the reversed DNS domain name of
1536 the author of the interface (in lower-case), like interface names
1537 in Java. It is conventional for the rest of the interface name
1538 to consist of words run together, with initial capital letters
1539 on all words ("CamelCase"). Several levels of hierarchy can be used.
1540 It is also a good idea to include the major version of the interface
1541 in the name, and increment it if incompatible changes are made;
1542 this way, a single object can implement several versions of an
1543 interface in parallel, if necessary.
1547 For instance, if the owner of <literal>example.com</literal> is
1548 developing a D-Bus API for a music player, they might define
1549 interfaces called <literal>com.example.MusicPlayer1</literal>,
1550 <literal>com.example.MusicPlayer1.Track</literal> and
1551 <literal>com.example.MusicPlayer1.Seekable</literal>.
1555 D-Bus does not distinguish between the concepts that would be
1556 called classes and interfaces in Java: either can be identified on
1557 D-Bus by an interface name.
1560 <sect3 id="message-protocol-names-bus">
1561 <title>Bus names</title>
1563 Connections have one or more bus names associated with them.
1564 A connection has exactly one bus name that is a <firstterm>unique
1565 connection name</firstterm>. The unique connection name remains
1566 with the connection for its entire lifetime.
1567 A bus name is of type <literal>STRING</literal>,
1568 meaning that it must be valid UTF-8. However, there are also
1569 some additional restrictions that apply to bus names
1572 <listitem><para>Bus names that start with a colon (':')
1573 character are unique connection names. Other bus names
1574 are called <firstterm>well-known bus names</firstterm>.
1577 <listitem><para>Bus names are composed of 1 or more elements separated by
1578 a period ('.') character. All elements must contain at least
1582 <listitem><para>Each element must only contain the ASCII characters
1583 "[A-Z][a-z][0-9]_-". Only elements that are part of a unique
1584 connection name may begin with a digit, elements in
1585 other bus names must not begin with a digit.
1589 <listitem><para>Bus names must contain at least one '.' (period)
1590 character (and thus at least two elements).
1593 <listitem><para>Bus names must not begin with a '.' (period) character.</para></listitem>
1594 <listitem><para>Bus names must not exceed the maximum name length.</para></listitem>
1598 Note that the hyphen ('-') character is allowed in bus names but
1599 not in interface names.
1603 Like <link linkend="message-protocol-names-interface">interface
1604 names</link>, well-known bus names should start with the
1605 reversed DNS domain name of the author of the interface (in
1606 lower-case), and it is conventional for the rest of the well-known
1607 bus name to consist of words run together, with initial
1608 capital letters. As with interface names, including a version
1609 number in well-known bus names is a good idea; it's possible to
1610 have the well-known bus name for more than one version
1611 simultaneously if backwards compatibility is required.
1615 If a well-known bus name implies the presence of a "main" interface,
1616 that "main" interface is often given the same name as
1617 the well-known bus name, and situated at the corresponding object
1618 path. For instance, if the owner of <literal>example.com</literal>
1619 is developing a D-Bus API for a music player, they might define
1620 that any application that takes the well-known name
1621 <literal>com.example.MusicPlayer1</literal> should have an object
1622 at the object path <literal>/com/example/MusicPlayer1</literal>
1623 which implements the interface
1624 <literal>com.example.MusicPlayer1</literal>.
1627 <sect3 id="message-protocol-names-member">
1628 <title>Member names</title>
1630 Member (i.e. method or signal) names:
1632 <listitem><para>Must only contain the ASCII characters
1633 "[A-Z][a-z][0-9]_" and may not begin with a
1634 digit.</para></listitem>
1635 <listitem><para>Must not contain the '.' (period) character.</para></listitem>
1636 <listitem><para>Must not exceed the maximum name length.</para></listitem>
1637 <listitem><para>Must be at least 1 byte in length.</para></listitem>
1642 It is conventional for member names on D-Bus to consist of
1643 capitalized words with no punctuation ("camel-case").
1644 Method names should usually be verbs, such as
1645 <literal>GetItems</literal>, and signal names should usually be
1646 a description of an event, such as <literal>ItemsChanged</literal>.
1649 <sect3 id="message-protocol-names-error">
1650 <title>Error names</title>
1652 Error names have the same restrictions as interface names.
1656 Error names have the same naming conventions as interface
1657 names, and often contain <literal>.Error.</literal>; for instance,
1658 the owner of <literal>example.com</literal> might define the
1659 errors <literal>com.example.MusicPlayer.Error.FileNotFound</literal>
1660 and <literal>com.example.MusicPlayer.Error.OutOfMemory</literal>.
1661 The errors defined by D-Bus itself, such as
1662 <literal>org.freedesktop.DBus.Error.Failed</literal>, follow a
1668 <sect2 id="message-protocol-types">
1669 <title>Message Types</title>
1671 Each of the message types (<literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, <literal>ERROR</literal>, and
1672 <literal>SIGNAL</literal>) has its own expected usage conventions and header fields.
1673 This section describes these conventions.
1675 <sect3 id="message-protocol-types-method">
1676 <title>Method Calls</title>
1678 Some messages invoke an operation on a remote object. These are
1679 called method call messages and have the type tag <literal>METHOD_CALL</literal>. Such
1680 messages map naturally to methods on objects in a typical program.
1683 A method call message is required to have a <literal>MEMBER</literal> header field
1684 indicating the name of the method. Optionally, the message has an
1685 <literal>INTERFACE</literal> field giving the interface the method is a part of. In the
1686 absence of an <literal>INTERFACE</literal> field, if two interfaces on the same object have
1687 a method with the same name, it is undefined which of the two methods
1688 will be invoked. Implementations may also choose to return an error in
1689 this ambiguous case. However, if a method name is unique
1690 implementations must not require an interface field.
1693 Method call messages also include a <literal>PATH</literal> field
1694 indicating the object to invoke the method on. If the call is passing
1695 through a message bus, the message will also have a
1696 <literal>DESTINATION</literal> field giving the name of the connection
1697 to receive the message.
1700 When an application handles a method call message, it is required to
1701 return a reply. The reply is identified by a <literal>REPLY_SERIAL</literal> header field
1702 indicating the serial number of the <literal>METHOD_CALL</literal> being replied to. The
1703 reply can have one of two types; either <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>.
1706 If the reply has type <literal>METHOD_RETURN</literal>, the arguments to the reply message
1707 are the return value(s) or "out parameters" of the method call.
1708 If the reply has type <literal>ERROR</literal>, then an "exception" has been thrown,
1709 and the call fails; no return value will be provided. It makes
1710 no sense to send multiple replies to the same method call.
1713 Even if a method call has no return values, a <literal>METHOD_RETURN</literal>
1714 reply is required, so the caller will know the method
1715 was successfully processed.
1718 The <literal>METHOD_RETURN</literal> or <literal>ERROR</literal> reply message must have the <literal>REPLY_SERIAL</literal>
1722 If a <literal>METHOD_CALL</literal> message has the flag <literal>NO_REPLY_EXPECTED</literal>,
1723 then as an optimization the application receiving the method
1724 call may choose to omit the reply message (regardless of
1725 whether the reply would have been <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>).
1726 However, it is also acceptable to ignore the <literal>NO_REPLY_EXPECTED</literal>
1727 flag and reply anyway.
1730 Unless a message has the flag <literal>NO_AUTO_START</literal>, if the
1731 destination name does not exist then a program to own the destination
1732 name will be started before the message is delivered. The message
1733 will be held until the new program is successfully started or has
1734 failed to start; in case of failure, an error will be returned. This
1735 flag is only relevant in the context of a message bus, it is ignored
1736 during one-to-one communication with no intermediate bus.
1738 <sect4 id="message-protocol-types-method-apis">
1739 <title>Mapping method calls to native APIs</title>
1741 APIs for D-Bus may map method calls to a method call in a specific
1742 programming language, such as C++, or may map a method call written
1743 in an IDL to a D-Bus message.
1746 In APIs of this nature, arguments to a method are often termed "in"
1747 (which implies sent in the <literal>METHOD_CALL</literal>), or "out" (which implies
1748 returned in the <literal>METHOD_RETURN</literal>). Some APIs such as CORBA also have
1749 "inout" arguments, which are both sent and received, i.e. the caller
1750 passes in a value which is modified. Mapped to D-Bus, an "inout"
1751 argument is equivalent to an "in" argument, followed by an "out"
1752 argument. You can't pass things "by reference" over the wire, so
1753 "inout" is purely an illusion of the in-process API.
1756 Given a method with zero or one return values, followed by zero or more
1757 arguments, where each argument may be "in", "out", or "inout", the
1758 caller constructs a message by appending each "in" or "inout" argument,
1759 in order. "out" arguments are not represented in the caller's message.
1762 The recipient constructs a reply by appending first the return value
1763 if any, then each "out" or "inout" argument, in order.
1764 "in" arguments are not represented in the reply message.
1767 Error replies are normally mapped to exceptions in languages that have
1771 In converting from native APIs to D-Bus, it is perhaps nice to
1772 map D-Bus naming conventions ("FooBar") to native conventions
1773 such as "fooBar" or "foo_bar" automatically. This is OK
1774 as long as you can say that the native API is one that
1775 was specifically written for D-Bus. It makes the most sense
1776 when writing object implementations that will be exported
1777 over the bus. Object proxies used to invoke remote D-Bus
1778 objects probably need the ability to call any D-Bus method,
1779 and thus a magic name mapping like this could be a problem.
1782 This specification doesn't require anything of native API bindings;
1783 the preceding is only a suggested convention for consistency
1789 <sect3 id="message-protocol-types-signal">
1790 <title>Signal Emission</title>
1792 Unlike method calls, signal emissions have no replies.
1793 A signal emission is simply a single message of type <literal>SIGNAL</literal>.
1794 It must have three header fields: <literal>PATH</literal> giving the object
1795 the signal was emitted from, plus <literal>INTERFACE</literal> and <literal>MEMBER</literal> giving
1796 the fully-qualified name of the signal. The <literal>INTERFACE</literal> header is required
1797 for signals, though it is optional for method calls.
1801 <sect3 id="message-protocol-types-errors">
1802 <title>Errors</title>
1804 Messages of type <literal>ERROR</literal> are most commonly replies
1805 to a <literal>METHOD_CALL</literal>, but may be returned in reply
1806 to any kind of message. The message bus for example
1807 will return an <literal>ERROR</literal> in reply to a signal emission if
1808 the bus does not have enough memory to send the signal.
1811 An <literal>ERROR</literal> may have any arguments, but if the first
1812 argument is a <literal>STRING</literal>, it must be an error message.
1813 The error message may be logged or shown to the user
1818 <sect3 id="message-protocol-types-notation">
1819 <title>Notation in this document</title>
1821 This document uses a simple pseudo-IDL to describe particular method
1822 calls and signals. Here is an example of a method call:
1824 org.freedesktop.DBus.StartServiceByName (in STRING name, in UINT32 flags,
1825 out UINT32 resultcode)
1827 This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = StartServiceByName,
1828 <literal>METHOD_CALL</literal> arguments are <literal>STRING</literal> and <literal>UINT32</literal>, <literal>METHOD_RETURN</literal> argument
1829 is <literal>UINT32</literal>. Remember that the <literal>MEMBER</literal> field can't contain any '.' (period)
1830 characters so it's known that the last part of the name in
1831 the "IDL" is the member name.
1834 In C++ that might end up looking like this:
1836 unsigned int org::freedesktop::DBus::StartServiceByName (const char *name,
1837 unsigned int flags);
1839 or equally valid, the return value could be done as an argument:
1841 void org::freedesktop::DBus::StartServiceByName (const char *name,
1843 unsigned int *resultcode);
1845 It's really up to the API designer how they want to make
1846 this look. You could design an API where the namespace wasn't used
1847 in C++, using STL or Qt, using varargs, or whatever you wanted.
1850 Signals are written as follows:
1852 org.freedesktop.DBus.NameLost (STRING name)
1854 Signals don't specify "in" vs. "out" because only
1855 a single direction is possible.
1858 It isn't especially encouraged to use this lame pseudo-IDL in actual
1859 API implementations; you might use the native notation for the
1860 language you're using, or you might use COM or CORBA IDL, for example.
1865 <sect2 id="message-protocol-handling-invalid">
1866 <title>Invalid Protocol and Spec Extensions</title>
1869 For security reasons, the D-Bus protocol should be strictly parsed and
1870 validated, with the exception of defined extension points. Any invalid
1871 protocol or spec violations should result in immediately dropping the
1872 connection without notice to the other end. Exceptions should be
1873 carefully considered, e.g. an exception may be warranted for a
1874 well-understood idiosyncrasy of a widely-deployed implementation. In
1875 cases where the other end of a connection is 100% trusted and known to
1876 be friendly, skipping validation for performance reasons could also make
1877 sense in certain cases.
1881 Generally speaking violations of the "must" requirements in this spec
1882 should be considered possible attempts to exploit security, and violations
1883 of the "should" suggestions should be considered legitimate (though perhaps
1884 they should generate an error in some cases).
1888 The following extension points are built in to D-Bus on purpose and must
1889 not be treated as invalid protocol. The extension points are intended
1890 for use by future versions of this spec, they are not intended for third
1891 parties. At the moment, the only way a third party could extend D-Bus
1892 without breaking interoperability would be to introduce a way to negotiate new
1893 feature support as part of the auth protocol, using EXTENSION_-prefixed
1894 commands. There is not yet a standard way to negotiate features.
1898 In the authentication protocol (see <xref linkend="auth-protocol"/>) unknown
1899 commands result in an ERROR rather than a disconnect. This enables
1900 future extensions to the protocol. Commands starting with EXTENSION_ are
1901 reserved for third parties.
1906 The authentication protocol supports pluggable auth mechanisms.
1911 The address format (see <xref linkend="addresses"/>) supports new
1917 Messages with an unknown type (something other than
1918 <literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>,
1919 <literal>ERROR</literal>, <literal>SIGNAL</literal>) are ignored.
1920 Unknown-type messages must still be well-formed in the same way
1921 as the known messages, however. They still have the normal
1927 Header fields with an unknown or unexpected field code must be ignored,
1928 though again they must still be well-formed.
1933 New standard interfaces (with new methods and signals) can of course be added.
1943 <sect1 id="auth-protocol">
1944 <title>Authentication Protocol</title>
1946 Before the flow of messages begins, two applications must
1947 authenticate. A simple plain-text protocol is used for
1948 authentication; this protocol is a SASL profile, and maps fairly
1949 directly from the SASL specification. The message encoding is
1950 NOT used here, only plain text messages.
1953 In examples, "C:" and "S:" indicate lines sent by the client and
1954 server respectively.
1956 <sect2 id="auth-protocol-overview">
1957 <title>Protocol Overview</title>
1959 The protocol is a line-based protocol, where each line ends with
1960 \r\n. Each line begins with an all-caps ASCII command name containing
1961 only the character range [A-Z_], a space, then any arguments for the
1962 command, then the \r\n ending the line. The protocol is
1963 case-sensitive. All bytes must be in the ASCII character set.
1965 Commands from the client to the server are as follows:
1968 <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
1969 <listitem><para>CANCEL</para></listitem>
1970 <listitem><para>BEGIN</para></listitem>
1971 <listitem><para>DATA <data in hex encoding></para></listitem>
1972 <listitem><para>ERROR [human-readable error explanation]</para></listitem>
1973 <listitem><para>NEGOTIATE_UNIX_FD</para></listitem>
1976 From server to client are as follows:
1979 <listitem><para>REJECTED <space-separated list of mechanism names></para></listitem>
1980 <listitem><para>OK <GUID in hex></para></listitem>
1981 <listitem><para>DATA <data in hex encoding></para></listitem>
1982 <listitem><para>ERROR</para></listitem>
1983 <listitem><para>AGREE_UNIX_FD</para></listitem>
1987 Unofficial extensions to the command set must begin with the letters
1988 "EXTENSION_", to avoid conflicts with future official commands.
1989 For example, "EXTENSION_COM_MYDOMAIN_DO_STUFF".
1992 <sect2 id="auth-nul-byte">
1993 <title>Special credentials-passing nul byte</title>
1995 Immediately after connecting to the server, the client must send a
1996 single nul byte. This byte may be accompanied by credentials
1997 information on some operating systems that use sendmsg() with
1998 SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain
1999 sockets. However, the nul byte must be sent even on other kinds of
2000 socket, and even on operating systems that do not require a byte to be
2001 sent in order to transmit credentials. The text protocol described in
2002 this document begins after the single nul byte. If the first byte
2003 received from the client is not a nul byte, the server may disconnect
2007 A nul byte in any context other than the initial byte is an error;
2008 the protocol is ASCII-only.
2011 The credentials sent along with the nul byte may be used with the
2012 SASL mechanism EXTERNAL.
2015 <sect2 id="auth-command-auth">
2016 <title>AUTH command</title>
2018 If an AUTH command has no arguments, it is a request to list
2019 available mechanisms. The server must respond with a REJECTED
2020 command listing the mechanisms it understands, or with an error.
2023 If an AUTH command specifies a mechanism, and the server supports
2024 said mechanism, the server should begin exchanging SASL
2025 challenge-response data with the client using DATA commands.
2028 If the server does not support the mechanism given in the AUTH
2029 command, it must send either a REJECTED command listing the mechanisms
2030 it does support, or an error.
2033 If the [initial-response] argument is provided, it is intended for use
2034 with mechanisms that have no initial challenge (or an empty initial
2035 challenge), as if it were the argument to an initial DATA command. If
2036 the selected mechanism has an initial challenge and [initial-response]
2037 was provided, the server should reject authentication by sending
2041 If authentication succeeds after exchanging DATA commands,
2042 an OK command must be sent to the client.
2045 The first octet received by the server after the \r\n of the BEGIN
2046 command from the client must be the first octet of the
2047 authenticated/encrypted stream of D-Bus messages.
2050 If BEGIN is received by the server, the first octet received
2051 by the client after the \r\n of the OK command must be the
2052 first octet of the authenticated/encrypted stream of D-Bus
2056 <sect2 id="auth-command-cancel">
2057 <title>CANCEL Command</title>
2059 At any time up to sending the BEGIN command, the client may send a
2060 CANCEL command. On receiving the CANCEL command, the server must
2061 send a REJECTED command and abort the current authentication
2065 <sect2 id="auth-command-data">
2066 <title>DATA Command</title>
2068 The DATA command may come from either client or server, and simply
2069 contains a hex-encoded block of data to be interpreted
2070 according to the SASL mechanism in use.
2073 Some SASL mechanisms support sending an "empty string";
2074 FIXME we need some way to do this.
2077 <sect2 id="auth-command-begin">
2078 <title>BEGIN Command</title>
2080 The BEGIN command acknowledges that the client has received an
2081 OK command from the server, and that the stream of messages
2085 The first octet received by the server after the \r\n of the BEGIN
2086 command from the client must be the first octet of the
2087 authenticated/encrypted stream of D-Bus messages.
2090 <sect2 id="auth-command-rejected">
2091 <title>REJECTED Command</title>
2093 The REJECTED command indicates that the current authentication
2094 exchange has failed, and further exchange of DATA is inappropriate.
2095 The client would normally try another mechanism, or try providing
2096 different responses to challenges.
2098 Optionally, the REJECTED command has a space-separated list of
2099 available auth mechanisms as arguments. If a server ever provides
2100 a list of supported mechanisms, it must provide the same list
2101 each time it sends a REJECTED message. Clients are free to
2102 ignore all lists received after the first.
2105 <sect2 id="auth-command-ok">
2106 <title>OK Command</title>
2108 The OK command indicates that the client has been
2109 authenticated. The client may now proceed with negotiating
2110 Unix file descriptor passing. To do that it shall send
2111 NEGOTIATE_UNIX_FD to the server.
2114 Otherwise, the client must respond to the OK command by
2115 sending a BEGIN command, followed by its stream of messages,
2116 or by disconnecting. The server must not accept additional
2117 commands using this protocol after the BEGIN command has been
2118 received. Further communication will be a stream of D-Bus
2119 messages (optionally encrypted, as negotiated) rather than
2123 If a client sends BEGIN the first octet received by the client
2124 after the \r\n of the OK command must be the first octet of
2125 the authenticated/encrypted stream of D-Bus messages.
2128 The OK command has one argument, which is the GUID of the server.
2129 See <xref linkend="addresses"/> for more on server GUIDs.
2132 <sect2 id="auth-command-error">
2133 <title>ERROR Command</title>
2135 The ERROR command indicates that either server or client did not
2136 know a command, does not accept the given command in the current
2137 context, or did not understand the arguments to the command. This
2138 allows the protocol to be extended; a client or server can send a
2139 command present or permitted only in new protocol versions, and if
2140 an ERROR is received instead of an appropriate response, fall back
2141 to using some other technique.
2144 If an ERROR is sent, the server or client that sent the
2145 error must continue as if the command causing the ERROR had never been
2146 received. However, the the server or client receiving the error
2147 should try something other than whatever caused the error;
2148 if only canceling/rejecting the authentication.
2151 If the D-Bus protocol changes incompatibly at some future time,
2152 applications implementing the new protocol would probably be able to
2153 check for support of the new protocol by sending a new command and
2154 receiving an ERROR from applications that don't understand it. Thus the
2155 ERROR feature of the auth protocol is an escape hatch that lets us
2156 negotiate extensions or changes to the D-Bus protocol in the future.
2159 <sect2 id="auth-command-negotiate-unix-fd">
2160 <title>NEGOTIATE_UNIX_FD Command</title>
2162 The NEGOTIATE_UNIX_FD command indicates that the client
2163 supports Unix file descriptor passing. This command may only
2164 be sent after the connection is authenticated, i.e. after OK
2165 was received by the client. This command may only be sent on
2166 transports that support Unix file descriptor passing.
2169 On receiving NEGOTIATE_UNIX_FD the server must respond with
2170 either AGREE_UNIX_FD or ERROR. It shall respond the former if
2171 the transport chosen supports Unix file descriptor passing and
2172 the server supports this feature. It shall respond the latter
2173 if the transport does not support Unix file descriptor
2174 passing, the server does not support this feature, or the
2175 server decides not to enable file descriptor passing due to
2176 security or other reasons.
2179 <sect2 id="auth-command-agree-unix-fd">
2180 <title>AGREE_UNIX_FD Command</title>
2182 The AGREE_UNIX_FD command indicates that the server supports
2183 Unix file descriptor passing. This command may only be sent
2184 after the connection is authenticated, and the client sent
2185 NEGOTIATE_UNIX_FD to enable Unix file descriptor passing. This
2186 command may only be sent on transports that support Unix file
2190 On receiving AGREE_UNIX_FD the client must respond with BEGIN,
2191 followed by its stream of messages, or by disconnecting. The
2192 server must not accept additional commands using this protocol
2193 after the BEGIN command has been received. Further
2194 communication will be a stream of D-Bus messages (optionally
2195 encrypted, as negotiated) rather than this protocol.
2198 <sect2 id="auth-command-future">
2199 <title>Future Extensions</title>
2201 Future extensions to the authentication and negotiation
2202 protocol are possible. For that new commands may be
2203 introduced. If a client or server receives an unknown command
2204 it shall respond with ERROR and not consider this fatal. New
2205 commands may be introduced both before, and after
2206 authentication, i.e. both before and after the OK command.
2209 <sect2 id="auth-examples">
2210 <title>Authentication examples</title>
2214 <title>Example of successful magic cookie authentication</title>
2216 (MAGIC_COOKIE is a made up mechanism)
2218 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2224 <title>Example of finding out mechanisms then picking one</title>
2227 S: REJECTED KERBEROS_V4 SKEY
2228 C: AUTH SKEY 7ab83f32ee
2229 S: DATA 8799cabb2ea93e
2230 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2236 <title>Example of client sends unknown command then falls back to regular auth</title>
2240 C: AUTH MAGIC_COOKIE 3736343435313230333039
2246 <title>Example of server doesn't support initial auth mechanism</title>
2248 C: AUTH MAGIC_COOKIE 3736343435313230333039
2249 S: REJECTED KERBEROS_V4 SKEY
2250 C: AUTH SKEY 7ab83f32ee
2251 S: DATA 8799cabb2ea93e
2252 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2258 <title>Example of wrong password or the like followed by successful retry</title>
2260 C: AUTH MAGIC_COOKIE 3736343435313230333039
2261 S: REJECTED KERBEROS_V4 SKEY
2262 C: AUTH SKEY 7ab83f32ee
2263 S: DATA 8799cabb2ea93e
2264 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2266 C: AUTH SKEY 7ab83f32ee
2267 S: DATA 8799cabb2ea93e
2268 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2274 <title>Example of skey cancelled and restarted</title>
2276 C: AUTH MAGIC_COOKIE 3736343435313230333039
2277 S: REJECTED KERBEROS_V4 SKEY
2278 C: AUTH SKEY 7ab83f32ee
2279 S: DATA 8799cabb2ea93e
2282 C: AUTH SKEY 7ab83f32ee
2283 S: DATA 8799cabb2ea93e
2284 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2290 <title>Example of successful magic cookie authentication with successful negotiation of Unix FD passing</title>
2292 (MAGIC_COOKIE is a made up mechanism)
2294 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2296 C: NEGOTIATE_UNIX_FD
2302 <title>Example of successful magic cookie authentication with unsuccessful negotiation of Unix FD passing</title>
2304 (MAGIC_COOKIE is a made up mechanism)
2306 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2308 C: NEGOTIATE_UNIX_FD
2315 <sect2 id="auth-states">
2316 <title>Authentication state diagrams</title>
2319 This section documents the auth protocol in terms of
2320 a state machine for the client and the server. This is
2321 probably the most robust way to implement the protocol.
2324 <sect3 id="auth-states-client">
2325 <title>Client states</title>
2328 To more precisely describe the interaction between the
2329 protocol state machine and the authentication mechanisms the
2330 following notation is used: MECH(CHALL) means that the
2331 server challenge CHALL was fed to the mechanism MECH, which
2337 CONTINUE(RESP) means continue the auth conversation
2338 and send RESP as the response to the server;
2344 OK(RESP) means that after sending RESP to the server
2345 the client side of the auth conversation is finished
2346 and the server should return "OK";
2352 ERROR means that CHALL was invalid and could not be
2358 Both RESP and CHALL may be empty.
2362 The Client starts by getting an initial response from the
2363 default mechanism and sends AUTH MECH RESP, or AUTH MECH if
2364 the mechanism did not provide an initial response. If the
2365 mechanism returns CONTINUE, the client starts in state
2366 <emphasis>WaitingForData</emphasis>, if the mechanism
2367 returns OK the client starts in state
2368 <emphasis>WaitingForOK</emphasis>.
2372 The client should keep track of available mechanisms and
2373 which it mechanisms it has already attempted. This list is
2374 used to decide which AUTH command to send. When the list is
2375 exhausted, the client should give up and close the
2380 <title><emphasis>WaitingForData</emphasis></title>
2388 MECH(CHALL) returns CONTINUE(RESP) → send
2390 <emphasis>WaitingForData</emphasis>
2394 MECH(CHALL) returns OK(RESP) → send DATA
2395 RESP, goto <emphasis>WaitingForOK</emphasis>
2399 MECH(CHALL) returns ERROR → send ERROR
2400 [msg], goto <emphasis>WaitingForData</emphasis>
2408 Receive REJECTED [mechs] →
2409 send AUTH [next mech], goto
2410 WaitingForData or <emphasis>WaitingForOK</emphasis>
2415 Receive ERROR → send
2417 <emphasis>WaitingForReject</emphasis>
2422 Receive OK → send
2423 BEGIN, terminate auth
2424 conversation, authenticated
2429 Receive anything else → send
2431 <emphasis>WaitingForData</emphasis>
2439 <title><emphasis>WaitingForOK</emphasis></title>
2444 Receive OK → send BEGIN, terminate auth
2445 conversation, <emphasis>authenticated</emphasis>
2450 Receive REJECTED [mechs] → send AUTH [next mech],
2451 goto <emphasis>WaitingForData</emphasis> or
2452 <emphasis>WaitingForOK</emphasis>
2458 Receive DATA → send CANCEL, goto
2459 <emphasis>WaitingForReject</emphasis>
2465 Receive ERROR → send CANCEL, goto
2466 <emphasis>WaitingForReject</emphasis>
2472 Receive anything else → send ERROR, goto
2473 <emphasis>WaitingForOK</emphasis>
2481 <title><emphasis>WaitingForReject</emphasis></title>
2486 Receive REJECTED [mechs] → send AUTH [next mech],
2487 goto <emphasis>WaitingForData</emphasis> or
2488 <emphasis>WaitingForOK</emphasis>
2494 Receive anything else → terminate auth
2495 conversation, disconnect
2504 <sect3 id="auth-states-server">
2505 <title>Server states</title>
2508 For the server MECH(RESP) means that the client response
2509 RESP was fed to the the mechanism MECH, which returns one of
2514 CONTINUE(CHALL) means continue the auth conversation and
2515 send CHALL as the challenge to the client;
2521 OK means that the client has been successfully
2528 REJECTED means that the client failed to authenticate or
2529 there was an error in RESP.
2534 The server starts out in state
2535 <emphasis>WaitingForAuth</emphasis>. If the client is
2536 rejected too many times the server must disconnect the
2541 <title><emphasis>WaitingForAuth</emphasis></title>
2547 Receive AUTH → send REJECTED [mechs], goto
2548 <emphasis>WaitingForAuth</emphasis>
2554 Receive AUTH MECH RESP
2558 MECH not valid mechanism → send REJECTED
2560 <emphasis>WaitingForAuth</emphasis>
2564 MECH(RESP) returns CONTINUE(CHALL) → send
2566 <emphasis>WaitingForData</emphasis>
2570 MECH(RESP) returns OK → send OK, goto
2571 <emphasis>WaitingForBegin</emphasis>
2575 MECH(RESP) returns REJECTED → send REJECTED
2577 <emphasis>WaitingForAuth</emphasis>
2585 Receive BEGIN → terminate
2586 auth conversation, disconnect
2592 Receive ERROR → send REJECTED [mechs], goto
2593 <emphasis>WaitingForAuth</emphasis>
2599 Receive anything else → send
2601 <emphasis>WaitingForAuth</emphasis>
2610 <title><emphasis>WaitingForData</emphasis></title>
2618 MECH(RESP) returns CONTINUE(CHALL) → send
2620 <emphasis>WaitingForData</emphasis>
2624 MECH(RESP) returns OK → send OK, goto
2625 <emphasis>WaitingForBegin</emphasis>
2629 MECH(RESP) returns REJECTED → send REJECTED
2631 <emphasis>WaitingForAuth</emphasis>
2639 Receive BEGIN → terminate auth conversation,
2646 Receive CANCEL → send REJECTED [mechs], goto
2647 <emphasis>WaitingForAuth</emphasis>
2653 Receive ERROR → send REJECTED [mechs], goto
2654 <emphasis>WaitingForAuth</emphasis>
2660 Receive anything else → send ERROR, goto
2661 <emphasis>WaitingForData</emphasis>
2669 <title><emphasis>WaitingForBegin</emphasis></title>
2674 Receive BEGIN → terminate auth conversation,
2675 client authenticated
2681 Receive CANCEL → send REJECTED [mechs], goto
2682 <emphasis>WaitingForAuth</emphasis>
2688 Receive ERROR → send REJECTED [mechs], goto
2689 <emphasis>WaitingForAuth</emphasis>
2695 Receive anything else → send ERROR, goto
2696 <emphasis>WaitingForBegin</emphasis>
2706 <sect2 id="auth-mechanisms">
2707 <title>Authentication mechanisms</title>
2709 This section describes some new authentication mechanisms.
2710 D-Bus also allows any standard SASL mechanism of course.
2712 <sect3 id="auth-mechanisms-sha">
2713 <title>DBUS_COOKIE_SHA1</title>
2715 The DBUS_COOKIE_SHA1 mechanism is designed to establish that a client
2716 has the ability to read a private file owned by the user being
2717 authenticated. If the client can prove that it has access to a secret
2718 cookie stored in this file, then the client is authenticated.
2719 Thus the security of DBUS_COOKIE_SHA1 depends on a secure home
2723 Throughout this description, "hex encoding" must output the digits
2724 from a to f in lower-case; the digits A to F must not be used
2725 in the DBUS_COOKIE_SHA1 mechanism.
2728 Authentication proceeds as follows:
2732 The client sends the username it would like to authenticate
2738 The server sends the name of its "cookie context" (see below); a
2739 space character; the integer ID of the secret cookie the client
2740 must demonstrate knowledge of; a space character; then a
2741 randomly-generated challenge string, all of this hex-encoded into
2747 The client locates the cookie and generates its own
2748 randomly-generated challenge string. The client then concatenates
2749 the server's decoded challenge, a ":" character, its own challenge,
2750 another ":" character, and the cookie. It computes the SHA-1 hash
2751 of this composite string as a hex digest. It concatenates the
2752 client's challenge string, a space character, and the SHA-1 hex
2753 digest, hex-encodes the result and sends it back to the server.
2758 The server generates the same concatenated string used by the
2759 client and computes its SHA-1 hash. It compares the hash with
2760 the hash received from the client; if the two hashes match, the
2761 client is authenticated.
2767 Each server has a "cookie context," which is a name that identifies a
2768 set of cookies that apply to that server. A sample context might be
2769 "org_freedesktop_session_bus". Context names must be valid ASCII,
2770 nonzero length, and may not contain the characters slash ("/"),
2771 backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"),
2772 tab ("\t"), or period ("."). There is a default context,
2773 "org_freedesktop_general" that's used by servers that do not specify
2777 Cookies are stored in a user's home directory, in the directory
2778 <filename>~/.dbus-keyrings/</filename>. This directory must
2779 not be readable or writable by other users. If it is,
2780 clients and servers must ignore it. The directory
2781 contains cookie files named after the cookie context.
2784 A cookie file contains one cookie per line. Each line
2785 has three space-separated fields:
2789 The cookie ID number, which must be a non-negative integer and
2790 may not be used twice in the same file.
2795 The cookie's creation time, in UNIX seconds-since-the-epoch
2801 The cookie itself, a hex-encoded random block of bytes. The cookie
2802 may be of any length, though obviously security increases
2803 as the length increases.
2809 Only server processes modify the cookie file.
2810 They must do so with this procedure:
2814 Create a lockfile name by appending ".lock" to the name of the
2815 cookie file. The server should attempt to create this file
2816 using <literal>O_CREAT | O_EXCL</literal>. If file creation
2817 fails, the lock fails. Servers should retry for a reasonable
2818 period of time, then they may choose to delete an existing lock
2819 to keep users from having to manually delete a stale
2820 lock. <footnote><para>Lockfiles are used instead of real file
2821 locking <literal>fcntl()</literal> because real locking
2822 implementations are still flaky on network
2823 filesystems.</para></footnote>
2828 Once the lockfile has been created, the server loads the cookie
2829 file. It should then delete any cookies that are old (the
2830 timeout can be fairly short), or more than a reasonable
2831 time in the future (so that cookies never accidentally
2832 become permanent, if the clock was set far into the future
2833 at some point). If no recent keys remain, the
2834 server may generate a new key.
2839 The pruned and possibly added-to cookie file
2840 must be resaved atomically (using a temporary
2841 file which is rename()'d).
2846 The lock must be dropped by deleting the lockfile.
2852 Clients need not lock the file in order to load it,
2853 because servers are required to save the file atomically.
2858 <sect1 id="addresses">
2859 <title>Server Addresses</title>
2861 Server addresses consist of a transport name followed by a colon, and
2862 then an optional, comma-separated list of keys and values in the form key=value.
2863 Each value is escaped.
2867 <programlisting>unix:path=/tmp/dbus-test</programlisting>
2868 Which is the address to a unix socket with the path /tmp/dbus-test.
2871 Value escaping is similar to URI escaping but simpler.
2875 The set of optionally-escaped bytes is:
2876 <literal>[0-9A-Za-z_-/.\]</literal>. To escape, each
2877 <emphasis>byte</emphasis> (note, not character) which is not in the
2878 set of optionally-escaped bytes must be replaced with an ASCII
2879 percent (<literal>%</literal>) and the value of the byte in hex.
2880 The hex value must always be two digits, even if the first digit is
2881 zero. The optionally-escaped bytes may be escaped if desired.
2886 To unescape, append each byte in the value; if a byte is an ASCII
2887 percent (<literal>%</literal>) character then append the following
2888 hex value instead. It is an error if a <literal>%</literal> byte
2889 does not have two hex digits following. It is an error if a
2890 non-optionally-escaped byte is seen unescaped.
2894 The set of optionally-escaped bytes is intended to preserve address
2895 readability and convenience.
2899 A server may specify a key-value pair with the key <literal>guid</literal>
2900 and the value a hex-encoded 16-byte sequence. <xref linkend="uuids"/>
2901 describes the format of the <literal>guid</literal> field. If present,
2902 this UUID may be used to distinguish one server address from another. A
2903 server should use a different UUID for each address it listens on. For
2904 example, if a message bus daemon offers both UNIX domain socket and TCP
2905 connections, but treats clients the same regardless of how they connect,
2906 those two connections are equivalent post-connection but should have
2907 distinct UUIDs to distinguish the kinds of connection.
2911 The intent of the address UUID feature is to allow a client to avoid
2912 opening multiple identical connections to the same server, by allowing the
2913 client to check whether an address corresponds to an already-existing
2914 connection. Comparing two addresses is insufficient, because addresses
2915 can be recycled by distinct servers, and equivalent addresses may look
2916 different if simply compared as strings (for example, the host in a TCP
2917 address can be given as an IP address or as a hostname).
2921 Note that the address key is <literal>guid</literal> even though the
2922 rest of the API and documentation says "UUID," for historical reasons.
2926 [FIXME clarify if attempting to connect to each is a requirement
2927 or just a suggestion]
2928 When connecting to a server, multiple server addresses can be
2929 separated by a semi-colon. The library will then try to connect
2930 to the first address and if that fails, it'll try to connect to
2931 the next one specified, and so forth. For example
2932 <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
2937 <sect1 id="transports">
2938 <title>Transports</title>
2940 [FIXME we need to specify in detail each transport and its possible arguments]
2942 Current transports include: unix domain sockets (including
2943 abstract namespace on linux), launchd, systemd, TCP/IP, an executed subprocess and a debug/testing transport
2944 using in-process pipes. Future possible transports include one that
2945 tunnels over X11 protocol.
2948 <sect2 id="transports-unix-domain-sockets">
2949 <title>Unix Domain Sockets</title>
2951 Unix domain sockets can be either paths in the file system or on Linux
2952 kernels, they can be abstract which are similar to paths but
2953 do not show up in the file system.
2957 When a socket is opened by the D-Bus library it truncates the path
2958 name right before the first trailing Nul byte. This is true for both
2959 normal paths and abstract paths. Note that this is a departure from
2960 previous versions of D-Bus that would create sockets with a fixed
2961 length path name. Names which were shorter than the fixed length
2962 would be padded by Nul bytes.
2965 Unix domain sockets are not available on Windows.
2967 <sect3 id="transports-unix-domain-sockets-addresses">
2968 <title>Server Address Format</title>
2970 Unix domain socket addresses are identified by the "unix:" prefix
2971 and support the following key/value pairs:
2978 <entry>Values</entry>
2979 <entry>Description</entry>
2985 <entry>(path)</entry>
2986 <entry>path of the unix domain socket. If set, the "tmpdir" and "abstract" key must not be set.</entry>
2989 <entry>tmpdir</entry>
2990 <entry>(path)</entry>
2991 <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>
2994 <entry>abstract</entry>
2995 <entry>(string)</entry>
2996 <entry>unique string (path) in the abstract namespace. If set, the "path" or "tempdir" key must not be set.</entry>
3003 <sect2 id="transports-launchd">
3004 <title>launchd</title>
3006 launchd is an open-source server management system that replaces init, inetd
3007 and cron on Apple Mac OS X versions 10.4 and above. It provides a common session
3008 bus address for each user and deprecates the X11-enabled D-Bus launcher on OSX.
3012 launchd allocates a socket and provides it with the unix path through the
3013 DBUS_LAUNCHD_SESSION_BUS_SOCKET variable in launchd's environment. Every process
3014 spawned by launchd (or dbus-daemon, if it was started by launchd) can access
3015 it through its environment.
3016 Other processes can query for the launchd socket by executing:
3017 $ launchctl getenv DBUS_LAUNCHD_SESSION_BUS_SOCKET
3018 This is normally done by the D-Bus client library so doesn't have to be done
3022 launchd is not available on Microsoft Windows.
3024 <sect3 id="transports-launchd-addresses">
3025 <title>Server Address Format</title>
3027 launchd addresses are identified by the "launchd:" prefix
3028 and support the following key/value pairs:
3035 <entry>Values</entry>
3036 <entry>Description</entry>
3042 <entry>(environment variable)</entry>
3043 <entry>path of the unix domain socket for the launchd created dbus-daemon.</entry>
3050 <sect2 id="transports-systemd">
3051 <title>systemd</title>
3053 systemd is an open-source server management system that
3054 replaces init and inetd on newer Linux systems. It supports
3055 socket activation. The D-Bus systemd transport is used to acquire
3056 socket activation file descriptors from systemd and use them
3057 as D-Bus transport when the current process is spawned by
3058 socket activation from it.
3061 The systemd transport accepts only one or more Unix domain or
3062 TCP streams sockets passed in via socket activation.
3065 The systemd transport is not available on non-Linux operating systems.
3068 The systemd transport defines no parameter keys.
3071 <sect2 id="transports-tcp-sockets">
3072 <title>TCP Sockets</title>
3074 The tcp transport provides TCP/IP based connections between clients
3075 located on the same or different hosts.
3078 Using tcp transport without any additional secure authentification mechanismus
3079 over a network is unsecure.
3082 Windows notes: Because of the tcp stack on Windows does not provide sending
3083 credentials over a tcp connection, the EXTERNAL authentification
3084 mechanismus does not work.
3086 <sect3 id="transports-tcp-sockets-addresses">
3087 <title>Server Address Format</title>
3089 TCP/IP socket addresses are identified by the "tcp:" prefix
3090 and support the following key/value pairs:
3097 <entry>Values</entry>
3098 <entry>Description</entry>
3104 <entry>(string)</entry>
3105 <entry>dns name or ip address</entry>
3109 <entry>(number)</entry>
3110 <entry>The tcp port the server will open. A zero value let the server
3111 choose a free port provided from the underlaying operating system.
3112 libdbus is able to retrieve the real used port from the server.
3116 <entry>family</entry>
3117 <entry>(string)</entry>
3118 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
3125 <sect2 id="transports-nonce-tcp-sockets">
3126 <title>Nonce-secured TCP Sockets</title>
3128 The nonce-tcp transport provides a secured TCP transport, using a
3129 simple authentication mechanism to ensure that only clients with read
3130 access to a certain location in the filesystem can connect to the server.
3131 The server writes a secret, the nonce, to a file and an incoming client
3132 connection is only accepted if the client sends the nonce right after
3133 the connect. The nonce mechanism requires no setup and is orthogonal to
3134 the higher-level authentication mechanisms described in the
3135 Authentication section.
3139 On start, the server generates a random 16 byte nonce and writes it
3140 to a file in the user's temporary directory. The nonce file location
3141 is published as part of the server's D-Bus address using the
3142 "noncefile" key-value pair.
3144 After an accept, the server reads 16 bytes from the socket. If the
3145 read bytes do not match the nonce stored in the nonce file, the
3146 server MUST immediately drop the connection.
3147 If the nonce match the received byte sequence, the client is accepted
3148 and the transport behaves like an unsecured tcp transport.
3151 After a successful connect to the server socket, the client MUST read
3152 the nonce from the file published by the server via the noncefile=
3153 key-value pair and send it over the socket. After that, the
3154 transport behaves like an unsecured tcp transport.
3156 <sect3 id="transports-nonce-tcp-sockets-addresses">
3157 <title>Server Address Format</title>
3159 Nonce TCP/IP socket addresses uses the "nonce-tcp:" prefix
3160 and support the following key/value pairs:
3167 <entry>Values</entry>
3168 <entry>Description</entry>
3174 <entry>(string)</entry>
3175 <entry>dns name or ip address</entry>
3179 <entry>(number)</entry>
3180 <entry>The tcp port the server will open. A zero value let the server
3181 choose a free port provided from the underlaying operating system.
3182 libdbus is able to retrieve the real used port from the server.
3186 <entry>family</entry>
3187 <entry>(string)</entry>
3188 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
3191 <entry>noncefile</entry>
3192 <entry>(path)</entry>
3193 <entry>file location containing the secret</entry>
3200 <sect2 id="transports-exec">
3201 <title>Executed Subprocesses on Unix</title>
3203 This transport forks off a process and connects its standard
3204 input and standard output with an anonymous Unix domain
3205 socket. This socket is then used for communication by the
3206 transport. This transport may be used to use out-of-process
3207 forwarder programs as basis for the D-Bus protocol.
3210 The forked process will inherit the standard error output and
3211 process group from the parent process.
3214 Executed subprocesses are not available on Windows.
3216 <sect3 id="transports-exec-addresses">
3217 <title>Server Address Format</title>
3219 Executed subprocess addresses are identified by the "unixexec:" prefix
3220 and support the following key/value pairs:
3227 <entry>Values</entry>
3228 <entry>Description</entry>
3234 <entry>(path)</entry>
3235 <entry>Path of the binary to execute, either an absolute
3236 path or a binary name that is searched for in the default
3237 search path of the OS. This corresponds to the first
3238 argument of execlp(). This key is mandatory.</entry>
3241 <entry>argv0</entry>
3242 <entry>(string)</entry>
3243 <entry>The program name to use when executing the
3244 binary. If omitted the same value as specified for path=
3245 will be used. This corresponds to the second argument of
3249 <entry>argv1, argv2, ...</entry>
3250 <entry>(string)</entry>
3251 <entry>Arguments to pass to the binary. This corresponds
3252 to the third and later arguments of execlp(). If a
3253 specific argvX is not specified no further argvY for Y > X
3254 are taken into account.</entry>
3262 <sect1 id="meta-transports">
3263 <title>Meta Transports</title>
3265 Meta transports are a kind of transport with special enhancements or
3266 behavior. Currently available meta transports include: autolaunch
3269 <sect2 id="meta-transports-autolaunch">
3270 <title>Autolaunch</title>
3271 <para>The autolaunch transport provides a way for dbus clients to autodetect
3272 a running dbus session bus and to autolaunch a session bus if not present.
3274 <sect3 id="meta-transports-autolaunch-addresses">
3275 <title>Server Address Format</title>
3277 Autolaunch addresses uses the "autolaunch:" prefix and support the
3278 following key/value pairs:
3285 <entry>Values</entry>
3286 <entry>Description</entry>
3291 <entry>scope</entry>
3292 <entry>(string)</entry>
3293 <entry>scope of autolaunch (Windows only)
3297 "*install-path" - limit session bus to dbus installation path.
3298 The dbus installation path is determined from the location of
3299 the shared dbus library. If the library is located in a 'bin'
3300 subdirectory the installation root is the directory above,
3301 otherwise the directory where the library lives is taken as
3304 <install-root>/bin/[lib]dbus-1.dll
3305 <install-root>/[lib]dbus-1.dll
3311 "*user" - limit session bus to the recent user.
3316 other values - specify dedicated session bus like "release",
3328 <sect3 id="meta-transports-autolaunch-windows-implementation">
3329 <title>Windows implementation</title>
3331 On start, the server opens a platform specific transport, creates a mutex
3332 and a shared memory section containing the related session bus address.
3333 This mutex will be inspected by the dbus client library to detect a
3334 running dbus session bus. The access to the mutex and the shared memory
3335 section are protected by global locks.
3338 In the recent implementation the autolaunch transport uses a tcp transport
3339 on localhost with a port choosen from the operating system. This detail may
3340 change in the future.
3343 Disclaimer: The recent implementation is in an early state and may not
3344 work in all cirumstances and/or may have security issues. Because of this
3345 the implementation is not documentated yet.
3352 <title>UUIDs</title>
3354 A working D-Bus implementation uses universally-unique IDs in two places.
3355 First, each server address has a UUID identifying the address,
3356 as described in <xref linkend="addresses"/>. Second, each operating
3357 system kernel instance running a D-Bus client or server has a UUID
3358 identifying that kernel, retrieved by invoking the method
3359 org.freedesktop.DBus.Peer.GetMachineId() (see <xref
3360 linkend="standard-interfaces-peer"/>).
3363 The term "UUID" in this document is intended literally, i.e. an
3364 identifier that is universally unique. It is not intended to refer to
3365 RFC4122, and in fact the D-Bus UUID is not compatible with that RFC.
3368 The UUID must contain 128 bits of data and be hex-encoded. The
3369 hex-encoded string may not contain hyphens or other non-hex-digit
3370 characters, and it must be exactly 32 characters long. To generate a
3371 UUID, the current reference implementation concatenates 96 bits of random
3372 data followed by the 32-bit time in seconds since the UNIX epoch (in big
3376 It would also be acceptable and probably better to simply generate 128
3377 bits of random data, as long as the random number generator is of high
3378 quality. The timestamp could conceivably help if the random bits are not
3379 very random. With a quality random number generator, collisions are
3380 extremely unlikely even with only 96 bits, so it's somewhat academic.
3383 Implementations should, however, stick to random data for the first 96 bits
3388 <sect1 id="standard-interfaces">
3389 <title>Standard Interfaces</title>
3391 See <xref linkend="message-protocol-types-notation"/> for details on
3392 the notation used in this section. There are some standard interfaces
3393 that may be useful across various D-Bus applications.
3395 <sect2 id="standard-interfaces-peer">
3396 <title><literal>org.freedesktop.DBus.Peer</literal></title>
3398 The <literal>org.freedesktop.DBus.Peer</literal> interface
3401 org.freedesktop.DBus.Peer.Ping ()
3402 org.freedesktop.DBus.Peer.GetMachineId (out STRING machine_uuid)
3406 On receipt of the <literal>METHOD_CALL</literal> message
3407 <literal>org.freedesktop.DBus.Peer.Ping</literal>, an application should do
3408 nothing other than reply with a <literal>METHOD_RETURN</literal> as
3409 usual. It does not matter which object path a ping is sent to. The
3410 reference implementation handles this method automatically.
3413 On receipt of the <literal>METHOD_CALL</literal> message
3414 <literal>org.freedesktop.DBus.Peer.GetMachineId</literal>, an application should
3415 reply with a <literal>METHOD_RETURN</literal> containing a hex-encoded
3416 UUID representing the identity of the machine the process is running on.
3417 This UUID must be the same for all processes on a single system at least
3418 until that system next reboots. It should be the same across reboots
3419 if possible, but this is not always possible to implement and is not
3421 It does not matter which object path a GetMachineId is sent to. The
3422 reference implementation handles this method automatically.
3425 The UUID is intended to be per-instance-of-the-operating-system, so may represent
3426 a virtual machine running on a hypervisor, rather than a physical machine.
3427 Basically if two processes see the same UUID, they should also see the same
3428 shared memory, UNIX domain sockets, process IDs, and other features that require
3429 a running OS kernel in common between the processes.
3432 The UUID is often used where other programs might use a hostname. Hostnames
3433 can change without rebooting, however, or just be "localhost" - so the UUID
3437 <xref linkend="uuids"/> explains the format of the UUID.
3441 <sect2 id="standard-interfaces-introspectable">
3442 <title><literal>org.freedesktop.DBus.Introspectable</literal></title>
3444 This interface has one method:
3446 org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data)
3450 Objects instances may implement
3451 <literal>Introspect</literal> which returns an XML description of
3452 the object, including its interfaces (with signals and methods), objects
3453 below it in the object path tree, and its properties.
3456 <xref linkend="introspection-format"/> describes the format of this XML string.
3459 <sect2 id="standard-interfaces-properties">
3460 <title><literal>org.freedesktop.DBus.Properties</literal></title>
3462 Many native APIs will have a concept of object <firstterm>properties</firstterm>
3463 or <firstterm>attributes</firstterm>. These can be exposed via the
3464 <literal>org.freedesktop.DBus.Properties</literal> interface.
3468 org.freedesktop.DBus.Properties.Get (in STRING interface_name,
3469 in STRING property_name,
3471 org.freedesktop.DBus.Properties.Set (in STRING interface_name,
3472 in STRING property_name,
3474 org.freedesktop.DBus.Properties.GetAll (in STRING interface_name,
3475 out DICT<STRING,VARIANT> props);
3479 It is conventional to give D-Bus properties names consisting of
3480 capitalized words without punctuation ("CamelCase"), like
3481 <link linkend="message-protocol-names-member">member names</link>.
3482 For instance, the GObject property
3483 <literal>connection-status</literal> or the Qt property
3484 <literal>connectionStatus</literal> could be represented on D-Bus
3485 as <literal>ConnectionStatus</literal>.
3488 Strictly speaking, D-Bus property names are not required to follow
3489 the same naming restrictions as member names, but D-Bus property
3490 names that would not be valid member names (in particular,
3491 GObject-style dash-separated property names) can cause interoperability
3492 problems and should be avoided.
3495 The available properties and whether they are writable can be determined
3496 by calling <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>,
3497 see <xref linkend="standard-interfaces-introspectable"/>.
3500 An empty string may be provided for the interface name; in this case,
3501 if there are multiple properties on an object with the same name,
3502 the results are undefined (picking one by according to an arbitrary
3503 deterministic rule, or returning an error, are the reasonable
3507 If one or more properties change on an object, the
3508 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3509 signal may be emitted (this signal was added in 0.14):
3513 org.freedesktop.DBus.Properties.PropertiesChanged (STRING interface_name,
3514 DICT<STRING,VARIANT> changed_properties,
3515 ARRAY<STRING> invalidated_properties);
3519 where <literal>changed_properties</literal> is a dictionary
3520 containing the changed properties with the new values and
3521 <literal>invalidated_properties</literal> is an array of
3522 properties that changed but the value is not conveyed.
3525 Whether the <literal>PropertiesChanged</literal> signal is
3526 supported can be determined by calling
3527 <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>. Note
3528 that the signal may be supported for an object but it may
3529 differ how whether and how it is used on a per-property basis
3530 (for e.g. performance or security reasons). Each property (or
3531 the parent interface) must be annotated with the
3532 <literal>org.freedesktop.DBus.Property.EmitsChangedSignal</literal>
3533 annotation to convey this (usually the default value
3534 <literal>true</literal> is sufficient meaning that the
3535 annotation does not need to be used). See <xref
3536 linkend="introspection-format"/> for details on this
3541 <sect2 id="standard-interfaces-objectmanager">
3542 <title><literal>org.freedesktop.DBus.ObjectManager</literal></title>
3544 An API can optionally make use of this interface for one or
3545 more sub-trees of objects. The root of each sub-tree implements
3546 this interface so other applications can get all objects,
3547 interfaces and properties in a single method call. It is
3548 appropriate to use this interface if users of the tree of
3549 objects are expected to be interested in all interfaces of all
3550 objects in the tree; a more granular API should be used if
3551 users of the objects are expected to be interested in a small
3552 subset of the objects, a small subset of their interfaces, or
3556 The method that applications can use to get all objects and
3557 properties is <literal>GetManagedObjects</literal>:
3561 org.freedesktop.DBus.ObjectManager.GetManagedObjects (out DICT<OBJPATH,DICT<STRING,DICT<STRING,VARIANT>>> objpath_interfaces_and_properties);
3565 The return value of this method is a dict whose keys are
3566 object paths. All returned object paths are children of the
3567 object path implementing this interface, i.e. their object
3568 paths start with the ObjectManager's object path plus '/'.
3571 Each value is a dict whose keys are interfaces names. Each
3572 value in this inner dict is the same dict that would be
3573 returned by the <link
3574 linkend="standard-interfaces-properties">org.freedesktop.DBus.Properties.GetAll()</link>
3575 method for that combination of object path and interface. If
3576 an interface has no properties, the empty dict is returned.
3579 Changes are emitted using the following two signals:
3583 org.freedesktop.DBus.ObjectManager.InterfacesAdded (OBJPATH object_path,
3584 DICT<STRING,DICT<STRING,VARIANT>> interfaces_and_properties);
3585 org.freedesktop.DBus.ObjectManager.InterfacesRemoved (OBJPATH object_path,
3586 ARRAY<STRING> interfaces);
3590 The <literal>InterfacesAdded</literal> signal is emitted when
3591 either a new object is added or when an existing object gains
3592 one or more interfaces. The
3593 <literal>InterfacesRemoved</literal> signal is emitted
3594 whenever an object is removed or it loses one or more
3595 interfaces. The second parameter of the
3596 <literal>InterfacesAdded</literal> signal contains a dict with
3597 the interfaces and properties (if any) that have been added to
3598 the given object path. Similarly, the second parameter of the
3599 <literal>InterfacesRemoved</literal> signal contains an array
3600 of the interfaces that were removed. Note that changes on
3601 properties on existing interfaces are not reported using this
3602 interface - an application should also monitor the existing <link
3603 linkend="standard-interfaces-properties">PropertiesChanged</link>
3604 signal on each object.
3607 Applications SHOULD NOT export objects that are children of an
3608 object (directly or otherwise) implementing this interface but
3609 which are not returned in the reply from the
3610 <literal>GetManagedObjects()</literal> method of this
3611 interface on the given object.
3614 The intent of the <literal>ObjectManager</literal> interface
3615 is to make it easy to write a robust client
3616 implementation. The trivial client implementation only needs
3617 to make two method calls:
3621 org.freedesktop.DBus.AddMatch (bus_proxy,
3622 "type='signal',name='org.example.App',path_namespace='/org/example/App'");
3623 objects = org.freedesktop.DBus.ObjectManager.GetManagedObjects (app_proxy);
3627 on the message bus and the remote application's
3628 <literal>ObjectManager</literal>, respectively. Whenever a new
3629 remote object is created (or an existing object gains a new
3630 interface), the <literal>InterfacesAdded</literal> signal is
3631 emitted, and since this signal contains all properties for the
3632 interfaces, no calls to the
3633 <literal>org.freedesktop.Properties</literal> interface on the
3634 remote object are needed. Additionally, since the initial
3635 <literal>AddMatch()</literal> rule already includes signal
3636 messages from the newly created child object, no new
3637 <literal>AddMatch()</literal> call is needed.
3642 The <literal>org.freedesktop.DBus.ObjectManager</literal>
3643 interface was added in version 0.17 of the D-Bus
3650 <sect1 id="introspection-format">
3651 <title>Introspection Data Format</title>
3653 As described in <xref linkend="standard-interfaces-introspectable"/>,
3654 objects may be introspected at runtime, returning an XML string
3655 that describes the object. The same XML format may be used in
3656 other contexts as well, for example as an "IDL" for generating
3657 static language bindings.
3660 Here is an example of introspection data:
3662 <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
3663 "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
3664 <node name="/org/freedesktop/sample_object">
3665 <interface name="org.freedesktop.SampleInterface">
3666 <method name="Frobate">
3667 <arg name="foo" type="i" direction="in"/>
3668 <arg name="bar" type="s" direction="out"/>
3669 <arg name="baz" type="a{us}" direction="out"/>
3670 <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
3672 <method name="Bazify">
3673 <arg name="bar" type="(iiu)" direction="in"/>
3674 <arg name="bar" type="v" direction="out"/>
3676 <method name="Mogrify">
3677 <arg name="bar" type="(iiav)" direction="in"/>
3679 <signal name="Changed">
3680 <arg name="new_value" type="b"/>
3682 <property name="Bar" type="y" access="readwrite"/>
3684 <node name="child_of_sample_object"/>
3685 <node name="another_child_of_sample_object"/>
3690 A more formal DTD and spec needs writing, but here are some quick notes.
3694 Only the root <node> element can omit the node name, as it's
3695 known to be the object that was introspected. If the root
3696 <node> does have a name attribute, it must be an absolute
3697 object path. If child <node> have object paths, they must be
3703 If a child <node> has any sub-elements, then they
3704 must represent a complete introspection of the child.
3705 If a child <node> is empty, then it may or may
3706 not have sub-elements; the child must be introspected
3707 in order to find out. The intent is that if an object
3708 knows that its children are "fast" to introspect
3709 it can go ahead and return their information, but
3710 otherwise it can omit it.
3715 The direction element on <arg> may be omitted,
3716 in which case it defaults to "in" for method calls
3717 and "out" for signals. Signals only allow "out"
3718 so while direction may be specified, it's pointless.
3723 The possible directions are "in" and "out",
3724 unlike CORBA there is no "inout"
3729 The possible property access flags are
3730 "readwrite", "read", and "write"
3735 Multiple interfaces can of course be listed for
3741 The "name" attribute on arguments is optional.
3747 Method, interface, property, and signal elements may have
3748 "annotations", which are generic key/value pairs of metadata.
3749 They are similar conceptually to Java's annotations and C# attributes.
3750 Well-known annotations:
3757 <entry>Values (separated by ,)</entry>
3758 <entry>Description</entry>
3763 <entry>org.freedesktop.DBus.Deprecated</entry>
3764 <entry>true,false</entry>
3765 <entry>Whether or not the entity is deprecated; defaults to false</entry>
3768 <entry>org.freedesktop.DBus.GLib.CSymbol</entry>
3769 <entry>(string)</entry>
3770 <entry>The C symbol; may be used for methods and interfaces</entry>
3773 <entry>org.freedesktop.DBus.Method.NoReply</entry>
3774 <entry>true,false</entry>
3775 <entry>If set, don't expect a reply to the method call; defaults to false.</entry>
3778 <entry>org.freedesktop.DBus.Property.EmitsChangedSignal</entry>
3779 <entry>true,invalidates,false</entry>
3782 If set to <literal>false</literal>, the
3783 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3785 linkend="standard-interfaces-properties"/> is not
3786 guaranteed to be emitted if the property changes.
3789 If set to <literal>invalidates</literal> the signal
3790 is emitted but the value is not included in the
3794 If set to <literal>true</literal> the signal is
3795 emitted with the value included.
3798 The value for the annotation defaults to
3799 <literal>true</literal> if the enclosing interface
3800 element does not specify the annotation. Otherwise it
3801 defaults to the value specified in the enclosing
3810 <sect1 id="message-bus">
3811 <title>Message Bus Specification</title>
3812 <sect2 id="message-bus-overview">
3813 <title>Message Bus Overview</title>
3815 The message bus accepts connections from one or more applications.
3816 Once connected, applications can exchange messages with other
3817 applications that are also connected to the bus.
3820 In order to route messages among connections, the message bus keeps a
3821 mapping from names to connections. Each connection has one
3822 unique-for-the-lifetime-of-the-bus name automatically assigned.
3823 Applications may request additional names for a connection. Additional
3824 names are usually "well-known names" such as
3825 "org.freedesktop.TextEditor". When a name is bound to a connection,
3826 that connection is said to <firstterm>own</firstterm> the name.
3829 The bus itself owns a special name,
3830 <literal>org.freedesktop.DBus</literal>, with an object
3831 located at <literal>/org/freedesktop/DBus</literal> that
3832 implements the <literal>org.freedesktop.DBus</literal>
3833 interface. This service allows applications to make
3834 administrative requests of the bus itself. For example,
3835 applications can ask the bus to assign a name to a connection.
3838 Each name may have <firstterm>queued owners</firstterm>. When an
3839 application requests a name for a connection and the name is already in
3840 use, the bus will optionally add the connection to a queue waiting for
3841 the name. If the current owner of the name disconnects or releases
3842 the name, the next connection in the queue will become the new owner.
3846 This feature causes the right thing to happen if you start two text
3847 editors for example; the first one may request "org.freedesktop.TextEditor",
3848 and the second will be queued as a possible owner of that name. When
3849 the first exits, the second will take over.
3853 Applications may send <firstterm>unicast messages</firstterm> to
3854 a specific recipient or to the message bus itself, or
3855 <firstterm>broadcast messages</firstterm> to all interested recipients.
3856 See <xref linkend="message-bus-routing"/> for details.
3860 <sect2 id="message-bus-names">
3861 <title>Message Bus Names</title>
3863 Each connection has at least one name, assigned at connection time and
3864 returned in response to the
3865 <literal>org.freedesktop.DBus.Hello</literal> method call. This
3866 automatically-assigned name is called the connection's <firstterm>unique
3867 name</firstterm>. Unique names are never reused for two different
3868 connections to the same bus.
3871 Ownership of a unique name is a prerequisite for interaction with
3872 the message bus. It logically follows that the unique name is always
3873 the first name that an application comes to own, and the last
3874 one that it loses ownership of.
3877 Unique connection names must begin with the character ':' (ASCII colon
3878 character); bus names that are not unique names must not begin
3879 with this character. (The bus must reject any attempt by an application
3880 to manually request a name beginning with ':'.) This restriction
3881 categorically prevents "spoofing"; messages sent to a unique name
3882 will always go to the expected connection.
3885 When a connection is closed, all the names that it owns are deleted (or
3886 transferred to the next connection in the queue if any).
3889 A connection can request additional names to be associated with it using
3890 the <literal>org.freedesktop.DBus.RequestName</literal> message. <xref
3891 linkend="message-protocol-names-bus"/> describes the format of a valid
3892 name. These names can be released again using the
3893 <literal>org.freedesktop.DBus.ReleaseName</literal> message.
3896 <sect3 id="bus-messages-request-name">
3897 <title><literal>org.freedesktop.DBus.RequestName</literal></title>
3901 UINT32 RequestName (in STRING name, in UINT32 flags)
3908 <entry>Argument</entry>
3910 <entry>Description</entry>
3916 <entry>STRING</entry>
3917 <entry>Name to request</entry>
3921 <entry>UINT32</entry>
3922 <entry>Flags</entry>
3932 <entry>Argument</entry>
3934 <entry>Description</entry>
3940 <entry>UINT32</entry>
3941 <entry>Return value</entry>
3948 This method call should be sent to
3949 <literal>org.freedesktop.DBus</literal> and asks the message bus to
3950 assign the given name to the method caller. Each name maintains a
3951 queue of possible owners, where the head of the queue is the primary
3952 or current owner of the name. Each potential owner in the queue
3953 maintains the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and
3954 DBUS_NAME_FLAG_DO_NOT_QUEUE settings from its latest RequestName
3955 call. When RequestName is invoked the following occurs:
3959 If the method caller is currently the primary owner of the name,
3960 the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and DBUS_NAME_FLAG_DO_NOT_QUEUE
3961 values are updated with the values from the new RequestName call,
3962 and nothing further happens.
3968 If the current primary owner (head of the queue) has
3969 DBUS_NAME_FLAG_ALLOW_REPLACEMENT set, and the RequestName
3970 invocation has the DBUS_NAME_FLAG_REPLACE_EXISTING flag, then
3971 the caller of RequestName replaces the current primary owner at
3972 the head of the queue and the current primary owner moves to the
3973 second position in the queue. If the caller of RequestName was
3974 in the queue previously its flags are updated with the values from
3975 the new RequestName in addition to moving it to the head of the queue.
3981 If replacement is not possible, and the method caller is
3982 currently in the queue but not the primary owner, its flags are
3983 updated with the values from the new RequestName call.
3989 If replacement is not possible, and the method caller is
3990 currently not in the queue, the method caller is appended to the
3997 If any connection in the queue has DBUS_NAME_FLAG_DO_NOT_QUEUE
3998 set and is not the primary owner, it is removed from the
3999 queue. This can apply to the previous primary owner (if it
4000 was replaced) or the method caller (if it updated the
4001 DBUS_NAME_FLAG_DO_NOT_QUEUE flag while still stuck in the
4002 queue, or if it was just added to the queue with that flag set).
4008 Note that DBUS_NAME_FLAG_REPLACE_EXISTING results in "jumping the
4009 queue," even if another application already in the queue had specified
4010 DBUS_NAME_FLAG_REPLACE_EXISTING. This comes up if a primary owner
4011 that does not allow replacement goes away, and the next primary owner
4012 does allow replacement. In this case, queued items that specified
4013 DBUS_NAME_FLAG_REPLACE_EXISTING <emphasis>do not</emphasis>
4014 automatically replace the new primary owner. In other words,
4015 DBUS_NAME_FLAG_REPLACE_EXISTING is not saved, it is only used at the
4016 time RequestName is called. This is deliberate to avoid an infinite loop
4017 anytime two applications are both DBUS_NAME_FLAG_ALLOW_REPLACEMENT
4018 and DBUS_NAME_FLAG_REPLACE_EXISTING.
4021 The flags argument contains any of the following values logically ORed
4028 <entry>Conventional Name</entry>
4029 <entry>Value</entry>
4030 <entry>Description</entry>
4035 <entry>DBUS_NAME_FLAG_ALLOW_REPLACEMENT</entry>
4039 If an application A specifies this flag and succeeds in
4040 becoming the owner of the name, and another application B
4041 later calls RequestName with the
4042 DBUS_NAME_FLAG_REPLACE_EXISTING flag, then application A
4043 will lose ownership and receive a
4044 <literal>org.freedesktop.DBus.NameLost</literal> signal, and
4045 application B will become the new owner. If DBUS_NAME_FLAG_ALLOW_REPLACEMENT
4046 is not specified by application A, or DBUS_NAME_FLAG_REPLACE_EXISTING
4047 is not specified by application B, then application B will not replace
4048 application A as the owner.
4053 <entry>DBUS_NAME_FLAG_REPLACE_EXISTING</entry>
4057 Try to replace the current owner if there is one. If this
4058 flag is not set the application will only become the owner of
4059 the name if there is no current owner. If this flag is set,
4060 the application will replace the current owner if
4061 the current owner specified DBUS_NAME_FLAG_ALLOW_REPLACEMENT.
4066 <entry>DBUS_NAME_FLAG_DO_NOT_QUEUE</entry>
4070 Without this flag, if an application requests a name that is
4071 already owned, the application will be placed in a queue to
4072 own the name when the current owner gives it up. If this
4073 flag is given, the application will not be placed in the
4074 queue, the request for the name will simply fail. This flag
4075 also affects behavior when an application is replaced as
4076 name owner; by default the application moves back into the
4077 waiting queue, unless this flag was provided when the application
4078 became the name owner.
4086 The return code can be one of the following values:
4092 <entry>Conventional Name</entry>
4093 <entry>Value</entry>
4094 <entry>Description</entry>
4099 <entry>DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER</entry>
4100 <entry>1</entry> <entry>The caller is now the primary owner of
4101 the name, replacing any previous owner. Either the name had no
4102 owner before, or the caller specified
4103 DBUS_NAME_FLAG_REPLACE_EXISTING and the current owner specified
4104 DBUS_NAME_FLAG_ALLOW_REPLACEMENT.</entry>
4107 <entry>DBUS_REQUEST_NAME_REPLY_IN_QUEUE</entry>
4110 <entry>The name already had an owner,
4111 DBUS_NAME_FLAG_DO_NOT_QUEUE was not specified, and either
4112 the current owner did not specify
4113 DBUS_NAME_FLAG_ALLOW_REPLACEMENT or the requesting
4114 application did not specify DBUS_NAME_FLAG_REPLACE_EXISTING.
4118 <entry>DBUS_REQUEST_NAME_REPLY_EXISTS</entry> <entry>3</entry>
4119 <entry>The name already has an owner,
4120 DBUS_NAME_FLAG_DO_NOT_QUEUE was specified, and either
4121 DBUS_NAME_FLAG_ALLOW_REPLACEMENT was not specified by the
4122 current owner, or DBUS_NAME_FLAG_REPLACE_EXISTING was not
4123 specified by the requesting application.</entry>
4126 <entry>DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER</entry>
4128 <entry>The application trying to request ownership of a name is already the owner of it.</entry>
4136 <sect3 id="bus-messages-release-name">
4137 <title><literal>org.freedesktop.DBus.ReleaseName</literal></title>
4141 UINT32 ReleaseName (in STRING name)
4148 <entry>Argument</entry>
4150 <entry>Description</entry>
4156 <entry>STRING</entry>
4157 <entry>Name to release</entry>
4167 <entry>Argument</entry>
4169 <entry>Description</entry>
4175 <entry>UINT32</entry>
4176 <entry>Return value</entry>
4183 This method call should be sent to
4184 <literal>org.freedesktop.DBus</literal> and asks the message bus to
4185 release the method caller's claim to the given name. If the caller is
4186 the primary owner, a new primary owner will be selected from the
4187 queue if any other owners are waiting. If the caller is waiting in
4188 the queue for the name, the caller will removed from the queue and
4189 will not be made an owner of the name if it later becomes available.
4190 If there are no other owners in the queue for the name, it will be
4191 removed from the bus entirely.
4193 The return code can be one of the following values:
4199 <entry>Conventional Name</entry>
4200 <entry>Value</entry>
4201 <entry>Description</entry>
4206 <entry>DBUS_RELEASE_NAME_REPLY_RELEASED</entry>
4207 <entry>1</entry> <entry>The caller has released his claim on
4208 the given name. Either the caller was the primary owner of
4209 the name, and the name is now unused or taken by somebody
4210 waiting in the queue for the name, or the caller was waiting
4211 in the queue for the name and has now been removed from the
4215 <entry>DBUS_RELEASE_NAME_REPLY_NON_EXISTENT</entry>
4217 <entry>The given name does not exist on this bus.</entry>
4220 <entry>DBUS_RELEASE_NAME_REPLY_NOT_OWNER</entry>
4222 <entry>The caller was not the primary owner of this name,
4223 and was also not waiting in the queue to own this name.</entry>
4231 <sect3 id="bus-messages-list-queued-owners">
4232 <title><literal>org.freedesktop.DBus.ListQueuedOwners</literal></title>
4236 ARRAY of STRING ListQueuedOwners (in STRING name)
4243 <entry>Argument</entry>
4245 <entry>Description</entry>
4251 <entry>STRING</entry>
4252 <entry>The well-known bus name to query, such as
4253 <literal>com.example.cappuccino</literal></entry>
4263 <entry>Argument</entry>
4265 <entry>Description</entry>
4271 <entry>ARRAY of STRING</entry>
4272 <entry>The unique bus names of connections currently queued
4273 for the name</entry>
4280 This method call should be sent to
4281 <literal>org.freedesktop.DBus</literal> and lists the connections
4282 currently queued for a bus name (see
4283 <xref linkend="term-queued-owner"/>).
4288 <sect2 id="message-bus-routing">
4289 <title>Message Bus Message Routing</title>
4292 Messages may have a <literal>DESTINATION</literal> field (see <xref
4293 linkend="message-protocol-header-fields"/>), resulting in a
4294 <firstterm>unicast message</firstterm>. If the
4295 <literal>DESTINATION</literal> field is present, it specifies a message
4296 recipient by name. Method calls and replies normally specify this field.
4297 The message bus must send messages (of any type) with the
4298 <literal>DESTINATION</literal> field set to the specified recipient,
4299 regardless of whether the recipient has set up a match rule matching
4304 When the message bus receives a signal, if the
4305 <literal>DESTINATION</literal> field is absent, it is considered to
4306 be a <firstterm>broadcast signal</firstterm>, and is sent to all
4307 applications with <firstterm>message matching rules</firstterm> that
4308 match the message. Most signal messages are broadcasts.
4312 Unicast signal messages (those with a <literal>DESTINATION</literal>
4313 field) are not commonly used, but they are treated like any unicast
4314 message: they are delivered to the specified receipient,
4315 regardless of its match rules. One use for unicast signals is to
4316 avoid a race condition in which a signal is emitted before the intended
4317 recipient can call <xref linkend="bus-messages-add-match"/> to
4318 receive that signal: if the signal is sent directly to that recipient
4319 using a unicast message, it does not need to add a match rule at all,
4320 and there is no race condition. Another use for unicast signals,
4321 on message buses whose security policy prevents eavesdropping, is to
4322 send sensitive information which should only be visible to one
4327 When the message bus receives a method call, if the
4328 <literal>DESTINATION</literal> field is absent, the call is taken to be
4329 a standard one-to-one message and interpreted by the message bus
4330 itself. For example, sending an
4331 <literal>org.freedesktop.DBus.Peer.Ping</literal> message with no
4332 <literal>DESTINATION</literal> will cause the message bus itself to
4333 reply to the ping immediately; the message bus will not make this
4334 message visible to other applications.
4338 Continuing the <literal>org.freedesktop.DBus.Peer.Ping</literal> example, if
4339 the ping message were sent with a <literal>DESTINATION</literal> name of
4340 <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
4341 forwarded, and the Yoyodyne Corporation screensaver application would be
4342 expected to reply to the ping.
4346 Message bus implementations may impose a security policy which
4347 prevents certain messages from being sent or received.
4348 When a message cannot be sent or received due to a security
4349 policy, the message bus should send an error reply, unless the
4350 original message had the <literal>NO_REPLY</literal> flag.
4353 <sect3 id="message-bus-routing-eavesdropping">
4354 <title>Eavesdropping</title>
4356 Receiving a unicast message whose <literal>DESTINATION</literal>
4357 indicates a different recipient is called
4358 <firstterm>eavesdropping</firstterm>. On a message bus which acts as
4359 a security boundary (like the standard system bus), the security
4360 policy should usually prevent eavesdropping, since unicast messages
4361 are normally kept private and may contain security-sensitive
4366 Eavesdropping is mainly useful for debugging tools, such as
4367 the <literal>dbus-monitor</literal> tool in the reference
4368 implementation of D-Bus. Tools which eavesdrop on the message bus
4369 should be careful to avoid sending a reply or error in response to
4370 messages intended for a different client.
4374 Clients may attempt to eavesdrop by adding match rules
4375 (see <xref linkend="message-bus-routing-match-rules"/>) containing
4376 the <literal>eavesdrop='true'</literal> match. If the message bus'
4377 security policy does not allow eavesdropping, the match rule can
4378 still be added, but will not have any practical effect. For
4379 compatibility with older message bus implementations, if adding such
4380 a match rule results in an error reply, the client may fall back to
4381 adding the same rule with the <literal>eavesdrop</literal> match
4386 <sect3 id="message-bus-routing-match-rules">
4387 <title>Match Rules</title>
4389 An important part of the message bus routing protocol is match
4390 rules. Match rules describe the messages that should be sent to a
4391 client, based on the contents of the message. Broadcast signals
4392 are only sent to clients which have a suitable match rule: this
4393 avoids waking up client processes to deal with signals that are
4394 not relevant to that client.
4397 Messages that list a client as their <literal>DESTINATION</literal>
4398 do not need to match the client's match rules, and are sent to that
4399 client regardless. As a result, match rules are mainly used to
4400 receive a subset of broadcast signals.
4403 Match rules can also be used for eavesdropping
4404 (see <xref linkend="message-bus-routing-eavesdropping"/>),
4405 if the security policy of the message bus allows it.
4408 Match rules are added using the AddMatch bus method
4409 (see <xref linkend="bus-messages-add-match"/>). Rules are
4410 specified as a string of comma separated key/value pairs.
4411 Excluding a key from the rule indicates a wildcard match.
4412 For instance excluding the the member from a match rule but
4413 adding a sender would let all messages from that sender through.
4414 An example of a complete rule would be
4415 "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='Foo',path='/bar/foo',destination=':452345.34',arg2='bar'"
4418 The following table describes the keys that can be used to create
4425 <entry>Possible Values</entry>
4426 <entry>Description</entry>
4431 <entry><literal>type</literal></entry>
4432 <entry>'signal', 'method_call', 'method_return', 'error'</entry>
4433 <entry>Match on the message type. An example of a type match is type='signal'</entry>
4436 <entry><literal>sender</literal></entry>
4437 <entry>A bus or unique name (see <xref linkend="term-bus-name"/>
4438 and <xref linkend="term-unique-name"/> respectively)
4440 <entry>Match messages sent by a particular sender. An example of a sender match
4441 is sender='org.freedesktop.Hal'</entry>
4444 <entry><literal>interface</literal></entry>
4445 <entry>An interface name (see <xref linkend="message-protocol-names-interface"/>)</entry>
4446 <entry>Match messages sent over or to a particular interface. An example of an
4447 interface match is interface='org.freedesktop.Hal.Manager'.
4448 If a message omits the interface header, it must not match any rule
4449 that specifies this key.</entry>
4452 <entry><literal>member</literal></entry>
4453 <entry>Any valid method or signal name</entry>
4454 <entry>Matches messages which have the give method or signal name. An example of
4455 a member match is member='NameOwnerChanged'</entry>
4458 <entry><literal>path</literal></entry>
4459 <entry>An object path (see <xref linkend="message-protocol-marshaling-object-path"/>)</entry>
4460 <entry>Matches messages which are sent from or to the given object. An example of a
4461 path match is path='/org/freedesktop/Hal/Manager'</entry>
4464 <entry><literal>path_namespace</literal></entry>
4465 <entry>An object path</entry>
4468 Matches messages which are sent from or to an
4469 object for which the object path is either the
4470 given value, or that value followed by one or
4471 more path components.
4476 <literal>path_namespace='/com/example/foo'</literal>
4477 would match signals sent by
4478 <literal>/com/example/foo</literal>
4480 <literal>/com/example/foo/bar</literal>,
4482 <literal>/com/example/foobar</literal>.
4486 Using both <literal>path</literal> and
4487 <literal>path_namespace</literal> in the same match
4488 rule is not allowed.
4493 This match key was added in version 0.16 of the
4494 D-Bus specification and implemented by the bus
4495 daemon in dbus 1.5.0 and later.
4501 <entry><literal>destination</literal></entry>
4502 <entry>A unique name (see <xref linkend="term-unique-name"/>)</entry>
4503 <entry>Matches messages which are being sent to the given unique name. An
4504 example of a destination match is destination=':1.0'</entry>
4507 <entry><literal>arg[0, 1, 2, 3, ...]</literal></entry>
4508 <entry>Any string</entry>
4509 <entry>Arg matches are special and are used for further restricting the
4510 match based on the arguments in the body of a message. Only arguments of type
4511 STRING can be matched in this way. An example of an argument match
4512 would be arg3='Foo'. Only argument indexes from 0 to 63 should be
4516 <entry><literal>arg[0, 1, 2, 3, ...]path</literal></entry>
4517 <entry>Any string</entry>
4519 <para>Argument path matches provide a specialised form of wildcard matching for
4520 path-like namespaces. They can match arguments whose type is either STRING or
4521 OBJECT_PATH. As with normal argument matches,
4522 if the argument is exactly equal to the string given in the match
4523 rule then the rule is satisfied. Additionally, there is also a
4524 match when either the string given in the match rule or the
4525 appropriate message argument ends with '/' and is a prefix of the
4526 other. An example argument path match is arg0path='/aa/bb/'. This
4527 would match messages with first arguments of '/', '/aa/',
4528 '/aa/bb/', '/aa/bb/cc/' and '/aa/bb/cc'. It would not match
4529 messages with first arguments of '/aa/b', '/aa' or even '/aa/bb'.</para>
4531 <para>This is intended for monitoring “directories” in file system-like
4532 hierarchies, as used in the <citetitle>dconf</citetitle> configuration
4533 system. An application interested in all nodes in a particular hierarchy would
4534 monitor <literal>arg0path='/ca/example/foo/'</literal>. Then the service could
4535 emit a signal with zeroth argument <literal>"/ca/example/foo/bar"</literal> to
4536 represent a modification to the “bar” property, or a signal with zeroth
4537 argument <literal>"/ca/example/"</literal> to represent atomic modification of
4538 many properties within that directory, and the interested application would be
4539 notified in both cases.</para>
4542 This match key was added in version 0.12 of the
4543 D-Bus specification, implemented for STRING
4544 arguments by the bus daemon in dbus 1.2.0 and later,
4545 and implemented for OBJECT_PATH arguments in dbus 1.5.0
4552 <entry><literal>arg0namespace</literal></entry>
4553 <entry>Like a bus name, except that the string is not
4554 required to contain a '.' (period)</entry>
4556 <para>Match messages whose first argument is of type STRING, and is a bus name
4557 or interface name within the specified namespace. This is primarily intended
4558 for watching name owner changes for a group of related bus names, rather than
4559 for a single name or all name changes.</para>
4561 <para>Because every valid interface name is also a valid
4562 bus name, this can also be used for messages whose
4563 first argument is an interface name.</para>
4565 <para>For example, the match rule
4566 <literal>member='NameOwnerChanged',arg0namespace='com.example.backend'</literal>
4567 matches name owner changes for bus names such as
4568 <literal>com.example.backend.foo</literal>,
4569 <literal>com.example.backend.foo.bar</literal>, and
4570 <literal>com.example.backend</literal> itself.</para>
4572 <para>See also <xref linkend='bus-messages-name-owner-changed'/>.</para>
4575 This match key was added in version 0.16 of the
4576 D-Bus specification and implemented by the bus
4577 daemon in dbus 1.5.0 and later.
4583 <entry><literal>eavesdrop</literal></entry>
4584 <entry><literal>'true'</literal>, <literal>'false'</literal></entry>
4585 <entry>Since D-Bus 1.5.6, match rules do not
4586 match messages which have a <literal>DESTINATION</literal>
4587 field unless the match rule specifically
4589 (see <xref linkend="message-bus-routing-eavesdropping"/>)
4590 by specifying <literal>eavesdrop='true'</literal>
4591 in the match rule. <literal>eavesdrop='false'</literal>
4592 restores the default behaviour. Messages are
4593 delivered to their <literal>DESTINATION</literal>
4594 regardless of match rules, so this match does not
4595 affect normal delivery of unicast messages.
4596 If the message bus has a security policy which forbids
4597 eavesdropping, this match may still be used without error,
4598 but will not have any practical effect.
4599 In older versions of D-Bus, this match was not allowed
4600 in match rules, and all match rules behaved as if
4601 <literal>eavesdrop='true'</literal> had been used.
4610 <sect2 id="message-bus-starting-services">
4611 <title>Message Bus Starting Services</title>
4613 The message bus can start applications on behalf of other applications.
4614 In CORBA terms, this would be called <firstterm>activation</firstterm>.
4615 An application that can be started in this way is called a
4616 <firstterm>service</firstterm>.
4619 With D-Bus, starting a service is normally done by name. That is,
4620 applications ask the message bus to start some program that will own a
4621 well-known name, such as <literal>org.freedesktop.TextEditor</literal>.
4622 This implies a contract documented along with the name
4623 <literal>org.freedesktop.TextEditor</literal> for which objects
4624 the owner of that name will provide, and what interfaces those
4628 To find an executable corresponding to a particular name, the bus daemon
4629 looks for <firstterm>service description files</firstterm>. Service
4630 description files define a mapping from names to executables. Different
4631 kinds of message bus will look for these files in different places, see
4632 <xref linkend="message-bus-types"/>.
4635 Service description files have the ".service" file
4636 extension. The message bus will only load service description files
4637 ending with .service; all other files will be ignored. The file format
4638 is similar to that of <ulink
4639 url="http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html">desktop
4640 entries</ulink>. All service description files must be in UTF-8
4641 encoding. To ensure that there will be no name collisions, service files
4642 must be namespaced using the same mechanism as messages and service
4647 [FIXME the file format should be much better specified than "similar to
4648 .desktop entries" esp. since desktop entries are already
4649 badly-specified. ;-)]
4650 These sections from the specification apply to service files as well:
4653 <listitem><para>General syntax</para></listitem>
4654 <listitem><para>Comment format</para></listitem>
4658 <title>Example service description file</title>
4660 # Sample service description file
4662 Names=org.freedesktop.ConfigurationDatabase;org.gnome.GConf;
4663 Exec=/usr/libexec/gconfd-2
4668 When an application asks to start a service by name, the bus daemon tries to
4669 find a service that will own that name. It then tries to spawn the
4670 executable associated with it. If this fails, it will report an
4671 error. [FIXME what happens if two .service files offer the same service;
4672 what kind of error is reported, should we have a way for the client to
4676 The executable launched will have the environment variable
4677 <literal>DBUS_STARTER_ADDRESS</literal> set to the address of the
4678 message bus so it can connect and request the appropriate names.
4681 The executable being launched may want to know whether the message bus
4682 starting it is one of the well-known message buses (see <xref
4683 linkend="message-bus-types"/>). To facilitate this, the bus must also set
4684 the <literal>DBUS_STARTER_BUS_TYPE</literal> environment variable if it is one
4685 of the well-known buses. The currently-defined values for this variable
4686 are <literal>system</literal> for the systemwide message bus,
4687 and <literal>session</literal> for the per-login-session message
4688 bus. The new executable must still connect to the address given
4689 in <literal>DBUS_STARTER_ADDRESS</literal>, but may assume that the
4690 resulting connection is to the well-known bus.
4693 [FIXME there should be a timeout somewhere, either specified
4694 in the .service file, by the client, or just a global value
4695 and if the client being activated fails to connect within that
4696 timeout, an error should be sent back.]
4699 <sect3 id="message-bus-starting-services-scope">
4700 <title>Message Bus Service Scope</title>
4702 The "scope" of a service is its "per-", such as per-session,
4703 per-machine, per-home-directory, or per-display. The reference
4704 implementation doesn't yet support starting services in a different
4705 scope from the message bus itself. So e.g. if you start a service
4706 on the session bus its scope is per-session.
4709 We could add an optional scope to a bus name. For example, for
4710 per-(display,session pair), we could have a unique ID for each display
4711 generated automatically at login and set on screen 0 by executing a
4712 special "set display ID" binary. The ID would be stored in a
4713 <literal>_DBUS_DISPLAY_ID</literal> property and would be a string of
4714 random bytes. This ID would then be used to scope names.
4715 Starting/locating a service could be done by ID-name pair rather than
4719 Contrast this with a per-display scope. To achieve that, we would
4720 want a single bus spanning all sessions using a given display.
4721 So we might set a <literal>_DBUS_DISPLAY_BUS_ADDRESS</literal>
4722 property on screen 0 of the display, pointing to this bus.
4727 <sect2 id="message-bus-types">
4728 <title>Well-known Message Bus Instances</title>
4730 Two standard message bus instances are defined here, along with how
4731 to locate them and where their service files live.
4733 <sect3 id="message-bus-types-login">
4734 <title>Login session message bus</title>
4736 Each time a user logs in, a <firstterm>login session message
4737 bus</firstterm> may be started. All applications in the user's login
4738 session may interact with one another using this message bus.
4741 The address of the login session message bus is given
4742 in the <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment
4743 variable. If that variable is not set, applications may
4744 also try to read the address from the X Window System root
4745 window property <literal>_DBUS_SESSION_BUS_ADDRESS</literal>.
4746 The root window property must have type <literal>STRING</literal>.
4747 The environment variable should have precedence over the
4748 root window property.
4750 <para>The address of the login session message bus is given in the
4751 <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment variable. If
4752 DBUS_SESSION_BUS_ADDRESS is not set, or if it's set to the string
4753 "autolaunch:", the system should use platform-specific methods of
4754 locating a running D-Bus session server, or starting one if a running
4755 instance cannot be found. Note that this mechanism is not recommended
4756 for attempting to determine if a daemon is running. It is inherently
4757 racy to attempt to make this determination, since the bus daemon may
4758 be started just before or just after the determination is made.
4759 Therefore, it is recommended that applications do not try to make this
4760 determination for their functionality purposes, and instead they
4761 should attempt to start the server.</para>
4763 <sect4 id="message-bus-types-login-x-windows">
4764 <title>X Windowing System</title>
4766 For the X Windowing System, the application must locate the
4767 window owner of the selection represented by the atom formed by
4771 <para>the literal string "_DBUS_SESSION_BUS_SELECTION_"</para>
4775 <para>the current user's username</para>
4779 <para>the literal character '_' (underscore)</para>
4783 <para>the machine's ID</para>
4789 The following properties are defined for the window that owns
4791 <informaltable frame="all">
4800 <para>meaning</para>
4806 <para>_DBUS_SESSION_BUS_ADDRESS</para>
4810 <para>the actual address of the server socket</para>
4816 <para>_DBUS_SESSION_BUS_PID</para>
4820 <para>the PID of the server process</para>
4829 At least the _DBUS_SESSION_BUS_ADDRESS property MUST be
4830 present in this window.
4834 If the X selection cannot be located or if reading the
4835 properties from the window fails, the implementation MUST conclude
4836 that there is no D-Bus server running and proceed to start a new
4837 server. (See below on concurrency issues)
4841 Failure to connect to the D-Bus server address thus obtained
4842 MUST be treated as a fatal connection error and should be reported
4847 As an alternative, an implementation MAY find the information
4848 in the following file located in the current user's home directory,
4849 in subdirectory .dbus/session-bus/:
4852 <para>the machine's ID</para>
4856 <para>the literal character '-' (dash)</para>
4860 <para>the X display without the screen number, with the
4861 following prefixes removed, if present: ":", "localhost:"
4862 ."localhost.localdomain:". That is, a display of
4863 "localhost:10.0" produces just the number "10"</para>
4869 The contents of this file NAME=value assignment pairs and
4870 lines starting with # are comments (no comments are allowed
4871 otherwise). The following variable names are defined:
4878 <para>Variable</para>
4882 <para>meaning</para>
4888 <para>DBUS_SESSION_BUS_ADDRESS</para>
4892 <para>the actual address of the server socket</para>
4898 <para>DBUS_SESSION_BUS_PID</para>
4902 <para>the PID of the server process</para>
4908 <para>DBUS_SESSION_BUS_WINDOWID</para>
4912 <para>the window ID</para>
4921 At least the DBUS_SESSION_BUS_ADDRESS variable MUST be present
4926 Failure to open this file MUST be interpreted as absence of a
4927 running server. Therefore, the implementation MUST proceed to
4928 attempting to launch a new bus server if the file cannot be
4933 However, success in opening this file MUST NOT lead to the
4934 conclusion that the server is running. Thus, a failure to connect to
4935 the bus address obtained by the alternative method MUST NOT be
4936 considered a fatal error. If the connection cannot be established,
4937 the implementation MUST proceed to check the X selection settings or
4938 to start the server on its own.
4942 If the implementation concludes that the D-Bus server is not
4943 running it MUST attempt to start a new server and it MUST also
4944 ensure that the daemon started as an effect of the "autolaunch"
4945 mechanism provides the lookup mechanisms described above, so
4946 subsequent calls can locate the newly started server. The
4947 implementation MUST also ensure that if two or more concurrent
4948 initiations happen, only one server remains running and all other
4949 initiations are able to obtain the address of this server and
4950 connect to it. In other words, the implementation MUST ensure that
4951 the X selection is not present when it attempts to set it, without
4952 allowing another process to set the selection between the
4953 verification and the setting (e.g., by using XGrabServer /
4960 On Unix systems, the session bus should search for .service files
4961 in <literal>$XDG_DATA_DIRS/dbus-1/services</literal> as defined
4963 <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG Base Directory Specification</ulink>.
4964 Implementations may also search additional locations, which
4965 should be searched with lower priority than anything in
4966 XDG_DATA_HOME, XDG_DATA_DIRS or their respective defaults;
4967 for example, the reference implementation also
4968 looks in <literal>${datadir}/dbus-1/services</literal> as
4969 set at compile time.
4972 As described in the XDG Base Directory Specification, software
4973 packages should install their session .service files to their
4974 configured <literal>${datadir}/dbus-1/services</literal>,
4975 where <literal>${datadir}</literal> is as defined by the GNU
4976 coding standards. System administrators or users can arrange
4977 for these service files to be read by setting XDG_DATA_DIRS or by
4978 symlinking them into the default locations.
4982 <sect3 id="message-bus-types-system">
4983 <title>System message bus</title>
4985 A computer may have a <firstterm>system message bus</firstterm>,
4986 accessible to all applications on the system. This message bus may be
4987 used to broadcast system events, such as adding new hardware devices,
4988 changes in the printer queue, and so forth.
4991 The address of the system message bus is given
4992 in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment
4993 variable. If that variable is not set, applications should try
4994 to connect to the well-known address
4995 <literal>unix:path=/var/run/dbus/system_bus_socket</literal>.
4998 The D-Bus reference implementation actually honors the
4999 <literal>$(localstatedir)</literal> configure option
5000 for this address, on both client and server side.
5005 On Unix systems, the system bus should default to searching
5006 for .service files in
5007 <literal>/usr/local/share/dbus-1/system-services</literal>,
5008 <literal>/usr/share/dbus-1/system-services</literal> and
5009 <literal>/lib/dbus-1/system-services</literal>, with that order
5010 of precedence. It may also search other implementation-specific
5011 locations, but should not vary these locations based on environment
5015 The system bus is security-sensitive and is typically executed
5016 by an init system with a clean environment. Its launch helper
5017 process is particularly security-sensitive, and specifically
5018 clears its own environment.
5023 Software packages should install their system .service
5024 files to their configured
5025 <literal>${datadir}/dbus-1/system-services</literal>,
5026 where <literal>${datadir}</literal> is as defined by the GNU
5027 coding standards. System administrators can arrange
5028 for these service files to be read by editing the system bus'
5029 configuration file or by symlinking them into the default
5035 <sect2 id="message-bus-messages">
5036 <title>Message Bus Messages</title>
5038 The special message bus name <literal>org.freedesktop.DBus</literal>
5039 responds to a number of additional messages.
5042 <sect3 id="bus-messages-hello">
5043 <title><literal>org.freedesktop.DBus.Hello</literal></title>
5054 <entry>Argument</entry>
5056 <entry>Description</entry>
5062 <entry>STRING</entry>
5063 <entry>Unique name assigned to the connection</entry>
5070 Before an application is able to send messages to other applications
5071 it must send the <literal>org.freedesktop.DBus.Hello</literal> message
5072 to the message bus to obtain a unique name. If an application without
5073 a unique name tries to send a message to another application, or a
5074 message to the message bus itself that isn't the
5075 <literal>org.freedesktop.DBus.Hello</literal> message, it will be
5076 disconnected from the bus.
5079 There is no corresponding "disconnect" request; if a client wishes to
5080 disconnect from the bus, it simply closes the socket (or other
5081 communication channel).
5084 <sect3 id="bus-messages-list-names">
5085 <title><literal>org.freedesktop.DBus.ListNames</literal></title>
5089 ARRAY of STRING ListNames ()
5096 <entry>Argument</entry>
5098 <entry>Description</entry>
5104 <entry>ARRAY of STRING</entry>
5105 <entry>Array of strings where each string is a bus name</entry>
5112 Returns a list of all currently-owned names on the bus.
5115 <sect3 id="bus-messages-list-activatable-names">
5116 <title><literal>org.freedesktop.DBus.ListActivatableNames</literal></title>
5120 ARRAY of STRING ListActivatableNames ()
5127 <entry>Argument</entry>
5129 <entry>Description</entry>
5135 <entry>ARRAY of STRING</entry>
5136 <entry>Array of strings where each string is a bus name</entry>
5143 Returns a list of all names that can be activated on the bus.
5146 <sect3 id="bus-messages-name-exists">
5147 <title><literal>org.freedesktop.DBus.NameHasOwner</literal></title>
5151 BOOLEAN NameHasOwner (in STRING name)
5158 <entry>Argument</entry>
5160 <entry>Description</entry>
5166 <entry>STRING</entry>
5167 <entry>Name to check</entry>
5177 <entry>Argument</entry>
5179 <entry>Description</entry>
5185 <entry>BOOLEAN</entry>
5186 <entry>Return value, true if the name exists</entry>
5193 Checks if the specified name exists (currently has an owner).
5197 <sect3 id="bus-messages-name-owner-changed">
5198 <title><literal>org.freedesktop.DBus.NameOwnerChanged</literal></title>
5202 NameOwnerChanged (STRING name, STRING old_owner, STRING new_owner)
5209 <entry>Argument</entry>
5211 <entry>Description</entry>
5217 <entry>STRING</entry>
5218 <entry>Name with a new owner</entry>
5222 <entry>STRING</entry>
5223 <entry>Old owner or empty string if none</entry>
5227 <entry>STRING</entry>
5228 <entry>New owner or empty string if none</entry>
5235 This signal indicates that the owner of a name has changed.
5236 It's also the signal to use to detect the appearance of
5237 new names on the bus.
5240 <sect3 id="bus-messages-name-lost">
5241 <title><literal>org.freedesktop.DBus.NameLost</literal></title>
5245 NameLost (STRING name)
5252 <entry>Argument</entry>
5254 <entry>Description</entry>
5260 <entry>STRING</entry>
5261 <entry>Name which was lost</entry>
5268 This signal is sent to a specific application when it loses
5269 ownership of a name.
5273 <sect3 id="bus-messages-name-acquired">
5274 <title><literal>org.freedesktop.DBus.NameAcquired</literal></title>
5278 NameAcquired (STRING name)
5285 <entry>Argument</entry>
5287 <entry>Description</entry>
5293 <entry>STRING</entry>
5294 <entry>Name which was acquired</entry>
5301 This signal is sent to a specific application when it gains
5302 ownership of a name.
5306 <sect3 id="bus-messages-start-service-by-name">
5307 <title><literal>org.freedesktop.DBus.StartServiceByName</literal></title>
5311 UINT32 StartServiceByName (in STRING name, in UINT32 flags)
5318 <entry>Argument</entry>
5320 <entry>Description</entry>
5326 <entry>STRING</entry>
5327 <entry>Name of the service to start</entry>
5331 <entry>UINT32</entry>
5332 <entry>Flags (currently not used)</entry>
5342 <entry>Argument</entry>
5344 <entry>Description</entry>
5350 <entry>UINT32</entry>
5351 <entry>Return value</entry>
5356 Tries to launch the executable associated with a name. For more information, see <xref linkend="message-bus-starting-services"/>.
5360 The return value can be one of the following values:
5365 <entry>Identifier</entry>
5366 <entry>Value</entry>
5367 <entry>Description</entry>
5372 <entry>DBUS_START_REPLY_SUCCESS</entry>
5374 <entry>The service was successfully started.</entry>
5377 <entry>DBUS_START_REPLY_ALREADY_RUNNING</entry>
5379 <entry>A connection already owns the given name.</entry>
5388 <sect3 id="bus-messages-update-activation-environment">
5389 <title><literal>org.freedesktop.DBus.UpdateActivationEnvironment</literal></title>
5393 UpdateActivationEnvironment (in ARRAY of DICT<STRING,STRING> environment)
5400 <entry>Argument</entry>
5402 <entry>Description</entry>
5408 <entry>ARRAY of DICT<STRING,STRING></entry>
5409 <entry>Environment to add or update</entry>
5414 Normally, session bus activated services inherit the environment of the bus daemon. This method adds to or modifies that environment when activating services.
5417 Some bus instances, such as the standard system bus, may disable access to this method for some or all callers.
5420 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.
5425 <sect3 id="bus-messages-get-name-owner">
5426 <title><literal>org.freedesktop.DBus.GetNameOwner</literal></title>
5430 STRING GetNameOwner (in STRING name)
5437 <entry>Argument</entry>
5439 <entry>Description</entry>
5445 <entry>STRING</entry>
5446 <entry>Name to get the owner of</entry>
5456 <entry>Argument</entry>
5458 <entry>Description</entry>
5464 <entry>STRING</entry>
5465 <entry>Return value, a unique connection name</entry>
5470 Returns the unique connection name of the primary owner of the name
5471 given. If the requested name doesn't have an owner, returns a
5472 <literal>org.freedesktop.DBus.Error.NameHasNoOwner</literal> error.
5476 <sect3 id="bus-messages-get-connection-unix-user">
5477 <title><literal>org.freedesktop.DBus.GetConnectionUnixUser</literal></title>
5481 UINT32 GetConnectionUnixUser (in STRING bus_name)
5488 <entry>Argument</entry>
5490 <entry>Description</entry>
5496 <entry>STRING</entry>
5497 <entry>Unique or well-known bus name of the connection to
5498 query, such as <literal>:12.34</literal> or
5499 <literal>com.example.tea</literal></entry>
5509 <entry>Argument</entry>
5511 <entry>Description</entry>
5517 <entry>UINT32</entry>
5518 <entry>Unix user ID</entry>
5523 Returns the Unix user ID of the process connected to the server. If
5524 unable to determine it (for instance, because the process is not on the
5525 same machine as the bus daemon), an error is returned.
5529 <sect3 id="bus-messages-get-connection-unix-process-id">
5530 <title><literal>org.freedesktop.DBus.GetConnectionUnixProcessID</literal></title>
5534 UINT32 GetConnectionUnixProcessID (in STRING bus_name)
5541 <entry>Argument</entry>
5543 <entry>Description</entry>
5549 <entry>STRING</entry>
5550 <entry>Unique or well-known bus name of the connection to
5551 query, such as <literal>:12.34</literal> or
5552 <literal>com.example.tea</literal></entry>
5562 <entry>Argument</entry>
5564 <entry>Description</entry>
5570 <entry>UINT32</entry>
5571 <entry>Unix process id</entry>
5576 Returns the Unix process ID of the process connected to the server. If
5577 unable to determine it (for instance, because the process is not on the
5578 same machine as the bus daemon), an error is returned.
5582 <sect3 id="bus-messages-add-match">
5583 <title><literal>org.freedesktop.DBus.AddMatch</literal></title>
5587 AddMatch (in STRING rule)
5594 <entry>Argument</entry>
5596 <entry>Description</entry>
5602 <entry>STRING</entry>
5603 <entry>Match rule to add to the connection</entry>
5608 Adds a match rule to match messages going through the message bus (see <xref linkend='message-bus-routing-match-rules'/>).
5609 If the bus does not have enough resources the <literal>org.freedesktop.DBus.Error.OOM</literal>
5613 <sect3 id="bus-messages-remove-match">
5614 <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title>
5618 RemoveMatch (in STRING rule)
5625 <entry>Argument</entry>
5627 <entry>Description</entry>
5633 <entry>STRING</entry>
5634 <entry>Match rule to remove from the connection</entry>
5639 Removes the first rule that matches (see <xref linkend='message-bus-routing-match-rules'/>).
5640 If the rule is not found the <literal>org.freedesktop.DBus.Error.MatchRuleNotFound</literal>
5645 <sect3 id="bus-messages-get-id">
5646 <title><literal>org.freedesktop.DBus.GetId</literal></title>
5650 GetId (out STRING id)
5657 <entry>Argument</entry>
5659 <entry>Description</entry>
5665 <entry>STRING</entry>
5666 <entry>Unique ID identifying the bus daemon</entry>
5671 Gets the unique ID of the bus. The unique ID here is shared among all addresses the
5672 bus daemon is listening on (TCP, UNIX domain socket, etc.) and its format is described in
5673 <xref linkend="uuids"/>. Each address the bus is listening on also has its own unique
5674 ID, as described in <xref linkend="addresses"/>. The per-bus and per-address IDs are not related.
5675 There is also a per-machine ID, described in <xref linkend="standard-interfaces-peer"/> and returned
5676 by org.freedesktop.DBus.Peer.GetMachineId().
5677 For a desktop session bus, the bus ID can be used as a way to uniquely identify a user's session.
5685 <appendix id="implementation-notes">
5686 <title>Implementation notes</title>
5687 <sect1 id="implementation-notes-subsection">
5695 <glossary><title>Glossary</title>
5697 This glossary defines some of the terms used in this specification.
5700 <glossentry id="term-bus-name"><glossterm>Bus Name</glossterm>
5703 The message bus maintains an association between names and
5704 connections. (Normally, there's one connection per application.) A
5705 bus name is simply an identifier used to locate connections. For
5706 example, the hypothetical <literal>com.yoyodyne.Screensaver</literal>
5707 name might be used to send a message to a screensaver from Yoyodyne
5708 Corporation. An application is said to <firstterm>own</firstterm> a
5709 name if the message bus has associated the application's connection
5710 with the name. Names may also have <firstterm>queued
5711 owners</firstterm> (see <xref linkend="term-queued-owner"/>).
5712 The bus assigns a unique name to each connection,
5713 see <xref linkend="term-unique-name"/>. Other names
5714 can be thought of as "well-known names" and are
5715 used to find applications that offer specific functionality.
5719 See <xref linkend="message-protocol-names-bus"/> for details of
5720 the syntax and naming conventions for bus names.
5725 <glossentry id="term-message"><glossterm>Message</glossterm>
5728 A message is the atomic unit of communication via the D-Bus
5729 protocol. It consists of a <firstterm>header</firstterm> and a
5730 <firstterm>body</firstterm>; the body is made up of
5731 <firstterm>arguments</firstterm>.
5736 <glossentry id="term-message-bus"><glossterm>Message Bus</glossterm>
5739 The message bus is a special application that forwards
5740 or routes messages between a group of applications
5741 connected to the message bus. It also manages
5742 <firstterm>names</firstterm> used for routing
5748 <glossentry id="term-name"><glossterm>Name</glossterm>
5751 See <xref linkend="term-bus-name"/>. "Name" may
5752 also be used to refer to some of the other names
5753 in D-Bus, such as interface names.
5758 <glossentry id="namespace"><glossterm>Namespace</glossterm>
5761 Used to prevent collisions when defining new interfaces, bus names
5762 etc. The convention used is the same one Java uses for defining
5763 classes: a reversed domain name.
5764 See <xref linkend="message-protocol-names-bus"/>,
5765 <xref linkend="message-protocol-names-interface"/>,
5766 <xref linkend="message-protocol-names-error"/>,
5767 <xref linkend="message-protocol-marshaling-object-path"/>.
5772 <glossentry id="term-object"><glossterm>Object</glossterm>
5775 Each application contains <firstterm>objects</firstterm>, which have
5776 <firstterm>interfaces</firstterm> and
5777 <firstterm>methods</firstterm>. Objects are referred to by a name,
5778 called a <firstterm>path</firstterm>.
5783 <glossentry id="one-to-one"><glossterm>One-to-One</glossterm>
5786 An application talking directly to another application, without going
5787 through a message bus. One-to-one connections may be "peer to peer" or
5788 "client to server." The D-Bus protocol has no concept of client
5789 vs. server after a connection has authenticated; the flow of messages
5790 is symmetrical (full duplex).
5795 <glossentry id="term-path"><glossterm>Path</glossterm>
5798 Object references (object names) in D-Bus are organized into a
5799 filesystem-style hierarchy, so each object is named by a path. As in
5800 LDAP, there's no difference between "files" and "directories"; a path
5801 can refer to an object, while still having child objects below it.
5806 <glossentry id="term-queued-owner"><glossterm>Queued Name Owner</glossterm>
5809 Each bus name has a primary owner; messages sent to the name go to the
5810 primary owner. However, certain names also maintain a queue of
5811 secondary owners "waiting in the wings." If the primary owner releases
5812 the name, then the first secondary owner in the queue automatically
5813 becomes the new owner of the name.
5818 <glossentry id="term-service"><glossterm>Service</glossterm>
5821 A service is an executable that can be launched by the bus daemon.
5822 Services normally guarantee some particular features, for example they
5823 may guarantee that they will request a specific name such as
5824 "org.freedesktop.Screensaver", have a singleton object
5825 "/org/freedesktop/Application", and that object will implement the
5826 interface "org.freedesktop.ScreensaverControl".
5831 <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
5834 ".service files" tell the bus about service applications that can be
5835 launched (see <xref linkend="term-service"/>). Most importantly they
5836 provide a mapping from bus names to services that will request those
5837 names when they start up.
5842 <glossentry id="term-unique-name"><glossterm>Unique Connection Name</glossterm>
5845 The special name automatically assigned to each connection by the
5846 message bus. This name will never change owner, and will be unique
5847 (never reused during the lifetime of the message bus).
5848 It will begin with a ':' character.
projects / platform / upstream / dbus.git / blob