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9 <title>D-BUS Specification</title>
10 <releaseinfo>Version 0.8</releaseinfo>
11 <date>06 September 2003</date>
14 <firstname>Havoc</firstname>
15 <surname>Pennington</surname>
17 <orgname>Red Hat, Inc.</orgname>
19 <email>hp@pobox.com</email>
24 <firstname>Anders</firstname>
25 <surname>Carlsson</surname>
27 <orgname>CodeFactory AB</orgname>
29 <email>andersca@codefactory.se</email>
34 <firstname>Alexander</firstname>
35 <surname>Larsson</surname>
37 <orgname>Red Hat, Inc.</orgname>
39 <email>alexl@redhat.com</email>
46 <sect1 id="introduction">
47 <title>Introduction</title>
49 D-BUS is a system for low-latency, low-overhead, easy to use
50 interprocess communication (IPC). In more detail:
54 D-BUS is <emphasis>low-latency</emphasis> because it is designed
55 to avoid round trips and allow asynchronous operation, much like
61 D-BUS is <emphasis>low-overhead</emphasis> because it uses a
62 binary protocol, and does not have to convert to and from a text
63 format such as XML. Because D-BUS is intended for potentially
64 high-resolution same-machine IPC, not primarily for Internet IPC,
65 this is an interesting optimization.
70 D-BUS is <emphasis>easy to use</emphasis> because it works in terms
71 of <firstterm>messages</firstterm> rather than byte streams, and
72 automatically handles a lot of the hard IPC issues. Also, the D-BUS
73 library is designed to be wrapped in a way that lets developers use
74 their framework's existing object/type system, rather than learning
75 a new one specifically for IPC.
81 The base D-BUS protocol is a peer-to-peer protocol, specified in <xref
82 linkend="message-protocol"/>. That is, it is a system for one application
83 to talk to a single other application. However, the primary intended
84 application of D-BUS is the D-BUS <firstterm>message bus</firstterm>,
85 specified in <xref linkend="message-bus"/>. The message bus is a special
86 application that accepts connections from multiple other applications, and
87 forwards messages among them.
90 Uses of D-BUS include notification of system changes (notification of when
91 a camera is plugged in to a computer, or a new version of some software
92 has been installed), or desktop interoperablity, for example a file
93 monitoring service or a configuration service.
97 <sect1 id="message-protocol">
98 <title>Message Protocol</title>
100 A <firstterm>message</firstterm> consists of a
101 <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you
102 think of a message as a package, the header is the address, and the body
103 contains the package contents. The message delivery system uses the header
104 information to figure out where to send the message and how to interpret
105 it; the recipient inteprets the body of the message.
109 The body of the message is made up of zero or more
110 <firstterm>arguments</firstterm>, which are typed
111 values, such as an integer or a byte array.
114 <sect2 id="message-protocol-header-encoding">
115 <title>Header Encoding</title>
117 Following the mandatory fields, there are zero or more named fields (see
118 <xref linkend="message-protocol-header-fields"/>), and then nul bytes
119 padding the header such that its total length in bytes is a multiple of
123 The header MUST begin with the following mandatory fields in the following
130 <entry>Description</entry>
135 <entry>1 byte</entry>
136 <entry>Endianness flag; ASCII 'l' for little-endian
137 or ASCII 'B' for big-endian.</entry>
140 <entry>1 byte</entry>
141 <entry>Type of message. Unknown types MUST be ignored.
142 Currently-defined types are described below.
146 <entry>1 byte</entry>
147 <entry>Bitwise OR of flags. Unknown flags
148 MUST be ignored. Currently-defined flags are described below.
152 <entry>1 byte</entry>
153 <entry>Major protocol version of the sending application. If
154 the major protocol version of the receiving application does not
155 match, the applications will not be able to communicate and the
156 D-BUS connection MUST be disconnected. The major protocol
157 version for this version of the specification is 0.
161 <entry>4 bytes</entry>
162 <entry>An unsigned 32-bit integer in the
163 message's byte order, indicating the total length in bytes of
164 the header including named fields and any alignment padding.
165 MUST be a multiple of 8.
169 <entry>4 bytes</entry>
170 <entry>An unsigned 32-bit integer in the
171 message's byte order, indicating the total length in bytes of
176 <entry>4 bytes</entry>
177 <entry>The message's serial number, an unsigned 32-bit integer in
178 the message's byte order. The serial number is a cookie used to
179 identify message replies; thus all outstanding unreplied-to messages
180 from the same connection MUST have a different serial number.
181 Zero is not a valid serial number, but all other numbers are
190 Types that can appear in the second byte of the header:
195 <entry>Conventional name</entry>
196 <entry>Decimal value</entry>
197 <entry>Description</entry>
202 <entry>INVALID</entry>
204 <entry>This is an invalid type, if seen in a message
205 the connection should be dropped immediately.</entry>
208 <entry>METHOD_CALL</entry>
210 <entry>Method call.</entry>
213 <entry>METHOD_RETURN</entry>
215 <entry>Method reply with returned data.</entry>
220 <entry>Error reply. If the first argument exists and is a
221 string, it is an error message.</entry>
224 <entry>SIGNAL</entry>
226 <entry>Signal emission.</entry>
233 Flags that can appear in the third byte of the header:
238 <entry>Conventional name</entry>
239 <entry>Hex value</entry>
240 <entry>Description</entry>
245 <entry>NO_REPLY_EXPECTED</entry>
247 <entry>This message does not expect method return replies or
248 error replies; the reply can be omitted as an
249 optimization. However, it is compliant with this specification
250 to return the reply despite this flag.</entry>
253 <entry>AUTO_ACTIVATION</entry>
255 <entry>This message automatically activates the
256 addressed service before the message is delivered.</entry>
264 <sect2 id="message-protocol-header-fields">
265 <title>Header Fields</title>
267 In addition to the required header information mentioned
268 in <xref linkend="message-protocol-header-encoding"/>,
269 the header may contain zero or more named
270 header fields. Future versions of this protocol
271 specification may add new fields. Implementations must
272 ignore fields they do not understand. Implementations
273 must not invent their own header fields; only changes to
274 this specification may introduce new header fields.
278 Header field names MUST consist of a single byte, possible values
279 of which are defined below. Following the name, the field MUST have
280 a type code represented as a single unsigned byte, and then a
281 properly-aligned value of that type. See <xref
282 linkend="message-protocol-arguments"/> for a description of how each
283 type is encoded. If an implementation sees a header field name that
284 it does not understand, it MUST ignore that field.
288 Here are the currently-defined named header fields:
293 <entry>Conventional Name</entry>
294 <entry>Decimal Value</entry>
296 <entry>Description</entry>
301 <entry>INVALID</entry>
303 <entry>INVALID</entry>
304 <entry>Not a valid field name (error if it appears in a message)</entry>
309 <entry>OBJECT_PATH</entry>
310 <entry>The object to send the message to; objects are identified by
311 a path, "/foo/bar"</entry>
314 <entry>INTERFACE</entry>
316 <entry>STRING</entry>
317 <entry>The interface to invoke a method call on, or
318 that a signal is emitted from. e.g. "org.freedesktop.Introspectable"</entry>
321 <entry>MEMBER</entry>
323 <entry>STRING</entry>
324 <entry>The member, either the method name or signal name.
325 e.g. "Frobate"</entry>
328 <entry>ERROR_NAME</entry>
330 <entry>STRING</entry>
331 <entry>The name of the error that occurred, for errors</entry>
334 <entry>REPLY_SERIAL</entry>
336 <entry>UINT32</entry>
337 <entry>The serial number of the message this message is a reply
338 to. (The serial number is one of the mandatory header fields,
339 see <xref linkend="message-protocol-header-encoding"/>.)</entry>
342 <entry>SERVICE</entry>
344 <entry>STRING</entry>
345 <entry>The name of the service this message should be routed to.
346 Only used in combination with the message bus, see
347 <xref linkend="message-bus"/>.</entry>
350 <entry>SENDER_SERVICE</entry>
352 <entry>STRING</entry>
353 <entry>Sender service. The name of the base service that sent
354 this message. The message bus fills in this field; the field is
355 only meaningful in combination with the message bus.</entry>
363 <sect2 id="message-protocol-header-padding">
364 <title>Header Alignment Padding</title>
366 To allow implementations to keep the header and the body in a single
367 buffer while keeping data types aligned, the total length of the header
368 must be a multiple of 8 bytes. To achieve this, the header MUST be padded
369 with nul bytes to align its total length on an 8-byte boundary.
370 The minimum number of padding bytes MUST be used. Because zero is an
371 invalid field name, implementations can distinguish padding (which must be
372 zero initialized) from additional named fields.
376 <sect2 id="message-protocol-arguments">
377 <title>Message Arguments</title>
379 The message body is made up of arguments. Each argument is a type code,
380 represented by a single unsigned byte, followed by the aligned value of
381 the argument in a type-dependent format. Alignment padding between the
382 typecode and the value is initialized to zero.
389 <entry>Type name</entry>
391 <entry>Description</entry>
396 <entry>INVALID</entry>
397 <entry>0 (ASCII NUL)</entry>
398 <entry>Not a valid type code (error if it appears in a message)</entry>
401 <entry>118 (ASCII 'v') </entry>
402 <entry>Marks a "void"/"unset"/"nonexistent"/"null" argument</entry>
405 <entry>121 (ASCII 'y')</entry>
406 <entry>8-bit unsigned integer</entry>
408 <entry>BOOLEAN</entry>
409 <entry>98 (ASCII 'b')</entry>
410 <entry>Boolean value, 0 is FALSE and 1 is TRUE. Everything else is invalid.</entry>
413 <entry>105 (ASCII 'i')</entry>
414 <entry>32-bit signed integer</entry>
416 <entry>UINT32</entry>
417 <entry>117 (ASCII 'u')</entry>
418 <entry>32-bit unsigned integer</entry>
421 <entry>120 (ASCII 'x')</entry>
422 <entry>64-bit signed integer</entry>
424 <entry>UINT64</entry>
425 <entry>116 (ASCII 't')</entry>
426 <entry>64-bit unsigned integer</entry>
428 <entry>DOUBLE</entry>
429 <entry>100 (ASCII 'd')</entry>
430 <entry>IEEE 754 double</entry>
432 <entry>STRING</entry>
433 <entry>115 (ASCII 's')</entry>
434 <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be zero terminated. </entry>
436 <entry>CUSTOM</entry>
437 <entry>99 (ASCII 'c')</entry>
438 <entry>A named byte array, used for custom types</entry>
441 <entry>97 (ASCII 'a')</entry>
445 <entry>109 (ASCII 'm')</entry>
446 <entry>A dictionary of key/value pairs</entry>
448 <entry>OBJECT_PATH</entry>
449 <entry>111 (ASCII 'o')</entry>
450 <entry>Name of an object</entry>
457 The types are encoded as follows:
462 <entry>Type name</entry>
463 <entry>Encoding</entry>
468 <entry>INVALID</entry>
469 <entry>Not applicable; cannot be encoded.</entry>
472 <entry>No data is encoded; the type code is followed immediately
473 by the type code of the next argument.</entry>
476 <entry>A byte.</entry>
478 <entry>BOOLEAN</entry>
479 <entry>A byte, with valid values 0 and 1.</entry>
482 <entry>32-bit signed integer in the message's byte order, aligned to 4-byte boundary.</entry>
484 <entry>UINT32</entry>
485 <entry>32-bit unsigned integer in the message's byte order, aligned to 4-byte boundary.</entry>
488 <entry>64-bit signed integer in the message's byte order, aligned to 8-byte boundary.</entry>
490 <entry>UINT64</entry>
491 <entry>64-bit unsigned integer in the message's byte order, aligned to 8-byte boundary.</entry>
493 <entry>DOUBLE</entry>
494 <entry>64-bit IEEE 754 double in the message's byte order, aligned to 8-byte boundary.</entry>
496 <entry>STRING</entry>
497 <entry>UINT32 aligned to 4-byte boundary indicating the string's
498 length in bytes excluding its terminating nul, followed by
499 string data of the given length, followed by a terminating nul
503 <entry>CUSTOM</entry>
504 <entry>A string (encoded as the STRING type above) giving the
505 name of the type followed by an UINT32 aligned to 4-byte boundary
506 indicating the data length in bytes, followed by the data.
507 The string has some restrictions on its content, see
508 <xref linkend="message-protocol-names"/>.
512 <entry>A sequence of bytes giving the element type of the array, terminated
513 by a type different from ARRAY (just one byte for one-dimensional arrays, but
514 larger for multi-dimensional arrays), followed by an UINT32 (aligned to 4 bytes)
515 giving the length of the array data in bytes. This is followed by each array entry
516 encoded the way it would normally be encoded, except arrays, which are encoded
517 without the type information, since that is already declared above. Arrays containing
522 <entry>UINT32 giving the length of the dictionary data in bytes.
523 This is followed by a number of keyname/value pairs, where the
524 keyname is encoded as a STRING above, and the value is encoded
525 as a byte with typecode and how that type normally would be encoded
529 <entry>OBJECT_PATH</entry>
530 <entry>Encoded as if it were a STRING.
539 <sect2 id="message-protocol-names">
540 <title>Valid names</title>
542 The various names in D-BUS messages have some restrictions.
544 <sect3 id="message-protocol-names-interface">
545 <title>Interface names</title>
547 Interfaces have names with type STRING, meaning that
548 they must be valid UTF-8. However, there are also some
549 additional restrictions that apply to interface names
552 <listitem><para>They are composed of 1 or more elements separated by
553 a period ('.') character. All elements must contain at least
557 <listitem><para>Each element must only contain the ASCII characters
558 "[A-Z][a-z][0-9]_" and must not begin with a digit.
562 <listitem><para>They must contain at least one '.' (period)
563 character (and thus at least two elements).
566 <listitem><para>They must not begin with a '.' (period) character.</para></listitem>
567 <listitem><para>They must not exceed 256 bytes in length.</para></listitem>
568 <listitem><para>They must be at least 1 byte in length.</para></listitem>
572 <sect3 id="message-protocol-names-service">
573 <title>Service names</title>
575 Service names have the same restrictions as interface names, with a
576 special exception for base services. A base service name's first
577 element must start with a colon (':') character. After the colon, any
578 characters in the range "[A-Z][a-z][0-9]_" may appear. Elements after
579 the first must follow the usual rules, except that they may start with
580 a digit. Service names not starting with a colon have none of these
581 exceptions and follow the same rules as interface names.
584 <sect3 id="message-protocol-names-method">
585 <title>Method names</title>
589 <listitem><para>Must only contain the ASCII characters
590 "[A-Z][a-z][0-9]_" and may not begin with a
591 digit.</para></listitem>
592 <listitem><para>Must not contain the '.' (period) character</para></listitem>
593 <listitem><para>Must not exceed 256 bytes in length</para></listitem>
594 <listitem><para>Must be at least 1 byte in length</para></listitem>
598 <sect3 id="message-protocol-names-path">
599 <title>Path names</title>
601 A path (type OBJECT_PATH) must begin with an ASCII '/' (slash)
602 character. Paths may not end with a slash character unless the path is
603 the one-byte string "/". Two slash characters may not appear adjacent
604 to one another (the empty string is not a valid "subdirectory"). Paths
605 may not exceed 256 bytes in length.
608 <sect3 id="message-protocol-names-error">
609 <title>Error names</title>
611 Error names have the same restrictions as interface names.
614 <sect3 id="message-protocol-names-custom">
615 <title>Custom types</title>
617 Custom type names for values of type CUSTOM follow the same
618 restrictions as interface names.
623 <sect2 id="message-protocol-types">
624 <title>Message types</title>
626 Each of the message types (METHOD_CALL, METHOD_RETURN, ERROR, and
627 SIGNAL) has its own expected usage conventions and header fields.
629 <sect3 id="message-protocol-types-method">
630 <title>Method Calls, Returns, and Errors</title>
632 Some messages invoke an operation on a remote object. These are
633 called method call messages and have the type tag METHOD_CALL. Such
634 messages map naturally to methods on objects in a typical program.
637 A method call message is expected to have a MEMBER header field
638 indicating the name of the method. Optionally, the message has an
639 INTERFACE field giving the interface the method is a part of. In the
640 absence of an INTERFACE field, if two interfaces on the same object have
641 a method with the same name, it is undefined which of the two methods
642 will be invoked. Implementations may also choose to return an error in
643 this ambiguous case. However, if a method name is unique
644 implementations should not require an interface field.
647 Method call messages also include a PATH field indicating the
648 object to invoke the method on. If the call is passing through
649 a message bus, the message will also have a SERVICE field giving
650 the service to receive the message.
653 When an application handles a method call message, it is expected to
654 return a reply. The reply is identified by a REPLY_SERIAL header field
655 indicating the serial number of the METHOD_CALL being replied to. The
656 reply can have one of two types; either METHOD_RETURN or ERROR.
659 If the reply has type METHOD_RETURN, the arguments to the reply message
660 are the return value(s) or "out parameters" of the method call.
661 If the reply has type ERROR, then an "exception" has been thrown,
662 and the call fails; no return value will be provided. It makes
663 no sense to send multiple replies to the same method call.
666 Even if a method call has no return values, a METHOD_RETURN
667 reply is expected, so the caller will know the method
668 was successfully processed.
671 The METHOD_RETURN or ERROR reply message MUST have the REPLY_SERIAL
672 header field. If this field is missing, it should be treated as
676 If a METHOD_CALL message has the flag NO_REPLY_EXPECTED,
677 then as an optimization the application receiving the method
678 call may choose to omit the reply message (regardless of
679 whether the reply would have been METHOD_RETURN or ERROR).
680 However, it is also acceptable to ignore the NO_REPLY_EXPECTED
681 flag and reply anyway.
684 If a message has the flag AUTO_ACTIVATION, then the addressed
685 service will be activated before the message is delivered, if
686 not already active. The message will be held until the service
687 is successfully activated or has failed to activate; in case
688 of failure, an activation error will be returned.
690 <sect4 id="message-protocol-types-method-apis">
691 <title>Mapping method calls to native APIs</title>
693 APIs for D-BUS may map method calls to a method call in a specific
694 programming language, such as C++, or may map a method call written
695 in an IDL to a D-BUS message.
698 In APIs of this nature, arguments to a method are often termed "in"
699 (which implies sent in the METHOD_CALL), or "out" (which implies
700 returned in the METHOD_RETURN). Some APIs such as CORBA also have
701 "inout" arguments, which are both sent and received, i.e. the caller
702 passes in a value which is modified. Mapped to D-BUS, an "inout"
703 argument is equivalent to an "in" argument, followed by an "out"
704 argument. You can't pass things "by reference" over the wire, so
705 "inout" is purely an illusion of the in-process API.
708 Given a method with zero or one return values, followed by zero or more
709 arguments, where each argument may be "in", "out", or "inout", the
710 caller constructs a message by appending each "in" or "inout" argument,
711 in order. "out" arguments are not represented in the caller's message.
714 The recipient constructs a reply by appending first the return value
715 if any, then each "out" or "inout" argument, in order.
716 "in" arguments are not represented in the reply message.
722 <sect3 id="message-protocol-types-signal">
723 <title>Signal Emission</title>
725 Unlike method calls, signal emissions have no replies.
726 A signal emission is simply a single message of type SIGNAL.
727 It must have three header fields: PATH giving the object
728 the signal was emitted from, plus INTERFACE and MEMBER giving
729 the fully-qualified name of the signal.
733 <sect3 id="message-protocol-types-notation">
734 <title>Notation in this document</title>
736 This document uses a simple pseudo-IDL to describe particular method
737 calls and signals. Here is an example of a method call:
739 org.freedesktop.DBus.ActivateService (in STRING service_name, in UINT32 flags,
740 out UINT32 resultcode)
742 This means INTERFACE = org.freedesktop.DBus, MEMBER = ActivateService,
743 METHOD_CALL arguments are STRING and UINT32, METHOD_RETURN argument
744 is UINT32. Remember that the MEMBER field can't contain any '.' (period)
745 characters so it's known that the last part of the name in
746 the "IDL" is the member name.
749 In C++ that might end up looking like this:
751 unsigned int org::freedesktop::DBus::ActivateService (const char *service_name,
754 or equally valid, the return value could be done as an argument:
756 void org::freedesktop::DBus::ActivateService (const char *service_name,
758 unsigned int *resultcode);
760 It's really up to the API designer how they want to make
761 this look. You could design an API where the namespace wasn't used
762 in C++, using STL or Qt, using varargs, or whatever you wanted.
765 Signals are written as follows:
767 org.freedesktop.DBus.ServiceLost (STRING service_name)
769 Signals don't specify "in" vs. "out" because only
770 a single direction is possible.
773 In this ad hoc notation, the special type name ANY means any type
774 other than NIL, and the special type name ANY_OR_NIL means any valid
778 It isn't especially encouraged to use this lame pseudo-IDL in actual
779 API implementations; you might use the native notation for the
780 language you're using, or you might use COM or CORBA IDL, for example.
787 <sect1 id="auth-protocol">
788 <title>Authentication Protocol</title>
790 Before the flow of messages begins, two applications must
791 authenticate. A simple plain-text protocol is used for
792 authentication; this protocol is a SASL profile, and maps fairly
793 directly from the SASL specification. The message encoding is
794 NOT used here, only plain text messages.
797 In examples, "C:" and "S:" indicate lines sent by the client and
800 <sect2 id="auth-protocol-overview">
801 <title>Protocol Overview</title>
803 The protocol is a line-based protocol, where each line ends with
804 \r\n. Each line begins with an all-caps ASCII command name containing
805 only the character range [A-Z], a space, then any arguments for the
806 command, then the \r\n ending the line. The protocol is
807 case-sensitive. All bytes must be in the ASCII character set.
809 Commands from the client to the server are as follows:
812 <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
813 <listitem><para>CANCEL</para></listitem>
814 <listitem><para>BEGIN</para></listitem>
815 <listitem><para>DATA <data in base 64 encoding></para></listitem>
816 <listitem><para>ERROR [human-readable error explanation]</para></listitem>
819 From server to client are as follows:
822 <listitem><para>REJECTED <space-separated list of mechanism names></para></listitem>
823 <listitem><para>OK</para></listitem>
824 <listitem><para>DATA <data in base 64 encoding></para></listitem>
825 <listitem><para>ERROR</para></listitem>
829 <sect2 id="auth-nul-byte">
830 <title>Special credentials-passing nul byte</title>
832 Immediately after connecting to the server, the client must send a
833 single nul byte. This byte may be accompanied by credentials
834 information on some operating systems that use sendmsg() with
835 SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain
836 sockets. However, the nul byte MUST be sent even on other kinds of
837 socket, and even on operating systems that do not require a byte to be
838 sent in order to transmit credentials. The text protocol described in
839 this document begins after the single nul byte. If the first byte
840 received from the client is not a nul byte, the server may disconnect
844 A nul byte in any context other than the initial byte is an error;
845 the protocol is ASCII-only.
848 The credentials sent along with the nul byte may be used with the
849 SASL mechanism EXTERNAL.
852 <sect2 id="auth-command-auth">
853 <title>AUTH command</title>
855 If an AUTH command has no arguments, it is a request to list
856 available mechanisms. The server SHOULD respond with a REJECTED
857 command listing the mechanisms it understands.
860 If an AUTH command specifies a mechanism, and the server supports
861 said mechanism, the server SHOULD begin exchanging SASL
862 challenge-response data with the client using DATA commands.
865 If the server does not support the mechanism given in the AUTH
866 command, it SHOULD send a REJECTED command listing the mechanisms
870 If the [initial-response] argument is provided, it is intended for
871 use with mechanisms that have no initial challenge (or an empty
872 initial challenge), as if it were the argument to an initial DATA
873 command. If the selected mechanism has an initial challenge, the
874 server should reject authentication by sending REJECTED.
877 If authentication succeeds after exchanging DATA commands,
878 an OK command should be sent to the client.
881 The first octet received by the client after the \r\n of the OK
882 command MUST be the first octet of the authenticated/encrypted
883 stream of D-BUS messages.
886 The first octet received by the server after the \r\n of the BEGIN
887 command from the client MUST be the first octet of the
888 authenticated/encrypted stream of D-BUS messages.
891 <sect2 id="auth-command-cancel">
892 <title>CANCEL Command</title>
894 At any time up to sending the BEGIN command, the client may send a
895 CANCEL command. On receiving the CANCEL command, the server MUST
896 send a REJECTED command and abort the current authentication
900 <sect2 id="auth-command-data">
901 <title>DATA Command</title>
903 The DATA command may come from either client or server, and simply
904 contains a base64-encoded block of data to be interpreted
905 according to the SASL mechanism in use.
908 Some SASL mechanisms support sending an "empty string";
909 FIXME we need some way to do this.
912 <sect2 id="auth-command-begin">
913 <title>BEGIN Command</title>
915 The BEGIN command acknowledges that the client has received an
916 OK command from the server, and that the stream of messages
920 The first octet received by the server after the \r\n of the BEGIN
921 command from the client MUST be the first octet of the
922 authenticated/encrypted stream of D-BUS messages.
925 <sect2 id="auth-command-rejected">
926 <title>REJECTED Command</title>
928 The REJECTED command indicates that the current authentication
929 exchange has failed, and further exchange of DATA is inappropriate.
930 The client would normally try another mechanism, or try providing
931 different responses to challenges.
933 Optionally, the REJECTED command has a space-separated list of
934 available auth mechanisms as arguments. If a server ever provides
935 a list of supported mechanisms, it MUST provide the same list
936 each time it sends a REJECTED message. Clients are free to
937 ignore all lists received after the first.
940 <sect2 id="auth-command-ok">
941 <title>OK Command</title>
943 The OK command indicates that the client has been authenticated,
944 and that further communication will be a stream of D-BUS messages
945 (optionally encrypted, as negotiated) rather than this protocol.
948 The first octet received by the client after the \r\n of the OK
949 command MUST be the first octet of the authenticated/encrypted
950 stream of D-BUS messages.
953 The client MUST respond to the OK command by sending a BEGIN
954 command, followed by its stream of messages, or by disconnecting.
955 The server MUST NOT accept additional commands using this protocol
956 after the OK command has been sent.
959 <sect2 id="auth-command-error">
960 <title>ERROR Command</title>
962 The ERROR command indicates that either server or client did not
963 know a command, does not accept the given command in the current
964 context, or did not understand the arguments to the command. This
965 allows the protocol to be extended; a client or server can send a
966 command present or permitted only in new protocol versions, and if
967 an ERROR is received instead of an appropriate response, fall back
968 to using some other technique.
971 If an ERROR is sent, the server or client that sent the
972 error MUST continue as if the command causing the ERROR had never been
973 received. However, the the server or client receiving the error
974 should try something other than whatever caused the error;
975 if only canceling/rejecting the authentication.
978 <sect2 id="auth-examples">
979 <title>Authentication examples</title>
983 <title>Example of successful magic cookie authentication</title>
985 (MAGIC_COOKIE is a made up mechanism)
987 C: AUTH MAGIC_COOKIE BsAY3g4gBNo=
993 <title>Example of finding out mechanisms then picking one</title>
996 S: REJECTED KERBEROS_V4 SKEY
997 C: AUTH SKEY bW9yZ2Fu
998 S: DATA OTUgUWE1ODMwOA==
999 C: DATA Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
1005 <title>Example of client sends unknown command then falls back to regular auth</title>
1009 C: AUTH MAGIC_COOKIE BsAY3g4gBNo=
1015 <title>Example of server doesn't support initial auth mechanism</title>
1017 C: AUTH MAGIC_COOKIE BsAY3g4gBNo=
1018 S: REJECTED KERBEROS_V4 SKEY
1019 C: AUTH SKEY bW9yZ2Fu
1020 S: DATA OTUgUWE1ODMwOA==
1021 C: DATA Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
1027 <title>Example of wrong password or the like followed by successful retry</title>
1029 C: AUTH MAGIC_COOKIE BsAY3g4gBNo=
1030 S: REJECTED KERBEROS_V4 SKEY
1031 C: AUTH SKEY bW9yZ2Fu
1032 S: DATA OTUgUWE1ODMwOA==
1033 C: DATA Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
1035 C: AUTH SKEY bW9yZ2Fu
1036 S: DATA OTUgUWE1ODMwOA==
1037 C: DATA Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
1043 <title>Example of skey cancelled and restarted</title>
1045 C: AUTH MAGIC_COOKIE BsAY3g4gBNo=
1046 S: REJECTED KERBEROS_V4 SKEY
1047 C: AUTH SKEY bW9yZ2Fu
1048 S: DATA OTUgUWE1ODMwOA==
1051 C: AUTH SKEY bW9yZ2Fu
1052 S: DATA OTUgUWE1ODMwOA==
1053 C: DATA Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
1060 <sect2 id="auth-states">
1061 <title>Authentication state diagrams</title>
1064 This section documents the auth protocol in terms of
1065 a state machine for the client and the server. This is
1066 probably the most robust way to implement the protocol.
1069 <sect3 id="auth-states-client">
1070 <title>Client states</title>
1073 <title><emphasis>Start</emphasis></title>
1076 <listitem><para>send AUTH with initial data -> <emphasis>WaitingForData</emphasis></para></listitem>
1077 <listitem><para>send AUTH with no initial data -> <emphasis>WaitingForData</emphasis> or <emphasis>NeedSendData</emphasis> (depends on mechanism)</para></listitem>
1079 The <emphasis>Start</emphasis> state is stateful (it has a list of
1080 available mechanisms and those it has already attempted). This list
1081 is used to decide which AUTH command to send. When the list is
1082 exhausted, the client should give up and close the connection.
1087 <title><emphasis>WaitingForData</emphasis></title>
1091 <listitem><para>receive OK -> <emphasis>NeedSendBegin</emphasis></para></listitem>
1092 <listitem><para>receive REJECTED -> <emphasis>Start</emphasis></para></listitem>
1093 <listitem><para>receive ERROR -> <emphasis>Start</emphasis></para></listitem>
1094 <listitem><para>receive DATA -> <emphasis>NeedSendData</emphasis></para></listitem>
1095 <listitem><para>receive anything else -> <emphasis>NeedSendError</emphasis></para></listitem>
1097 When going back to <emphasis>Start</emphasis>, the mechanism in
1098 progress should be marked as failed and not retried (at least not
1099 with the same parameters). When receiving REJECTED with a list of
1100 mechanisms, the list should be recorded and used to select
1106 <title><emphasis>NeedSendData</emphasis></title>
1109 <listitem><para>send DATA -> <emphasis>WaitingForData</emphasis></para></listitem>
1110 <listitem><para>send CANCEL -> <emphasis>Start</emphasis></para></listitem>
1116 <title><emphasis>NeedSendError</emphasis></title>
1120 <listitem><para>send ERROR -> return to previous state</para></listitem>
1126 <title><emphasis>NeedSendBegin</emphasis></title>
1130 <listitem><para>send BEGIN -> Authorized</para></listitem>
1136 <title><emphasis>Authorized</emphasis></title>
1138 This is the end state, flow of messages begins.
1144 <sect3 id="auth-states-server">
1145 <title>Server states</title>
1148 <title><emphasis>WaitingForAuth</emphasis></title>
1151 <listitem><para>receive AUTH with initial response -> <emphasis>NeedSendData</emphasis></para></listitem>
1152 <listitem><para>receive AUTH without initial response -> <emphasis>NeedSendData</emphasis> or <emphasis>WaitingForData</emphasis> depending on mechanism</para></listitem>
1158 <title><emphasis>NeedSendData</emphasis></title>
1161 <listitem><para>send DATA -> <emphasis>WaitingForData</emphasis></para></listitem>
1162 <listitem><para>send ERROR -> <emphasis>WaitingForData</emphasis></para></listitem>
1163 <listitem><para>send REJECTED -> <emphasis>WaitingForAuth</emphasis></para></listitem>
1164 <listitem><para>send OK -> <emphasis>WaitingForBegin</emphasis></para></listitem>
1170 <title><emphasis>WaitingForData</emphasis></title>
1173 <listitem><para>receive DATA -> <emphasis>NeedSendData</emphasis></para></listitem>
1174 <listitem><para>receive CANCEL -> <emphasis>NeedSendRejected</emphasis></para></listitem>
1175 <listitem><para>receive ERROR -> <emphasis>NeedSendRejected</emphasis></para></listitem>
1176 <listitem><para>receive anything else -> <emphasis>NeedSendError</emphasis></para></listitem>
1182 <title><emphasis>NeedSendError</emphasis></title>
1186 <listitem><para>send ERROR -> return to previous state</para></listitem>
1192 <title><emphasis>NeedSendRejected</emphasis></title>
1196 <listitem><para>send REJECTED -> <emphasis>WaitingForAuth</emphasis></para></listitem>
1202 <title><emphasis>WaitingForBegin</emphasis></title>
1206 <listitem><para>receive BEGIN -> <emphasis>Authorized</emphasis></para></listitem>
1207 <listitem><para>receive anything else -> <emphasis>NeedSendError</emphasis></para></listitem>
1213 <title><emphasis>Authorized</emphasis></title>
1215 This is the end state, flow of messages begins.
1222 <sect2 id="auth-mechanisms">
1223 <title>Authentication mechanisms</title>
1225 This section describes some new authentication mechanisms.
1226 D-BUS also allows any standard SASL mechanism of course.
1228 <sect3 id="auth-mechanisms-sha">
1229 <title>DBUS_COOKIE_SHA1</title>
1231 The DBUS_COOKIE_SHA1 mechanism is designed to establish that a client
1232 has the ability to read a private file owned by the user being
1233 authenticated. If the client can prove that it has access to a secret
1234 cookie stored in this file, then the client is authenticated.
1235 Thus the security of DBUS_COOKIE_SHA1 depends on a secure home
1239 Authentication proceeds as follows:
1243 The client sends the username it would like to authenticate
1249 The server sends the name of its "cookie context" (see below); a
1250 space character; the integer ID of the secret cookie the client
1251 must demonstrate knowledge of; a space character; then a
1252 hex-encoded randomly-generated challenge string.
1257 The client locates the cookie, and generates its own hex-encoded
1258 randomly-generated challenge string. The client then
1259 concatentates the server's hex-encoded challenge, a ":"
1260 character, its own hex-encoded challenge, another ":" character,
1261 and the hex-encoded cookie. It computes the SHA-1 hash of this
1262 composite string. It sends back to the server the client's
1263 hex-encoded challenge string, a space character, and the SHA-1
1269 The server generates the same concatenated string used by the
1270 client and computes its SHA-1 hash. It compares the hash with
1271 the hash received from the client; if the two hashes match, the
1272 client is authenticated.
1278 Each server has a "cookie context," which is a name that identifies a
1279 set of cookies that apply to that server. A sample context might be
1280 "org_freedesktop_session_bus". Context names must be valid ASCII,
1281 nonzero length, and may not contain the characters slash ("/"),
1282 backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"),
1283 tab ("\t"), or period ("."). There is a default context,
1284 "org_freedesktop_global" that's used by servers that do not specify
1288 Cookies are stored in a user's home directory, in the directory
1289 <filename>~/.dbus-keyrings/</filename>. This directory must
1290 not be readable or writable by other users. If it is,
1291 clients and servers must ignore it. The directory
1292 contains cookie files named after the cookie context.
1295 A cookie file contains one cookie per line. Each line
1296 has three space-separated fields:
1300 The cookie ID number, which must be a non-negative integer and
1301 may not be used twice in the same file.
1306 The cookie's creation time, in UNIX seconds-since-the-epoch
1312 The cookie itself, a hex-encoded random block of bytes.
1318 Only server processes modify the cookie file.
1319 They must do so with this procedure:
1323 Create a lockfile name by appending ".lock" to the name of the
1324 cookie file. The server should attempt to create this file
1325 using <literal>O_CREAT | O_EXCL</literal>. If file creation
1326 fails, the lock fails. Servers should retry for a reasonable
1327 period of time, then they may choose to delete an existing lock
1328 to keep users from having to manually delete a stale
1329 lock. <footnote><para>Lockfiles are used instead of real file
1330 locking <literal>fcntl()</literal> because real locking
1331 implementations are still flaky on network
1332 filesystems.</para></footnote>
1337 Once the lockfile has been created, the server loads the cookie
1338 file. It should then delete any cookies that are old (the
1339 timeout can be fairly short), or more than a reasonable
1340 time in the future (so that cookies never accidentally
1341 become permanent, if the clock was set far into the future
1342 at some point). If no recent keys remain, the
1343 server may generate a new key.
1348 The pruned and possibly added-to cookie file
1349 must be resaved atomically (using a temporary
1350 file which is rename()'d).
1355 The lock must be dropped by deleting the lockfile.
1361 Clients need not lock the file in order to load it,
1362 because servers are required to save the file atomically.
1367 <sect1 id="addresses">
1368 <title>Server Addresses</title>
1370 Server addresses consist of a transport name followed by a colon, and
1371 then an optional, comma-separated list of keys and values in the form key=value.
1372 [FIXME how do you escape colon, comma, and semicolon in the values of the key=value pairs?]
1376 <programlisting>unix:path=/tmp/dbus-test</programlisting>
1377 Which is the address to a unix socket with the path /tmp/dbus-test.
1380 [FIXME clarify if attempting to connect to each is a requirement
1381 or just a suggestion]
1382 When connecting to a server, multiple server addresses can be
1383 separated by a semi-colon. The library will then try to connect
1384 to the first address and if that fails, it'll try to connect to
1385 the next one specified, and so forth. For example
1386 <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
1389 [FIXME we need to specify in detail each transport and its possible arguments]
1390 Current transports include: unix domain sockets (including
1391 abstract namespace on linux), TCP/IP, and a debug/testing transport using
1392 in-process pipes. Future possible transports include one that
1393 tunnels over X11 protocol.
1397 <sect1 id="standard-messages">
1398 <title>Standard Peer-to-Peer Messages</title>
1400 See <xref linkend="message-protocol-types-notation"/> for details on
1401 the notation used in this section.
1403 <sect2 id="standard-messages-ping">
1404 <title><literal>org.freedesktop.Peer.Ping</literal></title>
1407 org.freedesktop.Peer.Ping ()
1411 On receipt of the METHOD_CALL
1412 message <literal>org.freedesktop.Peer.Ping</literal>, an application
1413 should do nothing other than reply with a METHOD_RETURN as usual.
1417 <sect2 id="standard-messages-get-props">
1418 <title><literal>org.freedesktop.Props.Get</literal></title>
1420 [FIXME this is just a bogus made-up method that isn't implemented
1421 or thought through, to save an example of table formatting for the
1422 argument descriptions]
1424 org.freedesktop.Props.Get (in STRING property_name,
1425 out ANY_OR_NIL property_value)
1432 <entry>Argument</entry>
1434 <entry>Description</entry>
1440 <entry>in STRING</entry>
1441 <entry>Name of the property to get</entry>
1445 <entry>out ANY_OR_NIL</entry>
1446 <entry>The value of the property. The type depends on the property.</entry>
1455 <sect1 id="message-bus">
1456 <title>Message Bus Specification</title>
1457 <sect2 id="message-bus-overview">
1458 <title>Message Bus Overview</title>
1460 The message bus accepts connections from one or more applications.
1461 Once connected, applications can send and receive messages from
1462 the message bus, as in the peer-to-peer case.
1465 The message bus keeps track of a set of
1466 <firstterm>services</firstterm>. A service is simply a name, such as
1467 <literal>com.yoyodyne.Screensaver</literal>, which can be
1468 <firstterm>owned</firstterm> by one or more of the connected
1469 applications. The message bus itself always owns the special service
1470 <literal>org.freedesktop.DBus</literal>.
1473 Services may have <firstterm>secondary owners</firstterm>. Secondary owners
1474 of a service are kept in a queue; if the primary owner of a service
1475 disconnects, or releases the service, the next secondary owner becomes
1476 the new owner of the service.
1479 Messages may have a <literal>SERVICE</literal> field (see <xref
1480 linkend="message-protocol-header-fields"/>). When the message bus
1481 receives a message, if the <literal>SERVICE</literal> field is absent, the
1482 message is taken to be a standard peer-to-peer message and interpreted
1483 by the message bus itself. For example, sending
1484 an <literal>org.freedesktop.Peer.Ping</literal> message with no
1485 <literal>SERVICE</literal> will cause the message bus itself to reply
1486 to the ping immediately; the message bus would never make
1487 this message visible to other applications.
1490 If the <literal>SERVICE</literal> field is present, then it indicates a
1491 request for the message bus to route the message. In the usual case,
1492 messages are routed to the owner of the named service.
1493 Messages may also be <firstterm>broadcast</firstterm>
1494 by sending them to the special service
1495 <literal>org.freedesktop.DBus.Broadcast</literal>. Broadcast messages are
1496 sent to all applications with <firstterm>message matching
1497 rules</firstterm> that match the message.
1500 Continuing the <literal>org.freedesktop.Peer.Ping</literal> example, if
1501 the ping message were sent with a <literal>SERVICE</literal> name of
1502 <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
1503 forwarded, and the Yoyodyne Corporation screensaver application would be
1504 expected to reply to the ping. If
1505 <literal>org.freedesktop.Peer.Ping</literal> were sent to
1506 <literal>org.freedesktop.DBus.Broadcast</literal>, then multiple applications
1507 might receive the ping, and all would normally reply to it.
1511 <sect2 id="message-bus-services">
1512 <title>Message Bus Services</title>
1514 A service is a name that identifies a certain application. Each
1515 application connected to the message bus has at least one service name
1516 assigned at connection time and returned in response to the
1517 <literal>org.freedesktop.DBus.Hello</literal> message.
1518 This automatically-assigned service name is called
1519 the application's <firstterm>base service</firstterm>.
1520 Base service names are unique and MUST never be reused for two different
1524 Ownership of the base service is a prerequisite for interaction with
1525 the message bus. It logically follows that the base service is always
1526 the first service that an application comes to own, and the last
1527 service that it loses ownership of.
1530 Base service names must begin with the character ':' (ASCII colon
1531 character); service names that are not base service names must not begin
1532 with this character. (The bus must reject any attempt by an application
1533 to manually create a service name beginning with ':'.) This restriction
1534 categorically prevents "spoofing"; messages sent to a base service name
1535 will always go to a single application instance and that instance only.
1538 An application can request additional service names to be associated
1540 <literal>org.freedesktop.DBus.AcquireService</literal>
1541 message. [FIXME what service names are allowed; ASCII or unicode;
1545 [FIXME this needs more detail, and should move the service-related message
1546 descriptions up into this section perhaps]
1547 Service ownership handling can be specified in the flags part
1548 of the <literal>org.freedesktop.DBus.AcquireService</literal>
1549 message. If an application specifies the
1550 DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT flag, then all applications
1551 trying to acquire the service will be put in a queue. When the
1552 primary owner disconnects from the bus or removes ownership
1553 from the service, the next application in the queue will be the
1554 primary owner. If the DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT
1555 flag is not specified, then the primary owner will lose
1556 ownership whenever another application requests ownership of the
1560 When a client disconnects from the bus, all the services that
1561 the clients own are deleted, or in the case of a service that
1562 prohibits replacement, ownership is transferred to the next
1563 client in the queue, if any.
1566 <sect2 id="message-bus-routing">
1567 <title>Message Bus Message Routing</title>
1569 When a message is received by the message bus, the message's
1570 <literal>sndr</literal> header field MUST be set to the base service of
1571 the application which sent the message. If the service already has
1572 a <literal>sndr</literal> field, the pre-existing field is replaced.
1573 This rule means that a replies are always sent to the base service name,
1574 i.e. to the same application that sent the message being replied to.
1577 [FIXME go into detail about broadcast, multicast, unicast, etc.]
1580 <sect2 id="message-bus-activation">
1581 <title>Message Bus Service Activation</title>
1583 <firstterm>Activation</firstterm> means to locate a service
1584 owner for a service that is currently unowned. For now, it
1585 means to launch an executable that will take ownership of
1586 a particular service.
1589 To find an executable corresponding to a particular service, the bus
1590 daemon looks for <firstterm>service description files</firstterm>.
1591 Service description files define a mapping from service names to
1592 executables. Different kinds of message bus will look for these files
1593 in different places, see <xref linkend="message-bus-types"/>.
1596 [FIXME the file format should be much better specified than
1597 "similar to .desktop entries" esp. since desktop entries are
1598 already badly-specified. ;-)] Service description files have
1599 the ".service" file extension. The message bus will only load
1600 service description files ending with .service; all other
1601 files will be ignored. The file format is similar to that of
1603 url="http://www.freedesktop.org/standards/desktop-entry-spec/desktop-entry-spec.html">desktop
1604 entries</ulink>. All service description files must be in
1605 UTF-8 encoding. To ensure that there will be no name
1606 collisions, service files must be namespaced using the same
1607 mechanism as messages and service names.
1610 <title>Example service description file</title>
1612 # Sample service description file
1614 Name=org.gnome.ConfigurationDatabase
1615 Exec=/usr/libexec/gconfd-2
1620 When an application requests a service to be activated, the
1621 bus daemon tries to find it in the list of activation
1622 entries. It then tries to spawn the executable associated with
1623 it. If this fails, it will report an error. [FIXME what
1624 happens if two .service files offer the same service; what
1625 kind of error is reported, should we have a way for the client
1629 The executable launched will have the environment variable
1630 <literal>DBUS_ACTIVATION_ADDRESS</literal> set to the address of the
1631 message bus so it can connect and register the appropriate services.
1634 The executable being launched may want to know whether the message bus
1635 activating it is one of the well-known message buses (see <xref
1636 linkend="message-bus-types"/>). To facilitate this, the bus MUST also set
1637 the <literal>DBUS_ACTIVATION_BUS_TYPE</literal> environment variable if it is one
1638 of the well-known buses. The currently-defined values for this variable
1639 are <literal>system</literal> for the systemwide message bus,
1640 and <literal>session</literal> for the per-login-session message
1641 bus. The activated executable must still connect to the address given
1642 in <literal>DBUS_ACTIVATION_ADDRESS</literal>, but may assume that the
1643 resulting connection is to the well-known bus.
1646 [FIXME there should be a timeout somewhere, either specified
1647 in the .service file, by the client, or just a global value
1648 and if the client being activated fails to connect within that
1649 timeout, an error should be sent back.]
1653 <sect2 id="message-bus-types">
1654 <title>Well-known Message Bus Instances</title>
1656 Two standard message bus instances are defined here, along with how
1657 to locate them and where their service files live.
1659 <sect3 id="message-bus-types-login">
1660 <title>Login session message bus</title>
1662 Each time a user logs in, a <firstterm>login session message
1663 bus</firstterm> may be started. All applications in the user's login
1664 session may interact with one another using this message bus.
1667 The address of the login session message bus is given
1668 in the <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment
1669 variable. If that variable is not set, applications may
1670 also try to read the address from the X Window System root
1671 window property <literal>_DBUS_SESSION_BUS_ADDRESS</literal>.
1672 The root window property must have type <literal>STRING</literal>.
1673 The environment variable should have precedence over the
1674 root window property.
1677 [FIXME specify location of .service files, probably using
1678 DESKTOP_DIRS etc. from basedir specification, though login session
1679 bus is not really desktop-specific]
1682 <sect3 id="message-bus-types-system">
1683 <title>System message bus</title>
1685 A computer may have a <firstterm>system message bus</firstterm>,
1686 accessible to all applications on the system. This message bus may be
1687 used to broadcast system events, such as adding new hardware devices,
1688 changes in the printer queue, and so forth.
1691 The address of the login session message bus is given
1692 in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment
1693 variable. If that variable is not set, applications should try
1694 to connect to the well-known address
1695 <literal>unix:path=/var/run/dbus/system_bus_socket</literal>.
1698 The D-BUS reference implementation actually honors the
1699 <literal>$(localstatedir)</literal> configure option
1700 for this address, on both client and server side.
1705 [FIXME specify location of system bus .service files]
1710 <sect2 id="message-bus-messages">
1711 <title>Message Bus Messages</title>
1713 The special message bus service <literal>org.freedesktop.DBus</literal>
1714 responds to a number of messages, allowing applications to
1715 interact with the message bus.
1718 <sect3 id="bus-messages-hello">
1719 <title><literal>org.freedesktop.DBus.Hello</literal></title>
1730 <entry>Argument</entry>
1732 <entry>Description</entry>
1738 <entry>STRING</entry>
1739 <entry>Name of the service assigned to the application</entry>
1746 Before an application is able to send messages to other
1747 applications it must send the
1748 <literal>org.freedesktop.DBus.Hello</literal> message to the
1749 message bus service. If an application tries to send a
1750 message to another application, or a message to the message
1751 bus service that isn't the
1752 <literal>org.freedesktop.DBus.Hello</literal> message, it
1753 will be disconnected from the bus. If a client wishes to
1754 disconnect from the bus, it just has to disconnect from the
1755 transport used. No de-registration message is necessary.
1758 The reply message contains the name of the application's base service.
1761 <sect3 id="bus-messages-list-services">
1762 <title><literal>org.freedesktop.DBus.ListServices</literal></title>
1766 STRING_ARRAY ListServices ()
1773 <entry>Argument</entry>
1775 <entry>Description</entry>
1781 <entry>STRING_ARRAY</entry>
1782 <entry>Array of strings where each string is the name of a service</entry>
1789 Returns a list of all existing services registered with the message bus.
1792 <sect3 id="bus-messages-service-exists">
1793 <title><literal>org.freedesktop.DBus.ServiceExists</literal></title>
1797 BOOLEAN ServiceExists (in STRING service_name)
1804 <entry>Argument</entry>
1806 <entry>Description</entry>
1812 <entry>STRING</entry>
1813 <entry>Name of the service</entry>
1823 <entry>Argument</entry>
1825 <entry>Description</entry>
1831 <entry>BOOLEAN</entry>
1832 <entry>Return value, true if the service exists</entry>
1839 Checks if a service with a specified name exists.
1843 <sect3 id="bus-messages-acquire-service">
1844 <title><literal>org.freedesktop.DBus.AcquireService</literal></title>
1848 UINT32 AcquireService (in STRING service_name)
1855 <entry>Argument</entry>
1857 <entry>Description</entry>
1863 <entry>STRING</entry>
1864 <entry>Name of the service</entry>
1868 <entry>UINT32</entry>
1869 <entry>Flags</entry>
1879 <entry>Argument</entry>
1881 <entry>Description</entry>
1887 <entry>UINT32</entry>
1888 <entry>Return value</entry>
1895 Tries to become owner of a specific service. The flags
1896 specified can be the following values logically ORed together:
1902 <entry>Identifier</entry>
1903 <entry>Value</entry>
1904 <entry>Description</entry>
1909 <entry>DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT</entry>
1912 If the application succeeds in being the owner of the specified service,
1913 then ownership of the service can't be transferred until the service
1914 disconnects. If this flag is not set, then any application trying to become
1915 the owner of the service will succeed and the previous owner will be
1916 sent a <literal>org.freedesktop.DBus.ServiceLost</literal> message.
1920 <entry>DBUS_SERVICE_FLAGS_REPLACE_EXISTING</entry>
1922 <entry>Try to replace the current owner if there is one. If this flag
1923 is not set the application will only become the owner of the service if
1924 there is no current owner.</entry>
1930 [FIXME if it's one of the following values, why are the values
1931 done as flags instead of just 0, 1, 2, 3, 4]
1932 The return value can be one of the following values:
1938 <entry>Identifier</entry>
1939 <entry>Value</entry>
1940 <entry>Description</entry>
1945 <entry>DBUS_SERVICE_REPLY_PRIMARY_OWNER</entry>
1947 <entry>The application is now the primary owner of the service.</entry>
1950 <entry>DBUS_SERVICE_REPLY_IN_QUEUE</entry>
1952 <entry>The service already has an owner which do not want to give up ownership and therefore the application has been put in a queue.</entry>
1955 <entry>DBUS_SERVICE_REPLY_SERVICE_EXISTS</entry>
1957 <entry>The service does already have a primary owner, and DBUS_SERVICE_FLAG_REPLACE_EXISTING was not specified when trying to acquire the service.</entry>
1960 <entry>DBUS_SERVICE_REPLY_ALREADY_OWNER</entry>
1962 <entry>The application trying to request ownership of the service is already the owner of it.</entry>
1969 <sect3 id="bus-messages-service-acquired">
1970 <title><literal>org.freedesktop.DBus.ServiceAcquired</literal></title>
1974 ServiceAcquired (in STRING service_name)
1981 <entry>Argument</entry>
1983 <entry>Description</entry>
1989 <entry>STRING</entry>
1990 <entry>Name of the service</entry>
1994 <entry>UINT32</entry>
1995 <entry>Flags</entry>
2002 This message is sent to a specific application when it becomes the
2003 primary owner of a service.
2006 <sect3 id="bus-messages-service-lost">
2007 <title><literal>org.freedesktop.DBus.ServiceLost</literal></title>
2011 ServiceLost (in STRING service_name)
2018 <entry>Argument</entry>
2020 <entry>Description</entry>
2026 <entry>STRING</entry>
2027 <entry>Name of the service</entry>
2031 <entry>UINT32</entry>
2032 <entry>Flags</entry>
2039 This message is sent to a specific application when it loses primary
2040 ownership of a service.
2042 [FIXME instead of ServiceLost/ServiceCreated going only to
2043 a specific app, why not just OwnerChanged that covers both
2044 lost and created and changed owner and deleted]
2048 <sect3 id="bus-messages-service-created">
2049 <title><literal>org.freedesktop.DBus.ServiceCreated</literal></title>
2053 ServiceCreated (in STRING service_name)
2060 <entry>Argument</entry>
2062 <entry>Description</entry>
2068 <entry>STRING</entry>
2069 <entry>Name of the service</entry>
2073 <entry>UINT32</entry>
2074 <entry>Flags</entry>
2081 This message is broadcast to all applications when a service has been
2082 successfully registered on the message bus.
2086 <sect3 id="bus-messages-service-deleted">
2087 <title><literal>org.freedesktop.DBus.ServiceDeleted</literal></title>
2091 ServiceDeleted (in STRING service_name)
2098 <entry>Argument</entry>
2100 <entry>Description</entry>
2106 <entry>STRING</entry>
2107 <entry>Name of the service</entry>
2111 <entry>UINT32</entry>
2112 <entry>Flags</entry>
2119 This message is broadcast to all applications when a service has been
2120 deleted from the message bus.
2124 <sect3 id="bus-messages-activate-service">
2125 <title><literal>org.freedesktop.DBus.ActivateService</literal></title>
2129 UINT32 ActivateService (in STRING service_name, in UINT32 flags)
2136 <entry>Argument</entry>
2138 <entry>Description</entry>
2144 <entry>STRING</entry>
2145 <entry>Name of the service to activate</entry>
2149 <entry>UINT32</entry>
2150 <entry>Flags (currently not used)</entry>
2160 <entry>Argument</entry>
2162 <entry>Description</entry>
2168 <entry>UINT32</entry>
2169 <entry>Return value</entry>
2174 Tries to launch the executable associated with a service. For more information, see <xref linkend="message-bus-activation"/>.
2176 [FIXME need semantics in much more detail here; for example,
2177 if I activate a service then send it a message, is the message
2178 queued for the new service or is there a race]
2181 The return value can be one of the following values:
2186 <entry>Identifier</entry>
2187 <entry>Value</entry>
2188 <entry>Description</entry>
2193 <entry>DBUS_ACTIVATION_REPLY_ACTIVATED</entry>
2195 <entry>The service was activated successfully.</entry>
2198 <entry>DBUS_ACTIVATION_REPLY_ALREADY_ACTIVE</entry>
2200 <entry>The service is already active.</entry>
2209 <sect3 id="bus-messages-out-of-memory">
2210 <title><literal>org.freedesktop.DBus.Error.NoMemory</literal></title>
2218 Sent by the message bus when it can't process a message due to an out of memory failure.
2222 <sect3 id="bus-messages-service-does-not-exist">
2223 <title><literal>org.freedesktop.DBus.Error.ServiceDoesNotExist</literal></title>
2227 void ServiceDoesNotExist (in STRING error)
2231 Sent by the message bus as a reply to a client that tried to send a message to a service that doesn't exist.
2238 <appendix id="implementation-notes">
2239 <title>Implementation notes</title>
2240 <sect1 id="implementation-notes-subsection">
2248 <glossary><title>Glossary</title>
2250 This glossary defines some of the terms used in this specification.
2253 <glossentry id="term-activation"><glossterm>Activation</glossterm>
2256 The process of creating an owner for a particular service,
2257 typically by launching an executable.
2262 <glossentry id="term-base-service"><glossterm>Base Service</glossterm>
2265 The special service automatically assigned to an application by the
2266 message bus. This service may never change owner, and the service
2267 name will be unique (never reused during the lifetime of the
2273 <glossentry id="term-broadcast"><glossterm>Broadcast</glossterm>
2276 A message sent to the special <literal>org.freedesktop.DBus.Broadcast</literal>
2277 service; the message bus will forward the broadcast message
2278 to all applications that have expressed interest in it.
2283 <glossentry id="term-message"><glossterm>Message</glossterm>
2286 A message is the atomic unit of communication via the D-BUS
2287 protocol. It consists of a <firstterm>header</firstterm> and a
2288 <firstterm>body</firstterm>; the body is made up of
2289 <firstterm>arguments</firstterm>.
2294 <glossentry id="term-message-bus"><glossterm>Message Bus</glossterm>
2297 The message bus is a special application that forwards
2298 or broadcasts messages between a group of applications
2299 connected to the message bus. It also manages
2300 <firstterm>services</firstterm>.
2305 <glossentry id="namespace"><glossterm>Namespace</glossterm>
2308 Used to prevent collisions when defining message and service
2309 names. The convention used is the same as Java uses for
2310 defining classes: a reversed domain name.
2315 <glossentry id="term-object"><glossterm>Object</glossterm>
2318 Each application contains <firstterm>objects</firstterm>,
2319 which have <firstterm>interfaces</firstterm> and
2320 <firstterm>methods</firstterm>. Objects are referred to
2321 by a name, called a <firstterm>path</firstterm> or
2322 <firstterm>object reference</firstterm>.
2327 <glossentry id="term-path"><glossterm>Path</glossterm>
2330 Object references (object names) in D-BUS are
2331 organized into a filesystem-style hierarchy, so
2332 each object is named by a path. As in LDAP,
2333 there's no difference between "files" and "directories";
2334 a path can refer to an object, while still having
2335 child objects below it.
2340 <glossentry id="peer-to-peer"><glossterm>Peer-to-peer</glossterm>
2343 An application talking directly to another application, without going through a message bus.
2347 <glossentry id="term-secondary-owner"><glossterm>Secondary service owner</glossterm>
2350 Each service has a primary owner; messages sent to the service name
2351 go to the primary owner. However, certain services also maintain
2352 a queue of secondary owners "waiting in the wings." If
2353 the primary owner releases the service, then the first secondary
2354 owner in the queue automatically becomes the primary owner.
2358 <glossentry id="term-service"><glossterm>Service</glossterm>
2361 A service is simply a named list of applications. For example, the
2362 hypothetical <literal>com.yoyodyne.Screensaver</literal> service might
2363 accept messages that affect a screensaver from Yoyodyne Corporation.
2364 An application is said to <firstterm>own</firstterm> a service if the
2365 message bus has associated the application with the service name.
2366 Services may also have <firstterm>secondary owners</firstterm> (see
2367 <xref linkend="term-secondary-owner"/>).
2371 <glossentry id="term-service-name"><glossterm>Service name</glossterm>
2374 The name used when referring to a service. If the service is
2375 a base service it has a unique service name, for example
2376 ":1-20", and otherwise it should be namespaced.
2380 <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
2383 ".service files" tell the bus how to activate a particular service.
2384 See <xref linkend="term-activation"/>
projects / platform / upstream / dbus.git / blob