-<?xml version="1.0" standalone="no"?>
+<?xml version="1.0" standalone="no" ?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"
[
<article id="index">
<articleinfo>
- <title>D-BUS Specification</title>
- <releaseinfo>Version 0.9</releaseinfo>
- <date>17 January 2005</date>
+ <title>D-Bus Specification</title>
+ <releaseinfo>Version 0.14</releaseinfo>
+ <date>May 12, 2010</date>
<authorgroup>
<author>
<firstname>Havoc</firstname>
<sect1 id="introduction">
<title>Introduction</title>
<para>
- D-BUS is a system for low-latency, low-overhead, easy to use
+ D-Bus is a system for low-latency, low-overhead, easy to use
interprocess communication (IPC). In more detail:
<itemizedlist>
<listitem>
<para>
- D-BUS is <emphasis>low-latency</emphasis> because it is designed
+ D-Bus is <emphasis>low-latency</emphasis> because it is designed
to avoid round trips and allow asynchronous operation, much like
the X protocol.
</para>
</listitem>
<listitem>
<para>
- D-BUS is <emphasis>low-overhead</emphasis> because it uses a
+ D-Bus is <emphasis>low-overhead</emphasis> because it uses a
binary protocol, and does not have to convert to and from a text
- format such as XML. Because D-BUS is intended for potentially
+ format such as XML. Because D-Bus is intended for potentially
high-resolution same-machine IPC, not primarily for Internet IPC,
this is an interesting optimization.
</para>
</listitem>
<listitem>
<para>
- D-BUS is <emphasis>easy to use</emphasis> because it works in terms
+ D-Bus is <emphasis>easy to use</emphasis> because it works in terms
of <firstterm>messages</firstterm> rather than byte streams, and
- automatically handles a lot of the hard IPC issues. Also, the D-BUS
+ automatically handles a lot of the hard IPC issues. Also, the D-Bus
library is designed to be wrapped in a way that lets developers use
their framework's existing object/type system, rather than learning
a new one specifically for IPC.
</para>
<para>
- The base D-BUS protocol is a one-to-one (peer-to-peer or client-server)
+ The base D-Bus protocol is a one-to-one (peer-to-peer or client-server)
protocol, specified in <xref linkend="message-protocol"/>. That is, it is
a system for one application to talk to a single other
application. However, the primary intended application of the protocol is the
- D-BUS <firstterm>message bus</firstterm>, specified in <xref
+ D-Bus <firstterm>message bus</firstterm>, specified in <xref
linkend="message-bus"/>. The message bus is a special application that
accepts connections from multiple other applications, and forwards
messages among them.
</para>
<para>
- Uses of D-BUS include notification of system changes (notification of when
+ Uses of D-Bus include notification of system changes (notification of when
a camera is plugged in to a computer, or a new version of some software
has been installed), or desktop interoperability, for example a file
monitoring service or a configuration service.
</para>
+ <para>
+ D-Bus is designed for two specific use cases:
+ <itemizedlist>
+ <listitem>
+ <para>
+ A "system bus" for notifications from the system to user sessions,
+ and to allow the system to request input from user sessions.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ A "session bus" used to implement desktop environments such as
+ GNOME and KDE.
+ </para>
+ </listitem>
+ </itemizedlist>
+ D-Bus is not intended to be a generic IPC system for any possible
+ application, and intentionally omits many features found in other
+ IPC systems for this reason.
+ </para>
+
+ <para>
+ At the same time, the bus daemons offer a number of features not found in
+ other IPC systems, such as single-owner "bus names" (similar to X
+ selections), on-demand startup of services, and security policies.
+ In many ways, these features are the primary motivation for developing
+ D-Bus; other systems would have sufficed if IPC were the only goal.
+ </para>
+
+ <para>
+ D-Bus may turn out to be useful in unanticipated applications, but future
+ versions of this spec and the reference implementation probably will not
+ incorporate features that interfere with the core use cases.
+ </para>
+
+ <para>
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+ document are to be interpreted as described in RFC 2119. However, the
+ document could use a serious audit to be sure it makes sense to do
+ so. Also, they are not capitalized.
+ </para>
+
+ <sect2 id="stability">
+ <title>Protocol and Specification Stability</title>
+ <para>
+ The D-Bus protocol is frozen (only compatible extensions are allowed) as
+ of November 8, 2006. However, this specification could still use a fair
+ bit of work to make interoperable reimplementation possible without
+ reference to the D-Bus reference implementation. Thus, this
+ specification is not marked 1.0. To mark it 1.0, we'd like to see
+ someone invest significant effort in clarifying the specification
+ language, and growing the specification to cover more aspects of the
+ reference implementation's behavior.
+ </para>
+ <para>
+ Until this work is complete, any attempt to reimplement D-Bus will
+ probably require looking at the reference implementation and/or asking
+ questions on the D-Bus mailing list about intended behavior.
+ Questions on the list are very welcome.
+ </para>
+ <para>
+ Nonetheless, this document should be a useful starting point and is
+ to our knowledge accurate, though incomplete.
+ </para>
+ </sect2>
+
</sect1>
<sect1 id="message-protocol">
think of a message as a package, the header is the address, and the body
contains the package contents. The message delivery system uses the header
information to figure out where to send the message and how to interpret
- it; the recipient inteprets the body of the message.
+ it; the recipient interprets the body of the message.
</para>
<para>
<title>Type Signatures</title>
<para>
- The D-BUS protocol does not include type tags in the marshaled data; a
+ The D-Bus protocol does not include type tags in the marshaled data; a
block of marshaled values must have a known <firstterm>type
signature</firstterm>. The type signature is made up of <firstterm>type
codes</firstterm>. A type code is an ASCII character representing the
<literal>INT32</literal> in this example. To marshal and unmarshal
basic types, you simply read one value from the data
block corresponding to each type code in the signature.
- In addition to basic types, there are three <firstterm>container</firstterm>
- types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, and <literal>VARIANT</literal>.
+ In addition to basic types, there are four <firstterm>container</firstterm>
+ types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, <literal>VARIANT</literal>,
+ and <literal>DICT_ENTRY</literal>.
</para>
<para>
</para>
<para>
- The <literal>STRUCT</literal> type code 'r' is not currently used in the D-BUS protocol,
+ The <literal>STRUCT</literal> type code 'r' is not currently used in the D-Bus protocol,
but is useful in code that implements the protocol. This type code
is specified to allow such code to interoperate in non-protocol contexts.
</para>
-
+
+ <para>
+ Empty structures are not allowed; there must be at least one
+ type code between the parentheses.
+ </para>
+
<para>
<literal>ARRAY</literal> has ASCII character 'a' as type code. The array type code must be
followed by a <firstterm>single complete type</firstterm>. The single
</para>
<para>
- The following table summarizes the D-BUS types.
+ A <literal>DICT_ENTRY</literal> works exactly like a struct, but rather
+ than parentheses it uses curly braces, and it has more restrictions.
+ The restrictions are: it occurs only as an array element type; it has
+ exactly two single complete types inside the curly braces; the first
+ single complete type (the "key") must be a basic type rather than a
+ container type. Implementations must not accept dict entries outside of
+ arrays, must not accept dict entries with zero, one, or more than two
+ fields, and must not accept dict entries with non-basic-typed keys. A
+ dict entry is always a key-value pair.
+ </para>
+
+ <para>
+ The first field in the <literal>DICT_ENTRY</literal> is always the key.
+ A message is considered corrupt if the same key occurs twice in the same
+ array of <literal>DICT_ENTRY</literal>. However, for performance reasons
+ implementations are not required to reject dicts with duplicate keys.
+ </para>
+
+ <para>
+ In most languages, an array of dict entry would be represented as a
+ map, hash table, or dict object.
+ </para>
+
+ <para>
+ The following table summarizes the D-Bus types.
<informaltable>
<tgroup cols="3">
<thead>
<entry>98 (ASCII 'b')</entry>
<entry>Boolean value, 0 is <literal>FALSE</literal> and 1 is <literal>TRUE</literal>. Everything else is invalid.</entry>
</row><row>
+ <entry><literal>INT16</literal></entry>
+ <entry>110 (ASCII 'n')</entry>
+ <entry>16-bit signed integer</entry>
+ </row><row>
+ <entry><literal>UINT16</literal></entry>
+ <entry>113 (ASCII 'q')</entry>
+ <entry>16-bit unsigned integer</entry>
+ </row><row>
<entry><literal>INT32</literal></entry>
<entry>105 (ASCII 'i')</entry>
<entry>32-bit signed integer</entry>
</row><row>
<entry><literal>STRING</literal></entry>
<entry>115 (ASCII 's')</entry>
- <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated.</entry>
+ <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated and contain no other nul bytes.</entry>
</row><row>
<entry><literal>OBJECT_PATH</literal></entry>
<entry>111 (ASCII 'o')</entry>
<entry><literal>VARIANT</literal></entry>
<entry>118 (ASCII 'v') </entry>
<entry>Variant type (the type of the value is part of the value itself)</entry>
+ </row><row>
+ <entry><literal>DICT_ENTRY</literal></entry>
+ <entry>101 (ASCII 'e'), 123 (ASCII '{'), 125 (ASCII '}') </entry>
+ <entry>Entry in a dict or map (array of key-value pairs)</entry>
+ </row><row>
+ <entry><literal>UNIX_FD</literal></entry>
+ <entry>104 (ASCII 'h')</entry>
+ <entry>Unix file descriptor</entry>
</row>
</tbody>
</tgroup>
<para>
Given a type signature, a block of bytes can be converted into typed
values. This section describes the format of the block of bytes. Byte
- order and alignment issues are handled uniformly for all D-BUS types.
+ order and alignment issues are handled uniformly for all D-Bus types.
</para>
<para>
A block of bytes has an associated byte order. The byte order
- has to be discovered in some way; for D-BUS messages, the
+ has to be discovered in some way; for D-Bus messages, the
byte order is part of the message header as described in
<xref linkend="message-protocol-messages"/>. For now, assume
that the byte order is known to be either little endian or big
<entry>As for <literal>UINT32</literal>, but only 0 and 1 are valid values.</entry>
<entry>4</entry>
</row><row>
+ <entry><literal>INT16</literal></entry>
+ <entry>16-bit signed integer in the message's byte order.</entry>
+ <entry>2</entry>
+ </row><row>
+ <entry><literal>UINT16</literal></entry>
+ <entry>16-bit unsigned integer in the message's byte order.</entry>
+ <entry>2</entry>
+ </row><row>
<entry><literal>INT32</literal></entry>
<entry>32-bit signed integer in the message's byte order.</entry>
<entry>4</entry>
<entry><literal>STRING</literal></entry>
<entry>A <literal>UINT32</literal> indicating the string's
length in bytes excluding its terminating nul, followed by
- string data of the given length, followed by a terminating nul
+ non-nul string data of the given length, followed by a terminating nul
byte.
</entry>
<entry>
given in the signature.
Unlike a message signature, the variant signature
can contain only a single complete type.
- So "i" is OK, "ii" is not.
+ So "i", "ai" or "(ii)" is OK, but "ii" is not.
</entry>
<entry>
1 (alignment of the signature)
</entry>
+ </row><row>
+ <entry><literal>DICT_ENTRY</literal></entry>
+ <entry>
+ Identical to STRUCT.
+ </entry>
+ <entry>
+ 8
+ </entry>
+ </row><row>
+ <entry><literal>UNIX_FD</literal></entry>
+ <entry>32-bit unsigned integer in the message's byte
+ order. The actual file descriptors need to be
+ transferred out-of-band via some platform specific
+ mechanism. On the wire, values of this type store the index to the
+ file descriptor in the array of file descriptors that
+ accompany the message.</entry>
+ <entry>4</entry>
</row>
</tbody>
</tgroup>
<para>
An object path is a name used to refer to an object instance.
- Conceptually, each participant in a D-BUS message exchange may have
+ Conceptually, each participant in a D-Bus message exchange may have
any number of object instances (think of C++ or Java objects) and each
such instance will have a path. Like a filesystem, the object
instances in an application form a hierarchical tree.
</row>
<row>
<entry>2nd <literal>BYTE</literal></entry>
- <entry><firstterm>Message type</firstterm>. Unknown types MUST be ignored.
+ <entry><firstterm>Message type</firstterm>. Unknown types must be ignored.
Currently-defined types are described below.
</entry>
</row>
<row>
<entry>3rd <literal>BYTE</literal></entry>
<entry>Bitwise OR of flags. Unknown flags
- MUST be ignored. Currently-defined flags are described below.
+ must be ignored. Currently-defined flags are described below.
</entry>
</row>
<row>
<entry>Major protocol version of the sending application. If
the major protocol version of the receiving application does not
match, the applications will not be able to communicate and the
- D-BUS connection MUST be disconnected. The major protocol
- version for this version of the specification is 0.
- FIXME this field is stupid and pointless to put in
- every message.
+ D-Bus connection must be disconnected. The major protocol
+ version for this version of the specification is 1.
</entry>
</row>
<row>
<entry>2nd <literal>UINT32</literal></entry>
<entry>The serial of this message, used as a cookie
by the sender to identify the reply corresponding
- to this request.
+ to this request. This must not be zero.
</entry>
</row>
<row>
<row>
<entry><literal>INVALID</literal></entry>
<entry>0</entry>
- <entry>This is an invalid type, if seen in a message
- the connection should be dropped immediately.</entry>
+ <entry>This is an invalid type.</entry>
</row>
<row>
<entry><literal>METHOD_CALL</literal></entry>
<entry>This message does not expect method return replies or
error replies; the reply can be omitted as an
optimization. However, it is compliant with this specification
- to return the reply despite this flag.</entry>
+ to return the reply despite this flag and the only harm
+ from doing so is extra network traffic.
+ </entry>
</row>
<row>
- <entry><literal>AUTO_ACTIVATION</literal></entry>
+ <entry><literal>NO_AUTO_START</literal></entry>
<entry>0x2</entry>
- <entry>This message automatically activates the
- addressed service before the message is delivered.</entry>
+ <entry>The bus must not launch an owner
+ for the destination name in response to this message.
+ </entry>
</row>
</tbody>
</tgroup>
<para>
Again, if an implementation sees a header field code that it does not
- expect, it MUST ignore that field, as it will be part of a new
+ expect, it must ignore that field, as it will be part of a new
(but compatible) version of this specification. This also applies
to known header fields appearing in unexpected messages, for
- example if a signal has a reply serial that should be ignored
+ example: if a signal has a reply serial it must be ignored
even though it has no meaning as of this version of the spec.
</para>
<para>
However, implementations must not send or accept known header fields
- with the wrong type stored in the field value. So for example
- a message with an <literal>INTERFACE</literal> field of type <literal>UINT32</literal> would be considered
- corrupt.
+ with the wrong type stored in the field value. So for example a
+ message with an <literal>INTERFACE</literal> field of type
+ <literal>UINT32</literal> would be considered corrupt.
</para>
<para>
<entry>1</entry>
<entry><literal>OBJECT_PATH</literal></entry>
<entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
- <entry>The object to send a call to,
+ <entry>The object to send a call to,
or the object a signal is emitted from.
+ The special path
+ <literal>/org/freedesktop/DBus/Local</literal> is reserved;
+ implementations should not send messages with this path,
+ and the reference implementation of the bus daemon will
+ disconnect any application that attempts to do so.
</entry>
</row>
<row>
The interface to invoke a method call on, or
that a signal is emitted from. Optional for
method calls, required for signals.
+ The special interface
+ <literal>org.freedesktop.DBus.Local</literal> is reserved;
+ implementations should not send messages with this
+ interface, and the reference implementation of the bus
+ daemon will disconnect any application that attempts to
+ do so.
</entry>
</row>
<row>
<entry>6</entry>
<entry><literal>STRING</literal></entry>
<entry>optional</entry>
- <entry>The name of the service this message should be routed to.
+ <entry>The name of the connection this message is intended for.
Only used in combination with the message bus, see
<xref linkend="message-bus"/>.</entry>
</row>
<entry>7</entry>
<entry><literal>STRING</literal></entry>
<entry>optional</entry>
- <entry>Sender service. The name of the base service that sent
- this message. The message bus fills in this field; the field is
+ <entry>Unique name of the sending connection.
+ The message bus fills in this field so it is reliable; the field is
only meaningful in combination with the message bus.</entry>
</row>
<row>
If omitted, it is assumed to be the
empty signature "" (i.e. the body must be 0-length).</entry>
</row>
+ <row>
+ <entry><literal>UNIX_FDS</literal></entry>
+ <entry>9</entry>
+ <entry><literal>UINT32</literal></entry>
+ <entry>optional</entry>
+ <entry>The number of Unix file descriptors that
+ accompany the message. If omitted, it is assumed
+ that no Unix file descriptors accompany the
+ message. The actual file descriptors need to be
+ transferred via platform specific mechanism
+ out-of-band. They must be sent at the same time as
+ part of the message itself. They may not be sent
+ before the first byte of the message itself is
+ transferred or after the last byte of the message
+ itself.</entry>
+ </row>
</tbody>
</tgroup>
</informaltable>
<sect2 id="message-protocol-names">
<title>Valid Names</title>
<para>
- The various names in D-BUS messages have some restrictions.
+ The various names in D-Bus messages have some restrictions.
</para>
<para>
There is a <firstterm>maximum name length</firstterm>
- of 255 which applies to service, interface, and member
- names.
+ of 255 which applies to bus names, interfaces, and members.
</para>
<sect3 id="message-protocol-names-interface">
<title>Interface names</title>
additional restrictions that apply to interface names
specifically:
<itemizedlist>
- <listitem><para>They are composed of 1 or more elements separated by
+ <listitem><para>Interface names are composed of 1 or more elements separated by
a period ('.') character. All elements must contain at least
one character.
</para>
</para>
</listitem>
- <listitem><para>They must contain at least one '.' (period)
+ <listitem><para>Interface names must contain at least one '.' (period)
character (and thus at least two elements).
</para></listitem>
- <listitem><para>They must not begin with a '.' (period) character.</para></listitem>
- <listitem><para>They must not exceed the maximum name length.</para></listitem>
+ <listitem><para>Interface names must not begin with a '.' (period) character.</para></listitem>
+ <listitem><para>Interface names must not exceed the maximum name length.</para></listitem>
</itemizedlist>
</para>
</sect3>
- <sect3 id="message-protocol-names-service">
- <title>Service names</title>
+ <sect3 id="message-protocol-names-bus">
+ <title>Bus names</title>
+ <para>
+ Connections have one or more bus names associated with them.
+ A connection has exactly one bus name that is a unique connection
+ name. The unique connection name remains with the connection for
+ its entire lifetime.
+ A bus name is of type <literal>STRING</literal>,
+ meaning that it must be valid UTF-8. However, there are also
+ some additional restrictions that apply to bus names
+ specifically:
+ <itemizedlist>
+ <listitem><para>Bus names that start with a colon (':')
+ character are unique connection names.
+ </para>
+ </listitem>
+ <listitem><para>Bus names are composed of 1 or more elements separated by
+ a period ('.') character. All elements must contain at least
+ one character.
+ </para>
+ </listitem>
+ <listitem><para>Each element must only contain the ASCII characters
+ "[A-Z][a-z][0-9]_-". Only elements that are part of a unique
+ connection name may begin with a digit, elements in
+ other bus names must not begin with a digit.
+ </para>
+ </listitem>
+
+ <listitem><para>Bus names must contain at least one '.' (period)
+ character (and thus at least two elements).
+ </para></listitem>
+
+ <listitem><para>Bus names must not begin with a '.' (period) character.</para></listitem>
+ <listitem><para>Bus names must not exceed the maximum name length.</para></listitem>
+ </itemizedlist>
+ </para>
<para>
- Service names have the same restrictions as interface names, with a
- special exception for base services. A base service name's first
- element must start with a colon (':') character. After the colon, any
- characters in "[A-Z][a-z][0-9]_" may appear. Elements after
- the first must follow the usual rules, except that they may start with
- a digit. Service names not starting with a colon have none of these
- exceptions and follow the same rules as interface names.
+ Note that the hyphen ('-') character is allowed in bus names but
+ not in interface names.
</para>
</sect3>
<sect3 id="message-protocol-names-member">
messages map naturally to methods on objects in a typical program.
</para>
<para>
- A method call message is expected to have a <literal>MEMBER</literal> header field
+ A method call message is required to have a <literal>MEMBER</literal> header field
indicating the name of the method. Optionally, the message has an
<literal>INTERFACE</literal> field giving the interface the method is a part of. In the
absence of an <literal>INTERFACE</literal> field, if two interfaces on the same object have
implementations must not require an interface field.
</para>
<para>
- Method call messages also include a <literal>PATH</literal> field indicating the
- object to invoke the method on. If the call is passing through
- a message bus, the message will also have a <literal>DESTINATION</literal> field giving
- the service to receive the message.
+ Method call messages also include a <literal>PATH</literal> field
+ indicating the object to invoke the method on. If the call is passing
+ through a message bus, the message will also have a
+ <literal>DESTINATION</literal> field giving the name of the connection
+ to receive the message.
</para>
<para>
- When an application handles a method call message, it is expected to
+ When an application handles a method call message, it is required to
return a reply. The reply is identified by a <literal>REPLY_SERIAL</literal> header field
indicating the serial number of the <literal>METHOD_CALL</literal> being replied to. The
reply can have one of two types; either <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>.
</para>
<para>
Even if a method call has no return values, a <literal>METHOD_RETURN</literal>
- reply is expected, so the caller will know the method
+ reply is required, so the caller will know the method
was successfully processed.
</para>
<para>
flag and reply anyway.
</para>
<para>
- If a message has the flag <literal>AUTO_ACTIVATION</literal>, then the addressed
- service will be activated before the message is delivered, if
- not already active. The message will be held until the service
- is successfully activated or has failed to activate; in case
- of failure, an activation error will be returned. Activation
- is only relevant in the context of a message bus, so this
- flag is ignored for one-to-one communication with no
- intermediate bus.
+ Unless a message has the flag <literal>NO_AUTO_START</literal>, if the
+ destination name does not exist then a program to own the destination
+ name will be started before the message is delivered. The message
+ will be held until the new program is successfully started or has
+ failed to start; in case of failure, an error will be returned. This
+ flag is only relevant in the context of a message bus, it is ignored
+ during one-to-one communication with no intermediate bus.
</para>
<sect4 id="message-protocol-types-method-apis">
<title>Mapping method calls to native APIs</title>
<para>
- APIs for D-BUS may map method calls to a method call in a specific
+ APIs for D-Bus may map method calls to a method call in a specific
programming language, such as C++, or may map a method call written
- in an IDL to a D-BUS message.
+ in an IDL to a D-Bus message.
</para>
<para>
In APIs of this nature, arguments to a method are often termed "in"
(which implies sent in the <literal>METHOD_CALL</literal>), or "out" (which implies
returned in the <literal>METHOD_RETURN</literal>). Some APIs such as CORBA also have
"inout" arguments, which are both sent and received, i.e. the caller
- passes in a value which is modified. Mapped to D-BUS, an "inout"
+ passes in a value which is modified. Mapped to D-Bus, an "inout"
argument is equivalent to an "in" argument, followed by an "out"
argument. You can't pass things "by reference" over the wire, so
"inout" is purely an illusion of the in-process API.
exceptions.
</para>
<para>
+ In converting from native APIs to D-Bus, it is perhaps nice to
+ map D-Bus naming conventions ("FooBar") to native conventions
+ such as "fooBar" or "foo_bar" automatically. This is OK
+ as long as you can say that the native API is one that
+ was specifically written for D-Bus. It makes the most sense
+ when writing object implementations that will be exported
+ over the bus. Object proxies used to invoke remote D-Bus
+ objects probably need the ability to call any D-Bus method,
+ and thus a magic name mapping like this could be a problem.
+ </para>
+ <para>
This specification doesn't require anything of native API bindings;
the preceding is only a suggested convention for consistency
among bindings.
</para>
</sect4>
-
</sect3>
<sect3 id="message-protocol-types-signal">
A signal emission is simply a single message of type <literal>SIGNAL</literal>.
It must have three header fields: <literal>PATH</literal> giving the object
the signal was emitted from, plus <literal>INTERFACE</literal> and <literal>MEMBER</literal> giving
- the fully-qualified name of the signal.
+ the fully-qualified name of the signal. The <literal>INTERFACE</literal> header is required
+ for signals, though it is optional for method calls.
</para>
</sect3>
This document uses a simple pseudo-IDL to describe particular method
calls and signals. Here is an example of a method call:
<programlisting>
- org.freedesktop.DBus.ActivateService (in STRING service_name, in UINT32 flags,
- out UINT32 resultcode)
+ org.freedesktop.DBus.StartServiceByName (in STRING name, in UINT32 flags,
+ out UINT32 resultcode)
</programlisting>
- This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = ActivateService,
+ This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = StartServiceByName,
<literal>METHOD_CALL</literal> arguments are <literal>STRING</literal> and <literal>UINT32</literal>, <literal>METHOD_RETURN</literal> argument
is <literal>UINT32</literal>. Remember that the <literal>MEMBER</literal> field can't contain any '.' (period)
characters so it's known that the last part of the name in
<para>
In C++ that might end up looking like this:
<programlisting>
- unsigned int org::freedesktop::DBus::ActivateService (const char *service_name,
- unsigned int flags);
+ unsigned int org::freedesktop::DBus::StartServiceByName (const char *name,
+ unsigned int flags);
</programlisting>
or equally valid, the return value could be done as an argument:
<programlisting>
- void org::freedesktop::DBus::ActivateService (const char *service_name,
- unsigned int flags,
- unsigned int *resultcode);
+ void org::freedesktop::DBus::StartServiceByName (const char *name,
+ unsigned int flags,
+ unsigned int *resultcode);
</programlisting>
It's really up to the API designer how they want to make
this look. You could design an API where the namespace wasn't used
<para>
Signals are written as follows:
<programlisting>
- org.freedesktop.DBus.ServiceLost (STRING service_name)
+ org.freedesktop.DBus.NameLost (STRING name)
</programlisting>
Signals don't specify "in" vs. "out" because only
a single direction is possible.
</sect3>
</sect2>
+ <sect2 id="message-protocol-handling-invalid">
+ <title>Invalid Protocol and Spec Extensions</title>
+
+ <para>
+ For security reasons, the D-Bus protocol should be strictly parsed and
+ validated, with the exception of defined extension points. Any invalid
+ protocol or spec violations should result in immediately dropping the
+ connection without notice to the other end. Exceptions should be
+ carefully considered, e.g. an exception may be warranted for a
+ well-understood idiosyncrasy of a widely-deployed implementation. In
+ cases where the other end of a connection is 100% trusted and known to
+ be friendly, skipping validation for performance reasons could also make
+ sense in certain cases.
+ </para>
+
+ <para>
+ Generally speaking violations of the "must" requirements in this spec
+ should be considered possible attempts to exploit security, and violations
+ of the "should" suggestions should be considered legitimate (though perhaps
+ they should generate an error in some cases).
+ </para>
+
+ <para>
+ The following extension points are built in to D-Bus on purpose and must
+ not be treated as invalid protocol. The extension points are intended
+ for use by future versions of this spec, they are not intended for third
+ parties. At the moment, the only way a third party could extend D-Bus
+ without breaking interoperability would be to introduce a way to negotiate new
+ feature support as part of the auth protocol, using EXTENSION_-prefixed
+ commands. There is not yet a standard way to negotiate features.
+ <itemizedlist>
+ <listitem>
+ <para>
+ In the authentication protocol (see <xref linkend="auth-protocol"/>) unknown
+ commands result in an ERROR rather than a disconnect. This enables
+ future extensions to the protocol. Commands starting with EXTENSION_ are
+ reserved for third parties.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The authentication protocol supports pluggable auth mechanisms.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The address format (see <xref linkend="addresses"/>) supports new
+ kinds of transport.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Messages with an unknown type (something other than
+ <literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>,
+ <literal>ERROR</literal>, <literal>SIGNAL</literal>) are ignored.
+ Unknown-type messages must still be well-formed in the same way
+ as the known messages, however. They still have the normal
+ header and body.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Header fields with an unknown or unexpected field code must be ignored,
+ though again they must still be well-formed.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ New standard interfaces (with new methods and signals) can of course be added.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+
+ </sect2>
+
</sect1>
<sect1 id="auth-protocol">
<para>
The protocol is a line-based protocol, where each line ends with
\r\n. Each line begins with an all-caps ASCII command name containing
- only the character range [A-Z], a space, then any arguments for the
+ only the character range [A-Z_], a space, then any arguments for the
command, then the \r\n ending the line. The protocol is
case-sensitive. All bytes must be in the ASCII character set.
<listitem><para>BEGIN</para></listitem>
<listitem><para>DATA <data in hex encoding></para></listitem>
<listitem><para>ERROR [human-readable error explanation]</para></listitem>
+ <listitem><para>NEGOTIATE_UNIX_FD</para></listitem>
</itemizedlist>
From server to client are as follows:
<itemizedlist>
<listitem><para>REJECTED <space-separated list of mechanism names></para></listitem>
- <listitem><para>OK</para></listitem>
+ <listitem><para>OK <GUID in hex></para></listitem>
<listitem><para>DATA <data in hex encoding></para></listitem>
<listitem><para>ERROR</para></listitem>
+ <listitem><para>AGREE_UNIX_FD</para></listitem>
</itemizedlist>
</para>
+ <para>
+ Unofficial extensions to the command set must begin with the letters
+ "EXTENSION_", to avoid conflicts with future official commands.
+ For example, "EXTENSION_COM_MYDOMAIN_DO_STUFF".
+ </para>
</sect2>
<sect2 id="auth-nul-byte">
<title>Special credentials-passing nul byte</title>
single nul byte. This byte may be accompanied by credentials
information on some operating systems that use sendmsg() with
SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain
- sockets. However, the nul byte MUST be sent even on other kinds of
+ sockets. However, the nul byte must be sent even on other kinds of
socket, and even on operating systems that do not require a byte to be
sent in order to transmit credentials. The text protocol described in
this document begins after the single nul byte. If the first byte
<title>AUTH command</title>
<para>
If an AUTH command has no arguments, it is a request to list
- available mechanisms. The server SHOULD respond with a REJECTED
- command listing the mechanisms it understands.
+ available mechanisms. The server must respond with a REJECTED
+ command listing the mechanisms it understands, or with an error.
</para>
<para>
If an AUTH command specifies a mechanism, and the server supports
- said mechanism, the server SHOULD begin exchanging SASL
+ said mechanism, the server should begin exchanging SASL
challenge-response data with the client using DATA commands.
</para>
<para>
If the server does not support the mechanism given in the AUTH
- command, it SHOULD send a REJECTED command listing the mechanisms
- it does support.
+ command, it must send either a REJECTED command listing the mechanisms
+ it does support, or an error.
</para>
<para>
- If the [initial-response] argument is provided, it is intended for
- use with mechanisms that have no initial challenge (or an empty
- initial challenge), as if it were the argument to an initial DATA
- command. If the selected mechanism has an initial challenge, the
- server should reject authentication by sending REJECTED.
+ If the [initial-response] argument is provided, it is intended for use
+ with mechanisms that have no initial challenge (or an empty initial
+ challenge), as if it were the argument to an initial DATA command. If
+ the selected mechanism has an initial challenge and [initial-response]
+ was provided, the server should reject authentication by sending
+ REJECTED.
</para>
<para>
If authentication succeeds after exchanging DATA commands,
- an OK command should be sent to the client.
+ an OK command must be sent to the client.
</para>
<para>
- The first octet received by the client after the \r\n of the OK
- command MUST be the first octet of the authenticated/encrypted
- stream of D-BUS messages.
+ The first octet received by the server after the \r\n of the BEGIN
+ command from the client must be the first octet of the
+ authenticated/encrypted stream of D-Bus messages.
</para>
<para>
- The first octet received by the server after the \r\n of the BEGIN
- command from the client MUST be the first octet of the
- authenticated/encrypted stream of D-BUS messages.
+ If BEGIN is received by the server, the first octet received
+ by the client after the \r\n of the OK command must be the
+ first octet of the authenticated/encrypted stream of D-Bus
+ messages.
</para>
</sect2>
<sect2 id="auth-command-cancel">
<title>CANCEL Command</title>
<para>
At any time up to sending the BEGIN command, the client may send a
- CANCEL command. On receiving the CANCEL command, the server MUST
+ CANCEL command. On receiving the CANCEL command, the server must
send a REJECTED command and abort the current authentication
exchange.
</para>
</para>
<para>
The first octet received by the server after the \r\n of the BEGIN
- command from the client MUST be the first octet of the
- authenticated/encrypted stream of D-BUS messages.
+ command from the client must be the first octet of the
+ authenticated/encrypted stream of D-Bus messages.
</para>
</sect2>
<sect2 id="auth-command-rejected">
</para><para>
Optionally, the REJECTED command has a space-separated list of
available auth mechanisms as arguments. If a server ever provides
- a list of supported mechanisms, it MUST provide the same list
+ a list of supported mechanisms, it must provide the same list
each time it sends a REJECTED message. Clients are free to
ignore all lists received after the first.
</para>
<sect2 id="auth-command-ok">
<title>OK Command</title>
<para>
- The OK command indicates that the client has been authenticated,
- and that further communication will be a stream of D-BUS messages
- (optionally encrypted, as negotiated) rather than this protocol.
+ The OK command indicates that the client has been
+ authenticated. The client may now proceed with negotiating
+ Unix file descriptor passing. To do that it shall send
+ NEGOTIATE_UNIX_FD to the server.
+ </para>
+ <para>
+ Otherwise, the client must respond to the OK command by
+ sending a BEGIN command, followed by its stream of messages,
+ or by disconnecting. The server must not accept additional
+ commands using this protocol after the BEGIN command has been
+ received. Further communication will be a stream of D-Bus
+ messages (optionally encrypted, as negotiated) rather than
+ this protocol.
</para>
<para>
- The first octet received by the client after the \r\n of the OK
- command MUST be the first octet of the authenticated/encrypted
- stream of D-BUS messages.
+ If a client sends BEGIN the first octet received by the client
+ after the \r\n of the OK command must be the first octet of
+ the authenticated/encrypted stream of D-Bus messages.
</para>
<para>
- The client MUST respond to the OK command by sending a BEGIN
- command, followed by its stream of messages, or by disconnecting.
- The server MUST NOT accept additional commands using this protocol
- after the OK command has been sent.
+ The OK command has one argument, which is the GUID of the server.
+ See <xref linkend="addresses"/> for more on server GUIDs.
</para>
</sect2>
<sect2 id="auth-command-error">
</para>
<para>
If an ERROR is sent, the server or client that sent the
- error MUST continue as if the command causing the ERROR had never been
+ error must continue as if the command causing the ERROR had never been
received. However, the the server or client receiving the error
should try something other than whatever caused the error;
if only canceling/rejecting the authentication.
</para>
+ <para>
+ If the D-Bus protocol changes incompatibly at some future time,
+ applications implementing the new protocol would probably be able to
+ check for support of the new protocol by sending a new command and
+ receiving an ERROR from applications that don't understand it. Thus the
+ ERROR feature of the auth protocol is an escape hatch that lets us
+ negotiate extensions or changes to the D-Bus protocol in the future.
+ </para>
+ </sect2>
+ <sect2 id="auth-command-negotiate-unix-fd">
+ <title>NEGOTIATE_UNIX_FD Command</title>
+ <para>
+ The NEGOTIATE_UNIX_FD command indicates that the client
+ supports Unix file descriptor passing. This command may only
+ be sent after the connection is authenticated, i.e. after OK
+ was received by the client. This command may only be sent on
+ transports that support Unix file descriptor passing.
+ </para>
+ <para>
+ On receiving NEGOTIATE_UNIX_FD the server must respond with
+ either AGREE_UNIX_FD or ERROR. It shall respond the former if
+ the transport chosen supports Unix file descriptor passing and
+ the server supports this feature. It shall respond the latter
+ if the transport does not support Unix file descriptor
+ passing, the server does not support this feature, or the
+ server decides not to enable file descriptor passing due to
+ security or other reasons.
+ </para>
+ </sect2>
+ <sect2 id="auth-command-agree-unix-fd">
+ <title>AGREE_UNIX_FD Command</title>
+ <para>
+ The AGREE_UNIX_FD command indicates that the server supports
+ Unix file descriptor passing. This command may only be sent
+ after the connection is authenticated, and the client sent
+ NEGOTIATE_UNIX_FD to enable Unix file descriptor passing. This
+ command may only be sent on transports that support Unix file
+ descriptor passing.
+ </para>
+ <para>
+ On receiving AGREE_UNIX_FD the client must respond with BEGIN,
+ followed by its stream of messages, or by disconnecting. The
+ server must not accept additional commands using this protocol
+ after the BEGIN command has been received. Further
+ communication will be a stream of D-Bus messages (optionally
+ encrypted, as negotiated) rather than this protocol.
+ </para>
+ </sect2>
+ <sect2 id="auth-command-future">
+ <title>Future Extensions</title>
+ <para>
+ Future extensions to the authentication and negotiation
+ protocol are possible. For that new commands may be
+ introduced. If a client or server receives an unknown command
+ it shall respond with ERROR and not consider this fatal. New
+ commands may be introduced both before, and after
+ authentication, i.e. both before and after the OK command.
+ </para>
</sect2>
<sect2 id="auth-examples">
<title>Authentication examples</title>
(MAGIC_COOKIE is a made up mechanism)
C: AUTH MAGIC_COOKIE 3138363935333137393635383634
- S: OK
+ S: OK 1234deadbeef
C: BEGIN
</programlisting>
</figure>
C: AUTH SKEY 7ab83f32ee
S: DATA 8799cabb2ea93e
C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
- S: OK
+ S: OK 1234deadbeef
C: BEGIN
</programlisting>
</figure>
C: FOOBAR
S: ERROR
C: AUTH MAGIC_COOKIE 3736343435313230333039
- S: OK
+ S: OK 1234deadbeef
C: BEGIN
</programlisting>
</figure>
C: AUTH SKEY 7ab83f32ee
S: DATA 8799cabb2ea93e
C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
- S: OK
+ S: OK 1234deadbeef
C: BEGIN
</programlisting>
</figure>
C: AUTH SKEY 7ab83f32ee
S: DATA 8799cabb2ea93e
C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
- S: OK
+ S: OK 1234deadbeef
C: BEGIN
</programlisting>
</figure>
C: AUTH SKEY 7ab83f32ee
S: DATA 8799cabb2ea93e
C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
- S: OK
+ S: OK 1234deadbeef
+ C: BEGIN
+ </programlisting>
+ </figure>
+ <figure>
+ <title>Example of successful magic cookie authentication with successful negotiation of Unix FD passing</title>
+ <programlisting>
+ (MAGIC_COOKIE is a made up mechanism)
+
+ C: AUTH MAGIC_COOKIE 3138363935333137393635383634
+ S: OK 1234deadbeef
+ C: NEGOTIATE_UNIX_FD
+ S: AGREE_UNIX_FD
+ C: BEGIN
+ </programlisting>
+ </figure>
+ <figure>
+ <title>Example of successful magic cookie authentication with unsuccessful negotiation of Unix FD passing</title>
+ <programlisting>
+ (MAGIC_COOKIE is a made up mechanism)
+
+ C: AUTH MAGIC_COOKIE 3138363935333137393635383634
+ S: OK 1234deadbeef
+ C: NEGOTIATE_UNIX_FD
+ S: ERROR
C: BEGIN
</programlisting>
</figure>
<title>Authentication mechanisms</title>
<para>
This section describes some new authentication mechanisms.
- D-BUS also allows any standard SASL mechanism of course.
+ D-Bus also allows any standard SASL mechanism of course.
</para>
<sect3 id="auth-mechanisms-sha">
<title>DBUS_COOKIE_SHA1</title>
directory.
</para>
<para>
+ Throughout this description, "hex encoding" must output the digits
+ from a to f in lower-case; the digits A to F must not be used
+ in the DBUS_COOKIE_SHA1 mechanism.
+ </para>
+ <para>
Authentication proceeds as follows:
<itemizedlist>
<listitem>
<para>
The client sends the username it would like to authenticate
- as.
+ as, hex-encoded.
</para>
</listitem>
<listitem>
The server sends the name of its "cookie context" (see below); a
space character; the integer ID of the secret cookie the client
must demonstrate knowledge of; a space character; then a
- hex-encoded randomly-generated challenge string.
+ randomly-generated challenge string, all of this hex-encoded into
+ one, single string.
</para>
</listitem>
<listitem>
<para>
- The client locates the cookie, and generates its own hex-encoded
- randomly-generated challenge string. The client then
- concatentates the server's hex-encoded challenge, a ":"
- character, its own hex-encoded challenge, another ":" character,
- and the hex-encoded cookie. It computes the SHA-1 hash of this
- composite string. It sends back to the server the client's
- hex-encoded challenge string, a space character, and the SHA-1
- hash.
+ The client locates the cookie and generates its own
+ randomly-generated challenge string. The client then concatenates
+ the server's decoded challenge, a ":" character, its own challenge,
+ another ":" character, and the cookie. It computes the SHA-1 hash
+ of this composite string as a hex digest. It concatenates the
+ client's challenge string, a space character, and the SHA-1 hex
+ digest, hex-encodes the result and sends it back to the server.
</para>
</listitem>
<listitem>
nonzero length, and may not contain the characters slash ("/"),
backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"),
tab ("\t"), or period ("."). There is a default context,
- "org_freedesktop_global" that's used by servers that do not specify
+ "org_freedesktop_general" that's used by servers that do not specify
otherwise.
</para>
<para>
</listitem>
<listitem>
<para>
- The cookie itself, a hex-encoded random block of bytes.
+ The cookie itself, a hex-encoded random block of bytes. The cookie
+ may be of any length, though obviously security increases
+ as the length increases.
</para>
</listitem>
</itemizedlist>
</para>
<para>
- Only server processes modify the cookie file.
+ Only server processes modify the cookie file.
They must do so with this procedure:
<itemizedlist>
<listitem>
<para>
Server addresses consist of a transport name followed by a colon, and
then an optional, comma-separated list of keys and values in the form key=value.
- [FIXME how do you escape colon, comma, and semicolon in the values of the key=value pairs?]
+ Each value is escaped.
</para>
<para>
For example:
Which is the address to a unix socket with the path /tmp/dbus-test.
</para>
<para>
+ Value escaping is similar to URI escaping but simpler.
+ <itemizedlist>
+ <listitem>
+ <para>
+ The set of optionally-escaped bytes is:
+ <literal>[0-9A-Za-z_-/.\]</literal>. To escape, each
+ <emphasis>byte</emphasis> (note, not character) which is not in the
+ set of optionally-escaped bytes must be replaced with an ASCII
+ percent (<literal>%</literal>) and the value of the byte in hex.
+ The hex value must always be two digits, even if the first digit is
+ zero. The optionally-escaped bytes may be escaped if desired.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ To unescape, append each byte in the value; if a byte is an ASCII
+ percent (<literal>%</literal>) character then append the following
+ hex value instead. It is an error if a <literal>%</literal> byte
+ does not have two hex digits following. It is an error if a
+ non-optionally-escaped byte is seen unescaped.
+ </para>
+ </listitem>
+ </itemizedlist>
+ The set of optionally-escaped bytes is intended to preserve address
+ readability and convenience.
+ </para>
+
+ <para>
+ A server may specify a key-value pair with the key <literal>guid</literal>
+ and the value a hex-encoded 16-byte sequence. <xref linkend="uuids"/>
+ describes the format of the <literal>guid</literal> field. If present,
+ this UUID may be used to distinguish one server address from another. A
+ server should use a different UUID for each address it listens on. For
+ example, if a message bus daemon offers both UNIX domain socket and TCP
+ connections, but treats clients the same regardless of how they connect,
+ those two connections are equivalent post-connection but should have
+ distinct UUIDs to distinguish the kinds of connection.
+ </para>
+
+ <para>
+ The intent of the address UUID feature is to allow a client to avoid
+ opening multiple identical connections to the same server, by allowing the
+ client to check whether an address corresponds to an already-existing
+ connection. Comparing two addresses is insufficient, because addresses
+ can be recycled by distinct servers, and equivalent addresses may look
+ different if simply compared as strings (for example, the host in a TCP
+ address can be given as an IP address or as a hostname).
+ </para>
+
+ <para>
+ Note that the address key is <literal>guid</literal> even though the
+ rest of the API and documentation says "UUID," for historical reasons.
+ </para>
+
+ <para>
[FIXME clarify if attempting to connect to each is a requirement
or just a suggestion]
When connecting to a server, multiple server addresses can be
the next one specified, and so forth. For example
<programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
</para>
+
+ </sect1>
+
+ <sect1 id="transports">
+ <title>Transports</title>
<para>
[FIXME we need to specify in detail each transport and its possible arguments]
+
Current transports include: unix domain sockets (including
abstract namespace on linux), TCP/IP, and a debug/testing transport using
in-process pipes. Future possible transports include one that
tunnels over X11 protocol.
</para>
- </sect1>
-
- <sect1 id="standard-messages">
- <title>Standard One-to-One Messages</title>
- <para>
- See <xref linkend="message-protocol-types-notation"/> for details on
- the notation used in this section.
- </para>
- <sect2 id="standard-messages-ping">
- <title><literal>org.freedesktop.Peer.Ping</literal></title>
- <para>
- <programlisting>
- org.freedesktop.Peer.Ping ()
- </programlisting>
- </para>
- <para>
- On receipt of the <literal>METHOD_CALL</literal>
- message <literal>org.freedesktop.Peer.Ping</literal>, an application
- should do nothing other than reply with a <literal>METHOD_RETURN</literal> as usual.
- </para>
- </sect2>
-
- <sect2 id="standard-messages-get-props">
- <title><literal>org.freedesktop.Props.Get</literal></title>
+
+ <sect2 id="transports-unix-domain-sockets">
+ <title>Unix Domain Sockets</title>
<para>
- [FIXME this is just a bogus made-up method that isn't implemented
- or thought through, to save an example of table formatting for the
- argument descriptions]
- <programlisting>
- org.freedesktop.Props.Get (in STRING property_name,
- out ANY_OR_NIL property_value)
- </programlisting>
- Message arguments:
- <informaltable>
- <tgroup cols="3">
- <thead>
- <row>
- <entry>Argument</entry>
- <entry>Type</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0</entry>
- <entry>in STRING</entry>
- <entry>Name of the property to get</entry>
- </row>
- <row>
- <entry>1</entry>
- <entry>out ANY_OR_NIL</entry>
- <entry>The value of the property. The type depends on the property.</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
+ Unix domain sockets can be either paths in the file system or on Linux
+ kernels, they can be abstract which are similar to paths but
+ do not show up in the file system.
</para>
- </sect2>
- </sect1>
- <sect1 id="message-bus">
- <title>Message Bus Specification</title>
- <sect2 id="message-bus-overview">
- <title>Message Bus Overview</title>
- <para>
- The message bus accepts connections from one or more applications.
- Once connected, applications can send and receive messages from
- the message bus, as in the one-to-one case.
- </para>
<para>
- The message bus keeps track of a set of
- <firstterm>services</firstterm>. A service is simply a name, such as
- <literal>com.yoyodyne.Screensaver</literal>, which can be
- <firstterm>owned</firstterm> by one or more of the connected
- applications. The message bus itself always owns the special service
- <literal>org.freedesktop.DBus</literal>.
+ When a socket is opened by the D-Bus library it truncates the path
+ name right before the first trailing Nul byte. This is true for both
+ normal paths and abstract paths. Note that this is a departure from
+ previous versions of D-Bus that would create sockets with a fixed
+ length path name. Names which were shorter than the fixed length
+ would be padded by Nul bytes.
</para>
<para>
- Services may have <firstterm>secondary owners</firstterm>. Secondary owners
- of a service are kept in a queue; if the primary owner of a service
- disconnects, or releases the service, the next secondary owner becomes
- the new owner of the service.
- </para>
- <para>
- Messages may have a <literal>DESTINATION</literal> field (see <xref
- linkend="message-protocol-header-fields"/>). When the message bus
- receives a message, if the <literal>DESTINATION</literal> field is absent, the
- message is taken to be a standard one-to-one message and interpreted
- by the message bus itself. For example, sending
- an <literal>org.freedesktop.Peer.Ping</literal> message with no
- <literal>DESTINATION</literal> will cause the message bus itself to reply
- to the ping immediately; the message bus would never make
- this message visible to other applications.
- </para>
- <para>
- If the <literal>DESTINATION</literal> field is present, then it indicates a
- request for the message bus to route the message. In the usual case,
- messages are routed to the owner of the named service.
- Messages may also be <firstterm>broadcast</firstterm>
- by sending them to the special service
- <literal>org.freedesktop.DBus.Broadcast</literal>. Broadcast messages are
- sent to all applications with <firstterm>message matching
- rules</firstterm> that match the message.
- </para>
- <para>
- Continuing the <literal>org.freedesktop.Peer.Ping</literal> example, if
- the ping message were sent with a <literal>DESTINATION</literal> name of
- <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
- forwarded, and the Yoyodyne Corporation screensaver application would be
- expected to reply to the ping. If
- <literal>org.freedesktop.Peer.Ping</literal> were sent to
- <literal>org.freedesktop.DBus.Broadcast</literal>, then multiple applications
- might receive the ping, and all would normally reply to it.
+ Unix domain sockets are not available on windows.
</para>
+ <sect3 id="transports-unix-domain-sockets-addresses">
+ <title>Server Address Format</title>
+ <para>
+ Unix domain socket addresses are identified by the "unix:" prefix
+ and support the following key/value pairs:
+ </para>
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Name</entry>
+ <entry>Values</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>path</entry>
+ <entry>(path)</entry>
+ <entry>path of the unix domain socket. If set, the "tmpdir" and "abstract" key must not be set.</entry>
+ </row>
+ <row>
+ <entry>tmpdir</entry>
+ <entry>(path)</entry>
+ <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>
+ </row>
+ <row>
+ <entry>abstract</entry>
+ <entry>(string)</entry>
+ <entry>unique string (path) in the abstract namespace. If set, the "path" or "tempdir" key must not be set.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </sect3>
</sect2>
-
- <sect2 id="message-bus-services">
- <title>Message Bus Services</title>
- <para>
- A service is a name that identifies a certain application. Each
- application connected to the message bus has at least one service name
- assigned at connection time and returned in response to the
- <literal>org.freedesktop.DBus.Hello</literal> message.
- This automatically-assigned service name is called
- the application's <firstterm>base service</firstterm>.
- Base service names are unique and MUST never be reused for two different
- applications.
- </para>
+ <sect2 id="transports-tcp-sockets">
+ <title>TCP Sockets</title>
<para>
- Ownership of the base service is a prerequisite for interaction with
- the message bus. It logically follows that the base service is always
- the first service that an application comes to own, and the last
- service that it loses ownership of.
+ The tcp transport provides TCP/IP based connections between clients
+ located on the same or different hosts.
</para>
<para>
- Base service names must begin with the character ':' (ASCII colon
- character); service names that are not base service names must not begin
- with this character. (The bus must reject any attempt by an application
- to manually create a service name beginning with ':'.) This restriction
- categorically prevents "spoofing"; messages sent to a base service name
- will always go to a single application instance and that instance only.
- </para>
- <para>
- An application can request additional service names to be associated
- with it using the
- <literal>org.freedesktop.DBus.AcquireService</literal>
- message. [FIXME what service names are allowed; ASCII or unicode;
- length limit; etc.]
- </para>
- <para>
- [FIXME this needs more detail, and should move the service-related message
- descriptions up into this section perhaps]
- Service ownership handling can be specified in the flags part
- of the <literal>org.freedesktop.DBus.AcquireService</literal>
- message. If an application specifies the
- <literal>DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT</literal> flag, then all applications
- trying to acquire the service will be put in a queue. When the
- primary owner disconnects from the bus or removes ownership
- from the service, the next application in the queue will be the
- primary owner. If the <literal>DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT</literal>
- flag is not specified, then the primary owner will lose
- ownership whenever another application requests ownership of the
- service.
- </para>
- <para>
- When a client disconnects from the bus, all the services that
- the clients own are deleted, or in the case of a service that
- prohibits replacement, ownership is transferred to the next
- client in the queue, if any.
- </para>
- </sect2>
- <sect2 id="message-bus-routing">
- <title>Message Bus Message Routing</title>
- <para>
- When a message is received by the message bus, the message's
- <literal>sndr</literal> header field MUST be set to the base service of
- the application which sent the message. If the service already has
- a <literal>sndr</literal> field, the pre-existing field is replaced.
- This rule means that a replies are always sent to the base service name,
- i.e. to the same application that sent the message being replied to.
+ Using tcp transport without any additional secure authentification mechanismus
+ over a network is unsecure.
</para>
- <para>
- [FIXME go into detail about broadcast, multicast, unicast, etc.]
+ <para>
+ Windows notes: Because of the tcp stack on windows does not provide sending
+ credentials over a tcp connection, the EXTERNAL authentification
+ mechanismus does not work.
</para>
+ <sect3 id="transports-tcp-sockets-addresses">
+ <title>Server Address Format</title>
+ <para>
+ TCP/IP socket addresses are identified by the "tcp:" prefix
+ and support the following key/value pairs:
+ </para>
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Name</entry>
+ <entry>Values</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>host</entry>
+ <entry>(string)</entry>
+ <entry>dns name or ip address</entry>
+ </row>
+ <row>
+ <entry>port</entry>
+ <entry>(number)</entry>
+ <entry>The tcp port the server will open. A zero value let the server
+ choose a free port provided from the underlaying operating system.
+ libdbus is able to retrieve the real used port from the server.
+ </entry>
+ </row>
+ <row>
+ <entry>family</entry>
+ <entry>(string)</entry>
+ <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </sect3>
</sect2>
- <sect2 id="message-bus-activation">
- <title>Message Bus Service Activation</title>
- <para>
- <firstterm>Activation</firstterm> means to locate a service
- owner for a service that is currently unowned. For now, it
- means to launch an executable that will take ownership of
- a particular service.
- </para>
+ <sect2 id="transports-nonce-tcp-sockets">
+ <title>Nonce-secured TCP Sockets</title>
<para>
- To find an executable corresponding to a particular service, the bus
- daemon looks for <firstterm>service description files</firstterm>.
- Service description files define a mapping from service names to
- executables. Different kinds of message bus will look for these files
- in different places, see <xref linkend="message-bus-types"/>.
+ The nonce-tcp transport provides a secured TCP transport, using a
+ simple authentication mechanism to ensure that only clients with read
+ access to a certain location in the filesystem can connect to the server.
+ The server writes a secret, the nonce, to a file and an incoming client
+ connection is only accepted if the client sends the nonce right after
+ the connect. The nonce mechanism requires no setup and is orthogonal to
+ the higher-level authentication mechanisms described in the
+ Authentication section.
</para>
+
<para>
- [FIXME the file format should be much better specified than
- "similar to .desktop entries" esp. since desktop entries are
- already badly-specified. ;-)] Service description files have
- the ".service" file extension. The message bus will only load
- service description files ending with .service; all other
- files will be ignored. The file format is similar to that of
- <ulink
- url="http://www.freedesktop.org/standards/desktop-entry-spec/desktop-entry-spec.html">desktop
- entries</ulink>. All service description files must be in
- UTF-8 encoding. To ensure that there will be no name
- collisions, service files must be namespaced using the same
- mechanism as messages and service names.
+ On start, the server generates a random 16 byte nonce and writes it
+ to a file in the user's temporary directory. The nonce file location
+ is published as part of the server's D-Bus address using the
+ "noncefile" key-value pair.
- <figure>
- <title>Example service description file</title>
- <programlisting>
- # Sample service description file
- [D-BUS Service]
- Name=org.gnome.ConfigurationDatabase
- Exec=/usr/libexec/gconfd-2
- </programlisting>
- </figure>
+ After an accept, the server reads 16 bytes from the socket. If the
+ read bytes do not match the nonce stored in the nonce file, the
+ server MUST immediately drop the connection.
+ If the nonce match the received byte sequence, the client is accepted
+ and the transport behaves like an unsecured tcp transport.
</para>
<para>
- When an application requests a service to be activated, the
- bus daemon tries to find it in the list of activation
- entries. It then tries to spawn the executable associated with
- it. If this fails, it will report an error. [FIXME what
- happens if two .service files offer the same service; what
- kind of error is reported, should we have a way for the client
- to choose one?]
+ After a successful connect to the server socket, the client MUST read
+ the nonce from the file published by the server via the noncefile=
+ key-value pair and send it over the socket. After that, the
+ transport behaves like an unsecured tcp transport.
</para>
- <para>
- The executable launched will have the environment variable
- <literal>DBUS_ACTIVATION_ADDRESS</literal> set to the address of the
- message bus so it can connect and register the appropriate services.
+ <sect3 id="transports-nonce-tcp-sockets-addresses">
+ <title>Server Address Format</title>
+ <para>
+ Nonce TCP/IP socket addresses uses the "nonce-tcp:" prefix
+ and support the following key/value pairs:
+ </para>
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Name</entry>
+ <entry>Values</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>host</entry>
+ <entry>(string)</entry>
+ <entry>dns name or ip address</entry>
+ </row>
+ <row>
+ <entry>port</entry>
+ <entry>(number)</entry>
+ <entry>The tcp port the server will open. A zero value let the server
+ choose a free port provided from the underlaying operating system.
+ libdbus is able to retrieve the real used port from the server.
+ </entry>
+ </row>
+ <row>
+ <entry>family</entry>
+ <entry>(string)</entry>
+ <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
+ </row>
+ <row>
+ <entry>noncefile</entry>
+ <entry>(path)</entry>
+ <entry>file location containing the secret</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </sect3>
+ </sect2>
+
+ </sect1>
+
+ <sect1 id="naming-conventions">
+ <title>Naming Conventions</title>
+
+ <para>
+ D-Bus namespaces are all lowercase and correspond to reversed domain
+ names, as with Java. e.g. "org.freedesktop"
+ </para>
+ <para>
+ Interface, signal, method, and property names are "WindowsStyleCaps", note
+ that the first letter is capitalized, unlike Java.
+ </para>
+ <para>
+ Object paths are normally all lowercase with underscores used rather than
+ hyphens.
+ </para>
+ </sect1>
+
+ <sect1 id="uuids">
+ <title>UUIDs</title>
+ <para>
+ A working D-Bus implementation uses universally-unique IDs in two places.
+ First, each server address has a UUID identifying the address,
+ as described in <xref linkend="addresses"/>. Second, each operating
+ system kernel instance running a D-Bus client or server has a UUID
+ identifying that kernel, retrieved by invoking the method
+ org.freedesktop.DBus.Peer.GetMachineId() (see <xref
+ linkend="standard-interfaces-peer"/>).
+ </para>
+ <para>
+ The term "UUID" in this document is intended literally, i.e. an
+ identifier that is universally unique. It is not intended to refer to
+ RFC4122, and in fact the D-Bus UUID is not compatible with that RFC.
+ </para>
+ <para>
+ The UUID must contain 128 bits of data and be hex-encoded. The
+ hex-encoded string may not contain hyphens or other non-hex-digit
+ characters, and it must be exactly 32 characters long. To generate a
+ UUID, the current reference implementation concatenates 96 bits of random
+ data followed by the 32-bit time in seconds since the UNIX epoch (in big
+ endian byte order).
+ </para>
+ <para>
+ It would also be acceptable and probably better to simply generate 128
+ bits of random data, as long as the random number generator is of high
+ quality. The timestamp could conceivably help if the random bits are not
+ very random. With a quality random number generator, collisions are
+ extremely unlikely even with only 96 bits, so it's somewhat academic.
+ </para>
+ <para>
+ Implementations should, however, stick to random data for the first 96 bits
+ of the UUID.
+ </para>
+ </sect1>
+
+ <sect1 id="standard-interfaces">
+ <title>Standard Interfaces</title>
+ <para>
+ See <xref linkend="message-protocol-types-notation"/> for details on
+ the notation used in this section. There are some standard interfaces
+ that may be useful across various D-Bus applications.
+ </para>
+ <sect2 id="standard-interfaces-peer">
+ <title><literal>org.freedesktop.DBus.Peer</literal></title>
+ <para>
+ The <literal>org.freedesktop.DBus.Peer</literal> interface
+ has two methods:
+ <programlisting>
+ org.freedesktop.DBus.Peer.Ping ()
+ org.freedesktop.DBus.Peer.GetMachineId (out STRING machine_uuid)
+ </programlisting>
+ </para>
+ <para>
+ On receipt of the <literal>METHOD_CALL</literal> message
+ <literal>org.freedesktop.DBus.Peer.Ping</literal>, an application should do
+ nothing other than reply with a <literal>METHOD_RETURN</literal> as
+ usual. It does not matter which object path a ping is sent to. The
+ reference implementation handles this method automatically.
+ </para>
+ <para>
+ On receipt of the <literal>METHOD_CALL</literal> message
+ <literal>org.freedesktop.DBus.Peer.GetMachineId</literal>, an application should
+ reply with a <literal>METHOD_RETURN</literal> containing a hex-encoded
+ UUID representing the identity of the machine the process is running on.
+ This UUID must be the same for all processes on a single system at least
+ until that system next reboots. It should be the same across reboots
+ if possible, but this is not always possible to implement and is not
+ guaranteed.
+ It does not matter which object path a GetMachineId is sent to. The
+ reference implementation handles this method automatically.
+ </para>
+ <para>
+ The UUID is intended to be per-instance-of-the-operating-system, so may represent
+ a virtual machine running on a hypervisor, rather than a physical machine.
+ Basically if two processes see the same UUID, they should also see the same
+ shared memory, UNIX domain sockets, process IDs, and other features that require
+ a running OS kernel in common between the processes.
+ </para>
+ <para>
+ The UUID is often used where other programs might use a hostname. Hostnames
+ can change without rebooting, however, or just be "localhost" - so the UUID
+ is more robust.
+ </para>
+ <para>
+ <xref linkend="uuids"/> explains the format of the UUID.
+ </para>
+ </sect2>
+
+ <sect2 id="standard-interfaces-introspectable">
+ <title><literal>org.freedesktop.DBus.Introspectable</literal></title>
+ <para>
+ This interface has one method:
+ <programlisting>
+ org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data)
+ </programlisting>
+ </para>
+ <para>
+ Objects instances may implement
+ <literal>Introspect</literal> which returns an XML description of
+ the object, including its interfaces (with signals and methods), objects
+ below it in the object path tree, and its properties.
+ </para>
+ <para>
+ <xref linkend="introspection-format"/> describes the format of this XML string.
+ </para>
+ </sect2>
+ <sect2 id="standard-interfaces-properties">
+ <title><literal>org.freedesktop.DBus.Properties</literal></title>
+ <para>
+ Many native APIs will have a concept of object <firstterm>properties</firstterm>
+ or <firstterm>attributes</firstterm>. These can be exposed via the
+ <literal>org.freedesktop.DBus.Properties</literal> interface.
+ </para>
+ <para>
+ <programlisting>
+ org.freedesktop.DBus.Properties.Get (in STRING interface_name,
+ in STRING property_name,
+ out VARIANT value);
+ org.freedesktop.DBus.Properties.Set (in STRING interface_name,
+ in STRING property_name,
+ in VARIANT value);
+ org.freedesktop.DBus.Properties.GetAll (in STRING interface_name,
+ out DICT<STRING,VARIANT> props);
+ </programlisting>
+ </para>
+ <para>
+ The available properties and whether they are writable can be determined
+ by calling <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>,
+ see <xref linkend="standard-interfaces-introspectable"/>.
+ </para>
+ <para>
+ An empty string may be provided for the interface name; in this case,
+ if there are multiple properties on an object with the same name,
+ the results are undefined (picking one by according to an arbitrary
+ deterministic rule, or returning an error, are the reasonable
+ possibilities).
+ </para>
+ <para>
+ If one or more properties change on an object, the
+ <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
+ signal may be emitted (this signal was added in 0.14):
+ </para>
+ <para>
+ <programlisting>
+ org.freedesktop.DBus.Properties.PropertiesChanged (STRING interface_name,
+ DICT<STRING,VARIANT> changed_properties,
+ ARRAY<STRING> invalidated_properties);
+ </programlisting>
+ </para>
+ <para>
+ where <literal>changed_properties</literal> is a dictionary
+ containing the changed properties with the new values and
+ <literal>invalidated_properties</literal> is an array of
+ properties that changed but the value is not conveyed.
+ </para>
+ <para>
+ Whether the <literal>PropertiesChanged</literal> signal is
+ supported can be determined by calling
+ <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>. Note
+ that the signal may be supported for an object but it may
+ differ how whether and how it is used on a per-property basis
+ (for e.g. performance or security reasons). Each property (or
+ the parent interface) must be annotated with the
+ <literal>org.freedesktop.DBus.Property.EmitsChangedSignal</literal>
+ annotation to convey this (usually the default value
+ <literal>true</literal> is sufficient meaning that the
+ annotation does not need to be used). See <xref
+ linkend="introspection-format"/> for details on this
+ annotation.
+ </para>
+ </sect2>
+ </sect1>
+
+ <sect1 id="introspection-format">
+ <title>Introspection Data Format</title>
+ <para>
+ As described in <xref linkend="standard-interfaces-introspectable"/>,
+ objects may be introspected at runtime, returning an XML string
+ that describes the object. The same XML format may be used in
+ other contexts as well, for example as an "IDL" for generating
+ static language bindings.
+ </para>
+ <para>
+ Here is an example of introspection data:
+ <programlisting>
+ <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
+ "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
+ <node name="/org/freedesktop/sample_object">
+ <interface name="org.freedesktop.SampleInterface">
+ <method name="Frobate">
+ <arg name="foo" type="i" direction="in"/>
+ <arg name="bar" type="s" direction="out"/>
+ <arg name="baz" type="a{us}" direction="out"/>
+ <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
+ </method>
+ <method name="Bazify">
+ <arg name="bar" type="(iiu)" direction="in"/>
+ <arg name="bar" type="v" direction="out"/>
+ </method>
+ <method name="Mogrify">
+ <arg name="bar" type="(iiav)" direction="in"/>
+ </method>
+ <signal name="Changed">
+ <arg name="new_value" type="b"/>
+ </signal>
+ <property name="Bar" type="y" access="readwrite"/>
+ </interface>
+ <node name="child_of_sample_object"/>
+ <node name="another_child_of_sample_object"/>
+ </node>
+ </programlisting>
+ </para>
+ <para>
+ A more formal DTD and spec needs writing, but here are some quick notes.
+ <itemizedlist>
+ <listitem>
+ <para>
+ Only the root <node> element can omit the node name, as it's
+ known to be the object that was introspected. If the root
+ <node> does have a name attribute, it must be an absolute
+ object path. If child <node> have object paths, they must be
+ relative.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ If a child <node> has any sub-elements, then they
+ must represent a complete introspection of the child.
+ If a child <node> is empty, then it may or may
+ not have sub-elements; the child must be introspected
+ in order to find out. The intent is that if an object
+ knows that its children are "fast" to introspect
+ it can go ahead and return their information, but
+ otherwise it can omit it.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The direction element on <arg> may be omitted,
+ in which case it defaults to "in" for method calls
+ and "out" for signals. Signals only allow "out"
+ so while direction may be specified, it's pointless.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The possible directions are "in" and "out",
+ unlike CORBA there is no "inout"
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The possible property access flags are
+ "readwrite", "read", and "write"
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Multiple interfaces can of course be listed for
+ one <node>.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The "name" attribute on arguments is optional.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ Method, interface, property, and signal elements may have
+ "annotations", which are generic key/value pairs of metadata.
+ They are similar conceptually to Java's annotations and C# attributes.
+ Well-known annotations:
+ </para>
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Name</entry>
+ <entry>Values (separated by ,)</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>org.freedesktop.DBus.Deprecated</entry>
+ <entry>true,false</entry>
+ <entry>Whether or not the entity is deprecated; defaults to false</entry>
+ </row>
+ <row>
+ <entry>org.freedesktop.DBus.GLib.CSymbol</entry>
+ <entry>(string)</entry>
+ <entry>The C symbol; may be used for methods and interfaces</entry>
+ </row>
+ <row>
+ <entry>org.freedesktop.DBus.Method.NoReply</entry>
+ <entry>true,false</entry>
+ <entry>If set, don't expect a reply to the method call; defaults to false.</entry>
+ </row>
+ <row>
+ <entry>org.freedesktop.DBus.Property.EmitsChangedSignal</entry>
+ <entry>true,invalidates,false</entry>
+ <entry>
+ <para>
+ If set to <literal>false</literal>, the
+ <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
+ signal, see <xref
+ linkend="standard-interfaces-properties"/> is not
+ guaranteed to be emitted if the property changes.
+ </para>
+ <para>
+ If set to <literal>invalidates</literal> the signal
+ is emitted but the value is not included in the
+ signal.
+ </para>
+ <para>
+ If set to <literal>true</literal> the signal is
+ emitted with the value included.
+ </para>
+ <para>
+ The value for the annotation defaults to
+ <literal>true</literal> if the enclosing interface
+ element does not specify the annotation. Otherwise it
+ defaults to the value specified in the enclosing
+ interface element.
+ </para>
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </sect1>
+ <sect1 id="message-bus">
+ <title>Message Bus Specification</title>
+ <sect2 id="message-bus-overview">
+ <title>Message Bus Overview</title>
+ <para>
+ The message bus accepts connections from one or more applications.
+ Once connected, applications can exchange messages with other
+ applications that are also connected to the bus.
+ </para>
+ <para>
+ In order to route messages among connections, the message bus keeps a
+ mapping from names to connections. Each connection has one
+ unique-for-the-lifetime-of-the-bus name automatically assigned.
+ Applications may request additional names for a connection. Additional
+ names are usually "well-known names" such as
+ "org.freedesktop.TextEditor". When a name is bound to a connection,
+ that connection is said to <firstterm>own</firstterm> the name.
+ </para>
+ <para>
+ The bus itself owns a special name, <literal>org.freedesktop.DBus</literal>.
+ This name routes messages to the bus, allowing applications to make
+ administrative requests. For example, applications can ask the bus
+ to assign a name to a connection.
+ </para>
+ <para>
+ Each name may have <firstterm>queued owners</firstterm>. When an
+ application requests a name for a connection and the name is already in
+ use, the bus will optionally add the connection to a queue waiting for
+ the name. If the current owner of the name disconnects or releases
+ the name, the next connection in the queue will become the new owner.
+ </para>
+
+ <para>
+ This feature causes the right thing to happen if you start two text
+ editors for example; the first one may request "org.freedesktop.TextEditor",
+ and the second will be queued as a possible owner of that name. When
+ the first exits, the second will take over.
+ </para>
+
+ <para>
+ Messages may have a <literal>DESTINATION</literal> field (see <xref
+ linkend="message-protocol-header-fields"/>). If the
+ <literal>DESTINATION</literal> field is present, it specifies a message
+ recipient by name. Method calls and replies normally specify this field.
+ </para>
+
+ <para>
+ Signals normally do not specify a destination; they are sent to all
+ applications with <firstterm>message matching rules</firstterm> that
+ match the message.
+ </para>
+
+ <para>
+ When the message bus receives a method call, if the
+ <literal>DESTINATION</literal> field is absent, the call is taken to be
+ a standard one-to-one message and interpreted by the message bus
+ itself. For example, sending an
+ <literal>org.freedesktop.DBus.Peer.Ping</literal> message with no
+ <literal>DESTINATION</literal> will cause the message bus itself to
+ reply to the ping immediately; the message bus will not make this
+ message visible to other applications.
+ </para>
+
+ <para>
+ Continuing the <literal>org.freedesktop.DBus.Peer.Ping</literal> example, if
+ the ping message were sent with a <literal>DESTINATION</literal> name of
+ <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
+ forwarded, and the Yoyodyne Corporation screensaver application would be
+ expected to reply to the ping.
+ </para>
+ </sect2>
+
+ <sect2 id="message-bus-names">
+ <title>Message Bus Names</title>
+ <para>
+ Each connection has at least one name, assigned at connection time and
+ returned in response to the
+ <literal>org.freedesktop.DBus.Hello</literal> method call. This
+ automatically-assigned name is called the connection's <firstterm>unique
+ name</firstterm>. Unique names are never reused for two different
+ connections to the same bus.
+ </para>
+ <para>
+ Ownership of a unique name is a prerequisite for interaction with
+ the message bus. It logically follows that the unique name is always
+ the first name that an application comes to own, and the last
+ one that it loses ownership of.
+ </para>
+ <para>
+ Unique connection names must begin with the character ':' (ASCII colon
+ character); bus names that are not unique names must not begin
+ with this character. (The bus must reject any attempt by an application
+ to manually request a name beginning with ':'.) This restriction
+ categorically prevents "spoofing"; messages sent to a unique name
+ will always go to the expected connection.
+ </para>
+ <para>
+ When a connection is closed, all the names that it owns are deleted (or
+ transferred to the next connection in the queue if any).
+ </para>
+ <para>
+ A connection can request additional names to be associated with it using
+ the <literal>org.freedesktop.DBus.RequestName</literal> message. <xref
+ linkend="message-protocol-names-bus"/> describes the format of a valid
+ name. These names can be released again using the
+ <literal>org.freedesktop.DBus.ReleaseName</literal> message.
+ </para>
+
+ <sect3 id="bus-messages-request-name">
+ <title><literal>org.freedesktop.DBus.RequestName</literal></title>
+ <para>
+ As a method:
+ <programlisting>
+ UINT32 RequestName (in STRING name, in UINT32 flags)
+ </programlisting>
+ Message arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>STRING</entry>
+ <entry>Name to request</entry>
+ </row>
+ <row>
+ <entry>1</entry>
+ <entry>UINT32</entry>
+ <entry>Flags</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Reply arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>UINT32</entry>
+ <entry>Return value</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ <para>
+ This method call should be sent to
+ <literal>org.freedesktop.DBus</literal> and asks the message bus to
+ assign the given name to the method caller. Each name maintains a
+ queue of possible owners, where the head of the queue is the primary
+ or current owner of the name. Each potential owner in the queue
+ maintains the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and
+ DBUS_NAME_FLAG_DO_NOT_QUEUE settings from its latest RequestName
+ call. When RequestName is invoked the following occurs:
+ <itemizedlist>
+ <listitem>
+ <para>
+ If the method caller is currently the primary owner of the name,
+ the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and DBUS_NAME_FLAG_DO_NOT_QUEUE
+ values are updated with the values from the new RequestName call,
+ and nothing further happens.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ If the current primary owner (head of the queue) has
+ DBUS_NAME_FLAG_ALLOW_REPLACEMENT set, and the RequestName
+ invocation has the DBUS_NAME_FLAG_REPLACE_EXISTING flag, then
+ the caller of RequestName replaces the current primary owner at
+ the head of the queue and the current primary owner moves to the
+ second position in the queue. If the caller of RequestName was
+ in the queue previously its flags are updated with the values from
+ the new RequestName in addition to moving it to the head of the queue.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ If replacement is not possible, and the method caller is
+ currently in the queue but not the primary owner, its flags are
+ updated with the values from the new RequestName call.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ If replacement is not possible, and the method caller is
+ currently not in the queue, the method caller is appended to the
+ queue.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ If any connection in the queue has DBUS_NAME_FLAG_DO_NOT_QUEUE
+ set and is not the primary owner, it is removed from the
+ queue. This can apply to the previous primary owner (if it
+ was replaced) or the method caller (if it updated the
+ DBUS_NAME_FLAG_DO_NOT_QUEUE flag while still stuck in the
+ queue, or if it was just added to the queue with that flag set).
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ Note that DBUS_NAME_FLAG_REPLACE_EXISTING results in "jumping the
+ queue," even if another application already in the queue had specified
+ DBUS_NAME_FLAG_REPLACE_EXISTING. This comes up if a primary owner
+ that does not allow replacement goes away, and the next primary owner
+ does allow replacement. In this case, queued items that specified
+ DBUS_NAME_FLAG_REPLACE_EXISTING <emphasis>do not</emphasis>
+ automatically replace the new primary owner. In other words,
+ DBUS_NAME_FLAG_REPLACE_EXISTING is not saved, it is only used at the
+ time RequestName is called. This is deliberate to avoid an infinite loop
+ anytime two applications are both DBUS_NAME_FLAG_ALLOW_REPLACEMENT
+ and DBUS_NAME_FLAG_REPLACE_EXISTING.
+ </para>
+ <para>
+ The flags argument contains any of the following values logically ORed
+ together:
+
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Conventional Name</entry>
+ <entry>Value</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>DBUS_NAME_FLAG_ALLOW_REPLACEMENT</entry>
+ <entry>0x1</entry>
+ <entry>
+
+ If an application A specifies this flag and succeeds in
+ becoming the owner of the name, and another application B
+ later calls RequestName with the
+ DBUS_NAME_FLAG_REPLACE_EXISTING flag, then application A
+ will lose ownership and receive a
+ <literal>org.freedesktop.DBus.NameLost</literal> signal, and
+ application B will become the new owner. If DBUS_NAME_FLAG_ALLOW_REPLACEMENT
+ is not specified by application A, or DBUS_NAME_FLAG_REPLACE_EXISTING
+ is not specified by application B, then application B will not replace
+ application A as the owner.
+
+ </entry>
+ </row>
+ <row>
+ <entry>DBUS_NAME_FLAG_REPLACE_EXISTING</entry>
+ <entry>0x2</entry>
+ <entry>
+
+ Try to replace the current owner if there is one. If this
+ flag is not set the application will only become the owner of
+ the name if there is no current owner. If this flag is set,
+ the application will replace the current owner if
+ the current owner specified DBUS_NAME_FLAG_ALLOW_REPLACEMENT.
+
+ </entry>
+ </row>
+ <row>
+ <entry>DBUS_NAME_FLAG_DO_NOT_QUEUE</entry>
+ <entry>0x4</entry>
+ <entry>
+
+ Without this flag, if an application requests a name that is
+ already owned, the application will be placed in a queue to
+ own the name when the current owner gives it up. If this
+ flag is given, the application will not be placed in the
+ queue, the request for the name will simply fail. This flag
+ also affects behavior when an application is replaced as
+ name owner; by default the application moves back into the
+ waiting queue, unless this flag was provided when the application
+ became the name owner.
+
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+
+ The return code can be one of the following values:
+
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Conventional Name</entry>
+ <entry>Value</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER</entry>
+ <entry>1</entry> <entry>The caller is now the primary owner of
+ the name, replacing any previous owner. Either the name had no
+ owner before, or the caller specified
+ DBUS_NAME_FLAG_REPLACE_EXISTING and the current owner specified
+ DBUS_NAME_FLAG_ALLOW_REPLACEMENT.</entry>
+ </row>
+ <row>
+ <entry>DBUS_REQUEST_NAME_REPLY_IN_QUEUE</entry>
+ <entry>2</entry>
+
+ <entry>The name already had an owner,
+ DBUS_NAME_FLAG_DO_NOT_QUEUE was not specified, and either
+ the current owner did not specify
+ DBUS_NAME_FLAG_ALLOW_REPLACEMENT or the requesting
+ application did not specify DBUS_NAME_FLAG_REPLACE_EXISTING.
+ </entry>
+ </row>
+ <row>
+ <entry>DBUS_REQUEST_NAME_REPLY_EXISTS</entry> <entry>3</entry>
+ <entry>The name already has an owner,
+ DBUS_NAME_FLAG_DO_NOT_QUEUE was specified, and either
+ DBUS_NAME_FLAG_ALLOW_REPLACEMENT was not specified by the
+ current owner, or DBUS_NAME_FLAG_REPLACE_EXISTING was not
+ specified by the requesting application.</entry>
+ </row>
+ <row>
+ <entry>DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER</entry>
+ <entry>4</entry>
+ <entry>The application trying to request ownership of a name is already the owner of it.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ </sect3>
+
+ <sect3 id="bus-messages-release-name">
+ <title><literal>org.freedesktop.DBus.ReleaseName</literal></title>
+ <para>
+ As a method:
+ <programlisting>
+ UINT32 ReleaseName (in STRING name)
+ </programlisting>
+ Message arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>STRING</entry>
+ <entry>Name to release</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Reply arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>UINT32</entry>
+ <entry>Return value</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ <para>
+ This method call should be sent to
+ <literal>org.freedesktop.DBus</literal> and asks the message bus to
+ release the method caller's claim to the given name. If the caller is
+ the primary owner, a new primary owner will be selected from the
+ queue if any other owners are waiting. If the caller is waiting in
+ the queue for the name, the caller will removed from the queue and
+ will not be made an owner of the name if it later becomes available.
+ If there are no other owners in the queue for the name, it will be
+ removed from the bus entirely.
+
+ The return code can be one of the following values:
+
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Conventional Name</entry>
+ <entry>Value</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>DBUS_RELEASE_NAME_REPLY_RELEASED</entry>
+ <entry>1</entry> <entry>The caller has released his claim on
+ the given name. Either the caller was the primary owner of
+ the name, and the name is now unused or taken by somebody
+ waiting in the queue for the name, or the caller was waiting
+ in the queue for the name and has now been removed from the
+ queue.</entry>
+ </row>
+ <row>
+ <entry>DBUS_RELEASE_NAME_REPLY_NON_EXISTENT</entry>
+ <entry>2</entry>
+ <entry>The given name does not exist on this bus.</entry>
+ </row>
+ <row>
+ <entry>DBUS_RELEASE_NAME_REPLY_NOT_OWNER</entry>
+ <entry>3</entry>
+ <entry>The caller was not the primary owner of this name,
+ and was also not waiting in the queue to own this name.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ </sect3>
+
+ <sect3 id="bus-messages-list-queued-owners">
+ <title><literal>org.freedesktop.DBus.ListQueuedOwners</literal></title>
+ <para>
+ As a method:
+ <programlisting>
+ ARRAY of STRING ListQueuedOwners (in STRING name)
+ </programlisting>
+ Message arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>STRING</entry>
+ <entry>The well-known bus name to query, such as
+ <literal>com.example.cappuccino</literal></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Reply arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>ARRAY of STRING</entry>
+ <entry>The unique bus names of connections currently queued
+ for the name</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ <para>
+ This method call should be sent to
+ <literal>org.freedesktop.DBus</literal> and lists the connections
+ currently queued for a bus name (see
+ <xref linkend="term-queued-owner"/>).
+ </para>
+ </sect3>
+ </sect2>
+
+ <sect2 id="message-bus-routing">
+ <title>Message Bus Message Routing</title>
+ <para>
+ FIXME
+ </para>
+ <sect3 id="message-bus-routing-match-rules">
+ <title>Match Rules</title>
+ <para>
+ An important part of the message bus routing protocol is match
+ rules. Match rules describe what messages can be sent to a client
+ based on the contents of the message. When a message is routed
+ through the bus it is compared to clients' match rules. If any
+ of the rules match, the message is dispatched to the client.
+ If none of the rules match the message never leaves the bus. This
+ is an effective way to control traffic over the bus and to make sure
+ only relevant message need to be processed by the client.
+ </para>
+ <para>
+ Match rules are added using the AddMatch bus method
+ (see <xref linkend="bus-messages-add-match"/>). Rules are
+ specified as a string of comma separated key/value pairs.
+ Excluding a key from the rule indicates a wildcard match.
+ For instance excluding the the member from a match rule but
+ adding a sender would let all messages from that sender through.
+ An example of a complete rule would be
+ "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='Foo',path='/bar/foo',destination=':452345.34',arg2='bar'"
+ </para>
+ <para>
+ The following table describes the keys that can be used to create
+ a match rule:
+ The following table summarizes the D-Bus types.
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Key</entry>
+ <entry>Possible Values</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><literal>type</literal></entry>
+ <entry>'signal', 'method_call', 'method_return', 'error'</entry>
+ <entry>Match on the message type. An example of a type match is type='signal'</entry>
+ </row>
+ <row>
+ <entry><literal>sender</literal></entry>
+ <entry>A bus or unique name (see <xref linkend="term-bus-name"/>
+ and <xref linkend="term-unique-name"/> respectively)
+ </entry>
+ <entry>Match messages sent by a particular sender. An example of a sender match
+ is sender='org.freedesktop.Hal'</entry>
+ </row>
+ <row>
+ <entry><literal>interface</literal></entry>
+ <entry>An interface name (see <xref linkend="message-protocol-names-interface"/>)</entry>
+ <entry>Match messages sent over or to a particular interface. An example of an
+ interface match is interface='org.freedesktop.Hal.Manager'.
+ If a message omits the interface header, it must not match any rule
+ that specifies this key.</entry>
+ </row>
+ <row>
+ <entry><literal>member</literal></entry>
+ <entry>Any valid method or signal name</entry>
+ <entry>Matches messages which have the give method or signal name. An example of
+ a member match is member='NameOwnerChanged'</entry>
+ </row>
+ <row>
+ <entry><literal>path</literal></entry>
+ <entry>An object path (see <xref linkend="message-protocol-marshaling-object-path"/>)</entry>
+ <entry>Matches messages which are sent from or to the given object. An example of a
+ path match is path='/org/freedesktop/Hal/Manager'</entry>
+ </row>
+ <row>
+ <entry><literal>destination</literal></entry>
+ <entry>A unique name (see <xref linkend="term-unique-name"/>)</entry>
+ <entry>Matches messages which are being sent to the given unique name. An
+ example of a destination match is destination=':1.0'</entry>
+ </row>
+ <row>
+ <entry><literal>arg[0, 1, 2, 3, ...]</literal></entry>
+ <entry>Any string</entry>
+ <entry>Arg matches are special and are used for further restricting the
+ match based on the arguments in the body of a message. As of this time
+ only string arguments can be matched. An example of an argument match
+ would be arg3='Foo'. Only argument indexes from 0 to 63 should be
+ accepted.</entry>
+ </row>
+ <row>
+ <entry><literal>arg[0, 1, 2, 3, ...]path</literal></entry>
+ <entry>Any string</entry>
+ <entry>Argument path matches provide a specialised form of wildcard
+ matching for path-like namespaces. As with normal argument matches,
+ if the argument is exactly equal to the string given in the match
+ rule then the rule is satisfied. Additionally, there is also a
+ match when either the string given in the match rule or the
+ appropriate message argument ends with '/' and is a prefix of the
+ other. An example argument path match is arg0path='/aa/bb/'. This
+ would match messages with first arguments of '/', '/aa/',
+ '/aa/bb/', '/aa/bb/cc/' and '/aa/bb/cc'. It would not match
+ messages with first arguments of '/aa/b', '/aa' or even '/aa/bb'.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ </sect3>
+ </sect2>
+ <sect2 id="message-bus-starting-services">
+ <title>Message Bus Starting Services</title>
+ <para>
+ The message bus can start applications on behalf of other applications.
+ In CORBA terms, this would be called <firstterm>activation</firstterm>.
+ An application that can be started in this way is called a
+ <firstterm>service</firstterm>.
+ </para>
+ <para>
+ With D-Bus, starting a service is normally done by name. That is,
+ applications ask the message bus to start some program that will own a
+ well-known name, such as <literal>org.freedesktop.TextEditor</literal>.
+ This implies a contract documented along with the name
+ <literal>org.freedesktop.TextEditor</literal> for which objects
+ the owner of that name will provide, and what interfaces those
+ objects will have.
+ </para>
+ <para>
+ To find an executable corresponding to a particular name, the bus daemon
+ looks for <firstterm>service description files</firstterm>. Service
+ description files define a mapping from names to executables. Different
+ kinds of message bus will look for these files in different places, see
+ <xref linkend="message-bus-types"/>.
+ </para>
+ <para>
+ [FIXME the file format should be much better specified than "similar to
+ .desktop entries" esp. since desktop entries are already
+ badly-specified. ;-)] Service description files have the ".service" file
+ extension. The message bus will only load service description files
+ ending with .service; all other files will be ignored. The file format
+ is similar to that of <ulink
+ url="http://www.freedesktop.org/standards/desktop-entry-spec/desktop-entry-spec.html">desktop
+ entries</ulink>. All service description files must be in UTF-8
+ encoding. To ensure that there will be no name collisions, service files
+ must be namespaced using the same mechanism as messages and service
+ names.
+
+ <figure>
+ <title>Example service description file</title>
+ <programlisting>
+ # Sample service description file
+ [D-BUS Service]
+ Names=org.freedesktop.ConfigurationDatabase;org.gnome.GConf;
+ Exec=/usr/libexec/gconfd-2
+ </programlisting>
+ </figure>
+ </para>
+ <para>
+ When an application asks to start a service by name, the bus daemon tries to
+ find a service that will own that name. It then tries to spawn the
+ executable associated with it. If this fails, it will report an
+ error. [FIXME what happens if two .service files offer the same service;
+ what kind of error is reported, should we have a way for the client to
+ choose one?]
+ </para>
+ <para>
+ The executable launched will have the environment variable
+ <literal>DBUS_STARTER_ADDRESS</literal> set to the address of the
+ message bus so it can connect and request the appropriate names.
</para>
<para>
The executable being launched may want to know whether the message bus
- activating it is one of the well-known message buses (see <xref
- linkend="message-bus-types"/>). To facilitate this, the bus MUST also set
- the <literal>DBUS_ACTIVATION_BUS_TYPE</literal> environment variable if it is one
+ starting it is one of the well-known message buses (see <xref
+ linkend="message-bus-types"/>). To facilitate this, the bus must also set
+ the <literal>DBUS_STARTER_BUS_TYPE</literal> environment variable if it is one
of the well-known buses. The currently-defined values for this variable
are <literal>system</literal> for the systemwide message bus,
and <literal>session</literal> for the per-login-session message
- bus. The activated executable must still connect to the address given
- in <literal>DBUS_ACTIVATION_ADDRESS</literal>, but may assume that the
+ bus. The new executable must still connect to the address given
+ in <literal>DBUS_STARTER_ADDRESS</literal>, but may assume that the
resulting connection is to the well-known bus.
</para>
<para>
and if the client being activated fails to connect within that
timeout, an error should be sent back.]
</para>
+
+ <sect3 id="message-bus-starting-services-scope">
+ <title>Message Bus Service Scope</title>
+ <para>
+ The "scope" of a service is its "per-", such as per-session,
+ per-machine, per-home-directory, or per-display. The reference
+ implementation doesn't yet support starting services in a different
+ scope from the message bus itself. So e.g. if you start a service
+ on the session bus its scope is per-session.
+ </para>
+ <para>
+ We could add an optional scope to a bus name. For example, for
+ per-(display,session pair), we could have a unique ID for each display
+ generated automatically at login and set on screen 0 by executing a
+ special "set display ID" binary. The ID would be stored in a
+ <literal>_DBUS_DISPLAY_ID</literal> property and would be a string of
+ random bytes. This ID would then be used to scope names.
+ Starting/locating a service could be done by ID-name pair rather than
+ only by name.
+ </para>
+ <para>
+ Contrast this with a per-display scope. To achieve that, we would
+ want a single bus spanning all sessions using a given display.
+ So we might set a <literal>_DBUS_DISPLAY_BUS_ADDRESS</literal>
+ property on screen 0 of the display, pointing to this bus.
+ </para>
+ </sect3>
</sect2>
<sect2 id="message-bus-types">
changes in the printer queue, and so forth.
</para>
<para>
- The address of the login session message bus is given
+ The address of the system message bus is given
in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment
variable. If that variable is not set, applications should try
to connect to the well-known address
<literal>unix:path=/var/run/dbus/system_bus_socket</literal>.
<footnote>
<para>
- The D-BUS reference implementation actually honors the
+ The D-Bus reference implementation actually honors the
<literal>$(localstatedir)</literal> configure option
for this address, on both client and server side.
</para>
<sect2 id="message-bus-messages">
<title>Message Bus Messages</title>
<para>
- The special message bus service <literal>org.freedesktop.DBus</literal>
- responds to a number of messages, allowing applications to
- interact with the message bus.
+ The special message bus name <literal>org.freedesktop.DBus</literal>
+ responds to a number of additional messages.
</para>
<sect3 id="bus-messages-hello">
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the service assigned to the application</entry>
+ <entry>Unique name assigned to the connection</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
- Before an application is able to send messages to other
- applications it must send the
- <literal>org.freedesktop.DBus.Hello</literal> message to the
- message bus service. If an application tries to send a
- message to another application, or a message to the message
- bus service that isn't the
- <literal>org.freedesktop.DBus.Hello</literal> message, it
- will be disconnected from the bus. If a client wishes to
- disconnect from the bus, it just has to disconnect from the
- transport used. No de-registration message is necessary.
+ Before an application is able to send messages to other applications
+ it must send the <literal>org.freedesktop.DBus.Hello</literal> message
+ to the message bus to obtain a unique name. If an application without
+ a unique name tries to send a message to another application, or a
+ message to the message bus itself that isn't the
+ <literal>org.freedesktop.DBus.Hello</literal> message, it will be
+ disconnected from the bus.
</para>
<para>
- The reply message contains the name of the application's base service.
+ There is no corresponding "disconnect" request; if a client wishes to
+ disconnect from the bus, it simply closes the socket (or other
+ communication channel).
</para>
</sect3>
- <sect3 id="bus-messages-list-services">
- <title><literal>org.freedesktop.DBus.ListServices</literal></title>
+ <sect3 id="bus-messages-list-names">
+ <title><literal>org.freedesktop.DBus.ListNames</literal></title>
<para>
As a method:
<programlisting>
- STRING_ARRAY ListServices ()
+ ARRAY of STRING ListNames ()
</programlisting>
Reply arguments:
<informaltable>
<tbody>
<row>
<entry>0</entry>
- <entry>STRING_ARRAY</entry>
- <entry>Array of strings where each string is the name of a service</entry>
+ <entry>ARRAY of STRING</entry>
+ <entry>Array of strings where each string is a bus name</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
- Returns a list of all existing services registered with the message bus.
+ Returns a list of all currently-owned names on the bus.
</para>
</sect3>
- <sect3 id="bus-messages-service-exists">
- <title><literal>org.freedesktop.DBus.ServiceExists</literal></title>
+ <sect3 id="bus-messages-list-activatable-names">
+ <title><literal>org.freedesktop.DBus.ListActivatableNames</literal></title>
<para>
As a method:
<programlisting>
- BOOLEAN ServiceExists (in STRING service_name)
+ ARRAY of STRING ListActivatableNames ()
</programlisting>
- Message arguments:
- <informaltable>
- <tgroup cols="3">
- <thead>
- <row>
- <entry>Argument</entry>
- <entry>Type</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0</entry>
- <entry>STRING</entry>
- <entry>Name of the service</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
Reply arguments:
<informaltable>
<tgroup cols="3">
<tbody>
<row>
<entry>0</entry>
- <entry>BOOLEAN</entry>
- <entry>Return value, true if the service exists</entry>
+ <entry>ARRAY of STRING</entry>
+ <entry>Array of strings where each string is a bus name</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
- Checks if a service with a specified name exists.
+ Returns a list of all names that can be activated on the bus.
</para>
</sect3>
-
- <sect3 id="bus-messages-acquire-service">
- <title><literal>org.freedesktop.DBus.AcquireService</literal></title>
+ <sect3 id="bus-messages-name-exists">
+ <title><literal>org.freedesktop.DBus.NameHasOwner</literal></title>
<para>
As a method:
<programlisting>
- UINT32 AcquireService (in STRING service_name)
+ BOOLEAN NameHasOwner (in STRING name)
</programlisting>
Message arguments:
<informaltable>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the service</entry>
+ <entry>Name to check</entry>
</row>
- <row>
- <entry>1</entry>
- <entry>UINT32</entry>
- <entry>Flags</entry>
- </row>
</tbody>
</tgroup>
</informaltable>
<tbody>
<row>
<entry>0</entry>
- <entry>UINT32</entry>
- <entry>Return value</entry>
+ <entry>BOOLEAN</entry>
+ <entry>Return value, true if the name exists</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
- Tries to become owner of a specific service. The flags
- specified can be the following values logically ORed together:
-
- <informaltable>
- <tgroup cols="3">
- <thead>
- <row>
- <entry>Identifier</entry>
- <entry>Value</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT</entry>
- <entry>0x1</entry>
- <entry>
- If the application succeeds in being the owner of the specified service,
- then ownership of the service can't be transferred until the service
- disconnects. If this flag is not set, then any application trying to become
- the owner of the service will succeed and the previous owner will be
- sent a <literal>org.freedesktop.DBus.ServiceLost</literal> message.
- </entry>
- </row>
- <row>
- <entry>DBUS_SERVICE_FLAGS_REPLACE_EXISTING</entry>
- <entry>0x2</entry>
- <entry>Try to replace the current owner if there is one. If this flag
- is not set the application will only become the owner of the service if
- there is no current owner.</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
-
- [FIXME if it's one of the following values, why are the values
- done as flags instead of just 0, 1, 2, 3, 4]
- The return value can be one of the following values:
-
- <informaltable>
- <tgroup cols="3">
- <thead>
- <row>
- <entry>Identifier</entry>
- <entry>Value</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>DBUS_SERVICE_REPLY_PRIMARY_OWNER</entry>
- <entry>0x1</entry>
- <entry>The application is now the primary owner of the service.</entry>
- </row>
- <row>
- <entry>DBUS_SERVICE_REPLY_IN_QUEUE</entry>
- <entry>0x2</entry>
- <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>
- </row>
- <row>
- <entry>DBUS_SERVICE_REPLY_SERVICE_EXISTS</entry>
- <entry>0x4</entry>
- <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>
- </row>
- <row>
- <entry>DBUS_SERVICE_REPLY_ALREADY_OWNER</entry>
- <entry>0x8</entry>
- <entry>The application trying to request ownership of the service is already the owner of it.</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
+ Checks if the specified name exists (currently has an owner).
</para>
</sect3>
- <sect3 id="bus-messages-service-acquired">
- <title><literal>org.freedesktop.DBus.ServiceAcquired</literal></title>
+
+ <sect3 id="bus-messages-name-owner-changed">
+ <title><literal>org.freedesktop.DBus.NameOwnerChanged</literal></title>
<para>
- As a method:
+ This is a signal:
<programlisting>
- ServiceAcquired (in STRING service_name)
+ NameOwnerChanged (STRING name, STRING old_owner, STRING new_owner)
</programlisting>
Message arguments:
<informaltable>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the service</entry>
+ <entry>Name with a new owner</entry>
</row>
<row>
<entry>1</entry>
- <entry>UINT32</entry>
- <entry>Flags</entry>
+ <entry>STRING</entry>
+ <entry>Old owner or empty string if none</entry>
+ </row>
+ <row>
+ <entry>2</entry>
+ <entry>STRING</entry>
+ <entry>New owner or empty string if none</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
- This message is sent to a specific application when it becomes the
- primary owner of a service.
+ This signal indicates that the owner of a name has changed.
+ It's also the signal to use to detect the appearance of
+ new names on the bus.
</para>
</sect3>
- <sect3 id="bus-messages-service-lost">
- <title><literal>org.freedesktop.DBus.ServiceLost</literal></title>
+ <sect3 id="bus-messages-name-lost">
+ <title><literal>org.freedesktop.DBus.NameLost</literal></title>
<para>
- As a method:
+ This is a signal:
<programlisting>
- ServiceLost (in STRING service_name)
+ NameLost (STRING name)
</programlisting>
Message arguments:
<informaltable>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the service</entry>
+ <entry>Name which was lost</entry>
</row>
- <row>
- <entry>1</entry>
- <entry>UINT32</entry>
- <entry>Flags</entry>
- </row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
- This message is sent to a specific application when it loses primary
- ownership of a service.
+ This signal is sent to a specific application when it loses
+ ownership of a name.
</para>
</sect3>
- <sect3 id="bus-messages-service-owner-changed">
- <title><literal>org.freedesktop.DBus.ServiceOwnerChanged</literal></title>
+ <sect3 id="bus-messages-name-acquired">
+ <title><literal>org.freedesktop.DBus.NameAcquired</literal></title>
<para>
+ This is a signal:
<programlisting>
- ServiceOwnerChanged (STRING service_name, STRING old_owner, STRING new_owner)
+ NameAcquired (STRING name)
</programlisting>
Message arguments:
<informaltable>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the service</entry>
+ <entry>Name which was acquired</entry>
</row>
- <row>
- <entry>1</entry>
- <entry>STRING</entry>
- <entry>Base service of previous owner, empty string if the
- service is newly created</entry>
- </row>
- <row>
- <entry>2</entry>
- <entry>STRING</entry>
- <entry>Base service of new owner, empty string if the
- service is no longer available</entry>
- </row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
- This message is broadcast to all applications when a service has been
- successfully registered on the message bus, has been deleted
- or its primary owner has changed.
+ This signal is sent to a specific application when it gains
+ ownership of a name.
</para>
</sect3>
- <sect3 id="bus-messages-activate-service">
- <title><literal>org.freedesktop.DBus.ActivateService</literal></title>
+ <sect3 id="bus-messages-start-service-by-name">
+ <title><literal>org.freedesktop.DBus.StartServiceByName</literal></title>
<para>
As a method:
<programlisting>
- UINT32 ActivateService (in STRING service_name, in UINT32 flags)
+ UINT32 StartServiceByName (in STRING name, in UINT32 flags)
</programlisting>
Message arguments:
<informaltable>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the service to activate</entry>
+ <entry>Name of the service to start</entry>
</row>
<row>
<entry>1</entry>
</tbody>
</tgroup>
</informaltable>
- Tries to launch the executable associated with a service. For more information, see <xref linkend="message-bus-activation"/>.
+ Tries to launch the executable associated with a name. For more information, see <xref linkend="message-bus-starting-services"/>.
- [FIXME need semantics in much more detail here; for example,
- if I activate a service then send it a message, is the message
- queued for the new service or is there a race]
</para>
<para>
The return value can be one of the following values:
- <informaltable>
+ <informaltable>
<tgroup cols="3">
<thead>
<row>
</thead>
<tbody>
<row>
- <entry>DBUS_ACTIVATION_REPLY_ACTIVATED</entry>
- <entry>0x0</entry>
- <entry>The service was activated successfully.</entry>
+ <entry>DBUS_START_REPLY_SUCCESS</entry>
+ <entry>1</entry>
+ <entry>The service was successfully started.</entry>
</row>
<row>
- <entry>DBUS_ACTIVATION_REPLY_ALREADY_ACTIVE</entry>
- <entry>0x1</entry>
- <entry>The service is already active.</entry>
+ <entry>DBUS_START_REPLY_ALREADY_RUNNING</entry>
+ <entry>2</entry>
+ <entry>A connection already owns the given name.</entry>
</row>
</tbody>
</tgroup>
</sect3>
- <sect3 id="bus-messages-get-service-owner">
- <title><literal>org.freedesktop.DBus.GetServiceOwner</literal></title>
+ <sect3 id="bus-messages-update-activation-environment">
+ <title><literal>org.freedesktop.DBus.UpdateActivationEnvironment</literal></title>
+ <para>
+ As a method:
+ <programlisting>
+ UpdateActivationEnvironment (in ARRAY of DICT<STRING,STRING> environment)
+ </programlisting>
+ Message arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>ARRAY of DICT<STRING,STRING></entry>
+ <entry>Environment to add or update</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Normally, session bus activated services inherit the environment of the bus daemon. This method adds to or modifies that environment when activating services.
+ </para>
+ <para>
+ Some bus instances, such as the standard system bus, may disable access to this method for some or all callers.
+ </para>
+ <para>
+ 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.
+ </para>
+
+ </sect3>
+
+ <sect3 id="bus-messages-get-name-owner">
+ <title><literal>org.freedesktop.DBus.GetNameOwner</literal></title>
<para>
As a method:
<programlisting>
- STRING GetServiceOwner (in STRING service_name)
+ STRING GetNameOwner (in STRING name)
</programlisting>
Message arguments:
<informaltable>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the service to query</entry>
+ <entry>Name to get the owner of</entry>
</row>
</tbody>
</tgroup>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Return value, a base service name</entry>
+ <entry>Return value, a unique connection name</entry>
</row>
</tbody>
</tgroup>
</informaltable>
- Returns the base service name of the primary owner of the
- service in argument. If the requested service isn't active,
- returns a
- <literal>org.freedesktop.DBus.Error.ServiceHasNoOwner</literal> error.
+ Returns the unique connection name of the primary owner of the name
+ given. If the requested name doesn't have an owner, returns a
+ <literal>org.freedesktop.DBus.Error.NameHasNoOwner</literal> error.
</para>
</sect3>
<row>
<entry>0</entry>
<entry>STRING</entry>
- <entry>Name of the connection/service to query</entry>
+ <entry>Name of the connection to query</entry>
</row>
</tbody>
</tgroup>
</para>
</sect3>
- <sect3 id="bus-messages-out-of-memory">
- <title><literal>org.freedesktop.DBus.Error.NoMemory</literal></title>
+ <sect3 id="bus-messages-get-connection-unix-process-id">
+ <title><literal>org.freedesktop.DBus.GetConnectionUnixProcessID</literal></title>
<para>
As a method:
<programlisting>
- void NoMemory ()
+ UINT32 GetConnectionUnixProcessID (in STRING bus_name)
</programlisting>
- </para>
- <para>
- Sent by the message bus when it can't process a message due to an out of memory failure.
- </para>
+ Message arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>STRING</entry>
+ <entry>Unique or well-known bus name of the connection to
+ query, such as <literal>:12.34</literal> or
+ <literal>com.example.tea</literal></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Reply arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>UINT32</entry>
+ <entry>Unix process id</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Returns the Unix process ID of the process connected to the server. If
+ unable to determine it (for instance, because the process is not on the
+ same machine as the bus daemon), an error is returned.
+ </para>
</sect3>
- <sect3 id="bus-messages-service-does-not-exist">
- <title><literal>org.freedesktop.DBus.Error.ServiceDoesNotExist</literal></title>
+ <sect3 id="bus-messages-add-match">
+ <title><literal>org.freedesktop.DBus.AddMatch</literal></title>
<para>
As a method:
<programlisting>
- void ServiceDoesNotExist (in STRING error)
+ AddMatch (in STRING rule)
</programlisting>
- </para>
+ Message arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>STRING</entry>
+ <entry>Match rule to add to the connection</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Adds a match rule to match messages going through the message bus (see <xref linkend='message-bus-routing-match-rules'/>).
+ If the bus does not have enough resources the <literal>org.freedesktop.DBus.Error.OOM</literal>
+ error is returned.
+ </para>
+ </sect3>
+ <sect3 id="bus-messages-remove-match">
+ <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title>
+ <para>
+ As a method:
+ <programlisting>
+ RemoveMatch (in STRING rule)
+ </programlisting>
+ Message arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>STRING</entry>
+ <entry>Match rule to remove from the connection</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Removes the first rule that matches (see <xref linkend='message-bus-routing-match-rules'/>).
+ If the rule is not found the <literal>org.freedesktop.DBus.Error.MatchRuleNotFound</literal>
+ error is returned.
+ </para>
+ </sect3>
+
+ <sect3 id="bus-messages-get-id">
+ <title><literal>org.freedesktop.DBus.GetId</literal></title>
<para>
- Sent by the message bus as a reply to a client that tried to send a message to a service that doesn't exist.
+ As a method:
+ <programlisting>
+ GetId (out STRING id)
+ </programlisting>
+ Reply arguments:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Argument</entry>
+ <entry>Type</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0</entry>
+ <entry>STRING</entry>
+ <entry>Unique ID identifying the bus daemon</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ Gets the unique ID of the bus. The unique ID here is shared among all addresses the
+ bus daemon is listening on (TCP, UNIX domain socket, etc.) and its format is described in
+ <xref linkend="uuids"/>. Each address the bus is listening on also has its own unique
+ ID, as described in <xref linkend="addresses"/>. The per-bus and per-address IDs are not related.
+ There is also a per-machine ID, described in <xref linkend="standard-interfaces-peer"/> and returned
+ by org.freedesktop.DBus.Peer.GetMachineId().
+ For a desktop session bus, the bus ID can be used as a way to uniquely identify a user's session.
</para>
</sect3>
+
</sect2>
</sect1>
This glossary defines some of the terms used in this specification.
</para>
- <glossentry id="term-activation"><glossterm>Activation</glossterm>
- <glossdef>
- <para>
- The process of creating an owner for a particular service,
- typically by launching an executable.
- </para>
- </glossdef>
- </glossentry>
-
- <glossentry id="term-base-service"><glossterm>Base Service</glossterm>
- <glossdef>
- <para>
- The special service automatically assigned to an application by the
- message bus. This service may never change owner, and the service
- name will be unique (never reused during the lifetime of the
- message bus).
- </para>
- </glossdef>
- </glossentry>
-
- <glossentry id="term-broadcast"><glossterm>Broadcast</glossterm>
+ <glossentry id="term-bus-name"><glossterm>Bus Name</glossterm>
<glossdef>
<para>
- A message sent to the special <literal>org.freedesktop.DBus.Broadcast</literal>
- service; the message bus will forward the broadcast message
- to all applications that have expressed interest in it.
+ The message bus maintains an association between names and
+ connections. (Normally, there's one connection per application.) A
+ bus name is simply an identifier used to locate connections. For
+ example, the hypothetical <literal>com.yoyodyne.Screensaver</literal>
+ name might be used to send a message to a screensaver from Yoyodyne
+ Corporation. An application is said to <firstterm>own</firstterm> a
+ name if the message bus has associated the application's connection
+ with the name. Names may also have <firstterm>queued
+ owners</firstterm> (see <xref linkend="term-queued-owner"/>).
+ The bus assigns a unique name to each connection,
+ see <xref linkend="term-unique-name"/>. Other names
+ can be thought of as "well-known names" and are
+ used to find applications that offer specific functionality.
</para>
</glossdef>
</glossentry>
<glossentry id="term-message"><glossterm>Message</glossterm>
<glossdef>
<para>
- A message is the atomic unit of communication via the D-BUS
+ A message is the atomic unit of communication via the D-Bus
protocol. It consists of a <firstterm>header</firstterm> and a
<firstterm>body</firstterm>; the body is made up of
<firstterm>arguments</firstterm>.
<glossdef>
<para>
The message bus is a special application that forwards
- or broadcasts messages between a group of applications
+ or routes messages between a group of applications
connected to the message bus. It also manages
- <firstterm>services</firstterm>.
+ <firstterm>names</firstterm> used for routing
+ messages.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="term-name"><glossterm>Name</glossterm>
+ <glossdef>
+ <para>
+ See <xref linkend="term-bus-name"/>. "Name" may
+ also be used to refer to some of the other names
+ in D-Bus, such as interface names.
</para>
</glossdef>
</glossentry>
<glossentry id="namespace"><glossterm>Namespace</glossterm>
<glossdef>
<para>
- Used to prevent collisions when defining message and service
- names. The convention used is the same as Java uses for
- defining classes: a reversed domain name.
+ Used to prevent collisions when defining new interfaces or bus
+ names. The convention used is the same one Java uses for defining
+ classes: a reversed domain name.
</para>
</glossdef>
</glossentry>
<glossentry id="term-object"><glossterm>Object</glossterm>
<glossdef>
<para>
- Each application contains <firstterm>objects</firstterm>,
- which have <firstterm>interfaces</firstterm> and
- <firstterm>methods</firstterm>. Objects are referred to
- by a name, called a <firstterm>path</firstterm> or
- <firstterm>object reference</firstterm>.
+ Each application contains <firstterm>objects</firstterm>, which have
+ <firstterm>interfaces</firstterm> and
+ <firstterm>methods</firstterm>. Objects are referred to by a name,
+ called a <firstterm>path</firstterm>.
</para>
</glossdef>
</glossentry>
- <glossentry id="term-path"><glossterm>Path</glossterm>
+ <glossentry id="one-to-one"><glossterm>One-to-One</glossterm>
<glossdef>
- <para>
- Object references (object names) in D-BUS are
- organized into a filesystem-style hierarchy, so
- each object is named by a path. As in LDAP,
- there's no difference between "files" and "directories";
- a path can refer to an object, while still having
- child objects below it.
+ <para>
+ An application talking directly to another application, without going
+ through a message bus. One-to-one connections may be "peer to peer" or
+ "client to server." The D-Bus protocol has no concept of client
+ vs. server after a connection has authenticated; the flow of messages
+ is symmetrical (full duplex).
</para>
</glossdef>
</glossentry>
- <glossentry id="one-to-one"><glossterm>One-to-One</glossterm>
+ <glossentry id="term-path"><glossterm>Path</glossterm>
<glossdef>
- <para>
- An application talking directly to another application, without going through a message bus.
+ <para>
+ Object references (object names) in D-Bus are organized into a
+ filesystem-style hierarchy, so each object is named by a path. As in
+ LDAP, there's no difference between "files" and "directories"; a path
+ can refer to an object, while still having child objects below it.
</para>
</glossdef>
</glossentry>
- <glossentry id="term-secondary-owner"><glossterm>Secondary service owner</glossterm>
+
+ <glossentry id="term-queued-owner"><glossterm>Queued Name Owner</glossterm>
<glossdef>
<para>
- Each service has a primary owner; messages sent to the service name
- go to the primary owner. However, certain services also maintain
- a queue of secondary owners "waiting in the wings." If
- the primary owner releases the service, then the first secondary
- owner in the queue automatically becomes the primary owner.
+ Each bus name has a primary owner; messages sent to the name go to the
+ primary owner. However, certain names also maintain a queue of
+ secondary owners "waiting in the wings." If the primary owner releases
+ the name, then the first secondary owner in the queue automatically
+ becomes the new owner of the name.
</para>
</glossdef>
</glossentry>
+
<glossentry id="term-service"><glossterm>Service</glossterm>
<glossdef>
<para>
- A service is simply a named list of applications. For example, the
- hypothetical <literal>com.yoyodyne.Screensaver</literal> service might
- accept messages that affect a screensaver from Yoyodyne Corporation.
- An application is said to <firstterm>own</firstterm> a service if the
- message bus has associated the application with the service name.
- Services may also have <firstterm>secondary owners</firstterm> (see
- <xref linkend="term-secondary-owner"/>).
+ A service is an executable that can be launched by the bus daemon.
+ Services normally guarantee some particular features, for example they
+ may guarantee that they will request a specific name such as
+ "org.freedesktop.Screensaver", have a singleton object
+ "/org/freedesktop/Application", and that object will implement the
+ interface "org.freedesktop.ScreensaverControl".
</para>
</glossdef>
</glossentry>
- <glossentry id="term-service-name"><glossterm>Service name</glossterm>
+
+ <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
<glossdef>
- <para>
- The name used when referring to a service. If the service is
- a base service it has a unique service name, for example
- ":1-20", and otherwise it should be namespaced.
+ <para>
+ ".service files" tell the bus about service applications that can be
+ launched (see <xref linkend="term-service"/>). Most importantly they
+ provide a mapping from bus names to services that will request those
+ names when they start up.
</para>
</glossdef>
</glossentry>
- <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
+
+ <glossentry id="term-unique-name"><glossterm>Unique Connection Name</glossterm>
<glossdef>
<para>
- ".service files" tell the bus how to activate a particular service.
- See <xref linkend="term-activation"/>
+ The special name automatically assigned to each connection by the
+ message bus. This name will never change owner, and will be unique
+ (never reused during the lifetime of the message bus).
+ It will begin with a ':' character.
</para>
</glossdef>
</glossentry>
</glossary>
</article>
-
projects / platform / upstream / dbus.git / blobdiff