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]>
-
<article id="index">
<articleinfo>
<title>D-Bus Specification</title>
- <releaseinfo>Version 0.14</releaseinfo>
- <date>May 12, 2010</date>
+ <releaseinfo>Version 0.19</releaseinfo>
+ <date>UNRELEASED</date>
<authorgroup>
<author>
<firstname>Havoc</firstname>
</address>
</affiliation>
</author>
+ <author>
+ <firstname>Sven</firstname>
+ <surname>Herzberg</surname>
+ <affiliation>
+ <orgname>Imendio AB</orgname>
+ <address>
+ <email>sven@imendio.com</email>
+ </address>
+ </affiliation>
+ </author>
+ <author>
+ <firstname>Simon</firstname>
+ <surname>McVittie</surname>
+ <affiliation>
+ <orgname>Collabora Ltd.</orgname>
+ <address>
+ <email>simon.mcvittie@collabora.co.uk</email>
+ </address>
+ </affiliation>
+ </author>
+ <author>
+ <firstname>David</firstname>
+ <surname>Zeuthen</surname>
+ <affiliation>
+ <orgname>Red Hat, Inc.</orgname>
+ <address>
+ <email>davidz@redhat.com</email>
+ </address>
+ </affiliation>
+ </author>
</authorgroup>
+ <revhistory>
+ <revision>
+ <revnumber>current</revnumber>
+ <date><ulink url='http://cgit.freedesktop.org/dbus/dbus/log/doc/dbus-specification.xml'>commit log</ulink></date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.18</revnumber>
+ <date>29 July 2011</date>
+ <authorinitials>smcv</authorinitials>
+ <revremark>define eavesdropping, unicast, broadcast; add eavesdrop
+ match keyword; promote type system to a top-level section</revremark>
+ </revision>
+ <revision>
+ <revnumber>0.17</revnumber>
+ <date>1 June 2011</date>
+ <authorinitials>smcv/davidz</authorinitials>
+ <revremark>define ObjectManager; reserve extra pseudo-type-codes used
+ by GVariant</revremark>
+ </revision>
+ <revision>
+ <revnumber>0.16</revnumber>
+ <date>11 April 2011</date>
+ <authorinitials></authorinitials>
+ <revremark>add path_namespace, arg0namespace; argNpath matches object
+ paths</revremark>
+ </revision>
+ <revision>
+ <revnumber>0.15</revnumber>
+ <date>3 November 2010</date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.14</revnumber>
+ <date>12 May 2010</date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.13</revnumber>
+ <date>23 Dezember 2009</date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.12</revnumber>
+ <date>7 November, 2006</date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.11</revnumber>
+ <date>6 February 2005</date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.10</revnumber>
+ <date>28 January 2005</date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.9</revnumber>
+ <date>7 Januar 2005</date>
+ <authorinitials></authorinitials>
+ <revremark></revremark>
+ </revision>
+ <revision>
+ <revnumber>0.8</revnumber>
+ <date>06 September 2003</date>
+ <authorinitials></authorinitials>
+ <revremark>First released document.</revremark>
+ </revision>
+ </revhistory>
</articleinfo>
<sect1 id="introduction">
</sect1>
- <sect1 id="message-protocol">
- <title>Message Protocol</title>
-
- <para>
- A <firstterm>message</firstterm> consists of a
- <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you
- 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 interprets the body of the message.
- </para>
-
- <para>
- The body of the message is made up of zero or more
- <firstterm>arguments</firstterm>, which are typed values, such as an
- integer or a byte array.
- </para>
+ <sect1 id="type-system">
+ <title>Type System</title>
<para>
- Both header and body use the same type system and format for
- serializing data. Each type of value has a wire format.
+ D-Bus has a type system, in which values of various types can be
+ serialized into a sequence of bytes referred to as the
+ <firstterm>wire format</firstterm> in a standard way.
Converting a value from some other representation into the wire
format is called <firstterm>marshaling</firstterm> and converting
it back from the wire format is <firstterm>unmarshaling</firstterm>.
</row><row>
<entry><literal>STRUCT</literal></entry>
<entry>114 (ASCII 'r'), 40 (ASCII '('), 41 (ASCII ')')</entry>
- <entry>Struct</entry>
+ <entry>Struct; type code 114 'r' is reserved for use in
+ bindings and implementations to represent the general
+ concept of a struct, and must not appear in signatures
+ used on D-Bus.</entry>
</row><row>
<entry><literal>VARIANT</literal></entry>
<entry>118 (ASCII 'v') </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>
+ <entry>Entry in a dict or map (array of key-value pairs).
+ Type code 101 'e' is reserved for use in bindings and
+ implementations to represent the general concept of a
+ dict or dict-entry, and must not appear in signatures
+ used on D-Bus.</entry>
</row><row>
<entry><literal>UNIX_FD</literal></entry>
<entry>104 (ASCII 'h')</entry>
<entry>Unix file descriptor</entry>
</row>
+ <row>
+ <entry>(reserved)</entry>
+ <entry>109 (ASCII 'm')</entry>
+ <entry>Reserved for <ulink
+ url="https://bugs.freedesktop.org/show_bug.cgi?id=27857">a
+ 'maybe' type compatible with the one in GVariant</ulink>,
+ and must not appear in signatures used on D-Bus until
+ specified here</entry>
+ </row>
+ <row>
+ <entry>(reserved)</entry>
+ <entry>42 (ASCII '*')</entry>
+ <entry>Reserved for use in bindings/implementations to
+ represent any <firstterm>single complete type</firstterm>,
+ and must not appear in signatures used on D-Bus.</entry>
+ </row>
+ <row>
+ <entry>(reserved)</entry>
+ <entry>63 (ASCII '?')</entry>
+ <entry>Reserved for use in bindings/implementations to
+ represent any <firstterm>basic type</firstterm>, and must
+ not appear in signatures used on D-Bus.</entry>
+ </row>
+ <row>
+ <entry>(reserved)</entry>
+ <entry>64 (ASCII '@'), 38 (ASCII '&'),
+ 94 (ASCII '^')</entry>
+ <entry>Reserved for internal use by bindings/implementations,
+ and must not appear in signatures used on D-Bus.
+ GVariant uses these type-codes to encode calling
+ conventions.</entry>
+ </row>
</tbody>
</tgroup>
</informaltable>
</row><row>
<entry><literal>VARIANT</literal></entry>
<entry>
- A variant type has a marshaled <literal>SIGNATURE</literal>
- followed by a marshaled value with the type
- given in the signature.
- Unlike a message signature, the variant signature
- can contain only a single complete type.
- So "i", "ai" or "(ii)" is OK, but "ii" is not.
+ A variant type has a marshaled
+ <literal>SIGNATURE</literal> followed by a marshaled
+ value with the type given in the signature. Unlike
+ a message signature, the variant signature can
+ contain only a single complete type. So "i", "ai"
+ or "(ii)" is OK, but "ii" is not. Use of variants may not
+ cause a total message depth to be larger than 64, including
+ other container types such as structures.
</entry>
<entry>
1 (alignment of the signature)
</sect2>
+ </sect1>
+
+ <sect1 id="message-protocol">
+ <title>Message Protocol</title>
+
+ <para>
+ A <firstterm>message</firstterm> consists of a
+ <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you
+ 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 interprets the body of the message.
+ </para>
+
+ <para>
+ The body of the message is made up of zero or more
+ <firstterm>arguments</firstterm>, which are typed values, such as an
+ integer or a byte array.
+ </para>
+
+ <para>
+ Both header and body use the D-Bus <link linkend="type-system">type
+ system</link> and format for serializing data.
+ </para>
+
<sect2 id="message-protocol-messages">
<title>Message Format</title>
[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
+ abstract namespace on linux), launchd, TCP/IP, and a debug/testing transport
+ using in-process pipes. Future possible transports include one that
tunnels over X11 protocol.
</para>
</informaltable>
</sect3>
</sect2>
+ <sect2 id="transports-launchd">
+ <title>launchd</title>
+ <para>
+ launchd is a open-source server management system that replaces init, inetd
+ and cron on Apple Mac OS X versions 10.4 and above. It provides a common session
+ bus address for each user and deprecates the X11-enabled D-Bus launcher on OSX.
+ </para>
+
+ <para>
+ launchd allocates a socket and provides it with the unix path through the
+ DBUS_LAUNCHD_SESSION_BUS_SOCKET variable in launchd's environment. Every process
+ spawned by launchd (or dbus-daemon, if it was started by launchd) can access
+ it through its environment.
+ Other processes can query for the launchd socket by executing:
+ $ launchctl getenv DBUS_LAUNCHD_SESSION_BUS_SOCKET
+ This is normally done by the D-Bus client library so doesn't have to be done
+ manually.
+ </para>
+ <para>
+ launchd is not available on Microsoft Windows.
+ </para>
+ <sect3 id="transports-launchd-addresses">
+ <title>Server Address Format</title>
+ <para>
+ launchd addresses are identified by the "launchd:" 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>env</entry>
+ <entry>(environment variable)</entry>
+ <entry>path of the unix domain socket for the launchd created dbus-daemon.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </sect3>
+ </sect2>
<sect2 id="transports-tcp-sockets">
<title>TCP Sockets</title>
<para>
</informaltable>
</sect3>
</sect2>
+ </sect1>
+ <sect1 id="meta-transports">
+ <title>Meta Transports</title>
+ <para>
+ Meta transports are a kind of transport with special enhancements or
+ behavior. Currently available meta transports include: autolaunch
+ </para>
- </sect1>
+ <sect2 id="meta-transports-autolaunch">
+ <title>Autolaunch</title>
+ <para>The autolaunch transport provides a way for dbus clients to autodetect
+ a running dbus session bus and to autolaunch a session bus if not present.
+ </para>
+ <sect3 id="meta-transports-autolaunch-addresses">
+ <title>Server Address Format</title>
+ <para>
+ Autolaunch addresses uses the "autolaunch:" 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>scope</entry>
+ <entry>(string)</entry>
+ <entry>scope of autolaunch (Windows only)
+ <itemizedlist>
+ <listitem>
+ <para>
+ "*install-path" - limit session bus to dbus installation path.
+ The dbus installation path is determined from the location of
+ the shared dbus library. If the library is located in a 'bin'
+ subdirectory the installation root is the directory above,
+ otherwise the directory where the library lives is taken as
+ installation root.
+ <programlisting>
+ <install-root>/bin/[lib]dbus-1.dll
+ <install-root>/[lib]dbus-1.dll
+ </programlisting>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ "*user" - limit session bus to the recent user.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ other values - specify dedicated session bus like "release",
+ "debug" or other
+ </para>
+ </listitem>
+ </itemizedlist>
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </sect3>
- <sect1 id="naming-conventions">
+ <sect3 id="meta-transports-autolaunch-windows-implementation">
+ <title>Windows implementation</title>
+ <para>
+ On start, the server opens a platform specific transport, creates a mutex
+ and a shared memory section containing the related session bus address.
+ This mutex will be inspected by the dbus client library to detect a
+ running dbus session bus. The access to the mutex and the shared memory
+ section are protected by global locks.
+ </para>
+ <para>
+ In the recent implementation the autolaunch transport uses a tcp transport
+ on localhost with a port choosen from the operating system. This detail may
+ change in the future.
+ </para>
+ <para>
+ Disclaimer: The recent implementation is in an early state and may not
+ work in all cirumstances and/or may have security issues. Because of this
+ the implementation is not documentated yet.
+ </para>
+ </sect3>
+ </sect2>
+ </sect1>
+ <sect1 id="naming-conventions">
<title>Naming Conventions</title>
<para>
annotation.
</para>
</sect2>
+
+ <sect2 id="standard-interfaces-objectmanager">
+ <title><literal>org.freedesktop.DBus.ObjectManager</literal></title>
+ <para>
+ An API can optionally make use of this interface for one or
+ more sub-trees of objects. The root of each sub-tree implements
+ this interface so other applications can get all objects,
+ interfaces and properties in a single method call. It is
+ appropriate to use this interface if users of the tree of
+ objects are expected to be interested in all interfaces of all
+ objects in the tree; a more granular API should be used if
+ users of the objects are expected to be interested in a small
+ subset of the objects, a small subset of their interfaces, or
+ both.
+ </para>
+ <para>
+ The method that applications can use to get all objects and
+ properties is <literal>GetManagedObjects</literal>:
+ </para>
+ <para>
+ <programlisting>
+ org.freedesktop.DBus.ObjectManager.GetManagedObjects (out DICT<OBJPATH,DICT<STRING,DICT<STRING,VARIANT>>> objpath_interfaces_and_properties);
+ </programlisting>
+ </para>
+ <para>
+ The return value of this method is a dict whose keys are
+ object paths. All returned object paths are children of the
+ object path implementing this interface, i.e. their object
+ paths start with the ObjectManager's object path plus '/'.
+ </para>
+ <para>
+ Each value is a dict whose keys are interfaces names. Each
+ value in this inner dict is the same dict that would be
+ returned by the <link
+ linkend="standard-interfaces-properties">org.freedesktop.DBus.Properties.GetAll()</link>
+ method for that combination of object path and interface. If
+ an interface has no properties, the empty dict is returned.
+ </para>
+ <para>
+ Changes are emitted using the following two signals:
+ </para>
+ <para>
+ <programlisting>
+ org.freedesktop.DBus.ObjectManager.InterfacesAdded (OBJPATH object_path,
+ DICT<STRING,DICT<STRING,VARIANT>> interfaces_and_properties);
+ org.freedesktop.DBus.ObjectManager.InterfacesRemoved (OBJPATH object_path,
+ ARRAY<STRING> interfaces);
+ </programlisting>
+ </para>
+ <para>
+ The <literal>InterfacesAdded</literal> signal is emitted when
+ either a new object is added or when an existing object gains
+ one or more interfaces. The
+ <literal>InterfacesRemoved</literal> signal is emitted
+ whenever an object is removed or it loses one or more
+ interfaces. The second parameter of the
+ <literal>InterfacesAdded</literal> signal contains a dict with
+ the interfaces and properties (if any) that have been added to
+ the given object path. Similarly, the second parameter of the
+ <literal>InterfacesRemoved</literal> signal contains an array
+ of the interfaces that were removed. Note that changes on
+ properties on existing interfaces are not reported using this
+ interface - an application should also monitor the existing <link
+ linkend="standard-interfaces-properties">PropertiesChanged</link>
+ signal on each object.
+ </para>
+ <para>
+ Applications SHOULD NOT export objects that are children of an
+ object (directly or otherwise) implementing this interface but
+ which are not returned in the reply from the
+ <literal>GetManagedObjects()</literal> method of this
+ interface on the given object.
+ </para>
+ <para>
+ The intent of the <literal>ObjectManager</literal> interface
+ is to make it easy to write a robust client
+ implementation. The trivial client implementation only needs
+ to make two method calls:
+ </para>
+ <para>
+ <programlisting>
+ org.freedesktop.DBus.AddMatch (bus_proxy,
+ "type='signal',name='org.example.App',path_namespace='/org/example/App'");
+ objects = org.freedesktop.DBus.ObjectManager.GetManagedObjects (app_proxy);
+ </programlisting>
+ </para>
+ <para>
+ on the message bus and the remote application's
+ <literal>ObjectManager</literal>, respectively. Whenever a new
+ remote object is created (or an existing object gains a new
+ interface), the <literal>InterfacesAdded</literal> signal is
+ emitted, and since this signal contains all properties for the
+ interfaces, no calls to the
+ <literal>org.freedesktop.Properties</literal> interface on the
+ remote object are needed. Additionally, since the initial
+ <literal>AddMatch()</literal> rule already includes signal
+ messages from the newly created child object, no new
+ <literal>AddMatch()</literal> call is needed.
+ </para>
+
+ <para>
+ <emphasis>
+ The <literal>org.freedesktop.DBus.ObjectManager</literal>
+ interface was added in version 0.17 of the D-Bus
+ specification.
+ </emphasis>
+ </para>
+ </sect2>
</sect1>
<sect1 id="introspection-format">
</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.
- The message bus must send messages (of any type) with the
- <literal>DESTINATION</literal> field set to the specified recipient,
- regardless of whether the recipient has set up a match rule matching
- the message.
- </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.
+ Applications may send <firstterm>unicast messages</firstterm> to
+ a specific recipient or to the message bus itself, or
+ <firstterm>broadcast messages</firstterm> to all interested recipients.
+ See <xref linkend="message-bus-routing"/> for details.
</para>
</sect2>
<sect2 id="message-bus-routing">
<title>Message Bus Message Routing</title>
+
+ <para>
+ Messages may have a <literal>DESTINATION</literal> field (see <xref
+ linkend="message-protocol-header-fields"/>), resulting in a
+ <firstterm>unicast message</firstterm>. If the
+ <literal>DESTINATION</literal> field is present, it specifies a message
+ recipient by name. Method calls and replies normally specify this field.
+ The message bus must send messages (of any type) with the
+ <literal>DESTINATION</literal> field set to the specified recipient,
+ regardless of whether the recipient has set up a match rule matching
+ the message.
+ </para>
+
+ <para>
+ When the message bus receives a signal, if the
+ <literal>DESTINATION</literal> field is absent, it is considered to
+ be a <firstterm>broadcast signal</firstterm>, and is sent to all
+ applications with <firstterm>message matching rules</firstterm> that
+ match the message. Most signal messages are broadcasts.
+ </para>
+
+ <para>
+ Unicast signal messages (those with a <literal>DESTINATION</literal>
+ field) are not commonly used, but they are treated like any unicast
+ message: they are delivered to the specified receipient,
+ regardless of its match rules. One use for unicast signals is to
+ avoid a race condition in which a signal is emitted before the intended
+ recipient can call <xref linkend="bus-messages-add-match"/> to
+ receive that signal: if the signal is sent directly to that recipient
+ using a unicast message, it does not need to add a match rule at all,
+ and there is no race condition. Another use for unicast signals,
+ on message buses whose security policy prevents eavesdropping, is to
+ send sensitive information which should only be visible to one
+ recipient.
+ </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>
+
<para>
- FIXME
+ Message bus implementations may impose a security policy which
+ prevents certain messages from being sent or received.
+ When a message cannot be sent or received due to a security
+ policy, the message bus should send an error reply, unless the
+ original message had the <literal>NO_REPLY</literal> flag.
</para>
+
+ <sect3 id="message-bus-routing-eavesdropping">
+ <title>Eavesdropping</title>
+ <para>
+ Receiving a unicast message whose <literal>DESTINATION</literal>
+ indicates a different recipient is called
+ <firstterm>eavesdropping</firstterm>. On a message bus which acts as
+ a security boundary (like the standard system bus), the security
+ policy should usually prevent eavesdropping, since unicast messages
+ are normally kept private and may contain security-sensitive
+ information.
+ </para>
+
+ <para>
+ Eavesdropping is mainly useful for debugging tools, such as
+ the <literal>dbus-monitor</literal> tool in the reference
+ implementation of D-Bus. Tools which eavesdrop on the message bus
+ should be careful to avoid sending a reply or error in response to
+ messages intended for a different client.
+ </para>
+
+ <para>
+ Clients may attempt to eavesdrop by adding match rules
+ (see <xref linkend="message-bus-routing-match-rules"/>) containing
+ the <literal>eavesdrop='true'</literal> match. If the message bus'
+ security policy does not allow eavesdropping, the match rule can
+ still be added, but will not have any practical effect. For
+ compatibility with older message bus implementations, if adding such
+ a match rule results in an error reply, the client may fall back to
+ adding the same rule with the <literal>eavesdrop</literal> match
+ omitted.
+ </para>
+ </sect3>
+
<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.
+ An important part of the message bus routing protocol is match
+ rules. Match rules describe the messages that should be sent to a
+ client, based on the contents of the message. Broadcast signals
+ are only sent to clients which have a suitable match rule: this
+ avoids waking up client processes to deal with signals that are
+ not relevant to that client.
+ </para>
+ <para>
+ Messages that list a client as their <literal>DESTINATION</literal>
+ do not need to match the client's match rules, and are sent to that
+ client regardless. As a result, match rules are mainly used to
+ receive a subset of broadcast signals.
+ </para>
+ <para>
+ Match rules can also be used for eavesdropping
+ (see <xref linkend="message-bus-routing-eavesdropping"/>),
+ if the security policy of the message bus allows it.
</para>
<para>
Match rules are added using the AddMatch bus method
path match is path='/org/freedesktop/Hal/Manager'</entry>
</row>
<row>
+ <entry><literal>path_namespace</literal></entry>
+ <entry>An object path</entry>
+ <entry>
+ <para>
+ Matches messages which are sent from or to an
+ object for which the object path is either the
+ given value, or that value followed by one or
+ more path components.
+ </para>
+
+ <para>
+ For example,
+ <literal>path_namespace='/com/example/foo'</literal>
+ would match signals sent by
+ <literal>/com/example/foo</literal>
+ or by
+ <literal>/com/example/foo/bar</literal>,
+ but not by
+ <literal>/com/example/foobar</literal>.
+ </para>
+
+ <para>
+ Using both <literal>path</literal> and
+ <literal>path_namespace</literal> in the same match
+ rule is not allowed.
+ </para>
+
+ <para>
+ <emphasis>
+ This match key was added in version 0.16 of the
+ D-Bus specification and implemented by the bus
+ daemon in dbus 1.5.0 and later.
+ </emphasis>
+ </para>
+ </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
<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
+ match based on the arguments in the body of a message. Only arguments of type
+ STRING can be matched in this way. 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>
+ <entry>
+ <para>Argument path matches provide a specialised form of wildcard matching for
+ path-like namespaces. They can match arguments whose type is either STRING or
+ OBJECT_PATH. 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'.</para>
+
+ <para>This is intended for monitoring “directories” in file system-like
+ hierarchies, as used in the <citetitle>dconf</citetitle> configuration
+ system. An application interested in all nodes in a particular hierarchy would
+ monitor <literal>arg0path='/ca/example/foo/'</literal>. Then the service could
+ emit a signal with zeroth argument <literal>"/ca/example/foo/bar"</literal> to
+ represent a modification to the “bar” property, or a signal with zeroth
+ argument <literal>"/ca/example/"</literal> to represent atomic modification of
+ many properties within that directory, and the interested application would be
+ notified in both cases.</para>
+ <para>
+ <emphasis>
+ This match key was added in version 0.12 of the
+ D-Bus specification, implemented for STRING
+ arguments by the bus daemon in dbus 1.2.0 and later,
+ and implemented for OBJECT_PATH arguments in dbus 1.5.0
+ and later.
+ </emphasis>
+ </para>
+ </entry>
+ </row>
+ <row>
+ <entry><literal>arg0namespace</literal></entry>
+ <entry>Like a bus name, except that the string is not
+ required to contain a '.' (period)</entry>
+ <entry>
+ <para>Match messages whose first argument is of type STRING, and is a bus name
+ or interface name within the specified namespace. This is primarily intended
+ for watching name owner changes for a group of related bus names, rather than
+ for a single name or all name changes.</para>
+
+ <para>Because every valid interface name is also a valid
+ bus name, this can also be used for messages whose
+ first argument is an interface name.</para>
+
+ <para>For example, the match rule
+ <literal>member='NameOwnerChanged',arg0namespace='com.example.backend'</literal>
+ matches name owner changes for bus names such as
+ <literal>com.example.backend.foo</literal>,
+ <literal>com.example.backend.foo.bar</literal>, and
+ <literal>com.example.backend</literal> itself.</para>
+
+ <para>See also <xref linkend='bus-messages-name-owner-changed'/>.</para>
+ <para>
+ <emphasis>
+ This match key was added in version 0.16 of the
+ D-Bus specification and implemented by the bus
+ daemon in dbus 1.5.0 and later.
+ </emphasis>
+ </para>
+ </entry>
+ </row>
+ <row>
+ <entry><literal>eavesdrop</literal></entry>
+ <entry><literal>'true'</literal>, <literal>'false'</literal></entry>
+ <entry>Since D-Bus 1.5.6, match rules do not
+ match messages which have a <literal>DESTINATION</literal>
+ field unless the match rule specifically
+ requests this
+ (see <xref linkend="message-bus-routing-eavesdropping"/>)
+ by specifying <literal>eavesdrop='true'</literal>
+ in the match rule. <literal>eavesdrop='false'</literal>
+ restores the default behaviour. Messages are
+ delivered to their <literal>DESTINATION</literal>
+ regardless of match rules, so this match does not
+ affect normal delivery of unicast messages.
+ If the message bus has a security policy which forbids
+ eavesdropping, this match may still be used without error,
+ but will not have any practical effect.
+ In older versions of D-Bus, this match was not allowed
+ in match rules, and all match rules behaved as if
+ <literal>eavesdrop='true'</literal> had been used.
+ </entry>
</row>
</tbody>
</tgroup>
<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
+ 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
+ url="http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.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.
+ </para>
+
+ <para>
+ [FIXME the file format should be much better specified than "similar to
+ .desktop entries" esp. since desktop entries are already
+ badly-specified. ;-)]
+ These sections from the specification apply to service files as well:
+
+ <itemizedlist>
+ <listitem><para>General syntax</para></listitem>
+ <listitem><para>Comment format</para></listitem>
+ </itemizedlist>
<figure>
<title>Example service description file</title>
The environment variable should have precedence over the
root window property.
</para>
- <para>
- [FIXME specify location of .service files, probably using
- DESKTOP_DIRS etc. from basedir specification, though login session
- bus is not really desktop-specific]
- </para>
+ <para>The address of the login session message bus is given in the
+ <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment variable. If
+ DBUS_SESSION_BUS_ADDRESS is not set, or if it's set to the string
+ "autolaunch:", the system should use platform-specific methods of
+ locating a running D-Bus session server, or starting one if a running
+ instance cannot be found. Note that this mechanism is not recommended
+ for attempting to determine if a daemon is running. It is inherently
+ racy to attempt to make this determination, since the bus daemon may
+ be started just before or just after the determination is made.
+ Therefore, it is recommended that applications do not try to make this
+ determination for their functionality purposes, and instead they
+ should attempt to start the server.</para>
+
+ <sect4 id="message-bus-types-login-x-windows">
+ <title>X Windowing System</title>
+ <para>
+ For the X Windowing System, the application must locate the
+ window owner of the selection represented by the atom formed by
+ concatenating:
+ <itemizedlist>
+ <listitem>
+ <para>the literal string "_DBUS_SESSION_BUS_SELECTION_"</para>
+ </listitem>
+
+ <listitem>
+ <para>the current user's username</para>
+ </listitem>
+
+ <listitem>
+ <para>the literal character '_' (underscore)</para>
+ </listitem>
+
+ <listitem>
+ <para>the machine's ID</para>
+ </listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ The following properties are defined for the window that owns
+ this X selection:
+ <informaltable frame="all">
+ <tgroup cols="2">
+ <tbody>
+ <row>
+ <entry>
+ <para>Atom</para>
+ </entry>
+
+ <entry>
+ <para>meaning</para>
+ </entry>
+ </row>
+
+ <row>
+ <entry>
+ <para>_DBUS_SESSION_BUS_ADDRESS</para>
+ </entry>
+
+ <entry>
+ <para>the actual address of the server socket</para>
+ </entry>
+ </row>
+
+ <row>
+ <entry>
+ <para>_DBUS_SESSION_BUS_PID</para>
+ </entry>
+
+ <entry>
+ <para>the PID of the server process</para>
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+
+ <para>
+ At least the _DBUS_SESSION_BUS_ADDRESS property MUST be
+ present in this window.
+ </para>
+
+ <para>
+ If the X selection cannot be located or if reading the
+ properties from the window fails, the implementation MUST conclude
+ that there is no D-Bus server running and proceed to start a new
+ server. (See below on concurrency issues)
+ </para>
+
+ <para>
+ Failure to connect to the D-Bus server address thus obtained
+ MUST be treated as a fatal connection error and should be reported
+ to the application.
+ </para>
+
+ <para>
+ As an alternative, an implementation MAY find the information
+ in the following file located in the current user's home directory,
+ in subdirectory .dbus/session-bus/:
+ <itemizedlist>
+ <listitem>
+ <para>the machine's ID</para>
+ </listitem>
+
+ <listitem>
+ <para>the literal character '-' (dash)</para>
+ </listitem>
+
+ <listitem>
+ <para>the X display without the screen number, with the
+ following prefixes removed, if present: ":", "localhost:"
+ ."localhost.localdomain:". That is, a display of
+ "localhost:10.0" produces just the number "10"</para>
+ </listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ The contents of this file NAME=value assignment pairs and
+ lines starting with # are comments (no comments are allowed
+ otherwise). The following variable names are defined:
+ <informaltable
+ frame="all">
+ <tgroup cols="2">
+ <tbody>
+ <row>
+ <entry>
+ <para>Variable</para>
+ </entry>
+
+ <entry>
+ <para>meaning</para>
+ </entry>
+ </row>
+
+ <row>
+ <entry>
+ <para>DBUS_SESSION_BUS_ADDRESS</para>
+ </entry>
+
+ <entry>
+ <para>the actual address of the server socket</para>
+ </entry>
+ </row>
+
+ <row>
+ <entry>
+ <para>DBUS_SESSION_BUS_PID</para>
+ </entry>
+
+ <entry>
+ <para>the PID of the server process</para>
+ </entry>
+ </row>
+
+ <row>
+ <entry>
+ <para>DBUS_SESSION_BUS_WINDOWID</para>
+ </entry>
+
+ <entry>
+ <para>the window ID</para>
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+
+ <para>
+ At least the DBUS_SESSION_BUS_ADDRESS variable MUST be present
+ in this file.
+ </para>
+
+ <para>
+ Failure to open this file MUST be interpreted as absence of a
+ running server. Therefore, the implementation MUST proceed to
+ attempting to launch a new bus server if the file cannot be
+ opened.
+ </para>
+
+ <para>
+ However, success in opening this file MUST NOT lead to the
+ conclusion that the server is running. Thus, a failure to connect to
+ the bus address obtained by the alternative method MUST NOT be
+ considered a fatal error. If the connection cannot be established,
+ the implementation MUST proceed to check the X selection settings or
+ to start the server on its own.
+ </para>
+
+ <para>
+ If the implementation concludes that the D-Bus server is not
+ running it MUST attempt to start a new server and it MUST also
+ ensure that the daemon started as an effect of the "autolaunch"
+ mechanism provides the lookup mechanisms described above, so
+ subsequent calls can locate the newly started server. The
+ implementation MUST also ensure that if two or more concurrent
+ initiations happen, only one server remains running and all other
+ initiations are able to obtain the address of this server and
+ connect to it. In other words, the implementation MUST ensure that
+ the X selection is not present when it attempts to set it, without
+ allowing another process to set the selection between the
+ verification and the setting (e.g., by using XGrabServer /
+ XungrabServer).
+ </para>
+ </sect4>
+ <sect4>
+ <title></title>
+ <para>
+ On Unix systems, the session bus should search for .service files
+ in <literal>$XDG_DATA_DIRS/dbus-1/services</literal> as defined
+ by the
+ <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG Base Directory Specification</ulink>.
+ Implementations may also search additional locations, which
+ should be searched with lower priority than anything in
+ XDG_DATA_HOME, XDG_DATA_DIRS or their respective defaults;
+ for example, the reference implementation also
+ looks in <literal>${datadir}/dbus-1/services</literal> as
+ set at compile time.
+ </para>
+ <para>
+ As described in the XDG Base Directory Specification, software
+ packages should install their session .service files to their
+ configured <literal>${datadir}/dbus-1/services</literal>,
+ where <literal>${datadir}</literal> is as defined by the GNU
+ coding standards. System administrators or users can arrange
+ for these service files to be read by setting XDG_DATA_DIRS or by
+ symlinking them into the default locations.
+ </para>
+ </sect4>
</sect3>
<sect3 id="message-bus-types-system">
<title>System message bus</title>
projects / platform / upstream / dbus.git / blobdiff