<article id="index">
<articleinfo>
- <title>D-BUS Specification</title>
- <releaseinfo>Version 0.8</releaseinfo>
- <date>06 September 2003</date>
+ <title>D-Bus Specification</title>
+ <releaseinfo>Version 0.12</releaseinfo>
+ <date>7 November 2006</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.
</listitem>
</itemizedlist>
</para>
+
<para>
- The base D-BUS protocol is a peer-to-peer 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 D-BUS is the 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.
+ 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
+ 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 interoperablity, for example a file
+ 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>
+
</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 inteprets the body of the message.
+ 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.
+ <firstterm>arguments</firstterm>, which are typed values, such as an
+ integer or a byte array.
+ </para>
+
+ <para>
+ Both header and body use the same type system and format for
+ serializing data. Each type of value has a wire format.
+ 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>.
</para>
- <sect2 id="message-protocol-header-encoding">
- <title>Header Encoding</title>
+ <sect2 id="message-protocol-signatures">
+ <title>Type Signatures</title>
+
<para>
- Following the mandatory fields, there are zero or more named fields (see
- <xref linkend="message-protocol-header-fields"/>), and then nul bytes
- padding the header such that its total length in bytes is a multiple of
- 8.
+ 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
+ type of a value. Because ASCII characters are used, the type signature
+ will always form a valid ASCII string. A simple string compare
+ determines whether two type signatures are equivalent.
</para>
+
<para>
- The header MUST begin with the following mandatory fields in the following
- order:
- <informaltable>
- <tgroup cols="2">
- <thead>
- <row>
- <entry>Size</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>1 byte</entry>
- <entry>Endianness flag; ASCII 'l' for little-endian
- or ASCII 'B' for big-endian.</entry>
- </row>
- <row>
- <entry>1 byte</entry>
- <entry>Type of message. Unknown types MUST be ignored.
- Currently-defined types are described below.
- </entry>
- </row>
- <row>
- <entry>1 byte</entry>
- <entry>Bitwise OR of flags. Unknown flags
- MUST be ignored. Currently-defined flags are described below.
- </entry>
- </row>
- <row>
- <entry>1 byte</entry>
- <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.
- </entry>
- </row>
- <row>
- <entry>4 bytes</entry>
- <entry>An unsigned 32-bit integer in the
- message's byte order, indicating the total length in bytes of
- the header including named fields and any alignment padding.
- MUST be a multiple of 8.
- </entry>
- </row>
- <row>
- <entry>4 bytes</entry>
- <entry>An unsigned 32-bit integer in the
- message's byte order, indicating the total length in bytes of
- the message body.
- </entry>
- </row>
- <row>
- <entry>4 bytes</entry>
- <entry>The message's serial number, an unsigned 32-bit integer in
- the message's byte order. The serial number is a cookie used to
- identify message replies; thus all outstanding unreplied-to messages
- from the same connection MUST have a different serial number.
- Zero is not a valid serial number, but all other numbers are
- allowed.
- </entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
+ As a simple example, the type code for 32-bit integer (<literal>INT32</literal>) is
+ the ASCII character 'i'. So the signature for a block of values
+ containing a single <literal>INT32</literal> would be:
+ <programlisting>
+ "i"
+ </programlisting>
+ A block of values containing two <literal>INT32</literal> would have this signature:
+ <programlisting>
+ "ii"
+ </programlisting>
</para>
+
<para>
- Types that can appear in the second byte of the header:
- <informaltable>
- <tgroup cols="3">
- <thead>
- <row>
- <entry>Conventional name</entry>
- <entry>Decimal value</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>INVALID</entry>
- <entry>0</entry>
- <entry>This is an invalid type, if seen in a message
- the connection should be dropped immediately.</entry>
- </row>
- <row>
- <entry>METHOD_CALL</entry>
- <entry>1</entry>
- <entry>Method call.</entry>
- </row>
- <row>
- <entry>METHOD_RETURN</entry>
- <entry>2</entry>
- <entry>Method reply with returned data.</entry>
- </row>
- <row>
- <entry>ERROR</entry>
- <entry>3</entry>
- <entry>Error reply. If the first argument exists and is a
- string, it is an error message.</entry>
- </row>
- <row>
- <entry>SIGNAL</entry>
- <entry>4</entry>
- <entry>Signal emission.</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
+ All <firstterm>basic</firstterm> types work like
+ <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 four <firstterm>container</firstterm>
+ types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, <literal>VARIANT</literal>,
+ and <literal>DICT_ENTRY</literal>.
</para>
+
<para>
- Flags that can appear in the third byte of the header:
- <informaltable>
- <tgroup cols="3">
- <thead>
- <row>
- <entry>Conventional name</entry>
- <entry>Hex value</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>NO_REPLY_EXPECTED</entry>
- <entry>0x1</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>
- </row>
- <row>
- <entry>AUTO_ACTIVATION</entry>
- <entry>0x2</entry>
- <entry>This message automatically activates the
- addressed service before the message is delivered.</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
+ <literal>STRUCT</literal> has a type code, ASCII character 'r', but this type
+ code does not appear in signatures. Instead, ASCII characters
+ '(' and ')' are used to mark the beginning and end of the struct.
+ So for example, a struct containing two integers would have this
+ signature:
+ <programlisting>
+ "(ii)"
+ </programlisting>
+ Structs can be nested, so for example a struct containing
+ an integer and another struct:
+ <programlisting>
+ "(i(ii))"
+ </programlisting>
+ The value block storing that struct would contain three integers; the
+ type signature allows you to distinguish "(i(ii))" from "((ii)i)" or
+ "(iii)" or "iii".
</para>
- </sect2>
- <sect2 id="message-protocol-header-fields">
- <title>Header Fields</title>
<para>
- In addition to the required header information mentioned
- in <xref linkend="message-protocol-header-encoding"/>,
- the header must contain the required named header
- fields and zero or more of the optional named
- header fields. Future versions of this protocol
- specification may add new fields. Implementations must
- ignore fields they do not understand. Implementations
- must not invent their own header fields; only changes to
- this specification may introduce new header fields.
+ 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>
+ <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
+ complete type following the array is the type of each array element. So
+ the simple example is:
+ <programlisting>
+ "ai"
+ </programlisting>
+ which is an array of 32-bit integers. But an array can be of any type,
+ such as this array-of-struct-with-two-int32-fields:
+ <programlisting>
+ "a(ii)"
+ </programlisting>
+ Or this array of array of integer:
+ <programlisting>
+ "aai"
+ </programlisting>
</para>
<para>
- Header field names MUST consist of a single byte, possible values
- of which are defined below. Following the name, the field MUST have
- a type code represented as a single unsigned byte, and then a
- properly-aligned value of that type. See <xref
- linkend="message-protocol-arguments"/> for a description of how each
- type is encoded. If an implementation sees a header field name that
- it does not understand, it MUST ignore that field.
+ The phrase <firstterm>single complete type</firstterm> deserves some
+ definition. A single complete type is a basic type code, a variant type code,
+ an array with its element type, or a struct with its fields.
+ So the following signatures are not single complete types:
+ <programlisting>
+ "aa"
+ </programlisting>
+ <programlisting>
+ "(ii"
+ </programlisting>
+ <programlisting>
+ "ii)"
+ </programlisting>
+ And the following signatures contain multiple complete types:
+ <programlisting>
+ "ii"
+ </programlisting>
+ <programlisting>
+ "aiai"
+ </programlisting>
+ <programlisting>
+ "(ii)(ii)"
+ </programlisting>
+ Note however that a single complete type may <emphasis>contain</emphasis>
+ multiple other single complete types.
</para>
<para>
- Here are the currently-defined named header fields:
- <informaltable>
- <tgroup cols="5">
- <thead>
- <row>
- <entry>Conventional Name</entry>
- <entry>Decimal Value</entry>
- <entry>Type</entry>
- <entry>Required</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>INVALID</entry>
- <entry>0</entry>
- <entry>INVALID</entry>
- <entry>no</entry>
- <entry>Not a valid field name (error if it appears in a message)</entry>
- </row>
- <row>
- <entry>PATH</entry>
- <entry>1</entry>
- <entry>OBJECT_PATH</entry>
- <entry>yes</entry>
- <entry>The object to send the message to; objects are identified by
- a path, "/foo/bar"</entry>
- </row>
- <row>
- <entry>INTERFACE</entry>
- <entry>2</entry>
- <entry>STRING</entry>
- <entry>yes</entry>
- <entry>The interface to invoke a method call on, or
- that a signal is emitted from. e.g. "org.freedesktop.Introspectable"</entry>
- </row>
- <row>
- <entry>MEMBER</entry>
- <entry>3</entry>
- <entry>STRING</entry>
- <entry>yes</entry>
- <entry>The member, either the method name or signal name.
- e.g. "Frobate"</entry>
- </row>
- <row>
- <entry>ERROR_NAME</entry>
- <entry>4</entry>
- <entry>STRING</entry>
- <entry>no</entry>
- <entry>The name of the error that occurred, for errors</entry>
- </row>
- <row>
- <entry>REPLY_SERIAL</entry>
- <entry>5</entry>
- <entry>UINT32</entry>
- <entry>no</entry>
- <entry>The serial number of the message this message is a reply
- to. (The serial number is one of the mandatory header fields,
- see <xref linkend="message-protocol-header-encoding"/>.)</entry>
- </row>
- <row>
- <entry>DESTINATION</entry>
- <entry>6</entry>
- <entry>STRING</entry>
- <entry>no</entry>
- <entry>The name of the service this message should be routed to.
- Only used in combination with the message bus, see
- <xref linkend="message-bus"/>.</entry>
- </row>
- <row>
- <entry>SENDER</entry>
- <entry>7</entry>
- <entry>STRING</entry>
- <entry>no</entry>
- <entry>Sender service. The name of the base service that sent
- this message. The message bus fills in this field; the field is
- only meaningful in combination with the message bus.</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
+ <literal>VARIANT</literal> has ASCII character 'v' as its type code. A marshaled value of
+ type <literal>VARIANT</literal> will have the signature of a single complete type as part
+ of the <emphasis>value</emphasis>. This signature will be followed by a
+ marshaled value of that type.
+ </para>
+
+ <para>
+ 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>
- </sect2>
- <sect2 id="message-protocol-header-padding">
- <title>Header Alignment Padding</title>
<para>
- To allow implementations to keep the header and the body in a single
- buffer while keeping data types aligned, the total length of the header
- must be a multiple of 8 bytes. To achieve this, the header MUST be padded
- with nul bytes to align its total length on an 8-byte boundary.
- The minimum number of padding bytes MUST be used. Because zero is an
- invalid field name, implementations can distinguish padding (which must be
- zero initialized) from additional named fields.
+ 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>
- </sect2>
- <sect2 id="message-protocol-arguments">
- <title>Message Arguments</title>
<para>
- The message body is made up of arguments. Each argument is a type code,
- represented by a single unsigned byte, followed by the aligned value of
- the argument in a type-dependent format. Alignment padding between the
- typecode and the value is initialized to zero.
+ 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>
<row>
- <entry>Type name</entry>
+ <entry>Conventional Name</entry>
<entry>Code</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
- <entry>INVALID</entry>
+ <entry><literal>INVALID</literal></entry>
<entry>0 (ASCII NUL)</entry>
- <entry>Not a valid type code (error if it appears in a message)</entry>
- </row><row>
- <entry>NIL</entry>
- <entry>118 (ASCII 'v') </entry>
- <entry>Marks a "void"/"unset"/"nonexistent"/"null" argument</entry>
+ <entry>Not a valid type code, used to terminate signatures</entry>
</row><row>
- <entry>BYTE</entry>
+ <entry><literal>BYTE</literal></entry>
<entry>121 (ASCII 'y')</entry>
<entry>8-bit unsigned integer</entry>
</row><row>
- <entry>BOOLEAN</entry>
+ <entry><literal>BOOLEAN</literal></entry>
<entry>98 (ASCII 'b')</entry>
- <entry>Boolean value, 0 is FALSE and 1 is TRUE. Everything else is invalid.</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>INT32</entry>
+ <entry><literal>INT32</literal></entry>
<entry>105 (ASCII 'i')</entry>
<entry>32-bit signed integer</entry>
</row><row>
- <entry>UINT32</entry>
+ <entry><literal>UINT32</literal></entry>
<entry>117 (ASCII 'u')</entry>
<entry>32-bit unsigned integer</entry>
</row><row>
- <entry>INT64</entry>
+ <entry><literal>INT64</literal></entry>
<entry>120 (ASCII 'x')</entry>
<entry>64-bit signed integer</entry>
</row><row>
- <entry>UINT64</entry>
+ <entry><literal>UINT64</literal></entry>
<entry>116 (ASCII 't')</entry>
<entry>64-bit unsigned integer</entry>
</row><row>
- <entry>DOUBLE</entry>
+ <entry><literal>DOUBLE</literal></entry>
<entry>100 (ASCII 'd')</entry>
<entry>IEEE 754 double</entry>
</row><row>
- <entry>STRING</entry>
+ <entry><literal>STRING</literal></entry>
<entry>115 (ASCII 's')</entry>
- <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be zero terminated. </entry>
+ <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated.</entry>
</row><row>
- <entry>CUSTOM</entry>
- <entry>99 (ASCII 'c')</entry>
- <entry>A named byte array, used for custom types</entry>
- </row><row>
- <entry>ARRAY</entry>
+ <entry><literal>OBJECT_PATH</literal></entry>
+ <entry>111 (ASCII 'o')</entry>
+ <entry>Name of an object instance</entry>
+ </row><row>
+ <entry><literal>SIGNATURE</literal></entry>
+ <entry>103 (ASCII 'g')</entry>
+ <entry>A type signature</entry>
+ </row><row>
+ <entry><literal>ARRAY</literal></entry>
<entry>97 (ASCII 'a')</entry>
<entry>Array</entry>
</row><row>
- <entry>DICT</entry>
- <entry>109 (ASCII 'm')</entry>
- <entry>A dictionary of key/value pairs</entry>
+ <entry><literal>STRUCT</literal></entry>
+ <entry>114 (ASCII 'r'), 40 (ASCII '('), 41 (ASCII ')')</entry>
+ <entry>Struct</entry>
</row><row>
- <entry>OBJECT_PATH</entry>
- <entry>111 (ASCII 'o')</entry>
- <entry>Name of an object</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>
</tbody>
</tgroup>
</informaltable>
</para>
+
+ </sect2>
+
+ <sect2 id="message-protocol-marshaling">
+ <title>Marshaling (Wire Format)</title>
+
+ <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.
+ </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
+ 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
+ endian.
+ </para>
+
<para>
- The types are encoded as follows:
+ Each value in a block of bytes is aligned "naturally," for example
+ 4-byte values are aligned to a 4-byte boundary, and 8-byte values to an
+ 8-byte boundary. To properly align a value, <firstterm>alignment
+ padding</firstterm> may be necessary. The alignment padding must always
+ be the minimum required padding to properly align the following value;
+ and it must always be made up of nul bytes. The alignment padding must
+ not be left uninitialized (it can't contain garbage), and more padding
+ than required must not be used.
+ </para>
+
+ <para>
+ Given all this, the types are marshaled on the wire as follows:
<informaltable>
- <tgroup cols="2">
+ <tgroup cols="3">
<thead>
<row>
- <entry>Type name</entry>
+ <entry>Conventional Name</entry>
<entry>Encoding</entry>
+ <entry>Alignment</entry>
</row>
</thead>
<tbody>
<row>
- <entry>INVALID</entry>
- <entry>Not applicable; cannot be encoded.</entry>
+ <entry><literal>INVALID</literal></entry>
+ <entry>Not applicable; cannot be marshaled.</entry>
+ <entry>N/A</entry>
</row><row>
- <entry>NIL</entry>
- <entry>No data is encoded; the type code is followed immediately
- by the type code of the next argument.</entry>
+ <entry><literal>BYTE</literal></entry>
+ <entry>A single 8-bit byte.</entry>
+ <entry>1</entry>
</row><row>
- <entry>BYTE</entry>
- <entry>A byte.</entry>
+ <entry><literal>BOOLEAN</literal></entry>
+ <entry>As for <literal>UINT32</literal>, but only 0 and 1 are valid values.</entry>
+ <entry>4</entry>
</row><row>
- <entry>BOOLEAN</entry>
- <entry>A byte, with valid values 0 and 1.</entry>
+ <entry><literal>INT16</literal></entry>
+ <entry>16-bit signed integer in the message's byte order.</entry>
+ <entry>2</entry>
</row><row>
- <entry>INT32</entry>
- <entry>32-bit signed integer in the message's byte order, aligned to 4-byte boundary.</entry>
+ <entry><literal>UINT16</literal></entry>
+ <entry>16-bit unsigned integer in the message's byte order.</entry>
+ <entry>2</entry>
</row><row>
- <entry>UINT32</entry>
- <entry>32-bit unsigned integer in the message's byte order, aligned to 4-byte boundary.</entry>
+ <entry><literal>INT32</literal></entry>
+ <entry>32-bit signed integer in the message's byte order.</entry>
+ <entry>4</entry>
</row><row>
- <entry>INT64</entry>
- <entry>64-bit signed integer in the message's byte order, aligned to 8-byte boundary.</entry>
+ <entry><literal>UINT32</literal></entry>
+ <entry>32-bit unsigned integer in the message's byte order.</entry>
+ <entry>4</entry>
</row><row>
- <entry>UINT64</entry>
- <entry>64-bit unsigned integer in the message's byte order, aligned to 8-byte boundary.</entry>
+ <entry><literal>INT64</literal></entry>
+ <entry>64-bit signed integer in the message's byte order.</entry>
+ <entry>8</entry>
</row><row>
- <entry>DOUBLE</entry>
- <entry>64-bit IEEE 754 double in the message's byte order, aligned to 8-byte boundary.</entry>
+ <entry><literal>UINT64</literal></entry>
+ <entry>64-bit unsigned integer in the message's byte order.</entry>
+ <entry>8</entry>
</row><row>
- <entry>STRING</entry>
- <entry>UINT32 aligned to 4-byte boundary indicating the string's
+ <entry><literal>DOUBLE</literal></entry>
+ <entry>64-bit IEEE 754 double in the message's byte order.</entry>
+ <entry>8</entry>
+ </row><row>
+ <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
byte.
</entry>
+ <entry>
+ 4 (for the length)
+ </entry>
</row><row>
- <entry>CUSTOM</entry>
- <entry>A string (encoded as the STRING type above) giving the
- name of the type followed by an UINT32 aligned to 4-byte boundary
- indicating the data length in bytes, followed by the data.
- The string has some restrictions on its content, see
- <xref linkend="message-protocol-names"/>.
+ <entry><literal>OBJECT_PATH</literal></entry>
+ <entry>Exactly the same as <literal>STRING</literal> except the
+ content must be a valid object path (see below).
+ </entry>
+ <entry>
+ 4 (for the length)
+ </entry>
+ </row><row>
+ <entry><literal>SIGNATURE</literal></entry>
+ <entry>The same as <literal>STRING</literal> except the length is a single
+ byte (thus signatures have a maximum length of 255)
+ and the content must be a valid signature (see below).
+ </entry>
+ <entry>
+ 1
</entry>
</row><row>
- <entry>ARRAY</entry>
- <entry>A sequence of bytes giving the element type of the array, terminated
- by a type different from ARRAY (just one byte for one-dimensional arrays, but
- larger for multi-dimensional arrays), followed by an UINT32 (aligned to 4 bytes)
- giving the length of the array data in bytes. This is followed by each array entry
- encoded the way it would normally be encoded, except arrays, which are encoded
- without the type information, since that is already declared above. Arrays containing
- NIL are not allowed.
+ <entry><literal>ARRAY</literal></entry>
+ <entry>
+ A <literal>UINT32</literal> giving the length of the array data in bytes, followed by
+ alignment padding to the alignment boundary of the array element type,
+ followed by each array element. The array length is from the
+ end of the alignment padding to the end of the last element,
+ i.e. it does not include the padding after the length,
+ or any padding after the last element.
+ Arrays have a maximum length defined to be 2 to the 26th power or
+ 67108864. Implementations must not send or accept arrays exceeding this
+ length.
+ </entry>
+ <entry>
+ 4 (for the length)
</entry>
</row><row>
- <entry>DICT</entry>
- <entry>UINT32 giving the length of the dictionary data in bytes.
- This is followed by a number of keyname/value pairs, where the
- keyname is encoded as a STRING above, and the value is encoded
- as a byte with typecode and how that type normally would be encoded
- alone.
+ <entry><literal>STRUCT</literal></entry>
+ <entry>
+ A struct must start on an 8-byte boundary regardless of the
+ type of the struct fields. The struct value consists of each
+ field marshaled in sequence starting from that 8-byte
+ alignment boundary.
+ </entry>
+ <entry>
+ 8
+ </entry>
+ </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" is OK, "ii" is not.
+ </entry>
+ <entry>
+ 1 (alignment of the signature)
</entry>
</row><row>
- <entry>OBJECT_PATH</entry>
- <entry>Encoded as if it were a STRING.
+ <entry><literal>DICT_ENTRY</literal></entry>
+ <entry>
+ Identical to STRUCT.
+ </entry>
+ <entry>
+ 8
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
- </sect2>
-
- <sect2 id="message-protocol-names">
- <title>Valid names</title>
- <para>
- The various names in D-BUS messages have some restrictions.
- </para>
- <sect3 id="message-protocol-names-interface">
- <title>Interface names</title>
+
+ <sect3 id="message-protocol-marshaling-object-path">
+ <title>Valid Object Paths</title>
+
<para>
- Interfaces have names with type STRING, meaning that
- they must be valid UTF-8. However, there are also some
- additional restrictions that apply to interface names
- specifically:
+ An object path is a name used to refer to an object instance.
+ 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.
+ </para>
+
+ <para>
+ The following rules define a valid object path. Implementations must
+ not send or accept messages with invalid object paths.
<itemizedlist>
- <listitem><para>They are composed of 1 or more elements separated by
- a period ('.') character. All elements must contain at least
- one character.
- </para>
+ <listitem>
+ <para>
+ The path may be of any length.
+ </para>
</listitem>
- <listitem><para>Each element must only contain the ASCII characters
- "[A-Z][a-z][0-9]_" and must not begin with a digit.
- </para>
+ <listitem>
+ <para>
+ The path must begin with an ASCII '/' (integer 47) character,
+ and must consist of elements separated by slash characters.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Each element must only contain the ASCII characters
+ "[A-Z][a-z][0-9]_"
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ No element may be the empty string.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Multiple '/' characters cannot occur in sequence.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ A trailing '/' character is not allowed unless the
+ path is the root path (a single '/' character).
+ </para>
</listitem>
-
- <listitem><para>They 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 256 bytes in length.</para></listitem>
- <listitem><para>They must be at least 1 byte in length.</para></listitem>
</itemizedlist>
</para>
+
</sect3>
- <sect3 id="message-protocol-names-service">
- <title>Service names</title>
- <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 the range "[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.
- </para>
- </sect3>
- <sect3 id="message-protocol-names-method">
- <title>Method names</title>
+
+
+ <sect3 id="message-protocol-marshaling-signature">
+ <title>Valid Signatures</title>
<para>
- Method names:
+ An implementation must not send or accept invalid signatures.
+ Valid signatures will conform to the following rules:
<itemizedlist>
- <listitem><para>Must only contain the ASCII characters
- "[A-Z][a-z][0-9]_" and may not begin with a
- digit.</para></listitem>
- <listitem><para>Must not contain the '.' (period) character</para></listitem>
- <listitem><para>Must not exceed 256 bytes in length</para></listitem>
- <listitem><para>Must be at least 1 byte in length</para></listitem>
+ <listitem>
+ <para>
+ The signature ends with a nul byte.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The signature is a list of single complete types.
+ Arrays must have element types, and structs must
+ have both open and close parentheses.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Only type codes and open and close parentheses are
+ allowed in the signature. The <literal>STRUCT</literal> type code
+ is not allowed in signatures, because parentheses
+ are used instead.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The maximum depth of container type nesting is 32 array type
+ codes and 32 open parentheses. This implies that the maximum
+ total depth of recursion is 64, for an "array of array of array
+ of ... struct of struct of struct of ..." where there are 32
+ array and 32 struct.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The maximum length of a signature is 255.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Signatures must be nul-terminated.
+ </para>
+ </listitem>
</itemizedlist>
</para>
</sect3>
- <sect3 id="message-protocol-names-path">
- <title>Path names</title>
- <para>
- A path (type OBJECT_PATH) must begin with an ASCII '/' (slash)
- character. Paths may not end with a slash character unless the path is
- the one-byte string "/". Two slash characters may not appear adjacent
- to one another (the empty string is not a valid "subdirectory"). Paths
- may not exceed 256 bytes in length.
- </para>
- </sect3>
- <sect3 id="message-protocol-names-error">
- <title>Error names</title>
- <para>
- Error names have the same restrictions as interface names.
- </para>
- </sect3>
- <sect3 id="message-protocol-names-custom">
- <title>Custom types</title>
- <para>
- Custom type names for values of type CUSTOM follow the same
- restrictions as interface names.
- </para>
- </sect3>
+
</sect2>
- <sect2 id="message-protocol-types">
- <title>Message types</title>
+ <sect2 id="message-protocol-messages">
+ <title>Message Format</title>
+
<para>
- Each of the message types (METHOD_CALL, METHOD_RETURN, ERROR, and
- SIGNAL) has its own expected usage conventions and header fields.
+ A message consists of a header and a body. The header is a block of
+ values with a fixed signature and meaning. The body is a separate block
+ of values, with a signature specified in the header.
</para>
- <sect3 id="message-protocol-types-method">
- <title>Method Calls, Returns, and Errors</title>
- <para>
- Some messages invoke an operation on a remote object. These are
- called method call messages and have the type tag METHOD_CALL. Such
- messages map naturally to methods on objects in a typical program.
- </para>
- <para>
- A method call message is expected to have a MEMBER header field
- indicating the name of the method. Optionally, the message has an
- INTERFACE field giving the interface the method is a part of. In the
- absence of an INTERFACE field, if two interfaces on the same object have
- a method with the same name, it is undefined which of the two methods
- will be invoked. Implementations may also choose to return an error in
- this ambiguous case. However, if a method name is unique
- implementations should not require an interface field.
- </para>
- <para>
- Method call messages also include a PATH field indicating the
- object to invoke the method on. If the call is passing through
- a message bus, the message will also have a SERVICE field giving
- the service to receive the message.
- </para>
- <para>
- When an application handles a method call message, it is expected to
- return a reply. The reply is identified by a REPLY_SERIAL header field
- indicating the serial number of the METHOD_CALL being replied to. The
- reply can have one of two types; either METHOD_RETURN or ERROR.
- </para>
- <para>
- If the reply has type METHOD_RETURN, the arguments to the reply message
- are the return value(s) or "out parameters" of the method call.
- If the reply has type ERROR, then an "exception" has been thrown,
- and the call fails; no return value will be provided. It makes
- no sense to send multiple replies to the same method call.
- </para>
- <para>
- Even if a method call has no return values, a METHOD_RETURN
- reply is expected, so the caller will know the method
- was successfully processed.
- </para>
- <para>
- The METHOD_RETURN or ERROR reply message MUST have the REPLY_SERIAL
- header field. If this field is missing, it should be treated as
- a corrupt message.
- </para>
- <para>
- If a METHOD_CALL message has the flag NO_REPLY_EXPECTED,
- then as an optimization the application receiving the method
- call may choose to omit the reply message (regardless of
- whether the reply would have been METHOD_RETURN or ERROR).
- However, it is also acceptable to ignore the NO_REPLY_EXPECTED
- flag and reply anyway.
- </para>
- <para>
- If a message has the flag AUTO_ACTIVATION, 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.
- </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
- programming language, such as C++, or may map a method call written
- 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 METHOD_CALL), or "out" (which implies
- returned in the METHOD_RETURN). 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"
- 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.
- </para>
- <para>
- Given a method with zero or one return values, followed by zero or more
- arguments, where each argument may be "in", "out", or "inout", the
- caller constructs a message by appending each "in" or "inout" argument,
- in order. "out" arguments are not represented in the caller's message.
- </para>
- <para>
- The recipient constructs a reply by appending first the return value
- if any, then each "out" or "inout" argument, in order.
- "in" arguments are not represented in the reply message.
- </para>
- </sect4>
-
- </sect3>
-
- <sect3 id="message-protocol-types-signal">
- <title>Signal Emission</title>
- <para>
- Unlike method calls, signal emissions have no replies.
- A signal emission is simply a single message of type SIGNAL.
- It must have three header fields: PATH giving the object
- the signal was emitted from, plus INTERFACE and MEMBER giving
- the fully-qualified name of the signal.
- </para>
- </sect3>
-
- <sect3 id="message-protocol-types-notation">
- <title>Notation in this document</title>
- <para>
- 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)
- </programlisting>
- This means INTERFACE = org.freedesktop.DBus, MEMBER = ActivateService,
- METHOD_CALL arguments are STRING and UINT32, METHOD_RETURN argument
- is UINT32. Remember that the MEMBER field can't contain any '.' (period)
- characters so it's known that the last part of the name in
- the "IDL" is the member name.
- </para>
- <para>
- In C++ that might end up looking like this:
- <programlisting>
- unsigned int org::freedesktop::DBus::ActivateService (const char *service_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);
- </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
- in C++, using STL or Qt, using varargs, or whatever you wanted.
- </para>
- <para>
- Signals are written as follows:
- <programlisting>
- org.freedesktop.DBus.ServiceLost (STRING service_name)
- </programlisting>
- Signals don't specify "in" vs. "out" because only
- a single direction is possible.
- </para>
- <para>
- In this ad hoc notation, the special type name ANY means any type
- other than NIL, and the special type name ANY_OR_NIL means any valid
- type.
- </para>
- <para>
- It isn't especially encouraged to use this lame pseudo-IDL in actual
- API implementations; you might use the native notation for the
- language you're using, or you might use COM or CORBA IDL, for example.
- </para>
- </sect3>
- </sect2>
- </sect1>
-
- <sect1 id="auth-protocol">
- <title>Authentication Protocol</title>
- <para>
- Before the flow of messages begins, two applications must
- authenticate. A simple plain-text protocol is used for
- authentication; this protocol is a SASL profile, and maps fairly
- directly from the SASL specification. The message encoding is
- NOT used here, only plain text messages.
- </para>
- <para>
- In examples, "C:" and "S:" indicate lines sent by the client and
- server respectively.
- </para>
- <sect2 id="auth-protocol-overview">
- <title>Protocol Overview</title>
<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
- command, then the \r\n ending the line. The protocol is
- case-sensitive. All bytes must be in the ASCII character set.
-
- Commands from the client to the server are as follows:
-
- <itemizedlist>
- <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
- <listitem><para>CANCEL</para></listitem>
- <listitem><para>BEGIN</para></listitem>
- <listitem><para>DATA <data in hex encoding></para></listitem>
- <listitem><para>ERROR [human-readable error explanation]</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>DATA <data in hex encoding></para></listitem>
- <listitem><para>ERROR</para></listitem>
- </itemizedlist>
+ The length of the header must be a multiple of 8, allowing the body to
+ begin on an 8-byte boundary when storing the entire message in a single
+ buffer. If the header does not naturally end on an 8-byte boundary
+ up to 7 bytes of nul-initialized alignment padding must be added.
</para>
- </sect2>
- <sect2 id="auth-nul-byte">
- <title>Special credentials-passing nul byte</title>
+
<para>
- Immediately after connecting to the server, the client must send a
- 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
- 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
- received from the client is not a nul byte, the server may disconnect
- that client.
+ The message body need not end on an 8-byte boundary.
</para>
+
<para>
- A nul byte in any context other than the initial byte is an error;
- the protocol is ASCII-only.
+ The maximum length of a message, including header, header alignment padding,
+ and body is 2 to the 27th power or 134217728. Implementations must not
+ send or accept messages exceeding this size.
</para>
+
<para>
- The credentials sent along with the nul byte may be used with the
- SASL mechanism EXTERNAL.
+ The signature of the header is:
+ <programlisting>
+ "yyyyuua(yv)"
+ </programlisting>
+ Written out more readably, this is:
+ <programlisting>
+ BYTE, BYTE, BYTE, BYTE, UINT32, UINT32, ARRAY of STRUCT of (BYTE,VARIANT)
+ </programlisting>
</para>
- </sect2>
- <sect2 id="auth-command-auth">
- <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.
- </para>
+ These values have the following meanings:
+ <informaltable>
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Value</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>1st <literal>BYTE</literal></entry>
+ <entry>Endianness flag; ASCII 'l' for little-endian
+ or ASCII 'B' for big-endian. Both header and body are
+ in this endianness.</entry>
+ </row>
+ <row>
+ <entry>2nd <literal>BYTE</literal></entry>
+ <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.
+ </entry>
+ </row>
+ <row>
+ <entry>4th <literal>BYTE</literal></entry>
+ <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.
+ </entry>
+ </row>
+ <row>
+ <entry>1st <literal>UINT32</literal></entry>
+ <entry>Length in bytes of the message body, starting
+ from the end of the header. The header ends after
+ its alignment padding to an 8-boundary.
+ </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.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>ARRAY</literal> of <literal>STRUCT</literal> of (<literal>BYTE</literal>,<literal>VARIANT</literal>)</entry>
+ <entry>An array of zero or more <firstterm>header
+ fields</firstterm> where the byte is the field code, and the
+ variant is the field value. The message type determines
+ which fields are required.
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ <para>
+ <firstterm>Message types</firstterm> that can appear in the second byte
+ of the header are:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Conventional name</entry>
+ <entry>Decimal value</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><literal>INVALID</literal></entry>
+ <entry>0</entry>
+ <entry>This is an invalid type.</entry>
+ </row>
+ <row>
+ <entry><literal>METHOD_CALL</literal></entry>
+ <entry>1</entry>
+ <entry>Method call.</entry>
+ </row>
+ <row>
+ <entry><literal>METHOD_RETURN</literal></entry>
+ <entry>2</entry>
+ <entry>Method reply with returned data.</entry>
+ </row>
+ <row>
+ <entry><literal>ERROR</literal></entry>
+ <entry>3</entry>
+ <entry>Error reply. If the first argument exists and is a
+ string, it is an error message.</entry>
+ </row>
+ <row>
+ <entry><literal>SIGNAL</literal></entry>
+ <entry>4</entry>
+ <entry>Signal emission.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ <para>
+ Flags that can appear in the third byte of the header:
+ <informaltable>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Conventional name</entry>
+ <entry>Hex value</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><literal>NO_REPLY_EXPECTED</literal></entry>
+ <entry>0x1</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 and the only harm
+ from doing so is extra network traffic.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>NO_AUTO_START</literal></entry>
+ <entry>0x2</entry>
+ <entry>The bus must not launch an owner
+ for the destination name in response to this message.
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+
+ <sect3 id="message-protocol-header-fields">
+ <title>Header Fields</title>
+
+ <para>
+ The array at the end of the header contains <firstterm>header
+ fields</firstterm>, where each field is a 1-byte field code followed
+ by a field value. A header must contain the required header fields for
+ its message type, and zero or more of any optional header
+ fields. Future versions of this protocol specification may add new
+ fields. Implementations must ignore fields they do not
+ understand. Implementations must not invent their own header fields;
+ only changes to this specification may introduce new header fields.
+ </para>
+
+ <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
+ (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 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.
+ </para>
+
+ <para>
+ Here are the currently-defined header fields:
+ <informaltable>
+ <tgroup cols="5">
+ <thead>
+ <row>
+ <entry>Conventional Name</entry>
+ <entry>Decimal Code</entry>
+ <entry>Type</entry>
+ <entry>Required In</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><literal>INVALID</literal></entry>
+ <entry>0</entry>
+ <entry>N/A</entry>
+ <entry>not allowed</entry>
+ <entry>Not a valid field name (error if it appears in a message)</entry>
+ </row>
+ <row>
+ <entry><literal>PATH</literal></entry>
+ <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,
+ or the object a signal is emitted from.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>INTERFACE</literal></entry>
+ <entry>2</entry>
+ <entry><literal>STRING</literal></entry>
+ <entry><literal>SIGNAL</literal></entry>
+ <entry>
+ The interface to invoke a method call on, or
+ that a signal is emitted from. Optional for
+ method calls, required for signals.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>MEMBER</literal></entry>
+ <entry>3</entry>
+ <entry><literal>STRING</literal></entry>
+ <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
+ <entry>The member, either the method name or signal name.</entry>
+ </row>
+ <row>
+ <entry><literal>ERROR_NAME</literal></entry>
+ <entry>4</entry>
+ <entry><literal>STRING</literal></entry>
+ <entry><literal>ERROR</literal></entry>
+ <entry>The name of the error that occurred, for errors</entry>
+ </row>
+ <row>
+ <entry><literal>REPLY_SERIAL</literal></entry>
+ <entry>5</entry>
+ <entry><literal>UINT32</literal></entry>
+ <entry><literal>ERROR</literal>, <literal>METHOD_RETURN</literal></entry>
+ <entry>The serial number of the message this message is a reply
+ to. (The serial number is the second <literal>UINT32</literal> in the header.)</entry>
+ </row>
+ <row>
+ <entry><literal>DESTINATION</literal></entry>
+ <entry>6</entry>
+ <entry><literal>STRING</literal></entry>
+ <entry>optional</entry>
+ <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>
+ <row>
+ <entry><literal>SENDER</literal></entry>
+ <entry>7</entry>
+ <entry><literal>STRING</literal></entry>
+ <entry>optional</entry>
+ <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>
+ <entry><literal>SIGNATURE</literal></entry>
+ <entry>8</entry>
+ <entry><literal>SIGNATURE</literal></entry>
+ <entry>optional</entry>
+ <entry>The signature of the message body.
+ If omitted, it is assumed to be the
+ empty signature "" (i.e. the body must be 0-length).</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ </sect3>
+ </sect2>
+
+ <sect2 id="message-protocol-names">
+ <title>Valid Names</title>
+ <para>
+ 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 bus names, interfaces, and members.
+ </para>
+ <sect3 id="message-protocol-names-interface">
+ <title>Interface names</title>
+ <para>
+ Interfaces have names with type <literal>STRING</literal>, meaning that
+ they must be valid UTF-8. However, there are also some
+ additional restrictions that apply to interface names
+ specifically:
+ <itemizedlist>
+ <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>
+ </listitem>
+ <listitem><para>Each element must only contain the ASCII characters
+ "[A-Z][a-z][0-9]_" and must not begin with a digit.
+ </para>
+ </listitem>
+
+ <listitem><para>Interface names must contain at least one '.' (period)
+ character (and thus at least two elements).
+ </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-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>
+ Note that the hyphen ('-') character is allowed in bus names but
+ not in interface names.
+ </para>
+ </sect3>
+ <sect3 id="message-protocol-names-member">
+ <title>Member names</title>
+ <para>
+ Member (i.e. method or signal) names:
+ <itemizedlist>
+ <listitem><para>Must only contain the ASCII characters
+ "[A-Z][a-z][0-9]_" and may not begin with a
+ digit.</para></listitem>
+ <listitem><para>Must not contain the '.' (period) character.</para></listitem>
+ <listitem><para>Must not exceed the maximum name length.</para></listitem>
+ <listitem><para>Must be at least 1 byte in length.</para></listitem>
+ </itemizedlist>
+ </para>
+ </sect3>
+ <sect3 id="message-protocol-names-error">
+ <title>Error names</title>
+ <para>
+ Error names have the same restrictions as interface names.
+ </para>
+ </sect3>
+ </sect2>
+
+ <sect2 id="message-protocol-types">
+ <title>Message Types</title>
+ <para>
+ Each of the message types (<literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, <literal>ERROR</literal>, and
+ <literal>SIGNAL</literal>) has its own expected usage conventions and header fields.
+ This section describes these conventions.
+ </para>
+ <sect3 id="message-protocol-types-method">
+ <title>Method Calls</title>
+ <para>
+ Some messages invoke an operation on a remote object. These are
+ called method call messages and have the type tag <literal>METHOD_CALL</literal>. Such
+ messages map naturally to methods on objects in a typical program.
+ </para>
+ <para>
+ 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
+ a method with the same name, it is undefined which of the two methods
+ will be invoked. Implementations may also choose to return an error in
+ this ambiguous case. However, if a method name is unique
+ 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 name of the connection
+ to receive the message.
+ </para>
+ <para>
+ 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>
+ If the reply has type <literal>METHOD_RETURN</literal>, the arguments to the reply message
+ are the return value(s) or "out parameters" of the method call.
+ If the reply has type <literal>ERROR</literal>, then an "exception" has been thrown,
+ and the call fails; no return value will be provided. It makes
+ no sense to send multiple replies to the same method call.
+ </para>
+ <para>
+ Even if a method call has no return values, a <literal>METHOD_RETURN</literal>
+ reply is required, so the caller will know the method
+ was successfully processed.
+ </para>
+ <para>
+ The <literal>METHOD_RETURN</literal> or <literal>ERROR</literal> reply message must have the <literal>REPLY_SERIAL</literal>
+ header field.
+ </para>
+ <para>
+ If a <literal>METHOD_CALL</literal> message has the flag <literal>NO_REPLY_EXPECTED</literal>,
+ then as an optimization the application receiving the method
+ call may choose to omit the reply message (regardless of
+ whether the reply would have been <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>).
+ However, it is also acceptable to ignore the <literal>NO_REPLY_EXPECTED</literal>
+ flag and reply anyway.
+ </para>
+ <para>
+ 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
+ programming language, such as C++, or may map a method call written
+ 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"
+ 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.
+ </para>
+ <para>
+ Given a method with zero or one return values, followed by zero or more
+ arguments, where each argument may be "in", "out", or "inout", the
+ caller constructs a message by appending each "in" or "inout" argument,
+ in order. "out" arguments are not represented in the caller's message.
+ </para>
+ <para>
+ The recipient constructs a reply by appending first the return value
+ if any, then each "out" or "inout" argument, in order.
+ "in" arguments are not represented in the reply message.
+ </para>
+ <para>
+ Error replies are normally mapped to exceptions in languages that have
+ 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">
+ <title>Signal Emission</title>
+ <para>
+ Unlike method calls, signal emissions have no replies.
+ 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 <literal>INTERFACE</literal> header is required
+ for signals, though it is optional for method calls.
+ </para>
+ </sect3>
+
+ <sect3 id="message-protocol-types-errors">
+ <title>Errors</title>
+ <para>
+ Messages of type <literal>ERROR</literal> are most commonly replies
+ to a <literal>METHOD_CALL</literal>, but may be returned in reply
+ to any kind of message. The message bus for example
+ will return an <literal>ERROR</literal> in reply to a signal emission if
+ the bus does not have enough memory to send the signal.
+ </para>
+ <para>
+ An <literal>ERROR</literal> may have any arguments, but if the first
+ argument is a <literal>STRING</literal>, it must be an error message.
+ The error message may be logged or shown to the user
+ in some way.
+ </para>
+ </sect3>
+
+ <sect3 id="message-protocol-types-notation">
+ <title>Notation in this document</title>
+ <para>
+ 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.StartServiceByName (in STRING name, in UINT32 flags,
+ out UINT32 resultcode)
+ </programlisting>
+ 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
+ the "IDL" is the member name.
+ </para>
+ <para>
+ In C++ that might end up looking like this:
+ <programlisting>
+ 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::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
+ in C++, using STL or Qt, using varargs, or whatever you wanted.
+ </para>
+ <para>
+ Signals are written as follows:
+ <programlisting>
+ org.freedesktop.DBus.NameLost (STRING name)
+ </programlisting>
+ Signals don't specify "in" vs. "out" because only
+ a single direction is possible.
+ </para>
+ <para>
+ It isn't especially encouraged to use this lame pseudo-IDL in actual
+ API implementations; you might use the native notation for the
+ language you're using, or you might use COM or CORBA IDL, for example.
+ </para>
+ </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">
+ <title>Authentication Protocol</title>
+ <para>
+ Before the flow of messages begins, two applications must
+ authenticate. A simple plain-text protocol is used for
+ authentication; this protocol is a SASL profile, and maps fairly
+ directly from the SASL specification. The message encoding is
+ NOT used here, only plain text messages.
+ </para>
+ <para>
+ In examples, "C:" and "S:" indicate lines sent by the client and
+ server respectively.
+ </para>
+ <sect2 id="auth-protocol-overview">
+ <title>Protocol Overview</title>
+ <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
+ command, then the \r\n ending the line. The protocol is
+ case-sensitive. All bytes must be in the ASCII character set.
+
+ Commands from the client to the server are as follows:
+
+ <itemizedlist>
+ <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
+ <listitem><para>CANCEL</para></listitem>
+ <listitem><para>BEGIN</para></listitem>
+ <listitem><para>DATA <data in hex encoding></para></listitem>
+ <listitem><para>ERROR [human-readable error explanation]</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 <GUID in hex></para></listitem>
+ <listitem><para>DATA <data in hex encoding></para></listitem>
+ <listitem><para>ERROR</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>
+ <para>
+ Immediately after connecting to the server, the client must send a
+ 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
+ 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
+ received from the client is not a nul byte, the server may disconnect
+ that client.
+ </para>
+ <para>
+ A nul byte in any context other than the initial byte is an error;
+ the protocol is ASCII-only.
+ </para>
+ <para>
+ The credentials sent along with the nul byte may be used with the
+ SASL mechanism EXTERNAL.
+ </para>
+ </sect2>
+ <sect2 id="auth-command-auth">
+ <title>AUTH command</title>
+ <para>
+ If an AUTH command has no arguments, it is a request to list
+ 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.
+ command 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.
+ command from the client 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>
<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
+ and that 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.
+ 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
+ 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
+ The server must not accept additional commands using this protocol
after the OK command has been sent.
</para>
+ <para>
+ 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">
<title>ERROR Command</title>
</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-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>
<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>
</listitem>
<listitem>
<para>
- 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.
+ 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.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The client locates the cookie, and generates its own hex-encoded
+ randomly-generated challenge string. The client then
+ concatenates 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.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The server generates the same concatenated string used by the
+ client and computes its SHA-1 hash. It compares the hash with
+ the hash received from the client; if the two hashes match, the
+ client is authenticated.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ Each server has a "cookie context," which is a name that identifies a
+ set of cookies that apply to that server. A sample context might be
+ "org_freedesktop_session_bus". Context names must be valid ASCII,
+ 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_general" that's used by servers that do not specify
+ otherwise.
+ </para>
+ <para>
+ Cookies are stored in a user's home directory, in the directory
+ <filename>~/.dbus-keyrings/</filename>. This directory must
+ not be readable or writable by other users. If it is,
+ clients and servers must ignore it. The directory
+ contains cookie files named after the cookie context.
+ </para>
+ <para>
+ A cookie file contains one cookie per line. Each line
+ has three space-separated fields:
+ <itemizedlist>
+ <listitem>
+ <para>
+ The cookie ID number, which must be a non-negative integer and
+ may not be used twice in the same file.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The cookie's creation time, in UNIX seconds-since-the-epoch
+ format.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 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.
+ They must do so with this procedure:
+ <itemizedlist>
+ <listitem>
+ <para>
+ Create a lockfile name by appending ".lock" to the name of the
+ cookie file. The server should attempt to create this file
+ using <literal>O_CREAT | O_EXCL</literal>. If file creation
+ fails, the lock fails. Servers should retry for a reasonable
+ period of time, then they may choose to delete an existing lock
+ to keep users from having to manually delete a stale
+ lock. <footnote><para>Lockfiles are used instead of real file
+ locking <literal>fcntl()</literal> because real locking
+ implementations are still flaky on network
+ filesystems.</para></footnote>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Once the lockfile has been created, the server loads the cookie
+ file. It should then delete any cookies that are old (the
+ timeout can be fairly short), or more than a reasonable
+ time in the future (so that cookies never accidentally
+ become permanent, if the clock was set far into the future
+ at some point). If no recent keys remain, the
+ server may generate a new key.
</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 pruned and possibly added-to cookie file
+ must be resaved atomically (using a temporary
+ file which is rename()'d).
</para>
</listitem>
<listitem>
<para>
- The server generates the same concatenated string used by the
- client and computes its SHA-1 hash. It compares the hash with
- the hash received from the client; if the two hashes match, the
- client is authenticated.
+ The lock must be dropped by deleting the lockfile.
</para>
</listitem>
</itemizedlist>
</para>
<para>
- Each server has a "cookie context," which is a name that identifies a
- set of cookies that apply to that server. A sample context might be
- "org_freedesktop_session_bus". Context names must be valid ASCII,
- 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
- otherwise.
+ Clients need not lock the file in order to load it,
+ because servers are required to save the file atomically.
</para>
+ </sect3>
+ </sect2>
+ </sect1>
+ <sect1 id="addresses">
+ <title>Server Addresses</title>
+ <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.
+ Each value is escaped.
+ </para>
+ <para>
+ For example:
+ <programlisting>unix:path=/tmp/dbus-test</programlisting>
+ 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. This globally unique ID must
+ be created by filling the first 4 bytes with a 32-bit UNIX time since the
+ epoch, and the remaining 12 bytes with random bytes. If present, the GUID
+ may be used to distinguish one server from another. A server should use a
+ different GUID 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 GUIDs to distinguish
+ the kinds of connection.
+ </para>
+
+ <para>
+ The intent of the GUID 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.
+ </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
+ separated by a semi-colon. The library will then try to connect
+ to the first address and if that fails, it'll try to connect to
+ 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>
+
+ <sect2 id="transports-unix-domain-sockets">
+ <title>Unix Domain Sockets</title>
+ <para>
+ 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>
+
+ <para>
+ 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>
+ </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="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>
+ The UUID must contain 128 bits of data and be hex-encoded (meaning, the hex
+ string contains 32 ASCII characters). 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 recommended algorithm is to put the current time in seconds
+ since the UNIX epoch in the last 32 bits of the UUID, and to put randomly-generated bits
+ in the first 96 bits 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);
+ </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>
+ </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>
+ </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>
- Cookies are stored in a user's home directory, in the directory
- <filename>~/.dbus-keyrings/</filename>. This directory must
- not be readable or writable by other users. If it is,
- clients and servers must ignore it. The directory
- contains cookie files named after the cookie context.
+ 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>
- A cookie file contains one cookie per line. Each line
- has three space-separated fields:
+ 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>
- The cookie ID number, which must be a non-negative integer and
- may not be used twice in the same file.
- </para>
- </listitem>
- <listitem>
- <para>
- The cookie's creation time, in UNIX seconds-since-the-epoch
- format.
- </para>
- </listitem>
- <listitem>
- <para>
- The cookie itself, a hex-encoded random block of bytes.
+ 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>
- </itemizedlist>
- </para>
- <para>
- Only server processes modify the cookie file.
- They must do so with this procedure:
- <itemizedlist>
+
<listitem>
<para>
- Create a lockfile name by appending ".lock" to the name of the
- cookie file. The server should attempt to create this file
- using <literal>O_CREAT | O_EXCL</literal>. If file creation
- fails, the lock fails. Servers should retry for a reasonable
- period of time, then they may choose to delete an existing lock
- to keep users from having to manually delete a stale
- lock. <footnote><para>Lockfiles are used instead of real file
- locking <literal>fcntl()</literal> because real locking
- implementations are still flaky on network
- filesystems.</para></footnote>
+ 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>
- Once the lockfile has been created, the server loads the cookie
- file. It should then delete any cookies that are old (the
- timeout can be fairly short), or more than a reasonable
- time in the future (so that cookies never accidentally
- become permanent, if the clock was set far into the future
- at some point). If no recent keys remain, the
- server may generate a new key.
+ 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>
- The pruned and possibly added-to cookie file
- must be resaved atomically (using a temporary
- file which is rename()'d).
+ 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>
- The lock must be dropped by deleting the lockfile.
+ 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>
- Clients need not lock the file in order to load it,
- because servers are required to save the file atomically.
+ 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>
- </sect3>
- </sect2>
- </sect1>
- <sect1 id="addresses">
- <title>Server Addresses</title>
- <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?]
- </para>
- <para>
- For example:
- <programlisting>unix:path=/tmp/dbus-test</programlisting>
- Which is the address to a unix socket with the path /tmp/dbus-test.
- </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
- separated by a semi-colon. The library will then try to connect
- to the first address and if that fails, it'll try to connect to
- the next one specified, and so forth. For example
- <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
- </para>
- <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>
+ <para>
+ The flags argument contains any of the following values logically ORed
+ together:
- <sect1 id="standard-messages">
- <title>Standard Peer-to-Peer 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 METHOD_CALL
- message <literal>org.freedesktop.Peer.Ping</literal>, an application
- should do nothing other than reply with a METHOD_RETURN as usual.
- </para>
- </sect2>
+ <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>
- <sect2 id="standard-messages-get-props">
- <title><literal>org.freedesktop.Props.Get</literal></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>
- </para>
- </sect2>
- </sect1>
+ 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.
- <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 peer-to-peer 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>.
- </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>SERVICE</literal> field (see <xref
- linkend="message-protocol-header-fields"/>). When the message bus
- receives a message, if the <literal>SERVICE</literal> field is absent, the
- message is taken to be a standard peer-to-peer message and interpreted
- by the message bus itself. For example, sending
- an <literal>org.freedesktop.Peer.Ping</literal> message with no
- <literal>SERVICE</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>SERVICE</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>SERVICE</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.
- </para>
- </sect2>
+ </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.
- <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>
- <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.
- </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
- DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT 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 DBUS_SERVICE_FLAGS_PROHIBIT_REPLACEMENT
- 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>
+ 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>
</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.
+ 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>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ </sect3>
+ </sect2>
+ <sect2 id="message-bus-starting-services">
+ <title>Message Bus Starting Services</title>
<para>
- [FIXME go into detail about broadcast, multicast, unicast, etc.]
+ 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>
- </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.
+ 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 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"/>.
+ 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
+ [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.
+ 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]
- Name=org.gnome.ConfigurationDatabase
+ Names=org.freedesktop.ConfigurationDatabase;org.gnome.GConf;
Exec=/usr/libexec/gconfd-2
</programlisting>
</figure>
</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?]
+ 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_ACTIVATION_ADDRESS</literal> set to the address of the
- message bus so it can connect and register the appropriate services.
+ <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-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-add-match">
+ <title><literal>org.freedesktop.DBus.AddMatch</literal></title>
<para>
As a method:
<programlisting>
- void NoMemory ()
+ AddMatch (in STRING rule)
</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>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-service-does-not-exist">
- <title><literal>org.freedesktop.DBus.Error.ServiceDoesNotExist</literal></title>
+ <sect3 id="bus-messages-remove-match">
+ <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title>
<para>
As a method:
<programlisting>
- void ServiceDoesNotExist (in STRING error)
+ RemoveMatch (in STRING rule)
</programlisting>
- </para>
- <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.
- </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 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>
+
</sect2>
</sect1>
This glossary defines some of the terms used in this specification.
</para>
- <glossentry id="term-activation"><glossterm>Activation</glossterm>
+ <glossentry id="term-bus-name"><glossterm>Bus Name</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>
- <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="peer-to-peer"><glossterm>Peer-to-peer</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>
projects / platform / upstream / dbus.git / blobdiff