\input texinfo  @c -*- coding: utf-8 -*-
@setfilename ../../info/dbus.info
@c %**start of header
@settitle Using of D-Bus
@include docstyle.texi
@c @setchapternewpage odd
@c %**end of header

@syncodeindex vr cp
@syncodeindex fn cp

@copying
Copyright @copyright{} 2007--2020 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being ``A GNU Manual'',
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License''.

(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
modify this GNU manual.''
@end quotation
@end copying

@dircategory Emacs lisp libraries
@direntry
* D-Bus: (dbus).                Using D-Bus in Emacs.
@end direntry

@titlepage
@title Using D-Bus in Emacs
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage


@contents


@node Top, Overview, (dir), (dir)
@top D-Bus integration in Emacs

This manual documents an API for usage of D-Bus in Emacs.  D-Bus is a
message bus system, a simple way for applications to talk to one
another.  An overview of D-Bus can be found at
@uref{https://dbus.freedesktop.org/}.

@ifnottex
@insertcopying
@end ifnottex

@menu
* Overview::                    An overview of D-Bus.
* Inspection::                  Inspection of D-Bus services.
* Type Conversion::             Mapping Lisp types and D-Bus types.
* Synchronous Methods::         Calling methods in a blocking way.
* Asynchronous Methods::        Calling methods non-blocking.
* Receiving Method Calls::      Offering own methods.
* Signals::                     Sending and receiving signals.
* Alternative Buses::           Alternative buses and environments.
* Errors and Events::           Errors and events.
* Index::                       Index including concepts, functions, variables.

* GNU Free Documentation License:: The license for this documentation.
@end menu


@node Overview
@chapter An overview of D-Bus
@cindex overview

D-Bus is an inter-process communication mechanism for applications
residing on the same host.  The communication is based on
@dfn{messages}.  Data in the messages is carried in a structured way,
it is not just a byte stream.

The communication is connection oriented to two kinds of message
buses: a so called @dfn{system bus}, and a @dfn{session bus}.  On a
given machine, there is always one single system bus for miscellaneous
system-wide communication, like changing of hardware configuration.
On the other hand, the session bus is always related to a single
user's session.

Every client application, which is connected to a bus, registers under
a @dfn{unique name} at the bus.  This name is used for identifying the
client application.  Such a unique name starts always with a colon,
and looks like @samp{:1.42}.

Additionally, a client application can register itself to a so called
@dfn{known name}, which is a series of identifiers separated by dots,
as in @samp{org.gnu.Emacs}.  If several applications register to the
same known name, these registrations are queued, and only the first
application which has registered for the known name is reachable via
this name.  If this application disconnects from the bus, the next
queued unique name becomes the owner of this known name.

An application can install one or several objects under its name.
Such objects are identified by an @dfn{object path}, which looks
similar to paths in a filesystem.  An example of such an object path
could be @samp{/org/gnu/Emacs/}.

Applications might send a request to an object, that means sending a
message with some data as input parameters, and receiving a message
from that object with the result of this message, the output
parameters.  Such a request is called @dfn{method} in D-Bus.

The other form of communication are @dfn{signals}.  The underlying
message is emitted from an object and will be received by all other
applications which have registered for such a signal.

All methods and signals an object supports are called @dfn{interface}
of the object.  Interfaces are specified under a hierarchical name in
D-Bus; an object can support several interfaces.  Such an interface
name could be @samp{org.gnu.Emacs.TextEditor} or
@samp{org.gnu.Emacs.FileManager}.


@node Inspection
@chapter Inspection of D-Bus services.
@cindex inspection

@menu
* Version::                     Determining the D-Bus version.
* Bus names::                   Discovering D-Bus names.
* Introspection::               Knowing the details of D-Bus services.
* Nodes and Interfaces::        Detecting object paths and interfaces.
* Methods and Signal::          Applying the functionality.
* Properties and Annotations::  What else to know about interfaces.
* Arguments and Signatures::    The final details.
@end menu


@node Version
@section D-Bus version.

D-Bus has evolved over the years.  New features have been added with
new D-Bus versions.  There are two variables, which allow the determination
of the D-Bus version used.

@defvar dbus-compiled-version
This variable, a string, determines the version of D-Bus Emacs is
compiled against.  If it cannot be determined the value is @code{nil}.
@end defvar

@defvar dbus-runtime-version
The other D-Bus version to be checked is the version of D-Bus Emacs
runs with.  This string can be different from @code{dbus-compiled-version}.
It is also @code{nil}, if it cannot be determined at runtime.
@end defvar


@node Bus names
@section Bus names.

There are several basic functions which inspect the buses for
registered names.  Internally they use the basic interface
@samp{org.freedesktop.DBus}, which is supported by all objects of a bus.

@defun dbus-list-activatable-names &optional bus
This function returns the D-Bus service names, which can be activated
for @var{bus}.  It must be either the symbol @code{:system} (the
default) or the symbol @code{:session}.  An activatable service is
described in a service registration file.  Under GNU/Linux, such files
are located at @file{/usr/share/dbus-1/system-services/} (for the
@code{:system} bus) or @file{/usr/share/dbus-1/services/}.  An
activatable service is not necessarily registered at @var{bus} already.

The result is a list of strings, which is @code{nil} when there are no
activatable service names at all.  Example:

@lisp
;; Check, whether the document viewer can be accessed via D-Bus.
(member "org.gnome.evince.Daemon"
        (dbus-list-activatable-names :session))
@end lisp
@end defun

@defun dbus-list-names bus
This function returns all service names, which are registered at D-Bus
@var{bus}.  The result is a list of strings, which is @code{nil} when
there are no registered service names at all.  Well known names are
strings like @samp{org.freedesktop.DBus}.  Names starting with
@samp{:} are unique names for services.

@var{bus} must be either the symbol @code{:system} or the symbol
@code{:session}.
@end defun

@defun dbus-list-known-names bus
This function retrieves all registered services which correspond to a
known name in @var{bus}.  A service has a known name if it doesn't
start with @samp{:}.  The result is a list of strings, which is
@code{nil} when there are no known names at all.

@var{bus} must be either the symbol @code{:system} or the symbol
@code{:session}.
@end defun

@defun dbus-list-queued-owners bus service
For a given service, registered at D-Bus @var{bus} under the name
@var{service}, this function returns all queued unique names.  The
result is a list of strings, or @code{nil} when there are no queued
names for @var{service} at all.

@var{bus} must be either the symbol @code{:system} or the symbol
@code{:session}.  @var{service} must be a known service name as
string.
@end defun

@defun dbus-get-name-owner bus service
For a given service, registered at D-Bus @var{bus} under the name
@var{service}, this function returns the unique name of the name
owner.  The result is a string, or @code{nil} when there is no name
owner of @var{service}.

@var{bus} must be either the symbol @code{:system} or the symbol
@code{:session}.  @var{service} must be a known service name as
string.
@end defun

@defun dbus-ping bus service &optional timeout
This function checks whether the service name @var{service} is
registered at D-Bus @var{bus}.  If @var{service} has not yet started,
it is autostarted if possible.  The result is either @code{t} or
@code{nil}.

@var{bus} must be either the symbol @code{:system} or the symbol
@code{:session}.  @var{service} must be a string.  @var{timeout}, a
nonnegative integer, specifies the maximum number of milliseconds
before @code{dbus-ping} must return.  The default value is 25,000.
Example:

@lisp
(message
 "%s screensaver on board."
 (cond
  ((dbus-ping :session "org.gnome.ScreenSaver" 100) "Gnome")
  ((dbus-ping :session "org.freedesktop.ScreenSaver" 100) "KDE")
  (t "No")))
@end lisp

To check whether @var{service} is already running without autostarting
it, you can instead write:

@lisp
(member service (dbus-list-known-names bus))
@end lisp
@end defun

@defun dbus-get-unique-name bus
@anchor{dbus-get-unique-name}
This function returns the unique name, under which Emacs is registered
at D-Bus @var{bus}, as a string.

@var{bus} must be either the symbol @code{:system} or the symbol
@code{:session}.
@end defun


@node Introspection
@section Knowing the details of D-Bus services.

D-Bus services publish their interfaces.  This can be retrieved and
analyzed during runtime, in order to understand the used
implementation.

The resulting introspection data are in XML format.  The root
introspection element is always a @code{node} element.  It might have
a @code{name} attribute, which denotes the (absolute) object path an
interface is introspected.

The root @code{node} element may have @code{node} and @code{interface}
children.  A child @code{node} element must have a @code{name}
attribute, this case it is the relative object path to the root
@code{node} element.

An @code{interface} element has just one attribute, @code{name}, which
is the full name of that interface.  The default interface
@samp{org.freedesktop.DBus.Introspectable} is always present.  Example:

@example
<node name="/org/bluez">
  <interface name="org.freedesktop.DBus.Introspectable">
    @dots{}
  </interface>
  <interface name="org.bluez.Manager">
    @dots{}
  </interface>
  <interface name="org.bluez.Database">
    @dots{}
  </interface>
  <interface name="org.bluez.Security">
    @dots{}
  </interface>
  <node name="service_audio"/>
  <node name="service_input"/>
  <node name="service_network"/>
  <node name="service_serial"/>
</node>
@end example

Children of an @code{interface} element can be @code{method},
@code{signal} and @code{property} elements.  A @code{method} element
stands for a D-Bus method of the surrounding interface.  The element
itself has a @code{name} attribute, showing the method name.  Children
elements @code{arg} stand for the arguments of a method.  Example:

@example
<method name="ResolveHostName">
  <arg name="interface" type="i" direction="in"/>
  <arg name="protocol" type="i" direction="in"/>
  <arg name="name" type="s" direction="in"/>
  <arg name="aprotocol" type="i" direction="in"/>
  <arg name="flags" type="u" direction="in"/>
  <arg name="interface" type="i" direction="out"/>
  <arg name="protocol" type="i" direction="out"/>
  <arg name="name" type="s" direction="out"/>
  <arg name="aprotocol" type="i" direction="out"/>
  <arg name="address" type="s" direction="out"/>
  <arg name="flags" type="u" direction="out"/>
</method>
@end example

@code{arg} elements can have the attributes @code{name}, @code{type}
and @code{direction}.  The @code{name} attribute is optional.  The
@code{type} attribute stands for the @dfn{signature} of the argument
in D-Bus.  For a discussion of D-Bus types and their Lisp
representation see @ref{Type Conversion}.@footnote{D-Bus signatures
are explained in the D-Bus specification
@uref{https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-signatures}.}
The @code{direction} attribute of an @code{arg} element can be only
@samp{in} or @samp{out}; in case it is omitted, it defaults to
@samp{in}.

A @code{signal} element of an @code{interface} has a similar
structure.  The @code{direction} attribute of an @code{arg} child
element can be only @samp{out} here; which is also the default value.
Example:

@example
<signal name="StateChanged">
  <arg name="state" type="i"/>
  <arg name="error" type="s"/>
</signal>
@end example

A @code{property} element has no @code{arg} child
element.  It just has the attributes @code{name}, @code{type} and
@code{access}, which are all mandatory.  The @code{access} attribute
allows the values @samp{readwrite}, @samp{read}, and @samp{write}.
Example:

@example
<property name="Status" type="u" direction="read"/>
@end example

@code{annotation} elements can be children of @code{interface},
@code{method}, @code{signal}, and @code{property} elements.  Unlike
properties, which can change their values during lifetime of a D-Bus
object, annotations are static.  Often they are used for code
generators of D-Bus language bindings.  Example:

@example
<annotation name="de.berlios.Pinot.GetStatistics" value="pinotDBus"/>
@end example

Annotations have just @code{name} and @code{value} attributes, both
must be strings.

@defun dbus-introspect bus service path
This function returns all interfaces and sub-nodes of @var{service},
registered at object path @var{path} at bus @var{bus}.

@var{bus} must be either the symbol @code{:system} or the symbol
@code{:session}.  @var{service} must be a known service name, and
@var{path} must be a valid object path.  The last two parameters are
strings.  The result, the introspection data, is a string in XML
format.  Example:

@lisp
(dbus-introspect
 :system "org.freedesktop.Hal"
 "/org/freedesktop/Hal/devices/computer")

@result{} "<!DOCTYPE node PUBLIC
    "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
    "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
    <node>
      <interface name="org.freedesktop.Hal.Device">
        <method name="GetAllProperties">
          <arg name="properties" direction="out" type="a@{sv@}"/>
        </method>
        @dots{}
        <signal name="PropertyModified">
          <arg name="num_updates" type="i"/>
          <arg name="updates" type="a(sbb)"/>
        </signal>
      </interface>
      @dots{}
    </node>"
@end lisp

This example informs us, that the service @samp{org.freedesktop.Hal}
at object path @samp{/org/freedesktop/Hal/devices/computer} offers the
interface @samp{org.freedesktop.Hal.Device} (and 2 other interfaces
not documented here).  This interface contains the method
@samp{GetAllProperties}, which needs no input parameters, but returns
as output parameter an array of dictionary entries (key-value pairs).
Every dictionary entry has a string as key, and a variant as value.

The interface offers also a signal, which returns 2 parameters: an
integer, and an array consisting of elements which are a struct of a
string and 2 boolean values.@footnote{ The interfaces of the service
@samp{org.freedesktop.Hal} are described in
@c Previous link is gone.  Since HAL is now obsolete, this URL
@c (unchanged in ~ 4 years) feels like it might go too...
@uref{https://people.freedesktop.org/~dkukawka/hal-spec-git/hal-spec.html#interfaces,
the HAL specification}.}
@end defun

@defun dbus-introspect-xml bus service path
This function serves a similar purpose to the function
@code{dbus-introspect}.  The returned value is a parsed XML tree,
which can be used for further analysis.  Example:

@lisp
(dbus-introspect-xml
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main")

@result{} (node ((name . "/org/freedesktop/xesam/searcher/main"))
     (interface ((name . "org.freedesktop.xesam.Search"))
       (method ((name . "GetHitData"))
         (arg ((name . "search") (type . "s") (direction . "in")))
         (arg ((name . "hit_ids") (type . "au") (direction . "in")))
         (arg ((name . "fields") (type . "as") (direction . "in")))
         (arg ((name . "hit_data") (type . "aav") (direction . "out"))))
       @dots{}
       (signal ((name . "HitsAdded"))
         (arg ((name . "search") (type . "s")))
         (arg ((name . "count") (type . "u")))))
     @dots{})
@end lisp
@end defun

@defun dbus-introspect-get-attribute object attribute
This function returns the @var{attribute} value of a D-Bus
introspection @var{object}.  The value of @var{object} can be any
subtree of a parsed XML tree as retrieved with
@code{dbus-introspect-xml}.  @var{attribute} must be a string
according to the attribute names in the D-Bus specification.  Example:

@lisp
(dbus-introspect-get-attribute
 (dbus-introspect-xml :system "org.freedesktop.SystemToolsBackends"
                      "/org/freedesktop/SystemToolsBackends/UsersConfig")
 "name")

@result{} "/org/freedesktop/SystemToolsBackends/UsersConfig"
@end lisp

If @var{object} has no @var{attribute}, the function returns
@code{nil}.
@end defun


@node Nodes and Interfaces
@section Detecting object paths and interfaces.

The first elements, to be introspected for a D-Bus object, are further
object paths and interfaces.

@defun dbus-introspect-get-node-names bus service path
This function returns all node names of @var{service} in D-Bus
@var{bus} at object path @var{path} as a list of strings.  Example:

@lisp
(dbus-introspect-get-node-names
 :session "org.gnome.seahorse" "/org/gnome/seahorse")

@result{} ("crypto" "keys")
@end lisp

The node names stand for further object paths of the D-Bus
@var{service}, relative to @var{path}.  In the example,
@samp{/org/gnome/seahorse/crypto} and @samp{/org/gnome/seahorse/keys}
are also object paths of the D-Bus service @samp{org.gnome.seahorse}.
@end defun

@defun dbus-introspect-get-all-nodes bus service path
This function returns all node names of @var{service} in D-Bus
@var{bus} at object path @var{path}.  It returns a list of strings
with all object paths of @var{service}, starting at @var{path}.
Example:

@lisp
(dbus-introspect-get-all-nodes :session "org.gnome.seahorse" "/")

@result{} ("/" "/org" "/org/gnome" "/org/gnome/seahorse"
    "/org/gnome/seahorse/crypto"
    "/org/gnome/seahorse/keys"
    "/org/gnome/seahorse/keys/openpgp"
    "/org/gnome/seahorse/keys/openpgp/local"
    "/org/gnome/seahorse/keys/openssh"
    "/org/gnome/seahorse/keys/openssh/local")
@end lisp
@end defun

@defun dbus-introspect-get-interface-names bus service path
This function returns a list strings of all interface names of
@var{service} in D-Bus @var{bus} at object path @var{path}.  This list
will contain the default interface
@samp{org.freedesktop.DBus.Introspectable}.

Another default interface is @samp{org.freedesktop.DBus.Properties}.
If present, @code{interface} elements can also have @code{property}
children.  Example:

@lisp
(dbus-introspect-get-interface-names
 :system "org.freedesktop.Hal"
 "/org/freedesktop/Hal/devices/computer")

@result{} ("org.freedesktop.DBus.Introspectable"
    "org.freedesktop.Hal.Device"
    "org.freedesktop.Hal.Device.SystemPowerManagement"
    "org.freedesktop.Hal.Device.CPUFreq")
@end lisp
@end defun

@defun dbus-introspect-get-interface bus service path interface
This function returns @var{interface} of @var{service} in D-Bus
@var{bus} at object path @var{path}.  The return value is an XML
element.  @var{interface} must be a string and a member of the list
returned by @code{dbus-introspect-get-interface-names}.  Example:

@lisp
(dbus-introspect-get-interface
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search")

@result{} (interface ((name . "org.freedesktop.xesam.Search"))
     (method ((name . "GetHitData"))
       (arg ((name . "search") (type . "s") (direction . "in")))
       (arg ((name . "hit_ids") (type . "au") (direction . "in")))
       (arg ((name . "fields") (type . "as") (direction . "in")))
       (arg ((name . "hit_data") (type . "aav") (direction . "out"))))
     @dots{}
     (signal ((name . "HitsAdded"))
       (arg ((name . "search") (type . "s")))
       (arg ((name . "count") (type . "u")))))
@end lisp
@end defun

@noindent
With these functions, it is possible to retrieve all introspection
data from a running system:

@lisp
(progn
  (pop-to-buffer "*introspect*")
  (erase-buffer)
  (dolist (service (dbus-list-known-names :session))
    (dolist (path (dbus-introspect-get-all-nodes :session service "/"))
      ;; We want to introspect only elements, which have more than
      ;; the default interface "org.freedesktop.DBus.Introspectable".
      (when (delete
             "org.freedesktop.DBus.Introspectable"
             (dbus-introspect-get-interface-names :session service path))
        (insert (format "\nservice: \"%s\" path: \"%s\"\n" service path)
                (dbus-introspect :session service path))
        (redisplay t)))))
@end lisp


@node Methods and Signal
@section Applying the functionality.

Methods and signals are the communication means to D-Bus.  The
following functions return their specifications.

@defun dbus-introspect-get-method-names bus service path interface
This function returns a list of strings of all method names of
@var{interface} of @var{service} in D-Bus @var{bus} at object path
@var{path}.  Example:

@lisp
(dbus-introspect-get-method-names
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search")

@result{} ("GetState" "StartSearch" "GetHitCount" "GetHits" "NewSession"
    "CloseSession" "GetHitData" "SetProperty" "NewSearch"
    "GetProperty" "CloseSearch")
@end lisp
@end defun

@defun dbus-introspect-get-method bus service path interface method
This function returns @var{method} of @var{interface} as an XML
element.  It must be located at @var{service} in D-Bus @var{bus} at
object path @var{path}.  @var{method} must be a string and a member of
the list returned by @code{dbus-introspect-get-method-names}.
Example:

@lisp
(dbus-introspect-get-method
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search" "GetHitData")

@result{} (method ((name . "GetHitData"))
     (arg ((name . "search") (type . "s") (direction . "in")))
     (arg ((name . "hit_ids") (type . "au") (direction . "in")))
     (arg ((name . "fields") (type . "as") (direction . "in")))
     (arg ((name . "hit_data") (type . "aav") (direction . "out"))))
@end lisp
@end defun

@defun dbus-introspect-get-signal-names bus service path interface
This function returns a list of strings of all signal names of
@var{interface} of @var{service} in D-Bus @var{bus} at object path
@var{path}.  Example:

@lisp
(dbus-introspect-get-signal-names
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search")

@result{} ("StateChanged" "SearchDone" "HitsModified"
    "HitsRemoved" "HitsAdded")
@end lisp
@end defun

@defun dbus-introspect-get-signal bus service path interface signal
This function returns @var{signal} of @var{interface} as an XML
element.  It must be located at @var{service} in D-Bus @var{bus} at
object path @var{path}.  @var{signal} must be a string and a member of
the list returned by @code{dbus-introspect-get-signal-names}.
Example:

@lisp
(dbus-introspect-get-signal
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search" "HitsAdded")

@result{} (signal ((name . "HitsAdded"))
     (arg ((name . "search") (type . "s")))
     (arg ((name . "count") (type . "u"))))
@end lisp
@end defun


@node Properties and Annotations
@section What else to know about interfaces.

Interfaces can have properties.  These can be exposed via the
@samp{org.freedesktop.DBus.Properties} interface@footnote{See
@uref{https://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-properties}}.
That is, properties can be retrieved and changed during the lifetime
of an element.

A generalized interface is
@samp{org.freedesktop.DBus.Objectmanager}@footnote{See
@uref{https://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-objectmanager}},
which returns objects, their interfaces and properties for a given
service in just one call.

Annotations, on the other hand, are static values for an element.
Often, they are used to instruct generators, how to generate code from
the interface for a given language binding.

@defun dbus-introspect-get-property-names bus service path interface
This function returns a list of strings with all property names of
@var{interface} of @var{service} in D-Bus @var{bus} at object path
@var{path}.  Example:

@lisp
(dbus-introspect-get-property-names
 :session "org.kde.kded" "/modules/networkstatus"
 "org.kde.Solid.Networking.Client")

@result{} ("Status")
@end lisp

If an interface declares properties, the corresponding element supports
also the @samp{org.freedesktop.DBus.Properties} interface.
@end defun

@defun dbus-introspect-get-property bus service path interface property
This function returns @var{property} of @var{interface} as an XML
element.  It must be located at @var{service} in D-Bus @var{bus} at
object path @var{path}.  @var{property} must be a string and a member
of the list returned by @code{dbus-introspect-get-property-names}.

A @var{property} value can be retrieved by the function
@code{dbus-introspect-get-attribute}.  Example:

@lisp
(dbus-introspect-get-property
 :session "org.kde.kded" "/modules/networkstatus"
 "org.kde.Solid.Networking.Client" "Status")

@result{} (property ((access . "read") (type . "u") (name . "Status")))

(dbus-introspect-get-attribute
 (dbus-introspect-get-property
  :session "org.kde.kded" "/modules/networkstatus"
  "org.kde.Solid.Networking.Client" "Status")
 "access")

@result{} "read"
@end lisp
@end defun

@defun dbus-get-property bus service path interface property
This function returns the value of @var{property} of @var{interface}.
It will be checked at @var{bus}, @var{service}, @var{path}.  The
result can be any valid D-Bus value, or @code{nil} if there is no
@var{property}.  Example:

@lisp
(dbus-get-property
 :session "org.kde.kded" "/modules/networkstatus"
 "org.kde.Solid.Networking.Client" "Status")

@result{} 4
@end lisp
@end defun

@defun dbus-set-property bus service path interface property value
This function sets the value of @var{property} of @var{interface} to
@var{value}.  It will be checked at @var{bus}, @var{service},
@var{path}.  When the value is successfully set, this function returns
@var{value}.  Otherwise, it returns @code{nil}.  Example:

@lisp
(dbus-set-property
 :session "org.kde.kaccess" "/MainApplication"
 "com.trolltech.Qt.QApplication" "doubleClickInterval" 500)

@result{} 500
@end lisp
@end defun

@defun dbus-get-all-properties bus service path interface
This function returns all properties of @var{interface}.  It will be
checked at @var{bus}, @var{service}, @var{path}.  The result is a list
of cons.  Every cons contains the name of the property, and its value.
If there are no properties, @code{nil} is returned.  Example:

@lisp
(dbus-get-all-properties
 :session "org.kde.kaccess" "/MainApplication"
 "com.trolltech.Qt.QApplication")

@result{} (("cursorFlashTime" . 1000) ("doubleClickInterval" . 500)
    ("keyboardInputInterval" . 400) ("wheelScrollLines" . 3)
    ("globalStrut" 0 0) ("startDragTime" . 500)
    ("startDragDistance" . 4) ("quitOnLastWindowClosed" . t)
    ("styleSheet" . ""))
@end lisp
@end defun

@defun dbus-get-all-managed-objects bus service path
This function returns all objects at @var{bus}, @var{service},
@var{path}, and the children of @var{path}.  The result is a list of
objects.  Every object is a cons of an existing path name, and the
list of available interface objects.  An interface object is another
cons, whose car is the interface name and cdr is the list of
properties as returned by @code{dbus-get-all-properties} for that path
and interface.  Example:

@lisp
(dbus-get-all-managed-objects
 :session "org.gnome.SettingsDaemon" "/")

@result{} (("/org/gnome/SettingsDaemon/MediaKeys"
     ("org.gnome.SettingsDaemon.MediaKeys")
     ("org.freedesktop.DBus.Peer")
     ("org.freedesktop.DBus.Introspectable")
     ("org.freedesktop.DBus.Properties")
     ("org.freedesktop.DBus.ObjectManager"))
    ("/org/gnome/SettingsDaemon/Power"
     ("org.gnome.SettingsDaemon.Power.Keyboard")
     ("org.gnome.SettingsDaemon.Power.Screen")
     ("org.gnome.SettingsDaemon.Power"
      ("Icon" . ". GThemedIcon battery-full-charged-symbolic ")
      ("Tooltip" . "Laptop battery is charged"))
     ("org.freedesktop.DBus.Peer")
     ("org.freedesktop.DBus.Introspectable")
     ("org.freedesktop.DBus.Properties")
     ("org.freedesktop.DBus.ObjectManager"))
    @dots{})
@end lisp

If possible, @samp{org.freedesktop.DBus.ObjectManager.GetManagedObjects}
is used for retrieving the information.  Otherwise, the information
is collected via @samp{org.freedesktop.DBus.Introspectable.Introspect}
and @samp{org.freedesktop.DBus.Properties.GetAll}, which is slow.

An overview of all existing object paths, their interfaces and
properties could be retrieved by the following code:

@lisp
(let ((result (mapcar (lambda (service)
                        (cons service
                              (dbus-get-all-managed-objects
                               :session service "/")))
                      (dbus-list-known-names :session))))
  (pop-to-buffer "*objectmanager*")
  (erase-buffer)
  (pp result (current-buffer)))
@end lisp
@end defun

@defun dbus-introspect-get-annotation-names bus service path interface &optional name
This function returns a list of all annotation names as list of
strings.  If @var{name} is @code{nil}, the annotations are children of
@var{interface}, otherwise @var{name} must be a @code{method},
@code{signal}, or @code{property} XML element, where the annotations
belong to.  Example:

@lisp
(dbus-introspect-get-annotation-names
 :session "de.berlios.Pinot" "/de/berlios/Pinot"
 "de.berlios.Pinot" "GetStatistics")

@result{} ("de.berlios.Pinot.GetStatistics")
@end lisp

Default annotation names@footnote{See
@uref{https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format}}
are

@table @samp
@item org.freedesktop.DBus.Deprecated
Whether or not the entity is deprecated; defaults to @code{nil}

@item org.freedesktop.DBus.GLib.CSymbol
The C symbol; may be used for @code{methods} and @code{interfaces}

@item org.freedesktop.DBus.Method.NoReply
If set, don't expect a reply to the @code{method} call; defaults to @code{nil}
@end table
@end defun

@defun dbus-introspect-get-annotation bus service path interface name annotation
This function returns @var{annotation} as an XML object.  If
@var{name} is @code{nil}, @var{annotation} is a child of
@var{interface}, otherwise @var{name} must be the name of a
@code{method}, @code{signal}, or @code{property} XML element, where
the @var{annotation} belongs to.

An attribute value can be retrieved by
@code{dbus-introspect-get-attribute}.  Example:

@lisp
(dbus-introspect-get-annotation
 :session "de.berlios.Pinot" "/de/berlios/Pinot"
 "de.berlios.Pinot" "GetStatistics"
 "de.berlios.Pinot.GetStatistics")

@result{} (annotation ((name . "de.berlios.Pinot.GetStatistics")
                (value . "pinotDBus")))

(dbus-introspect-get-attribute
 (dbus-introspect-get-annotation
  :session "de.berlios.Pinot" "/de/berlios/Pinot"
  "de.berlios.Pinot" "GetStatistics"
  "de.berlios.Pinot.GetStatistics")
 "value")

@result{} "pinotDBus"
@end lisp
@end defun


@node Arguments and Signatures
@section The final details.

Methods and signals have arguments.  They are described in the
@code{arg} XML elements.

@defun dbus-introspect-get-argument-names bus service path interface name
This function returns a list of all argument names as strings.
@var{name} must be a @code{method} or @code{signal} XML element.
Example:

@lisp
(dbus-introspect-get-argument-names
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search" "GetHitData")

@result{} ("search" "hit_ids" "fields" "hit_data")
@end lisp

Argument names are optional; the function can therefore return
@code{nil}, even if the method or signal has arguments.
@end defun

@defun dbus-introspect-get-argument bus service path interface name arg
This function returns the argument @var{arg} as an XML object.
@var{name} must be a @code{method} or @code{signal} XML element.
Example:

@lisp
(dbus-introspect-get-argument
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search" "GetHitData" "search")

@result{} (arg ((name . "search") (type . "s") (direction . "in")))
@end lisp
@end defun

@defun dbus-introspect-get-signature bus service path interface name &optional direction
This function returns the signature of a @code{method} or
@code{signal}, represented by @var{name}, as a string.

If @var{name} is a @code{method}, @var{direction} can be either
@samp{in} or @samp{out}.  If @var{direction} is @code{nil}, @samp{in}
is assumed.

If @var{name} is a @code{signal}, and @var{direction} is
non-@code{nil}, @var{direction} must be @samp{out}.  Example:

@lisp
(dbus-introspect-get-signature
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search" "GetHitData" "in")

@result{} "sauas"

(dbus-introspect-get-signature
 :session "org.freedesktop.xesam.searcher"
 "/org/freedesktop/xesam/searcher/main"
 "org.freedesktop.xesam.Search" "HitsAdded")

@result{} "su"
@end lisp
@end defun


@node Type Conversion
@chapter Mapping Lisp types and D-Bus types.
@cindex type conversion

D-Bus method calls and signals accept usually several arguments as
parameters, either as input parameter, or as output parameter.  Every
argument belongs to a D-Bus type.

Such arguments must be mapped between the value encoded as a D-Bus
type, and the corresponding type of Lisp objects.  The mapping is
applied Lisp object @expansion{} D-Bus type for input parameters, and
D-Bus type @expansion{} Lisp object for output parameters.


@section Input parameters.

Input parameters for D-Bus methods and signals occur as arguments of a
Lisp function call.  The following mapping to D-Bus types is
applied, when the corresponding D-Bus message is created:

@example
@multitable {negative integer} {@expansion{}} {DBUS_TYPE_BOOLEAN}
@item Lisp type               @tab              @tab D-Bus type
@item
@item @code{t} and @code{nil} @tab @expansion{} @tab DBUS_TYPE_BOOLEAN
@item natural number          @tab @expansion{} @tab DBUS_TYPE_UINT32
@item negative integer        @tab @expansion{} @tab DBUS_TYPE_INT32
@item float                   @tab @expansion{} @tab DBUS_TYPE_DOUBLE
@item string                  @tab @expansion{} @tab DBUS_TYPE_STRING
@item list                    @tab @expansion{} @tab DBUS_TYPE_ARRAY
@end multitable
@end example

Other Lisp objects, like symbols or hash tables, are not accepted as
input parameters.

If it is necessary to use another D-Bus type, a corresponding type
symbol can be prepended to the corresponding Lisp object.  Basic D-Bus
types are represented by the type symbols @code{:byte},
@code{:boolean}, @code{:int16}, @code{:uint16}, @code{:int32},
@code{:uint32}, @code{:int64}, @code{:uint64}, @code{:double},
@code{:string}, @code{:object-path}, @code{:signature} and
@code{:unix-fd}.

@noindent
Example:

@lisp
(dbus-call-method @dots{} @var{nat-number} @var{string})
@end lisp

is equivalent to

@lisp
(dbus-call-method @dots{} :uint32 @var{nat-number} :string @var{string})
@end lisp

but different to

@lisp
(dbus-call-method @dots{} :int32 @var{nat-number} :signature @var{string})
@end lisp

The value for a byte D-Bus type can be any integer in the range 0
through 255.  If a character is used as argument, modifiers
represented outside this range are stripped off.  For example,
@code{:byte ?x} is equal to @code{:byte ?\M-x}, but it is not equal to
@code{:byte ?\C-x} or @code{:byte ?\M-\C-x}.  Signed and unsigned
integer D-Bus types expect a corresponding integer value.

A D-Bus compound type is always represented as a list.  The @sc{car}
of this list can be the type symbol @code{:array}, @code{:variant},
@code{:struct} or @code{:dict-entry}, which would result in a
corresponding D-Bus container.  @code{:array} is optional, because
this is the default compound D-Bus type for a list.

The objects being elements of the list are checked according to the
D-Bus compound type rules.

@itemize
@item An array must contain only elements of the same D-Bus type.  It
can be empty.

@item A variant must contain only a single element.

@item A dictionary entry must be an element of an array, and it must
contain only a key-value pair of two elements, with a basic D-Bus type
key.

@item There are no restrictions for structs.
@end itemize

If an empty array needs an element D-Bus type other than string, it
can contain exactly one element of D-Bus type @code{:signature}.  The
value of this element (a string) is used as the signature of the
elements of this array.  Example:

@lisp
(dbus-call-method
 :session "org.freedesktop.Notifications"
 "/org/freedesktop/Notifications"
 "org.freedesktop.Notifications" "Notify"
 "GNU Emacs"                   ; Application name.
 0                             ; No replacement of other notifications.
 ""                            ; No icon.
 "Notification summary"        ; Summary.
 (format                       ; Body.
  "This is a test notification, raised from\n%S" (emacs-version))
 '(:array)                     ; No actions (empty array of strings).
 '(:array :signature "@{sv@}") ; No hints
                               ; (empty array of dictionary entries).
 :int32 -1)                    ; Default timeout.

@result{} 3
@end lisp

@defun dbus-string-to-byte-array string
Sometimes, D-Bus methods require as input parameter an array of bytes,
instead of a string.  If it is guaranteed, that @var{string} is a
UTF-8 string, this function performs the conversion.  Example:

@lisp
(dbus-string-to-byte-array "/etc/hosts")

@result{} (:array :byte 47 :byte 101 :byte 116 :byte 99 :byte 47
           :byte 104 :byte 111 :byte 115 :byte 116 :byte 115)
@end lisp
@end defun

@defun dbus-escape-as-identifier string
This function escapes an arbitrary @var{string} so it follows the
rules for a C identifier.  The escaped string can be used as object
path component, interface element component, bus name component or
member name in D-Bus.

The escaping consists of replacing all non-alphanumerics, and the
first character if it's a digit, with an underscore and two
lower-case hex digits.  As a special case, "" is escaped to
"_".  Example:

@lisp
(dbus-escape-as-identifier "0123abc_xyz\x01\xff")

@result{} "_30123abc_5fxyz_01_ff"
@end lisp
@end defun


@section Output parameters.

Output parameters of D-Bus methods and signals are mapped to Lisp
objects.

@example
@multitable {DBUS_TYPE_OBJECT_PATH} {@expansion{}} {natural number}
@item D-Bus type            @tab              @tab Lisp type
@item
@item DBUS_TYPE_BOOLEAN     @tab @expansion{} @tab @code{t} or @code{nil}
@item DBUS_TYPE_BYTE        @tab @expansion{} @tab natural number
@item DBUS_TYPE_UINT16      @tab @expansion{} @tab natural number
@item DBUS_TYPE_INT16       @tab @expansion{} @tab integer
@item DBUS_TYPE_UINT32      @tab @expansion{} @tab natural number
@item DBUS_TYPE_UNIX_FD     @tab @expansion{} @tab natural number
@item DBUS_TYPE_INT32       @tab @expansion{} @tab integer
@item DBUS_TYPE_UINT64      @tab @expansion{} @tab natural number
@item DBUS_TYPE_INT64       @tab @expansion{} @tab integer
@item DBUS_TYPE_DOUBLE      @tab @expansion{} @tab float
@item DBUS_TYPE_STRING      @tab @expansion{} @tab string
@item DBUS_TYPE_OBJECT_PATH @tab @expansion{} @tab string
@item DBUS_TYPE_SIGNATURE   @tab @expansion{} @tab string
@item DBUS_TYPE_ARRAY       @tab @expansion{} @tab list
@item DBUS_TYPE_VARIANT     @tab @expansion{} @tab list
@item DBUS_TYPE_STRUCT      @tab @expansion{} @tab list
@item DBUS_TYPE_DICT_ENTRY  @tab @expansion{} @tab list
@end multitable
@end example

The resulting list of the last 4 D-Bus compound types contains as
elements the elements of the D-Bus container, mapped according to the
same rules.

The signal @code{PropertyModified}, discussed as an example in
@ref{Inspection}, would offer as Lisp data the following object
(@var{bool} stands here for either @code{nil} or @code{t}):

@lisp
(@var{integer} ((@var{string} @var{bool} @var{bool}) (@var{string} @var{bool} @var{bool}) @dots{}))
@end lisp

@defun dbus-byte-array-to-string byte-array &optional multibyte
If a D-Bus method or signal returns an array of bytes, which are known
to represent a UTF-8 string, this function converts @var{byte-array}
to the corresponding string.  The string is unibyte encoded, unless
@var{multibyte} is non-@code{nil}.  Example:

@lisp
(dbus-byte-array-to-string '(47 101 116 99 47 104 111 115 116 115))

@result{} "/etc/hosts"
@end lisp
@end defun

@defun dbus-unescape-from-identifier string
This function retrieves the original string from the encoded
@var{string} as a unibyte string.  The value of @var{string} must have
been encoded with @code{dbus-escape-as-identifier}.  Example:

@lisp
(dbus-unescape-from-identifier "_30123abc_5fxyz_01_ff")

@result{} "0123abc_xyz\x01\xff"
@end lisp

If the original string used in @code{dbus-escape-as-identifier} is a
multibyte string, it cannot be expected that this function returns
that string:

@lisp
(string-equal
 (dbus-unescape-from-identifier
  (dbus-escape-as-identifier "Grüß Göttin"))
 "Grüß Göttin")

@result{} nil
@end lisp


@end defun


@node Synchronous Methods
@chapter Calling methods in a blocking way.
@cindex method calls, synchronous
@cindex synchronous method calls

Methods can be called synchronously (@dfn{blocking}) or asynchronously
(@dfn{non-blocking}).

At the D-Bus level, a method call consist of two messages: one message
which carries the input parameters to the object owning the method to
be called, and a reply message returning the resulting output
parameters from the object.

@defun dbus-call-method bus service path interface method &optional :timeout timeout &rest args
@anchor{dbus-call-method}
This function calls @var{method} on the D-Bus @var{bus}.  @var{bus} is
either the symbol @code{:system} or the symbol @code{:session}.

@var{service} is the D-Bus service name to be used.  @var{path} is the
D-Bus object path, @var{service} is registered at.  @var{interface} is
an interface offered by @var{service}.  It must provide @var{method}.

If the parameter @code{:timeout} is given, the following integer
@var{timeout} specifies the maximum number of milliseconds before the
method call must return.  The default value is 25,000.  If the method
call doesn't return in time, a D-Bus error is raised (@pxref{Errors
and Events}).

The remaining arguments @var{args} are passed to @var{method} as
arguments.  They are converted into D-Bus types as described in
@ref{Type Conversion}.

The function returns the resulting values of @var{method} as a list of
Lisp objects, according to the type conversion rules described in
@ref{Type Conversion}.  Example:

@lisp
(dbus-call-method
 :session "org.gnome.seahorse" "/org/gnome/seahorse/keys/openpgp"
 "org.gnome.seahorse.Keys" "GetKeyField"
 "openpgp:657984B8C7A966DD" "simple-name")

@result{} (t ("Philip R. Zimmermann"))
@end lisp

If the result of the method call is just one value, the converted Lisp
object is returned instead of a list containing this single Lisp
object.  Example:

@lisp
(dbus-call-method
 :system "org.freedesktop.Hal"
 "/org/freedesktop/Hal/devices/computer"
 "org.freedesktop.Hal.Device" "GetPropertyString"
 "system.kernel.machine")

@result{} "i686"
@end lisp

With the @code{dbus-introspect} function it is possible to explore the
interfaces of @samp{org.freedesktop.Hal} service. It offers the
interfaces @samp{org.freedesktop.Hal.Manager} for the object at the
path @samp{/org/freedesktop/Hal/Manager} as well as the interface
@samp{org.freedesktop.Hal.Device} for all objects prefixed with the
path @samp{/org/freedesktop/Hal/devices}.  With the methods
@samp{GetAllDevices} and @samp{GetAllProperties}, it is simple to
emulate the @code{lshal} command on GNU/Linux systems:

@lisp
(dolist (device
         (dbus-call-method
          :system "org.freedesktop.Hal"
          "/org/freedesktop/Hal/Manager"
          "org.freedesktop.Hal.Manager" "GetAllDevices"))
  (message "\nudi = %s" device)
  (dolist (properties
           (dbus-call-method
            :system "org.freedesktop.Hal" device
            "org.freedesktop.Hal.Device" "GetAllProperties"))
    (message "  %s = %S"
             (car properties) (or (caadr properties) ""))))

@print{} "udi = /org/freedesktop/Hal/devices/computer
      info.addons = (\"hald-addon-acpi\")
      info.bus = \"unknown\"
      info.product = \"Computer\"
      info.subsystem = \"unknown\"
      info.udi = \"/org/freedesktop/Hal/devices/computer\"
      linux.sysfs_path_device = \"(none)\"
      power_management.acpi.linux.version = \"20051216\"
      power_management.can_suspend_to_disk = t
      power_management.can_suspend_to_ram = \"\"
      power_management.type = \"acpi\"
      smbios.bios.release_date = \"11/07/2001\"
      system.chassis.manufacturer = \"COMPAL\"
      system.chassis.type = \"Notebook\"
      system.firmware.release_date = \"03/19/2005\"
      @dots{}"
@end lisp
@end defun


@node Asynchronous Methods
@chapter Calling methods non-blocking.
@cindex method calls, asynchronous
@cindex asynchronous method calls

@defun dbus-call-method-asynchronously bus service path interface method handler &optional :timeout timeout &rest args
This function calls @var{method} on the D-Bus @var{bus}
asynchronously.  @var{bus} is either the symbol @code{:system} or the
symbol @code{:session}.

@var{service} is the D-Bus service name to be used.  @var{path} is the
D-Bus object path, @var{service} is registered at.  @var{interface} is
an interface offered by @var{service}.  It must provide @var{method}.

@var{handler} is a Lisp function, which is called when the
corresponding return message arrives.  If @var{handler} is @code{nil},
no return message will be expected.

If the parameter @code{:timeout} is given, the following integer
@var{timeout} specifies the maximum number of milliseconds before a
reply message must arrive.  The default value is 25,000.  If there is
no reply message in time, a D-Bus error is raised (@pxref{Errors and
Events}).

The remaining arguments @var{args} are passed to @var{method} as
arguments.  They are converted into D-Bus types as described in
@ref{Type Conversion}.

If @var{handler} is a Lisp function, the function returns a key into
the hash table @code{dbus-registered-objects-table}.  The
corresponding entry in the hash table is removed, when the return
message arrives, and @var{handler} is called.  Example:

@lisp
(dbus-call-method-asynchronously
 :system "org.freedesktop.Hal"
 "/org/freedesktop/Hal/devices/computer"
 "org.freedesktop.Hal.Device" "GetPropertyString"
 (lambda (msg) (message "%s" msg))
 "system.kernel.machine")

@print{} i686

@result{} (:serial :system 2)
@end lisp
@end defun


@node Receiving Method Calls
@chapter Offering own methods.
@cindex method calls, returning
@cindex returning method calls

In order to register methods on the D-Bus, Emacs has to request a well
known name on the D-Bus under which it will be available for other
clients.  Names on the D-Bus can be registered and unregistered using
the following functions:

@defun dbus-register-service bus service &rest flags
This function registers the known name @var{service} on D-Bus
@var{bus}.

@var{bus} is either the symbol @code{:system} or the symbol
@code{:session}.

@var{service} is the service name to be registered on the D-Bus.  It
must be a known name.

@var{flags} is a subset of the following keywords:

@table @code
@item :allow-replacement
Allow another service to become the primary owner if requested.
@item :replace-existing
Request to replace the current primary owner.
@item :do-not-queue
If we can not become the primary owner do not place us in the queue.
@end table

One of the following keywords is returned:

@table @code
@item :primary-owner
We have become the primary owner of the name @var{service}.
@item :in-queue
We could not become the primary owner and have been placed in the
queue.
@item :exists
We already are in the queue.
@item :already-owner
We already are the primary owner.
@end table
@end defun

@defun dbus-unregister-service bus service
This function unregisters all objects from D-Bus @var{bus}, that were
registered by Emacs for @var{service}.

@var{bus} is either the symbol @code{:system} or the symbol
@code{:session}.

@var{service} is the D-Bus service name of the D-Bus.  It must be a
known name.  Emacs releases its association to @var{service} from
D-Bus.

One of the following keywords is returned:

@table @code
@item :released
We successfully released the name @var{service}.
@item :non-existent
The name @var{service} does not exist on the bus.
@item :not-owner
We are not an owner of the name @var{service}.
@end table
@end defun

When a name has been chosen, Emacs can offer its own methods, which
can be called by other applications.  These methods could be an
implementation of an interface of a well known service, like
@samp{org.freedesktop.TextEditor}.

They could also be an implementation of its own interface.  In this
case, the service name must be @samp{org.gnu.Emacs}.  The object path
shall begin with @samp{/org/gnu/Emacs/@var{application}}, and the
interface name shall be @code{org.gnu.Emacs.@var{application}}, where
@var{application} is the name of the application which provides the
interface.

@deffn Constant dbus-service-emacs
The well known service name @samp{org.gnu.Emacs} of Emacs.
@end deffn

@deffn Constant dbus-path-emacs
The object path namespace @samp{/org/gnu/Emacs} used by Emacs.
@end deffn

@deffn Constant dbus-interface-emacs
The interface namespace @code{org.gnu.Emacs} used by Emacs.
@end deffn

@defun dbus-register-method bus service path interface method handler dont-register-service
With this function, an application registers @var{method} on the D-Bus
@var{bus}.

@var{bus} is either the symbol @code{:system} or the symbol
@code{:session}.

@var{service} is the D-Bus service name of the D-Bus object
@var{method} is registered for.  It must be a known name (see
discussion of @var{dont-register-service} below).

@var{path} is the D-Bus object path @var{service} is registered (see
discussion of @var{dont-register-service} below).

@var{interface} is the interface offered by @var{service}.  It must
provide @var{method}.

@var{handler} is a Lisp function to be called when a @var{method} call
is received.  It must accept as arguments the input arguments of
@var{method}.  @var{handler} should return a list, whose elements are
to be used as arguments for the reply message of @var{method}.  This
list can be composed like the input parameters in @ref{Type
Conversion}.

If @var{handler} wants to return just one Lisp object and it is not a
cons cell, @var{handler} can return this object directly, instead of
returning a list containing the object.

If @var{handler} returns a reply message with an empty argument list,
@var{handler} must return the symbol @code{:ignore}.

When @var{dont-register-service} is non-@code{nil}, the known name
@var{service} is not registered.  This means that other D-Bus clients
have no way of noticing the newly registered method.  When interfaces
are constructed incrementally by adding single methods or properties
at a time, @var{dont-register-service} can be used to prevent other
clients from discovering the still incomplete interface.

The default D-Bus timeout when waiting for a message reply is 25
seconds.  This value could be even smaller, depending on the calling
client.  Therefore, @var{handler} should not last longer than
absolutely necessary.

@code{dbus-register-method} returns a Lisp object, which can be used
as argument in @code{dbus-unregister-object} for removing the
registration for @var{method}.  Example:

@lisp
(defun my-dbus-method-handler (filename)
  (if (find-file filename)
      '(:boolean t)
    '(:boolean nil)))

(dbus-register-method
 :session "org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"
 "org.freedesktop.TextEditor" "OpenFile"
 #'my-dbus-method-handler)

@result{} ((:method :session "org.freedesktop.TextEditor" "OpenFile")
    ("org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"
     my-dbus-method-handler))
@end lisp

If you invoke the method @samp{org.freedesktop.TextEditor.OpenFile}
from another D-Bus application with a file name as parameter, the file
is opened in Emacs, and the method returns either @var{true} or
@var{false}, indicating the success of the method.  As a test tool one
could use the command line tool @code{dbus-send} in a shell:

@example
# dbus-send --session --print-reply \
    --dest="org.freedesktop.TextEditor" \
    "/org/freedesktop/TextEditor" \
    "org.freedesktop.TextEditor.OpenFile" string:"/etc/hosts"

@print{} method return sender=:1.22 -> dest=:1.23 reply_serial=2
      boolean true
@end example

You can indicate an error by raising the Emacs signal
@code{dbus-error}.  The handler above could be changed like this:

@lisp
(defun my-dbus-method-handler (&rest args)
  (unless (and (= (length args) 1) (stringp (car args)))
    (signal 'dbus-error (list (format "Wrong argument list: %S" args))))
  (condition-case err
      (find-file (car args))
    (error (signal 'dbus-error (cdr err))))
  t)
@end lisp

The test then runs

@example
# dbus-send --session --print-reply \
    --dest="org.freedesktop.TextEditor" \
    "/org/freedesktop/TextEditor" \
    "org.freedesktop.TextEditor.OpenFile" \
    string:"/etc/hosts" string:"/etc/passwd"

@print{} Error org.freedesktop.DBus.Error.Failed:
   Wrong argument list: ("/etc/hosts" "/etc/passwd")
@end example
@end defun

@defun dbus-register-property bus service path interface property access value &optional emits-signal dont-register-service
With this function, an application declares a @var{property} on the D-Bus
@var{bus}.

@var{bus} is either the symbol @code{:system} or the symbol
@code{:session}.

@var{service} is the D-Bus service name of the D-Bus.  It must be a
known name.

@var{path} is the D-Bus object path @var{service} is registered (see
discussion of @var{dont-register-service} below).

@var{interface} is the name of the interface used at @var{path},
@var{property} is the name of the property of @var{interface}.

@var{access} indicates, whether the property can be changed by other
services via D-Bus.  It must be either the symbol @code{:read} or
@code{:readwrite}.  @var{value} is the initial value of the property,
it can be of any valid type (@xref{dbus-call-method}, for details).

If @var{property} already exists on @var{path}, it will be
overwritten.  For properties with access type @code{:read} this is the
only way to change their values.  Properties with access type
@code{:readwrite} can be changed by @code{dbus-set-property}.

The interface @samp{org.freedesktop.DBus.Properties} is added to
@var{path}, including a default handler for the @samp{Get},
@samp{GetAll} and @samp{Set} methods of this interface.  When
@var{emits-signal} is non-@code{nil}, the signal
@samp{PropertiesChanged} is sent when the property is changed by
@code{dbus-set-property}.

When @var{dont-register-service} is non-@code{nil}, the known name
@var{service} is not registered.  This means that other D-Bus clients
have no way of noticing the newly registered method.  When interfaces
are constructed incrementally by adding single methods or properties
at a time, @var{dont-register-service} can be used to prevent other
clients from discovering the still incomplete interface.

@noindent Example:

@lisp
(dbus-register-property
 :session "org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"
 "org.freedesktop.TextEditor" "name" :read "GNU Emacs")

@result{} ((:property :session "org.freedesktop.TextEditor" "name")
    ("org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"))

(dbus-register-property
 :session "org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"
 "org.freedesktop.TextEditor" "version" :readwrite emacs-version t)

@result{} ((:property :session "org.freedesktop.TextEditor" "version")
    ("org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"))
@end lisp

Other D-Bus applications can read the property via the default methods
@samp{org.freedesktop.DBus.Properties.Get} and
@samp{org.freedesktop.DBus.Properties.GetAll}.  Testing is also
possible via the command line tool @code{dbus-send} in a shell:

@example
# dbus-send --session --print-reply \
    --dest="org.freedesktop.TextEditor" \
    "/org/freedesktop/TextEditor" \
    "org.freedesktop.DBus.Properties.GetAll" \
    string:"org.freedesktop.TextEditor"

@print{} method return sender=:1.22 -> dest=:1.23 reply_serial=3
      array [
         dict entry(
            string "name"
            variant             string "GNU Emacs"
         )
         dict entry(
            string "version"
            variant             string "23.1.50.5"
         )
      ]
@end example

It is also possible to apply the @code{dbus-get-property},
@code{dbus-get-all-properties} and @code{dbus-set-property} functions
(@pxref{Properties and Annotations}).

@lisp
(dbus-set-property
 :session "org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"
 "org.freedesktop.TextEditor" "version" "23.1.50")

@result{} "23.1.50"

(dbus-get-property
 :session "org.freedesktop.TextEditor" "/org/freedesktop/TextEditor"
 "org.freedesktop.TextEditor" "version")

@result{} "23.1.50"
@end lisp
@end defun

@defun dbus-unregister-object object
This function unregisters @var{object} from the D-Bus.  @var{object}
must be the result of a preceding @code{dbus-register-method},
@code{dbus-register-property} or @code{dbus-register-signal} call
(@pxref{Signals}).  It returns @code{t} if @var{object} has been
unregistered, @code{nil} otherwise.

When @var{object} identifies the last method or property, which is
registered for the respective service, Emacs releases its association
to the service from D-Bus.
@end defun


@node Signals
@chapter Sending and receiving signals.
@cindex signals

Signals are one way messages.  They carry input parameters, which are
received by all objects which have registered for such a signal.

@defun dbus-send-signal bus service path interface signal &rest args
This function is similar to @code{dbus-call-method}.  The difference
is, that there are no returning output parameters.

The function emits @var{signal} on the D-Bus @var{bus}.  @var{bus} is
either the symbol @code{:system} or the symbol @code{:session}.  It
doesn't matter whether another object has registered for @var{signal}.

Signals can be unicast or broadcast messages.  For broadcast messages,
@var{service} must be @code{nil}.  Otherwise, @var{service} is the
D-Bus service name the signal is sent to as a unicast
message.@footnote{For backward compatibility, a broadcast message is
also emitted if @var{service} is the known or unique name Emacs is
registered at D-Bus @var{bus}.}  @var{path} is the D-Bus object path
@var{signal} is sent from.  @var{interface} is an interface available
at @var{path}.  It must provide @var{signal}.

The remaining arguments @var{args} are passed to @var{signal} as
arguments.  They are converted into D-Bus types as described in
@ref{Type Conversion}.  Example:

@lisp
(dbus-send-signal
 :session nil dbus-path-emacs
 (concat dbus-interface-emacs ".FileManager") "FileModified"
 "/home/albinus/.emacs")
@end lisp
@end defun

@defun dbus-register-signal bus service path interface signal handler &rest args
With this function, an application registers for a signal on the D-Bus
@var{bus}.

@var{bus} is either the symbol @code{:system} or the symbol
@code{:session}.

@var{service} is the D-Bus service name used by the sending D-Bus
object.  It can be either a known name or the unique name of the D-Bus
object sending the signal.  A known name will be mapped onto the
unique name of the object, owning @var{service} at registration time.
When the corresponding D-Bus object disappears, signals will no longer
be received.

@var{path} is the corresponding D-Bus object path that @var{service}
is registered at.  @var{interface} is an interface offered by
@var{service}.  It must provide @var{signal}.

@var{service}, @var{path}, @var{interface} and @var{signal} can be
@code{nil}.  This is interpreted as a wildcard for the respective
argument.

@var{handler} is a Lisp function to be called when the @var{signal} is
received.  It must accept as arguments the output parameters
@var{signal} is sending.

The remaining arguments @var{args} can be keywords or keyword string
pairs.@footnote{For backward compatibility, the arguments @var{args}
can also be just strings.  They stand for the respective arguments of
@var{signal} in their order, and are used for filtering as well.  A
@code{nil} argument might be used to preserve the order.}  Their
meaning is as follows:

@table @code
@item :arg@var{n} @var{string}
@item :path@var{n} @var{string}
This stands for the @var{n}th argument of the signal.
@code{:path@var{n}} arguments can be used for object path wildcard
matches as specified by D-Bus, while an @code{:argN} argument requires
an exact match.

@item :arg-namespace @var{string}
Register for those signals, whose first argument names a service or
interface within the namespace @var{string}.

@item :path-namespace @var{string}
Register for the object path namespace @var{string}.  All signals sent
from an object path, which has @var{string} as the preceding string,
are matched.  This requires @var{path} to be @code{nil}.

@item :eavesdrop
Register for unicast signals which are not directed to the D-Bus
object Emacs is registered at D-Bus BUS, if the security policy of BUS
allows this.  Otherwise, this argument is ignored.
@end table

@code{dbus-register-signal} returns a Lisp object, which can be used
as argument in @code{dbus-unregister-object} for removing the
registration for @var{signal}.  Example:

@lisp
(defun my-dbus-signal-handler (device)
  (message "Device %s added" device))

(dbus-register-signal
 :system "org.freedesktop.Hal" "/org/freedesktop/Hal/Manager"
 "org.freedesktop.Hal.Manager" "DeviceAdded"
 #'my-dbus-signal-handler)

@result{} ((:signal :system "org.freedesktop.Hal.Manager" "DeviceAdded")
    ("org.freedesktop.Hal" "/org/freedesktop/Hal/Manager"
     my-signal-handler))
@end lisp

As we know from the introspection data of interface
@samp{org.freedesktop.Hal.Manager}, the signal @samp{DeviceAdded}
provides one single parameter, which is mapped into a Lisp string.
The callback function @code{my-dbus-signal-handler} must therefore
define a single string argument.  Plugging a USB device into your
machine, when registered for signal @samp{DeviceAdded}, will show you
which objects the GNU/Linux @code{hal} daemon adds.

Some of the match rules have been added to a later version of D-Bus.
In order to test the availability of such features, you could register
for a dummy signal, and check the result:

@lisp
(dbus-ignore-errors
  (dbus-register-signal
   :system nil nil nil nil #'ignore :path-namespace "/invalid/path"))

@result{} nil
@end lisp
@end defun


@node Alternative Buses
@chapter Alternative buses and environments.
@cindex bus names
@cindex UNIX domain socket
@cindex TCP/IP socket

Until now, we have spoken about the system and the session buses,
which are the default buses to be connected to.  However, it is
possible to connect to any bus with a known address.  This is a UNIX
domain or TCP/IP socket.  Everywhere, where a @var{bus} is mentioned
as argument of a function (the symbol @code{:system} or the symbol
@code{:session}), this address can be used instead.  The connection to
this bus must be initialized first.

@defun dbus-init-bus bus &optional private
This function establishes the connection to D-Bus @var{bus}.

@var{bus} can be either the symbol @code{:system} or the symbol
@code{:session}, or it can be a string denoting the address of the
corresponding bus.  For the system and session buses, this function
is called when loading @file{dbus.el}, there is no need to call it
again.

The function returns the number of connections this Emacs session has
established to the @var{bus} under the same unique name
(@pxref{dbus-get-unique-name}).  It depends on the libraries Emacs is
linked with, and on the environment Emacs is running.  For example, if
Emacs is linked with the GTK+ toolkit, and it runs in a GTK+-aware
environment like GNOME, another connection might already be
established.

When @var{private} is non-@code{nil}, a new connection is established
instead of reusing an existing one.  It results in a new unique name
at the bus.  This can be used, if it is necessary to distinguish from
another connection used in the same Emacs process, like the one
established by GTK+.  It should be used with care for at least the
@code{:system} and @code{:session} buses, because other Emacs Lisp
packages might already use this connection to those buses.

Example: You initialize a connection to the AT-SPI bus on your host:

@lisp
(setq my-bus
      (dbus-call-method
       :session "org.a11y.Bus" "/org/a11y/bus"
       "org.a11y.Bus" "GetAddress"))

@result{} "unix:abstract=/tmp/dbus-2yzWHOCdSD,guid=a490dd26625870ca1298b6e10000fd7f"

;; If Emacs is built with GTK+ support, and you run in a GTK+-enabled
;; environment (like a GNOME session), the initialization reuses the
;; connection established by GTK+'s atk bindings.
(dbus-init-bus my-bus)

@result{} 2

(dbus-get-unique-name my-bus)

@result{} ":1.19"

;; Open a new connection to the same bus.  This supersedes the
;; previous one.
(dbus-init-bus my-bus 'private)

@result{} 1

(dbus-get-unique-name my-bus)

@result{} ":1.20"
@end lisp

D-Bus addresses can specify a different transport.  A possible address
could be based on TCP/IP sockets, see next example.  Which transport
is supported depends on the bus daemon configuration, however.
@end defun

@defun dbus-setenv bus variable value
This function sets the value of the @var{bus} environment
@var{variable} to @var{value}.

@var{bus} is either a Lisp symbol, @code{:system} or @code{:session},
or a string denoting the bus address.  Both @var{variable} and
@var{value} should be strings.

Normally, services inherit the environment of the bus daemon.  This
function adds to or modifies that environment when activating services.

Some bus instances, such as @code{:system}, may disable setting the
environment.  In such cases, or if this feature is not available in
older D-Bus versions, this function signals a @code{dbus-error}.

As an example, it might be desirable to start X11 enabled services on
a remote host's bus on the same X11 server the local Emacs is
running.  This could be achieved by

@lisp
(setq my-bus "unix:host=example.gnu.org,port=4711")

@result{} "unix:host=example.gnu.org,port=4711"

(dbus-init-bus my-bus)

@result{} 1

(dbus-setenv my-bus "DISPLAY" (getenv "DISPLAY"))

@result{} nil
@end lisp
@end defun


@node Errors and Events
@chapter Errors and events.
@cindex debugging
@cindex errors
@cindex events

The internal actions can be traced by running in a debug mode.

@defvar dbus-debug
If this variable is non-@code{nil}, D-Bus specific debug messages are raised.
@end defvar

Input parameters of @code{dbus-call-method},
@code{dbus-call-method-asynchronously}, @code{dbus-send-signal},
@code{dbus-register-method}, @code{dbus-register-property} and
@code{dbus-register-signal} are checked for correct D-Bus types. If
there is a type mismatch, the Lisp error @code{wrong-type-argument}
@code{D-Bus @var{arg}} is raised.

All errors raised by D-Bus are signaled with the error symbol
@code{dbus-error}.  If possible, error messages from D-Bus are
appended to the @code{dbus-error}.

@defspec dbus-ignore-errors forms@dots{}
This executes @var{forms} exactly like a @code{progn}, except that
@code{dbus-error} errors are ignored during the @var{forms}.  These
errors can be made visible when @code{dbus-debug} is set to @code{t}.
@end defspec

Incoming D-Bus messages are handled as Emacs events, @pxref{Misc
Events, , , elisp}.  They are retrieved only, when Emacs runs in
interactive mode.  The generated event has this form:

@lisp
(dbus-event @var{bus} @var{type} @var{serial} @var{service} @var{path} @var{interface} @var{member} @var{handler}
        &rest @var{args})
@end lisp

@var{bus} identifies the D-Bus the message is coming from.  It is
either the symbol @code{:system} or the symbol @code{:session}.

@var{type} is the D-Bus message type which has caused the event.  It
can be @code{dbus-message-type-invalid},
@code{dbus-message-type-method-call},
@code{dbus-message-type-method-return},
@code{dbus-message-type-error}, or @code{dbus-message-type-signal}.
@var{serial} is the serial number of the received D-Bus message.

@var{service} and @var{path} are the unique name and the object path
of the D-Bus object emitting the message.  @var{interface} and
@var{member} denote the message which has been sent.

@var{handler} is the callback function which has been registered for
this message (@pxref{Signals}).  When a @code{dbus-event} event
arrives, @var{handler} is called with @var{args} as arguments.

In order to inspect the @code{dbus-event} data, you could extend the
definition of the callback function in @ref{Signals}:

@lisp
(defun my-dbus-signal-handler (&rest args)
  (message "my-dbus-signal-handler: %S" last-input-event))
@end lisp

There exist convenience functions which could be called inside a
callback function in order to retrieve the information from the event.

@defun dbus-event-bus-name event
This function returns the bus name @var{event} is coming from.  The
result is either the symbol @code{:system} or the symbol
@code{:session}.
@end defun

@defun dbus-event-message-type event
This function returns the message type of the corresponding D-Bus
message.  The result is a natural number.
@end defun

@defun dbus-event-serial-number event
This function returns the serial number of the corresponding D-Bus
message.  The result is a natural number.
@end defun

@defun dbus-event-service-name event
This function returns the unique name of the D-Bus object @var{event}
is coming from.
@end defun

@defun dbus-event-path-name event
This function returns the object path of the D-Bus object @var{event}
is coming from.
@end defun

@defun dbus-event-interface-name event
This function returns the interface name of the D-Bus object
@var{event} is coming from.
@end defun

@defun dbus-event-member-name event
This function returns the member name of the D-Bus object @var{event}
is coming from.  It is either a signal name or a method name.
@end defun

D-Bus errors are not propagated during event handling, because it is
usually not desired.  D-Bus errors in events can be made visible by
setting the variable @code{dbus-debug} to @code{t}.  They can also be
handled by a hook function.

@defvar dbus-event-error-functions
This hook variable keeps a list of functions, which are called when a
D-Bus error happens in the event handler.  Every function must accept
two arguments, the event and the error variable caught in
@code{condition-case} by @code{dbus-error}.

Such functions can be used to adapt the error signal to be raised.
Example:

@lisp
(defun my-dbus-event-error-handler (event error)
  (when (string-equal (concat dbus-interface-emacs ".FileManager")
                      (dbus-event-interface-name event))
    (message "my-dbus-event-error-handler: %S %S" event error)
    (signal 'file-error (cdr error))))

(add-hook 'dbus-event-error-functions #'my-dbus-event-error-handler)
@end lisp
@end defvar

Hook functions should take into account that there might be other
D-Bus applications running.  They should therefore check carefully,
whether a given D-Bus error is related to them.


@node Index
@unnumbered Index

@printindex cp


@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include doclicense.texi

@bye