\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--2024 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 @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. * Register Objects:: Offering own services. * Signals:: Sending and receiving signals. * Alternative Buses:: Alternative buses and environments. * Errors and Events:: Errors and events. * Monitoring Messages:: Monitoring messages. * 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 keyword @code{:system} (the default) or the keyword @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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 @dots{} @dots{} @dots{} @dots{} @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 @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 @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 @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 @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 keyword @code{:system} or the keyword @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{} " @dots{} @dots{} " @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. If there is no @var{property}, or @var{property} cannot be read, an error is raised. 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 [type] 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}. @var{value} can be preceded by a @var{type} keyword. When the value is successfully set, this function returns @var{value}. Example: @lisp (dbus-set-property :session "org.kde.kaccess" "/MainApplication" "com.trolltech.Qt.QApplication" "doubleClickInterval" :uint16 500) @result{} 500 @end lisp @end defun @defun dbus-get-all-properties bus service path interface This function returns all readable properties of @var{interface}. It will be checked at @var{bus}, @var{service}, @var{path}. The result is a list of cons cells. Every cons cell 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 cell 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/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 keyword can be prepended to the corresponding Lisp object. Basic D-Bus types are represented by the type keywords @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 D-Bus byte type can be any natural number. If the number is larger than 255, it is truncated to the least significant byte. For example, @code{:byte 1025} is equal to @code{:byte 1}. 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 D-Bus integer types expect a corresponding integer value. A unix file descriptor is restricted to the values 0@dots{}9. If typed explicitly, a non-@code{nil} boolean value like @code{:boolean 'symbol} is handled like @code{t} or @code{:boolean t}. A D-Bus compound type is always represented as a list. The @sc{car} of this list can be the type keyword @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. This function converts @var{string} into an array of bytes of the UTF-8 encoding of @var{string}. 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 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 Lisp string. The contents of @var{byte-array} should be the byte sequence of a UTF-8 encoded string. 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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 Register Objects @chapter Offering own services. @cindex method calls, returning @cindex returning method calls @c https://wiki.ubuntu.com/DebuggingDBus You can offer an own service in D-Bus, which will be visible by other D-Bus clients. See @uref{https://dbus.freedesktop.org/doc/dbus-api-design.html} for a discussion of the design. 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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 When @var{service} is not a known name but a unique name, the function returns @code{nil}. @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 keyword @code{:system} or the keyword @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 keyword @code{:ignore} in order to distinguish it from @code{nil} (the boolean false). If @var{handler} detects an error, it shall return the list @code{(:error @var{error-name} @var{error-message})}. @var{error-name} is a namespaced string which characterizes the error type, and @var{error-message} is a free text string. Alternatively, any Emacs signal @code{dbus-error} in @var{handler} raises a D-Bus error message with the error name @samp{org.freedesktop.DBus.Error.Failed}. 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 returning an @code{:error} list reply, or by raising the Emacs signal @code{dbus-error}. The handler above could be changed like this: @lisp (defun my-dbus-method-handler (&rest args) (if (not (and (= (length args) 1) (stringp (car args)))) (list :error "org.freedesktop.TextEditor.Error.InvalidArgs" (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.TextEditor.Error.InvalidArgs: Wrong argument list: ("/etc/hosts" "/etc/passwd") @end example @example # dbus-send --session --print-reply \ --dest="org.freedesktop.TextEditor" \ "/org/freedesktop/TextEditor" \ "org.freedesktop.TextEditor.OpenFile" \ string:"/etc/crypttab" @print{} Error org.freedesktop.DBus.Error.Failed: D-Bus error: "File is not readable", "/etc/crypttab" @end example @end defun @defun dbus-register-property bus service path interface property access [type] 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 keyword @code{:system} or the keyword @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 keyword @code{:read}, @code{:write} 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). @var{value} can be preceded by a @var{type} keyword. 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{:write} or @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. @code{dbus-register-property} returns a Lisp object, which can be used as argument in @code{dbus-unregister-object} for removing the registration for @var{property}. 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}, @code{dbus-register-signal} (@pxref{Signals}) or @code{dbus-register-monitor} call. 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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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 keyword @code{:system} or the keyword @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. If Emacs was invoked when there was no D-Bus session bus available yet, you can set the environment variable @env{DBUS_SESSION_BUS_ADDRESS} once the session bus daemon is running and offering the address. Calling @code{dbus-init-bus} initializes the connection to the session bus. @lisp (setenv "DBUS_SESSION_BUS_ADDRESS" "unix:path=/run/user/1000/bus") @result{} "unix:path=/run/user/1000/bus" (dbus-init-bus :session) @result{} 2 @end lisp @code{dbus-init-bus} 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 @var{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+. If @var{bus} is the keyword @code{:system} or the keyword @code{:session}, the new private connection is identified by the keywords @code{:system-private} or @code{:session-private}, respectively. 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 keyword, @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} (the macro returns @code{nil} then). These errors can be made visible when @code{dbus-debug} is set to non-@code{nil}. @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{destination} @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 a Lisp keyword, @code{:system}, @code{:session}, @code{:system-private} or @code{:session-private}, or a string denoting the bus address. @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, unless @var{type} is equal @code{dbus-message-type-error}. @var{service} and @var{path} are the unique name and the object path of the D-Bus object emitting the message. @var{destination} is the D-Bus name the message is dedicated to, or @code{nil} in case the message is a broadcast signal. @var{interface} and @var{member} denote the message which has been sent. When @var{type} is @code{dbus-message-type-error}, @var{member} is the error name. @var{handler} is the callback function which has been registered for this message (@pxref{Signals}). @var{args} are the typed arguments as returned from the message. They are passed to @var{handler} without type information, when it is called during event handling in @code{dbus-handle-event}. 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 keyword @code{:system} or the keyword @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-destination-name event This function returns the unique name of the D-Bus object @var{event} is dedicated to. @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 @defun dbus-event-handler event This function returns the handler the D-Bus object @var{event} is applied with. @end defun @defun dbus-event-arguments event This function returns the arguments the D-Bus object @var{event} is carrying on. @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 non-@code{nil}. 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 Monitoring Messages @chapter Monitoring messages. @cindex monitoring @defun dbus-register-monitor bus &optional handler &key type sender destination path interface member This function registers @var{handler} for monitoring messages on the D-Bus @var{bus}. @var{bus} is either a Lisp keyword, @code{:system} or @code{:session}, or a string denoting the bus address. @findex dbus-monitor-handler @var{handler} is the function to be called when a D-Bus event to be monitored arrives. It is called with the @var{args} slot of the D-Bus event (@pxref{Errors and Events}), which are stripped off the type keywords. If @var{handler} is @code{nil}, the default handler @code{dbus-monitor-handler} is applied. This default handler behaves similar to the @command{dbus-monitor} program. The other arguments are keyword-value pairs. @code{:type @var{type}} defines the message type to be monitored. If given, it must be equal one of the strings @samp{method_call}, @samp{method_return}, @samp{error} or @samp{signal}. @code{:sender @var{sender}} and @code{:destination @var{destination}} are D-Bus names. They can be unique names, or well-known service names. @code{:path @var{path}} is the D-Bus object to be monitored. @code{:interface @var{interface}} is the name of an interface, and @code{:member @var{member}} is either a method name, a signal name, or an error name. @code{dbus-register-monitor} returns a Lisp object, which can be used as argument in @code{dbus-unregister-object} for removing the monitor. The following form shows all D-Bus events on the session bus in buffer @samp{*D-Bus Monitor*}: @lisp (dbus-register-monitor :session) @end lisp And this form restricts the monitoring on D-Bus errors: @lisp (dbus-register-monitor :session nil :type "error") @end lisp @end defun @deffn Command dbus-monitor &optional bus This command invokes @code{dbus-register-monitor} interactively, and switches to the monitor buffer. @end deffn @node Index @unnumbered Index @printindex cp @node GNU Free Documentation License @appendix GNU Free Documentation License @include doclicense.texi @bye