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diff --git a/doc/dbus-tutorial.html b/doc/dbus-tutorial.html deleted file mode 100644 index 37ab2eac..00000000 --- a/doc/dbus-tutorial.html +++ /dev/null @@ -1,991 +0,0 @@ -<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>D-Bus Tutorial</title><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="article" title="D-Bus Tutorial"><div class="titlepage"><div><div><h2 class="title"><a name="index"></a>D-Bus Tutorial</h2></div><div><div class="authorgroup"><div class="author"><h3 class="author"><span class="firstname">Havoc</span> <span class="surname">Pennington</span></h3><div class="affiliation"><span class="orgname">Red Hat, Inc.<br></span><div class="address"><p><code class="email"><<a class="email" href="mailto:hp@pobox.com">hp@pobox.com</a>></code></p></div></div></div><div class="author"><h3 class="author"><span class="firstname">David</span> <span class="surname">Wheeler</span></h3></div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="surname">Palmieri</span></h3><div class="affiliation"><span class="orgname">Red Hat, Inc.<br></span><div class="address"><p><code class="email"><<a class="email" href="mailto:johnp@redhat.com">johnp@redhat.com</a>></code></p></div></div></div><div class="author"><h3 class="author"><span class="firstname">Colin</span> <span class="surname">Walters</span></h3><div class="affiliation"><span class="orgname">Red Hat, Inc.<br></span><div class="address"><p><code class="email"><<a class="email" href="mailto:walters@redhat.com">walters@redhat.com</a>></code></p></div></div></div></div></div><div><p class="releaseinfo">Version 0.5.0</p></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#meta">Tutorial Work In Progress</a></span></dt><dt><span class="sect1"><a href="#whatis">What is D-Bus?</a></span></dt><dd><dl><dt><span class="sect2"><a href="#uses">D-Bus applications</a></span></dt></dl></dd><dt><span class="sect1"><a href="#concepts">Concepts</a></span></dt><dd><dl><dt><span class="sect2"><a href="#objects">Native Objects and Object Paths</a></span></dt><dt><span class="sect2"><a href="#members">Methods and Signals</a></span></dt><dt><span class="sect2"><a href="#interfaces">Interfaces</a></span></dt><dt><span class="sect2"><a href="#proxies">Proxies</a></span></dt><dt><span class="sect2"><a href="#bus-names">Bus Names</a></span></dt><dt><span class="sect2"><a href="#addresses">Addresses</a></span></dt><dt><span class="sect2"><a href="#bigpicture">Big Conceptual Picture</a></span></dt><dt><span class="sect2"><a href="#messages">Messages - Behind the Scenes</a></span></dt><dt><span class="sect2"><a href="#callprocedure">Calling a Method - Behind the Scenes</a></span></dt><dt><span class="sect2"><a href="#signalprocedure">Emitting a Signal - Behind the Scenes</a></span></dt><dt><span class="sect2"><a href="#introspection">Introspection</a></span></dt></dl></dd><dt><span class="sect1"><a href="#glib-client">GLib API: Using Remote Objects</a></span></dt><dd><dl><dt><span class="sect2"><a href="#glib-typemappings">D-Bus - GLib type mappings</a></span></dt><dt><span class="sect2"><a href="#sample-program-1">A sample program</a></span></dt><dt><span class="sect2"><a href="#glib-program-setup">Program initalization</a></span></dt><dt><span class="sect2"><a href="#glib-method-invocation">Understanding method invocation</a></span></dt><dt><span class="sect2"><a href="#glib-signal-connection">Connecting to object signals</a></span></dt><dt><span class="sect2"><a href="#glib-error-handling">Error handling and remote exceptions</a></span></dt><dt><span class="sect2"><a href="#glib-more-examples">More examples of method invocation</a></span></dt><dt><span class="sect2"><a href="#glib-generated-bindings">Generated Bindings</a></span></dt></dl></dd><dt><span class="sect1"><a href="#glib-server">GLib API: Implementing Objects</a></span></dt><dd><dl><dt><span class="sect2"><a href="#glib-annotations">Server-side Annotations</a></span></dt></dl></dd><dt><span class="sect1"><a href="#python-client">Python API</a></span></dt><dt><span class="sect1"><a href="#qt-client">Qt API: Using Remote Objects</a></span></dt><dt><span class="sect1"><a href="#qt-server">Qt API: Implementing Objects</a></span></dt></dl></div><div class="sect1" title="Tutorial Work In Progress"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="meta"></a>Tutorial Work In Progress</h2></div></div></div><p> - This tutorial is not complete; it probably contains some useful information, but - also has plenty of gaps. Right now, you'll also need to refer to the D-Bus specification, - Doxygen reference documentation, and look at some examples of how other apps use D-Bus. - </p><p> - Enhancing the tutorial is definitely encouraged - send your patches or suggestions to the - mailing list. If you create a D-Bus binding, please add a section to the tutorial for your - binding, if only a short section with a couple of examples. - </p></div><div class="sect1" title="What is D-Bus?"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="whatis"></a>What is D-Bus?</h2></div></div></div><p> - D-Bus is a system for <em class="firstterm">interprocess communication</em> - (IPC). Architecturally, it has several layers: - - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - A library, <em class="firstterm">libdbus</em>, that allows two - applications to connect to each other and exchange messages. - </p></li><li class="listitem"><p> - A <em class="firstterm">message bus daemon</em> executable, built on - libdbus, that multiple applications can connect to. The daemon can - route messages from one application to zero or more other - applications. - </p></li><li class="listitem"><p> - <em class="firstterm">Wrapper libraries</em> or <em class="firstterm">bindings</em> - based on particular application frameworks. For example, libdbus-glib and - libdbus-qt. There are also bindings to languages such as - Python. These wrapper libraries are the API most people should use, - as they simplify the details of D-Bus programming. libdbus is - intended to be a low-level backend for the higher level bindings. - Much of the libdbus API is only useful for binding implementation. - </p></li></ul></div><p> - </p><p> - libdbus only supports one-to-one connections, just like a raw network - socket. However, rather than sending byte streams over the connection, you - send <em class="firstterm">messages</em>. Messages have a header identifying - the kind of message, and a body containing a data payload. libdbus also - abstracts the exact transport used (sockets vs. whatever else), and - handles details such as authentication. - </p><p> - The message bus daemon forms the hub of a wheel. Each spoke of the wheel - is a one-to-one connection to an application using libdbus. An - application sends a message to the bus daemon over its spoke, and the bus - daemon forwards the message to other connected applications as - appropriate. Think of the daemon as a router. - </p><p> - The bus daemon has multiple instances on a typical computer. The - first instance is a machine-global singleton, that is, a system daemon - similar to sendmail or Apache. This instance has heavy security - restrictions on what messages it will accept, and is used for systemwide - communication. The other instances are created one per user login session. - These instances allow applications in the user's session to communicate - with one another. - </p><p> - The systemwide and per-user daemons are separate. Normal within-session - IPC does not involve the systemwide message bus process and vice versa. - </p><div class="sect2" title="D-Bus applications"><div class="titlepage"><div><div><h3 class="title"><a name="uses"></a>D-Bus applications</h3></div></div></div><p> - There are many, many technologies in the world that have "Inter-process - communication" or "networking" in their stated purpose: <a class="ulink" href="http://www.omg.org" target="_top">CORBA</a>, <a class="ulink" href="http://www.opengroup.org/dce/" target="_top">DCE</a>, <a class="ulink" href="http://www.microsoft.com/com/" target="_top">DCOM</a>, <a class="ulink" href="http://developer.kde.org/documentation/library/kdeqt/dcop.html" target="_top">DCOP</a>, <a class="ulink" href="http://www.xmlrpc.com" target="_top">XML-RPC</a>, <a class="ulink" href="http://www.w3.org/TR/SOAP/" target="_top">SOAP</a>, <a class="ulink" href="http://www.mbus.org/" target="_top">MBUS</a>, <a class="ulink" href="http://www.zeroc.com/ice.html" target="_top">Internet Communications Engine (ICE)</a>, - and probably hundreds more. - Each of these is tailored for particular kinds of application. - D-Bus is designed for two specific cases: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - Communication between desktop applications in the same desktop - session; to allow integration of the desktop session as a whole, - and address issues of process lifecycle (when do desktop components - start and stop running). - </p></li><li class="listitem"><p> - Communication between the desktop session and the operating system, - where the operating system would typically include the kernel - and any system daemons or processes. - </p></li></ul></div><p> - </p><p> - For the within-desktop-session use case, the GNOME and KDE desktops - have significant previous experience with different IPC solutions - such as CORBA and DCOP. D-Bus is built on that experience and - carefully tailored to meet the needs of these desktop projects - in particular. D-Bus may or may not be appropriate for other - applications; the FAQ has some comparisons to other IPC systems. - </p><p> - The problem solved by the systemwide or communication-with-the-OS case - is explained well by the following text from the Linux Hotplug project: - </p><div class="blockquote"><blockquote class="blockquote"><p> - A gap in current Linux support is that policies with any sort of - dynamic "interact with user" component aren't currently - supported. For example, that's often needed the first time a network - adapter or printer is connected, and to determine appropriate places - to mount disk drives. It would seem that such actions could be - supported for any case where a responsible human can be identified: - single user workstations, or any system which is remotely - administered. - </p><p> - This is a classic "remote sysadmin" problem, where in this case - hotplugging needs to deliver an event from one security domain - (operating system kernel, in this case) to another (desktop for - logged-in user, or remote sysadmin). Any effective response must go - the other way: the remote domain taking some action that lets the - kernel expose the desired device capabilities. (The action can often - be taken asynchronously, for example letting new hardware be idle - until a meeting finishes.) At this writing, Linux doesn't have - widely adopted solutions to such problems. However, the new D-Bus - work may begin to solve that problem. - </p></blockquote></div><p> - </p><p> - D-Bus may happen to be useful for purposes other than the one it was - designed for. Its general properties that distinguish it from - other forms of IPC are: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - Binary protocol designed to be used asynchronously - (similar in spirit to the X Window System protocol). - </p></li><li class="listitem"><p> - Stateful, reliable connections held open over time. - </p></li><li class="listitem"><p> - The message bus is a daemon, not a "swarm" or - distributed architecture. - </p></li><li class="listitem"><p> - Many implementation and deployment issues are specified rather - than left ambiguous/configurable/pluggable. - </p></li><li class="listitem"><p> - Semantics are similar to the existing DCOP system, allowing - KDE to adopt it more easily. - </p></li><li class="listitem"><p> - Security features to support the systemwide mode of the - message bus. - </p></li></ul></div><p> - </p></div></div><div class="sect1" title="Concepts"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="concepts"></a>Concepts</h2></div></div></div><p> - Some basic concepts apply no matter what application framework you're - using to write a D-Bus application. The exact code you write will be - different for GLib vs. Qt vs. Python applications, however. - </p><p> - Here is a diagram (<a class="ulink" href="diagram.png" target="_top">png</a> <a class="ulink" href="diagram.svg" target="_top">svg</a>) that may help you visualize the concepts - that follow. - </p><div class="sect2" title="Native Objects and Object Paths"><div class="titlepage"><div><div><h3 class="title"><a name="objects"></a>Native Objects and Object Paths</h3></div></div></div><p> - Your programming framework probably defines what an "object" is like; - usually with a base class. For example: java.lang.Object, GObject, QObject, - python's base Object, or whatever. Let's call this a <em class="firstterm">native object</em>. - </p><p> - The low-level D-Bus protocol, and corresponding libdbus API, does not care about native objects. - However, it provides a concept called an - <em class="firstterm">object path</em>. The idea of an object path is that - higher-level bindings can name native object instances, and allow remote applications - to refer to them. - </p><p> - The object path - looks like a filesystem path, for example an object could be - named <code class="literal">/org/kde/kspread/sheets/3/cells/4/5</code>. - Human-readable paths are nice, but you are free to create an - object named <code class="literal">/com/mycompany/c5yo817y0c1y1c5b</code> - if it makes sense for your application. - </p><p> - Namespacing object paths is smart, by starting them with the components - of a domain name you own (e.g. <code class="literal">/org/kde</code>). This - keeps different code modules in the same process from stepping - on one another's toes. - </p></div><div class="sect2" title="Methods and Signals"><div class="titlepage"><div><div><h3 class="title"><a name="members"></a>Methods and Signals</h3></div></div></div><p> - Each object has <em class="firstterm">members</em>; the two kinds of member - are <em class="firstterm">methods</em> and - <em class="firstterm">signals</em>. Methods are operations that can be - invoked on an object, with optional input (aka arguments or "in - parameters") and output (aka return values or "out parameters"). - Signals are broadcasts from the object to any interested observers - of the object; signals may contain a data payload. - </p><p> - Both methods and signals are referred to by name, such as - "Frobate" or "OnClicked". - </p></div><div class="sect2" title="Interfaces"><div class="titlepage"><div><div><h3 class="title"><a name="interfaces"></a>Interfaces</h3></div></div></div><p> - Each object supports one or more <em class="firstterm">interfaces</em>. - Think of an interface as a named group of methods and signals, - just as it is in GLib or Qt or Java. Interfaces define the - <span class="emphasis"><em>type</em></span> of an object instance. - </p><p> - DBus identifies interfaces with a simple namespaced string, - something like <code class="literal">org.freedesktop.Introspectable</code>. - Most bindings will map these interface names directly to - the appropriate programming language construct, for example - to Java interfaces or C++ pure virtual classes. - </p></div><div class="sect2" title="Proxies"><div class="titlepage"><div><div><h3 class="title"><a name="proxies"></a>Proxies</h3></div></div></div><p> - A <em class="firstterm">proxy object</em> is a convenient native object created to - represent a remote object in another process. The low-level DBus API involves manually creating - a method call message, sending it, then manually receiving and processing - the method reply message. Higher-level bindings provide proxies as an alternative. - Proxies look like a normal native object; but when you invoke a method on the proxy - object, the binding converts it into a DBus method call message, waits for the reply - message, unpacks the return value, and returns it from the native method.. - </p><p> - In pseudocode, programming without proxies might look like this: - </p><pre class="programlisting"> - Message message = new Message("/remote/object/path", "MethodName", arg1, arg2); - Connection connection = getBusConnection(); - connection.send(message); - Message reply = connection.waitForReply(message); - if (reply.isError()) { - - } else { - Object returnValue = reply.getReturnValue(); - } - </pre><p> - </p><p> - Programming with proxies might look like this: - </p><pre class="programlisting"> - Proxy proxy = new Proxy(getBusConnection(), "/remote/object/path"); - Object returnValue = proxy.MethodName(arg1, arg2); - </pre><p> - </p></div><div class="sect2" title="Bus Names"><div class="titlepage"><div><div><h3 class="title"><a name="bus-names"></a>Bus Names</h3></div></div></div><p> - When each application connects to the bus daemon, the daemon immediately - assigns it a name, called the <em class="firstterm">unique connection name</em>. - A unique name begins with a ':' (colon) character. These names are never - reused during the lifetime of the bus daemon - that is, you know - a given name will always refer to the same application. - An example of a unique name might be - <code class="literal">:34-907</code>. The numbers after the colon have - no meaning other than their uniqueness. - </p><p> - When a name is mapped - to a particular application's connection, that application is said to - <em class="firstterm">own</em> that name. - </p><p> - Applications may ask to own additional <em class="firstterm">well-known - names</em>. For example, you could write a specification to - define a name called <code class="literal">com.mycompany.TextEditor</code>. - Your definition could specify that to own this name, an application - should have an object at the path - <code class="literal">/com/mycompany/TextFileManager</code> supporting the - interface <code class="literal">org.freedesktop.FileHandler</code>. - </p><p> - Applications could then send messages to this bus name, - object, and interface to execute method calls. - </p><p> - You could think of the unique names as IP addresses, and the - well-known names as domain names. So - <code class="literal">com.mycompany.TextEditor</code> might map to something like - <code class="literal">:34-907</code> just as <code class="literal">mycompany.com</code> maps - to something like <code class="literal">192.168.0.5</code>. - </p><p> - Names have a second important use, other than routing messages. They - are used to track lifecycle. When an application exits (or crashes), its - connection to the message bus will be closed by the operating system - kernel. The message bus then sends out notification messages telling - remaining applications that the application's names have lost their - owner. By tracking these notifications, your application can reliably - monitor the lifetime of other applications. - </p><p> - Bus names can also be used to coordinate single-instance applications. - If you want to be sure only one - <code class="literal">com.mycompany.TextEditor</code> application is running for - example, have the text editor application exit if the bus name already - has an owner. - </p></div><div class="sect2" title="Addresses"><div class="titlepage"><div><div><h3 class="title"><a name="addresses"></a>Addresses</h3></div></div></div><p> - Applications using D-Bus are either servers or clients. A server - listens for incoming connections; a client connects to a server. Once - the connection is established, it is a symmetric flow of messages; the - client-server distinction only matters when setting up the - connection. - </p><p> - If you're using the bus daemon, as you probably are, your application - will be a client of the bus daemon. That is, the bus daemon listens - for connections and your application initiates a connection to the bus - daemon. - </p><p> - A D-Bus <em class="firstterm">address</em> specifies where a server will - listen, and where a client will connect. For example, the address - <code class="literal">unix:path=/tmp/abcdef</code> specifies that the server will - listen on a UNIX domain socket at the path - <code class="literal">/tmp/abcdef</code> and the client will connect to that - socket. An address can also specify TCP/IP sockets, or any other - transport defined in future iterations of the D-Bus specification. - </p><p> - When using D-Bus with a message bus daemon, - libdbus automatically discovers the address of the per-session bus - daemon by reading an environment variable. It discovers the - systemwide bus daemon by checking a well-known UNIX domain socket path - (though you can override this address with an environment variable). - </p><p> - If you're using D-Bus without a bus daemon, it's up to you to - define which application will be the server and which will be - the client, and specify a mechanism for them to agree on - the server's address. This is an unusual case. - </p></div><div class="sect2" title="Big Conceptual Picture"><div class="titlepage"><div><div><h3 class="title"><a name="bigpicture"></a>Big Conceptual Picture</h3></div></div></div><p> - Pulling all these concepts together, to specify a particular - method call on a particular object instance, a number of - nested components have to be named: - </p><pre class="programlisting"> - Address -> [Bus Name] -> Path -> Interface -> Method - </pre><p> - The bus name is in brackets to indicate that it's optional -- you only - provide a name to route the method call to the right application - when using the bus daemon. If you have a direct connection to another - application, bus names aren't used; there's no bus daemon. - </p><p> - The interface is also optional, primarily for historical - reasons; DCOP does not require specifying the interface, - instead simply forbidding duplicate method names - on the same object instance. D-Bus will thus let you - omit the interface, but if your method name is ambiguous - it is undefined which method will be invoked. - </p></div><div class="sect2" title="Messages - Behind the Scenes"><div class="titlepage"><div><div><h3 class="title"><a name="messages"></a>Messages - Behind the Scenes</h3></div></div></div><p> - D-Bus works by sending messages between processes. If you're using - a sufficiently high-level binding, you may never work with messages directly. - </p><p> - There are 4 message types: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - Method call messages ask to invoke a method - on an object. - </p></li><li class="listitem"><p> - Method return messages return the results - of invoking a method. - </p></li><li class="listitem"><p> - Error messages return an exception caused by - invoking a method. - </p></li><li class="listitem"><p> - Signal messages are notifications that a given signal - has been emitted (that an event has occurred). - You could also think of these as "event" messages. - </p></li></ul></div><p> - </p><p> - A method call maps very simply to messages: you send a method call - message, and receive either a method return message or an error message - in reply. - </p><p> - Each message has a <em class="firstterm">header</em>, including <em class="firstterm">fields</em>, - and a <em class="firstterm">body</em>, including <em class="firstterm">arguments</em>. You can think - of the header as the routing information for the message, and the body as the payload. - Header fields might include the sender bus name, destination bus name, method or signal name, - and so forth. One of the header fields is a <em class="firstterm">type signature</em> describing the - values found in the body. For example, the letter "i" means "32-bit integer" so the signature - "ii" means the payload has two 32-bit integers. - </p></div><div class="sect2" title="Calling a Method - Behind the Scenes"><div class="titlepage"><div><div><h3 class="title"><a name="callprocedure"></a>Calling a Method - Behind the Scenes</h3></div></div></div><p> - A method call in DBus consists of two messages; a method call message sent from process A to process B, - and a matching method reply message sent from process B to process A. Both the call and the reply messages - are routed through the bus daemon. The caller includes a different serial number in each call message, and the - reply message includes this number to allow the caller to match replies to calls. - </p><p> - The call message will contain any arguments to the method. - The reply message may indicate an error, or may contain data returned by the method. - </p><p> - A method invocation in DBus happens as follows: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - The language binding may provide a proxy, such that invoking a method on - an in-process object invokes a method on a remote object in another process. If so, the - application calls a method on the proxy, and the proxy - constructs a method call message to send to the remote process. - </p></li><li class="listitem"><p> - For more low-level APIs, the application may construct a method call message itself, without - using a proxy. - </p></li><li class="listitem"><p> - In either case, the method call message contains: a bus name belonging to the remote process; the name of the method; - the arguments to the method; an object path inside the remote process; and optionally the name of the - interface that specifies the method. - </p></li><li class="listitem"><p> - The method call message is sent to the bus daemon. - </p></li><li class="listitem"><p> - The bus daemon looks at the destination bus name. If a process owns that name, - the bus daemon forwards the method call to that process. Otherwise, the bus daemon - creates an error message and sends it back as the reply to the method call message. - </p></li><li class="listitem"><p> - The receiving process unpacks the method call message. In a simple low-level API situation, it - may immediately run the method and send a method reply message to the bus daemon. - When using a high-level binding API, the binding might examine the object path, interface, - and method name, and convert the method call message into an invocation of a method on - a native object (GObject, java.lang.Object, QObject, etc.), then convert the return - value from the native method into a method reply message. - </p></li><li class="listitem"><p> - The bus daemon receives the method reply message and sends it to the process that - made the method call. - </p></li><li class="listitem"><p> - The process that made the method call looks at the method reply and makes use of any - return values included in the reply. The reply may also indicate that an error occurred. - When using a binding, the method reply message may be converted into the return value of - of a proxy method, or into an exception. - </p></li></ul></div><p> - </p><p> - The bus daemon never reorders messages. That is, if you send two method call messages to the same recipient, - they will be received in the order they were sent. The recipient is not required to reply to the calls - in order, however; for example, it may process each method call in a separate thread, and return reply messages - in an undefined order depending on when the threads complete. Method calls have a unique serial - number used by the method caller to match reply messages to call messages. - </p></div><div class="sect2" title="Emitting a Signal - Behind the Scenes"><div class="titlepage"><div><div><h3 class="title"><a name="signalprocedure"></a>Emitting a Signal - Behind the Scenes</h3></div></div></div><p> - A signal in DBus consists of a single message, sent by one process to any number of other processes. - That is, a signal is a unidirectional broadcast. The signal may contain arguments (a data payload), but - because it is a broadcast, it never has a "return value." Contrast this with a method call - (see <a class="xref" href="#callprocedure" title="Calling a Method - Behind the Scenes">the section called “Calling a Method - Behind the Scenes”</a>) where the method call message has a matching method reply message. - </p><p> - The emitter (aka sender) of a signal has no knowledge of the signal recipients. Recipients register - with the bus daemon to receive signals based on "match rules" - these rules would typically include the sender and - the signal name. The bus daemon sends each signal only to recipients who have expressed interest in that - signal. - </p><p> - A signal in DBus happens as follows: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - A signal message is created and sent to the bus daemon. When using the low-level API this may be - done manually, with certain bindings it may be done for you by the binding when a native object - emits a native signal or event. - </p></li><li class="listitem"><p> - The signal message contains the name of the interface that specifies the signal; - the name of the signal; the bus name of the process sending the signal; and - any arguments - </p></li><li class="listitem"><p> - Any process on the message bus can register "match rules" indicating which signals it - is interested in. The bus has a list of registered match rules. - </p></li><li class="listitem"><p> - The bus daemon examines the signal and determines which processes are interested in it. - It sends the signal message to these processes. - </p></li><li class="listitem"><p> - Each process receiving the signal decides what to do with it; if using a binding, - the binding may choose to emit a native signal on a proxy object. If using the - low-level API, the process may just look at the signal sender and name and decide - what to do based on that. - </p></li></ul></div><p> - </p></div><div class="sect2" title="Introspection"><div class="titlepage"><div><div><h3 class="title"><a name="introspection"></a>Introspection</h3></div></div></div><p> - D-Bus objects may support the interface <code class="literal">org.freedesktop.DBus.Introspectable</code>. - This interface has one method <code class="literal">Introspect</code> which takes no arguments and returns - an XML string. The XML string describes the interfaces, methods, and signals of the object. - See the D-Bus specification for more details on this introspection format. - </p></div></div><div class="sect1" title="GLib API: Using Remote Objects"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="glib-client"></a>GLib API: Using Remote Objects</h2></div></div></div><p> - The GLib binding is defined in the header file - <code class="literal"><dbus/dbus-glib.h></code>. - </p><div class="sect2" title="D-Bus - GLib type mappings"><div class="titlepage"><div><div><h3 class="title"><a name="glib-typemappings"></a>D-Bus - GLib type mappings</h3></div></div></div><p> - The heart of the GLib bindings for D-Bus is the mapping it - provides between D-Bus "type signatures" and GLib types - (<code class="literal">GType</code>). The D-Bus type system is composed of - a number of "basic" types, along with several "container" types. - </p><div class="sect3" title="Basic type mappings"><div class="titlepage"><div><div><h4 class="title"><a name="glib-basic-typemappings"></a>Basic type mappings</h4></div></div></div><p> - Below is a list of the basic types, along with their associated - mapping to a <code class="literal">GType</code>. - </p><div class="informaltable"><table border="1"><colgroup><col><col><col><col></colgroup><thead><tr><th>D-Bus basic type</th><th>GType</th><th>Free function</th><th>Notes</th></tr></thead><tbody><tr><td><code class="literal">BYTE</code></td><td><code class="literal">G_TYPE_UCHAR</code></td><td> </td><td> </td></tr><tr><td><code class="literal">BOOLEAN</code></td><td><code class="literal">G_TYPE_BOOLEAN</code></td><td> </td><td> </td></tr><tr><td><code class="literal">INT16</code></td><td><code class="literal">G_TYPE_INT</code></td><td> </td><td>Will be changed to a <code class="literal">G_TYPE_INT16</code> once GLib has it</td></tr><tr><td><code class="literal">UINT16</code></td><td><code class="literal">G_TYPE_UINT</code></td><td> </td><td>Will be changed to a <code class="literal">G_TYPE_UINT16</code> once GLib has it</td></tr><tr><td><code class="literal">INT32</code></td><td><code class="literal">G_TYPE_INT</code></td><td> </td><td>Will be changed to a <code class="literal">G_TYPE_INT32</code> once GLib has it</td></tr><tr><td><code class="literal">UINT32</code></td><td><code class="literal">G_TYPE_UINT</code></td><td> </td><td>Will be changed to a <code class="literal">G_TYPE_UINT32</code> once GLib has it</td></tr><tr><td><code class="literal">INT64</code></td><td><code class="literal">G_TYPE_GINT64</code></td><td> </td><td> </td></tr><tr><td><code class="literal">UINT64</code></td><td><code class="literal">G_TYPE_GUINT64</code></td><td> </td><td> </td></tr><tr><td><code class="literal">DOUBLE</code></td><td><code class="literal">G_TYPE_DOUBLE</code></td><td> </td><td> </td></tr><tr><td><code class="literal">STRING</code></td><td><code class="literal">G_TYPE_STRING</code></td><td><code class="literal">g_free</code></td><td> </td></tr><tr><td><code class="literal">OBJECT_PATH</code></td><td><code class="literal">DBUS_TYPE_G_PROXY</code></td><td><code class="literal">g_object_unref</code></td><td>The returned proxy does not have an interface set; use <code class="literal">dbus_g_proxy_set_interface</code> to invoke methods</td></tr></tbody></table></div><p> - As you can see, the basic mapping is fairly straightforward. - </p></div><div class="sect3" title="Container type mappings"><div class="titlepage"><div><div><h4 class="title"><a name="glib-container-typemappings"></a>Container type mappings</h4></div></div></div><p> - The D-Bus type system also has a number of "container" - types, such as <code class="literal">DBUS_TYPE_ARRAY</code> and - <code class="literal">DBUS_TYPE_STRUCT</code>. The D-Bus type system - is fully recursive, so one can for example have an array of - array of strings (i.e. type signature - <code class="literal">aas</code>). - </p><p> - However, not all of these types are in common use; for - example, at the time of this writing the author knows of no - one using <code class="literal">DBUS_TYPE_STRUCT</code>, or a - <code class="literal">DBUS_TYPE_ARRAY</code> containing any non-basic - type. The approach the GLib bindings take is pragmatic; try - to map the most common types in the most obvious way, and - let using less common and more complex types be less - "natural". - </p><p> - First, D-Bus type signatures which have an "obvious" - corresponding built-in GLib type are mapped using that type: - </p><div class="informaltable"><table border="1"><colgroup><col><col><col><col><col><col></colgroup><thead><tr><th>D-Bus type signature</th><th>Description</th><th>GType</th><th>C typedef</th><th>Free function</th><th>Notes</th></tr></thead><tbody><tr><td><code class="literal">as</code></td><td>Array of strings</td><td><code class="literal">G_TYPE_STRV</code></td><td><code class="literal">char **</code></td><td><code class="literal">g_strfreev</code></td><td> </td></tr><tr><td><code class="literal">v</code></td><td>Generic value container</td><td><code class="literal">G_TYPE_VALUE</code></td><td><code class="literal">GValue *</code></td><td><code class="literal">g_value_unset</code></td><td>The calling conventions for values expect that method callers have allocated return values; see below.</td></tr></tbody></table></div><p> - </p><p> - The next most common recursive type signatures are arrays of - basic values. The most obvious mapping for arrays of basic - types is a <code class="literal">GArray</code>. Now, GLib does not - provide a builtin <code class="literal">GType</code> for - <code class="literal">GArray</code>. However, we actually need more than - that - we need a "parameterized" type which includes the - contained type. Why we need this we will see below. - </p><p> - The approach taken is to create these types in the D-Bus GLib - bindings; however, there is nothing D-Bus specific about them. - In the future, we hope to include such "fundamental" types in GLib - itself. - </p><div class="informaltable"><table border="1"><colgroup><col><col><col><col><col><col></colgroup><thead><tr><th>D-Bus type signature</th><th>Description</th><th>GType</th><th>C typedef</th><th>Free function</th><th>Notes</th></tr></thead><tbody><tr><td><code class="literal">ay</code></td><td>Array of bytes</td><td><code class="literal">DBUS_TYPE_G_BYTE_ARRAY</code></td><td><code class="literal">GArray *</code></td><td>g_array_free</td><td> </td></tr><tr><td><code class="literal">au</code></td><td>Array of uint</td><td><code class="literal">DBUS_TYPE_G_UINT_ARRAY</code></td><td><code class="literal">GArray *</code></td><td>g_array_free</td><td> </td></tr><tr><td><code class="literal">ai</code></td><td>Array of int</td><td><code class="literal">DBUS_TYPE_G_INT_ARRAY</code></td><td><code class="literal">GArray *</code></td><td>g_array_free</td><td> </td></tr><tr><td><code class="literal">ax</code></td><td>Array of int64</td><td><code class="literal">DBUS_TYPE_G_INT64_ARRAY</code></td><td><code class="literal">GArray *</code></td><td>g_array_free</td><td> </td></tr><tr><td><code class="literal">at</code></td><td>Array of uint64</td><td><code class="literal">DBUS_TYPE_G_UINT64_ARRAY</code></td><td><code class="literal">GArray *</code></td><td>g_array_free</td><td> </td></tr><tr><td><code class="literal">ad</code></td><td>Array of double</td><td><code class="literal">DBUS_TYPE_G_DOUBLE_ARRAY</code></td><td><code class="literal">GArray *</code></td><td>g_array_free</td><td> </td></tr><tr><td><code class="literal">ab</code></td><td>Array of boolean</td><td><code class="literal">DBUS_TYPE_G_BOOLEAN_ARRAY</code></td><td><code class="literal">GArray *</code></td><td>g_array_free</td><td> </td></tr></tbody></table></div><p> - </p><p> - D-Bus also includes a special type DBUS_TYPE_DICT_ENTRY which - is only valid in arrays. It's intended to be mapped to a "dictionary" - type by bindings. The obvious GLib mapping here is GHashTable. Again, - however, there is no builtin <code class="literal">GType</code> for a GHashTable. - Moreover, just like for arrays, we need a parameterized type so that - the bindings can communiate which types are contained in the hash table. - </p><p> - At present, only strings are supported. Work is in progress to - include more types. - </p><div class="informaltable"><table border="1"><colgroup><col><col><col><col><col><col></colgroup><thead><tr><th>D-Bus type signature</th><th>Description</th><th>GType</th><th>C typedef</th><th>Free function</th><th>Notes</th></tr></thead><tbody><tr><td><code class="literal">a{ss}</code></td><td>Dictionary mapping strings to strings</td><td><code class="literal">DBUS_TYPE_G_STRING_STRING_HASHTABLE</code></td><td><code class="literal">GHashTable *</code></td><td>g_hash_table_destroy</td><td> </td></tr></tbody></table></div><p> - </p></div><div class="sect3" title="Arbitrarily recursive type mappings"><div class="titlepage"><div><div><h4 class="title"><a name="glib-generic-typemappings"></a>Arbitrarily recursive type mappings</h4></div></div></div><p> - Finally, it is possible users will want to write or invoke D-Bus - methods which have arbitrarily complex type signatures not - directly supported by these bindings. For this case, we have a - <code class="literal">DBusGValue</code> which acts as a kind of special - variant value which may be iterated over manually. The - <code class="literal">GType</code> associated is - <code class="literal">DBUS_TYPE_G_VALUE</code>. - </p><p> - TODO insert usage of <code class="literal">DBUS_TYPE_G_VALUE</code> here. - </p></div></div><div class="sect2" title="A sample program"><div class="titlepage"><div><div><h3 class="title"><a name="sample-program-1"></a>A sample program</h3></div></div></div><p>Here is a D-Bus program using the GLib bindings. -</p><pre class="programlisting"> -int -main (int argc, char **argv) -{ - DBusGConnection *connection; - GError *error; - DBusGProxy *proxy; - char **name_list; - char **name_list_ptr; - - g_type_init (); - - error = NULL; - connection = dbus_g_bus_get (DBUS_BUS_SESSION, - &error); - if (connection == NULL) - { - g_printerr ("Failed to open connection to bus: %s\n", - error->message); - g_error_free (error); - exit (1); - } - - /* Create a proxy object for the "bus driver" (name "org.freedesktop.DBus") */ - - proxy = dbus_g_proxy_new_for_name (connection, - DBUS_SERVICE_DBUS, - DBUS_PATH_DBUS, - DBUS_INTERFACE_DBUS); - - /* Call ListNames method, wait for reply */ - error = NULL; - if (!dbus_g_proxy_call (proxy, "ListNames", &error, G_TYPE_INVALID, - G_TYPE_STRV, &name_list, G_TYPE_INVALID)) - { - /* Just do demonstrate remote exceptions versus regular GError */ - if (error->domain == DBUS_GERROR && error->code == DBUS_GERROR_REMOTE_EXCEPTION) - g_printerr ("Caught remote method exception %s: %s", - dbus_g_error_get_name (error), - error->message); - else - g_printerr ("Error: %s\n", error->message); - g_error_free (error); - exit (1); - } - - /* Print the results */ - - g_print ("Names on the message bus:\n"); - - for (name_list_ptr = name_list; *name_list_ptr; name_list_ptr++) - { - g_print (" %s\n", *name_list_ptr); - } - g_strfreev (name_list); - - g_object_unref (proxy); - - return 0; -} -</pre><p> - </p></div><div class="sect2" title="Program initalization"><div class="titlepage"><div><div><h3 class="title"><a name="glib-program-setup"></a>Program initalization</h3></div></div></div><p> - A connection to the bus is acquired using - <code class="literal">dbus_g_bus_get</code>. Next, a proxy - is created for the object "/org/freedesktop/DBus" with - interface <code class="literal">org.freedesktop.DBus</code> - on the service <code class="literal">org.freedesktop.DBus</code>. - This is a proxy for the message bus itself. - </p></div><div class="sect2" title="Understanding method invocation"><div class="titlepage"><div><div><h3 class="title"><a name="glib-method-invocation"></a>Understanding method invocation</h3></div></div></div><p> - You have a number of choices for method invocation. First, as - used above, <code class="literal">dbus_g_proxy_call</code> sends a - method call to the remote object, and blocks until a reply is - recieved. The outgoing arguments are specified in the varargs - array, terminated with <code class="literal">G_TYPE_INVALID</code>. - Next, pointers to return values are specified, followed again - by <code class="literal">G_TYPE_INVALID</code>. - </p><p> - To invoke a method asynchronously, use - <code class="literal">dbus_g_proxy_begin_call</code>. This returns a - <code class="literal">DBusGPendingCall</code> object; you may then set a - notification function using - <code class="literal">dbus_g_pending_call_set_notify</code>. - </p></div><div class="sect2" title="Connecting to object signals"><div class="titlepage"><div><div><h3 class="title"><a name="glib-signal-connection"></a>Connecting to object signals</h3></div></div></div><p> - You may connect to signals using - <code class="literal">dbus_g_proxy_add_signal</code> and - <code class="literal">dbus_g_proxy_connect_signal</code>. You must - invoke <code class="literal">dbus_g_proxy_add_signal</code> to specify - the signature of your signal handlers; you may then invoke - <code class="literal">dbus_g_proxy_connect_signal</code> multiple times. - </p><p> - Note that it will often be the case that there is no builtin - marshaller for the type signature of a remote signal. In that - case, you must generate a marshaller yourself by using - <span class="application">glib-genmarshal</span>, and then register - it using <code class="literal">dbus_g_object_register_marshaller</code>. - </p></div><div class="sect2" title="Error handling and remote exceptions"><div class="titlepage"><div><div><h3 class="title"><a name="glib-error-handling"></a>Error handling and remote exceptions</h3></div></div></div><p> - All of the GLib binding methods such as - <code class="literal">dbus_g_proxy_end_call</code> return a - <code class="literal">GError</code>. This <code class="literal">GError</code> can - represent two different things: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - An internal D-Bus error, such as an out-of-memory - condition, an I/O error, or a network timeout. Errors - generated by the D-Bus library itself have the domain - <code class="literal">DBUS_GERROR</code>, and a corresponding code - such as <code class="literal">DBUS_GERROR_NO_MEMORY</code>. It will - not be typical for applications to handle these errors - specifically. - </p></li><li class="listitem"><p> - A remote D-Bus exception, thrown by the peer, bus, or - service. D-Bus remote exceptions have both a textual - "name" and a "message". The GLib bindings store this - information in the <code class="literal">GError</code>, but some - special rules apply. - </p><p> - The set error will have the domain - <code class="literal">DBUS_GERROR</code> as above, and will also - have the code - <code class="literal">DBUS_GERROR_REMOTE_EXCEPTION</code>. In order - to access the remote exception name, you must use a - special accessor, such as - <code class="literal">dbus_g_error_has_name</code> or - <code class="literal">dbus_g_error_get_name</code>. The remote - exception detailed message is accessible via the regular - GError <code class="literal">message</code> member. - </p></li></ul></div><p> - </p></div><div class="sect2" title="More examples of method invocation"><div class="titlepage"><div><div><h3 class="title"><a name="glib-more-examples"></a>More examples of method invocation</h3></div></div></div><div class="sect3" title="Sending an integer and string, receiving an array of bytes"><div class="titlepage"><div><div><h4 class="title"><a name="glib-sending-stuff"></a>Sending an integer and string, receiving an array of bytes</h4></div></div></div><p> -</p><pre class="programlisting"> - GArray *arr; - - error = NULL; - if (!dbus_g_proxy_call (proxy, "Foobar", &error, - G_TYPE_INT, 42, G_TYPE_STRING, "hello", - G_TYPE_INVALID, - DBUS_TYPE_G_UCHAR_ARRAY, &arr, G_TYPE_INVALID)) - { - /* Handle error */ - } - g_assert (arr != NULL); - printf ("got back %u values", arr->len); -</pre><p> - </p></div><div class="sect3" title="Sending a GHashTable"><div class="titlepage"><div><div><h4 class="title"><a name="glib-sending-hash"></a>Sending a GHashTable</h4></div></div></div><p> -</p><pre class="programlisting"> - GHashTable *hash = g_hash_table_new (g_str_hash, g_str_equal); - guint32 ret; - - g_hash_table_insert (hash, "foo", "bar"); - g_hash_table_insert (hash, "baz", "whee"); - - error = NULL; - if (!dbus_g_proxy_call (proxy, "HashSize", &error, - DBUS_TYPE_G_STRING_STRING_HASH, hash, G_TYPE_INVALID, - G_TYPE_UINT, &ret, G_TYPE_INVALID)) - { - /* Handle error */ - } - g_assert (ret == 2); - g_hash_table_destroy (hash); -</pre><p> - </p></div><div class="sect3" title="Receiving a boolean and a string"><div class="titlepage"><div><div><h4 class="title"><a name="glib-receiving-bool-int"></a>Receiving a boolean and a string</h4></div></div></div><p> -</p><pre class="programlisting"> - gboolean boolret; - char *strret; - - error = NULL; - if (!dbus_g_proxy_call (proxy, "GetStuff", &error, - G_TYPE_INVALID, - G_TYPE_BOOLEAN, &boolret, - G_TYPE_STRING, &strret, - G_TYPE_INVALID)) - { - /* Handle error */ - } - printf ("%s %s", boolret ? "TRUE" : "FALSE", strret); - g_free (strret); -</pre><p> - </p></div><div class="sect3" title="Sending two arrays of strings"><div class="titlepage"><div><div><h4 class="title"><a name="glib-sending-str-arrays"></a>Sending two arrays of strings</h4></div></div></div><p> -</p><pre class="programlisting"> - /* NULL terminate */ - char *strs_static[] = {"foo", "bar", "baz", NULL}; - /* Take pointer to array; cannot pass array directly */ - char **strs_static_p = strs_static; - char **strs_dynamic; - - strs_dynamic = g_new (char *, 4); - strs_dynamic[0] = g_strdup ("hello"); - strs_dynamic[1] = g_strdup ("world"); - strs_dynamic[2] = g_strdup ("!"); - /* NULL terminate */ - strs_dynamic[3] = NULL; - - error = NULL; - if (!dbus_g_proxy_call (proxy, "TwoStrArrays", &error, - G_TYPE_STRV, strs_static_p, - G_TYPE_STRV, strs_dynamic, - G_TYPE_INVALID, - G_TYPE_INVALID)) - { - /* Handle error */ - } - g_strfreev (strs_dynamic); -</pre><p> - </p></div><div class="sect3" title="Sending a boolean, receiving an array of strings"><div class="titlepage"><div><div><h4 class="title"><a name="glib-getting-str-array"></a>Sending a boolean, receiving an array of strings</h4></div></div></div><p> -</p><pre class="programlisting"> - char **strs; - char **strs_p; - gboolean blah; - - error = NULL; - blah = TRUE; - if (!dbus_g_proxy_call (proxy, "GetStrs", &error, - G_TYPE_BOOLEAN, blah, - G_TYPE_INVALID, - G_TYPE_STRV, &strs, - G_TYPE_INVALID)) - { - /* Handle error */ - } - for (strs_p = strs; *strs_p; strs_p++) - printf ("got string: \"%s\"", *strs_p); - g_strfreev (strs); -</pre><p> - </p></div><div class="sect3" title="Sending a variant"><div class="titlepage"><div><div><h4 class="title"><a name="glib-sending-variant"></a>Sending a variant</h4></div></div></div><p> -</p><pre class="programlisting"> - GValue val = {0, }; - - g_value_init (&val, G_TYPE_STRING); - g_value_set_string (&val, "hello world"); - - error = NULL; - if (!dbus_g_proxy_call (proxy, "SendVariant", &error, - G_TYPE_VALUE, &val, G_TYPE_INVALID, - G_TYPE_INVALID)) - { - /* Handle error */ - } - g_assert (ret == 2); - g_value_unset (&val); -</pre><p> - </p></div><div class="sect3" title="Receiving a variant"><div class="titlepage"><div><div><h4 class="title"><a name="glib-receiving-variant"></a>Receiving a variant</h4></div></div></div><p> -</p><pre class="programlisting"> - GValue val = {0, }; - - error = NULL; - if (!dbus_g_proxy_call (proxy, "GetVariant", &error, G_TYPE_INVALID, - G_TYPE_VALUE, &val, G_TYPE_INVALID)) - { - /* Handle error */ - } - if (G_VALUE_TYPE (&val) == G_TYPE_STRING) - printf ("%s\n", g_value_get_string (&val)); - else if (G_VALUE_TYPE (&val) == G_TYPE_INT) - printf ("%d\n", g_value_get_int (&val)); - else - ... - g_value_unset (&val); -</pre><p> - </p></div></div><div class="sect2" title="Generated Bindings"><div class="titlepage"><div><div><h3 class="title"><a name="glib-generated-bindings"></a>Generated Bindings</h3></div></div></div><p> - By using the Introspection XML files, convenient client-side bindings - can be automatically created to ease the use of a remote DBus object. - </p><p> - Here is a sample XML file which describes an object that exposes - one method, named <code class="literal">ManyArgs</code>. - </p><pre class="programlisting"> -<?xml version="1.0" encoding="UTF-8" ?> -<node name="/com/example/MyObject"> - <interface name="com.example.MyObject"> - <method name="ManyArgs"> - <arg type="u" name="x" direction="in" /> - <arg type="s" name="str" direction="in" /> - <arg type="d" name="trouble" direction="in" /> - <arg type="d" name="d_ret" direction="out" /> - <arg type="s" name="str_ret" direction="out" /> - </method> - </interface> -</node> -</pre><p> - </p><p> - Run <code class="literal">dbus-binding-tool --mode=glib-client - <em class="replaceable"><code>FILENAME</code></em> > - <em class="replaceable"><code>HEADER_NAME</code></em></code> to generate the header - file. For example: <span class="command"><strong>dbus-binding-tool --mode=glib-client - my-object.xml > my-object-bindings.h</strong></span>. This will generate - inline functions with the following prototypes: - </p><pre class="programlisting"> -/* This is a blocking call */ -gboolean -com_example_MyObject_many_args (DBusGProxy *proxy, const guint IN_x, - const char * IN_str, const gdouble IN_trouble, - gdouble* OUT_d_ret, char ** OUT_str_ret, - GError **error); - -/* This is a non-blocking call */ -DBusGProxyCall* -com_example_MyObject_many_args_async (DBusGProxy *proxy, const guint IN_x, - const char * IN_str, const gdouble IN_trouble, - com_example_MyObject_many_args_reply callback, - gpointer userdata); - -/* This is the typedef for the non-blocking callback */ -typedef void -(*com_example_MyObject_many_args_reply) -(DBusGProxy *proxy, gdouble OUT_d_ret, char * OUT_str_ret, - GError *error, gpointer userdata); -</pre><p> - The first argument in all functions is a <code class="literal">DBusGProxy - *</code>, which you should create with the usual - <code class="literal">dbus_g_proxy_new_*</code> functions. Following that are the - "in" arguments, and then either the "out" arguments and a - <code class="literal">GError *</code> for the synchronous (blocking) function, or - callback and user data arguments for the asynchronous (non-blocking) - function. The callback in the asynchronous function passes the - <code class="literal">DBusGProxy *</code>, the returned "out" arguments, an - <code class="literal">GError *</code> which is set if there was an error otherwise - <code class="literal">NULL</code>, and the user data. - </p><p> - As with the server-side bindings support (see <a class="xref" href="#glib-server" title="GLib API: Implementing Objects">the section called “GLib API: Implementing Objects”</a>), the exact behaviour of the client-side - bindings can be manipulated using "annotations". Currently the only - annotation used by the client bindings is - <code class="literal">org.freedesktop.DBus.GLib.NoReply</code>, which sets the - flag indicating that the client isn't expecting a reply to the method - call, so a reply shouldn't be sent. This is often used to speed up - rapid method calls where there are no "out" arguments, and not knowing - if the method succeeded is an acceptable compromise to half the traffic - on the bus. - </p></div></div><div class="sect1" title="GLib API: Implementing Objects"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="glib-server"></a>GLib API: Implementing Objects</h2></div></div></div><p> - At the moment, to expose a GObject via D-Bus, you must - write XML by hand which describes the methods exported - by the object. In the future, this manual step will - be obviated by the upcoming GLib introspection support. - </p><p> - Here is a sample XML file which describes an object that exposes - one method, named <code class="literal">ManyArgs</code>. -</p><pre class="programlisting"> -<?xml version="1.0" encoding="UTF-8" ?> - -<node name="/com/example/MyObject"> - - <interface name="com.example.MyObject"> - <annotation name="org.freedesktop.DBus.GLib.CSymbol" value="my_object"/> - <method name="ManyArgs"> - <!-- This is optional, and in this case is redunundant --> - <annotation name="org.freedesktop.DBus.GLib.CSymbol" value="my_object_many_args"/> - <arg type="u" name="x" direction="in" /> - <arg type="s" name="str" direction="in" /> - <arg type="d" name="trouble" direction="in" /> - <arg type="d" name="d_ret" direction="out" /> - <arg type="s" name="str_ret" direction="out" /> - </method> - </interface> -</node> -</pre><p> - </p><p> - This XML is in the same format as the D-Bus introspection XML - format. Except we must include an "annotation" which give the C - symbols corresponding to the object implementation prefix - (<code class="literal">my_object</code>). In addition, if particular - methods symbol names deviate from C convention - (i.e. <code class="literal">ManyArgs</code> -> - <code class="literal">many_args</code>), you may specify an annotation - giving the C symbol. - </p><p> - Once you have written this XML, run <code class="literal">dbus-binding-tool --mode=glib-server <em class="replaceable"><code>FILENAME</code></em> > <em class="replaceable"><code>HEADER_NAME</code></em>.</code> to - generate a header file. For example: <span class="command"><strong>dbus-binding-tool --mode=glib-server my-object.xml > my-object-glue.h</strong></span>. - </p><p> - Next, include the generated header in your program, and invoke - <code class="literal">dbus_g_object_class_install_info</code> in the class - initializer, passing the object class and "object info" included in the - header. For example: - </p><pre class="programlisting"> - dbus_g_object_type_install_info (COM_FOO_TYPE_MY_OBJECT, &com_foo_my_object_info); - </pre><p> - This should be done exactly once per object class. - </p><p> - To actually implement the method, just define a C function named e.g. - <code class="literal">my_object_many_args</code> in the same file as the info - header is included. At the moment, it is required that this function - conform to the following rules: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - The function must return a value of type <code class="literal">gboolean</code>; - <code class="literal">TRUE</code> on success, and <code class="literal">FALSE</code> - otherwise. - </p></li><li class="listitem"><p> - The first parameter is a pointer to an instance of the object. - </p></li><li class="listitem"><p> - Following the object instance pointer are the method - input values. - </p></li><li class="listitem"><p> - Following the input values are pointers to return values. - </p></li><li class="listitem"><p> - The final parameter must be a <code class="literal">GError **</code>. - If the function returns <code class="literal">FALSE</code> for an - error, the error parameter must be initalized with - <code class="literal">g_set_error</code>. - </p></li></ul></div><p> - </p><p> - Finally, you can export an object using <code class="literal">dbus_g_connection_register_g_object</code>. For example: - </p><pre class="programlisting"> - dbus_g_connection_register_g_object (connection, - "/com/foo/MyObject", - obj); - </pre><p> - </p><div class="sect2" title="Server-side Annotations"><div class="titlepage"><div><div><h3 class="title"><a name="glib-annotations"></a>Server-side Annotations</h3></div></div></div><p> - There are several annotations that are used when generating the - server-side bindings. The most common annotation is - <code class="literal">org.freedesktop.DBus.GLib.CSymbol</code> but there are other - annotations which are often useful. - </p><div class="variablelist"><dl><dt><span class="term"><code class="literal">org.freedesktop.DBus.GLib.CSymbol</code></span></dt><dd><p> - This annotation is used to specify the C symbol names for - the various types (interface, method, etc), if it differs from the - name DBus generates. - </p></dd><dt><span class="term"><code class="literal">org.freedesktop.DBus.GLib.Async</code></span></dt><dd><p> - This annotation marks the method implementation as an - asynchronous function, which doesn't return a response straight - away but will send the response at some later point to complete - the call. This is used to implement non-blocking services where - method calls can take time. - </p><p> - When a method is asynchronous, the function prototype is - different. It is required that the function conform to the - following rules: - </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> - The function must return a value of type <code class="literal">gboolean</code>; - <code class="literal">TRUE</code> on success, and <code class="literal">FALSE</code> - otherwise. TODO: the return value is currently ignored. - </p></li><li class="listitem"><p> - The first parameter is a pointer to an instance of the object. - </p></li><li class="listitem"><p> - Following the object instance pointer are the method - input values. - </p></li><li class="listitem"><p> - The final parameter must be a - <code class="literal">DBusGMethodInvocation *</code>. This is used - when sending the response message back to the client, by - calling <code class="literal">dbus_g_method_return</code> or - <code class="literal">dbus_g_method_return_error</code>. - </p></li></ul></div><p> - </p></dd><dt><span class="term"><code class="literal">org.freedesktop.DBus.GLib.Const</code></span></dt><dd><p>This attribute can only be applied to "out" - <code class="literal"><arg></code> nodes, and specifies that the - parameter isn't being copied when returned. For example, this - turns a 's' argument from a <code class="literal">char **</code> to a - <code class="literal">const char **</code>, and results in the argument not - being freed by DBus after the message is sent. - </p></dd><dt><span class="term"><code class="literal">org.freedesktop.DBus.GLib.ReturnVal</code></span></dt><dd><p> - This attribute can only be applied to "out" - <code class="literal"><arg></code> nodes, and alters the expected - function signature. It currently can be set to two values: - <code class="literal">""</code> or <code class="literal">"error"</code>. The - argument marked with this attribute is not returned via a - pointer argument, but by the function's return value. If the - attribute's value is the empty string, the <code class="literal">GError - *</code> argument is also omitted so there is no standard way - to return an error value. This is very useful for interfacing - with existing code, as it is possible to match existing APIs. - If the attribute's value is <code class="literal">"error"</code>, then the - final argument is a <code class="literal">GError *</code> as usual. - </p><p> - Some examples to demonstrate the usage. This introspection XML: - </p><pre class="programlisting"> -<method name="Increment"> - <arg type="u" name="x" /> - <arg type="u" direction="out" /> -</method> - </pre><p> - Expects the following function declaration: - </p><pre class="programlisting"> -gboolean -my_object_increment (MyObject *obj, gint32 x, gint32 *ret, GError **error); - </pre><p> - </p><p> - This introspection XML: - </p><pre class="programlisting"> -<method name="IncrementRetval"> - <arg type="u" name="x" /> - <arg type="u" direction="out" > - <annotation name="org.freedesktop.DBus.GLib.ReturnVal" value=""/> - </arg> -</method> - </pre><p> - Expects the following function declaration: - </p><pre class="programlisting"> -gint32 -my_object_increment_retval (MyObject *obj, gint32 x) - </pre><p> - </p><p> - This introspection XML: - </p><pre class="programlisting"> -<method name="IncrementRetvalError"> - <arg type="u" name="x" /> - <arg type="u" direction="out" > - <annotation name="org.freedesktop.DBus.GLib.ReturnVal" value="error"/> - </arg> -</method> - </pre><p> - Expects the following function declaration: - </p><pre class="programlisting"> -gint32 -my_object_increment_retval_error (MyObject *obj, gint32 x, GError **error) - </pre><p> - </p></dd></dl></div><p> - </p></div></div><div class="sect1" title="Python API"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="python-client"></a>Python API</h2></div></div></div><p> - The Python API, dbus-python, is now documented separately in - <a class="ulink" href="http://dbus.freedesktop.org/doc/dbus-python/doc/tutorial.html" target="_top">the dbus-python tutorial</a> (also available in doc/tutorial.txt, - and doc/tutorial.html if built with python-docutils, in the dbus-python - source distribution). - </p></div><div class="sect1" title="Qt API: Using Remote Objects"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="qt-client"></a>Qt API: Using Remote Objects</h2></div></div></div><p> - - The Qt bindings are not yet documented. - - </p></div><div class="sect1" title="Qt API: Implementing Objects"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="qt-server"></a>Qt API: Implementing Objects</h2></div></div></div><p> - The Qt bindings are not yet documented. - </p></div></div></body></html> |