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| 4 | [ |
| 5 | ]> |
| 6 | |
| 7 | <article id="index"> |
| 8 | <articleinfo> |
| 9 | <title>D-Bus Tutorial</title> |
| 10 | <releaseinfo>Version 0.5.0</releaseinfo> |
| 11 | <date>20 August 2006</date> |
| 12 | <authorgroup> |
| 13 | <author> |
| 14 | <firstname>Havoc</firstname> |
| 15 | <surname>Pennington</surname> |
| 16 | <affiliation> |
| 17 | <orgname>Red Hat, Inc.</orgname> |
| 18 | <address><email>hp@pobox.com</email></address> |
| 19 | </affiliation> |
| 20 | </author> |
| 21 | <author> |
| 22 | <firstname>David</firstname> |
| 23 | <surname>Wheeler</surname> |
| 24 | </author> |
| 25 | <author> |
| 26 | <firstname>John</firstname> |
| 27 | <surname>Palmieri</surname> |
| 28 | <affiliation> |
| 29 | <orgname>Red Hat, Inc.</orgname> |
| 30 | <address><email>johnp@redhat.com</email></address> |
| 31 | </affiliation> |
| 32 | </author> |
| 33 | <author> |
| 34 | <firstname>Colin</firstname> |
| 35 | <surname>Walters</surname> |
| 36 | <affiliation> |
| 37 | <orgname>Red Hat, Inc.</orgname> |
| 38 | <address><email>walters@redhat.com</email></address> |
| 39 | </affiliation> |
| 40 | </author> |
| 41 | </authorgroup> |
| 42 | </articleinfo> |
| 43 | |
| 44 | <sect1 id="meta"> |
| 45 | <title>Tutorial Work In Progress</title> |
| 46 | |
| 47 | <para> |
| 48 | This tutorial is not complete; it probably contains some useful information, but |
| 49 | also has plenty of gaps. Right now, you'll also need to refer to the D-Bus specification, |
| 50 | Doxygen reference documentation, and look at some examples of how other apps use D-Bus. |
| 51 | </para> |
| 52 | |
| 53 | <para> |
| 54 | Enhancing the tutorial is definitely encouraged - send your patches or suggestions to the |
| 55 | mailing list. If you create a D-Bus binding, please add a section to the tutorial for your |
| 56 | binding, if only a short section with a couple of examples. |
| 57 | </para> |
| 58 | |
| 59 | </sect1> |
| 60 | |
| 61 | <sect1 id="whatis"> |
| 62 | <title>What is D-Bus?</title> |
| 63 | <para> |
| 64 | D-Bus is a system for <firstterm>interprocess communication</firstterm> |
| 65 | (IPC). Architecturally, it has several layers: |
| 66 | |
| 67 | <itemizedlist> |
| 68 | <listitem> |
| 69 | <para> |
| 70 | A library, <firstterm>libdbus</firstterm>, that allows two |
| 71 | applications to connect to each other and exchange messages. |
| 72 | </para> |
| 73 | </listitem> |
| 74 | <listitem> |
| 75 | <para> |
| 76 | A <firstterm>message bus daemon</firstterm> executable, built on |
| 77 | libdbus, that multiple applications can connect to. The daemon can |
| 78 | route messages from one application to zero or more other |
| 79 | applications. |
| 80 | </para> |
| 81 | </listitem> |
| 82 | <listitem> |
| 83 | <para> |
| 84 | <firstterm>Wrapper libraries</firstterm> or <firstterm>bindings</firstterm> |
| 85 | based on particular application frameworks. For example, libdbus-glib and |
| 86 | libdbus-qt. There are also bindings to languages such as |
| 87 | Python. These wrapper libraries are the API most people should use, |
| 88 | as they simplify the details of D-Bus programming. libdbus is |
| 89 | intended to be a low-level backend for the higher level bindings. |
| 90 | Much of the libdbus API is only useful for binding implementation. |
| 91 | </para> |
| 92 | </listitem> |
| 93 | </itemizedlist> |
| 94 | </para> |
| 95 | |
| 96 | <para> |
| 97 | libdbus only supports one-to-one connections, just like a raw network |
| 98 | socket. However, rather than sending byte streams over the connection, you |
| 99 | send <firstterm>messages</firstterm>. Messages have a header identifying |
| 100 | the kind of message, and a body containing a data payload. libdbus also |
| 101 | abstracts the exact transport used (sockets vs. whatever else), and |
| 102 | handles details such as authentication. |
| 103 | </para> |
| 104 | |
| 105 | <para> |
| 106 | The message bus daemon forms the hub of a wheel. Each spoke of the wheel |
| 107 | is a one-to-one connection to an application using libdbus. An |
| 108 | application sends a message to the bus daemon over its spoke, and the bus |
| 109 | daemon forwards the message to other connected applications as |
| 110 | appropriate. Think of the daemon as a router. |
| 111 | </para> |
| 112 | |
| 113 | <para> |
| 114 | The bus daemon has multiple instances on a typical computer. The |
| 115 | first instance is a machine-global singleton, that is, a system daemon |
| 116 | similar to sendmail or Apache. This instance has heavy security |
| 117 | restrictions on what messages it will accept, and is used for systemwide |
| 118 | communication. The other instances are created one per user login session. |
| 119 | These instances allow applications in the user's session to communicate |
| 120 | with one another. |
| 121 | </para> |
| 122 | |
| 123 | <para> |
| 124 | The systemwide and per-user daemons are separate. Normal within-session |
| 125 | IPC does not involve the systemwide message bus process and vice versa. |
| 126 | </para> |
| 127 | |
| 128 | <sect2 id="uses"> |
| 129 | <title>D-Bus applications</title> |
| 130 | <para> |
| 131 | There are many, many technologies in the world that have "Inter-process |
| 132 | communication" or "networking" in their stated purpose: <ulink |
| 133 | url="http://www.omg.org">CORBA</ulink>, <ulink |
| 134 | url="http://www.opengroup.org/dce/">DCE</ulink>, <ulink |
| 135 | url="http://www.microsoft.com/com/">DCOM</ulink>, <ulink |
| 136 | url="http://developer.kde.org/documentation/library/kdeqt/dcop.html">DCOP</ulink>, <ulink |
| 137 | url="http://www.xmlrpc.com">XML-RPC</ulink>, <ulink |
| 138 | url="http://www.w3.org/TR/SOAP/">SOAP</ulink>, <ulink |
| 139 | url="http://www.mbus.org/">MBUS</ulink>, <ulink |
| 140 | url="http://www.zeroc.com/ice.html">Internet Communications Engine (ICE)</ulink>, |
| 141 | and probably hundreds more. |
| 142 | Each of these is tailored for particular kinds of application. |
| 143 | D-Bus is designed for two specific cases: |
| 144 | <itemizedlist> |
| 145 | <listitem> |
| 146 | <para> |
| 147 | Communication between desktop applications in the same desktop |
| 148 | session; to allow integration of the desktop session as a whole, |
| 149 | and address issues of process lifecycle (when do desktop components |
| 150 | start and stop running). |
| 151 | </para> |
| 152 | </listitem> |
| 153 | <listitem> |
| 154 | <para> |
| 155 | Communication between the desktop session and the operating system, |
| 156 | where the operating system would typically include the kernel |
| 157 | and any system daemons or processes. |
| 158 | </para> |
| 159 | </listitem> |
| 160 | </itemizedlist> |
| 161 | </para> |
| 162 | <para> |
| 163 | For the within-desktop-session use case, the GNOME and KDE desktops |
| 164 | have significant previous experience with different IPC solutions |
| 165 | such as CORBA and DCOP. D-Bus is built on that experience and |
| 166 | carefully tailored to meet the needs of these desktop projects |
| 167 | in particular. D-Bus may or may not be appropriate for other |
| 168 | applications; the FAQ has some comparisons to other IPC systems. |
| 169 | </para> |
| 170 | <para> |
| 171 | The problem solved by the systemwide or communication-with-the-OS case |
| 172 | is explained well by the following text from the Linux Hotplug project: |
| 173 | <blockquote> |
| 174 | <para> |
| 175 | A gap in current Linux support is that policies with any sort of |
| 176 | dynamic "interact with user" component aren't currently |
| 177 | supported. For example, that's often needed the first time a network |
| 178 | adapter or printer is connected, and to determine appropriate places |
| 179 | to mount disk drives. It would seem that such actions could be |
| 180 | supported for any case where a responsible human can be identified: |
| 181 | single user workstations, or any system which is remotely |
| 182 | administered. |
| 183 | </para> |
| 184 | |
| 185 | <para> |
| 186 | This is a classic "remote sysadmin" problem, where in this case |
| 187 | hotplugging needs to deliver an event from one security domain |
| 188 | (operating system kernel, in this case) to another (desktop for |
| 189 | logged-in user, or remote sysadmin). Any effective response must go |
| 190 | the other way: the remote domain taking some action that lets the |
| 191 | kernel expose the desired device capabilities. (The action can often |
| 192 | be taken asynchronously, for example letting new hardware be idle |
| 193 | until a meeting finishes.) At this writing, Linux doesn't have |
| 194 | widely adopted solutions to such problems. However, the new D-Bus |
| 195 | work may begin to solve that problem. |
| 196 | </para> |
| 197 | </blockquote> |
| 198 | </para> |
| 199 | <para> |
| 200 | D-Bus may happen to be useful for purposes other than the one it was |
| 201 | designed for. Its general properties that distinguish it from |
| 202 | other forms of IPC are: |
| 203 | <itemizedlist> |
| 204 | <listitem> |
| 205 | <para> |
| 206 | Binary protocol designed to be used asynchronously |
| 207 | (similar in spirit to the X Window System protocol). |
| 208 | </para> |
| 209 | </listitem> |
| 210 | <listitem> |
| 211 | <para> |
| 212 | Stateful, reliable connections held open over time. |
| 213 | </para> |
| 214 | </listitem> |
| 215 | <listitem> |
| 216 | <para> |
| 217 | The message bus is a daemon, not a "swarm" or |
| 218 | distributed architecture. |
| 219 | </para> |
| 220 | </listitem> |
| 221 | <listitem> |
| 222 | <para> |
| 223 | Many implementation and deployment issues are specified rather |
| 224 | than left ambiguous/configurable/pluggable. |
| 225 | </para> |
| 226 | </listitem> |
| 227 | <listitem> |
| 228 | <para> |
| 229 | Semantics are similar to the existing DCOP system, allowing |
| 230 | KDE to adopt it more easily. |
| 231 | </para> |
| 232 | </listitem> |
| 233 | <listitem> |
| 234 | <para> |
| 235 | Security features to support the systemwide mode of the |
| 236 | message bus. |
| 237 | </para> |
| 238 | </listitem> |
| 239 | </itemizedlist> |
| 240 | </para> |
| 241 | </sect2> |
| 242 | </sect1> |
| 243 | <sect1 id="concepts"> |
| 244 | <title>Concepts</title> |
| 245 | <para> |
| 246 | Some basic concepts apply no matter what application framework you're |
| 247 | using to write a D-Bus application. The exact code you write will be |
| 248 | different for GLib vs. Qt vs. Python applications, however. |
| 249 | </para> |
| 250 | |
| 251 | <para> |
| 252 | Here is a diagram (<ulink url="diagram.png">png</ulink> <ulink |
| 253 | url="diagram.svg">svg</ulink>) that may help you visualize the concepts |
| 254 | that follow. |
| 255 | </para> |
| 256 | |
| 257 | <sect2 id="objects"> |
| 258 | <title>Native Objects and Object Paths</title> |
| 259 | <para> |
| 260 | Your programming framework probably defines what an "object" is like; |
| 261 | usually with a base class. For example: java.lang.Object, GObject, QObject, |
| 262 | python's base Object, or whatever. Let's call this a <firstterm>native object</firstterm>. |
| 263 | </para> |
| 264 | <para> |
| 265 | The low-level D-Bus protocol, and corresponding libdbus API, does not care about native objects. |
| 266 | However, it provides a concept called an |
| 267 | <firstterm>object path</firstterm>. The idea of an object path is that |
| 268 | higher-level bindings can name native object instances, and allow remote applications |
| 269 | to refer to them. |
| 270 | </para> |
| 271 | <para> |
| 272 | The object path |
| 273 | looks like a filesystem path, for example an object could be |
| 274 | named <literal>/org/kde/kspread/sheets/3/cells/4/5</literal>. |
| 275 | Human-readable paths are nice, but you are free to create an |
| 276 | object named <literal>/com/mycompany/c5yo817y0c1y1c5b</literal> |
| 277 | if it makes sense for your application. |
| 278 | </para> |
| 279 | <para> |
| 280 | Namespacing object paths is smart, by starting them with the components |
| 281 | of a domain name you own (e.g. <literal>/org/kde</literal>). This |
| 282 | keeps different code modules in the same process from stepping |
| 283 | on one another's toes. |
| 284 | </para> |
| 285 | </sect2> |
| 286 | |
| 287 | <sect2 id="members"> |
| 288 | <title>Methods and Signals</title> |
| 289 | |
| 290 | <para> |
| 291 | Each object has <firstterm>members</firstterm>; the two kinds of member |
| 292 | are <firstterm>methods</firstterm> and |
| 293 | <firstterm>signals</firstterm>. Methods are operations that can be |
| 294 | invoked on an object, with optional input (aka arguments or "in |
| 295 | parameters") and output (aka return values or "out parameters"). |
| 296 | Signals are broadcasts from the object to any interested observers |
| 297 | of the object; signals may contain a data payload. |
| 298 | </para> |
| 299 | |
| 300 | <para> |
| 301 | Both methods and signals are referred to by name, such as |
| 302 | "Frobate" or "OnClicked". |
| 303 | </para> |
| 304 | |
| 305 | </sect2> |
| 306 | |
| 307 | <sect2 id="interfaces"> |
| 308 | <title>Interfaces</title> |
| 309 | <para> |
| 310 | Each object supports one or more <firstterm>interfaces</firstterm>. |
| 311 | Think of an interface as a named group of methods and signals, |
| 312 | just as it is in GLib or Qt or Java. Interfaces define the |
| 313 | <emphasis>type</emphasis> of an object instance. |
| 314 | </para> |
| 315 | <para> |
| 316 | DBus identifies interfaces with a simple namespaced string, |
| 317 | something like <literal>org.freedesktop.Introspectable</literal>. |
| 318 | Most bindings will map these interface names directly to |
| 319 | the appropriate programming language construct, for example |
| 320 | to Java interfaces or C++ pure virtual classes. |
| 321 | </para> |
| 322 | </sect2> |
| 323 | |
| 324 | <sect2 id="proxies"> |
| 325 | <title>Proxies</title> |
| 326 | <para> |
| 327 | A <firstterm>proxy object</firstterm> is a convenient native object created to |
| 328 | represent a remote object in another process. The low-level DBus API involves manually creating |
| 329 | a method call message, sending it, then manually receiving and processing |
| 330 | the method reply message. Higher-level bindings provide proxies as an alternative. |
| 331 | Proxies look like a normal native object; but when you invoke a method on the proxy |
| 332 | object, the binding converts it into a DBus method call message, waits for the reply |
| 333 | message, unpacks the return value, and returns it from the native method.. |
| 334 | </para> |
| 335 | <para> |
| 336 | In pseudocode, programming without proxies might look like this: |
| 337 | <programlisting> |
| 338 | Message message = new Message("/remote/object/path", "MethodName", arg1, arg2); |
| 339 | Connection connection = getBusConnection(); |
| 340 | connection.send(message); |
| 341 | Message reply = connection.waitForReply(message); |
| 342 | if (reply.isError()) { |
| 343 | |
| 344 | } else { |
| 345 | Object returnValue = reply.getReturnValue(); |
| 346 | } |
| 347 | </programlisting> |
| 348 | </para> |
| 349 | <para> |
| 350 | Programming with proxies might look like this: |
| 351 | <programlisting> |
| 352 | Proxy proxy = new Proxy(getBusConnection(), "/remote/object/path"); |
| 353 | Object returnValue = proxy.MethodName(arg1, arg2); |
| 354 | </programlisting> |
| 355 | </para> |
| 356 | </sect2> |
| 357 | |
| 358 | <sect2 id="bus-names"> |
| 359 | <title>Bus Names</title> |
| 360 | |
| 361 | <para> |
| 362 | When each application connects to the bus daemon, the daemon immediately |
| 363 | assigns it a name, called the <firstterm>unique connection name</firstterm>. |
| 364 | A unique name begins with a ':' (colon) character. These names are never |
| 365 | reused during the lifetime of the bus daemon - that is, you know |
| 366 | a given name will always refer to the same application. |
| 367 | An example of a unique name might be |
| 368 | <literal>:34-907</literal>. The numbers after the colon have |
| 369 | no meaning other than their uniqueness. |
| 370 | </para> |
| 371 | |
| 372 | <para> |
| 373 | When a name is mapped |
| 374 | to a particular application's connection, that application is said to |
| 375 | <firstterm>own</firstterm> that name. |
| 376 | </para> |
| 377 | |
| 378 | <para> |
| 379 | Applications may ask to own additional <firstterm>well-known |
| 380 | names</firstterm>. For example, you could write a specification to |
| 381 | define a name called <literal>com.mycompany.TextEditor</literal>. |
| 382 | Your definition could specify that to own this name, an application |
| 383 | should have an object at the path |
| 384 | <literal>/com/mycompany/TextFileManager</literal> supporting the |
| 385 | interface <literal>org.freedesktop.FileHandler</literal>. |
| 386 | </para> |
| 387 | |
| 388 | <para> |
| 389 | Applications could then send messages to this bus name, |
| 390 | object, and interface to execute method calls. |
| 391 | </para> |
| 392 | |
| 393 | <para> |
| 394 | You could think of the unique names as IP addresses, and the |
| 395 | well-known names as domain names. So |
| 396 | <literal>com.mycompany.TextEditor</literal> might map to something like |
| 397 | <literal>:34-907</literal> just as <literal>mycompany.com</literal> maps |
| 398 | to something like <literal>192.168.0.5</literal>. |
| 399 | </para> |
| 400 | |
| 401 | <para> |
| 402 | Names have a second important use, other than routing messages. They |
| 403 | are used to track lifecycle. When an application exits (or crashes), its |
| 404 | connection to the message bus will be closed by the operating system |
| 405 | kernel. The message bus then sends out notification messages telling |
| 406 | remaining applications that the application's names have lost their |
| 407 | owner. By tracking these notifications, your application can reliably |
| 408 | monitor the lifetime of other applications. |
| 409 | </para> |
| 410 | |
| 411 | <para> |
| 412 | Bus names can also be used to coordinate single-instance applications. |
| 413 | If you want to be sure only one |
| 414 | <literal>com.mycompany.TextEditor</literal> application is running for |
| 415 | example, have the text editor application exit if the bus name already |
| 416 | has an owner. |
| 417 | </para> |
| 418 | |
| 419 | </sect2> |
| 420 | |
| 421 | <sect2 id="addresses"> |
| 422 | <title>Addresses</title> |
| 423 | |
| 424 | <para> |
| 425 | Applications using D-Bus are either servers or clients. A server |
| 426 | listens for incoming connections; a client connects to a server. Once |
| 427 | the connection is established, it is a symmetric flow of messages; the |
| 428 | client-server distinction only matters when setting up the |
| 429 | connection. |
| 430 | </para> |
| 431 | |
| 432 | <para> |
| 433 | If you're using the bus daemon, as you probably are, your application |
| 434 | will be a client of the bus daemon. That is, the bus daemon listens |
| 435 | for connections and your application initiates a connection to the bus |
| 436 | daemon. |
| 437 | </para> |
| 438 | |
| 439 | <para> |
| 440 | A D-Bus <firstterm>address</firstterm> specifies where a server will |
| 441 | listen, and where a client will connect. For example, the address |
| 442 | <literal>unix:path=/tmp/abcdef</literal> specifies that the server will |
| 443 | listen on a UNIX domain socket at the path |
| 444 | <literal>/tmp/abcdef</literal> and the client will connect to that |
| 445 | socket. An address can also specify TCP/IP sockets, or any other |
| 446 | transport defined in future iterations of the D-Bus specification. |
| 447 | </para> |
| 448 | |
| 449 | <para> |
| 450 | When using D-Bus with a message bus daemon, |
| 451 | libdbus automatically discovers the address of the per-session bus |
| 452 | daemon by reading an environment variable. It discovers the |
| 453 | systemwide bus daemon by checking a well-known UNIX domain socket path |
| 454 | (though you can override this address with an environment variable). |
| 455 | </para> |
| 456 | |
| 457 | <para> |
| 458 | If you're using D-Bus without a bus daemon, it's up to you to |
| 459 | define which application will be the server and which will be |
| 460 | the client, and specify a mechanism for them to agree on |
| 461 | the server's address. This is an unusual case. |
| 462 | </para> |
| 463 | |
| 464 | </sect2> |
| 465 | |
| 466 | <sect2 id="bigpicture"> |
| 467 | <title>Big Conceptual Picture</title> |
| 468 | |
| 469 | <para> |
| 470 | Pulling all these concepts together, to specify a particular |
| 471 | method call on a particular object instance, a number of |
| 472 | nested components have to be named: |
| 473 | <programlisting> |
| 474 | Address -> [Bus Name] -> Path -> Interface -> Method |
| 475 | </programlisting> |
| 476 | The bus name is in brackets to indicate that it's optional -- you only |
| 477 | provide a name to route the method call to the right application |
| 478 | when using the bus daemon. If you have a direct connection to another |
| 479 | application, bus names aren't used; there's no bus daemon. |
| 480 | </para> |
| 481 | |
| 482 | <para> |
| 483 | The interface is also optional, primarily for historical |
| 484 | reasons; DCOP does not require specifying the interface, |
| 485 | instead simply forbidding duplicate method names |
| 486 | on the same object instance. D-Bus will thus let you |
| 487 | omit the interface, but if your method name is ambiguous |
| 488 | it is undefined which method will be invoked. |
| 489 | </para> |
| 490 | |
| 491 | </sect2> |
| 492 | |
| 493 | <sect2 id="messages"> |
| 494 | <title>Messages - Behind the Scenes</title> |
| 495 | <para> |
| 496 | D-Bus works by sending messages between processes. If you're using |
| 497 | a sufficiently high-level binding, you may never work with messages directly. |
| 498 | </para> |
| 499 | <para> |
| 500 | There are 4 message types: |
| 501 | <itemizedlist> |
| 502 | <listitem> |
| 503 | <para> |
| 504 | Method call messages ask to invoke a method |
| 505 | on an object. |
| 506 | </para> |
| 507 | </listitem> |
| 508 | <listitem> |
| 509 | <para> |
| 510 | Method return messages return the results |
| 511 | of invoking a method. |
| 512 | </para> |
| 513 | </listitem> |
| 514 | <listitem> |
| 515 | <para> |
| 516 | Error messages return an exception caused by |
| 517 | invoking a method. |
| 518 | </para> |
| 519 | </listitem> |
| 520 | <listitem> |
| 521 | <para> |
| 522 | Signal messages are notifications that a given signal |
| 523 | has been emitted (that an event has occurred). |
| 524 | You could also think of these as "event" messages. |
| 525 | </para> |
| 526 | </listitem> |
| 527 | </itemizedlist> |
| 528 | </para> |
| 529 | <para> |
| 530 | A method call maps very simply to messages: you send a method call |
| 531 | message, and receive either a method return message or an error message |
| 532 | in reply. |
| 533 | </para> |
| 534 | <para> |
| 535 | Each message has a <firstterm>header</firstterm>, including <firstterm>fields</firstterm>, |
| 536 | and a <firstterm>body</firstterm>, including <firstterm>arguments</firstterm>. You can think |
| 537 | of the header as the routing information for the message, and the body as the payload. |
| 538 | Header fields might include the sender bus name, destination bus name, method or signal name, |
| 539 | and so forth. One of the header fields is a <firstterm>type signature</firstterm> describing the |
| 540 | values found in the body. For example, the letter "i" means "32-bit integer" so the signature |
| 541 | "ii" means the payload has two 32-bit integers. |
| 542 | </para> |
| 543 | </sect2> |
| 544 | |
| 545 | <sect2 id="callprocedure"> |
| 546 | <title>Calling a Method - Behind the Scenes</title> |
| 547 | |
| 548 | <para> |
| 549 | A method call in DBus consists of two messages; a method call message sent from process A to process B, |
| 550 | and a matching method reply message sent from process B to process A. Both the call and the reply messages |
| 551 | are routed through the bus daemon. The caller includes a different serial number in each call message, and the |
| 552 | reply message includes this number to allow the caller to match replies to calls. |
| 553 | </para> |
| 554 | |
| 555 | <para> |
| 556 | The call message will contain any arguments to the method. |
| 557 | The reply message may indicate an error, or may contain data returned by the method. |
| 558 | </para> |
| 559 | |
| 560 | <para> |
| 561 | A method invocation in DBus happens as follows: |
| 562 | <itemizedlist> |
| 563 | <listitem> |
| 564 | <para> |
| 565 | The language binding may provide a proxy, such that invoking a method on |
| 566 | an in-process object invokes a method on a remote object in another process. If so, the |
| 567 | application calls a method on the proxy, and the proxy |
| 568 | constructs a method call message to send to the remote process. |
| 569 | </para> |
| 570 | </listitem> |
| 571 | <listitem> |
| 572 | <para> |
| 573 | For more low-level APIs, the application may construct a method call message itself, without |
| 574 | using a proxy. |
| 575 | </para> |
| 576 | </listitem> |
| 577 | <listitem> |
| 578 | <para> |
| 579 | In either case, the method call message contains: a bus name belonging to the remote process; the name of the method; |
| 580 | the arguments to the method; an object path inside the remote process; and optionally the name of the |
| 581 | interface that specifies the method. |
| 582 | </para> |
| 583 | </listitem> |
| 584 | <listitem> |
| 585 | <para> |
| 586 | The method call message is sent to the bus daemon. |
| 587 | </para> |
| 588 | </listitem> |
| 589 | <listitem> |
| 590 | <para> |
| 591 | The bus daemon looks at the destination bus name. If a process owns that name, |
| 592 | the bus daemon forwards the method call to that process. Otherwise, the bus daemon |
| 593 | creates an error message and sends it back as the reply to the method call message. |
| 594 | </para> |
| 595 | </listitem> |
| 596 | <listitem> |
| 597 | <para> |
| 598 | The receiving process unpacks the method call message. In a simple low-level API situation, it |
| 599 | may immediately run the method and send a method reply message to the bus daemon. |
| 600 | When using a high-level binding API, the binding might examine the object path, interface, |
| 601 | and method name, and convert the method call message into an invocation of a method on |
| 602 | a native object (GObject, java.lang.Object, QObject, etc.), then convert the return |
| 603 | value from the native method into a method reply message. |
| 604 | </para> |
| 605 | </listitem> |
| 606 | <listitem> |
| 607 | <para> |
| 608 | The bus daemon receives the method reply message and sends it to the process that |
| 609 | made the method call. |
| 610 | </para> |
| 611 | </listitem> |
| 612 | <listitem> |
| 613 | <para> |
| 614 | The process that made the method call looks at the method reply and makes use of any |
| 615 | return values included in the reply. The reply may also indicate that an error occurred. |
| 616 | When using a binding, the method reply message may be converted into the return value of |
| 617 | of a proxy method, or into an exception. |
| 618 | </para> |
| 619 | </listitem> |
| 620 | </itemizedlist> |
| 621 | </para> |
| 622 | |
| 623 | <para> |
| 624 | The bus daemon never reorders messages. That is, if you send two method call messages to the same recipient, |
| 625 | they will be received in the order they were sent. The recipient is not required to reply to the calls |
| 626 | in order, however; for example, it may process each method call in a separate thread, and return reply messages |
| 627 | in an undefined order depending on when the threads complete. Method calls have a unique serial |
| 628 | number used by the method caller to match reply messages to call messages. |
| 629 | </para> |
| 630 | |
| 631 | </sect2> |
| 632 | |
| 633 | <sect2 id="signalprocedure"> |
| 634 | <title>Emitting a Signal - Behind the Scenes</title> |
| 635 | |
| 636 | <para> |
| 637 | A signal in DBus consists of a single message, sent by one process to any number of other processes. |
| 638 | That is, a signal is a unidirectional broadcast. The signal may contain arguments (a data payload), but |
| 639 | because it is a broadcast, it never has a "return value." Contrast this with a method call |
| 640 | (see <xref linkend="callprocedure"/>) where the method call message has a matching method reply message. |
| 641 | </para> |
| 642 | |
| 643 | <para> |
| 644 | The emitter (aka sender) of a signal has no knowledge of the signal recipients. Recipients register |
| 645 | with the bus daemon to receive signals based on "match rules" - these rules would typically include the sender and |
| 646 | the signal name. The bus daemon sends each signal only to recipients who have expressed interest in that |
| 647 | signal. |
| 648 | </para> |
| 649 | |
| 650 | <para> |
| 651 | A signal in DBus happens as follows: |
| 652 | <itemizedlist> |
| 653 | <listitem> |
| 654 | <para> |
| 655 | A signal message is created and sent to the bus daemon. When using the low-level API this may be |
| 656 | done manually, with certain bindings it may be done for you by the binding when a native object |
| 657 | emits a native signal or event. |
| 658 | </para> |
| 659 | </listitem> |
| 660 | <listitem> |
| 661 | <para> |
| 662 | The signal message contains the name of the interface that specifies the signal; |
| 663 | the name of the signal; the bus name of the process sending the signal; and |
| 664 | any arguments |
| 665 | </para> |
| 666 | </listitem> |
| 667 | <listitem> |
| 668 | <para> |
| 669 | Any process on the message bus can register "match rules" indicating which signals it |
| 670 | is interested in. The bus has a list of registered match rules. |
| 671 | </para> |
| 672 | </listitem> |
| 673 | <listitem> |
| 674 | <para> |
| 675 | The bus daemon examines the signal and determines which processes are interested in it. |
| 676 | It sends the signal message to these processes. |
| 677 | </para> |
| 678 | </listitem> |
| 679 | <listitem> |
| 680 | <para> |
| 681 | Each process receiving the signal decides what to do with it; if using a binding, |
| 682 | the binding may choose to emit a native signal on a proxy object. If using the |
| 683 | low-level API, the process may just look at the signal sender and name and decide |
| 684 | what to do based on that. |
| 685 | </para> |
| 686 | </listitem> |
| 687 | </itemizedlist> |
| 688 | </para> |
| 689 | |
| 690 | </sect2> |
| 691 | |
| 692 | <sect2 id="introspection"> |
| 693 | <title>Introspection</title> |
| 694 | |
| 695 | <para> |
| 696 | D-Bus objects may support the interface <literal>org.freedesktop.DBus.Introspectable</literal>. |
| 697 | This interface has one method <literal>Introspect</literal> which takes no arguments and returns |
| 698 | an XML string. The XML string describes the interfaces, methods, and signals of the object. |
| 699 | See the D-Bus specification for more details on this introspection format. |
| 700 | </para> |
| 701 | |
| 702 | </sect2> |
| 703 | |
| 704 | </sect1> |
| 705 | |
| 706 | <sect1 id="glib-client"> |
| 707 | <title>GLib API: Using Remote Objects</title> |
| 708 | |
| 709 | <para> |
| 710 | The GLib binding is defined in the header file |
| 711 | <literal><dbus/dbus-glib.h></literal>. |
| 712 | </para> |
| 713 | |
| 714 | <sect2 id="glib-typemappings"> |
| 715 | <title>D-Bus - GLib type mappings</title> |
| 716 | <para> |
| 717 | The heart of the GLib bindings for D-Bus is the mapping it |
| 718 | provides between D-Bus "type signatures" and GLib types |
| 719 | (<literal>GType</literal>). The D-Bus type system is composed of |
| 720 | a number of "basic" types, along with several "container" types. |
| 721 | </para> |
| 722 | <sect3 id="glib-basic-typemappings"> |
| 723 | <title>Basic type mappings</title> |
| 724 | <para> |
| 725 | Below is a list of the basic types, along with their associated |
| 726 | mapping to a <literal>GType</literal>. |
| 727 | <informaltable> |
| 728 | <tgroup cols="4"> |
| 729 | <thead> |
| 730 | <row> |
| 731 | <entry>D-Bus basic type</entry> |
| 732 | <entry>GType</entry> |
| 733 | <entry>Free function</entry> |
| 734 | <entry>Notes</entry> |
| 735 | </row> |
| 736 | </thead> |
| 737 | <tbody> |
| 738 | <row> |
| 739 | <entry><literal>BYTE</literal></entry> |
| 740 | <entry><literal>G_TYPE_UCHAR</literal></entry> |
| 741 | <entry></entry> |
| 742 | <entry></entry> |
| 743 | </row><row> |
| 744 | <entry><literal>BOOLEAN</literal></entry> |
| 745 | <entry><literal>G_TYPE_BOOLEAN</literal></entry> |
| 746 | <entry></entry> |
| 747 | <entry></entry> |
| 748 | </row><row> |
| 749 | <entry><literal>INT16</literal></entry> |
| 750 | <entry><literal>G_TYPE_INT</literal></entry> |
| 751 | <entry></entry> |
| 752 | <entry>Will be changed to a <literal>G_TYPE_INT16</literal> once GLib has it</entry> |
| 753 | </row><row> |
| 754 | <entry><literal>UINT16</literal></entry> |
| 755 | <entry><literal>G_TYPE_UINT</literal></entry> |
| 756 | <entry></entry> |
| 757 | <entry>Will be changed to a <literal>G_TYPE_UINT16</literal> once GLib has it</entry> |
| 758 | </row><row> |
| 759 | <entry><literal>INT32</literal></entry> |
| 760 | <entry><literal>G_TYPE_INT</literal></entry> |
| 761 | <entry></entry> |
| 762 | <entry>Will be changed to a <literal>G_TYPE_INT32</literal> once GLib has it</entry> |
| 763 | </row><row> |
| 764 | <entry><literal>UINT32</literal></entry> |
| 765 | <entry><literal>G_TYPE_UINT</literal></entry> |
| 766 | <entry></entry> |
| 767 | <entry>Will be changed to a <literal>G_TYPE_UINT32</literal> once GLib has it</entry> |
| 768 | </row><row> |
| 769 | <entry><literal>INT64</literal></entry> |
| 770 | <entry><literal>G_TYPE_GINT64</literal></entry> |
| 771 | <entry></entry> |
| 772 | <entry></entry> |
| 773 | </row><row> |
| 774 | <entry><literal>UINT64</literal></entry> |
| 775 | <entry><literal>G_TYPE_GUINT64</literal></entry> |
| 776 | <entry></entry> |
| 777 | <entry></entry> |
| 778 | </row><row> |
| 779 | <entry><literal>DOUBLE</literal></entry> |
| 780 | <entry><literal>G_TYPE_DOUBLE</literal></entry> |
| 781 | <entry></entry> |
| 782 | <entry></entry> |
| 783 | </row><row> |
| 784 | <entry><literal>STRING</literal></entry> |
| 785 | <entry><literal>G_TYPE_STRING</literal></entry> |
| 786 | <entry><literal>g_free</literal></entry> |
| 787 | <entry></entry> |
| 788 | </row><row> |
| 789 | <entry><literal>OBJECT_PATH</literal></entry> |
| 790 | <entry><literal>DBUS_TYPE_G_PROXY</literal></entry> |
| 791 | <entry><literal>g_object_unref</literal></entry> |
| 792 | <entry>The returned proxy does not have an interface set; use <literal>dbus_g_proxy_set_interface</literal> to invoke methods</entry> |
| 793 | </row> |
| 794 | </tbody> |
| 795 | </tgroup> |
| 796 | </informaltable> |
| 797 | As you can see, the basic mapping is fairly straightforward. |
| 798 | </para> |
| 799 | </sect3> |
| 800 | <sect3 id="glib-container-typemappings"> |
| 801 | <title>Container type mappings</title> |
| 802 | <para> |
| 803 | The D-Bus type system also has a number of "container" |
| 804 | types, such as <literal>DBUS_TYPE_ARRAY</literal> and |
| 805 | <literal>DBUS_TYPE_STRUCT</literal>. The D-Bus type system |
| 806 | is fully recursive, so one can for example have an array of |
| 807 | array of strings (i.e. type signature |
| 808 | <literal>aas</literal>). |
| 809 | </para> |
| 810 | <para> |
| 811 | However, not all of these types are in common use; for |
| 812 | example, at the time of this writing the author knows of no |
| 813 | one using <literal>DBUS_TYPE_STRUCT</literal>, or a |
| 814 | <literal>DBUS_TYPE_ARRAY</literal> containing any non-basic |
| 815 | type. The approach the GLib bindings take is pragmatic; try |
| 816 | to map the most common types in the most obvious way, and |
| 817 | let using less common and more complex types be less |
| 818 | "natural". |
| 819 | </para> |
| 820 | <para> |
| 821 | First, D-Bus type signatures which have an "obvious" |
| 822 | corresponding built-in GLib type are mapped using that type: |
| 823 | <informaltable> |
| 824 | <tgroup cols="6"> |
| 825 | <thead> |
| 826 | <row> |
| 827 | <entry>D-Bus type signature</entry> |
| 828 | <entry>Description</entry> |
| 829 | <entry>GType</entry> |
| 830 | <entry>C typedef</entry> |
| 831 | <entry>Free function</entry> |
| 832 | <entry>Notes</entry> |
| 833 | </row> |
| 834 | </thead> |
| 835 | <tbody> |
| 836 | <row> |
| 837 | <entry><literal>as</literal></entry> |
| 838 | <entry>Array of strings</entry> |
| 839 | <entry><literal>G_TYPE_STRV</literal></entry> |
| 840 | <entry><literal>char **</literal></entry> |
| 841 | <entry><literal>g_strfreev</literal></entry> |
| 842 | <entry></entry> |
| 843 | </row><row> |
| 844 | <entry><literal>v</literal></entry> |
| 845 | <entry>Generic value container</entry> |
| 846 | <entry><literal>G_TYPE_VALUE</literal></entry> |
| 847 | <entry><literal>GValue *</literal></entry> |
| 848 | <entry><literal>g_value_unset</literal></entry> |
| 849 | <entry>The calling conventions for values expect that method callers have allocated return values; see below.</entry> |
| 850 | </row> |
| 851 | </tbody> |
| 852 | </tgroup> |
| 853 | </informaltable> |
| 854 | </para> |
| 855 | <para> |
| 856 | The next most common recursive type signatures are arrays of |
| 857 | basic values. The most obvious mapping for arrays of basic |
| 858 | types is a <literal>GArray</literal>. Now, GLib does not |
| 859 | provide a builtin <literal>GType</literal> for |
| 860 | <literal>GArray</literal>. However, we actually need more than |
| 861 | that - we need a "parameterized" type which includes the |
| 862 | contained type. Why we need this we will see below. |
| 863 | </para> |
| 864 | <para> |
| 865 | The approach taken is to create these types in the D-Bus GLib |
| 866 | bindings; however, there is nothing D-Bus specific about them. |
| 867 | In the future, we hope to include such "fundamental" types in GLib |
| 868 | itself. |
| 869 | <informaltable> |
| 870 | <tgroup cols="6"> |
| 871 | <thead> |
| 872 | <row> |
| 873 | <entry>D-Bus type signature</entry> |
| 874 | <entry>Description</entry> |
| 875 | <entry>GType</entry> |
| 876 | <entry>C typedef</entry> |
| 877 | <entry>Free function</entry> |
| 878 | <entry>Notes</entry> |
| 879 | </row> |
| 880 | </thead> |
| 881 | <tbody> |
| 882 | <row> |
| 883 | <entry><literal>ay</literal></entry> |
| 884 | <entry>Array of bytes</entry> |
| 885 | <entry><literal>DBUS_TYPE_G_BYTE_ARRAY</literal></entry> |
| 886 | <entry><literal>GArray *</literal></entry> |
| 887 | <entry>g_array_free</entry> |
| 888 | <entry></entry> |
| 889 | </row> |
| 890 | <row> |
| 891 | <entry><literal>au</literal></entry> |
| 892 | <entry>Array of uint</entry> |
| 893 | <entry><literal>DBUS_TYPE_G_UINT_ARRAY</literal></entry> |
| 894 | <entry><literal>GArray *</literal></entry> |
| 895 | <entry>g_array_free</entry> |
| 896 | <entry></entry> |
| 897 | </row> |
| 898 | <row> |
| 899 | <entry><literal>ai</literal></entry> |
| 900 | <entry>Array of int</entry> |
| 901 | <entry><literal>DBUS_TYPE_G_INT_ARRAY</literal></entry> |
| 902 | <entry><literal>GArray *</literal></entry> |
| 903 | <entry>g_array_free</entry> |
| 904 | <entry></entry> |
| 905 | </row> |
| 906 | <row> |
| 907 | <entry><literal>ax</literal></entry> |
| 908 | <entry>Array of int64</entry> |
| 909 | <entry><literal>DBUS_TYPE_G_INT64_ARRAY</literal></entry> |
| 910 | <entry><literal>GArray *</literal></entry> |
| 911 | <entry>g_array_free</entry> |
| 912 | <entry></entry> |
| 913 | </row> |
| 914 | <row> |
| 915 | <entry><literal>at</literal></entry> |
| 916 | <entry>Array of uint64</entry> |
| 917 | <entry><literal>DBUS_TYPE_G_UINT64_ARRAY</literal></entry> |
| 918 | <entry><literal>GArray *</literal></entry> |
| 919 | <entry>g_array_free</entry> |
| 920 | <entry></entry> |
| 921 | </row> |
| 922 | <row> |
| 923 | <entry><literal>ad</literal></entry> |
| 924 | <entry>Array of double</entry> |
| 925 | <entry><literal>DBUS_TYPE_G_DOUBLE_ARRAY</literal></entry> |
| 926 | <entry><literal>GArray *</literal></entry> |
| 927 | <entry>g_array_free</entry> |
| 928 | <entry></entry> |
| 929 | </row> |
| 930 | <row> |
| 931 | <entry><literal>ab</literal></entry> |
| 932 | <entry>Array of boolean</entry> |
| 933 | <entry><literal>DBUS_TYPE_G_BOOLEAN_ARRAY</literal></entry> |
| 934 | <entry><literal>GArray *</literal></entry> |
| 935 | <entry>g_array_free</entry> |
| 936 | <entry></entry> |
| 937 | </row> |
| 938 | </tbody> |
| 939 | </tgroup> |
| 940 | </informaltable> |
| 941 | </para> |
| 942 | <para> |
| 943 | D-Bus also includes a special type DBUS_TYPE_DICT_ENTRY which |
| 944 | is only valid in arrays. It's intended to be mapped to a "dictionary" |
| 945 | type by bindings. The obvious GLib mapping here is GHashTable. Again, |
| 946 | however, there is no builtin <literal>GType</literal> for a GHashTable. |
| 947 | Moreover, just like for arrays, we need a parameterized type so that |
| 948 | the bindings can communiate which types are contained in the hash table. |
| 949 | </para> |
| 950 | <para> |
| 951 | At present, only strings are supported. Work is in progress to |
| 952 | include more types. |
| 953 | <informaltable> |
| 954 | <tgroup cols="6"> |
| 955 | <thead> |
| 956 | <row> |
| 957 | <entry>D-Bus type signature</entry> |
| 958 | <entry>Description</entry> |
| 959 | <entry>GType</entry> |
| 960 | <entry>C typedef</entry> |
| 961 | <entry>Free function</entry> |
| 962 | <entry>Notes</entry> |
| 963 | </row> |
| 964 | </thead> |
| 965 | <tbody> |
| 966 | <row> |
| 967 | <entry><literal>a{ss}</literal></entry> |
| 968 | <entry>Dictionary mapping strings to strings</entry> |
| 969 | <entry><literal>DBUS_TYPE_G_STRING_STRING_HASHTABLE</literal></entry> |
| 970 | <entry><literal>GHashTable *</literal></entry> |
| 971 | <entry>g_hash_table_destroy</entry> |
| 972 | <entry></entry> |
| 973 | </row> |
| 974 | </tbody> |
| 975 | </tgroup> |
| 976 | </informaltable> |
| 977 | </para> |
| 978 | </sect3> |
| 979 | <sect3 id="glib-generic-typemappings"> |
| 980 | <title>Arbitrarily recursive type mappings</title> |
| 981 | <para> |
| 982 | Finally, it is possible users will want to write or invoke D-Bus |
| 983 | methods which have arbitrarily complex type signatures not |
| 984 | directly supported by these bindings. For this case, we have a |
| 985 | <literal>DBusGValue</literal> which acts as a kind of special |
| 986 | variant value which may be iterated over manually. The |
| 987 | <literal>GType</literal> associated is |
| 988 | <literal>DBUS_TYPE_G_VALUE</literal>. |
| 989 | </para> |
| 990 | <para> |
| 991 | TODO insert usage of <literal>DBUS_TYPE_G_VALUE</literal> here. |
| 992 | </para> |
| 993 | </sect3> |
| 994 | </sect2> |
| 995 | <sect2 id="sample-program-1"> |
| 996 | <title>A sample program</title> |
| 997 | <para>Here is a D-Bus program using the GLib bindings. |
| 998 | <programlisting> |
| 999 | int |
| 1000 | main (int argc, char **argv) |
| 1001 | { |
| 1002 | DBusGConnection *connection; |
| 1003 | GError *error; |
| 1004 | DBusGProxy *proxy; |
| 1005 | char **name_list; |
| 1006 | char **name_list_ptr; |
| 1007 | |
| 1008 | g_type_init (); |
| 1009 | |
| 1010 | error = NULL; |
| 1011 | connection = dbus_g_bus_get (DBUS_BUS_SESSION, |
| 1012 | &error); |
| 1013 | if (connection == NULL) |
| 1014 | { |
| 1015 | g_printerr ("Failed to open connection to bus: %s\n", |
| 1016 | error->message); |
| 1017 | g_error_free (error); |
| 1018 | exit (1); |
| 1019 | } |
| 1020 | |
| 1021 | /* Create a proxy object for the "bus driver" (name "org.freedesktop.DBus") */ |
| 1022 | |
| 1023 | proxy = dbus_g_proxy_new_for_name (connection, |
| 1024 | DBUS_SERVICE_DBUS, |
| 1025 | DBUS_PATH_DBUS, |
| 1026 | DBUS_INTERFACE_DBUS); |
| 1027 | |
| 1028 | /* Call ListNames method, wait for reply */ |
| 1029 | error = NULL; |
| 1030 | if (!dbus_g_proxy_call (proxy, "ListNames", &error, G_TYPE_INVALID, |
| 1031 | G_TYPE_STRV, &name_list, G_TYPE_INVALID)) |
| 1032 | { |
| 1033 | /* Just do demonstrate remote exceptions versus regular GError */ |
| 1034 | if (error->domain == DBUS_GERROR && error->code == DBUS_GERROR_REMOTE_EXCEPTION) |
| 1035 | g_printerr ("Caught remote method exception %s: %s", |
| 1036 | dbus_g_error_get_name (error), |
| 1037 | error->message); |
| 1038 | else |
| 1039 | g_printerr ("Error: %s\n", error->message); |
| 1040 | g_error_free (error); |
| 1041 | exit (1); |
| 1042 | } |
| 1043 | |
| 1044 | /* Print the results */ |
| 1045 | |
| 1046 | g_print ("Names on the message bus:\n"); |
| 1047 | |
| 1048 | for (name_list_ptr = name_list; *name_list_ptr; name_list_ptr++) |
| 1049 | { |
| 1050 | g_print (" %s\n", *name_list_ptr); |
| 1051 | } |
| 1052 | g_strfreev (name_list); |
| 1053 | |
| 1054 | g_object_unref (proxy); |
| 1055 | |
| 1056 | return 0; |
| 1057 | } |
| 1058 | </programlisting> |
| 1059 | </para> |
| 1060 | </sect2> |
| 1061 | <sect2 id="glib-program-setup"> |
| 1062 | <title>Program initalization</title> |
| 1063 | <para> |
| 1064 | A connection to the bus is acquired using |
| 1065 | <literal>dbus_g_bus_get</literal>. Next, a proxy |
| 1066 | is created for the object "/org/freedesktop/DBus" with |
| 1067 | interface <literal>org.freedesktop.DBus</literal> |
| 1068 | on the service <literal>org.freedesktop.DBus</literal>. |
| 1069 | This is a proxy for the message bus itself. |
| 1070 | </para> |
| 1071 | </sect2> |
| 1072 | <sect2 id="glib-method-invocation"> |
| 1073 | <title>Understanding method invocation</title> |
| 1074 | <para> |
| 1075 | You have a number of choices for method invocation. First, as |
| 1076 | used above, <literal>dbus_g_proxy_call</literal> sends a |
| 1077 | method call to the remote object, and blocks until a reply is |
| 1078 | recieved. The outgoing arguments are specified in the varargs |
| 1079 | array, terminated with <literal>G_TYPE_INVALID</literal>. |
| 1080 | Next, pointers to return values are specified, followed again |
| 1081 | by <literal>G_TYPE_INVALID</literal>. |
| 1082 | </para> |
| 1083 | <para> |
| 1084 | To invoke a method asynchronously, use |
| 1085 | <literal>dbus_g_proxy_begin_call</literal>. This returns a |
| 1086 | <literal>DBusGPendingCall</literal> object; you may then set a |
| 1087 | notification function using |
| 1088 | <literal>dbus_g_pending_call_set_notify</literal>. |
| 1089 | </para> |
| 1090 | </sect2> |
| 1091 | <sect2 id="glib-signal-connection"> |
| 1092 | <title>Connecting to object signals</title> |
| 1093 | <para> |
| 1094 | You may connect to signals using |
| 1095 | <literal>dbus_g_proxy_add_signal</literal> and |
| 1096 | <literal>dbus_g_proxy_connect_signal</literal>. You must |
| 1097 | invoke <literal>dbus_g_proxy_add_signal</literal> to specify |
| 1098 | the signature of your signal handlers; you may then invoke |
| 1099 | <literal>dbus_g_proxy_connect_signal</literal> multiple times. |
| 1100 | </para> |
| 1101 | <para> |
| 1102 | Note that it will often be the case that there is no builtin |
| 1103 | marshaller for the type signature of a remote signal. In that |
| 1104 | case, you must generate a marshaller yourself by using |
| 1105 | <application>glib-genmarshal</application>, and then register |
| 1106 | it using <literal>dbus_g_object_register_marshaller</literal>. |
| 1107 | </para> |
| 1108 | </sect2> |
| 1109 | <sect2 id="glib-error-handling"> |
| 1110 | <title>Error handling and remote exceptions</title> |
| 1111 | <para> |
| 1112 | All of the GLib binding methods such as |
| 1113 | <literal>dbus_g_proxy_end_call</literal> return a |
| 1114 | <literal>GError</literal>. This <literal>GError</literal> can |
| 1115 | represent two different things: |
| 1116 | <itemizedlist> |
| 1117 | <listitem> |
| 1118 | <para> |
| 1119 | An internal D-Bus error, such as an out-of-memory |
| 1120 | condition, an I/O error, or a network timeout. Errors |
| 1121 | generated by the D-Bus library itself have the domain |
| 1122 | <literal>DBUS_GERROR</literal>, and a corresponding code |
| 1123 | such as <literal>DBUS_GERROR_NO_MEMORY</literal>. It will |
| 1124 | not be typical for applications to handle these errors |
| 1125 | specifically. |
| 1126 | </para> |
| 1127 | </listitem> |
| 1128 | <listitem> |
| 1129 | <para> |
| 1130 | A remote D-Bus exception, thrown by the peer, bus, or |
| 1131 | service. D-Bus remote exceptions have both a textual |
| 1132 | "name" and a "message". The GLib bindings store this |
| 1133 | information in the <literal>GError</literal>, but some |
| 1134 | special rules apply. |
| 1135 | </para> |
| 1136 | <para> |
| 1137 | The set error will have the domain |
| 1138 | <literal>DBUS_GERROR</literal> as above, and will also |
| 1139 | have the code |
| 1140 | <literal>DBUS_GERROR_REMOTE_EXCEPTION</literal>. In order |
| 1141 | to access the remote exception name, you must use a |
| 1142 | special accessor, such as |
| 1143 | <literal>dbus_g_error_has_name</literal> or |
| 1144 | <literal>dbus_g_error_get_name</literal>. The remote |
| 1145 | exception detailed message is accessible via the regular |
| 1146 | GError <literal>message</literal> member. |
| 1147 | </para> |
| 1148 | </listitem> |
| 1149 | </itemizedlist> |
| 1150 | </para> |
| 1151 | </sect2> |
| 1152 | <sect2 id="glib-more-examples"> |
| 1153 | <title>More examples of method invocation</title> |
| 1154 | <sect3 id="glib-sending-stuff"> |
| 1155 | <title>Sending an integer and string, receiving an array of bytes</title> |
| 1156 | <para> |
| 1157 | <programlisting> |
| 1158 | GArray *arr; |
| 1159 | |
| 1160 | error = NULL; |
| 1161 | if (!dbus_g_proxy_call (proxy, "Foobar", &error, |
| 1162 | G_TYPE_INT, 42, G_TYPE_STRING, "hello", |
| 1163 | G_TYPE_INVALID, |
| 1164 | DBUS_TYPE_G_UCHAR_ARRAY, &arr, G_TYPE_INVALID)) |
| 1165 | { |
| 1166 | /* Handle error */ |
| 1167 | } |
| 1168 | g_assert (arr != NULL); |
| 1169 | printf ("got back %u values", arr->len); |
| 1170 | </programlisting> |
| 1171 | </para> |
| 1172 | </sect3> |
| 1173 | <sect3 id="glib-sending-hash"> |
| 1174 | <title>Sending a GHashTable</title> |
| 1175 | <para> |
| 1176 | <programlisting> |
| 1177 | GHashTable *hash = g_hash_table_new (g_str_hash, g_str_equal); |
| 1178 | guint32 ret; |
| 1179 | |
| 1180 | g_hash_table_insert (hash, "foo", "bar"); |
| 1181 | g_hash_table_insert (hash, "baz", "whee"); |
| 1182 | |
| 1183 | error = NULL; |
| 1184 | if (!dbus_g_proxy_call (proxy, "HashSize", &error, |
| 1185 | DBUS_TYPE_G_STRING_STRING_HASH, hash, G_TYPE_INVALID, |
| 1186 | G_TYPE_UINT, &ret, G_TYPE_INVALID)) |
| 1187 | { |
| 1188 | /* Handle error */ |
| 1189 | } |
| 1190 | g_assert (ret == 2); |
| 1191 | g_hash_table_destroy (hash); |
| 1192 | </programlisting> |
| 1193 | </para> |
| 1194 | </sect3> |
| 1195 | <sect3 id="glib-receiving-bool-int"> |
| 1196 | <title>Receiving a boolean and a string</title> |
| 1197 | <para> |
| 1198 | <programlisting> |
| 1199 | gboolean boolret; |
| 1200 | char *strret; |
| 1201 | |
| 1202 | error = NULL; |
| 1203 | if (!dbus_g_proxy_call (proxy, "GetStuff", &error, |
| 1204 | G_TYPE_INVALID, |
| 1205 | G_TYPE_BOOLEAN, &boolret, |
| 1206 | G_TYPE_STRING, &strret, |
| 1207 | G_TYPE_INVALID)) |
| 1208 | { |
| 1209 | /* Handle error */ |
| 1210 | } |
| 1211 | printf ("%s %s", boolret ? "TRUE" : "FALSE", strret); |
| 1212 | g_free (strret); |
| 1213 | </programlisting> |
| 1214 | </para> |
| 1215 | </sect3> |
| 1216 | <sect3 id="glib-sending-str-arrays"> |
| 1217 | <title>Sending two arrays of strings</title> |
| 1218 | <para> |
| 1219 | <programlisting> |
| 1220 | /* NULL terminate */ |
| 1221 | char *strs_static[] = {"foo", "bar", "baz", NULL}; |
| 1222 | /* Take pointer to array; cannot pass array directly */ |
| 1223 | char **strs_static_p = strs_static; |
| 1224 | char **strs_dynamic; |
| 1225 | |
| 1226 | strs_dynamic = g_new (char *, 4); |
| 1227 | strs_dynamic[0] = g_strdup ("hello"); |
| 1228 | strs_dynamic[1] = g_strdup ("world"); |
| 1229 | strs_dynamic[2] = g_strdup ("!"); |
| 1230 | /* NULL terminate */ |
| 1231 | strs_dynamic[3] = NULL; |
| 1232 | |
| 1233 | error = NULL; |
| 1234 | if (!dbus_g_proxy_call (proxy, "TwoStrArrays", &error, |
| 1235 | G_TYPE_STRV, strs_static_p, |
| 1236 | G_TYPE_STRV, strs_dynamic, |
| 1237 | G_TYPE_INVALID, |
| 1238 | G_TYPE_INVALID)) |
| 1239 | { |
| 1240 | /* Handle error */ |
| 1241 | } |
| 1242 | g_strfreev (strs_dynamic); |
| 1243 | </programlisting> |
| 1244 | </para> |
| 1245 | </sect3> |
| 1246 | <sect3 id="glib-getting-str-array"> |
| 1247 | <title>Sending a boolean, receiving an array of strings</title> |
| 1248 | <para> |
| 1249 | <programlisting> |
| 1250 | char **strs; |
| 1251 | char **strs_p; |
| 1252 | gboolean blah; |
| 1253 | |
| 1254 | error = NULL; |
| 1255 | blah = TRUE; |
| 1256 | if (!dbus_g_proxy_call (proxy, "GetStrs", &error, |
| 1257 | G_TYPE_BOOLEAN, blah, |
| 1258 | G_TYPE_INVALID, |
| 1259 | G_TYPE_STRV, &strs, |
| 1260 | G_TYPE_INVALID)) |
| 1261 | { |
| 1262 | /* Handle error */ |
| 1263 | } |
| 1264 | for (strs_p = strs; *strs_p; strs_p++) |
| 1265 | printf ("got string: \"%s\"", *strs_p); |
| 1266 | g_strfreev (strs); |
| 1267 | </programlisting> |
| 1268 | </para> |
| 1269 | </sect3> |
| 1270 | <sect3 id="glib-sending-variant"> |
| 1271 | <title>Sending a variant</title> |
| 1272 | <para> |
| 1273 | <programlisting> |
| 1274 | GValue val = {0, }; |
| 1275 | |
| 1276 | g_value_init (&val, G_TYPE_STRING); |
| 1277 | g_value_set_string (&val, "hello world"); |
| 1278 | |
| 1279 | error = NULL; |
| 1280 | if (!dbus_g_proxy_call (proxy, "SendVariant", &error, |
| 1281 | G_TYPE_VALUE, &val, G_TYPE_INVALID, |
| 1282 | G_TYPE_INVALID)) |
| 1283 | { |
| 1284 | /* Handle error */ |
| 1285 | } |
| 1286 | g_assert (ret == 2); |
| 1287 | g_value_unset (&val); |
| 1288 | </programlisting> |
| 1289 | </para> |
| 1290 | </sect3> |
| 1291 | <sect3 id="glib-receiving-variant"> |
| 1292 | <title>Receiving a variant</title> |
| 1293 | <para> |
| 1294 | <programlisting> |
| 1295 | GValue val = {0, }; |
| 1296 | |
| 1297 | error = NULL; |
| 1298 | if (!dbus_g_proxy_call (proxy, "GetVariant", &error, G_TYPE_INVALID, |
| 1299 | G_TYPE_VALUE, &val, G_TYPE_INVALID)) |
| 1300 | { |
| 1301 | /* Handle error */ |
| 1302 | } |
| 1303 | if (G_VALUE_TYPE (&val) == G_TYPE_STRING) |
| 1304 | printf ("%s\n", g_value_get_string (&val)); |
| 1305 | else if (G_VALUE_TYPE (&val) == G_TYPE_INT) |
| 1306 | printf ("%d\n", g_value_get_int (&val)); |
| 1307 | else |
| 1308 | ... |
| 1309 | g_value_unset (&val); |
| 1310 | </programlisting> |
| 1311 | </para> |
| 1312 | </sect3> |
| 1313 | </sect2> |
| 1314 | |
| 1315 | <sect2 id="glib-generated-bindings"> |
| 1316 | <title>Generated Bindings</title> |
| 1317 | <para> |
| 1318 | By using the Introspection XML files, convenient client-side bindings |
| 1319 | can be automatically created to ease the use of a remote DBus object. |
| 1320 | </para> |
| 1321 | <para> |
| 1322 | Here is a sample XML file which describes an object that exposes |
| 1323 | one method, named <literal>ManyArgs</literal>. |
| 1324 | <programlisting> |
| 1325 | <?xml version="1.0" encoding="UTF-8" ?> |
| 1326 | <node name="/com/example/MyObject"> |
| 1327 | <interface name="com.example.MyObject"> |
| 1328 | <method name="ManyArgs"> |
| 1329 | <arg type="u" name="x" direction="in" /> |
| 1330 | <arg type="s" name="str" direction="in" /> |
| 1331 | <arg type="d" name="trouble" direction="in" /> |
| 1332 | <arg type="d" name="d_ret" direction="out" /> |
| 1333 | <arg type="s" name="str_ret" direction="out" /> |
| 1334 | </method> |
| 1335 | </interface> |
| 1336 | </node> |
| 1337 | </programlisting> |
| 1338 | </para> |
| 1339 | <para> |
| 1340 | Run <literal>dbus-binding-tool --mode=glib-client |
| 1341 | <replaceable>FILENAME</replaceable> > |
| 1342 | <replaceable>HEADER_NAME</replaceable></literal> to generate the header |
| 1343 | file. For example: <command>dbus-binding-tool --mode=glib-client |
| 1344 | my-object.xml > my-object-bindings.h</command>. This will generate |
| 1345 | inline functions with the following prototypes: |
| 1346 | <programlisting> |
| 1347 | /* This is a blocking call */ |
| 1348 | gboolean |
| 1349 | com_example_MyObject_many_args (DBusGProxy *proxy, const guint IN_x, |
| 1350 | const char * IN_str, const gdouble IN_trouble, |
| 1351 | gdouble* OUT_d_ret, char ** OUT_str_ret, |
| 1352 | GError **error); |
| 1353 | |
| 1354 | /* This is a non-blocking call */ |
| 1355 | DBusGProxyCall* |
| 1356 | com_example_MyObject_many_args_async (DBusGProxy *proxy, const guint IN_x, |
| 1357 | const char * IN_str, const gdouble IN_trouble, |
| 1358 | com_example_MyObject_many_args_reply callback, |
| 1359 | gpointer userdata); |
| 1360 | |
| 1361 | /* This is the typedef for the non-blocking callback */ |
| 1362 | typedef void |
| 1363 | (*com_example_MyObject_many_args_reply) |
| 1364 | (DBusGProxy *proxy, gdouble OUT_d_ret, char * OUT_str_ret, |
| 1365 | GError *error, gpointer userdata); |
| 1366 | </programlisting> |
| 1367 | The first argument in all functions is a <literal>DBusGProxy |
| 1368 | *</literal>, which you should create with the usual |
| 1369 | <literal>dbus_g_proxy_new_*</literal> functions. Following that are the |
| 1370 | "in" arguments, and then either the "out" arguments and a |
| 1371 | <literal>GError *</literal> for the synchronous (blocking) function, or |
| 1372 | callback and user data arguments for the asynchronous (non-blocking) |
| 1373 | function. The callback in the asynchronous function passes the |
| 1374 | <literal>DBusGProxy *</literal>, the returned "out" arguments, an |
| 1375 | <literal>GError *</literal> which is set if there was an error otherwise |
| 1376 | <literal>NULL</literal>, and the user data. |
| 1377 | </para> |
| 1378 | <para> |
| 1379 | As with the server-side bindings support (see <xref |
| 1380 | linkend="glib-server"/>), the exact behaviour of the client-side |
| 1381 | bindings can be manipulated using "annotations". Currently the only |
| 1382 | annotation used by the client bindings is |
| 1383 | <literal>org.freedesktop.DBus.GLib.NoReply</literal>, which sets the |
| 1384 | flag indicating that the client isn't expecting a reply to the method |
| 1385 | call, so a reply shouldn't be sent. This is often used to speed up |
| 1386 | rapid method calls where there are no "out" arguments, and not knowing |
| 1387 | if the method succeeded is an acceptable compromise to half the traffic |
| 1388 | on the bus. |
| 1389 | </para> |
| 1390 | </sect2> |
| 1391 | </sect1> |
| 1392 | |
| 1393 | <sect1 id="glib-server"> |
| 1394 | <title>GLib API: Implementing Objects</title> |
| 1395 | <para> |
| 1396 | At the moment, to expose a GObject via D-Bus, you must |
| 1397 | write XML by hand which describes the methods exported |
| 1398 | by the object. In the future, this manual step will |
| 1399 | be obviated by the upcoming GLib introspection support. |
| 1400 | </para> |
| 1401 | <para> |
| 1402 | Here is a sample XML file which describes an object that exposes |
| 1403 | one method, named <literal>ManyArgs</literal>. |
| 1404 | <programlisting> |
| 1405 | <?xml version="1.0" encoding="UTF-8" ?> |
| 1406 | |
| 1407 | <node name="/com/example/MyObject"> |
| 1408 | |
| 1409 | <interface name="com.example.MyObject"> |
| 1410 | <annotation name="org.freedesktop.DBus.GLib.CSymbol" value="my_object"/> |
| 1411 | <method name="ManyArgs"> |
| 1412 | <!-- This is optional, and in this case is redunundant --> |
| 1413 | <annotation name="org.freedesktop.DBus.GLib.CSymbol" value="my_object_many_args"/> |
| 1414 | <arg type="u" name="x" direction="in" /> |
| 1415 | <arg type="s" name="str" direction="in" /> |
| 1416 | <arg type="d" name="trouble" direction="in" /> |
| 1417 | <arg type="d" name="d_ret" direction="out" /> |
| 1418 | <arg type="s" name="str_ret" direction="out" /> |
| 1419 | </method> |
| 1420 | </interface> |
| 1421 | </node> |
| 1422 | </programlisting> |
| 1423 | </para> |
| 1424 | <para> |
| 1425 | This XML is in the same format as the D-Bus introspection XML |
| 1426 | format. Except we must include an "annotation" which give the C |
| 1427 | symbols corresponding to the object implementation prefix |
| 1428 | (<literal>my_object</literal>). In addition, if particular |
| 1429 | methods symbol names deviate from C convention |
| 1430 | (i.e. <literal>ManyArgs</literal> -> |
| 1431 | <literal>many_args</literal>), you may specify an annotation |
| 1432 | giving the C symbol. |
| 1433 | </para> |
| 1434 | <para> |
| 1435 | Once you have written this XML, run <literal>dbus-binding-tool --mode=glib-server <replaceable>FILENAME</replaceable> > <replaceable>HEADER_NAME</replaceable>.</literal> to |
| 1436 | generate a header file. For example: <command>dbus-binding-tool --mode=glib-server my-object.xml > my-object-glue.h</command>. |
| 1437 | </para> |
| 1438 | <para> |
| 1439 | Next, include the generated header in your program, and invoke |
| 1440 | <literal>dbus_g_object_class_install_info</literal> in the class |
| 1441 | initializer, passing the object class and "object info" included in the |
| 1442 | header. For example: |
| 1443 | <programlisting> |
| 1444 | dbus_g_object_type_install_info (COM_FOO_TYPE_MY_OBJECT, &com_foo_my_object_info); |
| 1445 | </programlisting> |
| 1446 | This should be done exactly once per object class. |
| 1447 | </para> |
| 1448 | <para> |
| 1449 | To actually implement the method, just define a C function named e.g. |
| 1450 | <literal>my_object_many_args</literal> in the same file as the info |
| 1451 | header is included. At the moment, it is required that this function |
| 1452 | conform to the following rules: |
| 1453 | <itemizedlist> |
| 1454 | <listitem> |
| 1455 | <para> |
| 1456 | The function must return a value of type <literal>gboolean</literal>; |
| 1457 | <literal>TRUE</literal> on success, and <literal>FALSE</literal> |
| 1458 | otherwise. |
| 1459 | </para> |
| 1460 | </listitem> |
| 1461 | <listitem> |
| 1462 | <para> |
| 1463 | The first parameter is a pointer to an instance of the object. |
| 1464 | </para> |
| 1465 | </listitem> |
| 1466 | <listitem> |
| 1467 | <para> |
| 1468 | Following the object instance pointer are the method |
| 1469 | input values. |
| 1470 | </para> |
| 1471 | </listitem> |
| 1472 | <listitem> |
| 1473 | <para> |
| 1474 | Following the input values are pointers to return values. |
| 1475 | </para> |
| 1476 | </listitem> |
| 1477 | <listitem> |
| 1478 | <para> |
| 1479 | The final parameter must be a <literal>GError **</literal>. |
| 1480 | If the function returns <literal>FALSE</literal> for an |
| 1481 | error, the error parameter must be initalized with |
| 1482 | <literal>g_set_error</literal>. |
| 1483 | </para> |
| 1484 | </listitem> |
| 1485 | </itemizedlist> |
| 1486 | </para> |
| 1487 | <para> |
| 1488 | Finally, you can export an object using <literal>dbus_g_connection_register_g_object</literal>. For example: |
| 1489 | <programlisting> |
| 1490 | dbus_g_connection_register_g_object (connection, |
| 1491 | "/com/foo/MyObject", |
| 1492 | obj); |
| 1493 | </programlisting> |
| 1494 | </para> |
| 1495 | |
| 1496 | <sect2 id="glib-annotations"> |
| 1497 | <title>Server-side Annotations</title> |
| 1498 | <para> |
| 1499 | There are several annotations that are used when generating the |
| 1500 | server-side bindings. The most common annotation is |
| 1501 | <literal>org.freedesktop.DBus.GLib.CSymbol</literal> but there are other |
| 1502 | annotations which are often useful. |
| 1503 | <variablelist> |
| 1504 | <varlistentry> |
| 1505 | <term><literal>org.freedesktop.DBus.GLib.CSymbol</literal></term> |
| 1506 | <listitem> |
| 1507 | <para> |
| 1508 | This annotation is used to specify the C symbol names for |
| 1509 | the various types (interface, method, etc), if it differs from the |
| 1510 | name DBus generates. |
| 1511 | </para> |
| 1512 | </listitem> |
| 1513 | </varlistentry> |
| 1514 | <varlistentry> |
| 1515 | <term><literal>org.freedesktop.DBus.GLib.Async</literal></term> |
| 1516 | <listitem> |
| 1517 | <para> |
| 1518 | This annotation marks the method implementation as an |
| 1519 | asynchronous function, which doesn't return a response straight |
| 1520 | away but will send the response at some later point to complete |
| 1521 | the call. This is used to implement non-blocking services where |
| 1522 | method calls can take time. |
| 1523 | </para> |
| 1524 | <para> |
| 1525 | When a method is asynchronous, the function prototype is |
| 1526 | different. It is required that the function conform to the |
| 1527 | following rules: |
| 1528 | <itemizedlist> |
| 1529 | <listitem> |
| 1530 | <para> |
| 1531 | The function must return a value of type <literal>gboolean</literal>; |
| 1532 | <literal>TRUE</literal> on success, and <literal>FALSE</literal> |
| 1533 | otherwise. TODO: the return value is currently ignored. |
| 1534 | </para> |
| 1535 | </listitem> |
| 1536 | <listitem> |
| 1537 | <para> |
| 1538 | The first parameter is a pointer to an instance of the object. |
| 1539 | </para> |
| 1540 | </listitem> |
| 1541 | <listitem> |
| 1542 | <para> |
| 1543 | Following the object instance pointer are the method |
| 1544 | input values. |
| 1545 | </para> |
| 1546 | </listitem> |
| 1547 | <listitem> |
| 1548 | <para> |
| 1549 | The final parameter must be a |
| 1550 | <literal>DBusGMethodInvocation *</literal>. This is used |
| 1551 | when sending the response message back to the client, by |
| 1552 | calling <literal>dbus_g_method_return</literal> or |
| 1553 | <literal>dbus_g_method_return_error</literal>. |
| 1554 | </para> |
| 1555 | </listitem> |
| 1556 | </itemizedlist> |
| 1557 | </para> |
| 1558 | </listitem> |
| 1559 | </varlistentry> |
| 1560 | <varlistentry> |
| 1561 | <term><literal>org.freedesktop.DBus.GLib.Const</literal></term> |
| 1562 | <listitem> |
| 1563 | <para>This attribute can only be applied to "out" |
| 1564 | <literal><arg></literal> nodes, and specifies that the |
| 1565 | parameter isn't being copied when returned. For example, this |
| 1566 | turns a 's' argument from a <literal>char **</literal> to a |
| 1567 | <literal>const char **</literal>, and results in the argument not |
| 1568 | being freed by DBus after the message is sent. |
| 1569 | </para> |
| 1570 | </listitem> |
| 1571 | </varlistentry> |
| 1572 | <varlistentry> |
| 1573 | <term><literal>org.freedesktop.DBus.GLib.ReturnVal</literal></term> |
| 1574 | <listitem> |
| 1575 | <para> |
| 1576 | This attribute can only be applied to "out" |
| 1577 | <literal><arg></literal> nodes, and alters the expected |
| 1578 | function signature. It currently can be set to two values: |
| 1579 | <literal>""</literal> or <literal>"error"</literal>. The |
| 1580 | argument marked with this attribute is not returned via a |
| 1581 | pointer argument, but by the function's return value. If the |
| 1582 | attribute's value is the empty string, the <literal>GError |
| 1583 | *</literal> argument is also omitted so there is no standard way |
| 1584 | to return an error value. This is very useful for interfacing |
| 1585 | with existing code, as it is possible to match existing APIs. |
| 1586 | If the attribute's value is <literal>"error"</literal>, then the |
| 1587 | final argument is a <literal>GError *</literal> as usual. |
| 1588 | </para> |
| 1589 | <para> |
| 1590 | Some examples to demonstrate the usage. This introspection XML: |
| 1591 | <programlisting> |
| 1592 | <method name="Increment"> |
| 1593 | <arg type="u" name="x" /> |
| 1594 | <arg type="u" direction="out" /> |
| 1595 | </method> |
| 1596 | </programlisting> |
| 1597 | Expects the following function declaration: |
| 1598 | <programlisting> |
| 1599 | gboolean |
| 1600 | my_object_increment (MyObject *obj, gint32 x, gint32 *ret, GError **error); |
| 1601 | </programlisting> |
| 1602 | </para> |
| 1603 | <para> |
| 1604 | This introspection XML: |
| 1605 | <programlisting> |
| 1606 | <method name="IncrementRetval"> |
| 1607 | <arg type="u" name="x" /> |
| 1608 | <arg type="u" direction="out" > |
| 1609 | <annotation name="org.freedesktop.DBus.GLib.ReturnVal" value=""/> |
| 1610 | </arg> |
| 1611 | </method> |
| 1612 | </programlisting> |
| 1613 | Expects the following function declaration: |
| 1614 | <programlisting> |
| 1615 | gint32 |
| 1616 | my_object_increment_retval (MyObject *obj, gint32 x) |
| 1617 | </programlisting> |
| 1618 | </para> |
| 1619 | <para> |
| 1620 | This introspection XML: |
| 1621 | <programlisting> |
| 1622 | <method name="IncrementRetvalError"> |
| 1623 | <arg type="u" name="x" /> |
| 1624 | <arg type="u" direction="out" > |
| 1625 | <annotation name="org.freedesktop.DBus.GLib.ReturnVal" value="error"/> |
| 1626 | </arg> |
| 1627 | </method> |
| 1628 | </programlisting> |
| 1629 | Expects the following function declaration: |
| 1630 | <programlisting> |
| 1631 | gint32 |
| 1632 | my_object_increment_retval_error (MyObject *obj, gint32 x, GError **error) |
| 1633 | </programlisting> |
| 1634 | </para> |
| 1635 | </listitem> |
| 1636 | </varlistentry> |
| 1637 | </variablelist> |
| 1638 | </para> |
| 1639 | </sect2> |
| 1640 | </sect1> |
| 1641 | |
| 1642 | <sect1 id="python-client"> |
| 1643 | <title>Python API</title> |
| 1644 | <para> |
| 1645 | The Python API, dbus-python, is now documented separately in |
| 1646 | <ulink url="http://dbus.freedesktop.org/doc/dbus-python/doc/tutorial.html">the dbus-python tutorial</ulink> (also available in doc/tutorial.txt, |
| 1647 | and doc/tutorial.html if built with python-docutils, in the dbus-python |
| 1648 | source distribution). |
| 1649 | </para> |
| 1650 | </sect1> |
| 1651 | |
| 1652 | <sect1 id="qt-client"> |
| 1653 | <title>Qt API: Using Remote Objects</title> |
| 1654 | <para> |
| 1655 | |
| 1656 | The Qt bindings are not yet documented. |
| 1657 | |
| 1658 | </para> |
| 1659 | </sect1> |
| 1660 | |
| 1661 | <sect1 id="qt-server"> |
| 1662 | <title>Qt API: Implementing Objects</title> |
| 1663 | <para> |
| 1664 | The Qt bindings are not yet documented. |
| 1665 | </para> |
| 1666 | </sect1> |
| 1667 | </article> |