| blob | c15ad447d622345d4c48b1567dc0b22cb6ff9916 |
1 <part>
2 <title>GIO Overview</title>
4 <chapter>
5 <title>Introduction</title>
7 <para>
8 GIO is striving to provide a modern, easy-to-use VFS API that sits
9 at the right level in the library stack, as well as other generally
10 useful APIs for desktop applications (such as networking and
11 D-Bus support). The goal is to overcome the shortcomings of GnomeVFS
12 and provide an API that is so good that developers prefer it over raw
13 POSIX calls. Among other things that means using GObject. It also means
14 not cloning the POSIX API, but providing higher-level, document-centric
15 interfaces.
16 </para>
18 <para>
19 The abstract file system model of GIO consists of a number of
20 interfaces and base classes for I/O and files:
21 <variablelist>
22 <varlistentry>
23 <term>GFile</term>
24 <listitem><para>reference to a file</para></listitem>
25 </varlistentry>
26 <varlistentry>
27 <term>GFileInfo</term>
28 <listitem><para>information about a file or filesystem</para></listitem>
29 </varlistentry>
30 <varlistentry>
31 <term>GFileEnumerator</term>
32 <listitem><para>list files in directories</para></listitem>
33 </varlistentry>
34 <varlistentry>
35 <term>GDrive</term>
36 <listitem><para>represents a drive</para></listitem>
37 </varlistentry>
38 <varlistentry>
39 <term>GVolume</term>
40 <listitem><para>represents a file system in an abstract way</para></listitem>
41 </varlistentry>
42 <varlistentry>
43 <term>GMount</term>
44 <listitem><para>represents a mounted file system</para></listitem>
45 </varlistentry>
46 </variablelist>
47 Then there is a number of stream classes, similar to the input and
48 output stream hierarchies that can be found in frameworks like Java:
49 <variablelist>
50 <varlistentry>
51 <term>GInputStream</term>
52 <listitem><para>read data</para></listitem>
53 </varlistentry>
54 <varlistentry>
55 <term>GOutputStream</term>
56 <listitem><para>write data</para></listitem>
57 </varlistentry>
58 <varlistentry>
59 <term>GIOStream</term>
60 <listitem><para>read and write data</para></listitem>
61 </varlistentry>
62 <varlistentry>
63 <term>GSeekable</term>
64 <listitem><para>interface optionally implemented by streams to support seeking</para></listitem>
65 </varlistentry>
66 </variablelist>
67 There are interfaces related to applications and the types
68 of files they handle:
69 <variablelist>
70 <varlistentry>
71 <term>GAppInfo</term>
72 <listitem><para>information about an installed application</para></listitem>
73 </varlistentry>
74 <varlistentry>
75 <term>GIcon</term>
76 <listitem><para>abstract type for file and application icons</para></listitem>
77 </varlistentry>
78 </variablelist>
79 There is a framework for storing and retrieving application settings:
80 <variablelist>
81 <varlistentry>
82 <term>GSettings</term>
83 <listitem><para>stores and retrieves application settings</para></listitem>
84 </varlistentry>
85 </variablelist>
86 There is support for network programming, including connectivity monitoring,
87 name resolution, lowlevel socket APIs and highlevel client and server
88 helper classes:
89 <variablelist>
90 <varlistentry>
91 <term>GSocket</term>
92 <listitem><para>lowlevel platform independent socket object</para></listitem>
93 </varlistentry>
94 <varlistentry>
95 <term>GResolver</term>
96 <listitem><para>asynchronous and cancellable DNS resolver</para></listitem>
97 </varlistentry>
98 <varlistentry>
99 <term>GSocketClient</term>
100 <listitem><para>high-level network client helper</para></listitem>
101 </varlistentry>
102 <varlistentry>
103 <term>GSocketService</term>
104 <listitem><para>high-level network server helper</para></listitem>
105 </varlistentry>
106 <varlistentry>
107 <term>GSocketConnection</term>
108 <listitem><para>network connection stream</para></listitem>
109 </varlistentry>
110 <varlistentry>
111 <term>GNetworkMonitor</term>
112 <listitem><para>network connectivity monitoring</para></listitem>
113 </varlistentry>
114 </variablelist>
115 There is support for connecting to <link linkend="http://www.freedesktop.org/wiki/Software/dbus">D-Bus</link>,
116 sending and receiving messages, owning and watching bus names,
117 and making objects available on the bus:
118 <variablelist>
119 <varlistentry>
120 <term>GDBusConnection</term>
121 <listitem><para>a D-Bus connection</para></listitem>
122 </varlistentry>
124 <varlistentry>
125 <term>GDBusMethodInvocation</term>
126 <listitem><para>for handling remote calls</para></listitem>
127 </varlistentry>
129 <varlistentry>
130 <term>GDBusServer</term>
131 <listitem><para>helper for accepting connections</para></listitem>
132 </varlistentry>
134 <varlistentry>
135 <term>GDBusProxy</term>
136 <listitem><para>proxy to access D-Bus interfaces on a remote object</para></listitem>
137 </varlistentry>
139 </variablelist>
140 Beyond these, GIO provides facilities for file monitoring,
141 asynchronous I/O and filename completion. In addition to the
142 interfaces, GIO provides implementations for the local case.
143 Implementations for various network file systems are provided
144 by the GVFS package as loadable modules.
145 </para>
147 <para>
148 Other design choices which consciously break with the GnomeVFS
149 design are to move backends out-of-process, which minimizes the
150 dependency bloat and makes the whole system more robust. The backends
151 are not included in GIO, but in the separate GVFS package. The GVFS
152 package also contains the GVFS daemon, which spawn further mount
153 daemons for each individual connection.
154 </para>
156 <figure id="gvfs-overview">
157 <title>GIO in the GTK+ library stack</title>
158 <graphic fileref="gvfs-overview.png" format="PNG"></graphic>
159 </figure>
161 <para>
162 The GIO model of I/O is stateful: if an application establishes e.g.
163 a SFTP connection to a server, it becomes available to all applications
164 in the session; the user does not have to enter his password over
165 and over again.
166 </para>
167 <para>
168 One of the big advantages of putting the VFS in the GLib layer
169 is that GTK+ can directly use it, e.g. in the filechooser.
170 </para>
171 </chapter>
173 <chapter>
174 <title>Writing GIO applications</title>
176 <para>
177 The information in the GLib <ulink url="http://developer.gnome.org/glib/stable/glib-programming.html">documentation</ulink> about writing GLib
178 applications is generally applicable when writing GIO applications.
179 </para>
181 <simplesect><title>Threads</title>
183 <para>
184 GDBus has its own private worker thread, so applications using
185 GDBus have at least 3 threads. GIO makes heavy use of the concept
186 of a <link linkend="g-main-context-push-thread-default">thread-default
187 main context</link> to execute callbacks of asynchronous
188 methods in the same context in which the operation was started.
189 </para>
191 </simplesect>
193 <simplesect id="async-programming"><title>Asynchronous Programming</title>
195 <para>
196 Many GIO functions come in two versions: synchronous and asynchronous,
197 denoted by an <code>_async</code> suffix. It is important to use these
198 appropriately: synchronous calls should not be used from
199 within a main loop which is shared with other code, such as one in the
200 application’s main thread. Synchronous calls block until they complete,
201 and I/O operations can take noticeable amounts of time (even on ‘fast’
202 SSDs). Blocking a main loop iteration while waiting for I/O means that
203 other sources in the main loop will not be dispatched, such as input and
204 redraw handlers for the application’s UI. This can cause the application
205 to ‘freeze’ until I/O completes.
206 </para>
208 <para>
209 A few self-contained groups of functions, such as code generated by
210 <link linkend="gdbus-codegen"><application>gdbus-codegen</application></link>,
211 use a different convention: functions are asynchronous default, and it is
212 the <emphasis>synchronous</emphasis> version which has a
213 <code>_sync</code>
214 suffix. Aside from naming differences, they should be treated the same
215 way as functions following the normal convention above.
216 </para>
218 <para>
219 The asynchronous (<code>_async</code>) versions of functions return
220 control to the caller immediately, after scheduling the I/O in the kernel
221 and adding a callback for it to the main loop. This callback will be
222 invoked when the operation has completed. From the callback, the paired
223 <code>_finish</code> function should be called to retrieve the return
224 value of the I/O operation, and any errors which occurred. For more
225 information on using and implementing asynchronous functions, see
226 <link linkend="GAsyncResult.description"><type>GAsyncResult</type></link>
227 and <link linkend="GTask.description"><type>GTask</type></link>.
228 </para>
230 <para>
231 By starting multiple asynchronous operations in succession, they will be
232 executed in parallel (up to an arbitrary limit imposed by GIO’s internal
233 worker thread pool).
234 </para>
236 <para>
237 The synchronous versions of functions can be used early in application
238 startup when there is no main loop to block, for example to load initial
239 configuration files. They can also be used for I/O on files which are
240 guaranteed to be small and on the local disk. Note that the user’s home
241 directory is not guaranteed to be on the local disk.
242 </para>
243 </simplesect>
245 <simplesect><title>Security</title>
247 <para>
248 When your program needs to carry out some privileged operation (say,
249 create a new user account), there are various ways in which you can go
250 about this:
251 <itemizedlist>
252 <listitem><para>
253 Implement a daemon that offers the privileged operation. A convenient
254 way to do this is as a D-Bus system-bus service. The daemon will probably
255 need ways to check the identity and authorization of the caller before
256 executing the operation. <ulink url="http://www.freedesktop.org/software/polkit/docs/latest/polkit.8.html">polkit</ulink> is a framework that allows this.
257 </para></listitem>
258 <listitem><para>
259 Use a small helper that is executed with elevated privileges via
260 pkexec. <ulink url="http://www.freedesktop.org/software/polkit/docs/latest/pkexec.1.html">pkexec</ulink> is a small program launcher that is part of polkit.
261 </para></listitem>
262 <listitem><para>
263 Use a small helper that is executed with elevated privileges by
264 being suid root.
265 </para></listitem>
266 </itemizedlist>
267 None of these approaches is the clear winner, they all have their
268 advantages and disadvantages.
269 </para>
271 <para>
272 When writing code that runs with elevated privileges, it is important
273 to follow some basic rules of secure programming. David Wheeler has an
274 excellent book on this topic,
275 <ulink url="http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/index.html">Secure Programming for Linux and Unix HOWTO</ulink>.
276 </para>
278 <para>
279 When using GIO in code that runs with elevated privileges, you have to
280 be careful. GIO has extension points whose implementations get loaded
281 from modules (executable code in shared objects), which could allow
282 an attacker to sneak his own code into your application by tricking it
283 into loading the code as a module. However, GIO will never load modules
284 from your home directory except when explictly asked to do so via an
285 environment variable.
286 </para>
288 <para>
289 In most cases, your helper program should be so small that you don't
290 need GIO, whose APIs are largely designed to support full-blown desktop
291 applications. If you can't resist the convenience of these APIs, here
292 are some steps you should take:
293 <itemizedlist>
294 <listitem><para>
295 Clear the environment, e.g. using the <function>clearenv()</function>
296 function.
297 David Wheeler has a good <ulink url="http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/environment-variables.html">explanation</ulink> for why it is
298 important to sanitize the environment.
299 See <xref linkend="running-gio-apps"/>
300 for a list of all environment variables affecting GIO. In particular,
301 <envar>PATH</envar> (used to locate binaries), <envar>GIO_EXTRA_MODULES</envar> (used to locate loadable modules) and <envar>DBUS_{SYSTEM,SESSION}_BUS_ADDRESS</envar> (used to locate the D-Bus system and session bus) are important.
302 </para></listitem>
303 <listitem><para>
304 Don't use GVfs, by setting <envar>GIO_USE_VFS=local</envar> in the environment.
305 The reason to avoid GVfs in security-sensitive programs is that it uses
306 many libraries which have not necessarily been audited for security problems.
307 Gvfs is also heavily distributed and relies on a session bus to be present.
308 </para></listitem>
309 </itemizedlist>
310 </para>
312 </simplesect>
314 </chapter>
316 <chapter>
317 <title>Compiling GIO applications</title>
319 <para>
320 GIO comes with a <filename>gio-2.0.pc</filename> file that you
321 should use together with <literal>pkg-config</literal> to obtain
322 the necessary information about header files and libraries. See
323 the <literal>pkg-config</literal> man page or the GLib documentation
324 for more information on how to use <literal>pkg-config</literal>
325 to compile your application.
326 </para>
328 <para>
329 If you are using GIO on UNIX-like systems, you may want to use
330 UNIX-specific GIO interfaces such as #GUnixInputStream,
331 #GUnixOutputStream, #GUnixMount or #GDesktopAppInfo.
332 To do so, use the <filename>gio-unix-2.0.pc</filename> file
333 instead of <filename>gio-2.0.pc</filename>
334 </para>
335 </chapter>
337 <chapter id="running-gio-apps">
338 <title>Running GIO applications</title>
340 <para>
341 GIO inspects a few environment variables in addition to the
342 ones used by GLib.
343 </para>
345 <formalpara>
346 <title><envar>XDG_DATA_HOME</envar>, <envar>XDG_DATA_DIRS</envar></title>
348 <para>
349 GIO uses these environment variables to locate MIME information.
350 For more information, see the <ulink url="http://freedesktop.org/Standards/shared-mime-info-spec">Shared MIME-info Database</ulink>
351 and the <ulink url="http://freedesktop.org/Standards/basedir-spec">Base Directory Specification</ulink>.
352 </para>
353 </formalpara>
355 <formalpara>
356 <title><envar>GVFS_DISABLE_FUSE</envar></title>
358 <para>
359 This variable can be set to keep #Gvfs from starting the fuse backend,
360 which may be unwanted or unnecessary in certain situations.
361 </para>
362 </formalpara>
364 <formalpara>
365 <title><envar>GIO_USE_VFS</envar></title>
367 <para>
368 This environment variable can be set to the name of a #GVfs
369 implementation to override the default for debugging purposes.
370 The #GVfs implementation for local files that is included in GIO
371 has the name "local", the implementation in the gvfs module has
372 the name "gvfs". Most commonly, system software will set this to "local"
373 to avoid having `GFile` APIs perform unnecessary DBus calls.
374 </para>
375 </formalpara>
377 <para>
378 The following environment variables are only useful for debugging
379 GIO itself or modules that it loads. They should not be set in a
380 production environment.
381 </para>
383 <formalpara>
384 <title><envar>GIO_USE_FILE_MONITOR</envar></title>
386 <para>
387 This variable can be set to the name of a #GFileMonitor
388 implementation to override the default for debugging purposes.
389 The #GFileMonitor implementation for local files that is included
390 in GIO on Linux has the name "inotify", others that are built
391 are built as modules (depending on the platform) are called
392 "fam" and "fen".
393 </para>
394 </formalpara>
396 <formalpara>
397 <title><envar>GIO_USE_VOLUME_MONITOR</envar></title>
399 <para>
400 This variable can be set to the name of a #GVolumeMonitor
401 implementation to override the default for debugging purposes.
402 The #GVolumeMonitor implementation for local files that is included
403 in GIO has the name "unix", the udisks2-based implementation in the
404 gvfs module has the name "udisks2".
405 </para>
406 </formalpara>
408 <formalpara>
409 <title><envar>GIO_USE_TLS</envar></title>
411 <para>
412 This variable can be set to the name of a #GTlsBackend
413 implementation to override the default for debugging purposes.
414 GIO does not include a #GTlsBackend implementation, the gnutls-based
415 implementation in the glib-networking module has the name "gnutls".
416 </para>
417 </formalpara>
419 <formalpara>
420 <title><envar>GIO_MODULE_DIR</envar></title>
422 <para>
423 When this environment variable is set to a path, GIO will load
424 modules from this alternate directory instead of the directory
425 built into GIO. This is useful when running tests, for example.
426 </para>
427 </formalpara>
429 <formalpara>
430 <title><envar>GIO_EXTRA_MODULES</envar></title>
432 <para>
433 When this environment variable is set to a path, or a set of
434 paths separated by a colon, GIO will attempt to load
435 additional modules from within the path.
436 </para>
437 </formalpara>
439 <formalpara>
440 <title><envar>GSETTINGS_BACKEND</envar></title>
442 <para>
443 This variable can be set to the name of a #GSettingsBackend
444 implementation to override the default for debugging purposes.
445 The memory-based implementation that is included in GIO has
446 the name "memory", the one in dconf has the name "dconf-settings".
447 </para>
448 </formalpara>
450 <formalpara>
451 <title><envar>GSETTINGS_SCHEMA_DIR</envar></title>
453 <para>
454 This variable can be set to the name of a directory that is
455 considered in addition to the <filename>glib-2.0/schemas</filename>
456 subdirectories of the XDG system data dirs when looking
457 for compiled schemas for #GSettings.
458 </para>
459 </formalpara>
461 <formalpara>
462 <title><envar>DBUS_SYSTEM_BUS_ADDRESS</envar></title>
464 <para>
465 This variable is consulted to find the address of the D-Bus system
466 bus. For the format of D-Bus addresses, see the D-Bus
467 <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html#addresses">specification</ulink>.
468 </para>
469 <para>
470 Setting this variable overrides platform-specific ways of determining
471 the system bus address.
472 </para>
473 </formalpara>
475 <formalpara>
476 <title><envar>DBUS_SESSION_BUS_ADDRESS</envar></title>
478 <para>
479 This variable is consulted to find the address of the D-Bus session bus.
480 </para>
481 <para>
482 Setting this variable overrides platform-specific ways of determining
483 the session bus address.
484 </para>
485 </formalpara>
487 <formalpara>
488 <title><envar>DBUS_STARTER_BUS_TYPE</envar></title>
490 <para>
491 This variable is consulted to find out the 'starter' bus for an
492 application that has been started via D-Bus activation. The possible
493 values are 'system' or 'session'.
494 </para>
495 </formalpara>
497 <formalpara>
498 <title><envar>G_DBUS_DEBUG</envar></title>
500 <para>
501 This variable can be set to a list of debug options, which
502 cause GLib to print out different types of debugging
503 information when using the D-Bus routines.
504 <variablelist>
505 <varlistentry>
506 <term>transport</term>
507 <listitem><para>Show IO activity (e.g. reads and writes)</para></listitem>
508 </varlistentry>
509 <varlistentry>
510 <term>message</term>
511 <listitem><para>Show all sent and received D-Bus messages</para></listitem>
512 </varlistentry>
513 <varlistentry>
514 <term>payload</term>
515 <listitem><para>Show payload for all sent and received D-Bus messages (implies message)</para></listitem>
516 </varlistentry>
517 <varlistentry>
518 <term>call</term>
519 <listitem><para>Trace g_dbus_connection_call() and g_dbus_connection_call_sync() API usage</para></listitem>
520 </varlistentry>
521 <varlistentry>
522 <term>signal</term>
523 <listitem><para>Show when a D-Bus signal is received</para></listitem>
524 </varlistentry>
525 <varlistentry>
526 <term>incoming</term>
527 <listitem><para>Show when an incoming D-Bus method call is received</para></listitem>
528 </varlistentry>
529 <varlistentry>
530 <term>return</term>
531 <listitem><para>Show when a reply is returned via the #GDBusMethodInvocation API</para></listitem>
532 </varlistentry>
533 <varlistentry>
534 <term>emission</term>
535 <listitem><para>Trace g_dbus_connection_emit_signal() API usage</para></listitem>
536 </varlistentry>
537 <varlistentry>
538 <term>authentication</term>
539 <listitem><para>Show information about connection authentication</para></listitem>
540 </varlistentry>
541 <varlistentry>
542 <term>address</term>
543 <listitem><para>Show information about D-Bus address lookups and autolaunching</para></listitem>
544 </varlistentry>
545 </variablelist>
546 The special value <literal>all</literal> can be used to turn
547 on all debug options. The special value
548 <literal>help</literal> can be used to print a list of
549 supported options to standard output.
550 </para>
551 </formalpara>
553 <formalpara>
554 <title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR</envar></title>
556 <para>
557 Can be used to override the directory used to store the
558 keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
559 authentication mechanism. Normally the directory used is
560 <filename>.dbus-keyrings</filename> in the user's home
561 directory.
562 </para>
563 </formalpara>
565 <formalpara>
566 <title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR_IGNORE_PERMISSION</envar></title>
568 <para>
569 If set, the permissions of the directory used to store the
570 keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
571 authentication mechanism won't be checked. Normally the
572 directory must be readable only by the user.
573 </para>
574 </formalpara>
575 </chapter>
577 <chapter id="extending-gio">
578 <title>Extending GIO</title>
580 <para>
581 A lot of the functionality that is accessible through GIO
582 is implemented in loadable modules, and modules provide a convenient
583 way to extend GIO. In addition to the #GIOModule API which supports
584 writing such modules, GIO has a mechanism to define extension points,
585 and register implementations thereof, see #GIOExtensionPoint.
586 </para>
587 <para>
588 The following extension points are currently defined by GIO:
589 </para>
591 <formalpara>
592 <title>G_VFS_EXTENSION_POINT_NAME</title>
594 <para>
595 Allows to override the functionality of the #GVfs class.
596 Implementations of this extension point must be derived from #GVfs.
597 GIO uses the implementation with the highest priority that is active,
598 see g_vfs_is_active().
599 </para>
600 <para>
601 GIO implements this extension point for local files, gvfs contains
602 an implementation that supports all the backends in gvfs.
603 </para>
604 </formalpara>
606 <formalpara>
607 <title>G_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
609 <para>
610 Allows to add more volume monitors.
611 Implementations of this extension point must be derived from
612 #GVolumeMonitor. GIO uses all registered extensions.
613 </para>
614 <para>
615 gvfs contains an implementation that works together with the #GVfs
616 implementation in gvfs.
617 </para>
618 </formalpara>
620 <formalpara>
621 <title>G_NATIVE_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
623 <para>
624 Allows to override the 'native' volume monitor.
625 Implementations of this extension point must be derived from
626 #GNativeVolumeMonitor. GIO uses the implementation with
627 the highest priority that is supported, as determined by the
628 is_supported() vfunc in #GVolumeMonitorClass.
629 </para>
630 <para>
631 GIO implements this extension point for local mounts,
632 gvfs contains a udisks2-based implementation.
633 </para>
634 </formalpara>
636 <formalpara>
637 <title>G_LOCAL_FILE_MONITOR_EXTENSION_POINT_NAME</title>
639 <para>
640 Allows to override the file monitor implementation for
641 local files. Implementations of this extension point must
642 be derived from #GLocalFileMonitor. GIO uses the implementation
643 with the highest priority that is supported, as determined by the
644 is_supported() vfunc in #GLocalFileMonitorClass.
645 </para>
646 <para>
647 GIO uses this extension point internally, to switch between
648 its fam-based and inotify-based file monitoring implementations.
649 </para>
650 </formalpara>
652 <formalpara>
653 <title>G_LOCAL_DIRECTORY_MONITOR_EXTENSION_POINT_NAME</title>
655 <para>
656 Allows to override the directory monitor implementation for
657 local files. Implementations of this extension point must be
658 derived from #GLocalDirectoryMonitor. GIO uses the implementation
659 with the highest priority that is supported, as determined by the
660 is_supported() vfunc in #GLocalDirectoryMonitorClass.
661 </para>
662 <para>
663 GIO uses this extension point internally, to switch between
664 its fam-based and inotify-based directory monitoring implementations.
665 </para>
666 </formalpara>
668 <formalpara>
669 <title>G_DESKTOP_APP_INFO_LOOKUP_EXTENSION_POINT_NAME</title>
671 <para>
672 Unix-only. Allows to provide a way to associate default handlers
673 with URI schemes. Implementations of this extension point must
674 implement the #GDesktopAppInfoLookup interface. GIO uses the
675 implementation with the highest priority.
676 </para>
677 <para>
678 This extension point has been discontinued in GLib 2.28. It is
679 still available to keep API and ABI stability, but GIO is no
680 longer using it for default handlers. Instead, the mime handler
681 mechanism is used, together with x-scheme-handler pseudo-mimetypes.
682 </para>
683 </formalpara>
685 <formalpara>
686 <title>G_SETTINGS_BACKEND_EXTENSION_POINT_NAME</title>
688 <para>
689 Allows to provide an alternative storage for #GSettings.
690 Implementations of this extension point must derive from the
691 #GSettingsBackend type. GIO contains a keyfile-based
692 implementation of this extension point, another one is provided
693 by dconf.
694 </para>
695 </formalpara>
697 <formalpara>
698 <title>G_PROXY_EXTENSION_POINT_NAME</title>
700 <para>
701 Allows to provide implementations for network proxying.
702 Implementations of this extension point must provide the
703 #GProxy interface, and must be named after the network
704 protocol they are proxying.
705 </para>
706 <para>
707 glib-networking contains an implementation of this extension
708 point based on libproxy.
709 </para>
710 </formalpara>
711 <formalpara>
712 <title>G_TLS_BACKEND_EXTENSION_POINT_NAME</title>
714 <para>
715 Allows to provide implementations for TLS support.
716 Implementations of this extension point must implement
717 the #GTlsBackend interface.
718 </para>
719 <para>
720 glib-networking contains an implementation of this extension
721 point.
722 </para>
723 </formalpara>
725 <formalpara>
726 <title>G_NETWORK_MONITOR_EXTENSION_POINT_NAME</title>
728 <para>
729 Allows to provide implementations for network connectivity
730 monitoring.
731 Implementations of this extension point must implement
732 the #GNetworkMonitorInterface interface.
733 </para>
734 <para>
735 GIO contains an implementation of this extension point
736 that is using the netlink interface of the Linux kernel.
737 </para>
738 </formalpara>
739 </chapter>
740 </part>