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Diffstat (limited to 'doc/afb-plugin-writing.md')
| -rw-r--r-- | doc/afb-plugin-writing.md | 179 |
1 files changed, 131 insertions, 48 deletions
diff --git a/doc/afb-plugin-writing.md b/doc/afb-plugin-writing.md index 734b15a5..7861021b 100644 --- a/doc/afb-plugin-writing.md +++ b/doc/afb-plugin-writing.md @@ -178,6 +178,65 @@ This plugin example is in *plugins/samples/tic-tac-toe.c*. This plugin is named ***tictactoe***. +Dependencies when compiling +--------------------------- + +Afb-daemon provides a configuration file for *pkg-config*. +Typing the command + + pkg-config --cflags afb-daemon + +will print the flags to use for compiling, like this: + + $ pkg-config --cflags afb-daemon + -I/opt/local/include -I/usr/include/json-c + +For linking, you should use + + $ pkg-config --libs afb-daemon + -ljson-c + +As you see, afb-daemon automatically includes dependency to json-c. +This is done through the **Requires** keyword of pkg-config +because almost all plugin will use **json-c**. + +If this behaviour is a problem, let us know. + +Internally, afb-daemon uses **libsystemd** for its event loop +and for its binding to D-Bus. +Plugins developpers are encouraged to also use this library. +But it is a matter of choice. +Thus there is no dependency to **libsystemd**. + +> Afb-daemon provides no library for plugins. +> The functions that the plugin need to have are given +> to the plugin at runtime through pointer using read-only +> memory. + +Header files to include +----------------------- + +The plugin *tictactoe* has the following lines for its includes: + + #define _GNU_SOURCE + #include <stdio.h> + #include <string.h> + #include <json-c/json.h> + #include <afb/afb-plugin.h> + +The header *afb/afb-plugin.h* includes all the features that a plugin +needs except two foreign header that must be included by the plugin +if it needs it: + +- *json-c/json.h*: this header must be include to handle json objects; +- *systemd/sd-event.h*: this must be include to access the main loop; +- *systemd/sd-bus.h*: this may be include to use dbus connections. + +The *tictactoe* plugin does not use systemd features so it is not included. + +When including *afb/afb-plugin.h*, the macro **_GNU_SOURCE** must be +defined. + Choosing names -------------- @@ -248,53 +307,6 @@ It is also a good practice, even for arguments, to not rely on the case sensitivity and to avoid the use of names different only by the case. -Options to set when compiling plugins -------------------------------------- - -Afb-daemon provides a configuration file for *pkg-config*. -Typing the command - - pkg-config --cflags afb-daemon - -will print the flags to use for compiling, like this: - - $ pkg-config --cflags afb-daemon - -I/opt/local/include -I/usr/include/json-c - -For linking, you should use - - $ pkg-config --libs afb-daemon - -ljson-c - -As you see, afb-daemon automatically includes dependency to json-c. -This is done through the **Requires** keyword of pkg-config. - -If this behaviour is a problem, let us know. - -Header files to include ------------------------ - -The plugin *tictactoe* has the following lines for its includes: - - #define _GNU_SOURCE - #include <stdio.h> - #include <string.h> - #include <json-c/json.h> - #include <afb/afb-plugin.h> - -The header *afb/afb-plugin.h* includes all the features that a plugin -needs except two foreign header that must be included by the plugin -if it needs it: - -- *json-c/json.h*: this header must be include to handle json objects; -- *systemd/sd-event.h*: this must be include to access the main loop; -- *systemd/sd-bus.h*: this may be include to use dbus connections. - -The *tictactoe* plugin does not use systemd features so it is not included. - -When including *afb/afb-plugin.h*, the macro **_GNU_SOURCE** must be -defined. - Writing a synchronous verb implementation ----------------------------------------- @@ -755,7 +767,7 @@ The description of the plugin is defined as below. static const struct AFB_verb_desc_v1 plugin_verbs[] = { /* VERB'S NAME SESSION MANAGEMENT FUNCTION TO CALL SHORT DESCRIPTION */ { .name= "new", .session= AFB_SESSION_NONE, .callback= new, .info= "Starts a new game" }, - { .name= "play", .session= AFB_SESSION_NONE, .callback= play, .info= "Tells the server to play" }, + { .name= "play", .session= AFB_SESSION_NONE, .callback= play, .info= "Asks the server to play" }, { .name= "move", .session= AFB_SESSION_NONE, .callback= move, .info= "Tells the client move" }, { .name= "board", .session= AFB_SESSION_NONE, .callback= board, .info= "Get the current board" }, { .name= "level", .session= AFB_SESSION_NONE, .callback= level, .info= "Set the server level" }, @@ -920,10 +932,81 @@ journal, syslog or kmsg. (See man sd-daemon). Sending events -------------- +Since version 0.5, plugins can broadcast events to any potential listener. +This kind of bradcast is not targeted. Event targeted will come in a future +version of afb-daemon. + +The plugin *tic-tac-toe* broadcasts events when the board changes. +This is done in the function **changed**: + + /* + * signals a change of the board + */ + static void changed(struct board *board, const char *reason) + { + ... + struct json_object *description; + + /* get the description */ + description = describe(board); + + ... + + afb_daemon_broadcast_event(afbitf->daemon, reason, description); + } + +The description of the changed board is pushed via the daemon interface. + +Within the plugin *tic-tac-toe*, the *reason* indicates the origin of +the change. For the function **afb_daemon_broadcast_event**, the second +parameter is the name of the broadcasted event. The third argument is the +object that is transmitted with the event. + +The function **afb_daemon_broadcast_event** is defined as below: + + /* + * Broadcasts widely the event of 'name' with the data 'object'. + * 'object' can be NULL. + * 'daemon' MUST be the daemon given in interface when activating the plugin. + */ + void afb_daemon_broadcast_event(struct afb_daemon daemon, const char *name, struct json_object *object); + +In fact the event name received by the listener is prefixed with +the name of the plugin. So when the change occurs after a move, the +reason is **move** and then the clients receive the event **tictactoe/move**. + +> Note that nothing is said about the case sensitivity of event names. +> However, the event is always prefixed with the name that the plugin +> declared, with the same case, followed with a slash /. +> Thus it is safe to compare event using a case sensitive comparison. + Writing an asynchronous verb implementation ------------------------------------------- +/* + * signals a change of the board + */ +static void changed(struct board *board, const char *reason) +{ + struct waiter *waiter, *next; + struct json_object *description; + + /* get the description */ + description = describe(board); + + waiter = board->waiters; + board->waiters = NULL; + while (waiter != NULL) { + next = waiter->next; + afb_req_success(waiter->req, json_object_get(description), reason); + afb_req_unref(waiter->req); + free(waiter); + waiter = next; + } + + afb_event_sender_push(afb_daemon_get_event_sender(afbitf->daemon), reason, description); +} How to build a plugin --------------------- |