Wed Apr 6 11:29:45 2011

Asterisk developer's documentation


framehook.h

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 2010, Digium, Inc.
00005  *
00006  * David Vossel <dvossel@digium.com>
00007  *
00008  * See http://www.asterisk.org for more information about
00009  * the Asterisk project. Please do not directly contact
00010  * any of the maintainers of this project for assistance;
00011  * the project provides a web site, mailing lists and IRC
00012  * channels for your use.
00013  *
00014  * This program is free software, distributed under the terms of
00015  * the GNU General Public License Version 2. See the LICENSE file
00016  * at the top of the source tree.
00017  */
00018 
00019 /*! \file
00020  * \brief FrameHook Architecture
00021  */
00022 
00023 /*!
00024 
00025 \page AstFrameHookAPI Asterisk FrameHook API
00026 
00027 \section FrameHookFunctionality How FrameHooks Work
00028     FrameHooks work by intercepting all frames being written and read off
00029     a channel and allowing those frames to be viewed and manipulated within a
00030     call back function.  Frame interception occurs before any processing is
00031     done on the frame, which means this hook can be used to transparently
00032     manipulate a frame before it is read from the channel or written
00033     to the tech_pvt.  This API can be thought of as a layer between the
00034     channel API and the Asterisk core when going in the READ direction, and
00035     as a layer between the Channel API and the tech_pvt when going in the
00036     WRITE direction.
00037 
00038 \section FrameHookAPIUsage How to Use an FrameHook
00039     Attaching and detaching an FrameHook to a channel is very simple.  There are only
00040     two functions involved, ast_framehook_attach() which will return an id representing
00041     the new FrameHook on the channel, and ast_framehook_detach() which signals the
00042     FrameHook for detachment and destruction. Below is detailed information each of these
00043     functions and their usage.
00044 
00045 \code
00046     struct ast_framehook_interface interface = {
00047         .version = AST_FRAMEHOOK_INTERFACE_VERSION,
00048         .event_cb = hook_event_cb,
00049         .destroy_cb = hook_destroy_cb,
00050         .data = data, // where the data ptr points to any custom data used later by the hook cb.
00051     };
00052     int id = ast_framehook_attach(channel, &interface);
00053 \endcode
00054 
00055     The ast_framehook_attach() function creates and attaches a new FrameHook onto
00056     a channel. Once attached to the channel, the FrameHook will call the event_callback
00057     function each time a frame is written or read on the channel.  A custom data
00058     pointer can be provided to this function to store on the FrameHook as well.  This
00059     pointer can be used to keep up with any statefull information associated with the FrameHook
00060     and is provided during the event_callback function.  The destroy_callback function is optional.
00061     This function exists so any custom data stored on the FrameHook can be destroyed before
00062     the Framehook if destroyed.
00063 
00064 \code
00065     ast_framehook_detach(channel, id);
00066 \endcode
00067 
00068     The ast_framehook_detach() function signals the FrameHook represented by an id to
00069     be detached and destroyed on a channel.  Since it is possible this function may be called
00070     during the FrameHook's event callback, it is impossible to synchronously detach the
00071     FrameHook from the channel during this function call.  It is guaranteed that the next
00072     event proceeding the ast_framehook_detach() will be of type AST_FRAMEHOOK_EVENT_DETACH,
00073     and that after that event occurs no other event will ever be issued for that FrameHook.
00074     Once the FrameHook is destroyed, the destroy callback function will be called if it was
00075     provided. Note that if this function is never called, the FrameHook will be detached
00076     on channel destruction.
00077 
00078 \section FrameHookAPICodeExample FrameHook Example Code
00079     The example code below attaches an FrameHook on a channel, and then detachs it when
00080     the first ast_frame is read or written to the event callback function.  The Framehook's id
00081     is stored on the FrameHook's data pointer so it can be detached within the callback.
00082 
00083 \code
00084     static void destroy_cb(void *data) {
00085        ast_free(data);
00086     }
00087 
00088     static struct ast_frame *event_cb(struct ast_channel *chan,
00089             struct ast_frame *frame,
00090             enum ast_framehook_event event,
00091             void *data) {
00092 
00093         int *id = data;
00094 
00095         if (!frame) {
00096             return frame;
00097         }
00098 
00099         if (event == AST_FRAMEHOOK_EVENT_WRITE) {
00100             ast_log(LOG_NOTICE, "YAY we received a frame in the write direction, Type: %d\n", frame->frametype)
00101             ast_framehook_detach(chan, id); // the channel is guaranteed to be locked during this function call.
00102         } else if (event == AST_FRAMEHOOK_EVENT_READ) {
00103             ast_log(LOG_NOTICE, "YAY we received a frame in the read direction: Type: %d\n", frame->frametype);
00104             ast_framehook_detach(chan, id); // the channel is guaranteed to be locked during this function call.
00105         }
00106 
00107         return frame;
00108     {
00109 
00110     int some_function()
00111     {
00112         struct ast_framehook_interface interface = {
00113             .version = AST_FRAMEHOOK_INTERFACE_VERSION,
00114             .event_cb = hook_event_cb,
00115             .destroy_cb = hook_destroy_cb,
00116         };
00117         int *id = ast_calloc(1, sizeof(int));
00118 
00119         if (!id) {
00120             return -1;
00121         }
00122 
00123         interface.data = id; // This data will be returned to us in the callbacks.
00124 
00125         ast_channel_lock(chan);
00126         *id = ast_framehook_attach(chan, &interface);
00127         ast_channel_unlock(chan);
00128 
00129         if (*id < 0) {
00130             // framehook attach failed, free data
00131             ast_free(id);
00132             return -1;
00133         }
00134         return 0;
00135     }
00136 \endcode
00137 */
00138 
00139 #ifndef _AST_FRAMEHOOK_H_
00140 #define _AST_FRAMEHOOK_H_
00141 #include "asterisk/linkedlists.h"
00142 #include "asterisk/frame.h"
00143 
00144 struct ast_framehook;
00145 struct ast_framehook_list;
00146 
00147 /*!
00148  * \brief These are the types of events that the framehook's event callback can receive
00149  * \since 1.8
00150  */
00151 enum ast_framehook_event {
00152    AST_FRAMEHOOK_EVENT_READ, /*!< frame is intercepted in the read direction on the channel. */
00153    AST_FRAMEHOOK_EVENT_WRITE, /*!< frame is intercepted on the write direction on the channel. */
00154    AST_FRAMEHOOK_EVENT_ATTACHED, /*!< framehook is attached and running on the channel, the first message sent to event_cb. */
00155    AST_FRAMEHOOK_EVENT_DETACHED /*!< framehook is detached from the channel, last message sent to event_cb. */
00156 };
00157 
00158 /*!
00159  * \brief This callback is called every time an event occurs on the framehook.
00160  * \since 1.8
00161  *
00162  * \details Two events are guaranteed to occur once the ast_framehook_attach()
00163  * function is called. These events are AST_FRAMEHOOK_EVENT_ATTACHED, which occurs
00164  * immediately after the framehook is attached to a channel, and
00165  * AST_FRAMEHOOK_EVENT_DETACHED, which occurs right after the framehook is 
00166  * detached.
00167  *
00168  * It is completely valid for the frame variable to be set to NULL. Always do a NULL
00169  * check on the frame before attempted to access it. When the frame variable is present,
00170  * it is safe to view and manipulate that frame in any way possible.  It is even safe
00171  * to return a completely different frame, but when that occurs this function is in
00172  * charge of freeing the previous frame.
00173  *
00174  * The ast_channel will always be locked during this callback. Never attempt to unlock the
00175  * channel for any reason.
00176  *
00177  * \param channel, The ast_channel this framehook is attached to
00178  * \param frame, The ast_frame being intercepted for viewing and manipulation
00179  * \param event, The type of event which is occurring
00180  * \param data, The data pointer provided at framehook initilization.
00181  *
00182  * \retval the resulting frame.
00183  */
00184 typedef struct ast_frame *(*ast_framehook_event_callback)(
00185    struct ast_channel *chan,
00186    struct ast_frame *frame,
00187    enum ast_framehook_event event,
00188    void *data);
00189 
00190 /*!
00191  * \brief This callback is called immediately before the framehook is destroyed.
00192  * \since 1.8
00193  * \note  This function should be used to clean up any pointers pointing to the
00194  * framehook structure as the framehook will be freed immediately afterwards.
00195  *
00196  * \param data, The data pointer provided at framehook initialization. This
00197  * is a good place to clean up any state data allocated for the framehook stored in this
00198  * pointer.
00199  */
00200 typedef void (*ast_framehook_destroy_callback)(void *data);
00201 
00202 #define AST_FRAMEHOOK_INTERFACE_VERSION 1
00203 /*! This interface is required for attaching a framehook to a channel. */
00204 struct ast_framehook_interface {
00205    /*! framehook interface version number */
00206    uint16_t version;
00207    /*! event_cb represents the function that will be called everytime an event occurs on the framehook. */
00208    ast_framehook_event_callback event_cb;
00209    /*! destroy_cb is optional.  This function is called immediately before the framehook
00210     * is destroyed to allow for stored_data cleanup. */
00211    ast_framehook_destroy_callback destroy_cb;
00212     /*! This pointer can represent any custom data to be stored on the !framehook. This
00213     * data pointer will be provided during each event callback which allows the framehook
00214     * to store any stateful data associated with the application using the hook. */
00215    void *data;
00216 };
00217 
00218 /*!
00219  * \brief Attach an framehook onto a channel for frame interception.
00220  * \since 1.8
00221  *
00222  * \param ast_channel, The channel to attach the hook on to.
00223  * \param framehook interface, The framehook's callback functions and stored data.
00224 *
00225  * \pre XXX The Channel must be locked during this function all.
00226  *
00227  * \note The data pointer is never touched by the framehook API except to
00228  * provide it during the event and destruction callbacks.  It is entirely up to the
00229  * application using this API to manage the memory associated with the data pointer.
00230  *
00231  * \retval On success, positive id representing this hook on the channel 
00232  * \retval On failure, -1
00233  */
00234 int ast_framehook_attach(struct ast_channel *chan, struct ast_framehook_interface *i);
00235 
00236 /*!
00237  * \brief Detach an framehook from a channel.
00238  * \since 1.8
00239  * 
00240  * \pre XXX The Channel must be locked during this function all.
00241  * If this function is never called after attaching an framehook,
00242  * the framehook will be detached and destroyed during channel
00243  * destruction.
00244  *
00245  * \param The channel the framehook is attached to
00246  * \param The framehook's id
00247  *
00248  * \retval 0 success
00249  * \retval -1 framehook did not exist on the channel. This means the
00250  * framehook either never existed on the channel, or was already detached.
00251  */
00252 int ast_framehook_detach(struct ast_channel *chan, int framehook_id);
00253 
00254 /*!
00255  * \brief This is used by the channel API to detach and destroy all
00256  * framehooks on a channel during channel destruction.
00257  * \since 1.8
00258  *
00259  * \pre XXX The Channel must be locked during this function all.
00260  * 
00261  * \param channel containing the framehook list to destroy.
00262  * \retval 0 success
00263  * \retval -1 failure
00264  */
00265 int ast_framehook_list_destroy(struct ast_channel *chan);
00266 
00267 /*!
00268  * \brief This is used by the channel API push a frame read event to a channel's framehook list.
00269  * \since 1.8
00270  *
00271  * \details After this function completes, the resulting frame that is returned could be anything,
00272  * even NULL.  There is nothing to keep up with after this function. If the frame is modified, the
00273  * framehook callback is in charge of any memory management associated with that modification.
00274  *
00275  * \pre XXX The Channel must be locked during this function all.
00276  *
00277  * \param framehook list to push event to.
00278  * \param frame being pushed to the framehook list.
00279  *
00280  * \return The resulting frame after being viewed and modified by the framehook callbacks.
00281  */
00282 struct ast_frame *ast_framehook_list_read_event(struct ast_framehook_list *framehooks, struct ast_frame *frame);
00283 
00284 /*!
00285  * \brief This is used by the channel API push a frame write event to a channel's framehook list.
00286  * \since 1.8
00287  *
00288  * \details After this function completes, the resulting frame that is returned could be anything,
00289  * even NULL.  There is nothing to keep up with after this function. If the frame is modified, the
00290  * framehook callback is in charge of any memory management associated with that modification.
00291  *
00292  * \pre XXX The Channel must be locked during this function all.
00293  *
00294  * \param framehook list to push event to.
00295  * \param frame being pushed to the framehook list.
00296  *
00297  * \return The resulting frame after being viewed and modified by the framehook callbacks.
00298  */
00299 struct ast_frame *ast_framehook_list_write_event(struct ast_framehook_list *framehooks, struct ast_frame *frame);
00300 
00301 /*!
00302  * \brief Determine if an framehook list is empty or not
00303  * \since 1.8
00304  * \pre XXX The Channel must be locked during this function all.
00305  *
00306  * \param the framehook list
00307  * \retval 0, not empty
00308  * \retval 1, is empty
00309  */
00310 int ast_framehook_list_is_empty(struct ast_framehook_list *framehooks);
00311 #endif /* _AST_FRAMEHOOK_H */

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