channel.h

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	int (* const write_video)(struct ast_channel *chan, struct ast_frame *frame);

	/*! \brief Write a text frame, in standard format */
	int (* const write_text)(struct ast_channel *chan, struct ast_frame *frame);

	/*! \brief Find bridged channel */
	struct ast_channel *(* const bridged_channel)(struct ast_channel *chan, struct ast_channel *bridge);

	/*! \brief Provide additional read items for CHANNEL() dialplan function */
	int (* func_channel_read)(struct ast_channel *chan, const char *function, char *data, char *buf, size_t len);

	/*! \brief Provide additional write items for CHANNEL() dialplan function */
	int (* func_channel_write)(struct ast_channel *chan, const char *function, char *data, const char *value);

	/*! \brief Retrieve base channel (agent and local) */
	struct ast_channel* (* get_base_channel)(struct ast_channel *chan);
	
	/*! \brief Set base channel (agent and local) */
	int (* set_base_channel)(struct ast_channel *chan, struct ast_channel *base);

	/*! \brief Get the unique identifier for the PVT, i.e. SIP call-ID for SIP */
	const char * (* get_pvt_uniqueid)(struct ast_channel *chan);
};

struct ast_epoll_data;

/*!
 * The high bit of the frame count is used as a debug marker, so
 * increments of the counters must be done with care.
 * Please use c->fin = FRAMECOUNT_INC(c->fin) and the same for c->fout.
 */
#define	DEBUGCHAN_FLAG  0x80000000

/* XXX not ideal to evaluate x twice... */
#define	FRAMECOUNT_INC(x)	( ((x) & DEBUGCHAN_FLAG) | (((x)+1) & ~DEBUGCHAN_FLAG) )

/*!
 * The current value of the debug flags is stored in the two
 * variables global_fin and global_fout (declared in main/channel.c)
 */
extern unsigned long global_fin, global_fout;

enum ast_channel_adsicpe {
	AST_ADSI_UNKNOWN,
	AST_ADSI_AVAILABLE,
	AST_ADSI_UNAVAILABLE,
	AST_ADSI_OFFHOOKONLY,
};

/*! 
 * \brief ast_channel states
 *
 * \note Bits 0-15 of state are reserved for the state (up/down) of the line
 *       Bits 16-32 of state are reserved for flags
 */
enum ast_channel_state {
	AST_STATE_DOWN,			/*!< Channel is down and available */
	AST_STATE_RESERVED,		/*!< Channel is down, but reserved */
	AST_STATE_OFFHOOK,		/*!< Channel is off hook */
	AST_STATE_DIALING,		/*!< Digits (or equivalent) have been dialed */
	AST_STATE_RING,			/*!< Line is ringing */
	AST_STATE_RINGING,		/*!< Remote end is ringing */
	AST_STATE_UP,			/*!< Line is up */
	AST_STATE_BUSY,			/*!< Line is busy */
	AST_STATE_DIALING_OFFHOOK,	/*!< Digits (or equivalent) have been dialed while offhook */
	AST_STATE_PRERING,		/*!< Channel has detected an incoming call and is waiting for ring */

	AST_STATE_MUTE = (1 << 16),	/*!< Do not transmit voice data */
};

/*!
 * \brief Possible T38 states on channels
 */
enum ast_t38_state {
	T38_STATE_UNAVAILABLE,	/*!< T38 is unavailable on this channel or disabled by configuration */
	T38_STATE_UNKNOWN,	/*!< The channel supports T38 but the current status is unknown */
	T38_STATE_NEGOTIATING,	/*!< T38 is being negotiated */
	T38_STATE_REJECTED,	/*!< Remote side has rejected our offer */
	T38_STATE_NEGOTIATED,	/*!< T38 established */
};

/*! \brief Main Channel structure associated with a channel. 
 * This is the side of it mostly used by the pbx and call management.
 *
 * \note XXX It is important to remember to increment .cleancount each time
 *       this structure is changed. XXX
 */

struct ast_channel {
	const struct ast_channel_tech *tech;		/*!< Technology (point to channel driver) */

	void *tech_pvt;					/*!< Private data used by the technology driver */

	AST_DECLARE_STRING_FIELDS(
		AST_STRING_FIELD(name);			/*!< ASCII unique channel name */
		AST_STRING_FIELD(language);		/*!< Language requested for voice prompts */
		AST_STRING_FIELD(musicclass);		/*!< Default music class */
		AST_STRING_FIELD(accountcode);		/*!< Account code for billing */
		AST_STRING_FIELD(call_forward);		/*!< Where to forward to if asked to dial on this interface */
		AST_STRING_FIELD(uniqueid);		/*!< Unique Channel Identifier */
	);
	
	int fds[AST_MAX_FDS];				/*!< File descriptors for channel -- Drivers will poll on
								these file descriptors, so at least one must be non -1.
								 See \arg \ref AstFileDesc */

	void *music_state;				/*!< Music State*/
	void *generatordata;				/*!< Current generator data if there is any */
	struct ast_generator *generator;		/*!< Current active data generator */

	struct ast_channel *_bridge;			/*!< Who are we bridged to, if we're bridged.
								Who is proxying for us, if we are proxied (i.e. chan_agent).
								Do not access directly, use ast_bridged_channel(chan) */

	struct ast_channel *masq;			/*!< Channel that will masquerade as us */
	struct ast_channel *masqr;			/*!< Who we are masquerading as */
	int cdrflags;					/*!< Call Detail Record Flags */

	int _softhangup;				/*!< Whether or not we have been hung up...  Do not set this value
	    							directly, use ast_softhangup() */
	time_t	whentohangup;				/*!< Non-zero, set to actual time when channel is to be hung up */
	pthread_t blocker;				/*!< If anyone is blocking, this is them */
	ast_mutex_t lock_dont_use;			/*!< Lock a channel for some operations. See ast_channel_lock() */
	const char *blockproc;				/*!< Procedure causing blocking */

	const char *appl;				/*!< Current application */
	const char *data;				/*!< Data passed to current application */
	int fdno;					/*!< Which fd had an event detected on */
	struct sched_context *sched;			/*!< Schedule context */
	int streamid;					/*!< For streaming playback, the schedule ID */
	struct ast_filestream *stream;			/*!< Stream itself. */
	int vstreamid;					/*!< For streaming video playback, the schedule ID */
	struct ast_filestream *vstream;			/*!< Video Stream itself. */
	int oldwriteformat;				/*!< Original writer format */
	
	int timingfd;					/*!< Timing fd */
	int (*timingfunc)(const void *data);
	void *timingdata;

	enum ast_channel_state _state;			/*!< State of line -- Don't write directly, use ast_setstate() */
	int rings;					/*!< Number of rings so far */
	struct ast_callerid cid;			/*!< Caller ID, name, presentation etc */
	char unused_old_dtmfq[AST_MAX_EXTENSION];			/*!< (deprecated, use the readq) Any/all queued DTMF characters */
	struct ast_frame dtmff;				/*!< DTMF frame */

	char context[AST_MAX_CONTEXT];			/*!< Dialplan: Current extension context */
	char exten[AST_MAX_EXTENSION];			/*!< Dialplan: Current extension number */
	int priority;					/*!< Dialplan: Current extension priority */
	char macrocontext[AST_MAX_CONTEXT];		/*!< Macro: Current non-macro context. See app_macro.c */
	char macroexten[AST_MAX_EXTENSION];		/*!< Macro: Current non-macro extension. See app_macro.c */
	int macropriority;				/*!< Macro: Current non-macro priority. See app_macro.c */
	char dialcontext[AST_MAX_CONTEXT];              /*!< Dial: Extension context that we were called from */

	struct ast_pbx *pbx;				/*!< PBX private structure for this channel */
	int amaflags;					/*!< Set BEFORE PBX is started to determine AMA flags */
	struct ast_cdr *cdr;				/*!< Call Detail Record */
	enum ast_channel_adsicpe adsicpe;		/*!< Whether or not ADSI is detected on CPE */

	struct tone_zone *zone;			/*!< Tone zone as set in indications.conf or
								in the CHANNEL dialplan function */

	struct ast_channel_monitor *monitor;		/*!< Channel monitoring */

	unsigned long insmpl;				/*!< Track the read/written samples for monitor use */
	unsigned long outsmpl;				/*!< Track the read/written samples for monitor use */

	unsigned int fin;				/*!< Frames in counters. The high bit is a debug mask, so
								the counter is only in the remaining bits */
	unsigned int fout;				/*!< Frames out counters. The high bit is a debug mask, so
								the counter is only in the remaining bits */
	int hangupcause;				/*!< Why is the channel hanged up. See causes.h */
	struct varshead varshead;			/*!< A linked list for channel variables. See \ref AstChanVar */
	ast_group_t callgroup;				/*!< Call group for call pickups */
	ast_group_t pickupgroup;			/*!< Pickup group - which calls groups can be picked up? */
	unsigned int flags;				/*!< channel flags of AST_FLAG_ type */
	unsigned short transfercapability;		/*!< ISDN Transfer Capbility - AST_FLAG_DIGITAL is not enough */
	AST_LIST_HEAD_NOLOCK(, ast_frame) readq;
	int alertpipe[2];

	int nativeformats;				/*!< Kinds of data this channel can natively handle */
	int readformat;					/*!< Requested read format */
	int writeformat;				/*!< Requested write format */
	struct ast_trans_pvt *writetrans;		/*!< Write translation path */
	struct ast_trans_pvt *readtrans;		/*!< Read translation path */
	int rawreadformat;				/*!< Raw read format */
	int rawwriteformat;				/*!< Raw write format */

	struct ast_audiohook_list *audiohooks;

	AST_LIST_ENTRY(ast_channel) chan_list;		/*!< For easy linking */
	
	struct ast_jb jb;				/*!< The jitterbuffer state  */

	char emulate_dtmf_digit;			/*!< Digit being emulated */
	unsigned int emulate_dtmf_duration;		/*!< Number of ms left to emulate DTMF for */
	struct timeval dtmf_tv;				/*!< The time that an in process digit began, or the last digit ended */

	AST_LIST_HEAD_NOLOCK(datastores, ast_datastore) datastores; /*!< Data stores on the channel */

#ifdef HAVE_EPOLL
	int epfd;
	struct ast_epoll_data *epfd_data[AST_MAX_FDS];
#endif
	int visible_indication;                         /*!< Indication currently playing on the channel */
};

/*! \brief ast_channel_tech Properties */
enum {
	/*! \brief Channels have this property if they can accept input with jitter; 
	 *         i.e. most VoIP channels */
	AST_CHAN_TP_WANTSJITTER = (1 << 0),
	/*! \brief Channels have this property if they can create jitter; 
	 *         i.e. most VoIP channels */
	AST_CHAN_TP_CREATESJITTER = (1 << 1),
};

/*! \brief ast_channel flags */
enum {
	/*! Queue incoming dtmf, to be released when this flag is turned off */
	AST_FLAG_DEFER_DTMF =    (1 << 1),
	/*! write should be interrupt generator */
	AST_FLAG_WRITE_INT =     (1 << 2),
	/*! a thread is blocking on this channel */
	AST_FLAG_BLOCKING =      (1 << 3),
	/*! This is a zombie channel */
	AST_FLAG_ZOMBIE =        (1 << 4),
	/*! There is an exception pending */
	AST_FLAG_EXCEPTION =     (1 << 5),
	/*! Listening to moh XXX anthm promises me this will disappear XXX */
	AST_FLAG_MOH =           (1 << 6),
	/*! This channel is spying on another channel */
	AST_FLAG_SPYING =        (1 << 7),
	/*! This channel is in a native bridge */
	AST_FLAG_NBRIDGE =       (1 << 8),
	/*! the channel is in an auto-incrementing dialplan processor,
	 *  so when ->priority is set, it will get incremented before
	 *  finding the next priority to run */
	AST_FLAG_IN_AUTOLOOP =   (1 << 9),
	/*! This is an outgoing call */
	AST_FLAG_OUTGOING =      (1 << 10),
	/*! A DTMF_BEGIN frame has been read from this channel, but not yet an END */
	AST_FLAG_IN_DTMF =       (1 << 12),
	/*! A DTMF_END was received when not IN_DTMF, so the length of the digit is 
	 *  currently being emulated */
	AST_FLAG_EMULATE_DTMF =  (1 << 13),
	/*! This is set to tell the channel not to generate DTMF begin frames, and
	 *  to instead only generate END frames. */
	AST_FLAG_END_DTMF_ONLY = (1 << 14),
	/*! Flag to show channels that this call is hangup due to the fact that the call
	    was indeed anwered, but in another channel */
	AST_FLAG_ANSWERED_ELSEWHERE = (1 << 15),
	/*! This flag indicates that on a masquerade, an active stream should not
	 *  be carried over */
	AST_FLAG_MASQ_NOSTREAM = (1 << 16),
	/*! This flag indicates that the hangup exten was run when the bridge terminated,
	 *  a message aimed at preventing a subsequent hangup exten being run at the pbx_run
	 *  level */
	AST_FLAG_BRIDGE_HANGUP_RUN = (1 << 17),
	/*! This flag indicates that the hangup exten should NOT be run when the 
	 *  bridge terminates, this will allow the hangup in the pbx loop to be run instead.
	 *  */
	AST_FLAG_BRIDGE_HANGUP_DONT = (1 << 18),
};

/*! \brief ast_bridge_config flags */
enum {
	AST_FEATURE_PLAY_WARNING = (1 << 0),
	AST_FEATURE_REDIRECT =     (1 << 1),
	AST_FEATURE_DISCONNECT =   (1 << 2),
	AST_FEATURE_ATXFER =       (1 << 3),
	AST_FEATURE_AUTOMON =      (1 << 4),
	AST_FEATURE_PARKCALL =     (1 << 5),
	AST_FEATURE_AUTOMIXMON =   (1 << 6),
	AST_FEATURE_NO_H_EXTEN =   (1 << 7),
};

/*! \brief bridge configuration */
struct ast_bridge_config {
	struct ast_flags features_caller;
	struct ast_flags features_callee;
	struct timeval start_time;
	long feature_timer;
	long timelimit;
	long play_warning;
	long warning_freq;
	const char *warning_sound;
	const char *end_sound;
	const char *start_sound;
	int firstpass;
	unsigned int flags;
	void (* end_bridge_callback)(void *);   /*!< A callback that is called after a bridge attempt */
	void *end_bridge_callback_data;         /*!< Data passed to the callback */
	/*! If the end_bridge_callback_data refers to a channel which no longer is going to
	 * exist when the end_bridge_callback is called, then it needs to be fixed up properly
	 */
	void (*end_bridge_callback_data_fixup)(struct ast_bridge_config *bconfig, struct ast_channel *originator, struct ast_channel *terminator);
};

struct chanmon;

struct outgoing_helper {
	const char *context;
	const char *exten;
	int priority;
	const char *cid_num;
	const char *cid_name;
	const char *account;
	struct ast_variable *vars;
	struct ast_channel *parent_channel;
};

enum {
	AST_CDR_TRANSFER =   (1 << 0),
	AST_CDR_FORWARD =    (1 << 1),
	AST_CDR_CALLWAIT =   (1 << 2),
	AST_CDR_CONFERENCE = (1 << 3),
};

enum {
	/*! Soft hangup by device */
	AST_SOFTHANGUP_DEV =       (1 << 0),
	/*! Soft hangup for async goto */
	AST_SOFTHANGUP_ASYNCGOTO = (1 << 1),
	AST_SOFTHANGUP_SHUTDOWN =  (1 << 2),
	AST_SOFTHANGUP_TIMEOUT =   (1 << 3),
	AST_SOFTHANGUP_APPUNLOAD = (1 << 4),
	AST_SOFTHANGUP_EXPLICIT =  (1 << 5),
	AST_SOFTHANGUP_UNBRIDGE =  (1 << 6),
};


/*! \brief Channel reload reasons for manager events at load or reload of configuration */
enum channelreloadreason {
	CHANNEL_MODULE_LOAD,
	CHANNEL_MODULE_RELOAD,
	CHANNEL_CLI_RELOAD,