FreeSWITCH 1.10 源码阅读(7)-uuid_bridge 命令原理解析

news2024/12/27 18:47:33

文章目录

  • 1. uuid_bridge 命令执行
  • 2. 源码分析
  • 3. uuid_bridge 问题处理

1. uuid_bridge 命令执行

uuid_bridge 命令用于将两条腿桥接在一起，以实现双方的通话。下图是该命令在 FreeSWITCH 中的处理流程，大致的流程可以分成以下几个步骤：

  1. uuid_bridge 命令的执行
  2. a-leg 与 b-leg 的状态机流转
  3. 桥接时的处理

在这里插入图片描述

2. 源码分析

  1. uuid_bridge 命令被下发送到 FreeSWITCH 时，会被 mod_commands.c#uuid_bridge_function() 函数处理，这个函数将解析命令参数，接着调用 switch_ivr_bridge.c#switch_ivr_uuid_bridge() 函数去触发桥接

    #define UUID_SYNTAX "<uuid> <other_uuid>"
SWITCH_STANDARD_API(uuid_bridge_function)
{
   char *mycmd = NULL, *argv[4] = { 0 };
   int argc = 0;

   if (!zstr(cmd) && (mycmd = strdup(cmd))) {
 	 argc = switch_separate_string(mycmd, ' ', argv, (sizeof(argv) / sizeof(argv[0])));
   }

   if (zstr(cmd) || argc < 2) {
 	 stream->write_function(stream, "-USAGE: %s\n", UUID_SYNTAX);
   } else {
 	switch_status_t status;
 	char *who = NULL;

 	if ((status = switch_ivr_uuid_bridge(argv[0], argv[1])) != SWITCH_STATUS_SUCCESS) {
 		if (argv[2]) {
 			if ((status = switch_ivr_uuid_bridge(argv[0], argv[2])) == SWITCH_STATUS_SUCCESS) {
 				who = argv[2];
 			}
 		}
 	} else {
 		who = argv[1];
 	}

 	if (status == SWITCH_STATUS_SUCCESS) {
 		stream->write_function(stream, "+OK %s\n", who);
 	} else {
 		stream->write_function(stream, "-ERR Invalid uuid\n");
 	}
  }

  switch_safe_free(mycmd);
  return SWITCH_STATUS_SUCCESS;
}

  2. switch_ivr_bridge.c#switch_ivr_uuid_bridge() 函数会做许多状态校验之类的工作，但是核心其实只有两步：

    1. 调用switch_channel.c#switch_channel_add_state_handler() 将 switch_ivr_bridge.c#uuid_bridge_state_handlers 状态机回调函数表加在将要桥接的两条腿上，当这两条腿状态流转时会回调函数表中相应的函数，不了解这部分的读者可参考 FreeSWITCH 1.10 源码阅读(4)-从呼入处理分析核心状态机
    2. 调用 switch_channel.h#switch_channel_set_state() 将两条腿切换为指定状态 CS_HIBERNATE，从而驱动状态机流转
    SWITCH_DECLARE(switch_status_t) switch_ivr_uuid_bridge(const char *originator_uuid, const char *originatee_uuid)
{
 switch_core_session_t *originator_session, *originatee_session, *swap_session;
 switch_channel_t *originator_channel, *originatee_channel, *swap_channel;
 switch_status_t status = SWITCH_STATUS_FALSE;
 switch_caller_profile_t *originator_cp, *originatee_cp;
 switch_channel_state_t state;

 if ((originator_session = switch_core_session_locate(originator_uuid))) {
 	if ((originatee_session = switch_core_session_locate(originatee_uuid))) {
 		originator_channel = switch_core_session_get_channel(originator_session);
 		originatee_channel = switch_core_session_get_channel(originatee_session);

 		switch_ivr_check_hold(originator_session);
 		switch_ivr_check_hold(originatee_session);
 

 		if (switch_channel_test_flag(originator_channel, CF_LEG_HOLDING)) {
 			switch_channel_set_flag(originator_channel, CF_HOLD_ON_BRIDGE);
 		}

 		if (switch_channel_test_flag(originatee_channel, CF_LEG_HOLDING)) {
 			switch_channel_set_flag(originatee_channel, CF_HOLD_ON_BRIDGE);
 		}


 		if (switch_channel_direction(originator_channel) == SWITCH_CALL_DIRECTION_OUTBOUND && !switch_channel_test_flag(originator_channel, CF_DIALPLAN)) {
 			if (!switch_channel_test_flag(originator_channel, CF_RECOVERING_BRIDGE)) {
 				switch_channel_flip_cid(originator_channel);
 			}
 			switch_channel_set_flag(originator_channel, CF_DIALPLAN);
 		}

 		if (switch_channel_down_nosig(originator_channel)) {
 			switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(originator_session), SWITCH_LOG_DEBUG, "%s is hungup refusing to bridge.\n", switch_channel_get_name(originatee_channel));
 			switch_core_session_rwunlock(originator_session);
 			switch_core_session_rwunlock(originatee_session);
 			return SWITCH_STATUS_FALSE;
 		}

 		if (!switch_channel_media_up(originator_channel)) {
 			if (switch_channel_media_up(originatee_channel)) {
 				swap_session = originator_session;
 				originator_session = originatee_session;
 				originatee_session = swap_session;

 				swap_channel = originator_channel;
 				originator_channel = originatee_channel;
 				originatee_channel = swap_channel;
 				switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(originatee_session), SWITCH_LOG_WARNING, "reversing order of channels so this will work!\n");
 			} else {
 				switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(originator_session), SWITCH_LOG_CRIT, "Neither channel is answered, cannot bridge them.\n");
 				switch_core_session_rwunlock(originator_session);
 				switch_core_session_rwunlock(originatee_session);
 				return SWITCH_STATUS_FALSE;
 			}
 		}

 		if (switch_channel_direction(originatee_channel) == SWITCH_CALL_DIRECTION_OUTBOUND && switch_channel_test_flag(originatee_channel, CF_DIALPLAN)) {
 			switch_channel_clear_flag(originatee_channel, CF_DIALPLAN);
 		}

 		cleanup_proxy_mode_a(originator_session);
 		cleanup_proxy_mode_a(originatee_session);

 		/* override transmit state for originator_channel to bridge to originatee_channel
 		 * install pointer to originatee_session into originator_channel
 		 * set CF_TRANSFER on both channels and change state to CS_SOFT_EXECUTE to
 		 * interrupt anything they are already doing.
 		 * originatee_session will fall asleep and originator_session will bridge to it
 		 */

 		switch_channel_set_flag(originator_channel, CF_REDIRECT);
 		switch_channel_set_flag(originatee_channel, CF_REDIRECT);


 		switch_channel_set_variable(originator_channel, SWITCH_UUID_BRIDGE, switch_core_session_get_uuid(originatee_session));
 		switch_channel_set_variable(originator_channel, SWITCH_BRIDGE_CHANNEL_VARIABLE, switch_channel_get_name(originatee_channel));
 		switch_channel_set_variable(originator_channel, SWITCH_BRIDGE_UUID_VARIABLE, switch_core_session_get_uuid(originatee_session));
 		switch_channel_set_variable(originator_channel, SWITCH_SIGNAL_BOND_VARIABLE, switch_core_session_get_uuid(originatee_session));
 		switch_channel_set_variable(originatee_channel, SWITCH_BRIDGE_CHANNEL_VARIABLE, switch_channel_get_name(originator_channel));
 		switch_channel_set_variable(originatee_channel, SWITCH_BRIDGE_UUID_VARIABLE, switch_core_session_get_uuid(originator_session));
 		switch_channel_set_variable(originatee_channel, SWITCH_SIGNAL_BOND_VARIABLE, switch_core_session_get_uuid(originator_session));


 		originator_cp = switch_channel_get_caller_profile(originator_channel);
 		originatee_cp = switch_channel_get_caller_profile(originatee_channel);



 		if (switch_channel_outbound_display(originator_channel)) {
 			switch_channel_invert_cid(originator_channel);

 			if (switch_channel_direction(originator_channel) == SWITCH_CALL_DIRECTION_INBOUND) {
 				switch_channel_clear_flag(originatee_channel, CF_BLEG);
 			}
 		}

 		if (switch_channel_inbound_display(originatee_channel)) {
 			switch_channel_invert_cid(originatee_channel);

 			if (switch_channel_direction(originatee_channel) == SWITCH_CALL_DIRECTION_INBOUND) {
 				switch_channel_set_flag(originatee_channel, CF_BLEG);
 			}

 		}


 		switch_channel_set_variable(originatee_channel, "original_destination_number", originatee_cp->destination_number);
 		switch_channel_set_variable(originatee_channel, "original_caller_id_name", originatee_cp->caller_id_name);
 		switch_channel_set_variable(originatee_channel, "original_caller_id_number", originatee_cp->caller_id_number);

 		switch_channel_set_variable(originator_channel, "original_destination_number", originator_cp->destination_number);
 		switch_channel_set_variable(originator_channel, "original_caller_id_name", originator_cp->caller_id_name);
 		switch_channel_set_variable(originator_channel, "original_caller_id_number", originator_cp->caller_id_number);

 		switch_channel_step_caller_profile(originatee_channel);
 		switch_channel_step_caller_profile(originator_channel);

 		originator_cp = switch_channel_get_caller_profile(originator_channel);
 		originatee_cp = switch_channel_get_caller_profile(originatee_channel);


#ifdef DEEP_DEBUG_CID
 		{
 			switch_event_t *event;

 			if (switch_event_create_plain(&event, SWITCH_EVENT_CHANNEL_DATA) == SWITCH_STATUS_SUCCESS) {
 				//switch_channel_event_set_basic_data(originator_channel, event);
 				switch_caller_profile_event_set_data(originator_cp, "ORIGINATOR", event);
 				switch_caller_profile_event_set_data(originatee_cp, "ORIGINATEE", event);
 				DUMP_EVENT(event);
 				switch_event_destroy(&event);
 			}
 		}
#endif

 		switch_channel_set_originator_caller_profile(originatee_channel, switch_caller_profile_clone(originatee_session, originator_cp));
 		switch_channel_set_originatee_caller_profile(originator_channel, switch_caller_profile_clone(originator_session, originatee_cp));

 		originator_cp->callee_id_name = switch_core_strdup(originator_cp->pool, originatee_cp->callee_id_name);
 		originator_cp->callee_id_number = switch_core_strdup(originator_cp->pool, originatee_cp->callee_id_number);

 		originatee_cp->caller_id_name = switch_core_strdup(originatee_cp->pool, originator_cp->caller_id_name);
 		originatee_cp->caller_id_number = switch_core_strdup(originatee_cp->pool, originator_cp->caller_id_number);

#ifdef DEEP_DEBUG_CID
 		{
 			switch_event_t *event;

 			if (switch_event_create_plain(&event, SWITCH_EVENT_CHANNEL_DATA) == SWITCH_STATUS_SUCCESS) {
 				//switch_channel_event_set_basic_data(originator_channel, event);
 				switch_caller_profile_event_set_data(originator_cp, "POST-ORIGINATOR", event);
 				switch_caller_profile_event_set_data(originatee_cp, "POST-ORIGINATEE", event);
 				DUMP_EVENT(event);
 				switch_event_destroy(&event);
 			}
 		}
#endif

 		switch_channel_stop_broadcast(originator_channel);
 		switch_channel_stop_broadcast(originatee_channel);

 		switch_channel_set_flag(originator_channel, CF_TRANSFER);
 		switch_channel_set_flag(originatee_channel, CF_TRANSFER);


 		switch_channel_clear_flag(originator_channel, CF_ORIGINATING);
 		switch_channel_clear_flag(originatee_channel, CF_ORIGINATING);


 		originator_cp->transfer_source = switch_core_sprintf(originator_cp->pool,
 															 "%ld:%s:uuid_br:%s", (long)switch_epoch_time_now(NULL), originator_cp->uuid_str,
 															 switch_core_session_get_uuid(originatee_session));
 		switch_channel_add_variable_var_check(originator_channel, SWITCH_TRANSFER_HISTORY_VARIABLE,
 											  originator_cp->transfer_source, SWITCH_FALSE, SWITCH_STACK_PUSH);
 		switch_channel_set_variable(originator_channel, SWITCH_TRANSFER_SOURCE_VARIABLE, originator_cp->transfer_source);


 		originatee_cp->transfer_source = switch_core_sprintf(originatee_cp->pool,
 															 "%ld:%s:uuid_br:%s", (long)switch_epoch_time_now(NULL), originatee_cp->uuid_str,
 															 switch_core_session_get_uuid(originator_session));
 		switch_channel_add_variable_var_check(originatee_channel, SWITCH_TRANSFER_HISTORY_VARIABLE,
 											  originatee_cp->transfer_source, SWITCH_FALSE, SWITCH_STACK_PUSH);
 		switch_channel_set_variable(originatee_channel, SWITCH_TRANSFER_SOURCE_VARIABLE, originatee_cp->transfer_source);

 		/* change the states and let the chips fall where they may */

 		//switch_channel_set_variable(originator_channel, SWITCH_PARK_AFTER_BRIDGE_VARIABLE, NULL);
 		//switch_channel_set_variable(originatee_channel, SWITCH_PARK_AFTER_BRIDGE_VARIABLE, NULL);
 		switch_channel_clear_state_handler(originator_channel, NULL);
 		switch_channel_clear_state_handler(originatee_channel, NULL);



 		switch_channel_clear_state_flag(originator_channel, CF_BRIDGE_ORIGINATOR);
 		switch_channel_clear_state_flag(originatee_channel, CF_BRIDGE_ORIGINATOR);

 		switch_channel_clear_flag(originator_channel, CF_UUID_BRIDGE_ORIGINATOR);
 		switch_channel_clear_flag(originatee_channel, CF_UUID_BRIDGE_ORIGINATOR);
 		switch_channel_set_state_flag(originator_channel, CF_UUID_BRIDGE_ORIGINATOR);

 		switch_channel_add_state_handler(originator_channel, &uuid_bridge_state_handlers);
 		switch_channel_add_state_handler(originatee_channel, &uuid_bridge_state_handlers);

 		state = switch_channel_get_state(originator_channel);
 		switch_channel_set_state(originator_channel, state == CS_HIBERNATE ? CS_CONSUME_MEDIA : CS_HIBERNATE);
 		state = switch_channel_get_state(originatee_channel);
 		switch_channel_set_state(originatee_channel, state == CS_HIBERNATE ? CS_CONSUME_MEDIA : CS_HIBERNATE);

 		status = SWITCH_STATUS_SUCCESS;

 		//switch_ivr_bridge_display(originator_session, originatee_session);

 		/* release the read locks we have on the channels */
 		switch_core_session_rwunlock(originator_session);
 		switch_core_session_rwunlock(originatee_session);

 	} else {
 		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(originator_session), SWITCH_LOG_DEBUG, "originatee uuid %s is not present\n", originatee_uuid);
 		switch_core_session_rwunlock(originator_session);
 	}
 } else {
 	switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(originator_session), SWITCH_LOG_DEBUG, "originator uuid %s is not present\n", originator_uuid);
 }

 return status;
}

  3. 当 a-leg 状态切换为 CS_HIBERNATE，在核心状态机的调度下，安装在这条腿上的回调函数 switch_ivr_bridge.c#uuid_bridge_state_handlers.uuid_bridge_on_hibernate() 将被执行，推动当前腿的状态向 CS_RESET 切换。当状态发生改变，同理switch_ivr_bridge.c#uuid_bridge_state_handlers.uuid_bridge_on_reset() 将被执行

    static switch_status_t uuid_bridge_on_hibernate(switch_core_session_t *session)
{
 switch_channel_set_state(switch_core_session_get_channel(session), CS_RESET);
 return SWITCH_STATUS_FALSE;
}

  4. switch_ivr_bridge.c#uuid_bridge_state_handlers.uuid_bridge_on_reset() 函数会判断当前腿是否为主叫腿，也就是是否为 a-leg，如是则将其状态进一步驱动为 CS_SOFT_EXECUTE，而 b-leg 在此处则停留在 CS_RESET 状态

    static switch_status_t uuid_bridge_on_reset(switch_core_session_t *session)
{
 switch_channel_t *channel = switch_core_session_get_channel(session);

 switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session), SWITCH_LOG_DEBUG, "%s CUSTOM RESET\n", switch_channel_get_name(channel));

 switch_channel_clear_flag(channel, CF_ORIGINATING);

 cleanup_proxy_mode_b(session);

 if (switch_channel_test_flag(channel, CF_UUID_BRIDGE_ORIGINATOR)) {
 	switch_channel_set_state(channel, CS_SOFT_EXECUTE);
 }

 return SWITCH_STATUS_SUCCESS;
}

  5. switch_ivr_bridge.c#uuid_bridge_state_handlers.uuid_bridge_on_soft_execute() 函数只会在 a-leg 上执行，其核心逻辑为以下几步：

    1. 清除 a-leg 上的回调函数表 switch_ivr_bridge.c#uuid_bridge_state_handlers，检测 b-leg 状态，如果 b-leg 抵达了CS_RESET 状态，则将其向 CS_SOFT_EXECUTE 状态推动，只有 b-leg 也到达这个状态才能继续向下处理
    2. 两条腿的状态都就绪后，继续执行 switch_ivr_bridge.c#switch_ivr_multi_threaded_bridge() 完成实际的桥接处理
    static switch_status_t uuid_bridge_on_soft_execute(switch_core_session_t *session)
{
 switch_channel_t *channel = switch_core_session_get_channel(session);
 switch_core_session_t *other_session = NULL;
 const char *other_uuid = NULL;

 switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session), SWITCH_LOG_DEBUG, "%s CUSTOM SOFT_EXECUTE\n", switch_channel_get_name(channel));
 switch_channel_clear_state_handler(channel, &uuid_bridge_state_handlers);

 if (!switch_channel_test_flag(channel, CF_UUID_BRIDGE_ORIGINATOR)) {
 	return SWITCH_STATUS_SUCCESS;
 }

 if ((other_uuid = switch_channel_get_variable(channel, SWITCH_UUID_BRIDGE)) && (other_session = switch_core_session_locate(other_uuid))) {
 	switch_channel_t *other_channel = switch_core_session_get_channel(other_session);
 	switch_event_t *event;
 	int ready_a, ready_b;
 	switch_channel_state_t state, running_state;
 	int max = 1000, loops = max;

 	switch_channel_set_variable(channel, SWITCH_UUID_BRIDGE, NULL);

 	for (;;) {
 		state = switch_channel_get_state(other_channel);
 		running_state = switch_channel_get_running_state(other_channel);

 		if (switch_channel_down_nosig(other_channel) || switch_channel_down(channel)) {
 			break;
 		}

 		if (state < CS_HANGUP && state == running_state) {

 			if (--loops < 1) {
 				switch_channel_hangup(channel, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 				switch_channel_hangup(other_channel, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 			}

 			if (running_state == CS_RESET) {
 				switch_channel_set_state(other_channel, CS_SOFT_EXECUTE);
 			}

 			if (running_state == CS_SOFT_EXECUTE) {

 				if (switch_channel_test_flag(other_channel, CF_UUID_BRIDGE_ORIGINATOR)) {
 					goto done;
 				} else {
 					break;
 				}
 			}

 		} else {
 			loops = max;
 		}

 		switch_yield(20000);
 	}

 	switch_core_session_reset(session, SWITCH_TRUE, SWITCH_TRUE);

 	if (switch_ivr_wait_for_answer(session, other_session) != SWITCH_STATUS_SUCCESS) {
 		if (switch_true(switch_channel_get_variable(channel, "uuid_bridge_continue_on_cancel"))) {
 			switch_channel_set_state(channel, CS_EXECUTE);
 		} else if (switch_true(switch_channel_get_variable(channel, "uuid_bridge_park_on_cancel"))) {
 			switch_ivr_park_session(session);
 		} else if (!switch_channel_test_flag(channel, CF_TRANSFER)) {
 			switch_channel_hangup(channel, SWITCH_CAUSE_ORIGINATOR_CANCEL);
 		}
 		goto done;
 	}

 	ready_a = switch_channel_ready(channel);
 	ready_b = switch_channel_ready(other_channel);

 	if (!ready_a || !ready_b) {
 		if (!ready_a) {
 			switch_channel_hangup(other_channel, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 		}

 		if (!ready_b) {
 			const char *cid = switch_channel_get_variable(other_channel, "rdnis");
 			if (ready_a && cid) {
 				switch_ivr_session_transfer(session, cid, NULL, NULL);
 			} else {
 				switch_channel_hangup(channel, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 			}
 		}
 		goto done;
 	}

 	/* fire events that will change the data table from "show channels" */
 	if (switch_event_create(&event, SWITCH_EVENT_CHANNEL_EXECUTE) == SWITCH_STATUS_SUCCESS) {
 		switch_channel_event_set_data(channel, event);
 		switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Application", "uuid_bridge");
 		switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Application-Data", switch_core_session_get_uuid(other_session));
 		switch_event_fire(&event);
 	}

 	if (switch_event_create(&event, SWITCH_EVENT_CHANNEL_EXECUTE) == SWITCH_STATUS_SUCCESS) {
 		switch_channel_event_set_data(other_channel, event);
 		switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Application", "uuid_bridge");
 		switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Application-Data", switch_core_session_get_uuid(session));
 		switch_event_fire(&event);
 	}

 	switch_ivr_multi_threaded_bridge(session, other_session, NULL, NULL, NULL);

 	state = switch_channel_get_state(channel);
 	if (!switch_channel_test_flag(channel, CF_TRANSFER) &&
 		!switch_channel_test_flag(channel, CF_REDIRECT) && state < CS_HANGUP && state != CS_ROUTING && state != CS_PARK) {
 		switch_channel_set_state(channel, CS_EXECUTE);
 	}
 } else {
 	int hup = 1;
 	const char *var;
 	
 	if (switch_true(switch_channel_get_variable(channel, SWITCH_PARK_AFTER_BRIDGE_VARIABLE))) {
 		switch_ivr_park_session(session);
 		hup = 0;
 	} else if ((var = switch_channel_get_variable(channel, SWITCH_TRANSFER_AFTER_BRIDGE_VARIABLE))) {
 		transfer_after_bridge(session, var);
 		hup = 0;
 	}
 	
 	if (hup) {
 		switch_channel_hangup(channel, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 	}
 }

done:

 if (other_session) {
 	switch_core_session_rwunlock(other_session);
 	other_session = NULL;
 }

 switch_channel_clear_flag(channel, CF_UUID_BRIDGE_ORIGINATOR);

 return SWITCH_STATUS_FALSE;
}

  6. switch_ivr_bridge.c#switch_ivr_multi_threaded_bridge() 函数比较长，不过核心步骤显而易见：

    1. 首先调用 switch_channel.c#switch_channel_add_state_handler() 将回调函数表switch_ivr_bridge.c#audio_bridge_peer_state_handlers 安装在 b-leg 上，随后发送 SWITCH_MESSAGE_INDICATE_BRIDGE 消息 通知底层 Sofia 模块将要进行桥接处理
    2. 完成后首先将 b-leg 驱动到 CS_EXCHANGE_MEDIA 状态，然后 a-leg 执行 switch_ivr_bridge.c#audio_bridge_thread() 函数开始和 b-leg 的媒体交互处理
    3. 媒体交互结束后还要检查 b-leg 是否停留在 CS_EXCHANGE_MEDIA 状态，不是则表明对端的媒体交互也结束了，此时发送 SWITCH_MESSAGE_INDICATE_UNBRIDGE消息 通知底层 Sofia 模块桥接结束
    4. 桥接结束后，检查相关配置，如果 a-leg 上有 park_after_bridge 之类的参数，则调用 switch_ivr_park_session() 函数将 a-leg 设置为 CS_PARK 状态
     SWITCH_DECLARE(switch_status_t) switch_ivr_multi_threaded_bridge(switch_core_session_t *session,
 															 switch_core_session_t *peer_session,
 															 switch_input_callback_function_t input_callback, void *session_data,
 															 void *peer_session_data)
{
 switch_ivr_bridge_data_t *a_leg = switch_core_session_alloc(session, sizeof(*a_leg));
 switch_ivr_bridge_data_t *b_leg = switch_core_session_alloc(peer_session, sizeof(*b_leg));
 switch_channel_t *caller_channel = switch_core_session_get_channel(session);
 switch_channel_t *peer_channel = switch_core_session_get_channel(peer_session);
 int stream_id = 0;
 switch_status_t status = SWITCH_STATUS_SUCCESS;
 switch_channel_state_t state;
 switch_event_t *event;
 int br = 0;
 int inner_bridge = switch_channel_test_flag(caller_channel, CF_INNER_BRIDGE);
 const char *var;
 switch_call_cause_t cause;
 switch_core_session_message_t msg = { 0 };

 if (switch_channel_test_flag(caller_channel, CF_PROXY_MODE)) {
 	switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session), SWITCH_LOG_DEBUG, "Call has no media... Redirecting to signal bridge.\n");
 	return switch_ivr_signal_bridge(session, peer_session);
 }

 check_bridge_export(caller_channel, peer_channel);

 switch_channel_set_flag_recursive(caller_channel, CF_MEDIA_BRIDGE_TTL);
 switch_channel_set_flag_recursive(peer_channel, CF_MEDIA_BRIDGE_TTL);

 switch_channel_set_flag_recursive(caller_channel, CF_BRIDGE_ORIGINATOR);
 switch_channel_clear_flag(peer_channel, CF_BRIDGE_ORIGINATOR);

 switch_channel_audio_sync(caller_channel);
 switch_channel_audio_sync(peer_channel);

 b_leg->session = peer_session;
 switch_copy_string(b_leg->b_uuid, switch_core_session_get_uuid(session), sizeof(b_leg->b_uuid));
 b_leg->stream_id = stream_id;
 b_leg->input_callback = input_callback;
 b_leg->session_data = peer_session_data;
 b_leg->clean_exit = 0;
 b_leg->other_leg_data = a_leg;

 a_leg->session = session;
 switch_copy_string(a_leg->b_uuid, switch_core_session_get_uuid(peer_session), sizeof(a_leg->b_uuid));
 a_leg->stream_id = stream_id;
 a_leg->input_callback = input_callback;
 a_leg->session_data = session_data;
 a_leg->clean_exit = 0;
 a_leg->other_leg_data = b_leg;

 switch_channel_add_state_handler(peer_channel, &audio_bridge_peer_state_handlers);

 if (switch_channel_test_flag(peer_channel, CF_ANSWERED) && !switch_channel_test_flag(caller_channel, CF_ANSWERED)) {
 	switch_channel_pass_callee_id(peer_channel, caller_channel);
 	switch_channel_answer(caller_channel);
 }

 if (switch_channel_test_flag(peer_channel, CF_ANSWERED) || switch_channel_test_flag(peer_channel, CF_EARLY_MEDIA) ||
 	switch_channel_test_flag(peer_channel, CF_RING_READY)) {
 	const char *app, *data;

 	if (!switch_channel_ready(caller_channel)) {
 		abort_call(caller_channel, peer_channel);
 		goto done;
 	}

 	if (!switch_channel_test_flag(peer_channel, CF_ARRANGED_BRIDGE)) {
 		switch_channel_set_state(peer_channel, CS_CONSUME_MEDIA);
 	}

 	switch_channel_set_variable(peer_channel, "call_uuid", switch_core_session_get_uuid(session));

 	switch_channel_set_bridge_time(caller_channel);
 	switch_channel_set_bridge_time(peer_channel);

 	if (switch_event_create(&event, SWITCH_EVENT_CHANNEL_BRIDGE) == SWITCH_STATUS_SUCCESS) {
 		switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Bridge-A-Unique-ID", switch_core_session_get_uuid(session));
 		switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Bridge-B-Unique-ID", switch_core_session_get_uuid(peer_session));
 		switch_channel_event_set_data(caller_channel, event);
 		switch_event_add_presence_data_cols(peer_channel, event, "Bridge-B-PD-");
 		switch_event_fire(&event);
 		br = 1;
 	}

 	if (switch_core_session_read_lock(peer_session) == SWITCH_STATUS_SUCCESS) {
 		switch_channel_set_variable(caller_channel, SWITCH_BRIDGE_VARIABLE, switch_core_session_get_uuid(peer_session));
 		switch_channel_set_variable(peer_channel, SWITCH_BRIDGE_VARIABLE, switch_core_session_get_uuid(session));
 		switch_channel_set_variable(caller_channel, SWITCH_LAST_BRIDGE_VARIABLE, switch_core_session_get_uuid(peer_session));
 		switch_channel_set_variable(peer_channel, SWITCH_LAST_BRIDGE_VARIABLE, switch_core_session_get_uuid(session));

 		if (!switch_channel_ready(caller_channel)) {
 			abort_call(caller_channel, peer_channel);
 			switch_core_session_rwunlock(peer_session);
 			goto done;
 		}

 		if (!switch_channel_media_ready(caller_channel) ||
 			(!switch_channel_test_flag(peer_channel, CF_ANSWERED) && !switch_channel_test_flag(peer_channel, CF_EARLY_MEDIA))) {
 			if ((status = switch_ivr_wait_for_answer(session, peer_session)) != SWITCH_STATUS_SUCCESS || !switch_channel_ready(caller_channel)) {
 				switch_channel_state_t w_state = switch_channel_get_state(caller_channel);
 				switch_channel_hangup(peer_channel, SWITCH_CAUSE_ALLOTTED_TIMEOUT);
 				if (w_state < CS_HANGUP && w_state != CS_ROUTING && w_state != CS_PARK &&
 					!switch_channel_test_flag(caller_channel, CF_REDIRECT) && !switch_channel_test_flag(caller_channel, CF_TRANSFER) &&
 					w_state != CS_EXECUTE) {
 					const char *ext = switch_channel_get_variable(peer_channel, "original_destination_number");
 					if (!ext) {
 						ext = switch_channel_get_variable(peer_channel, "destination_number");
 					}

 					if (ext) {
 						switch_ivr_session_transfer(session, ext, NULL, NULL);
 					} else {
 						switch_channel_hangup(caller_channel, SWITCH_CAUSE_ALLOTTED_TIMEOUT);
 					}
 				}
 				abort_call(caller_channel, peer_channel);
 				switch_core_session_rwunlock(peer_session);
 				goto done;
 			}
 		}

 		if (switch_channel_test_flag(peer_channel, CF_ANSWERED) && !switch_channel_test_flag(caller_channel, CF_ANSWERED)) {
 			switch_channel_answer(caller_channel);
 		}

 		switch_channel_wait_for_flag(peer_channel, CF_BROADCAST, SWITCH_FALSE, 10000, caller_channel);
 		switch_ivr_parse_all_events(peer_session);
 		switch_ivr_parse_all_events(session);

 		msg.message_id = SWITCH_MESSAGE_INDICATE_BRIDGE;
 		msg.from = __FILE__;
 		msg.string_arg = switch_core_session_strdup(peer_session, switch_core_session_get_uuid(session));

 		if (switch_core_session_receive_message(peer_session, &msg) != SWITCH_STATUS_SUCCESS) {
 			status = SWITCH_STATUS_FALSE;
 			abort_call(caller_channel, peer_channel);
 			switch_core_session_rwunlock(peer_session);
 			goto done;
 		}

 		msg.string_arg = switch_core_session_strdup(session, switch_core_session_get_uuid(peer_session));
 		if (switch_core_session_receive_message(session, &msg) != SWITCH_STATUS_SUCCESS) {
 			status = SWITCH_STATUS_FALSE;
 			abort_call(caller_channel, peer_channel);
 			switch_core_session_rwunlock(peer_session);
 			goto done;
 		}

 		switch_channel_set_variable(caller_channel, SWITCH_BRIDGE_CHANNEL_VARIABLE, switch_channel_get_name(peer_channel));
 		switch_channel_set_variable(caller_channel, SWITCH_BRIDGE_UUID_VARIABLE, switch_core_session_get_uuid(peer_session));
 		switch_channel_set_variable(caller_channel, SWITCH_SIGNAL_BOND_VARIABLE, switch_core_session_get_uuid(peer_session));
 		switch_channel_set_variable(peer_channel, SWITCH_BRIDGE_CHANNEL_VARIABLE, switch_channel_get_name(caller_channel));
 		switch_channel_set_variable(peer_channel, SWITCH_BRIDGE_UUID_VARIABLE, switch_core_session_get_uuid(session));
 		switch_channel_set_variable(peer_channel, SWITCH_SIGNAL_BOND_VARIABLE, switch_core_session_get_uuid(session));

 		if ((app = switch_channel_get_variable(caller_channel, "bridge_pre_execute_aleg_app"))) {
 			switch_channel_set_variable(caller_channel, "bridge_pre_execute_app", app);

 			if ((data = switch_channel_get_variable(caller_channel, "bridge_pre_execute_aleg_data"))) {
 				switch_channel_set_variable(caller_channel, "bridge_pre_execute_data", data);
 			}
 		}

 		if ((app = switch_channel_get_variable(caller_channel, "bridge_pre_execute_bleg_app"))) {
 			switch_channel_set_variable(peer_channel, "bridge_pre_execute_app", app);

 			if ((data = switch_channel_get_variable(caller_channel, "bridge_pre_execute_bleg_data"))) {
 				switch_channel_set_variable(peer_channel, "bridge_pre_execute_data", data);
 			}

 		}

 		switch_channel_set_private(peer_channel, "_bridge_", b_leg);

 		if (switch_channel_test_flag(peer_channel, CF_ARRANGED_BRIDGE)) {
 			switch_channel_clear_flag(peer_channel, CF_ARRANGED_BRIDGE);
 		} else {
 			switch_channel_set_state(peer_channel, CS_EXCHANGE_MEDIA);
 		}
 		
 		audio_bridge_thread(NULL, (void *) a_leg);

 		switch_channel_clear_flag_recursive(caller_channel, CF_BRIDGE_ORIGINATOR);

 		switch_channel_stop_broadcast(peer_channel);


 		while (switch_channel_get_state(peer_channel) == CS_EXCHANGE_MEDIA) {
 			switch_ivr_parse_all_messages(session);
 			switch_cond_next();
 		}

 		if (inner_bridge) {
 			if (switch_channel_ready(caller_channel)) {
 				switch_channel_set_flag(caller_channel, CF_BRIDGED);
 			}

 			if (switch_channel_ready(peer_channel)) {
 				switch_channel_set_flag(peer_channel, CF_BRIDGED);
 			}
 		}

 		if ((cause = switch_channel_get_cause(caller_channel))) {
 			switch_channel_set_variable(peer_channel, SWITCH_BRIDGE_HANGUP_CAUSE_VARIABLE, switch_channel_cause2str(cause));
 		}

 		if ((cause = switch_channel_get_cause(peer_channel))) {
 			switch_channel_set_variable(caller_channel, SWITCH_BRIDGE_HANGUP_CAUSE_VARIABLE, switch_channel_cause2str(cause));
 		}

 		if (switch_channel_down_nosig(peer_channel)) {
 			switch_bool_t copy_xml_cdr = switch_true(switch_channel_get_variable(peer_channel, SWITCH_COPY_XML_CDR_VARIABLE));
 			switch_bool_t copy_json_cdr = switch_true(switch_channel_get_variable(peer_channel, SWITCH_COPY_JSON_CDR_VARIABLE));

 			if (copy_xml_cdr || copy_json_cdr) {
 				char *cdr_text = NULL;

 				switch_channel_wait_for_state(peer_channel, caller_channel, CS_DESTROY);

 				if (copy_xml_cdr) {
 					switch_xml_t cdr = NULL;

 					if (switch_ivr_generate_xml_cdr(peer_session, &cdr) == SWITCH_STATUS_SUCCESS) {
 						cdr_text = switch_xml_toxml(cdr, SWITCH_FALSE);
 						switch_xml_free(cdr);
 					}
 				}
 				if (copy_json_cdr) {
 					cJSON *cdr = NULL;

 					if (switch_ivr_generate_json_cdr(peer_session, &cdr, SWITCH_TRUE) == SWITCH_STATUS_SUCCESS) {
 						cdr_text = cJSON_PrintUnformatted(cdr);
 						cJSON_Delete(cdr);
 					}
 				}

 				if (cdr_text) {
 					switch_channel_set_variable(caller_channel, "b_leg_cdr", cdr_text);
 					switch_channel_set_variable_name_printf(caller_channel, cdr_text, "b_leg_cdr_%s", switch_core_session_get_uuid(peer_session));
 					switch_safe_free(cdr_text);
 				}
 			}

 		}

 		switch_core_session_rwunlock(peer_session);

 	} else {
 		status = SWITCH_STATUS_FALSE;
 	}
 } else {
 	status = SWITCH_STATUS_FALSE;
 }

 if (status != SWITCH_STATUS_SUCCESS) {
 	switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session), SWITCH_LOG_WARNING, "Bridge Failed %s->%s\n",
 					  switch_channel_get_name(caller_channel), switch_channel_get_name(peer_channel)
 		);
 	switch_channel_hangup(peer_channel, SWITCH_CAUSE_NO_ANSWER);
 }

done:

 switch_channel_set_variable(peer_channel, "call_uuid", switch_core_session_get_uuid(peer_session));

 if (br && switch_event_create(&event, SWITCH_EVENT_CHANNEL_UNBRIDGE) == SWITCH_STATUS_SUCCESS) {
 	switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Bridge-A-Unique-ID", switch_core_session_get_uuid(session));
 	switch_event_add_header_string(event, SWITCH_STACK_BOTTOM, "Bridge-B-Unique-ID", switch_core_session_get_uuid(peer_session));
 	switch_channel_event_set_data(caller_channel, event);
 	switch_event_add_presence_data_cols(peer_channel, event, "Bridge-B-PD-");
 	switch_event_fire(&event);
 }

 msg.message_id = SWITCH_MESSAGE_INDICATE_UNBRIDGE;
 msg.from = __FILE__;
 msg.string_arg = switch_core_session_strdup(peer_session, switch_core_session_get_uuid(session));
 switch_core_session_receive_message(peer_session, &msg);

 msg.string_arg = switch_core_session_strdup(session, switch_core_session_get_uuid(peer_session));
 switch_core_session_receive_message(session, &msg);

 state = switch_channel_get_state(caller_channel);

 if (!switch_channel_test_flag(caller_channel, CF_TRANSFER) && !switch_channel_test_flag(caller_channel, CF_REDIRECT) &&
 	!switch_channel_test_flag(caller_channel, CF_XFER_ZOMBIE) && !a_leg->clean_exit && !inner_bridge) {
 	switch_call_cause_t cause = switch_channel_get_cause(peer_channel);
 	const char *hup = switch_channel_get_variable(caller_channel, SWITCH_HANGUP_AFTER_BRIDGE_VARIABLE);
 	int explicit = 0;
 	int answered = 0;
 	int early = 0;

 	if (cause == SWITCH_CAUSE_NONE) {
 		cause = SWITCH_CAUSE_NORMAL_CLEARING;
 	}

 	if (hup) {
 		explicit = !strcasecmp(hup, "explicit");
 	}

 	if (!switch_channel_test_flag(peer_channel, CF_ANSWERED)) {
 		switch_channel_handle_cause(caller_channel, cause);
 	}

 	if (explicit) {
 		if (switch_channel_test_flag(peer_channel, CF_INTERCEPTED)) {
 			switch_channel_set_flag(peer_channel, CF_INTERCEPT);
 		}
 		switch_channel_hangup(caller_channel, cause);
 	}

 	answered = switch_channel_test_flag(peer_channel, CF_ANSWERED);
 	early = switch_channel_test_flag(peer_channel, CF_EARLY_MEDIA);

 	if ((state != CS_EXECUTE && state != CS_SOFT_EXECUTE && state != CS_PARK && state != CS_ROUTING) || ((answered || early) && state < CS_HANGUP)) {

 		if (!switch_channel_test_flag(caller_channel, CF_TRANSFER)) {

 			if ((answered && switch_true(switch_channel_get_variable(caller_channel, SWITCH_PARK_AFTER_BRIDGE_VARIABLE))) ||
 				switch_true(switch_channel_get_variable(caller_channel, SWITCH_PARK_AFTER_EARLY_BRIDGE_VARIABLE))) {
 				switch_ivr_park_session(session);
 			} else if ((answered && (var = switch_channel_get_variable(caller_channel, SWITCH_TRANSFER_AFTER_BRIDGE_VARIABLE))) ||
 					   (var = switch_channel_get_variable(caller_channel, SWITCH_TRANSFER_AFTER_EARLY_BRIDGE_VARIABLE))) {
 				transfer_after_bridge(session, var);
 			} else if (answered) {
 				if (switch_true(hup)) {
 					if (switch_channel_test_flag(peer_channel, CF_INTERCEPTED)) {
 						switch_channel_set_flag(peer_channel, CF_INTERCEPT);
 					}
 					switch_channel_hangup(caller_channel, cause);
 				}
 			}
 		}
 	}
 }

 if (switch_channel_test_flag(caller_channel, CF_REDIRECT)) {
 	if (switch_channel_test_flag(caller_channel, CF_RESET)) {
 		switch_channel_clear_flag(caller_channel, CF_RESET);
 	} else {
 		state = switch_channel_get_state(caller_channel);
 		if (!(state == CS_RESET || state == CS_PARK || state == CS_ROUTING || state == CS_EXECUTE)) {
 			switch_channel_set_state(caller_channel, CS_RESET);
 		}
 	}
 }

 return status;
}

  7. b-leg 状态流转到 CS_EXCHANGE_MEDIA，则将回调执行 switch_ivr_bridge.c#audio_bridge_peer_state_handlers.audio_bridge_on_exchange_media() 函数，此处核心是在 b-leg 上执行 switch_ivr_bridge.c#audio_bridge_thread() 函数进行与 a-leg 的媒体交互

     static switch_status_t audio_bridge_on_exchange_media(switch_core_session_t *session)
{
 switch_channel_t *channel = switch_core_session_get_channel(session);
 switch_ivr_bridge_data_t *bd = switch_channel_get_private(channel, "_bridge_");
 switch_channel_state_t state;
 const char *var;

 if (bd) {
 	switch_channel_set_private(channel, "_bridge_", NULL);
 	if (bd->session == session && *bd->b_uuid) {
 		audio_bridge_thread(NULL, (void *) bd);
 		switch_core_session_reset(session, SWITCH_TRUE, SWITCH_TRUE);
 	} else {
 		switch_channel_hangup(channel, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 	}
 } else {
 	switch_channel_hangup(channel, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 }
 switch_channel_clear_state_handler(channel, &audio_bridge_peer_state_handlers);

 state = switch_channel_get_state(channel);

 if (!switch_channel_test_flag(channel, CF_TRANSFER) && !switch_channel_test_flag(channel, CF_REDIRECT) &&
 	!switch_channel_test_flag(channel, CF_XFER_ZOMBIE) && bd && !bd->clean_exit && state != CS_PARK && state != CS_ROUTING &&
 	state == CS_EXCHANGE_MEDIA && !switch_channel_test_flag(channel, CF_INNER_BRIDGE)) {

 	if (state < CS_HANGUP && switch_true(switch_channel_get_variable(channel, SWITCH_PARK_AFTER_BRIDGE_VARIABLE))) {
 		switch_ivr_park_session(session);
 		return SWITCH_STATUS_FALSE;
 	} else if (state < CS_HANGUP && (var = switch_channel_get_variable(channel, SWITCH_TRANSFER_AFTER_BRIDGE_VARIABLE))) {
 		transfer_after_bridge(session, var);
 		return SWITCH_STATUS_FALSE;
 	}

 	if (switch_channel_test_flag(channel, CF_INTERCEPTED)) {
 		switch_channel_clear_flag(channel, CF_INTERCEPT);
 		switch_channel_clear_flag(channel, CF_INTERCEPTED);
 		return SWITCH_STATUS_FALSE;
 	} else {
 		if (switch_channel_test_flag(channel, CF_INTERCEPT)) {
 			switch_channel_hangup(channel, SWITCH_CAUSE_PICKED_OFF);
 		} else {
 			if (!switch_channel_test_flag(channel, CF_ANSWERED)) {
 				int x = 0;

 				if (switch_channel_execute_on(channel, "execute_on_orphaned_bleg") == SWITCH_STATUS_SUCCESS) {
 					x++;
 				}

 				if (switch_channel_api_on(channel, "api_on_orphaned_bleg") == SWITCH_STATUS_SUCCESS) {
 					x++;
 				}

 				if (!x) {
 					switch_channel_hangup(channel, SWITCH_CAUSE_ORIGINATOR_CANCEL);
 				}
 				
 			} else {
 				switch_channel_hangup(channel, SWITCH_CAUSE_NORMAL_CLEARING);
 			}
 		}
 	}
 }

 if (switch_channel_get_state(channel) == CS_EXCHANGE_MEDIA) {
 	switch_channel_set_variable(channel, "park_timeout", "3");
 	switch_channel_set_state(channel, CS_PARK);
 }

 return SWITCH_STATUS_FALSE;
}

  8. switch_ivr_bridge.c#audio_bridge_thread() 函数的核心是从当前腿调用 switch_core_io.c#switch_core_session_read_frame() 读取媒体流，再调用 switch_core_io.c#switch_core_session_write_frame() 将其写入对端，完成媒体的交换，至此桥接的主体逻辑基本结束

     static void *audio_bridge_thread(switch_thread_t *thread, void *obj)
{
 switch_ivr_bridge_data_t *data = obj;
 int stream_id = 0, pre_b = 0, ans_a = 0, ans_b = 0, originator = 0;
 switch_input_callback_function_t input_callback;
 switch_core_session_message_t msg = { 0 };
 void *user_data;
 switch_channel_t *chan_a, *chan_b;
 switch_frame_t *read_frame;
 switch_core_session_t *session_a, *session_b;
 uint32_t read_frame_count = 0;
 const char *app_name = NULL, *app_arg = NULL;
 int inner_bridge = 0, exec_check = 0;
 switch_codec_t silence_codec = { 0 };
 switch_frame_t silence_frame = { 0 };
 int16_t silence_data[SWITCH_RECOMMENDED_BUFFER_SIZE / 2] = { 0 };
 const char *silence_var;
 int silence_val = 0, bypass_media_after_bridge = 0;
 const char *bridge_answer_timeout = NULL;
 int bridge_filter_dtmf, answer_timeout, sent_update = 0;
 time_t answer_limit = 0;
 const char *exec_app = NULL;
 const char *exec_data = NULL;
 switch_codec_implementation_t read_impl = { 0 };
 uint32_t txt_launch = 0;
 struct vid_helper th = { 0 };
 const char *banner_file = NULL;
 int played_banner = 0, banner_counter = 0;
 int pass_val = 0, last_pass_val = 0;

#ifdef SWITCH_VIDEO_IN_THREADS
 struct vid_helper vh = { 0 };
 uint32_t vid_launch = 0;
#endif
 data->clean_exit = 0;

 session_a = data->session;
 if (!(session_b = switch_core_session_locate(data->b_uuid))) {
 	return NULL;
 }

 switch_core_session_get_read_impl(session_a, &read_impl);

 input_callback = data->input_callback;
 user_data = data->session_data;
 stream_id = data->stream_id;

 chan_a = switch_core_session_get_channel(session_a);
 chan_b = switch_core_session_get_channel(session_b);

 if ((exec_app = switch_channel_get_variable(chan_a, "bridge_pre_execute_app"))) {
 	exec_data = switch_channel_get_variable(chan_a, "bridge_pre_execute_data");
 }

 bypass_media_after_bridge = switch_channel_test_flag(chan_a, CF_BYPASS_MEDIA_AFTER_BRIDGE);
 switch_channel_clear_flag(chan_a, CF_BYPASS_MEDIA_AFTER_BRIDGE);

 ans_a = switch_channel_test_flag(chan_a, CF_ANSWERED);

 if ((originator = switch_channel_test_flag(chan_a, CF_BRIDGE_ORIGINATOR))) {
 	pre_b = switch_channel_test_flag(chan_a, CF_EARLY_MEDIA);
 	ans_b = switch_channel_test_flag(chan_b, CF_ANSWERED);
 }

 inner_bridge = switch_channel_test_flag(chan_a, CF_INNER_BRIDGE);

 if (!switch_channel_test_flag(chan_a, CF_ANSWERED) && (bridge_answer_timeout = switch_channel_get_variable(chan_a, "bridge_answer_timeout"))) {
 	if ((answer_timeout = atoi(bridge_answer_timeout)) >= 0) {
 		answer_limit = switch_epoch_time_now(NULL) + answer_timeout;
 	}
 }

 switch_channel_clear_flag(chan_a, CF_INTERCEPT);
 switch_channel_clear_flag(chan_a, CF_INTERCEPTED);

 switch_channel_set_flag(chan_a, CF_BRIDGED);

 switch_channel_wait_for_flag(chan_b, CF_BRIDGED, SWITCH_TRUE, 10000, chan_a);

 if (!switch_channel_test_flag(chan_b, CF_BRIDGED)) {
 	if (!(switch_channel_test_flag(chan_b, CF_TRANSFER) || switch_channel_test_flag(chan_b, CF_REDIRECT)
 		  || switch_channel_get_state(chan_b) == CS_RESET)) {
 		switch_channel_hangup(chan_b, SWITCH_CAUSE_DESTINATION_OUT_OF_ORDER);
 	}
 	goto end_of_bridge_loop;
 }


 if (switch_channel_test_flag(chan_a, CF_BRIDGE_ORIGINATOR) && (banner_file = switch_channel_get_variable(chan_a, "video_pre_call_banner"))) {
 	switch_channel_set_flag(chan_a, CF_AUDIO_PAUSE_READ);
 	switch_channel_set_flag(chan_b, CF_AUDIO_PAUSE_READ);
 	switch_channel_set_flag(chan_a, CF_AUDIO_PAUSE_WRITE);
 	switch_channel_set_flag(chan_b, CF_AUDIO_PAUSE_WRITE);
 	switch_channel_set_flag(chan_a, CF_VIDEO_PAUSE_READ);
 	switch_channel_set_flag(chan_b, CF_VIDEO_PAUSE_READ);
 }


 if (bypass_media_after_bridge) {
 	const char *source_a = switch_channel_get_variable(chan_a, "source");
 	const char *source_b = switch_channel_get_variable(chan_b, "source");

 	if (!source_a) source_a = "";
 	if (!source_b) source_b = "";

 	if (switch_stristr("loopback", source_a) || switch_stristr("loopback", source_b)) {
 		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_WARNING, "Cannot bypass media while bridged to a loopback address.\n");
 		bypass_media_after_bridge = 0;
 	}
 }

 if ((silence_var = switch_channel_get_variable(chan_a, "bridge_generate_comfort_noise"))) {

 	if (!switch_channel_media_up(chan_a)) {
 		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_ERROR, "Channel has no media!\n");
 		goto end_of_bridge_loop;
 	}

 	if (switch_true(silence_var)) {
 		silence_val = 1400;
 	} else {
 		if ((silence_val = atoi(silence_var)) < -1) {
 			silence_val = 0;
 		}
 	}

 	if (silence_val) {
 		if (switch_core_codec_init(&silence_codec,
 								   "L16",
 								   NULL,
 								   NULL,
 								   read_impl.actual_samples_per_second,
 								   read_impl.microseconds_per_packet / 1000,
 								   1,
 								   SWITCH_CODEC_FLAG_ENCODE | SWITCH_CODEC_FLAG_DECODE,
 								   NULL, switch_core_session_get_pool(session_a)) != SWITCH_STATUS_SUCCESS) {

 			silence_val = 0;
 		} else {
 			switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "Setup generated silence from %s to %s at %d\n", switch_channel_get_name(chan_a),
 							  switch_channel_get_name(chan_b), silence_val);
 			silence_frame.codec = &silence_codec;
 			silence_frame.data = silence_data;
 			silence_frame.buflen = sizeof(silence_data);
 			silence_frame.datalen = read_impl.decoded_bytes_per_packet;
 			silence_frame.samples = silence_frame.datalen / sizeof(int16_t);
 		}
 	}
 }

 bridge_filter_dtmf = switch_true(switch_channel_get_variable(chan_a, "bridge_filter_dtmf"));


 for (;;) {
 	switch_channel_state_t b_state;
 	switch_status_t status;
 	switch_event_t *event;

 	if (switch_core_session_transcoding(session_a, session_b, SWITCH_MEDIA_TYPE_AUDIO)) {
 		pass_val = 1;
 	} else {
 		pass_val = 2;
 	}
 	
 	if (pass_val != last_pass_val) {
 		switch_core_session_passthru(session_a, SWITCH_MEDIA_TYPE_AUDIO, pass_val == 2 ? SWITCH_TRUE : SWITCH_FALSE);
 		last_pass_val = pass_val;
 	}
 	
 	if (switch_channel_test_flag(chan_a, CF_TRANSFER)) {
 		data->clean_exit = 1;
 	}

 	if (data->clean_exit || switch_channel_test_flag(chan_b, CF_TRANSFER)) {
 		switch_channel_clear_flag(chan_a, CF_HOLD);
 		switch_channel_clear_flag(chan_a, CF_SUSPEND);
 		goto end_of_bridge_loop;
 	}

 	if (!switch_channel_test_flag(chan_b, CF_BRIDGED)) {
 		goto end_of_bridge_loop;
 	}

 	if (!switch_channel_ready(chan_a)) {
 		if (switch_channel_up(chan_a)) {
 			data->clean_exit = 1;
 		}
 		goto end_of_bridge_loop;
 	}

 	if ((b_state = switch_channel_down_nosig(chan_b))) {
 		goto end_of_bridge_loop;
 	}

 	if (switch_channel_test_flag(chan_a, CF_HOLD_ON_BRIDGE)) {
 		switch_core_session_message_t hmsg = { 0 };
 		switch_channel_clear_flag(chan_a, CF_HOLD_ON_BRIDGE);
 		hmsg.message_id = SWITCH_MESSAGE_INDICATE_HOLD;
 		hmsg.from = __FILE__;
 		hmsg.numeric_arg = 1;
 		switch_core_session_receive_message(session_a, &hmsg);
 	}

 	if (read_frame_count > DEFAULT_LEAD_FRAMES && switch_channel_media_ack(chan_a) && switch_core_session_private_event_count(session_a)) {
 		switch_channel_set_flag(chan_b, CF_SUSPEND);
 		msg.numeric_arg = 42;
 		msg.string_arg = data->b_uuid;
 		msg.message_id = SWITCH_MESSAGE_INDICATE_UNBRIDGE;
 		msg.from = __FILE__;
 		switch_core_session_receive_message(session_a, &msg);
 		switch_ivr_parse_next_event(session_a);
 		msg.message_id = SWITCH_MESSAGE_INDICATE_BRIDGE;
 		switch_core_session_receive_message(session_a, &msg);
 		switch_channel_clear_flag(chan_b, CF_SUSPEND);
 		switch_core_session_kill_channel(session_b, SWITCH_SIG_BREAK);
 	}

 	switch_ivr_parse_all_messages(session_a);

 	if (!inner_bridge && (switch_channel_test_flag(chan_a, CF_SUSPEND) || switch_channel_test_flag(chan_b, CF_SUSPEND))) {
 		status = switch_core_session_read_frame(session_a, &read_frame, SWITCH_IO_FLAG_NONE, stream_id);

 		if (!SWITCH_READ_ACCEPTABLE(status)) {
 			goto end_of_bridge_loop;
 		}
 		continue;
 	}

 	if (switch_channel_test_flag(chan_a, CF_HAS_TEXT) && switch_channel_test_flag(chan_b, CF_HAS_TEXT) && !txt_launch) {
 		txt_launch++;

 		th.session_a = session_a;
 		th.session_b = session_b;
 		switch_core_media_start_engine_function(th.session_a, SWITCH_MEDIA_TYPE_TEXT, text_bridge_thread, &th);

 	}

#ifdef SWITCH_VIDEO_IN_THREADS
 	if (switch_channel_test_flag(chan_a, CF_VIDEO) && switch_channel_test_flag(chan_b, CF_VIDEO) && !vid_launch) {
 		vid_launch++;
 		vh.session_a = session_a;
 		vh.session_b = session_b;
 		switch_channel_clear_flag(chan_a, CF_VIDEO_BLANK);
 		switch_channel_clear_flag(chan_b, CF_VIDEO_BLANK);
 		launch_video(&vh);
 	} else {
 		if (switch_channel_test_flag(chan_a, CF_VIDEO)) {
 			switch_channel_set_flag(chan_a, CF_VIDEO_BLANK);
 		}

 		if (switch_channel_test_flag(chan_b, CF_VIDEO)) {
 			switch_channel_set_flag(chan_b, CF_VIDEO_BLANK);
 		}
 	}
#endif

 	if (read_frame_count >= DEFAULT_LEAD_FRAMES && switch_channel_media_ack(chan_a)) {
 		if (!played_banner && switch_channel_test_flag(chan_a, CF_VIDEO) && switch_channel_test_flag(chan_b, CF_VIDEO) &&
 			switch_channel_test_flag(chan_a, CF_ANSWERED) && switch_channel_test_flag(chan_b, CF_ANSWERED) &&
 			++banner_counter > 100 &&
 			switch_channel_test_flag(chan_a, CF_VIDEO_READY) && switch_channel_test_flag(chan_b, CF_VIDEO_READY) &&
 			switch_channel_test_flag(chan_a, CF_BRIDGE_ORIGINATOR) && banner_file) {
 			const char *b_banner_file = switch_channel_get_variable(chan_b, "video_pre_call_banner");

 			if (!b_banner_file) {
 				b_banner_file = switch_channel_get_variable(chan_a, "video_pre_call_banner_bleg");
 			}


 			switch_channel_clear_flag(chan_a, CF_VIDEO_PAUSE_READ);
 			switch_channel_clear_flag(chan_b, CF_VIDEO_PAUSE_READ);

 			if (b_banner_file) {
 				switch_ivr_broadcast(switch_core_session_get_uuid(session_a), banner_file, SMF_ECHO_ALEG);
 				switch_ivr_broadcast(switch_core_session_get_uuid(session_b), b_banner_file, SMF_ECHO_ALEG);
 			} else {
 				switch_ivr_broadcast(switch_core_session_get_uuid(session_a), banner_file, SMF_ECHO_ALEG | SMF_ECHO_BLEG);
 			}

 			played_banner = 1;

 			switch_channel_clear_flag(chan_a, CF_AUDIO_PAUSE_READ);
 			switch_channel_clear_flag(chan_b, CF_AUDIO_PAUSE_READ);
 			switch_channel_clear_flag(chan_a, CF_AUDIO_PAUSE_WRITE);
 			switch_channel_clear_flag(chan_b, CF_AUDIO_PAUSE_WRITE);
 		}



 		if (!exec_check) {
 			switch_channel_execute_on(chan_a, SWITCH_CHANNEL_EXECUTE_ON_PRE_BRIDGE_VARIABLE);

 			if (!inner_bridge) {
 				switch_channel_api_on(chan_a, SWITCH_API_BRIDGE_START_VARIABLE);
 			}
 			exec_check = 1;
 		}

 		if (exec_app) {
 			switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "%s Bridge execute app %s(%s)\n",
 							  switch_channel_get_name(chan_a), exec_app, exec_data);

 			switch_core_session_execute_application_async(session_a, exec_app, exec_data);
 			exec_app = exec_data = NULL;
 		}

 		if ((bypass_media_after_bridge || switch_channel_test_flag(chan_b, CF_BYPASS_MEDIA_AFTER_BRIDGE)) && switch_channel_test_flag(chan_a, CF_ANSWERED)
 			&& switch_channel_test_flag(chan_b, CF_ANSWERED)) {

 			if (switch_true(switch_channel_get_variable_dup(chan_a, "bypass_media_after_bridge_oldschool", SWITCH_FALSE, -1))) {
 				switch_ivr_nomedia(switch_core_session_get_uuid(session_a), SMF_REBRIDGE);
 			} else {
 				switch_ivr_3p_nomedia(switch_core_session_get_uuid(session_a), SMF_REBRIDGE);
 			}
 			switch_channel_clear_flag(chan_b, CF_BYPASS_MEDIA_AFTER_BRIDGE);
 			goto end_of_bridge_loop;
 		}
 	}

 	/* if 1 channel has DTMF pass it to the other */
 	while (switch_channel_has_dtmf(chan_a)) {
 		switch_dtmf_t dtmf = { 0, 0 };
 		if (switch_channel_dequeue_dtmf(chan_a, &dtmf) == SWITCH_STATUS_SUCCESS) {
 			int send_dtmf = 1;

 			if (input_callback) {
 				switch_status_t cb_status = input_callback(session_a, (void *) &dtmf, SWITCH_INPUT_TYPE_DTMF, user_data, 0);

 				if (cb_status == SWITCH_STATUS_IGNORE) {
 					send_dtmf = 0;
 				} else if (cb_status != SWITCH_STATUS_SUCCESS) {
 					switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "%s ended call via DTMF\n", switch_channel_get_name(chan_a));
 					switch_core_session_kill_channel(session_b, SWITCH_SIG_BREAK);
 					goto end_of_bridge_loop;
 				}
 			}

 			if (bridge_filter_dtmf) {
 				send_dtmf = 0;
 				switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "Dropping filtered DTMF received on %s\n", switch_channel_get_name(chan_a));
 			}

 			if (send_dtmf) {
 				switch_core_session_send_dtmf(session_b, &dtmf);
 				switch_core_session_kill_channel(session_b, SWITCH_SIG_BREAK);
 			}
 		}
 	}

 	if (switch_core_session_dequeue_event(session_a, &event, SWITCH_FALSE) == SWITCH_STATUS_SUCCESS) {
 		if (input_callback) {
 			input_callback(session_a, event, SWITCH_INPUT_TYPE_EVENT, user_data, 0);
 		}

 		if ((event->event_id != SWITCH_EVENT_COMMAND && event->event_id != SWITCH_EVENT_MESSAGE)
 			|| switch_core_session_receive_event(session_b, &event) != SWITCH_STATUS_SUCCESS) {
 			switch_event_destroy(&event);
 		}

 	}

 	if (!switch_channel_test_flag(chan_a, CF_ANSWERED) && answer_limit && switch_epoch_time_now(NULL) > answer_limit) {
 		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "Answer timeout hit on %s.\n", switch_channel_get_name(chan_a));
 		if (switch_true(switch_channel_get_variable_dup(chan_a, "continue_on_answer_timeout", SWITCH_FALSE, -1))) {
 			data->clean_exit = 1;
 			goto end_of_bridge_loop;
 		} else {
 			switch_channel_hangup(chan_a, SWITCH_CAUSE_ALLOTTED_TIMEOUT);
 		}
 	}

 	if (!switch_channel_test_flag(chan_a, CF_ANSWERED)) {
 		if (originator) {
 			if (!ans_b && switch_channel_test_flag(chan_b, CF_ANSWERED)) {
 				switch_channel_pass_callee_id(chan_b, chan_a);
 				if (switch_channel_answer(chan_a) != SWITCH_STATUS_SUCCESS) {
 					switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "%s Media Establishment Failed.\n", switch_channel_get_name(chan_a));
 					goto end_of_bridge_loop;
 				}
 				ans_a = 1;
 			} else if (!pre_b && switch_channel_test_flag(chan_b, CF_EARLY_MEDIA)) {
 				if (switch_channel_pre_answer(chan_a) != SWITCH_STATUS_SUCCESS) {
 					switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "%s Media Establishment Failed.\n", switch_channel_get_name(chan_a));
 					goto end_of_bridge_loop;
 				}
 				pre_b = 1;
 			}
 			if (!pre_b) {
 				switch_yield(10000);
 				continue;
 			}
 		} else {
 			ans_a = switch_channel_test_flag(chan_b, CF_ANSWERED);
 		}
 	}

 	if (ans_a != ans_b) {
 		switch_channel_t *un = ans_a ? chan_b : chan_a;
 		switch_channel_t *a = un == chan_b ? chan_a : chan_b;

 		if (switch_channel_direction(un) == SWITCH_CALL_DIRECTION_INBOUND) {
 			if (switch_channel_direction(a) == SWITCH_CALL_DIRECTION_OUTBOUND || (un == chan_a && !originator)) {
 				switch_channel_pass_callee_id(a, un);
 			}

 			if (switch_channel_answer(un) != SWITCH_STATUS_SUCCESS) {
 				switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "%s Media Establishment Failed.\n", switch_channel_get_name(un));
 				goto end_of_bridge_loop;
 			}

 			if (ans_a) {
 				ans_b = 1;
 			} else {
 				ans_a = 1;
 			}
 		}
 	}

 	if (originator && !ans_b) ans_b = switch_channel_test_flag(chan_b, CF_ANSWERED);

 	if (originator && !sent_update && ans_a && ans_b && switch_channel_media_ack(chan_a) && switch_channel_media_ack(chan_b)) {
 		switch_ivr_bridge_display(session_a, session_b);
 		sent_update = 1;
 	}
#ifndef SWITCH_VIDEO_IN_THREADS
 	if (switch_channel_test_flag(chan_a, CF_VIDEO) && switch_channel_test_flag(chan_b, CF_VIDEO)) {
 		/* read video from 1 channel and write it to the other */
 		status = switch_core_session_read_video_frame(session_a, &read_frame, SWITCH_IO_FLAG_NONE, 0);

 		if (!SWITCH_READ_ACCEPTABLE(status)) {
 			goto end_of_bridge_loop;
 		}

 		switch_core_session_write_video_frame(session_b, read_frame, SWITCH_IO_FLAG_NONE, 0);
 	}
#endif

 	if (!switch_channel_test_flag(chan_a, CF_AUDIO)) {
 		switch_ivr_sleep(session_a, 5000, SWITCH_FALSE, NULL);
 		continue;
 	}


 	/* read audio from 1 channel and write it to the other */
 	status = switch_core_session_read_frame(session_a, &read_frame, SWITCH_IO_FLAG_NONE, stream_id);

 	if (SWITCH_READ_ACCEPTABLE(status)) {
 		read_frame_count++;
 		if (switch_test_flag(read_frame, SFF_CNG)) {
 			if (silence_val) {
 				switch_generate_sln_silence((int16_t *) silence_frame.data, silence_frame.samples,
 											read_impl.number_of_channels, silence_val);
 				read_frame = &silence_frame;
 			} else if (!switch_channel_test_flag(chan_b, CF_ACCEPT_CNG)) {
 				continue;
 			}
 		}

 		if (switch_channel_test_flag(chan_a, CF_BRIDGE_NOWRITE)) {
 			continue;
 		}

 		if (status != SWITCH_STATUS_BREAK && !switch_channel_test_flag(chan_a, CF_HOLD) && !switch_channel_test_flag(chan_b, CF_LEG_HOLDING)) {
 			if (switch_core_session_write_frame(session_b, read_frame, SWITCH_IO_FLAG_NONE, stream_id) != SWITCH_STATUS_SUCCESS) {
 				switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG,
 								  "%s ending bridge by request from write function\n", switch_channel_get_name(chan_b));
 				goto end_of_bridge_loop;
 			}
 		}
 	} else {
 		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "%s ending bridge by request from read function\n", switch_channel_get_name(chan_a));
 		goto end_of_bridge_loop;
 	}
 }

 end_of_bridge_loop:

 switch_core_session_passthru(session_a, SWITCH_MEDIA_TYPE_AUDIO, SWITCH_FALSE);


#ifdef SWITCH_VIDEO_IN_THREADS
 if (vh.up > 0) {
 	vh.up = -1;
 	switch_channel_set_flag(chan_a, CF_NOT_READY);
 	//switch_channel_set_flag(chan_b, CF_NOT_READY);
 	switch_core_session_kill_channel(session_a, SWITCH_SIG_BREAK);
 	switch_core_session_kill_channel(session_b, SWITCH_SIG_BREAK);
 	switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "Ending video thread.\n");
 }
#endif


 if (silence_val) {
 	switch_core_codec_destroy(&silence_codec);
 }

 switch_channel_execute_on(chan_a, SWITCH_CHANNEL_EXECUTE_ON_POST_BRIDGE_VARIABLE);

 if (!inner_bridge) {
 	switch_channel_api_on(chan_a, SWITCH_API_BRIDGE_END_VARIABLE);
 }

 if (!inner_bridge && switch_channel_up_nosig(chan_a) && !switch_channel_test_flag(chan_a, CF_REDIRECT)) {
 	if ((app_name = switch_channel_get_variable(chan_a, SWITCH_EXEC_AFTER_BRIDGE_APP_VARIABLE))) {
 		switch_caller_extension_t *extension = NULL;
 		if ((extension = switch_caller_extension_new(session_a, app_name, app_name)) == 0) {
 			switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_CRIT, "memory error!\n");
 			goto end;
 		}
 		app_arg = switch_channel_get_variable(chan_a, SWITCH_EXEC_AFTER_BRIDGE_ARG_VARIABLE);

 		switch_caller_extension_add_application(session_a, extension, (char *) app_name, app_arg);
 		switch_channel_set_caller_extension(chan_a, extension);

 		if (switch_channel_get_state(chan_a) == CS_EXECUTE) {
 			switch_channel_set_flag(chan_a, CF_RESET);
 		} else {
 			switch_channel_set_state(chan_a, CS_EXECUTE);
 		}
 	}
 }

  end:


 if (switch_core_media_check_engine_function(session_a, SWITCH_MEDIA_TYPE_TEXT)) {
 	if (th.up == 1) {
 		th.up = -1;
 	}

 	switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "Ending text thread.\n");
 	switch_core_media_end_engine_function(session_a, SWITCH_MEDIA_TYPE_TEXT);
 }

#ifdef SWITCH_VIDEO_IN_THREADS
 if (switch_core_media_check_engine_function(session_a, SWITCH_MEDIA_TYPE_VIDEO)) {
 	if (vh.up == 1) {
 		vh.up = -1;
 	}

 	switch_channel_set_flag(chan_a, CF_VIDEO_BREAK);
 	switch_channel_set_flag(chan_b, CF_VIDEO_BREAK);
 	switch_core_session_kill_channel(session_a, SWITCH_SIG_BREAK);
 	switch_core_session_kill_channel(session_b, SWITCH_SIG_BREAK);

 	switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "Ending video thread.\n");
 	switch_core_media_end_engine_function(session_a, SWITCH_MEDIA_TYPE_VIDEO);
 	switch_channel_clear_flag(chan_a, CF_NOT_READY);
 	switch_channel_clear_flag(chan_b, CF_NOT_READY);
 }
#endif



 switch_core_session_reset(session_a, SWITCH_TRUE, SWITCH_TRUE);
 switch_channel_set_variable(chan_a, SWITCH_BRIDGE_VARIABLE, NULL);
 switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session_a), SWITCH_LOG_DEBUG, "BRIDGE THREAD DONE [%s]\n", switch_channel_get_name(chan_a));
 switch_channel_clear_flag(chan_a, CF_BRIDGED);

 if (switch_channel_test_flag(chan_a, CF_LEG_HOLDING) || switch_channel_test_flag(chan_a, CF_HANGUP_HELD)) {
 	if (switch_channel_ready(chan_b) &&
 		switch_channel_get_state(chan_b) != CS_PARK && !data->other_leg_data->clean_exit && !switch_channel_test_flag(chan_b, CF_3P_NOMEDIA_REQUESTED)) {
 		const char *ext = switch_channel_get_variable(chan_a, "hold_hangup_xfer_exten");

 		switch_channel_stop_broadcast(chan_b);

 		if (zstr(ext)) {
 			switch_call_cause_t cause = switch_channel_get_cause(chan_b);
 			if (cause == SWITCH_CAUSE_NONE) {
 				cause = SWITCH_CAUSE_NORMAL_CLEARING;
 			}
 			switch_channel_hangup(chan_b, cause);
 		} else {
 			switch_channel_set_variable(chan_b, SWITCH_TRANSFER_AFTER_BRIDGE_VARIABLE, ext);
 		}
 	}

 	if (switch_channel_test_flag(chan_a, CF_LEG_HOLDING)) {
 		switch_channel_mark_hold(chan_a, SWITCH_FALSE);
 	}
 }

 if (switch_channel_test_flag(chan_a, CF_INTERCEPTED)) {
 	switch_channel_set_flag(chan_b, CF_INTERCEPT);
 }

 switch_channel_clear_flag(chan_a, CF_VIDEO_BLANK);
 switch_channel_clear_flag(chan_b, CF_VIDEO_BLANK);

 switch_core_session_kill_channel(session_b, SWITCH_SIG_BREAK);
 data->done = 1;
 switch_core_session_video_reset(session_a);
 switch_core_session_video_reset(session_b);

 switch_core_session_rwunlock(session_b);
 return NULL;
}

3. uuid_bridge 问题处理

uuid_bridge 命令的使用实际上有一个时机问题需要格外注意，当监听到 CHANNEL_PROGRESS_MEDIA 事件就立即使用这个命令时，非常有可能遇到命令执行不成功的问题。这个问题发生的前提是使用尚未接通的腿作为 a-leg 去 bridge 另一条就绪的 b-leg，具体流程如下所示：

在这里插入图片描述

  1. originate 命令呼叫，拉起 a-leg。在完整的 originate 命令执行周期内状态机流转为 CS_NEW -> CS_INIT -> CS_ROUTING -> CS_EXECUTE，而在流转到 CS_ROUTING 之前 CHANNEL_PROGRESS_MEDIA 事件 就发出来了
  2. esl 监听到 CHANNEL_PROGRESS_MEDIA 事件 时下发 uuid_bridge 命令，在这个命令执行后 a-leg 完整的状态流转为 ANY -> CS_HIBERNATE/CS_CONSUME_MEDIA -> CS_RESET -> CS_SOFT_EXECUTE。a-leg 在 CS_SOFT_EXECUTE 状态时会驱动 b-leg 也到达 CS_SOFT_EXECUTE 状态，所以一旦 a-leg 在 uuid_bridge 周期内的状态流转出现异常，则 b-leg 会一直停留在 CS_RESET
  3. 从上图可以看到，如果 originate 和 uuid_bridge 执行后推动的状态机流转在时间上有重叠，则 a-leg 桥接 b-leg 时预期的状态流转很可能被打断，无法到达 CS_SOFT_EXECUTE 导致桥接事实上失败，双方无法通话。另一个影响是导致 b-leg 一直停留在 CS_RESET，而在这个状态时 FreeSWITCH 不会读这条腿上发过来的 RTP 数据，也就不会反馈 RTCP 数据给发送端，如果 b-leg 的 SIP 设备有 RTP 超时检测则可能认为媒体服务器异常，会主动发送 BYE 结束会话

这个问题的本质是 uuid_bridge 执行后 a-leg 的状态机未按照预期流转，解决方案有 2 个，读者如遇到相似问题可以参考：

  1. 修改 FreeSWITCH 源码
    uuid_bridge 命令执行后，a-leg 上安装的回调函数表 uuid_bridge_state_handlers 函数会在状态机流转相应状态时执行，从此处将 a-leg 向 CS_SOFT_EXECUTE 状态驱动。这个过程被 CS_EXECUTE 状态打断后，只需要在 uuid_bridge_state_handlers 的 on_execute 阶段安装相应的回调函数让状态机重新流转起来即可
  2. 修改上层业务逻辑
    修改 uuid_bridge 命令的发送时机，将其延后到 a-leg CS_EXECUTE 状态后再发送，这样就避免了命令执行时序混乱导致的状态机流转异常

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