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

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：

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

在这里插入图片描述

2. 源码分析

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;
}

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：

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
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);}}
#endifswitch_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);}}
#endifswitch_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;
}

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;
}
```

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;
}

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：

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
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;
}

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

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
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
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
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;
}

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;
}

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_THREADSstruct vid_helper vh = { 0 };uint32_t vid_launch = 0;
#endifdata->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_THREADSif (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);}}
#endifif (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_THREADSif (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);}
#endifif (!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_THREADSif (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");}
#endifif (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_THREADSif (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);}
#endifswitch_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

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
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
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：

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
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