RTMP推流到SRS流媒体服务器消息处理

1. SRS和客户端是怎么交换消息的？各个消息有什么作用？
2. 握手成功后，SRS和客户端进行消息交换，对应wiresharek这部分截图：

3. 流程图（之前画的，可能不够详细，后面补充）：

1. 客户端发送connect连接请求到SRS服务端

1. connect命令，⽤于客户端向服务器发送连接请求。
2. wiresharek截图：

1. connect消息解析

1. Chunk Stream Id：接收端根据相同的chunk stream id拼装出message， 这⾥是3，对应ffmpeg的枚举RTMP_SYSTEM_CHANNEL。
2. Type ID （即是message type id） ⽐如8⾳频，9视频，20命令消息，这⾥是20命令消息，对应ffmpeg的枚举RTMP_PT_INVOKE。
3. Stream ID为0。
4. RTMP body是⼀个connect 命令消息，这些信息是以AMF格式发送的，消息的结构如下：

6. 第三个字段中的Command Object中会涉及到很多键值对，使⽤时可以参考协议的官⽅⽂档。消息的回应有两种，_result表示接受连接，_error表示连接失败。
7. 以下是连接命令对象中使⽤的健值对的描述：

2. connect消息代码分析

1. 客户端生成connect消息发送到SRS服务器

1. 对应FFmpeg代码在：

	gen_connect(s, rt)static int gen_connect(URLContext *s, RTMPContext *rt)//部分代码如下：ff_amf_write_string(&p, "connect");ff_amf_write_number(&p, ++rt->nb_invokes);ff_amf_write_object_start(&p);ff_amf_write_field_name(&p, "app");ff_amf_write_string2(&p, rt->app, rt->auth_params);

2. SRS服务端接收connect消息并解析

1. 对应SRS代码在：

	rtmp->connect_app(req)) != srs_success)
srs_error_t SrsRtmpServer::connect_app(SrsRequest* req) {srs_error_t err = srs_success;SrsCommonMessage* msg = NULL;SrsConnectAppPacket* pkt = NULL;if ((err = expect_message<SrsConnectAppPacket>(&msg, &pkt)) != srs_success) { //解析connect消息，从流式数据->chunk->message->packetreturn srs_error_wrap(err, "expect connect app response");}SrsAutoFree(SrsCommonMessage, msg);SrsAutoFree(SrsConnectAppPacket, pkt);SrsAmf0Any* prop = NULL;if ((prop = pkt->command_object->ensure_property_string("tcUrl")) == NULL) {return srs_error_new(ERROR_RTMP_REQ_CONNECT, "invalid request without tcUrl");}req->tcUrl = prop->to_str();if ((prop = pkt->command_object->ensure_property_string("pageUrl")) != NULL) {req->pageUrl = prop->to_str();}if ((prop = pkt->command_object->ensure_property_string("swfUrl")) != NULL) {req->swfUrl = prop->to_str();}if ((prop = pkt->command_object->ensure_property_number("objectEncoding")) != NULL) {req->objectEncoding = prop->to_number();}if (pkt->args) {srs_freep(req->args);req->args = pkt->args->copy()->to_object();}srs_discovery_tc_url(req->tcUrl, req->schema, req->host, req->vhost, req->app, req->stream, req->port, req->param);req->strip();return err;
}

2. 具体解析为packet代码为：

srs_error_t SrsProtocol::do_decode_message(SrsMessageHeader& header, SrsBuffer* stream, SrsPacket** ppacket)
{...        // decode command object.if (command == RTMP_AMF0_COMMAND_CONNECT) { //第一个接收到的message为"connect"消息*ppacket = packet = new SrsConnectAppPacket();return packet->decode(stream);} ...
}

3. gdb显示调用栈为：

(gdb) bt
#0  SrsProtocol::do_decode_message (this=0xac1280, header=..., stream=0xadb560, ppacket=0xadb550) at src/protocol/srs_rtmp_stack.cpp:700
#1  0x00000000004655ec in SrsProtocol::decode_message (this=0xac1280, msg=0xade990, ppacket=0xadb5e0) at src/protocol/srs_rtmp_stack.cpp:430
#2  0x000000000047f8c0 in SrsProtocol::expect_message<SrsConnectAppPacket> (this=0xac1280, pmsg=0xadb670, ppacket=0xadb678) at src/protocol/srs_rtmp_stack.hpp:335
#3  0x000000000047dc7d in SrsRtmpServer::expect_message<SrsConnectAppPacket> (this=0xac1250, pmsg=0xadb670, ppacket=0xadb678) at src/protocol/srs_rtmp_stack.hpp:776
#4  0x000000000046df7b in SrsRtmpServer::connect_app (this=0xac1250, req=0xacab30) at src/protocol/srs_rtmp_stack.cpp:2310
#5  0x00000000004d3594 in SrsRtmpConn::do_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:170
#6  0x00000000004d1d99 in SrsConnection::cycle (this=0xac0f88) at src/app/srs_app_conn.cpp:171
#7  0x000000000050ab08 in SrsSTCoroutine::cycle (this=0xac11f0) at src/app/srs_app_st.cpp:198
#8  0x000000000050ab7d in SrsSTCoroutine::pfn (arg=0xac11f0) at src/app/srs_app_st.cpp:213
#9  0x00000000005bed1a in _st_thread_main () at sched.c:337
#10 0x00000000005bf492 in st_thread_create (start=0x5be696 <_st_vp_schedule+170>, arg=0x700000001, joinable=1, stk_size=1) at sched.c:616
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

2. SRS服务器发送Window Acknowledgement Size消息给客户端，默认2500000

1. Window Acknowledgement Size消息解析

1. wiresharek截图：

2. Type Id：0x5 对应ffmepg的RTMP_PT_WINDOW_ACK_SIZE
3. Window Acknowledgement Size⽤于设置窗⼝确认⼤⼩，⽐如这⾥是服务器发送给客户端的，当客户端收到每次该size就要Acknowledgement (0x3)。
4. 对于ffmpeg，在接收到Window Acknowledgement Size的⼀半后发送确认包（Acknowledgement），以确保对等⽅可以继续发送⽽不等待确认。
5. 注意点：
   1. 客户端作为推流端时，⼀般即使没有收到服务器的ack，客户端也不会停⽌码流的推送。
   2. 当客户端作为拉流端时，⼀般即使拉流端不回应ack，服务器也不会停⽌码流的发送。
   3. 但彼此如果作为接收⽅时，收到1/2Windows size的数据后对会ack对⽅。

2. Window Acknowledgement Size消息代码分析

1. SRS服务器发送Window Acknowledgement Size消息给客户端

rtmp->set_window_ack_size(out_ack_size)
srs_error_t SrsRtmpServer::set_window_ack_size(int ack_size){srs_error_t err = srs_success;SrsSetWindowAckSizePacket* pkt = new SrsSetWindowAckSizePacket();pkt->ackowledgement_window_size = ack_size;if ((err = protocol->send_and_free_packet(pkt, 0)) != srs_success) {return srs_error_wrap(err, "send ack");}return err;
}

2. FFmpeg客户端处理SRS服务器发送过来的

static int handle_window_ack_size(URLContext *s, RTMPPacket *pkt)
{RTMPContext *rt = s->priv_data;if (pkt->size < 4) {av_log(s, AV_LOG_ERROR,"Too short window acknowledgement size packet (%d)\n",pkt->size);return AVERROR_INVALIDDATA;}rt->receive_report_size = AV_RB32(pkt->data);if (rt->receive_report_size <= 0) {av_log(s, AV_LOG_ERROR, "Incorrect window acknowledgement size %d\n",rt->receive_report_size);return AVERROR_INVALIDDATA;}av_log(s, AV_LOG_DEBUG, "Window acknowledgement size = %d\n", rt->receive_report_size);// Send an Acknowledgement packet after receiving half the maximum// size, to make sure the peer can keep on sending without waiting// for acknowledgements.rt->receive_report_size >>= 1;return 0;
}

3. srs服务器发送Peer Bandiwdth消息给客户端，默认2500000

1. Peer Bandiwdth消息解析

1. wiresharek截图：

2. 客户端或服务器端发送此消息更新对端的输出带宽，作用是限制对端的输出带宽。和Window Acknowledgement Size相⽐，重点是更新
3. Type ID：0x6 对应ffmpeg的RTMP_PT_SET_PEER_BW
4. 如果消息中的Window ACK Size与上⼀次发送给发送端的size不同的话要回馈⼀个Window Acknowledgement Size的控制消息
   1. 
      1. Hard(Limit Type＝0)：接收端应该将Window Ack Size设置为消息中的值
      2. Soft(Limit Type=1)：接收端可以将Window Ack Size设为消息中的值，也可以保存原来的值（前提是原来的Size⼩与该控制消息中的Window Ack Size）
      3. Dynamic(Limit Type=2)：如果上次的Set Peer Bandwidth消息中的Limit Type为0，本次也按Hard处理，否则忽略本消息，不去设置Window Ack Size

2. Peer Bandiwdth消息代码分析

1. SRS服务器发送 Peer Bandiwdth消息给客户端。

srs_error_t SrsRtmpServer::set_peer_bandwidth(int bandwidth, int type)
{srs_error_t err = srs_success;SrsSetPeerBandwidthPacket* pkt = new SrsSetPeerBandwidthPacket();pkt->bandwidth = bandwidth;pkt->type = type;if ((err = protocol->send_and_free_packet(pkt, 0)) != srs_success) {return srs_error_wrap(err, "send set peer bandwidth");}return err;
}

4. srs服务器发送Set Chunk Size消息给客户端

1. Set Chunk Size消息解析

1. wiresharek截图：
2. Set Chunk Size(Message Type ID=1)：设置chunk中Data字段所能承载的最⼤字节数，默认为128B，通信过程中可以通过发送该消息来设置chunk Size的⼤⼩（不得⼩于128B），⽽且通信双⽅会各⾃维护⼀个chunkSize，两端的chunkSize是独⽴的。
   1. ⽐如当A想向B发送⼀个200B的Message，但默认的chunkSize是128B，因此就要将该消息拆分为Data分别为128B和72B的两个chunk发送，如果此时先发送⼀个设置chunkSize为256B的消息，再发送Data为200B的chunk，本地不再划分Message，B接受到Set Chunk Size的协议控制消息时会调整的接受的chunk的Data的⼤⼩，也不⽤再将两个chunk组成为⼀个Message。
   2. 在实际中⼀般会把chunk size设置的很⼤，有的会设置为4096，FFMPEG推流的时候设置的是 60*1000，这样设置的好处是避免了频繁的拆包组包，占⽤过多的CPU。
3. 以下为代表Set Chunk Size消息的chunk的Data：
   1. 
   2. 其中第⼀位必须为0，chunk Size占31个位，最⼤可代表2147483647＝0x7FFFFFFF＝2 -1，但实际上所有⼤于16777215=0xFFFFFF的值都⽤不上，因为chunk size不能⼤于Message的⻓度，表示Message的⻓度字段是⽤3个字节表示的，最⼤只能为0xFFFFFF。

2. Set Chunk Size消息代码分析

1. SRS服务器向客户端发送Set Chunk Size消息

srs_error_t SrsRtmpServer::set_chunk_size(int chunk_size)
{srs_error_t err = srs_success;SrsSetChunkSizePacket* pkt = new SrsSetChunkSizePacket();pkt->chunk_size = chunk_size;if ((err = protocol->send_and_free_packet(pkt, 0)) != srs_success) {return srs_error_wrap(err, "send set chunk size");}return err;
}

2. FFmpeg客户端处理SRS服务器发送过来的Set Chunk Size消息

static int handle_chunk_size(URLContext *s, RTMPPacket *pkt)
{RTMPContext *rt = s->priv_data;int ret;if (pkt->size < 4) {av_log(s, AV_LOG_ERROR,"Too short chunk size change packet (%d)\n",pkt->size);return AVERROR_INVALIDDATA;}if (!rt->is_input) {/* Send the same chunk size change packet back to the server,* setting the outgoing chunk size to the same as the incoming one. */if ((ret = ff_rtmp_packet_write(rt->stream, pkt, rt->out_chunk_size,&rt->prev_pkt[1], &rt->nb_prev_pkt[1])) < 0)return ret;rt->out_chunk_size = AV_RB32(pkt->data);}rt->in_chunk_size = AV_RB32(pkt->data);if (rt->in_chunk_size <= 0) {av_log(s, AV_LOG_ERROR, "Incorrect chunk size %d\n",rt->in_chunk_size);return AVERROR_INVALIDDATA;}av_log(s, AV_LOG_DEBUG, "New incoming chunk size = %d\n",rt->in_chunk_size);return 0;
}

5. SRS服务器发送response_connect_app消息给客户端

1. SRS服务器是会发送response_connect_app消息给客户端用来响应客户端发送的connect消息，但这部分wiresharek是没有抓取到此包的。
2. 通过tcpdump命令查看包信息：

sudo tcpdump -i any port 1935 -XX and dst 36.112.32.2 #不是公网地址

3. 是有返回result消息的，只是wiresharek没有抓取到此包。

1. response_connect_app消息代码分析

1. SRS服务器向客户端发送esponse_connect_app消息

srs_error_t SrsRtmpServer::response_connect_app(SrsRequest *req, const char* server_ip)
{srs_error_t err = srs_success;SrsConnectAppResPacket* pkt = new SrsConnectAppResPacket();// @remark For windows, there must be a space between const string and macro.pkt->props->set("fmsVer", SrsAmf0Any::str("FMS/" RTMP_SIG_FMS_VER));pkt->props->set("capabilities", SrsAmf0Any::number(127));pkt->props->set("mode", SrsAmf0Any::number(1));pkt->info->set(StatusLevel, SrsAmf0Any::str(StatusLevelStatus));pkt->info->set(StatusCode, SrsAmf0Any::str(StatusCodeConnectSuccess));pkt->info->set(StatusDescription, SrsAmf0Any::str("Connection succeeded"));pkt->info->set("objectEncoding", SrsAmf0Any::number(req->objectEncoding));SrsAmf0EcmaArray* data = SrsAmf0Any::ecma_array();pkt->info->set("data", data);data->set("version", SrsAmf0Any::str(RTMP_SIG_FMS_VER));data->set("srs_sig", SrsAmf0Any::str(RTMP_SIG_SRS_KEY));data->set("srs_server", SrsAmf0Any::str(RTMP_SIG_SRS_SERVER));data->set("srs_license", SrsAmf0Any::str(RTMP_SIG_SRS_LICENSE));data->set("srs_url", SrsAmf0Any::str(RTMP_SIG_SRS_URL));data->set("srs_version", SrsAmf0Any::str(RTMP_SIG_SRS_VERSION));if (server_ip) {data->set("srs_server_ip", SrsAmf0Any::str(server_ip));}// for edge to directly get the id of client.data->set("srs_pid", SrsAmf0Any::number(getpid()));data->set("srs_id", SrsAmf0Any::number(_srs_context->get_id()));if ((err = protocol->send_and_free_packet(pkt, 0)) != srs_success) {return srs_error_wrap(err, "send connect app response");}return err;
}

6. 客户端发送Set Chunk Size消息给SRS服务器

1. wiresharek截图：

2. 客户端也会发送Set Chunk Size消息给SRS服务器，值为60000。

7. 客户端发送releaseStream、FCPublish、CreateStream和checkbw消息给SRS服务器

1. 客户端还需要发送 releaseStream , FCPublish，CreateStream和checkbw消息给SRS服务器，具体可以参考ffmpeg的handle_invoke_result函数和gen_check_bw函数。
2. handle_invoke_result函数部分代码：

static int handle_invoke_result(URLContext *s, RTMPPacket *pkt)
{...if (!strcmp(tracked_method, "connect")) {if (!rt->is_input) { //输出if ((ret = gen_release_stream(s, rt)) < 0) //生成releaseStream发送给服务器goto fail;if ((ret = gen_fcpublish_stream(s, rt)) < 0)//生成FCPublish发送给服务器goto fail;} else {    //输入if ((ret = gen_window_ack_size(s, rt)) < 0)goto fail;}if ((ret = gen_create_stream(s, rt)) < 0)//生成createStream发送给服务器goto fail;...} else if (!strcmp(tracked_method, "createStream")) {...}fail:av_free(tracked_method);return ret;
}

1. 客户端发送releaseStream消息给srs服务器

1. 对应的值liveStream是要处理的流，作用是生成’releaseStream’调用并发送到服务器，让服务器为媒体流释放一些通道。
2. wiresharek截图：

1. releaseStream消息代码分析

1. 客户端生成releaseStream消息发送给SRS服务端，代码：

static int gen_release_stream(URLContext *s, RTMPContext *rt)
{RTMPPacket pkt;uint8_t *p;int ret;if ((ret = ff_rtmp_packet_create(&pkt, RTMP_SYSTEM_CHANNEL, RTMP_PT_INVOKE,0, 29 + strlen(rt->playpath))) < 0)return ret;av_log(s, AV_LOG_DEBUG, "Releasing stream...\n");p = pkt.data;ff_amf_write_string(&p, "releaseStream");ff_amf_write_number(&p, ++rt->nb_invokes);ff_amf_write_null(&p);ff_amf_write_string(&p, rt->playpath);return rtmp_send_packet(rt, &pkt, 1);
}

2. SRS服务端接收到后会解析成对应的packet，然后返回_result消息。如下wiresharek所示：

3. SRS服务器解析releaseStream消息代码：

    // SrsProtocol::do_decode_message函数下} else if (command == RTMP_AMF0_COMMAND_RELEASE_STREAM) {*ppacket = packet = new SrsFMLEStartPacket(); // 处理"releaseStream"消息，rtmp推流时是这个包return packet->decode(stream);}

4. 调用栈：
   1. 是从SrsRtmpServer::identify_client函数进去的

Breakpoint 3, SrsProtocol::do_decode_message (this=0xac1280, header=..., stream=0xadb540, ppacket=0xadb530) at src/protocol/srs_rtmp_stack.cpp:712
712	            *ppacket = packet = new SrsFMLEStartPacket();
(gdb) bt
#0  SrsProtocol::do_decode_message (this=0xac1280, header=..., stream=0xadb540, ppacket=0xadb530) at src/protocol/srs_rtmp_stack.cpp:712
#1  0x00000000004655ec in SrsProtocol::decode_message (this=0xac1280, msg=0xadce30, ppacket=0xadb5c8) at src/protocol/srs_rtmp_stack.cpp:430
#2  0x00000000004702bb in SrsRtmpServer::identify_client (this=0xac1250, stream_id=1, type=@0xacab08: SrsRtmpConnUnknown, stream_name="", duration=@0xacac88: -1) at src/protocol/srs_rtmp_stack.cpp:2521
#3  0x00000000004d519a in SrsRtmpConn::stream_service_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:440
#4  0x00000000004d4ddf in SrsRtmpConn::service_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:388
#5  0x00000000004d3ba7 in SrsRtmpConn::do_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:209
#6  0x00000000004d1d99 in SrsConnection::cycle (this=0xac0f88) at src/app/srs_app_conn.cpp:171
#7  0x000000000050ab08 in SrsSTCoroutine::cycle (this=0xac11f0) at src/app/srs_app_st.cpp:198
#8  0x000000000050ab7d in SrsSTCoroutine::pfn (arg=0xac11f0) at src/app/srs_app_st.cpp:213
#9  0x00000000005bed1a in _st_thread_main () at sched.c:337
#10 0x00000000005bf492 in st_thread_create (start=0x5be696 <_st_vp_schedule+170>, arg=0x700000001, joinable=1, stk_size=1) at sched.c:616
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

5. 根据packet类型返回对应响应，ReleaseStream/PublishStream/FCPublish/FCUnpublish都是用SrsRtmpServer::identify_fmle_publish_client函数返回_result消息。

srs_error_t SrsRtmpServer::identify_fmle_publish_client(SrsFMLEStartPacket* req, SrsRtmpConnType& type, string& stream_name)
{srs_error_t err = srs_success;type = SrsRtmpConnFMLEPublish;stream_name = req->stream_name;// releaseStream responseif (true) {SrsFMLEStartResPacket* pkt = new SrsFMLEStartResPacket(req->transaction_id);if ((err = protocol->send_and_free_packet(pkt, 0)) != srs_success) {return srs_error_wrap(err, "send releaseStream response");}}return err;
}

2. 客户端发送FCPublish消息给srs服务器

1. FCPublish消息作用是使服务器为接收媒体流做好准备。
2. wiresharek截图：

1. FCPublish消息代码解析

1. 客户端生成FCPublish消息发送给SRS服务器：

static int gen_fcpublish_stream(URLContext *s, RTMPContext *rt)
{RTMPPacket pkt;uint8_t *p;int ret;if ((ret = ff_rtmp_packet_create(&pkt, RTMP_SYSTEM_CHANNEL, RTMP_PT_INVOKE,0, 25 + strlen(rt->playpath))) < 0)return ret;av_log(s, AV_LOG_DEBUG, "FCPublish stream...\n");p = pkt.data;ff_amf_write_string(&p, "FCPublish");ff_amf_write_number(&p, ++rt->nb_invokes);ff_amf_write_null(&p);ff_amf_write_string(&p, rt->playpath);return rtmp_send_packet(rt, &pkt, 1);
}

2. SRS服务器解析FCPublish消息：

    } else if (command == RTMP_AMF0_COMMAND_FC_PUBLISH) {*ppacket = packet = new SrsFMLEStartPacket(); //第四个接收到的message为"FCPublish"return packet->decode(stream);}

3. 调用栈：
   1. FCPublish、createStream、publish、onFCPublish、onStatus都是通过SrsRtmpServer::start_fmle_publish函数进行处理

Breakpoint 4, SrsProtocol::do_decode_message (this=0xac1280, header=..., stream=0xadb480, ppacket=0xadb470) at src/protocol/srs_rtmp_stack.cpp:715
715	            *ppacket = packet = new SrsFMLEStartPacket();
(gdb) bt
#0  SrsProtocol::do_decode_message (this=0xac1280, header=..., stream=0xadb480, ppacket=0xadb470) at src/protocol/srs_rtmp_stack.cpp:715
#1  0x00000000004655ec in SrsProtocol::decode_message (this=0xac1280, msg=0xadeca0, ppacket=0xadb500) at src/protocol/srs_rtmp_stack.cpp:430
#2  0x000000000047fd40 in SrsProtocol::expect_message<SrsFMLEStartPacket> (this=0xac1280, pmsg=0xadb588, ppacket=0xadb590) at src/protocol/srs_rtmp_stack.hpp:335
#3  0x000000000047dfd9 in SrsRtmpServer::expect_message<SrsFMLEStartPacket> (this=0xac1250, pmsg=0xadb588, ppacket=0xadb590) at src/protocol/srs_rtmp_stack.hpp:776
#4  0x000000000047190c in SrsRtmpServer::start_fmle_publish (this=0xac1250, stream_id=1) at src/protocol/srs_rtmp_stack.cpp:2714
#5  0x00000000004d5e81 in SrsRtmpConn::stream_service_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:530
#6  0x00000000004d4ddf in SrsRtmpConn::service_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:388
#7  0x00000000004d3ba7 in SrsRtmpConn::do_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:209
#8  0x00000000004d1d99 in SrsConnection::cycle (this=0xac0f88) at src/app/srs_app_conn.cpp:171
#9  0x000000000050ab08 in SrsSTCoroutine::cycle (this=0xac11f0) at src/app/srs_app_st.cpp:198
#10 0x000000000050ab7d in SrsSTCoroutine::pfn (arg=0xac11f0) at src/app/srs_app_st.cpp:213
#11 0x00000000005bed1a in _st_thread_main () at sched.c:337
#12 0x00000000005bf492 in st_thread_create (start=0x5be696 <_st_vp_schedule+170>, arg=0x700000001, joinable=1, stk_size=1) at sched.c:616
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

4. SRS服务器发送_result消息给客户端进行响应FCPublish消息，见如上代码：SrsRtmpServer::identify_fmle_publish_client

3. 客户端发送CreateStream消息给srs服务器

1. wiresharek截图：

2. Create Stream：创建传递具体信息的通道，从⽽可以在这个流中传递具体信息，传输信息单元为Chunk。
3. 当发送完createStream消息之后，解析服务器返回的消息会得到⼀个stream ID，这个ID也就是以后和服务器通信的 message stream ID，⼀般返回的是1，不固定。

1. CreateStream消息代码解析

1. 客户端生成CreateStream消息发送给SRS服务器：

static int gen_create_stream(URLContext *s, RTMPContext *rt)
{RTMPPacket pkt;uint8_t *p;int ret;av_log(s, AV_LOG_DEBUG, "Creating stream...\n");if ((ret = ff_rtmp_packet_create(&pkt, RTMP_SYSTEM_CHANNEL, RTMP_PT_INVOKE,0, 25)) < 0)return ret;p = pkt.data;ff_amf_write_string(&p, "createStream");ff_amf_write_number(&p, ++rt->nb_invokes);ff_amf_write_null(&p);return rtmp_send_packet(rt, &pkt, 1);
}

2. SRS服务器解析CreateStream消息：

        } else if (command == RTMP_AMF0_COMMAND_CREATE_STREAM) {*ppacket = packet = new SrsCreateStreamPacket(); //第五个接收到的message为"createStream"消息return packet->decode(stream);}

3. SRS服务器发送_result消息给客户端进行响应CreateStream消息，见如上代码：SrsRtmpServer::identify_fmle_publish_client

4. 客户端发送checkbw消息给srs服务器

1. 客户端生成检查带宽消息发送给服务器。
2. wiresharek截图：

1. checkbw消息代码解析

1. 客户端生成checkbw消息发送给SRS服务器：

static int gen_check_bw(URLContext *s, RTMPContext *rt)
{RTMPPacket pkt;uint8_t *p;int ret;if ((ret = ff_rtmp_packet_create(&pkt, RTMP_SYSTEM_CHANNEL, RTMP_PT_INVOKE,0, 21)) < 0)return ret;p = pkt.data;ff_amf_write_string(&p, "_checkbw");ff_amf_write_number(&p, ++rt->nb_invokes);ff_amf_write_null(&p);return rtmp_send_packet(rt, &pkt, 1);
}

8. 客户端向SRS服务器发送publish消息以及SRS服务器向客户端发送onFCPublish消息和onStatue消息

1. publish消息解析

1. 推流客户端使用publish消息向SRS服务器端发布一个命名的流，发布之后，任意客户端都可以通过该名称请求视频、音频和数据。
2. wiresharek截图：

1. publish消息代码解析

1. 客户端生成publish消息并发送到SRS服务器：

static int gen_publish(URLContext *s, RTMPContext *rt)
{RTMPPacket pkt;uint8_t *p;int ret;av_log(s, AV_LOG_DEBUG, "Sending publish command for '%s'\n", rt->playpath);if ((ret = ff_rtmp_packet_create(&pkt, RTMP_SOURCE_CHANNEL, RTMP_PT_INVOKE,0, 30 + strlen(rt->playpath))) < 0)return ret;pkt.extra = rt->stream_id;p = pkt.data;ff_amf_write_string(&p, "publish");ff_amf_write_number(&p, ++rt->nb_invokes);ff_amf_write_null(&p);ff_amf_write_string(&p, rt->playpath);ff_amf_write_string(&p, "live");return rtmp_send_packet(rt, &pkt, 1);
}

2. SRS服务器解析publish消息：

    } else if (command == RTMP_AMF0_COMMAND_PUBLISH) { //message为"publish"*ppacket = packet = new SrsPublishPacket();return packet->decode(stream);}

3. 调用栈：

(gdb) bt
#0  SrsProtocol::do_decode_message (this=0xac1280, header=..., stream=0xadb480, ppacket=0xadb470) at src/protocol/srs_rtmp_stack.cpp:718
#1  0x00000000004655ec in SrsProtocol::decode_message (this=0xac1280, msg=0xaded60, ppacket=0xadb500) at src/protocol/srs_rtmp_stack.cpp:430
#2  0x00000000004801c0 in SrsProtocol::expect_message<SrsPublishPacket> (this=0xac1280, pmsg=0xadb588, ppacket=0xadb590) at src/protocol/srs_rtmp_stack.hpp:335
#3  0x000000000047e35b in SrsRtmpServer::expect_message<SrsPublishPacket> (this=0xac1250, pmsg=0xadb588, ppacket=0xadb590) at src/protocol/srs_rtmp_stack.hpp:776
#4  0x0000000000471c42 in SrsRtmpServer::start_fmle_publish (this=0xac1250, stream_id=1) at src/protocol/srs_rtmp_stack.cpp:2757
#5  0x00000000004d5e81 in SrsRtmpConn::stream_service_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:530
#6  0x00000000004d4ddf in SrsRtmpConn::service_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:388
#7  0x00000000004d3ba7 in SrsRtmpConn::do_cycle (this=0xac0f10) at src/app/srs_app_rtmp_conn.cpp:209
#8  0x00000000004d1d99 in SrsConnection::cycle (this=0xac0f88) at src/app/srs_app_conn.cpp:171
#9  0x000000000050ab08 in SrsSTCoroutine::cycle (this=0xac11f0) at src/app/srs_app_st.cpp:198
#10 0x000000000050ab7d in SrsSTCoroutine::pfn (arg=0xac11f0) at src/app/srs_app_st.cpp:213
#11 0x00000000005bed1a in _st_thread_main () at sched.c:337
#12 0x00000000005bf492 in st_thread_create (start=0x5be696 <_st_vp_schedule+170>, arg=0x700000001, joinable=1, stk_size=1) at sched.c:616
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

4. 解析成功后SRS服务器会生成onFCPublish消息返回给客户端。

2. onFCPublish消息解析

1. wiresharek截图：

2. onFCPublish消息是回应publish消息。

1. onFCPublish消息代码解析

1. SRS服务器生成onFCPublish消息并发送到客户端：

    // publish response onFCPublish(NetStream.Publish.Start)if (true) { //客户端发送publish消息，服务端返回onFCPublish消息。SrsOnStatusCallPacket* pkt = new SrsOnStatusCallPacket();pkt->command_name = RTMP_AMF0_COMMAND_ON_FC_PUBLISH;pkt->data->set(StatusCode, SrsAmf0Any::str(StatusCodePublishStart));pkt->data->set(StatusDescription, SrsAmf0Any::str("Started publishing stream."));if ((err = protocol->send_and_free_packet(pkt, stream_id)) != srs_success) { //onFCPublishreturn srs_error_wrap(err, "send NetStream.Publish.Start");}}

3. onStatue消息解析

1. SRS服务器还会生成onStatus消息向客户端发送，描述的状态内容中code为NetStream.Publish.Start，description为Start publishing，目的就是告诉推流客户端，现在可以推流了。

1. onStatue消息代码解析

1. SRS服务器生成onStatue消息并发送到客户端：

    // publish response onStatus(NetStream.Publish.Start)if (true) { //服务器发送onStatus消息给客户端，wiresharek无法解析SrsOnStatusCallPacket* pkt = new SrsOnStatusCallPacket();pkt->data->set(StatusLevel, SrsAmf0Any::str(StatusLevelStatus));pkt->data->set(StatusCode, SrsAmf0Any::str(StatusCodePublishStart));pkt->data->set(StatusDescription, SrsAmf0Any::str("Started publishing stream."));pkt->data->set(StatusClientId, SrsAmf0Any::str(RTMP_SIG_CLIENT_ID));if ((err = protocol->send_and_free_packet(pkt, stream_id)) != srs_success) {return srs_error_wrap(err, "send NetStream.Publish.Start");}}

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