srs流媒体服务器-基本流程分析

全文以srs3.0为例进行分析

分析srs源码必须辅助gdb调试

root@e370746341b0:/srs/trunk# gdb ./objs/srs

root@e370746341b0:/srs/trunk# set args -c conf/srs.conf

root@e370746341b0:/srs/trunk#b main

Breakpoint 1 at 0xab858e: file ./src/main/srs_main_server.cpp, line 255.

 从上面可以看到/src/main/srs_main_server.cpp中的main函数是全局入口函数

进入do_main函数,在该函数中主要做了三件事

1. _srs_config，全局配置文件

2. _srs_log,全局log文件

3. 重点创建SrsServer对象并运行

//解析命令行参数
if ((err = _srs_config->parse_options(argc, argv)) != srs_success) {return srs_error_wrap(err, "config parse options");}//设置工作目录和当前目录
string cwd = _srs_config->get_work_dir();
if (!cwd.empty() && cwd != "./" && (r0 = chdir(cwd.c_str())) == -1) {return srs_error_new(-1, "chdir to %s, r0=%d", cwd.c_str(), r0);
}
if ((err = _srs_config->initialize_cwd()) != srs_success) {return srs_error_wrap(err, "config cwd");
}// 初始化log
if ((err = _srs_log->initialize()) != srs_success) {return srs_error_wrap(err, "log initialize");
}//创建SrsServer对象
_srs_server = new SrsServer();
if ((err = run(_srs_server)) != srs_success) {return srs_error_wrap(err, "run");
}

在构造SrsServer对象会初始化http_api_mux和http_server 

http_api_mux = new SrsHttpServeMux(); 	// HTTP请求多路复用器，不是http拉流的
http_server = new SrsHttpServer(this); // http服务

run(SrsServer* svr) 会初始化服务器和获取守护进程配置in_daemon（默认为false），如果in_daemon为false，直接执行 run_master(SrsServer* svr)；否则会创建守护进程，在守护进程中运行

 bool in_daemon = _srs_config->get_daemon();if (in_daemon && _srs_in_docker && _srs_config->disable_daemon_for_docker()) {srs_warn("disable daemon for docker");in_daemon = false;}// If not daemon, directly run master.if (!in_daemon) {if ((err = run_master(svr)) != srs_success) {return srs_error_wrap(err, "run master");}return srs_success;}srs_trace("start daemon mode...");int pid = fork();if(pid < 0) {return srs_error_new(-1, "fork father process");}// grandpaif(pid > 0) {int status = 0;waitpid(pid, &status, 0);srs_trace("grandpa process exit.");exit(0);}// fatherpid = fork();if(pid < 0) {return srs_error_new(-1, "fork child process");}if(pid > 0) {srs_trace("father process exit");exit(0);}// sonsrs_trace("son(daemon) process running.");if ((err = run_master(svr)) != srs_success) {return srs_error_wrap(err, "daemon run master");}

run_master(SrsServer* svr) 函数中，服务器做一些初始化工作并调用listern监听客户端的连接，然后调用do_cycle函数(死循环)，做一些监控，更新时间及缓存等。

svr->initialize_st() 		//初始化st协程库
svr->initialize_signal()	//初始化信号
svr->acquire_pid_file()		//将pid线程写入文件
svr->listen()				//监听客户端请求
svr->register_signal()		//注册信号
svr->http_handle()    		//注册http的处理模块
svr->ingest()				//开启流采集
svr->cycle()				//消息循环处理

 重点关注SrsServer::listen(),使用gdb debug一下

(gdb) bt
#0  SrsServer::listen (this=0x555555a65ad0) at src/app/srs_app_server.cpp:872
#1  0x0000555555617442 in run_master (svr=0x555555a65ad0) at src/main/srs_main_server.cpp:470
#2  0x0000555555617058 in run (svr=0x555555a65ad0) at src/main/srs_main_server.cpp:410
#3  0x0000555555615b6e in do_main (argc=3, argv=0x7fffffffe738) at src/main/srs_main_server.cpp:185
#4  0x0000555555615c94 in main (argc=3, argv=0x7fffffffe738) at src/main/srs_main_server.cpp:193

 下一个阶段

srs_error_t SrsServer::listen()
{srs_error_t err = srs_success;if ((err = listen_rtmp()) != srs_success) {return srs_error_wrap(err, "rtmp listen");}if ((err = listen_http_api()) != srs_success) {return srs_error_wrap(err, "http api listen");}if ((err = listen_http_stream()) != srs_success) {return srs_error_wrap(err, "http stream listen");}if ((err = listen_stream_caster()) != srs_success) {return srs_error_wrap(err, "stream caster listen");}if ((err = conn_manager->start()) != srs_success) {return srs_error_wrap(err, "connection manager");}return err;
}

 这里我们以分析rtmp为主，因此重点关注SrsServer::listen_rtmp()

srs_error_t SrsServer::listen_rtmp()
{srs_error_t err = srs_success;// stream service port.std::vector ip_ports = _srs_config->get_listens();srs_assert((int)ip_ports.size() > 0);//关闭SrsListenerRtmpStream类型的监听器，从listeners管理器中删除监听对象//从监听队列中删除已有的该类监听器，防止冲突close_listeners(SrsListenerRtmpStream);for (int i = 0; i < (int)ip_ports.size(); i++) {SrsListener* listener = new SrsBufferListener(this, SrsListenerRtmpStream);listeners.push_back(listener);int port; string ip;srs_parse_endpoint(ip_ports[i], ip, port); //获取ip和port//注意这里是多态，调用的子类的listen,即SrsBufferListener::listenif ((err = listener->listen(ip, port)) != srs_success) {srs_error_wrap(err, "rtmp listen %s:%d", ip.c_str(), port);}}return err;
}

srs_error_t SrsBufferListener::listen(string i, int p)
{srs_error_t err = srs_success;ip = i;port = p;srs_freep(listener);listener = new SrsTcpListener(this, ip, port);//注意这里同样是虚函数，调用的是子类SrsTcpListener::listenif ((err = listener->listen()) != srs_success) {return srs_error_wrap(err, "buffered tcp listen");}string v = srs_listener_type2string(type);srs_trace("%s listen at tcp://%s:%d, fd=%d", v.c_str(), ip.c_str(), port, listener->fd());return err;
}

srs_error_t SrsTcpListener::listen()
{srs_error_t err = srs_success;if ((err = srs_tcp_listen(ip, port, &lfd)) != srs_success) { //创建监听的fd,并将fd注册到st库上return srs_error_wrap(err, "listen at %s:%d", ip.c_str(), port);}srs_freep(trd);trd = new SrsSTCoroutine("tcp", this); //创建一个协程if ((err = trd->start()) != srs_success) { //启动协程return srs_error_wrap(err, "start coroutine");}return err;
}

分析一下SrsSTCoroutine::start

srs_error_t SrsSTCoroutine::start()
{srs_error_t err = srs_success;if (started || disposed) {if (disposed) {err = srs_error_new(ERROR_THREAD_DISPOSED, "disposed");} else {err = srs_error_new(ERROR_THREAD_STARTED, "started");}if (trd_err == srs_success) {trd_err = srs_error_copy(err);}return err;}//这里就是创建协程if ((trd = (srs_thread_t)_pfn_st_thread_create(pfn, this, 1, 0)) == NULL) {err = srs_error_new(ERROR_ST_CREATE_CYCLE_THREAD, "create failed");srs_freep(trd_err);trd_err = srs_error_copy(err);return err;}started = true;return err;
}

void* SrsSTCoroutine::pfn(void* arg)
{SrsSTCoroutine* p = (SrsSTCoroutine*)arg;srs_error_t err = p->cycle();// Set the err for function pull to fetch it.// @see https://github.com/ossrs/srs/pull/1304#issuecomment-480484151if (err != srs_success) {srs_freep(p->trd_err);// It's ok to directly use it, because it's returned by st_thread_join.p->trd_err = err;}return (void*)err;
}

srs_error_t SrsSTCoroutine::cycle()
{if (_srs_context) {if (context) {_srs_context->set_id(context);} else {context = _srs_context->generate_id();}}srs_error_t err = handler->cycle();if (err != srs_success) {return srs_error_wrap(err, "coroutine cycle");}// Set cycle done, no need to interrupt it.cycle_done = true;return err;
}

SrsSTCoroutine::start创建一个协程，并在协程中调用handler->cycle(),而handler是基类ISrsCoroutineHandler，而该类中的cycle又是一个虚函数，因此就是调用的是子类中的cycle()。

trd = new SrsSTCoroutine("tcp", this);if ((err = trd->start()) != srs_success) { //调用this对象中的cycle,即SrsTcpListener::cycle()return srs_error_wrap(err, "start coroutine");}

srs_error_t SrsTcpListener::cycle()
{srs_error_t err = srs_success;while (true) {if ((err = trd->pull()) != srs_success) {return srs_error_wrap(err, "tcp listener");}srs_netfd_t fd = srs_accept(lfd, NULL, NULL, SRS_UTIME_NO_TIMEOUT);if(fd == NULL){return srs_error_new(ERROR_SOCKET_ACCEPT, "accept at fd=%d", srs_netfd_fileno(lfd));}if ((err = srs_fd_closeexec(srs_netfd_fileno(fd))) != srs_success) {return srs_error_wrap(err, "set closeexec");}if ((err = handler->on_tcp_client(fd)) != srs_success) {return srs_error_wrap(err, "handle fd=%d", srs_netfd_fileno(fd));}}return err;
}

srs_accept函数内部accept阻塞，等待客户端的连接。当有RTMP客户端请求连接时触发该断点，比如进行RTMP推流，则会进入handler->on_tcp_client，这里handler是ISrsTcpHandler基类，而on_tcp_client是纯虚函数，因此指向子类SrsBufferListener::on_tcp_client

srs_error_t SrsBufferListener::on_tcp_client(srs_netfd_t stfd)
{srs_error_t err = server->accept_client(type, stfd);if (err != srs_success) {srs_warn("accept client failed, err is %s", srs_error_desc(err).c_str());srs_freep(err);}return srs_success;
}

srs_error_t SrsServer::accept_client(SrsListenerType type, srs_netfd_t stfd)
{srs_error_t err = srs_success;SrsConnection* conn = NULL;if ((err = fd2conn(type, stfd, &conn)) != srs_success) {if (srs_error_code(err) == ERROR_SOCKET_GET_PEER_IP && _srs_config->empty_ip_ok()) {srs_close_stfd(stfd); srs_error_reset(err);return srs_success;}return srs_error_wrap(err, "fd2conn");}srs_assert(conn);// directly enqueue, the cycle thread will remove the client.conns.push_back(conn);// cycle will start process thread and when finished remove the client.// @remark never use the conn, for it maybe destroyed.if ((err = conn->start()) != srs_success) {return srs_error_wrap(err, "start conn coroutine");}return err;
}

fd2conn函数将fd和conn进行绑定

srs_error_t SrsServer::fd2conn(SrsListenerType type, srs_netfd_t stfd, SrsConnection** pconn)
{srs_error_t err = srs_success;int fd = srs_netfd_fileno(stfd);string ip = srs_get_peer_ip(fd);// for some keep alive application, for example, the keepalived,// will send some tcp packet which we cann't got the ip,// we just ignore it.if (ip.empty()) {return srs_error_new(ERROR_SOCKET_GET_PEER_IP, "ignore empty ip, fd=%d", fd);}// check connection limitation.int max_connections = _srs_config->get_max_connections();if (handler && (err = handler->on_accept_client(max_connections, (int)conns.size())) != srs_success) {return srs_error_wrap(err, "drop client fd=%d, max=%d, cur=%d for err: %s",fd, max_connections, (int)conns.size(), srs_error_desc(err).c_str());}if ((int)conns.size() >= max_connections) {return srs_error_new(ERROR_EXCEED_CONNECTIONS,"drop fd=%d, max=%d, cur=%d for exceed connection limits",fd, max_connections, (int)conns.size());}// avoid fd leak when fork.// @see https://github.com/ossrs/srs/issues/518if (true) {int val;if ((val = fcntl(fd, F_GETFD, 0)) < 0) {return srs_error_new(ERROR_SYSTEM_PID_GET_FILE_INFO, "fnctl F_GETFD error! fd=%d", fd);}val |= FD_CLOEXEC;if (fcntl(fd, F_SETFD, val) < 0) {return srs_error_new(ERROR_SYSTEM_PID_SET_FILE_INFO, "fcntl F_SETFD error! fd=%d", fd);}}if (type == SrsListenerRtmpStream) {*pconn = new SrsRtmpConn(this, stfd, ip);} else if (type == SrsListenerHttpApi) {*pconn = new SrsHttpApi(this, stfd, http_api_mux, ip);} else if (type == SrsListenerHttpStream) {*pconn = new SrsResponseOnlyHttpConn(this, stfd, http_server, ip);} else {srs_warn("close for no service handler. fd=%d, ip=%s", fd, ip.c_str());srs_close_stfd(stfd);return err;}return err;
}

根据传入的类型type,pconn指向不同的子类，如果是rtmp,则指向SrsRtmpConn,那么conn->start()，开启一个协程，专门用来处理数据流(推流或拉流)，调用SrsConnection::cycle()

srs_error_t SrsConnection::cycle()
{srs_error_t err = do_cycle();// Notify manager to remove it.manager->remove(this);// success.if (err == srs_success) {srs_trace("client finished.");return err;}// client close peer.// TODO: FIXME: Only reset the error when client closed it.if (srs_is_client_gracefully_close(err)) {srs_warn("client disconnect peer. ret=%d", srs_error_code(err));} else if (srs_is_server_gracefully_close(err)) {srs_warn("server disconnect. ret=%d", srs_error_code(err));} else {srs_error("serve error %s", srs_error_desc(err).c_str());}srs_freep(err);return srs_success;
}

而do_cycle()是纯虚函数，connyou又指向SrsRtmpConn,所以调用子类SrsRtmpConn::do_cycle()

srs_error_t SrsRtmpConn::do_cycle()
{srs_error_t err = srs_success;srs_trace("RTMP client ip=%s, fd=%d", ip.c_str(), srs_netfd_fileno(stfd));rtmp->set_recv_timeout(SRS_CONSTS_RTMP_TIMEOUT);rtmp->set_send_timeout(SRS_CONSTS_RTMP_TIMEOUT);if ((err = rtmp->handshake()) != srs_success) {return srs_error_wrap(err, "rtmp handshake");}uint32_t rip = rtmp->proxy_real_ip();if (rip > 0) {srs_trace("RTMP proxy real client ip=%d.%d.%d.%d",uint8_t(rip>>24), uint8_t(rip>>16), uint8_t(rip>>8), uint8_t(rip));}SrsRequest* req = info->req;if ((err = rtmp->connect_app(req)) != srs_success) {return srs_error_wrap(err, "rtmp connect tcUrl");}// set client ip to request.req->ip = ip;srs_trace("connect app, tcUrl=%s, pageUrl=%s, swfUrl=%s, schema=%s, vhost=%s, port=%d, app=%s, args=%s",req->tcUrl.c_str(), req->pageUrl.c_str(), req->swfUrl.c_str(),req->schema.c_str(), req->vhost.c_str(), req->port,req->app.c_str(), (req->args? "(obj)":"null"));// show client identityif(req->args) {std::string srs_version;std::string srs_server_ip;int srs_pid = 0;int srs_id = 0;SrsAmf0Any* prop = NULL;if ((prop = req->args->ensure_property_string("srs_version")) != NULL) {srs_version = prop->to_str();}if ((prop = req->args->ensure_property_string("srs_server_ip")) != NULL) {srs_server_ip = prop->to_str();}if ((prop = req->args->ensure_property_number("srs_pid")) != NULL) {srs_pid = (int)prop->to_number();}if ((prop = req->args->ensure_property_number("srs_id")) != NULL) {srs_id = (int)prop->to_number();}if (srs_pid > 0) {srs_trace("edge-srs ip=%s, version=%s, pid=%d, id=%d",srs_server_ip.c_str(), srs_version.c_str(), srs_pid, srs_id);}}if ((err = service_cycle()) != srs_success) {err = srs_error_wrap(err, "service cycle");}srs_error_t r0 = srs_success;if ((r0 = on_disconnect()) != srs_success) {err = srs_error_wrap(err, "on disconnect %s", srs_error_desc(r0).c_str());srs_freep(r0);}// If client is redirect to other servers, we already logged the event.if (srs_error_code(err) == ERROR_CONTROL_REDIRECT) {srs_error_reset(err);}return err;
}

srs_error_t SrsRtmpConn::service_cycle()
{srs_error_t err = srs_success;SrsRequest* req = info->req;int out_ack_size = _srs_config->get_out_ack_size(req->vhost);if (out_ack_size && (err = rtmp->set_window_ack_size(out_ack_size)) != srs_success) {return srs_error_wrap(err, "rtmp: set out window ack size");}int in_ack_size = _srs_config->get_in_ack_size(req->vhost);if (in_ack_size && (err = rtmp->set_in_window_ack_size(in_ack_size)) != srs_success) {return srs_error_wrap(err, "rtmp: set in window ack size");}if ((err = rtmp->set_peer_bandwidth((int)(2.5 * 1000 * 1000), 2)) != srs_success) {return srs_error_wrap(err, "rtmp: set peer bandwidth");}// get the ip which client connected.std::string local_ip = srs_get_local_ip(srs_netfd_fileno(stfd));// do bandwidth test if connect to the vhost which is for bandwidth check.if (_srs_config->get_bw_check_enabled(req->vhost)) {if ((err = bandwidth->bandwidth_check(rtmp, skt, req, local_ip)) != srs_success) {return srs_error_wrap(err, "rtmp: bandwidth check");}return err;}// set chunk size to larger.// set the chunk size before any larger response greater than 128,// to make OBS happy, @see https://github.com/ossrs/srs/issues/454int chunk_size = _srs_config->get_chunk_size(req->vhost);if ((err = rtmp->set_chunk_size(chunk_size)) != srs_success) {return srs_error_wrap(err, "rtmp: set chunk size %d", chunk_size);}// response the client connect ok.if ((err = rtmp->response_connect_app(req, local_ip.c_str())) != srs_success) {return srs_error_wrap(err, "rtmp: response connect app");}if ((err = rtmp->on_bw_done()) != srs_success) {return srs_error_wrap(err, "rtmp: on bw down");}while (true) {if ((err = trd->pull()) != srs_success) {return srs_error_wrap(err, "rtmp: thread quit");}err = stream_service_cycle();// stream service must terminated with error, never success.// when terminated with success, it's user required to stop.// TODO: FIXME: Support RTMP client timeout, https://github.com/ossrs/srs/issues/1134if (err == srs_success) {continue;}// when not system control error, fatal error, return.if (!srs_is_system_control_error(err)) {return srs_error_wrap(err, "rtmp: stream service");}// for republish, continue serviceif (srs_error_code(err) == ERROR_CONTROL_REPUBLISH) {// set timeout to a larger value, wait for encoder to republish.rtmp->set_send_timeout(SRS_REPUBLISH_RECV_TIMEOUT);rtmp->set_recv_timeout(SRS_REPUBLISH_SEND_TIMEOUT);srs_info("rtmp: retry for republish");srs_freep(err);continue;}// for "some" system control error,// logical accept and retry stream service.if (srs_error_code(err) == ERROR_CONTROL_RTMP_CLOSE) {// TODO: FIXME: use ping message to anti-death of socket.// @see: https://github.com/ossrs/srs/issues/39// set timeout to a larger value, for user paused.rtmp->set_recv_timeout(SRS_PAUSED_RECV_TIMEOUT);rtmp->set_send_timeout(SRS_PAUSED_SEND_TIMEOUT);srs_trace("rtmp: retry for close");srs_freep(err);continue;}// for other system control message, fatal error.return srs_error_wrap(err, "rtmp: reject");}return err;
}

srs_error_t SrsRtmpConn::stream_service_cycle()
{srs_error_t err = srs_success;SrsRequest* req = info->req;if ((err = rtmp->identify_client(info->res->stream_id, info->type, req->stream, req->duration)) != srs_success) {return srs_error_wrap(err, "rtmp: identify client");}srs_discovery_tc_url(req->tcUrl, req->schema, req->host, req->vhost, req->app, req->stream, req->port, req->param);req->strip();srs_trace("client identified, type=%s, vhost=%s, app=%s, stream=%s, param=%s, duration=%dms",srs_client_type_string(info->type).c_str(), req->vhost.c_str(), req->app.c_str(), req->stream.c_str(), req->param.c_str(), srsu2msi(req->duration));// discovery vhost, resolve the vhost from configSrsConfDirective* parsed_vhost = _srs_config->get_vhost(req->vhost);if (parsed_vhost) {req->vhost = parsed_vhost->arg0();}if (req->schema.empty() || req->vhost.empty() || req->port == 0 || req->app.empty()) {return srs_error_new(ERROR_RTMP_REQ_TCURL, "discovery tcUrl failed, tcUrl=%s, schema=%s, vhost=%s, port=%d, app=%s",req->tcUrl.c_str(), req->schema.c_str(), req->vhost.c_str(), req->port, req->app.c_str());}// check vhost, allow default vhost.if ((err = check_vhost(true)) != srs_success) {return srs_error_wrap(err, "check vhost");}srs_trace("connected stream, tcUrl=%s, pageUrl=%s, swfUrl=%s, schema=%s, vhost=%s, port=%d, app=%s, stream=%s, param=%s, args=%s",req->tcUrl.c_str(), req->pageUrl.c_str(), req->swfUrl.c_str(), req->schema.c_str(), req->vhost.c_str(), req->port,req->app.c_str(), req->stream.c_str(), req->param.c_str(), (req->args? "(obj)":"null"));// do token traverse before serve it.// @see https://github.com/ossrs/srs/pull/239if (true) {info->edge = _srs_config->get_vhost_is_edge(req->vhost);bool edge_traverse = _srs_config->get_vhost_edge_token_traverse(req->vhost);if (info->edge && edge_traverse) {if ((err = check_edge_token_traverse_auth()) != srs_success) {return srs_error_wrap(err, "rtmp: check token traverse");}}}// security checkif ((err = security->check(info->type, ip, req)) != srs_success) {return srs_error_wrap(err, "rtmp: security check");}// Never allow the empty stream name, for HLS may write to a file with empty name.// @see https://github.com/ossrs/srs/issues/834if (req->stream.empty()) {return srs_error_new(ERROR_RTMP_STREAM_NAME_EMPTY, "rtmp: empty stream");}// client is identified, set the timeout to service timeout.rtmp->set_recv_timeout(SRS_CONSTS_RTMP_TIMEOUT);rtmp->set_send_timeout(SRS_CONSTS_RTMP_TIMEOUT);// find a source to serve.SrsSource* source = NULL;if ((err = _srs_sources->fetch_or_create(req, server, &source)) != srs_success) {return srs_error_wrap(err, "rtmp: fetch source");}srs_assert(source != NULL);// update the statistic when source disconveried.SrsStatistic* stat = SrsStatistic::instance();if ((err = stat->on_client(srs_int2str(_srs_context->get_id()), req, this, info->type)) != srs_success) {return srs_error_wrap(err, "rtmp: stat client");}bool enabled_cache = _srs_config->get_gop_cache(req->vhost);srs_trace("source url=%s, ip=%s, cache=%d, is_edge=%d, source_id=%d/%d",req->get_stream_url().c_str(), ip.c_str(), enabled_cache, info->edge, source->source_id(), source->pre_source_id());source->set_cache(enabled_cache);switch (info->type) {case SrsRtmpConnPlay: {// response connection start playif ((err = rtmp->start_play(info->res->stream_id)) != srs_success) {return srs_error_wrap(err, "rtmp: start play");}if ((err = http_hooks_on_play()) != srs_success) {return srs_error_wrap(err, "rtmp: callback on play");}err = playing(source);http_hooks_on_stop();return err;}case SrsRtmpConnFMLEPublish: {if ((err = rtmp->start_fmle_publish(info->res->stream_id)) != srs_success) {return srs_error_wrap(err, "rtmp: start FMLE publish");}return publishing(source);}case SrsRtmpConnHaivisionPublish: {if ((err = rtmp->start_haivision_publish(info->res->stream_id)) != srs_success) {return srs_error_wrap(err, "rtmp: start HAIVISION publish");}return publishing(source);}case SrsRtmpConnFlashPublish: {if ((err = rtmp->start_flash_publish(info->res->stream_id)) != srs_success) {return srs_error_wrap(err, "rtmp: start FLASH publish");}return publishing(source);}default: {return srs_error_new(ERROR_SYSTEM_CLIENT_INVALID, "rtmp: unknown client type=%d", info->type);}}return err;
}

SrsRtmpConn::stream_service_cycle()真正地处理推拉流，如果推流则进入，SrsRtmpConn::publishing，而拉流则进入SrsRtmpConn::playing

 后面接着分析推拉流，有不对之处欢迎指正

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