4 live555源码分析（四）——live555 工作流程（一）

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本文继续对live555源码进行分析。以testOnDemandRTSPServer.cpp为例进行分析。本文只分析传输H264文件的过程。

一、 mian函数

int main(int argc, char** argv) {
  // Begin by setting up our usage environment:
  TaskScheduler* scheduler = BasicTaskScheduler::createNew();
  env = BasicUsageEnvironment::createNew(*scheduler);

  UserAuthenticationDatabase* authDB = NULL;
#ifdef ACCESS_CONTROL
  // To implement client access control to the RTSP server, do the following:
  authDB = new UserAuthenticationDatabase;
  authDB->addUserRecord("username1", "password1"); // replace these with real strings
  // Repeat the above with each <username>, <password> that you wish to allow
  // access to the server.
#endif

  // Create the RTSP server:
  RTSPServer* rtspServer = RTSPServer::createNew(*env, 8554, authDB);
  if (rtspServer == NULL) {
    *env << "Failed to create RTSP server: " << env->getResultMsg() << "\n";
    exit(1);
  }

  char const* descriptionString
    = "Session streamed by \"testOnDemandRTSPServer\"";
  // A H.264 video elementary stream:
  {
    char const* streamName = "h264ESVideoTest";
    char const* inputFileName = "test.264";
    ServerMediaSession* sms
      = ServerMediaSession::createNew(*env, streamName, streamName,
				      descriptionString);
    sms->addSubsession(H264VideoFileServerMediaSubsession
		       ::createNew(*env, inputFileName, reuseFirstSource));
    rtspServer->addServerMediaSession(sms);

    announceStream(rtspServer, sms, streamName, inputFileName);
  }
  ...
  ...
  env->taskScheduler().doEventLoop(); // does not return

省略掉发送其他格式文件，以及Http相关的代码进行分析。
首先创建了任务调度器和基础运行环境；
然后如果需要认证的话就添加用户名密码；
然后创建一个RTSPServer用来传输建立RTSP通信；
然后创建了一个ServerMediaSession，并在ServerMediaSession中添加了H264VideoFileServerMediaSubsession格式的subsession。

然后就进入了doEventLoop()一直处理任务了。

二、RTSPServer

RTSPServer*
RTSPServer::createNew(UsageEnvironment& env, Port ourPort,
		      UserAuthenticationDatabase* authDatabase,
		      unsigned reclamationSeconds) {
  int ourSocketIPv4 = setUpOurSocket(env, ourPort, AF_INET);
  int ourSocketIPv6 = setUpOurSocket(env, ourPort, AF_INET6);
  if (ourSocketIPv4 < 0 && ourSocketIPv6 < 0) return NULL;
  
  return new RTSPServer(env, ourSocketIPv4, ourSocketIPv6, ourPort, authDatabase, reclamationSeconds);
}

创建RTSPServer，并根据端口创建了IPv4和IPv6的TCP Socket（后面分析就忽略IPv6了）。
这里有个参数reclamationSeconds，表明回收的时间，也就是说，当在这个超过这个时间还没收到客户端的RTSP或RTCP RR包信息，那么就任务这个客户端失联了，并把这个客户端相关的资源全部回收。

RTSPServer::RTSPServer(UsageEnvironment& env,
		       int ourSocketIPv4, int ourSocketIPv6, Port ourPort,
		       UserAuthenticationDatabase* authDatabase,
		       unsigned reclamationSeconds)
  : GenericMediaServer(env, ourSocketIPv4, ourSocketIPv6, ourPort, reclamationSeconds),
    fHTTPServerSocketIPv4(-1), fHTTPServerSocketIPv6(-1), fHTTPServerPort(0),
    fClientConnectionsForHTTPTunneling(NULL), // will get created if needed
    fTCPStreamingDatabase(HashTable::create(ONE_WORD_HASH_KEYS)),
    fPendingRegisterOrDeregisterRequests(HashTable::create(ONE_WORD_HASH_KEYS)),
    fRegisterOrDeregisterRequestCounter(0), fAuthDB(authDatabase), fAllowStreamingRTPOverTCP(True) {
}

可以看到RTSPServer继承自GenericMediaServer，在构造RTSPServer时也对父类进行构造。

GenericMediaServer
::GenericMediaServer(UsageEnvironment& env, int ourSocketIPv4, int ourSocketIPv6, Port ourPort,
		     unsigned reclamationSeconds)
  : Medium(env),
    fServerSocketIPv4(ourSocketIPv4), fServerSocketIPv6(ourSocketIPv6),
    fServerPort(ourPort), fReclamationSeconds(reclamationSeconds),
    fServerMediaSessions(HashTable::create(STRING_HASH_KEYS)),
    fClientConnections(HashTable::create(ONE_WORD_HASH_KEYS)),
    fClientSessions(HashTable::create(STRING_HASH_KEYS)),
    fPreviousClientSessionId(0)
{
  ignoreSigPipeOnSocket(fServerSocketIPv4); // so that clients on the same host that are killed don't also kill us
  ignoreSigPipeOnSocket(fServerSocketIPv6); // ditto
  
  // Arrange to handle connections from others:
  env.taskScheduler().turnOnBackgroundReadHandling(fServerSocketIPv4, incomingConnectionHandlerIPv4, this);
  env.taskScheduler().turnOnBackgroundReadHandling(fServerSocketIPv6, incomingConnectionHandlerIPv6, this);
}

在构造GenericMediaServer时，把刚刚创建的TCP socket加入到后台IO读任务中。当有客户端连接时，就会触发incomingConnectionHandlerIPv4函数。

void GenericMediaServer::incomingConnectionHandlerOnSocket(int serverSocket) {
  struct sockaddr_storage clientAddr;
  SOCKLEN_T clientAddrLen = sizeof clientAddr;
  int clientSocket = accept(serverSocket, (struct sockaddr*)&clientAddr, &clientAddrLen);
  if (clientSocket < 0) {
    int err = envir().getErrno();
    if (err != EWOULDBLOCK) {
      envir().setResultErrMsg("accept() failed: ");
    }
    return;
  }
  ignoreSigPipeOnSocket(clientSocket); // so that clients on the same host that are killed don't also kill us
  makeSocketNonBlocking(clientSocket);
  increaseSendBufferTo(envir(), clientSocket, 50*1024);
  
#ifdef DEBUG
  envir() << "accept()ed connection from " << AddressString(clientAddr).val() << "\n";
#endif
  
  // Create a new object for handling this connection:
  (void)createNewClientConnection(clientSocket, clientAddr);
}

在incomingConnectionHandlerOnSocket函数中，首先accept与客户端建立连接。然后创建了一个客户端连接的对象。
createNewClientConnection是一个纯虚函数，由于实际对象的类型是RTSPServer，所以调用RTSPServer的createNewClientConnection。

三、RTSPClientConnection

GenericMediaServer::ClientConnection*
RTSPServer::createNewClientConnection(int clientSocket, struct sockaddr_storage const& clientAddr) {
  return new RTSPClientConnection(*this, clientSocket, clientAddr);
}
...
...
RTSPServer::RTSPClientConnection
::RTSPClientConnection(RTSPServer& ourServer, int clientSocket, struct sockaddr_storage const& clientAddr)
  : GenericMediaServer::ClientConnection(ourServer, clientSocket, clientAddr),
    fOurRTSPServer(ourServer), fClientInputSocket(fOurSocket), fClientOutputSocket(fOurSocket),
    fAddressFamily(clientAddr.ss_family),
    fIsActive(True), fRecursionCount(0), fOurSessionCookie(NULL), fScheduledDelayedTask(0) {
  resetRequestBuffer();
}

RTSPClientConnection继承自GenericMediaServer::ClientConnection，在构造时也会先构造父类。

GenericMediaServer::ClientConnection
::ClientConnection(GenericMediaServer& ourServer, int clientSocket, struct sockaddr_storage const& clientAddr)
  : fOurServer(ourServer), fOurSocket(clientSocket), fClientAddr(clientAddr) {
  // Add ourself to our 'client connections' table:
  fOurServer.fClientConnections->Add((char const*)this, this);
  
  // Arrange to handle incoming requests:
  resetRequestBuffer();
  envir().taskScheduler()
    .setBackgroundHandling(fOurSocket, SOCKET_READABLE|SOCKET_EXCEPTION, incomingRequestHandler, this);
}

构造GenericMediaServer::ClientConnection时，将连接的socket加入到后台IO可读和异常任务队列中。
当有客户端数据到来时，会触发incomingRequestHandler函数。

void GenericMediaServer::ClientConnection::incomingRequestHandler() {
  struct sockaddr_storage dummy; // 'from' address, meaningless in this case
  
  int bytesRead = readSocket(envir(), fOurSocket, &fRequestBuffer[fRequestBytesAlreadySeen], fRequestBufferBytesLeft, dummy);
  handleRequestBytes(bytesRead);
}

incomingRequestHandler函数将数据读取到fRequestBuffer中，并执行handleRequestBytes。
handleRequestBytes也是个虚函数，所以执行的是RTSPClientConnection::handleRequestBytes。

Boolean parseSucceeded = parseRTSPRequestString((char*)fRequestBuffer, fLastCRLF+2 - fRequestBuffer,
						    cmdName, sizeof cmdName,
						    urlPreSuffix, sizeof urlPreSuffix,
						    urlSuffix, sizeof urlSuffix,
						    cseq, sizeof cseq,
						    sessionIdStr, sizeof sessionIdStr,
						    contentLength);
...
...
handleCmd_OPTIONS();
...
handleCmd_GET_PARAMETER((char const*)fRequestBuffer);
...
handleCmd_SET_PARAMETER((char const*)fRequestBuffer);
...
handleCmd_DESCRIBE(urlPreSuffix, urlSuffix, (char const*)fRequestBuffer);
...
clientSession->handleCmd_SETUP(this, urlPreSuffix, urlSuffix, (char const*)fRequestBuffer);
...
handleCmd_PLAY(ourClientConnection, subsession, fullRequestStr);

在handleRequestBytes中，先是对收到的数据进行解析，解析出本次通信是哪个命令，然后根据命令类型分别进行处理。