前面几篇文章分析了 live555 中 RTSP 的处理逻辑，RTSP 处理有关组件的处理逻辑有点复杂，本文就再来梳理一下它们之间的关系。

live555 中 RTSP 处理有关组件关系如下图：

事件和执行流程的源头在 TaskScheduler。GenericMediaServer 对象在创建的时候，会向 TaskScheduler 注册一个 server socket 及处理该 socket 上的事件的处理程序 GenericMediaServer::incomingConnectionHandler(void* instance, int /*mask*/)。

当有客户端连接服务器时，触发 server socket 上的事件处理器执行。此时会基于客户端 socket 创建 ClientConnection 对象，及 RTSPClientConnection。 RTSPClientConnection 对象在创建过程中，会将该客户端 socket 及
ClientConnection 中处理该 socket 上的事件的处理程序 GenericMediaServer::ClientConnection::incomingRequestHandler(void* instance, int /*mask*/) 注册给 TaskScheduler。

在客户端发送的 RTSP 请求数据到达之后，GenericMediaServer::ClientConnection 会读取这些数据，并交给 RTSPServer::RTSPClientConnection::handleRequestBytes(int newBytesRead) 处理。

RTSPServer::RTSPClientConnection 解析 RTSP 请求，并处理 OPTIONS、DESCRIBE 和 “SETUP 等无需流媒体会话建立即可处理的请求。

RTSPServer::RTSPClientConnection 在处理 SETUP 请求时，会创建流媒体会话的 RTSPServer::RTSPClientSession，具体的会话建立过程都会被委托给后者处理。

需要会话建立之后才能处理的请求，也会被交给 RTSPServer::RTSPClientSession 处理。

这里来看一下 RTSPServer::RTSPClientConnection 的完整定义：

class RTSPServer: public GenericMediaServer {
. . . . . .
public: // should be protected, but some old compilers complain otherwise// The state of a TCP connection used by a RTSP client:class RTSPClientSession; // forwardclass RTSPClientConnection: public GenericMediaServer::ClientConnection {public:// A data structure that's used to implement the "REGISTER" command:class ParamsForREGISTER {public:ParamsForREGISTER(char const* cmd/*"REGISTER" or "DEREGISTER"*/,RTSPClientConnection* ourConnection, char const* url, char const* urlSuffix,Boolean reuseConnection, Boolean deliverViaTCP, char const* proxyURLSuffix);virtual ~ParamsForREGISTER();private:friend class RTSPClientConnection;char const* fCmd;RTSPClientConnection* fOurConnection;char* fURL;char* fURLSuffix;Boolean fReuseConnection, fDeliverViaTCP;char* fProxyURLSuffix;};protected: // redefined virtual functions:virtual void handleRequestBytes(int newBytesRead);protected:RTSPClientConnection(RTSPServer& ourServer, int clientSocket, struct sockaddr_in clientAddr);virtual ~RTSPClientConnection();friend class RTSPServer;friend class RTSPClientSession;// Make the handler functions for each command virtual, to allow subclasses to reimplement them, if necessary:virtual void handleCmd_OPTIONS();// You probably won't need to subclass/reimplement this function; reimplement "RTSPServer::allowedCommandNames()" instead.virtual void handleCmd_GET_PARAMETER(char const* fullRequestStr); // when operating on the entire servervirtual void handleCmd_SET_PARAMETER(char const* fullRequestStr); // when operating on the entire servervirtual void handleCmd_DESCRIBE(char const* urlPreSuffix, char const* urlSuffix, char const* fullRequestStr);virtual void handleCmd_REGISTER(char const* cmd/*"REGISTER" or "DEREGISTER"*/,char const* url, char const* urlSuffix, char const* fullRequestStr,Boolean reuseConnection, Boolean deliverViaTCP, char const* proxyURLSuffix);// You probably won't need to subclass/reimplement this function;//     reimplement "RTSPServer::weImplementREGISTER()" and "RTSPServer::implementCmd_REGISTER()" instead.virtual void handleCmd_bad();virtual void handleCmd_notSupported();virtual void handleCmd_notFound();virtual void handleCmd_sessionNotFound();virtual void handleCmd_unsupportedTransport();// Support for optional RTSP-over-HTTP tunneling:virtual Boolean parseHTTPRequestString(char* resultCmdName, unsigned resultCmdNameMaxSize,char* urlSuffix, unsigned urlSuffixMaxSize,char* sessionCookie, unsigned sessionCookieMaxSize,char* acceptStr, unsigned acceptStrMaxSize);virtual void handleHTTPCmd_notSupported();virtual void handleHTTPCmd_notFound();virtual void handleHTTPCmd_OPTIONS();virtual void handleHTTPCmd_TunnelingGET(char const* sessionCookie);virtual Boolean handleHTTPCmd_TunnelingPOST(char const* sessionCookie, unsigned char const* extraData, unsigned extraDataSize);virtual void handleHTTPCmd_StreamingGET(char const* urlSuffix, char const* fullRequestStr);protected:void resetRequestBuffer();void closeSocketsRTSP();static void handleAlternativeRequestByte(void*, u_int8_t requestByte);void handleAlternativeRequestByte1(u_int8_t requestByte);Boolean authenticationOK(char const* cmdName, char const* urlSuffix, char const* fullRequestStr);void changeClientInputSocket(int newSocketNum, unsigned char const* extraData, unsigned extraDataSize);// used to implement RTSP-over-HTTP tunnelingstatic void continueHandlingREGISTER(ParamsForREGISTER* params);virtual void continueHandlingREGISTER1(ParamsForREGISTER* params);// Shortcuts for setting up a RTSP response (prior to sending it):void setRTSPResponse(char const* responseStr);void setRTSPResponse(char const* responseStr, u_int32_t sessionId);void setRTSPResponse(char const* responseStr, char const* contentStr);void setRTSPResponse(char const* responseStr, u_int32_t sessionId, char const* contentStr);RTSPServer& fOurRTSPServer; // same as ::fOurServerint& fClientInputSocket; // aliased to ::fOurSocketint fClientOutputSocket;Boolean fIsActive;unsigned char* fLastCRLF;unsigned fRecursionCount;char const* fCurrentCSeq;Authenticator fCurrentAuthenticator; // used if access control is neededchar* fOurSessionCookie; // used for optional RTSP-over-HTTP tunnelingunsigned fBase64RemainderCount; // used for optional RTSP-over-HTTP tunneling (possible values: 0,1,2,3)};

RTSPServer::RTSPClientConnection 继承自 GenericMediaServer::ClientConnection：

class GenericMediaServer: public Medium {
. . . . . .
public: // should be protected, but some old compilers complain otherwise// The state of a TCP connection used by a client:class ClientConnection {protected:ClientConnection(GenericMediaServer& ourServer, int clientSocket, struct sockaddr_in clientAddr);virtual ~ClientConnection();UsageEnvironment& envir() { return fOurServer.envir(); }void closeSockets();static void incomingRequestHandler(void*, int /*mask*/);void incomingRequestHandler();virtual void handleRequestBytes(int newBytesRead) = 0;void resetRequestBuffer();protected:friend class GenericMediaServer;friend class ClientSession;friend class RTSPServer; // needed to make some broken Windows compilers work; remove this in the future when we end support for WindowsGenericMediaServer& fOurServer;int fOurSocket;struct sockaddr_in fClientAddr;unsigned char fRequestBuffer[REQUEST_BUFFER_SIZE];unsigned char fResponseBuffer[RESPONSE_BUFFER_SIZE];unsigned fRequestBytesAlreadySeen, fRequestBufferBytesLeft;};

从它们的定义，不难理解它们的职责主要在于处理网络 I/O，处理 RTSP 请求，并建立会话。

再来看 RTSPServer::RTSPClientSession 的定义：

class RTSPServer: public GenericMediaServer {
. . . . . .// The state of an individual client session (using one or more sequential TCP connections) handled by a RTSP server:class RTSPClientSession: public GenericMediaServer::ClientSession {protected:RTSPClientSession(RTSPServer& ourServer, u_int32_t sessionId);virtual ~RTSPClientSession();friend class RTSPServer;friend class RTSPClientConnection;// Make the handler functions for each command virtual, to allow subclasses to redefine them:virtual void handleCmd_SETUP(RTSPClientConnection* ourClientConnection,char const* urlPreSuffix, char const* urlSuffix, char const* fullRequestStr);virtual void handleCmd_withinSession(RTSPClientConnection* ourClientConnection,char const* cmdName,char const* urlPreSuffix, char const* urlSuffix,char const* fullRequestStr);virtual void handleCmd_TEARDOWN(RTSPClientConnection* ourClientConnection,ServerMediaSubsession* subsession);virtual void handleCmd_PLAY(RTSPClientConnection* ourClientConnection,ServerMediaSubsession* subsession, char const* fullRequestStr);virtual void handleCmd_PAUSE(RTSPClientConnection* ourClientConnection,ServerMediaSubsession* subsession);virtual void handleCmd_GET_PARAMETER(RTSPClientConnection* ourClientConnection,ServerMediaSubsession* subsession, char const* fullRequestStr);virtual void handleCmd_SET_PARAMETER(RTSPClientConnection* ourClientConnection,ServerMediaSubsession* subsession, char const* fullRequestStr);protected:void deleteStreamByTrack(unsigned trackNum);void reclaimStreamStates();Boolean isMulticast() const { return fIsMulticast; }// Shortcuts for setting up a RTSP response (prior to sending it):void setRTSPResponse(RTSPClientConnection* ourClientConnection, char const* responseStr) { ourClientConnection->setRTSPResponse(responseStr); }void setRTSPResponse(RTSPClientConnection* ourClientConnection, char const* responseStr, u_int32_t sessionId) { ourClientConnection->setRTSPResponse(responseStr, sessionId); }void setRTSPResponse(RTSPClientConnection* ourClientConnection, char const* responseStr, char const* contentStr) { ourClientConnection->setRTSPResponse(responseStr, contentStr); }void setRTSPResponse(RTSPClientConnection* ourClientConnection, char const* responseStr, u_int32_t sessionId, char const* contentStr) { ourClientConnection->setRTSPResponse(responseStr, sessionId, contentStr); }protected:RTSPServer& fOurRTSPServer; // same as ::fOurServerBoolean fIsMulticast, fStreamAfterSETUP;unsigned char fTCPStreamIdCount; // used for (optional) RTP/TCPBoolean usesTCPTransport() const { return fTCPStreamIdCount > 0; }unsigned fNumStreamStates;struct streamState {ServerMediaSubsession* subsession;int tcpSocketNum;void* streamToken;} * fStreamStates;};

RTSPServer::RTSPClientSession 继承自 GenericMediaServer::ClientSession：

  // The state of an individual client session (using one or more sequential TCP connections) handled by a server:class ClientSession {protected:ClientSession(GenericMediaServer& ourServer, u_int32_t sessionId);virtual ~ClientSession();UsageEnvironment& envir() { return fOurServer.envir(); }void noteLiveness();static void noteClientLiveness(ClientSession* clientSession);static void livenessTimeoutTask(ClientSession* clientSession);protected:friend class GenericMediaServer;friend class ClientConnection;GenericMediaServer& fOurServer;u_int32_t fOurSessionId;ServerMediaSession* fOurServerMediaSession;TaskToken fLivenessCheckTask;};

不难理解 RTSPServer::RTSPClientSession 用于封装整个流媒体会话，处理那些要求流媒体会话已经建立的 RTSP 请求，如 PLAY 等。

具体的流媒体数据的交互，如音视频文件/数据的解析，RTP/RTCP 数据的打包及收发等，则依赖于 ServerMediaSession 和 ServerMediaSubsession。

Done。

live555 源码分析系列文章

live555 源码分析：简介
live555 源码分析：基础设施
live555 源码分析：MediaSever
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live555 源码分析：RTSPServer
live555 源码分析：DESCRIBE 的处理
live555 源码分析：SETUP 的处理
live555 源码分析：PLAY 的处理
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