[网络协议]live555源码分析（二）Groupsock

　　Groupsock内部封装了udp套接字，用来实现组播消息群发。

　　Groupsock在其父类构造函数中，执行setupDatagramSocket函数初始化，创建套接字并绑定端口：

Socket::Socket(UsageEnvironment& env, Port port, int family)
  : fEnv(DefaultUsageEnvironment != NULL ? *DefaultUsageEnvironment : env),
    fPort(port), fFamily(family) {
  fSocketNum = setupDatagramSocket(fEnv, port, family);
}

int setupDatagramSocket(UsageEnvironment& env, Port port, int domain) {
  ……
  int newSocket = createSocket(domain, SOCK_DGRAM);
  ……
  if (domain == AF_INET) {
    // Note: Windoze requires binding, even if the port number is 0
    ipv4AddressBits addr = INADDR_ANY;
    if (port.num() != 0 || ReceivingInterfaceAddr != INADDR_ANY) {
      if (port.num() == 0) addr = ReceivingInterfaceAddr;

      MAKE_SOCKADDR_IN(name, addr, port.num());
      if (bind(newSocket, (struct sockaddr*)&name, sizeof name) != 0) {
	    char tmpBuffer[100]

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