学习live555的点点滴滴（一）

1.让系统自动分配可用端口给socket

看到live555有一段关于socket 端口判断的代码：

RTSPServer.cpp -- setUpOurSocket中的一个调用：

if (ourPort.num() == 0) { // bind() will have chosen a port for us; return it also: if (!getSourcePort(env, ourSocket, ourPort)) break; }

getSourcePort的具体实现在GroupsockHelper.cpp中，如下：

 

static Boolean getSourcePort0(int socket, portNumBits& resultPortNum/*host order*/) { sockaddr_in test; test.sin_port = 0; SOCKLEN_T len = sizeof test; if (getsockname(socket, (struct sockaddr*)&test, &len) < 0) return False; resultPortNum = ntohs(test.sin_port); return True;}Boolean getSourcePort(UsageEnvironment& env, int socket, Port& port) { portNumBits portNum = 0; if (!getSourcePort0(socket, portNum) || portNum == 0) { // Hack - call bind(), then try again: MAKE_SOCKADDR_IN(name, INADDR_ANY, 0); bind(socket, (struct sockaddr*)&name, sizeof name); if (!getSourcePort0(socket, portNum) || portNum == 0) { socketErr(env, "getsockname() error: "); return False; } } port = Port(portNum); return True;}

 

认真实践了下，原来是当端口号为0的时候就让系统自动分配一个端口给socket。

实验代码如下：

#include "stdafx.h"#include <WinSock2.h>#pragma comment(lib, "wsock32.lib")int _tmain(int argc, _TCHAR* argv[]){WORD wVersionRequested;WSADATA wsaData;int err;wVersionRequested = MAKEWORD( 2, 2 );err = WSAStartup( wVersionRequested, &wsaData ); //初始化if ( err != 0 ) {/* Tell the user that we could not find a usable *//* WinSock DLL.*/printf("init error./n");return 1;}SOCKET socketf;int port1, len;socketf = socket(AF_INET, SOCK_STREAM, 0); //创建一个socketstruct sockaddr_in test;test.sin_family = AF_INET;test.sin_addr.s_addr = htonl(INADDR_ANY);test.sin_port = 0; //这里一定要置0，在绑定中系统才会自动分配可用端口给socketlen = sizeof test;bind(socketf, (struct sockaddr *)&test, sizeof test); //绑定socket与地址getsockname(socketf, (struct sockaddr *) &test, &len); //获取系统分配的端口号port1 = ntohs(test.sin_port);printf("new port = %d./n", port1);closesocket(socketf);getchar();return 0;}

感觉比较有用就记录下来了。