利用 getsockname 和 getpeername 来获取某一个链接的本地地址和远端地址

在两台计算机上建立一个网络连接,需要五个要素:本机地址 本机端口 协议类型 远端端口 远端地址.那么如何从一个建立好的连接上获取这些信息呢.就需要用到

getsockname 和 getpeername 这两个函数.

但前提是要在建立好的连接上.

作为客户端,要在正确调用connect()之后,才能使用这两个函数

作为服务端,要在正确调用accept()之后,才能使用这两个函数

以下为测试代码, windows/linux 下均可编译运行.

#include <stdint.h>
#include <stdio.h>
#include <memory.h>

#ifdef WIN32
#include <windows.h>
typedef int32_t socklen_t;
#define close(x) closesocket(x)
#else
#include <errno.h>
#include <arpa/inet.h>
#include <unistd.h>
#define INVALID_SOCKET (-1)
typedef int32_t SOCKET;
#endif

int32_t Errno()
{
#ifdef WIN32
return WSAGetLastError();
#else
return errno;
#endif
}

void test_getname(SOCKET sock, const char *desc)
{
printf("%s\n", desc);
struct sockaddr_in addr;
socklen_t addr_len = sizeof(addr);
int32_t ret = getsockname(sock, (struct sockaddr *)&addr, &addr_len);
if(ret == 0)
{
printf("getsockname succ:%s:%d\n", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
}
else
{
printf("getsockname failed,error=%d\n", Errno());
}

memset(&addr, 0, sizeof(addr));
ret = getpeername(sock, (struct sockaddr *)&addr, &addr_len);
if(ret == 0)
{
printf("getpeername succ:%s:%d\n", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
}
else
{
printf("getpeername failed,error=%d\n", Errno());
}
}

void test_connect()
{
sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(5000);

SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
test_getname(sock, "before connect");

int32_t ret = connect(sock, (sockaddr*)&addr, sizeof(addr));
if(ret != 0)
{
printf("connect error, errno: %d\n", Errno());
return;
}
test_getname(sock, "after connect");
close(sock);
}

void test_accept()
{
SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if(INVALID_SOCKET == sock)
{
printf("create socket error,errno=%d\n", Errno());
return;
}

sockaddr_in srvAddr;
memset(&srvAddr, 0, sizeof(srvAddr));
srvAddr.sin_family = AF_INET;
srvAddr.sin_addr.s_addr = htonl(INADDR_ANY);
srvAddr.sin_port = htons(5000);

test_getname(sock, "before bind");
int32_t ret = bind(sock, (sockaddr*)&srvAddr, sizeof(srvAddr));
printf("bind:%s:%d\n", inet_ntoa(srvAddr.sin_addr), ntohs(srvAddr.sin_port));
test_getname(sock, "after bind");
if(ret != 0)
{
printf("bind listen socket error,errno=%d\n", Errno());
return;
}
ret = listen(sock, SOMAXCONN);
if(ret != 0)
{
return;
}
sockaddr_in cliAddr;
socklen_t cliAddrLen = sizeof(cliAddr);
SOCKET new_sock = accept(sock, (sockaddr*)&cliAddr, &cliAddrLen);
printf("accept:%s:%d\n", inet_ntoa(cliAddr.sin_addr), ntohs(cliAddr.sin_port));
test_getname(new_sock, "after accept");
close(sock);
close(new_sock);
}

int32_t main()
{
#ifdef WIN32
WSADATA wsaData;
WSAStartup(MAKEWORD(2, 2), &wsaData);
#endif
//test_connect();
test_accept();
#ifdef WIN32
WSACleanup();
#endif
getchar();
return 0;
}

测试结果:

connect:

before connect
getsockname failed,error=10022
getpeername failed,error=10057
after connect
getsockname succ:127.0.0.1:4618
getpeername succ:127.0.0.1:5000

accept:

before bind
getsockname failed,error=10022
getpeername failed,error=10057
bind:0.0.0.0:5000
after bind
getsockname succ:0.0.0.0:5000
getpeername failed,error=10057
accept:127.0.0.1:4630
after accept
getsockname succ:127.0.0.1:5000
getpeername succ:127.0.0.1:4630