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

Posted 2020-10-02 阿汤的博客

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