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前言

socketpair是Linux下的函数,其主要作用是创建一对套节字来进行进程间通信,其与匿名管道(PIPE)的作用相似,这两个套节字均可读可写. 具体介绍见本博客另一篇文章: https://blog.csdn.net/wufuhuai/article/details/79747912

实现

我们都知道socket不仅能够进行跨进程通信, 而且socket是可以双向通信的, 即是可读可写的; 故本文主要设计思想是创建两个回环的socket进行进程间通信, 即创建两个socket进行本机跟本机间通信.

#include <stdlib.h>
#include <stdio.h>
#include <WS2tcpip.h>

#pragma comment(lib,"ws2_32.lib")

static int __stream_socketpair(struct addrinfo* addr_info, SOCKET sock[2]){
    SOCKET listener, client, server;
    int opt = 1;

    listener = server = client = INVALID_SOCKET;
    listener = socket(addr_info->ai_family, addr_info->ai_socktype, addr_info->ai_protocol); //创建服务器socket并进行绑定监听等
    if (INVALID_SOCKET == listener)
        goto fail;

    setsockopt(listener, SOL_SOCKET, SO_REUSEADDR,(const char*)&opt, sizeof(opt));

    if(SOCKET_ERROR == bind(listener, addr_info->ai_addr, addr_info->ai_addrlen))
        goto fail;

    if (SOCKET_ERROR == getsockname(listener, addr_info->ai_addr, (int*)&addr_info->ai_addrlen))
        goto fail;

    if(SOCKET_ERROR == listen(listener, 5))
        goto fail;

    client = socket(addr_info->ai_family, addr_info->ai_socktype, addr_info->ai_protocol); //创建客户端socket，并连接服务器

    if (INVALID_SOCKET == client)
        goto fail;

    if (SOCKET_ERROR == connect(client,addr_info->ai_addr,addr_info->ai_addrlen))
        goto fail;

    server = accept(listener, 0, 0);

    if (INVALID_SOCKET == server)
        goto fail;

    closesocket(listener);

    sock[0] = client;
    sock[1] = server;

    return 0;
fail:
    if(INVALID_SOCKET!=listener)
        closesocket(listener);
    if (INVALID_SOCKET!=client)
        closesocket(client);
    return -1;
}

static int __dgram_socketpair(struct addrinfo* addr_info,SOCKET sock[2])
{
    SOCKET client, server;
    struct addrinfo addr, *result = NULL;
    const char* address;
    int opt = 1;

    server = client = INVALID_SOCKET;

    server = socket(addr_info->ai_family, addr_info->ai_socktype, addr_info->ai_protocol);  
    if (INVALID_SOCKET == server)
        goto fail;

    setsockopt(server, SOL_SOCKET,SO_REUSEADDR, (const char*)&opt, sizeof(opt));

    if(SOCKET_ERROR == bind(server, addr_info->ai_addr, addr_info->ai_addrlen))
        goto fail;

    if (SOCKET_ERROR == getsockname(server, addr_info->ai_addr, (int*)&addr_info->ai_addrlen))
        goto fail;

    client = socket(addr_info->ai_family, addr_info->ai_socktype, addr_info->ai_protocol); 
    if (INVALID_SOCKET == client)
        goto fail;

    memset(&addr,0,sizeof(addr));
    addr.ai_family = addr_info->ai_family;
    addr.ai_socktype = addr_info->ai_socktype;
    addr.ai_protocol = addr_info->ai_protocol;

    if (AF_INET6==addr.ai_family)
        address = "0:0:0:0:0:0:0:1";
    else
        address = "127.0.0.1";

    if (getaddrinfo(address, "0", &addr, &result))
        goto fail;

    setsockopt(client,SOL_SOCKET,SO_REUSEADDR,(const char*)&opt, sizeof(opt));
    if(SOCKET_ERROR == bind(client, result->ai_addr, result->ai_addrlen))
        goto fail;

    if (SOCKET_ERROR == getsockname(client, result->ai_addr, (int*)&result->ai_addrlen))
        goto fail;

    if (SOCKET_ERROR == connect(server, result->ai_addr, result->ai_addrlen))
        goto fail;

    if (SOCKET_ERROR == connect(client, addr_info->ai_addr, addr_info->ai_addrlen))
        goto fail;

    freeaddrinfo(result);
    sock[0] = client;
    sock[1] = server;
    return 0;

fail:
    if (INVALID_SOCKET!=client)
        closesocket(client);
    if (INVALID_SOCKET!=server)
        closesocket(server);
    if (result)
        freeaddrinfo(result);
    return -1;
}

int socketpair(int family, int type, int protocol,SOCKET recv[2]){
    const char* address;
    struct addrinfo addr_info,*p_addrinfo;
    int result = -1;

    memset(&addr_info, 0, sizeof(addr_info));
    addr_info.ai_family = family;
    addr_info.ai_socktype = type;
    addr_info.ai_protocol = protocol;
    if (AF_INET6==family)
        address = "0:0:0:0:0:0:0:1";
    else
        address = "127.0.0.1";

    if (0 == getaddrinfo(address, "0", &addr_info, &p_addrinfo)){
        if (SOCK_STREAM == type)
            result = __stream_socketpair(p_addrinfo, recv);   //use for tcp
        else if(SOCK_DGRAM == type)
            result = __dgram_socketpair(p_addrinfo, recv);    //use for udp
        freeaddrinfo(p_addrinfo);
    }
    return result;
}

int main ()
{
    int recv_pair[2];       /* A socket pair to unblock select, when needed */

    WSADATA wsaData;
    WORD socketVersion = MAKEWORD(2,0);
    if (WSAStartup(socketVersion, &wsaData) != 0)
    {
        printf("Init socket dll err");
    }

    if(socketpair(AF_INET, SOCK_STREAM, 0, recv_pair) < 0)
        printf("Error setting Socket pair...");

    WSACleanup();
    return 0;
}