Linux-根据IP创建Socket_ip socket建立-优快云博客

本文链接：https://blog.youkuaiyun.com/menghaocheng/article/details/79756817

本文介绍如何根据IP地址创建Socket连接，并实现非阻塞式的连接等待。通过使用C语言的网络编程接口，文中提供了详细的代码示例，展示了如何设置Socket选项以优化数据传输，并使用select机制监控连接状态。

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根据IP创建Socket

#include <sys/socket.h>
#include <netinet/tcp.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <sys/select.h>
#include <sys/time.h>
#include <errno.h>
#include <netdb.h>

#define LOGD printf
#define LOGI printf
#define LOGE printf

int just_sock_connect_ip(const char* ip, int port)
{
    int reval = 0;
    struct sockaddr_in servaddr;

    int sockfd;
    int on = 1;
    int flags  = 0;
    struct timeval timev = {45, 0};

    if (ip == NULL) return -EINVAL;
    
    LOGI("just_sock_connect_ip(%s:%d)", ip, port);
    
    sockfd = socket(AF_INET,SOCK_STREAM,0);
    if(sockfd == -1)
    {
        LOGI("socket create failed, reval=%d", sockfd);
        return -EFAULT;
    }

    //设置sock快速收发，防止粘包
    setsockopt(sockfd, IPPROTO_TCP, TCP_NODELAY,&on,sizeof(on));        
    setsockopt(sockfd, SOL_SOCKET, SO_SNDTIMEO,&timev,sizeof(timev));  

    //设置非阻塞
    //flags = fcntl(sockfd, F_GETFL, 0);
    //fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

    LOGI("socket create success, fd =%d", sockfd);

    memset((void*)&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(port);
    servaddr.sin_addr.s_addr = inet_addr(ip);

    reval = connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
    if (reval == 0) return sockfd;
    
    switch(errno)
    {
        case EISCONN:
            reval = 0;
            break;
        case EINPROGRESS:
        case EALREADY:
            reval = socket_wait_writable(sockfd, JUST_SOCK_DEFAULT_TIMEOUT);
            break;
        default:
            reval = -EFAULT;
            break;
    }
    if (reval < 0)
    {
        LOGE("connect [%s:%d] failed, reval=%d", ip, port, reval);
        close(sockfd);
        return reval;
    }
    LOGI("connect [%s:%d] Success!", ip, port);

    return sockfd;
}

当connect返回负值但errno=EINPROGRESS/EALREADY时表示“正在处理中”，可用select机制来监控可写性，socket一旦可写就说明连接成功了：

static int socket_wait_writable(int sockfd, int timeout_ms)
{
    struct timeval tpstart,tpend,timeout_v;
    fd_set wset, eset;
    long time_used = 0;
    int reval = 0;

    LOGI("socket_wait(sockfd=%d,timeout_ms=%d)", sockfd, timeout_ms);

    gettimeofday(&tpstart,NULL);

    while(1)
    {
        gettimeofday(&tpend,NULL);
        time_used=1000*(tpend.tv_sec-tpstart.tv_sec);
        time_used += (tpend.tv_usec-tpstart.tv_usec)/1000;
        if (time_used > timeout_ms)
        {
            LOGI("write timeout1 [%d ms]", timeout_ms);
            return -ETIME;
        }
        long time_seft = timeout_ms - time_used;
        timeout_v.tv_sec = time_seft/1000;
        timeout_v.tv_usec = time_seft%1000 * 1000;

        FD_ZERO(&wset);
        FD_ZERO(&eset);
        FD_SET(sockfd, &wset);
        FD_SET(sockfd, &eset);
        reval = select(sockfd + 1, NULL, &wset, &eset , &timeout_v);
        if(reval == -1 && errno != EINTR)
        {
            LOGE("error in socket_wait 1:%s", strerror(errno));
            return -EFAULT;
        }
        else if( reval == 0)
        {
            LOGI("write timeout2 [%d ms]", JUST_SOCK_DEFAULT_TIMEOUT);
            return -ETIME;
        }
        else if(reval > 0 && FD_ISSET(sockfd, &eset))
        {
            LOGE("error in socket_wait 2:%s", strerror(errno));
            return -EFAULT;
        }
        else if ( reval > 0 && FD_ISSET(sockfd, &wset))
        {
            //write event:
            LOGI("socket[%d] writable ...", sockfd);
            break;
        }
        else
        {
            LOGE("unexpected err in socket_wait");
        }
    }
    return 0;
}

【测试用例】

void just_sock_connect_test(void)
{
    int reval = 0;
    int fd = -1;

    char *this_ip = "111.13.101.208";
    
    fd = just_sock_connect_ip(this_ip, 80);
    if (fd < 0)
    {
        LOGE("just_sock_connect_ip failed, reval = %d", fd);
        return;
    }
    LOGE("just_sock_connect_ip success");
}