网络编程读写与连接超时实现-优快云博客

本文链接：https://blog.youkuaiyun.com/dashoumeixi/article/details/85111109

本文详细介绍了在网络编程中如何实现可靠的数据读写操作，包括自定义的readn和writen函数，确保数据能完全发送和接收。同时，深入探讨了如何设置连接超时，使用fcntl和select系统调用结合实现连接状态的非阻塞检查，避免长时间等待无效连接，提高程序的健壮性和效率。

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略

#define SA struct sockaddr
ssize_t readn(int fd , void *ptr, size_t n)
{
    size_t left = n;
    char * p = (char *)ptr;
    int nread = 0;
    while (left > 0){
        if((nread = read(fd,p,left)) < 0){
                if(errno == EINTR)
                    nread = 0;
                else
                    return -1;
        }
        else if(nread == 0)
            break;
        left -= nread;
        p += nread;
    }
    return n - left;
}
ssize_t writen(int fd , void * ptr , size_t n)
{
    size_t left = n;
    char * p = (char*)ptr;
    int nwrite = 0;
    while( left > 0){
        if((nwrite = write(fd,p,left)) <= 0){
            if(errno == EINTR && nwrite < 0)
                nwrite = 0;
            else
                return -1;
        }
        left -= nwrite;
        p += nwrite;
    }
    return n - left;
}


int conn_timeout(int sockfd , const struct sockaddr_in * sin, socklen_t socklen, int secs)
{
    int old_flag = fcntl(sockfd,F_GETFL,0);
    if( fcntl(sockfd,F_SETFL,old_flag|O_NONBLOCK) < 0){
        perror("fcntl failed");
        return -1;
    }

    int ret = 0;
    if((ret = connect(sockfd,(SA*)&sin,socklen)) < 0){
        if(errno != EINPROGRESS){
            perror("connect error");
            return -1;
        }
    }
    if(0 == ret)
        goto done;

    fd_set rset,wset;
    FD_ZERO(&rset);
    FD_SET(sockfd,&rset);
    wset = rset;
    struct timeval timeout;
    timeout.tv_sec= secs;
    timeout.tv_usec = 0;
    ret = select(sockfd+1,&rset,&wset,NULL,secs?&timeout:NULL);
    if(ret < 0){
        perror("select error");
        return -1;
    }
    else if( 0 == ret){
        close(sockfd);
        return -1;
    }
    if(!(FD_ISSET(sockfd,&rset) || FD_ISSET(sockfd,&wset))){
        return -1;
    }
    done:
    fcntl(sockfd,F_SETFL,old_flag);
    return 0;
}