Question

我有一个非常简单的TCP客户端，如下所示。问题是，即使另一方没有服务器，connect()调用也总是返回0。

int TcpSend(struct sockaddr_in* ipv4_client, const void* buffer, size_t size) {

    int sd_client = 0;
    int status = -1;

    // Grab an ipv4 TCP socket.
    sd_client = socket(AF_INET, SOCK_STREAM, 0);
    if (sd_client == -1) {
        return -1;
    }

    // Make the socket non-blocking so that connect may fail immediately
    status = fcntl(sd_client, F_SETFL, O_NONBLOCK);
    if (status < 0) {
        close(sd_client);
        return -1;
    }

    // Bind and connect
    status = connect(sd_client, (struct sockaddr*)ipv4_client, sizeof(*ipv4_client));
    if (status == -1) {
        close(sd_client);
        return -1;
    }

    printf("Status: %d %s\n", status, strerror(errno)); //// ??? : I always get status = 0 here

    // Send a message to the server PORT on machine HOST.
    // Ignore the fact that send might not have sent the complete data
    status = send(sd_client, buffer, size, 0);  //// Consequently I get a SIGPIPE here
    if (status == -1) {
        close(sd_client);
        return -1;
    }

    close(sd_client);

    return 0;
}

我知道如果绑定成功并且连接没有发生，connect()将会通过。但是，当套接字O_NONBLOCK时，它不应该发生。该代码始终在connect()处传递，SIGPIPE内出现send()错误。

Answer 1

在非阻塞模式下连接后，你需要在可写集合中调用带有套接字FD的select（），即等到它变为可写，然后（1）通过{{1}检查套接字上的错误}或（2）再次调用connect（）并检查错误。只有这样才能开始调用getsockopt(),或send()

Answer 2

问题是ipv4_client->sin_family不知何故为0。

执行以下操作可以解决问题。

ipv4_client->sin_family = AF_INET;

TCP connect（）总是通过

2 个答案: