客户端相同的套接字描述符

Question

我有一个服务器-客户端系统(并发服务器)。我在不同的机器上有不同的客户。我正在尝试向特定客户发送通知。但是，我遇到了一个问题，因为客户端都具有相同的套接字描述符。在两台计算机上，客户端的套接字描述符为 3，在服务器上的 sd 为 5。有人能告诉我如何识别这些不同的客户端以及为什么会这样吗？

int main(int argc, char *argv[]) {
    pid_t pid;
    int buff_size = 1024;
    char buff[buff_size];
    int listen_fd, client_conn;
    struct sockaddr_in serv_addr;
    int server_port = 5001;
    char remote_file[255];

    listen_fd = socket(AF_INET, SOCK_STREAM, 0);

    if (listen_fd < 0) {
        perror("Socket cannot be opened");
        exit(1);
    }

    /*Turning off address checking in order to allow port numbers to be
      reused before the TIME_WAIT. Otherwise it will not be possible to bind
      in a very short time after the server has been shut down*/
    int on = 1;
    int status = setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR,
                            (const char *) &on, sizeof(on));

    if (status == -1) {
        perror("Failed to Reuse Address on Binding");
    }

    // Initialise socket structure
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY; // Accept connections from any address
    serv_addr.sin_port = htons(server_port);

    // Bind the host address
    if (bind(listen_fd, (struct sockaddr *) &serv_addr, sizeof(serv_addr))
        < 0) {
        perror("ERROR on binding");
        exit(1);
    }

    // Start listening for the clients, here process will
    // go in sleep mode and will wait for the incoming connection
    listen(listen_fd, 5);

    while (1) {
        //Accepting client connection
        client_conn = accept(listen_fd, (struct sockaddr *) NULL, NULL);

        if (client_conn < 0) {
            perror("Client was not accepted...");
            exit(1);
        }

        if ((pid = fork()) == 0) {
            close(listen_fd);
            bzero(buff, buff_size);

            while ((bytes_read = read(client_conn, buff, buff_size)) > 0) {

                fclose(file);
            }

        }

        //Terminating child process and closing socket
        close(client_conn);
        exit(0);

        bzero(buff, buff_size);

    }

    //parent process closing socket connection
    close(client_conn);
}

return 0;
}

Answer 1

在服务器派生一个 child 之后，它会执行close(client_conn)。当 accept 为新连接分配套接字描述符时，它使用最低的关闭描述符。由于您之前关闭了套接字，它可以用于下一个进来的客户端。

这不是问题，因为连接由子进程管理。它们每个都有自己的描述符5，并且它们不会相互干扰。