c - Socket C 同时处理 recv() 和 send()

Question

我正在开发客户端和服务器之间的 TCP 握手。具体在客户端向服务器发送消息，服务器分析消息并提供答案。问题是，当服务器必须发回消息时，似乎出现了一些问题，即客户端和服务器被阻塞。

这是我的代码客户端:

    if (connect(sock, (struct sockaddr *) &server_addr, sizeof(struct sockaddr))
        == -1) {
    perror("Connect");
    exit(1);
}
char recv_data[2048];
first_message(user, mode, sock);
    do {
        bytes_recieved = recv(sock, recv_data, 1024, 0);
        if (bytes_recieved == -1) {
            printf("Error");
            exit(1);
        }
        printf("BYTE RECEIVED: %d\n", bytes_recieved);
    } while (bytes_recieved != 0);
    recv_data[bytes_recieved] = '\0';
    printf("%s", recv_data);

服务器端:

    sin_size = sizeof(struct sockaddr_in);

    connected = accept(sock, (struct sockaddr *) &client_addr, &sin_size);

    printf("\n I got a connection from (%s , %d)",
            inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
    char recv_data[2048];
    do {
        res = length_true - total;
        bytes_recieved = recv(connected, recv_data + total, res, 0);
        if (bytes_recieved == -1) {
            printf("Recv() failed\n");
            break;
        }
        if (bytes_recieved > 0) {
            total += bytes_recieved;
        }
    } while (bytes_recieved != 0);
    int size_rcv = total;
    recv_data[length_true - 1] = '\0';
    int b = 0;
    printf("DATA RECEIVED:%s\n", recv_data);
    send(connected,r,strlen(r),0);
    fflush(stdout);
    close (sock);
    exit(1);
    pause();
    return 0;

编辑:

void common_frame(int sock, char *mode) {

    const char *string_course = "DISTRIB2016";
    char *buf = (char*) malloc(22 * sizeof(char));
    char *buf_first = (char*) malloc(2 * sizeof(char));
    gethexes(buf_first, mode); //1 byte di modalità
    gethexes(buf, string_course); //11 byte lunghezza del corso stringa
    send(sock, buf, 22, 0);
    send(sock, buf_first, 2, 0);
    free(buf_first);
    free(buf);
}

void first_command(int sock, char* user) {
    char *frame = "T1";
    char *buf_second = (char*) malloc(4 * sizeof(char));
    char *username_length = (char*) malloc(sizeof(char));
    int user_len = strlen(user);
    char *us = (char*) malloc(user_len *2 * (sizeof(char)));
    gethexes(us, user);
    gethexes(buf_second, frame); //2 byte of first command label T1
    sprintf(username_length, "%d", user_len);
    send(sock, buf_second, 4, 0);
    send(sock, username_length, strlen(username_length), 0); //n byte username length
    send(sock, us, strlen(us), 0); //username
    free(username_length);
    free(buf_second);

}

void first_message(char *user, char*mode, int sock) {
    unsigned short int message_length;
    char *length;
    int user_len;
    message_length = htons(17 + strlen(user));
    length = decimal_to_binary(message_length); //2 byte di lunghezza binaria in network order
    send(sock, length, strlen(length), 0);
    common_frame(sock, mode);
    first_command(sock, user);
}

在这个实现中，客户端和服务器都停止了，服务器无法接收任何消息，但是如果我神奇地停止客户端，服务器就会正常工作，它会正确地接收和发送数据。

Answer 1

如注释中所述，您的服务器在 recv() 返回零或 -1 之前不执行任何操作，这分别意味着客户端已断开连接或中止连接。由于您的客户端没有执行任何这些操作，因此您会遇到应用程序引发的死锁。