c - 如果我想从客户端向服务器一一写入多个请求，该怎么办？

Question

例如，一个文件中有多个请求，我读取它们然后使用写入函数逐行发送到服务器。但是，服务器只有一个响应，我无法读取对服务器的整个请求。有谁可以帮我解决这个问题。非常感谢!

有服务器代码:

    <pre> <code>
    int main(int argc, char *argv[]){
    int sockfd, newsockfd, n;
    unsigned int clientLen;
    char bufferSK[256];
    struct sockaddr_in serv_addr,cli_addr;
    FILE *fp = NULL;

    //create an endpoint for bind, listen and accept.
    sockfd = socket(AF_INET,SOCK_STREAM,0);
    if (sockfd < 0) {
        printf("Failed to create socket for server!\n");
    }
    bzero((char *)&serv_addr, sizeof(serv_addr));

    //set the address of server.
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(port_number);

    //bind the port with server address
    if (bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        printf("Error on bind!\n");
    }
    listen(sockfd,port_number);
    printf("\nI am listening for connection\n");
    clientLen = sizeof(cli_addr);

    //using accept function to accept the connection from client
    newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &clientLen);
    if (newsockfd < 0) {
        printf("Error on accept!\n");
    }
    printf("\nI have accepted your connection\n");
    bzero(bufferSK,256);
    n = read (newsockfd, bufferSK,255);
    if (n < 0) {
        printf("Error reading message from socket\n");
    }

    printf("\nThe message from client is: %s",bufferSK);
    n = write(newsockfd, "SERVER: I got your message!\n", 27);
    if (n < 0) {
        printf("Error writing to socket\n");
    }
    close(newsockfd);
    close(sockfd);
    return 0;
}

有客户端代码:

<pre> <code>

    FILE *fp_queue;

    int main(int argc, char *argv[]){
    int sockfd, server_port_number, n, connectRes;
    struct sockaddr_in serv_addr;
    struct hostent *server;
    char buffer[256];

    //Three parameters must be provided.
    if(argc != 4){
        fprintf(stderr, "Usage: %s server_host_name server_port_number file_path\n",argv[0]);
        exit(0);
    }
    server_port_number = atoi(argv[2]);
    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    //create socket for client.
    if (sockfd < 0) {
        printf("Failed to create socket for client\n");
        exit(0);
    }

    server = gethostbyname(argv[1]);
    if (server == NULL) {
        printf("Oops! There is no such host!\n");
        exit(0);
    }

    //set the attributes of server as zeros.
    bzero((char *)&serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    //copy the server address from serv_addr.sin_addr.s_addr to server->h_adddr.
    bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr, server->h_length);

    serv_addr.sin_port = htons(server_port_number);
    connectRes = connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
    if (connectRes < 0) {
        printf("Error connection\n");
        exit(0);
    }
    printf("connect successfully\n");
    fp_queue = fopen(argv[3], "r");
    if (fp_queue == NULL) {
        printf("Failed open client file %s\n", argv[3]);
        exit(1);
    }

    bzero(buffer, 256);
    while ((fgets(buffer,sizeof(buffer),fp_queue)) != NULL) {
        buffer[strlen(buffer) - 1] = '\0';
        printf("buffer is %s\n", buffer);
        n = write(sockfd, buffer, strlen(buffer));
        if (n < 0) {
            printf("Error write to socket\n");
        }
        bzero(cliBuffer, 256);
        n = read(sockfd, buffer, 256);
        if (n <0) {
            printf("Error read from socket\n");
        }
        printf("%s\n", buffer);
    }
    close(sockfd);
    return 0;
}

Answer 1

代码中至少存在 2 个设计问题。

服务器代码接收一个请求，发送一个响应，然后服务器终止。如果您想通过一个连接处理更多请求，那么服务器代码必须包含像客户端一样的循环。服务器代码应该包含类似的内容

while ((n = read (newsockfd, bufferSK, 255) > 0) {
    printf("\nThe message from client is: %s",bufferSK);
    n = write(newsockfd, "SERVER: I got your message!\n", 27);
    if (n < 0) {
        printf("Error writing to socket\n");
        break;
    }
}
close(newsockfd);

下一个问题是 TCP 是面向流的协议(protocol)，而您的代码没有考虑这一点。面向流意味着协议(protocol)不保留消息边界。当发件人调用write("a"); write("b")时接收器可以在两次单独的读取中获取字符，也可以在一次读取中接收 2 个字符。为了克服这个问题，对等方必须定义一些协议(protocol)来确定消息边界。通常客户端在消息开头发送消息长度或者使用控制字符作为消息边界或者消息具有固定长度。