c - UDP 套接字 - 服务器卡在 recvfrom 上

Question

我正在尝试实现客户端-服务器网络。我正在关注Beej's Guide to Network Programming

我的程序扫描键盘输入，在数组中查找关联值，然后通过 UDP 向我的服务器发送 GET 请求。但是，我的服务器似乎没有收到我的请求。

这是我的客户端代码摘录:

    // loop through all the results and make a socket
for(p = servinfo; p != NULL; p = p->ai_next) {
    if ((sockfd = socket(p->ai_family, p->ai_socktype,
            p->ai_protocol)) == -1) {
        perror("talker: socket");
        continue;
    }

    break;
}

if (p == NULL) {
    fprintf(stderr, "talker: failed to bind socket\n");
    return 2;
}

printf("Please Enter Your Search (USC, UCLA etc.):");
char searchKey[5];
fgets(searchKey, sizeof(searchKey), stdin);
int len, bytes_sent;
char value[8];
len = strlen(value);
char request[10];
for(int i = 0; i < sizeof(clientMap) / sizeof(struct Mapping); i++) {
  if (strcmp(clientMap[i].key, searchKey) == 0) {
    //value = clientMap[i].value;
    memcpy(value, clientMap[i].value, sizeof(char) * 6);
    strcat(request, "GET ");
    strcat(request, value);
    break;
  }
}
printf("The Client 1 has received a request with search word %s, which maps to key %s\n", searchKey, value);
printf("The Client 1 sends the request %s to the Server 1 with port number %s and IP address %s\n", request, SERVERPORT, argv[1]);
printf("The Client1's port number is TODO and the IP address is TODO\n");
if ((numbytes = sendto(sockfd, request, strlen(request), 0,
         p->ai_addr, p->ai_addrlen)) == -1) {
    perror("talker: sendto");
    exit(1);
}

freeaddrinfo(servinfo);

printf("talker: sent %d bytes to %s\n", numbytes, argv[1]);

这是我的服务器摘录:

// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
    if ((sockfd = socket(p->ai_family, p->ai_socktype,
            p->ai_protocol)) == -1) {
        perror("listener: socket");
        continue;
    }

    if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
        close(sockfd);
        perror("listener: bind");
        continue;
    }

    break;
}

if (p == NULL) {
    fprintf(stderr, "listener: failed to bind socket\n");
    return 2;
}

freeaddrinfo(servinfo);

printf("listener: waiting to recvfrom...\n");

addr_len = sizeof their_addr;
if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
    (struct sockaddr *)&their_addr, &addr_len)) == -1) {
    perror("recvfrom");
    exit(1);
}

buf[numbytes] = '\0';
printf("The Server 1 has received a request with key %s\n", buf);
for(int i = 0; i < sizeof(serverMap) / sizeof(struct Mapping); i++) {
  if (strcmp(serverMap[i].key, buf) == 0) {
    char post[13];
    strcpy(post, "POST ");
    strcat(post, serverMap[i].value);
    printf("The Server 1 sends the reply %s to TODO: Finish this!", post);
    sendto(sockfd, post, strlen(post), 0, (struct sockaddr *)&their_addr, addr_len);
    break;
  }
}
close(sockfd);

我知道问题是我的服务器没有接收到数据报。我想我犯了一些明显很容易的错误，但我对 C 和 Networks 的理解并不是那么强。

顺便说一句，您可能会注意到我的打印语句包含TODO。我不确定如何获取这些IP 地址 和端口号。有人可以帮忙解决这个问题吗？

Answer 1

无论如何，您的服务器需要一个固定端口来监听。您如何期望您的客户端知道它应该发送到哪个端口？只需在服务器和客户端上使用任意端口即可。

由于您是新手，因此首先在本地尝试所有内容。服务器应该监听 INADDR_ANY 和您选择的任意端口。