C UDP 客户端未读取服务器回复

Question

我有以下简单的 UDP 服务器客户端。当客户端向服务器发送某些内容时，它工作正常，但我无法让服务器向客户端发回回复。我不确定问题是服务器回复还是客户端读取或两者兼而有之。我已经评论了服务器回复/客户端读取的位置。

客户端

#define PORT     8080 
#define MAXLINE 1024 

// Driver code 
int main() { 
    int sockfd; 
    char buffer[MAXLINE]; 
    char *hello = "Hello from client"; 
    struct sockaddr_in   servaddr; 

    // Creating socket file descriptor 
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) { 
        perror("socket creation failed"); 
        exit(EXIT_FAILURE); 
    } 

    memset(&servaddr, 0, sizeof(servaddr)); 

    // Filling server information 
    servaddr.sin_family = AF_INET; 
    servaddr.sin_port = htons(PORT); 
    //servaddr.sin_addr.s_addr = INADDR_ANY; 
    servaddr.sin_addr.s_addr = inet_addr("192.168.0.111"); //server address to send message to

    int n, len; 

    sendto(sockfd, (const char *)hello, strlen(hello), 
        MSG_CONFIRM, (const struct sockaddr *) &servaddr, 
            sizeof(servaddr)); 
    printf("Hello message sent.\n"); 
    //**NOT READING THE REPLY FROM SERVER HERE**
    n = recvfrom(sockfd, (char *)buffer, MAXLINE, 
                MSG_WAITALL, (struct sockaddr *) &servaddr, 
                &len); 
    buffer[n] = '\0'; 
    printf("Server : %s\n", buffer); 

    close(sockfd); 
    return 0; 
} 

服务器

    #define PORT     8080 
    #define MAXLINE 1024 

    // Driver code 
    int main() { 
        int sockfd; 
        char buffer[MAXLINE]; 
        char *hello = "Hello from server"; 
        struct sockaddr_in servaddr, cliaddr; 


    // Creating socket file descriptor 
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) { 
        perror("socket creation failed"); 
        exit(EXIT_FAILURE); 
    } 

    memset(&servaddr, 0, sizeof(servaddr)); 
    memset(&cliaddr, 0, sizeof(cliaddr)); 

    // Filling server information 
    servaddr.sin_family = AF_INET; // IPv4 
    servaddr.sin_addr.s_addr = INADDR_ANY; //ip of all local interfaces i.e. ip of wlan, ethernet etc
    servaddr.sin_port = htons(PORT); 

    // Bind the socket with the server address 
    if ( bind(sockfd, (const struct sockaddr *)&servaddr, 
            sizeof(servaddr)) < 0 ) 
    { 
        perror("bind failed"); 
        exit(EXIT_FAILURE); 
    } 

    int len, n; 
    n = recvfrom(sockfd, (char *)buffer, MAXLINE, 
                MSG_WAITALL, ( struct sockaddr *) &cliaddr, 
                &len); 
    buffer[n] = '\0'; 
    printf("Client : %s\n", buffer); 
    //**Client not receiving this message****
    sendto(sockfd, (const char *)hello, strlen(hello), 
        MSG_CONFIRM, (const struct sockaddr *) &cliaddr, 
            len); 
    printf("Hello message sent.\n"); 

    return 0; 
} 

Answer 1

从服务器发送到的最后一个参数是错误的。它不是 len 而不是

sendto(sockfd, (const char *)hello, strlen(hello), 
    MSG_CONFIRM, (const struct sockaddr *) &cliaddr, 
        len); 

放

sendto(sockfd, (const char *)hello, strlen(hello), 
    MSG_CONFIRM, (const struct sockaddr *) &cliaddr, 
        sizeof(cliaddr));