在套接字编程 UDP 中从服务器接收消息时出现问题

问：

我的任务是用 C 语言创建一个具有 3 个服务器和一个客户端的代码。客户端启动后，它应该无限期地在端口上侦听新服务器到达的通知。

我想出了服务器将发送 hello 消息的代码，当客户端收到消息时，它会将服务器添加到已知服务器列表中。但客户根本没有收到它。

客户端逻辑：

int bytes_received = recvfrom(client_socket, buffer, MAX_BUFFER_SIZE, 0, NULL, NULL);

if (bytes_received == -1) {
    printf("ERROR: %s (%s:%d)\n", strerror(errno), __FILE__, __LINE__);
    exit(-1);
}

buffer[bytes_received] = '\0';

if (strncmp(buffer, "HELLO: ", 7) == 0) {
    
    char *content = buffer + 7;  
    printf("Received HELLO message from server: %s\n", content);
    printf("Received HELLO message from (%s:%d): %s\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), buffer + 1);
    if (num_known_servers < MAX_SERVERS) {
        struct Server new_server;
        memcpy(&new_server.addr, (struct sockaddr_in *)(&client_addr), sizeof(struct sockaddr_in));
        new_server.last_message_time = time(NULL);
        known_servers[num_known_servers++] = new_server;
        char log_message[MAX_BUFFER_SIZE];
        snprintf(log_message, MAX_BUFFER_SIZE, "New server discovered at %s:%d", inet_ntoa(new_server.addr.sin_addr), ntohs(new_server.addr.sin_port));
        logMessage(log_message);
    }
} else if {
  continue;
} 

服务器逻辑：

char server_message[] = "HELLO: Hello from server";
            
if (sendto(server_socket, server_message, strlen(server_message), 0, (struct sockaddr *)&client_addr, sizeof(client_addr)) == -1) {
    printf("ERROR: %s (%s:%d)\n", strerror(errno), __FILE__, __LINE__);
    exit(-1);
}