在UDP客户端pingpong中接收消息的问题

如何解决在UDP客户端pingpong中接收消息的问题

我在Ping / Pong软件中完成测量RTT的UDP客户端时遇到问题。 客户端似乎与服务器建立了连接（第一次使用TCP连接），但是在发送消息和接收答案时，它失败了，即使经过一些尝试也没有接收到数据报。 我必须实现一个具有超时功能的非阻塞recv。 我将保留整个do_ping函数： 我的解决方案是：

/*
* This function sends and waits for a reply on a socket.
* char message[]: message to send
* size_t msg_size: message length
*/
double do_ping(size_t msg_size,int msg_no,char message[msg_size],int ping_socket,double timeout)
{
   int lost_count = 0,recv_errno;
   char answer_buffer[msg_size];
   ssize_t recv_bytes,sent_bytes;
   struct timespec send_time,recv_time;
   double roundtrip_time_ms;
   int re_try = 0;

   /*** write msg_no at the beginning of the message buffer ***/
   /*** TO BE DONE START ***/

   sprintf(message,"%d\n",msg_no);

   /*** TO BE DONE END ***/

   do {
       debug(" ... sending message %d\n",msg_no);
   /*** Store the current time in send_time ***/
   /*** TO BE DONE START ***/

   if(clock_gettime(CLOCK_REALTIME,&send_time) != 0)
       fail_errno("clock_gettime");

   /*** TO BE DONE END ***/

   /*** Send the message through the socket (non blocking mode) ***/
   /*** TO BE DONE START ***/

   sent_bytes = send(ping_socket,message,msg_size,MSG_DONTWAIT);
   if(sent_bytes != msg_size && errno != EAGAIN && errno != EWOULDBLOCK)
       fail_errno("send failure");

   /*** TO BE DONE END ***/

我认为问题出在这部分（超时是3000毫秒，两倍）：

   /*** Receive answer through the socket (non blocking mode,with timeout) ***/
   /*** TO BE DONE START ***/

   struct timeval to;
   to.tv_sec = (long) (timeout*pow(10,-3));
   to.tv_usec = 0;

   if(setsockopt(ping_socket,SOL_SOCKET,SO_RCVTIMEO,&to,sizeof(to)) != 0)
       fail_errno("setsockopt timeout");

   for (int offset = 0; (offset + (recv_bytes = recv(ping_socket,answer_buffer + offset,sent_bytes - offset,MSG_WAITALL))) < msg_size; offset += recv_bytes){
        debug(" ... received %zd bytes back\n",recv_bytes);
        if (recv_bytes < 0)
            fail_errno("Error receiving data");
   }
    
    
   /*** TO BE DONE END **/

这是本节的结尾。

   /*** Store the current time in recv_time ***/
   /*** TO BE DONE START ***/

   if(clock_gettime(CLOCK_REALTIME,&recv_time) != 0)
       fail_errno("clock_gettime");

   /*** TO BE DONE END ***/

    roundtrip_time_ms = timespec_delta2milliseconds(&recv_time,&send_time);

    while ( recv_bytes < 0 && (recv_errno == EAGAIN || recv_errno == EWOULDBLOCK)
                && roundtrip_time_ms < timeout ) {
        recv_bytes = recv(ping_socket,answer_buffer,sizeof(answer_buffer),0);
                    recv_errno = errno;
                    if ( recv_bytes < 0 && errno != EAGAIN && errno != EWOULDBLOCK )
                fail_errno("UDP ping could not recv from UDP socket");
                    
            if (clock_gettime(CLOCK_TYPE,&recv_time))
            fail_errno("Cannot get receive-time");
        roundtrip_time_ms = timespec_delta2milliseconds(&recv_time,&send_time);
                    sscanf(answer_buffer,"%ld %ld,%ld %ld\n",&(recv_time.tv_sec),&(recv_time.tv_nsec),&(send_time.tv_sec),&(send_time.tv_nsec));
                roundtrip_time_ms -= timespec_delta2milliseconds(&send_time,&recv_time);
    }
    if (recv_bytes < sent_bytes) {  /*time-out elapsed: packet was lost */
        lost_count++;
        if (recv_bytes < 0)
            recv_bytes = 0;
        printf("\n ... received %zd bytes instead of %zd (lost count = %d); re-trying ...\n",recv_bytes,sent_bytes,lost_count);
        if (++re_try > MAXUDPRESEND) {
            printf(" ... giving-up!\n");
            fail("too many lost datagrams");
        }
        printf(" ... re-trying ...\n");
    }
} while (sent_bytes != recv_bytes);

return roundtrip_time_ms;
}

非常感谢您提供的帮助和时间。