C ++ TCP Winsock Server多次接收相同的数据包

Question

I have written a very simple C++ server which I am connecting to from a Java application. The C++ server uses winsock2. I am sending UTF8 encoded numbers to the server from my client and on receipt of these numbers I would like the server to perform an action. However my server seems to be receiving a series of numbers as one. At the moment I have the server listening every 1 millisecond for a new message.

This is my C++ server code which receives the message:

  bool receive()
     {
          char buffer[1024];
          int inDataLength=recv(Socket,buffer,sizeof(buffer),0);
          if(buffer[0] != '\0')
          {
                     std::cout<<"Client: ";
                     std::cout << buffer;
                     sendKey(string(buffer));  
          }
          else if (inDataLength == 0) //Properly closed connection
          {
             std::cout<<"Connection lost..\r\n";
             return false;
          }    
          return true;
     }

This is called within a loop like so:

 while ( receive() )
{
      Sleep(1);
}

This is my java client code to send a message where out is OutputStream = socket.getOutputStream():

public void send(String msg)
{
        try {
            out.write( msg.getBytes("UTF8") );
            out.flush();
            Thread.sleep(100);
        } catch (SocketException e) {
            Global.error("Connection error..");
            //e.printStackTrace();
        } catch (UnsupportedEncodingException e) {

        } catch (IOException e) {
            Global.error("Never connected..\r\n");
        } catch (Exception e)
        { Global.error("Sending failed..\r\n"); }
    }

What I am getting is the server receiving for example the number 1, then 2, then 12, then 121 etc.. in no specific pattern except once the server is receiving 2 numbers at once it will never start receiving only one again. This is the only place in my java code where anything is sent to the server and I flush the buffer after each message so I think the issue is on my server but I'm at a loss as to the problem.

Any help would be much appreciated.

Thanks.

Answer 1

You are forgetting the most important check:

int inDataLength=recv(Socket,buffer,sizeof(buffer),0);
if (inDataLength == -1 ) {
    std::cerr << "receive error: " << GetLastError() << std::endl;
    return false;
}
...

This actually might be the reason your loop took so much CPU time.

Answer 2

Given the sleeps it seems as the recv is not blocking.. Take a look at Winsock recv() does not block . You need to check for errors in the return value.