服务器中收到的消息不正确

Question

I have an issue with receiving messages in client-server. I have set a default string for testing. It receives the message just fine but it sticks the string together when it sends the second loop. What should i do with this?

Here is the code for sending data(client)

NetworkStream networkStream = tcpclnt.GetStream();
String data = "";
     for (int i = 0; i < 4; i++)
         {
           data = " output here";
           if (networkStream.CanWrite)
              {
                var bytes = Encoding.ASCII.GetBytes(data);
                networkStream.Write(bytes, 0, bytes.Length);
                networkStream.Flush();
              }
          }

And here when it receives the data(server)

private void recieveData()
{
  NetworkStream nStream = tcpClient.GetStream();
  while (!stopReceiving)
      {
         if (nStream.CanRead)
           {
              byte[] buffer = new byte[1024];
              var bytesRead = nStream.Read(buffer, 0, buffer.Length);
              if (bytesRead > 0) recvDt = Encoding.ASCII.GetString(buffer, 0, bytesRead);
              bool f = false;
              f = recvDt.Contains("+@@+");
                    if (f)
                    {
                        string d = "+@@+";
                        recvDt = recvDt.TrimStart(d.ToCharArray());
                        clientDis();
                        stopReceiving = true;
                    }


                    else 
                    {
                        this.Invoke(new rcvData(addHere));
                    }
                }
                Thread.Sleep(1000);
            }

        }


public void addHere() 
        {
            if (recvDt != null && recvDt != "")
            {
                output.Text += "Received Data: " + recvDt;
                recvDt = null;
            }

        }

The output looks like this

Answer 1

You are assuming that TCP preserves your messages. It does not. TCP offers a boundaryless stream of bytes. You can receive bytes in any chunk size, including one, but also including all of them at once.

You need to devise an application protocol that allows you to tell messages apart from that stream of bytes. Maybe, prefix the message with its length.

Or, send line-wise and use StreamReader.ReadLine. It handles this for you.

This is a bug:

                    string d = "+@@+";
                    recvDt = recvDt.TrimStart(d.ToCharArray());

You are basically trimming away all chars "+@". Not what you wanted.

Why are you testing CanRead and CanWrite ? They are known to be true and even if they were false your program would just ignore the problem and keep going doing nothing. Don't do superstitious checks like that if you can't handle the result anyway.

Probably, you should not use TCP at all. It's hard. Use a higher level technology such as WCF, HTTP, protobuf.