Why doesnt java tcp socket send all data when called repeatetly in a while-loop?

Question

I am sending data over a socket but the java socket seems to change ordering and loose data and I can't fix it. Here is my java code:

Socket socket;
...
while(isSending){
  try {
    DataOutputStream out = new DataOutputStream(socket.getOutputStream());
    String data = getMyData();
    out.writeBytes(data);//data is a csv string parsed on server-side
    out.flush();
  } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
  }
}

Server.cpp:

while(1){
    char recv_buffer[4096];
    memset(recv_buffer,0,4096);
    //receive data from socket
   int ret = recv(socket , recv_buffer , 4095 , 0);
   if (ret == 0){
      error_print("Socket not connected");
      ret = 0;
   } else if (ret < 0) {
      error_print("Error reading from socket!");
      ret = 0;
   }
  if(ret<=0) break;
  recv_buffer[ret]='\0';

  //parse recv_buffer
}

If I put a Thread.sleep(2000) in the java while-loop, the values are received correctly. What could be the reason for this behavior and how can I fix it?

Maybe you are not getting data from stream as quickly as you are sending. — Darshan Lila
– Darshan Lila, Commented Jul 28, 2014 at 9:51
@DarshanLila Isn't that EXACTLY what should NOT happen when using TCP sockets? — user2212461
– user2212461, Commented Jul 28, 2014 at 9:52
It does send all the data. The Java API and Posix require it. Your receiving code is where the bug is. Post it (edited into your question) and we'll show you where. — user207421
– user207421, Commented Jul 28, 2014 at 9:55
@DarshanLila TCP provides flow control. Your comment doesn't make sense. — user207421
– user207421, Commented Jul 28, 2014 at 10:01

user207421 · Accepted Answer · 2014-07-28 10:30:59Z

1

Just as I suspected. You are completely ignoring the value returned by the recv() function. It can be -1 indicating an error, or zero indicating end of stream, or a positive integer indicating the length received. Instead you are assuming not only that the read aucceeded but also that it returns a null-terminated string.

answered Jul 28, 2014 at 10:30

user207421

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user2212461 Over a year ago

I added the detailed server code. If you know where in the code the reason for the in the question stated problem lies, please share.

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