Question

I’ve implemented a C server and a Java client which communicate to each other through TCP. The problem is when the client sends a string, the recv() call in C server just reads a character and returns immediately. If I put a breakpoint at recv() and then do a step-over, the server receives the whole string that was sent.
Here’s the recv call I’m using in C

char tempBuffer[256] = {'\0'};  
int retVal = recv(hClientSocket, tempBuffer, sizeof(tempBuffer), 0);

And here’s the Java client.

clientSocket = new Socket("127.0.0.1", 24886);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
outToServer.writeBytes("alert(\"hi\")");

My question is, is there a way in which I can make this work without having to put a while loop in my C server code to receive each character separately? What’s the best way to do this?
I implemented the C++ client given here and it works fine. So I’m guessing it’s some problem in Java+C++ interoperability. Thanks!

Answer 1

Although what Scott M says is true on a Java side ( about using flush ), you will have to rework your whole communication protocol.

You will have to either tell to C-code, how many bytes are expected to be sent (this will be the easiest to track), or use some sort of termination character, to recognize that the string input is over ( e.g. null terminator byte ).

There is absolutely no guarantee that the network layer will not chop the transition arbitrarily, so code defensively and expect recv always to recieve a partial data, which you will have to assemble for your internal consumption.