Python Java Socket Issues

Question

I am having an issue with Java ServerSocket and Python where I have an multithreaded echo server (Written in Java) that can communicate with multiple java clients. This all works fine.

When I try to connect with a python client, the python client can receive data from the server but when it sends data the server appears never to receive it.

I can only see the data at the server when i try to send 500K + bytes. While i can now see the data its is incomplete and out of sync.

I tested the follwing example code and it works fine with python: http://norwied.wordpress.com/2012/04/17/how-to-connect-a-python-client-to-java-server-with-tcp-sockets/

The only real difference is that in the code from the link it uses:

BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
PrintWriter out = new PrintWriter(client.getOutputStream(),

Where as in my server I use:

streamOut = new DataOutputStream(new BufferedOutputStream(s.getOutputStream())); 
streamIn = new DataInputStream(new BufferedInputStream(socket.getInputStream()));

Could this be causing the issue ?

Answer 1

In your code example, the PrintWriter was set to autoflush. This means that when println() is called, the buffer will be flushed and, consequently, sent to the network. You however, use a BufferedOutputStream and probably forgot to flush() your OutputStream.

• DevilCode: Yea, it seems to be that issue but there is no way that I have found at the moment to flush the buffer in python. It seems to rely on a EOL to send. Is there an alternative way to make it flush ?
• kutschkem: Is there a method flush()?
• DevilCode: unfortunately not. We have re coded into java all is good now =)

Answer 2

I think your python client isn't flushing the stream, which is why java server only gets data after the buffer on the client is full.