Question

I am using a Java socket program to write integers and characters from the server back to the client

    PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);

I want to write an int32 and a char of 8B on the wire. For the integer when I write

    out.printf("%04x",1);

it appears on the wireshark as “30 30 30 31”, whereas I want it to appear “01 00 00 00”. Similarly for out.printf(“%d”,1); it appears as “31” whereas I want it “01 00 00 00”. How can I write on the wire an integer of 4B and a character of 8B? Does the representation has to do with encoding?

Answer 1

Using PrintWrite to write text to a socket is not ideal as it will hide any errors.

In your case you appear to want to write binary in so I would suggest you try.

DataOutputStream out = new DataOutputStream(
                       new BufferedOutputStream(clientSocket.getOutputStream()));

out.writeInt(1);

However if you want to sue little endian format, I would use blocking NIO.

SocketChannel sc = 
ByteBuffer bb= ByteBuffer.allocateDirect(1024).order(ByteOrder.LITTLE_ENDIAN);

bb.putInt(1);
// put whatever else
bb.flip();
while(bb.remaining() > 0) sc.write(bb);