Question

I have a Java program that mirrors a connection from a client server to a remote server. The mirror send data find, but does not receive. I cannot for the life of me figure out why. Here is my code:

Socket client = new Socket("127.0.0.1", 42001);
System.out.println("Connected to client!");
Socket server = new Socket(serverAddress, serverPort);
System.out.println("Connected to server!");

BufferedReader clientin = new BufferedReader(new InputStreamReader(client.getInputStream()));
BufferedWriter scratchout = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));

BufferedReader serverin = new BufferedReader(new InputStreamReader(server.getInputStream()));
BufferedWriter serverout = new BufferedWriter(new OutputStreamWriter(server.getOutputStream()));

int i;
boolean serverNeedsFlush = false;
boolean clientNeedsFlush = false;
while (true)
{
    while (clientin.ready())
    {
        i = clientin.read();
        serverout.write(i);
        serverNeedsFlush = true;
    }
    if(serverNeedsFlush)
    {
        serverout.flush();
        serverNeedsFlush = false;
    }
    while (serverin.ready())
    {
        i = serverin.read();
        System.out.print((char)i);
        scratchout.write(i);
        clientNeedsFlush = true;
    }
    if(clientNeedsFlush)
    {
        scratchout.flush();
        clientNeedsFlush = false;
    }
}

Answer 1

If your trying to forward data from one socket to another it would probably be a better idea to use the socket streams directly rather than decorating them.

As other posters have suggested you should use threads to do this. It will make life easier. You can then use the threads to do a basic in to out stream copy like below.

public static void streamCopy(InputStream in, OutputStream out)
       throws IOException{

        byte[] data = new byte[1024];
        int length;
        do{
            length = in.read(data);
            if(length > 0){
                out.write(data, 0, length);
                out.flush();
            }
        }while(length != -1);

}

When the method above returns you will have read the entire in stream and written it in to the out stream. Your run method for your thread or runnable could look something like this.

public void run() {

    Socket inSock = null;
    Socket outSock = null;
    try{
        inSock = new Socket(inHost, inPort);
        outSock = new Socket(inHost, inPort);
        /* Set up some socket options here (timeouts, buffers etc)*/

        /* Insert pre copy actions */

        /* This method won't return until inSock's inputStream hits end of stream. 
         * and all the data has been written to outSock's outputStream and flushed. */
        streamCopy(inSock.getInputStream(), outSock.getOutputStream());

        /* In order to really do this correctly you should create an 
         * application protocol that verifies the upstream receiver 
         * is actually getting the data before you close the socket. */

        /* Insert post copy actions */

    }catch(Exception e){
        /* Corrective action or logging here */
    }finally{
        /* Don't forget to close the sockets. */
        if(inSock != null){
            try{
                inSock.close();
            }catch(Exception e){
                /* Don't care */
            }
        }
        if(outSock != null){
            try{
                outSock.close();
            }catch(Exception e){
                /* Don't care */
            }
        }
    }
}