使用套接字写入代理并将响应返回给客户端

Question

I'm trying to create a proxy server in Java that rotates proxies. What I mean is, I am creating a proxy server that passes on the request to another random proxy, gets the response from that random proxy and returns it back to the client.

Something like this:

• Client Request -> My proxy server
• My proxy server -> random proxy server
• random proxy server -> My proxy server
• My proxy server -> Client

I have 2 main classes handling this. The first class is called RunnableRequestLayer and it is responsible for reading the client's request, and sending the response back. The second class is RequestMaker which connects to a random proxy, and has a send() and receive() method which send/receive from the random proxy.

Here is the relevant code from both classes:

Class #1: RunnableRequestRelayer

public class RunnableRequestRelayer implements Runnable {

    private Socket socket;
    private final int maxTries = 5;

    public RunnableRequestRelayer(Socket socket) {
        this.socket = socket; //This socket is the serverSocket.accept() socket
    }

    @Override
    public void run() {

        System.out.println("Got a request!");

        try(
                PrintWriter out =
                new PrintWriter(socket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(
                new InputStreamReader(socket.getInputStream()));
                ){

            RequestMaker rm = new RequestMaker();
            int tries = 0;

            while(tries++ < maxTries){
                try{
                    rm.connect();   
                } catch(IOException e){
                    continue;
                }

                String inputLine;

                //This while loop reads the input HttpRequest fine.
                while((inputLine = in.readLine()) != null){
                    if(inputLine.equals(""))
                        break;

                    rm.send(inputLine + "\r\n");
                    //System.out.println(rm.receive());
                }

                System.out.println("Test"); //This is successfully printing.


                String outputLine;
                //This output loop is never entered... why?
                while((outputLine = rm.receive()) != null){
                    System.out.println("In output loop");
                    if(outputLine.equals(""))
                        break;

                    out.print(outputLine + "\r\n");
                    out.flush();
                    System.out.println(outputLine);
                }

                rm.disconnect();
                tries = maxTries;
            }

        } catch(IOException e) {
            System.out.println("Bad");
        }

    }

Class #2: RequestMaker

public class RequestMaker {

    private Socket socket;

    PrintWriter out;
    BufferedReader in;

    public void connect() throws IOException {
        String[] proxy = ProxyGenerator.generate().split(":"); 
        socket = new Socket(proxy[0], Integer.parseInt(proxy[1]));

        System.out.println("Connected to proxy - " + proxy[0] + ":" + proxy[1]);
        out = new PrintWriter(socket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    }

    public void send(String s) {
        out.write(s);
        out.flush();
    }

    public String receive() throws IOException {
        return in.readLine();
    }

    public void disconnect() {
        try{
            out.flush();
            out.close();
            in.close();
            socket.close(); 
        } catch(IOException e) {}
    }

}

I tried testing this with fiddler too. I set the proxy to connect to 127.0.0.1:8888 which is Fiddler's proxy server. Once again, the request was received from the client, but the proxy on Fiddler never received it.

My question is: Why is the while loop that reads from the proxy not entering in the first place? I checked if the rm.receive() was returning "" or null using an if, and it wasn't.

Answer 1

Turns out I was not following the HTTP protocol properly. Had to send an empty line after writing the input request to the proxy server.