Java中的简单代理：POST请求异常

Question

I wrote a simple HTTP proxy in java. The code is as follows:

public class SampleProxy {

    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        boolean listening = true;
        int port = 1234;
        try {
            serverSocket = new ServerSocket(port);
        } catch (IOException e) {
            System.out.println("Port Error");
            System.exit(-1);
        }
        while (listening) {
            new ProxyThread(serverSocket.accept()).start();
        }
        serverSocket.close();
    }
}

class ProxyThread extends Thread {

    private final Socket clientSocket;

    public ProxyThread(Socket socket) {
        this.clientSocket = socket;
    }

    public void run() {
        try {
            String parts[];
            // Read request
            InputStream incomingIS = clientSocket.getInputStream();
            int incomingLen = incomingIS.available();

            byte[] b = new byte[8196];

            int len = incomingIS.read(b);

            if (len > 0) {

                System.out.println("The Request is : \n" + new String(b, 0, len) + "\n*********\n");

                Socket socket = new Socket("localhost", 80);

                OutputStream outgoingOS = socket.getOutputStream();

                outgoingOS.write(b, 0, len);

                OutputStream incomingOS = clientSocket.getOutputStream();
                InputStream outgoingIS = socket.getInputStream();


                int length;
                //Read from server
                byte[] b2=new byte[8196];
                length = outgoingIS.available();

                outgoingIS.read(b2);

                incomingOS.write(b2, 0, b2.length);

                incomingOS.close();
                outgoingIS.close();
                outgoingOS.close();
                incomingIS.close();

                socket.close();
            } else {
                incomingIS.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception ex) {
            Logger.getLogger(ProxyThread.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            try {
                clientSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

As seen, the client requests at port 1234, the proxy forwards the request to the server and gets the response which is then returned back to the client.

In normal scenarios, this works fine, but, I tried testing the same for high traffic scenarios using a shell script which sends multiple(around 50) POST requests, one after another and found out that for some requests, only the headers are getting received. The POST data is omitted but the Content-Length shows the appropriate length of the variables which ought to be sent. This does not happen for specific requests, but at random, maybe 3 or 4 out of 50 Requests.

The same error however, does not seem to exist for GET requests.

Any suggestions as to whats actually causing the error?

Answer 1

Usual mistakes here. Misuse of available(), and failure to actually implement the HTTP protocol correctly. You need to read RFC 2616 thoroughly, especially the parts about request and response length; and reread the Javadoc for InputStream.available(), where you will find a specific warning against using it as you are doing here.