Java Proxy - Can't receive response from host/Socket issue

Question

I am coding a simple Java proxy. The general architecture was given to me (method signatures etc), and this is how the Main class looks:

private static Socket clientSocket;
private static ServerSocket client;
private static int myPort;

public static void init(int port) throws IOException {
    client = new ServerSocket(port);
    clientSocket = client.accept();
}
public static void handle(Socket clientSocket) {
    try {
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        HttpRequest httpRequest = new HttpRequest(in);

        String hostname = httpRequest.getHost();
        //443 hardcoded from reading the http headers. 
        //Testing using isitchristmas.com
        Socket serverSocket = new Socket(hostname, 443);
        BufferedReader out = new BufferedReader(new InputStreamReader(serverSocket.getInputStream()));
        HttpResponse httpResponse = new HttpResponse(out);
        serverSocket.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

}
public static void main(String args[]) {
    try {
        myPort = Integer.parseInt(args[0]);
        try {
            System.out.println("Initializing socket...");
            init(myPort);
        } catch (IOException e) {
            System.out.println("[ERROR]: " + e.getMessage());
        }
        handle(clientSocket);
    } catch (Exception e) {
        System.out.println("[ERROR]: " + e.getMessage());
    }
}

However the console hangs and never completes a request when reading in HttpResponse class:

    public HttpResponse(BufferedReader fromServer) throws IOException {
    String line;
    String statusLine = "";
    // Never goes past here
    while ((line = fromServer.readLine()) != null) {
        if (line.isEmpty()) {
            break;
        }

        if (line.toLowerCase().contains("status")) {
            statusLine = line;
        }

        response.append(line);
    }

    if (!response.toString().isEmpty()) {
        getDataAndHeadersFromResponse(response.toString());
        System.out.println("\n\nHTTP Response:\n");
        System.out.println("Status Line: " + statusLine);
        System.out.println("Header Lines: " + headerLines + "\n\n");
        System.out.println("Data: " + data);
    }

}

I suspect it has something to do with how I am creating the sockets... not calling close() on ServerSocket gives off a Address already in use: JVM_Bind exception. I also don't seem to get the serverSocket parameters right. As you can tell by now I'm not very versed in socket programming. What is wrong here?

Answer 1

• You need to listen on port 80: nothing in the assignment about HTTPS.
• The request body won't be terminated by end of stream, because the client still has the socket open to read the response.
• You need to read the Content-length header from the client and then read exactly that many bytes of request body.
• You therefore cannot solve this problem with a BufferedReader , as you have to count bytes, not chars.
• Having sent the request on to the server, all you really need to do afterwards is copy the response bytes directly from the server to the client: not what it says in the assignment.
• To stick with what the assignment says, you would similarly have to read the Content-Length header from the server, and all the other headers, and the blank line, and exactly content-length bytes of response from the server, and copy them all to the client. You can see this is a waste of time compared to just copying bytes.
• The line terminator in HTTP is \\r\\n , not \\n .

The assignment is deficient in:

• specifying the infeasible BufferedReader
• then inconsistently specifying DataInputStream for reading from the server
• there is no reason to use DataInputStream at all: InputStream would suffice
• not referring to RFC 2616 or its predecessors or successors
• not specifying whether HTTP 1.0 or 1.1
• not saying more about 'to cache Web pages', which is only mentioned on page 2 and never thereafter.

Students should complain.