Java代理：如何从HttpRequest中提取目标主机和端口？

Question

I am working on a Http Proxy in java. Basically I have 3 applications:

• a client application, where I just submit a request to a server VIA a proxy
• a proxy that captures the request, modifies it and then forwards it to the web server

• the web server Here is my code for the Client (taken from the apache httpcore examples, but works well):

  public class ClientExecuteProxy () {

   public static void main(String[] args)throws Exception { HttpHost proxy = new HttpHost("127.0.0.1", 8080, "http"); DefaultHttpClient httpclient = new DefaultHttpClient(); try { httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy); HttpHost target = new HttpHost("issues.apache.org", 443, "https"); HttpGet req = new HttpGet("/"); System.out.println("executing request to " + target + " via " + proxy); HttpResponse rsp = httpclient.execute(target, req); HttpEntity entity = rsp.getEntity(); System.out.println("----------------------------------------"); System.out.println(rsp.getStatusLine()); Header[] headers = rsp.getAllHeaders(); for (int i = 0; i<headers.length; i++) { System.out.println(headers[i]); } System.out.println("----------------------------------------"); if (entity != null) { System.out.println(EntityUtils.toString(entity)); } } finally { // When HttpClient instance is no longer needed, // shut down the connection manager to ensure // immediate deallocation of all system resources httpclient.getConnectionManager().shutdown(); } } 

  }

If I do a direct execution of the request to the server (if I comment the line "httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);"), it works without any problem. But if I leave it like that, it will pass by the proxy. Here is the part that I do not know how to handle for the proxy: The proxy listens for the requests, reads its content and verifies if it respects certain policies. If OK it will forward it to the server, else it will drop the request and it will send a HttpResponse with an error. The problem is when the request is OK and it needs to be forwarded. How does the proxy know to what address to forward it? My question is: How do I get the information from the request entered at the line "HttpHost target = new HttpHost("issues.apache.org", 443, "https");"? I've googled for a couple of hours but found nothing. Can anybody help me please?

Answer 1

When you define an HTTP proxy to an application or browser, either:

1. There will be a preceding CONNECT request to form a tunnel, that tells you the target host:port, or

2. The entire target URL is placed in the middle of the GET/POST/... request line. Normally, without a proxy, this is just a relative URL, relative to the host:port of the TCP connection.