Problems with the Proxy Programme--Please help

Question

Hi All,
I have written a simple proxy server in the form of a servlet. I changed the proxy config of my browser to connect to this servlet hosted on the default context(http://localhost:8080) of the Tomcat 5.0.25 . Well , this servlet internally connects to the proxy of the corporate LAN . The logic that I have applied is as follows. The servlet gets the request from the client (ie the browser in this case) , extracts the headers and contents from the request, sets them to a new request that it forms and finally send this new request to the proxy. When the proxy responds, the servlet collects the response headers and contents adn writes them in its response. To sum up , this servlet transparently carries the requests and responses between the client(browser) and the corporate LAN proxy. Now the problem is this. Let's say , now I am accessing http://www.google.com.The browser sends a request to my servlet with the following headers as they are extracted by my servlet.
ProxyServer:::>posting request
ProxyServer:::>headerValue::> headerName = accept : headerValue=*/*
ProxyServer:::>headerValue::> headerName = referer : headerValue=http://www.google.com/
ProxyServer:::>headerValue::> headerName = accept-language : headerValue=en-us
ProxyServer:::>headerValue::> headerName = proxy-connection : headerValue=Keep-Alive
ProxyServer:::>headerValue::> headerName = user-agent : headerValue=Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; UB1.4_IE6.0_SP1; .NET CLR 1.0.3705; .NET CLR 1.1.4322)
ProxyServer:::>headerValue::> headerName = host : headerValue=www.google.com
ProxyServer:::>headerValue::> headerName = cookie : headerValue=PREF=ID=1be27c0a74f198ca:TM=1082058853:LM=1082058853:S=bu6ORrygzm8AUkm8
ProxyServer:::>postRequest
I set these headers into a new connection opened to the proxy and post a fresh request to the proxy,which, in turn responds with the following headers.
ProxyServer:::>posted request successfully
ProxyServer:::>writing response
ProxyServer:::>writeResponse-->headerName = Proxy-Connection : headerValue = [close]
ProxyServer:::>writeResponse-->headerName = Content-Length : headerValue = [257]
ProxyServer:::>writeResponse-->headerName = Date : headerValue = [Tue, 13 Jul 2004 14:01:40 GMT]
ProxyServer:::>writeResponse-->headerName = Content-Type : headerValue = [text/html]
ProxyServer:::>writeResponse-->headerName = Server : headerValue = [NetCache appliance (NetApp/5.5R2)]
ProxyServer:::>writeResponse-->headerName = Proxy-Authenticate : headerValue = [Basic realm="Charlotte - napxyclt2"]
ProxyServer:::>writeResponse-->headerName = null : headerValue = [HTTP/1.1 407 Proxy Authentication Required]
ProxyServer:::>writeResponse exiting
ProxyServer:::>wrote response successfully
I write these headers back to the client. According to what I was thinking, the client ie the browser would open a new dialog box asking for username/password owing to the presence of the "Proxy-Authenticate " header. But it does not happen that way. Rather the browser stops responsding and displays a blank page. Does anyone know why it happens this way? I am pasting the server prog below for everybody's reference.
package server.proxy;
//import all servlet related classes
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import java.io.*;
import java.net.*;
import server.resources.*;
//My Proxy server --->Currently it is very simplea and relies on
//other proxy servers of an already connected network.
public class ProxyServer extends HttpServlet
//stores the resource bundle
private ServerResBundle resBundle = null;
//checks for the mode of operation
private boolean proxySet = false;
private String proxy = null;
//storing the original System out/err etc
private PrintStream sysOutOrig = null;
private PrintStream sysErrOrig = null;
private InputStream sysInOrig = null;
//initialise certain features that are required later
public void init() throws ServletException
try
//initialise the resource bundle
this.initResBundle();
System.out.println("ProxyServer:::>res bundle init");
//set the mode of operation
this.setMode();
System.out.println("ProxyServer:::>mode set");
//set the system out and err --System.setOut etc
this.setSystemOutErr();
System.out.println("ProxyServer:::>in/out/err set");
}//End try
catch(Exception e)
System.out.println("Exception in init..."+(e.getMessage()));
throw new ServletException(e);
}//Edn
catch(Throwable e)
System.out.println("Irrecoverable Error...");
throw new ServletException(e);
}//End
}//End init
//method to init the resource bundle;
private void initResBundle()
this.resBundle = ServerResBundle.getBundle();
}//End
//method to set the mode of the server--proxy or direct
private void setMode()
//read the target proxy property from the bundle and
//if it is set,take that URL
String temp = (String)(this.resBundle.getResource(ResKeys.PROXY_SERVER));
if ( (temp != null) && (temp.length() > 0) )
this.proxySet = true;
this.proxy = temp;
temp = null;
}//End
}//End
//method to set the system out and err etc
private void setSystemOutErr() throws Exception
//keep a copy of the original system out and error
this.sysOutOrig = System.out;
this.sysErrOrig = System.err;
try
//read the options adn if they are set, take the values directly
String newOutStr = (String)(this.resBundle.getResource(ResKeys.SYSTEM_OUT));
String newErrStr = (String)(this.resBundle.getResource(ResKeys.SYSTEM_ERR));
if ((newOutStr != null) && (newOutStr.length() > 0))
System.setOut(new PrintStream(new FileOutputStream(new File(newOutStr),true),true));
}//End if
if ((newErrStr != null) && (newErrStr.length() > 0))
System.setErr(new PrintStream(new FileOutputStream(new File(newErrStr),true),true));
}//End if
}//End
catch(Exception e)
//restore the stuff
System.setOut(this.sysOutOrig);
System.setErr(this.sysErrOrig);
}//End
}//End
//this is where the proxy functionalities will be embedded
public void service(HttpServletRequest req,HttpServletResponse resp)
throws ServletException,java.io.IOException
//conenction URL
URL target = null;
//conenction to the remote object
URLConnection targetConn = null;
//stores the OOS and the OIS
ObjectOutputStream oos = null;
ObjectInputStream ois = null;
try
//check for the mode of operation
if (proxySet)
URLConnection objects go through two phases: first they are created, then they are connected.
After being created, and before being connected, various options can be specified
(e.g., doInput and UseCaches). After connecting, it is an error to try to set them.
Operations that depend on being connected, like getContentLength, will implicitly perform the connection,
if necessary.
//for the URL to the proxy
target=new URL(this.proxy);
//conenct to the proxy
targetConn = target.openConnection();
//set the details of the connectuon
targetConn.setDoInput(true);
targetConn.setDoOutput(true);
targetConn.setUseCaches(false);
// If true, this URL is being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog. If false, then no user interaction is allowed
targetConn.setAllowUserInteraction(true);
//connect to the remote object
// targetConn.connect();//call this only when all the request properties are set
System.out.println("ProxyServer:::>posting request");
//post the received request to the URL
this.postRequest(targetConn,req);
System.out.println("ProxyServer:::>posted request successfully");
System.out.println("ProxyServer:::>writing response");
//receive the response
//write the received response to the client
this.writeResponse(targetConn,resp);
System.out.println("ProxyServer:::>wrote response successfully");
}//End if
else
//currently this functionality is not supported
throw new ServletException(
(String)(this.resBundle.getResource(ResKeys.ERR_FUNC_NOTSUPPORTED)));
}//End
}//End try
catch(Exception e)
if(e instanceof ServletException)
throw (ServletException)e;
}//End
if (e instanceof IOException)
throw (IOException)e;
}//End
//wrap it up in ServletException
throw new ServletException(e);
}//End
}//End
//method to write the response back to the client
private void writeResponse(URLConnection targetConn,HttpServletResponse resp)
throws ServletException
//get all the header fields from the response connection and set them to the
//response of the servlet
Map headerFields = null;
Iterator headerFieldEntries = null;
Map.Entry header = null;
//stores the input stream to the conn
BufferedReader brConn = null;
//stores the writer to the response
PrintWriter prResp = null;
//checks if the proxy authentication needed or not
boolean proxyAuthReqd = false;
try
//juste ensuring that the proxy authentication is reset
proxyAuthReqd = false;
if( (targetConn != null) && (resp != null) )
//Returns an unmodifiable Map of the header fields.
//The Map keys are Strings that represent the response-header field names.
//Each Map value is an unmodifiable List of Strings that represents the corresponding
//field values
headerFields = targetConn.getHeaderFields();
//Returns a set view of the mappings contained in this map
Set temp = headerFields.entrySet();
//Returns an iterator over the elements in this set
headerFieldEntries = temp.iterator();
if (headerFieldEntries != null)
while (headerFieldEntries.hasNext())
Object tempHeader = headerFieldEntries.next();
if (tempHeader instanceof Map.Entry)
header = (Map.Entry)tempHeader;
Object headerName = header.getKey();
Object headerValue=header.getValue();
System.out.println("ProxyServer:::>writeResponse-->headerName = "+headerName+" : headerValue = "+headerValue);
//do not select the key-value pair if both the key adn the value are null
if ( ( headerName == null) && (headerValue == null) )
continue;
}//Enmd
if (headerValue != null)
List headerValList = null;
if (headerValue instanceof List)
headerValList = (List)headerValue;
}//End
if(headerValList != null)
for (int i=0;i<headerValList.size();i++)
Object headerValueStr = headerValList.get(i);
if (headerValueStr instanceof String)
//note that the header-key can not be null for addHeader
//I have made this temporary provision to make the programme work.
resp.addHeader(( (headerName==null)? ("null_header"+i) :(String)headerName),
(String)headerValueStr);
//check if the proxy authentication required or not
if (((String)headerValueStr).
indexOf(resp.SC_PROXY_AUTHENTICATION_REQUIRED+"") != -1)
System.out.println("ProxyServer:::>writeResponse-->proxy auth needed");
//proxy authentication is needed
proxyAuthReqd = true;
}//End
}//Ednd of
else if (headerValueStr == null)
resp.addHeader(( (headerName==null)? null :(String)headerName),
null);
}//End
}//End for
}//End if
}//End if
}//End
}//End while
}//End if
//get the writer to the client
prResp = resp.getWriter();
System.out.println("ProxyServer:::>writeResponse-->proxyAuthReqd="+proxyAuthReqd);
//juste test a simple header
System.out.println("Proxy-Authenticate = "+(resp.containsHeader("Proxy-Authenticate")));
//if the proxy asks you for authentication,pass on the same to the client
//from whom you have received the request.When this flag is true,the connection
//is closed by the remotehost adn hence any attempt to open in input steram
//results in an error ie IOException
if (!proxyAuthReqd)
//now get the content adn write it to the response too
brConn = new BufferedReader(new InputStreamReader(
targetConn.getInputStream()));
String tempStr = null;
while ((tempStr = brConn.readLine())!=null)
prResp.println(tempStr);
}//End while
//close the connections
brConn.close();
}//End if
else
prResp.println("Proxy Authentication needed...");
}//End
//close the streams
prResp.flush();
prResp.close();
}//End if
System.out.println("ProxyServer:::>writeResponse exiting\n");
}//End try
catch(Exception e)
throw new ServletException(e);
}//End
}//End
//method to post request to the internet
private void postRequest(URLConnection targetConn,HttpServletRequest req)
throws ServletException
//extract the header parameters and the body content from the incoming request
//and set them to the new connection
Enumeration reqHeaders = null;
//reads the incoming request's content
BufferedReader brReqRd = null;
PrintWriter prResWt = null;
//stores temp header names and values
String headerName = null;
String headerValue = null;
try
if( (targetConn != null) && (req != null) )
reqHeaders = req.getHeaderNames();
//extract a header adn set it to the new connection
while (reqHeaders.hasMoreElements())
headerName = (String)(reqHeaders.nextElement());
headerValue = req.getHeader(headerName);
targetConn.setRequestProperty(headerName,headerValue);
System.out.println("ProxyServer:::>headerValue::> headerName = "+headerName+" : headerValue="+headerValue);
}//End
System.out.println("ProxyServer:::>postRequest\n");
//establis the actual connection
//calling this method bfore the above loop results in IllegalStateException
targetConn.connect();
//NOTE : try reading from and writing into OIS and OOS respectively
//now read the contents and write them to the connection
// brReqRd = req.getReader(); //this hangs for some reason
brReqRd = new BufferedReader(new InputStreamReader(req.getInputStream()));
System.out.println("Got the reader..brReqRd = "+brReqRd);
if (brReqRd != null)
String temp = null;
//establish the printwriter
// prResWt = new PrintWriter(targetConn.getOutputStream(),true);
prResWt = new PrintWriter(targetConn.getOutputStream());
System.out.println("trying to read in a loop from brReqRd.. ready="+(brReqRd.ready()));
while( (brReqRd.ready()) && ((temp=brReqRd.readLine()) != null) )
System.out.println("In while::>temp = "+temp);
prResWt.println(temp);
}//Emd while
//close the streams adn go back
brReqRd.close();
prResWt.flush();
prResWt.close();
}//End
}//End outer if
System.out.println("ProxyServer:::>postRequest exiting\n");
}//End try
catch(Exception e)
throw new ServletException(e);
}//End
}//End
}//End

Answer 1

Hi serlank ,
Thanks for your reply. Well , I initially I thought of not pasting the code,as it was too long. But I could not help it,as I thought I must show in code what I exactly meant. That's why I followed a description of my problem with the code. You could probably have copied the code and pasted it in one of your favourite editors to take a look at it. Did you,by any chance, try to read it on the browser? And as regards reposting the same message, I can say that I did it as I felt the subject was not quite appropriate in the first posting and I was not sure as to how I could delete/alter the posting. I am not asking for a code-fix,but some suggestions from some one who might ever have come across such a thing.Anyway, lemme know if you have any idea on it. Thanks...