Re: Filter on url example - Filter out hack attempts

[Nathan Maves]

First of this is not a Tomcat question.  This type of information is 
always available at http://java.sun.com or http://forum.java.sun.com/

To answer your question....Yes.  in-fact you can place the class where 
ever you want as long as it is in your classpath.  Of course you will 
also have to change the <filter-class> attribute accordingly.

Nathan
On May 11, 2004, at 7:42 AM, lrnobs wrote:
Yoav,

So from what I know so far my
/usr/local/tomcat/webapps/myapplication/WEB-INF/web.xml should look 
like the
following:

<web-app>
  <filter>
    <filter-name>UrlFilter</filter-name>
    <filter-class>UrlFilter</filter-class> *Don't know how this should
layout.*
  </filter>
  <filter-mapping>
    <filter-name>UrlFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
</web-app>
Do I then create
/usr/local/tomcat/webapps/myapplication/WEB-INF/classes/URLFilter.java?
 public class UrlFilter implements Filter {
   ...
   public void doFilter(...) {
     if(req instance of HttpServletRequest) {
       HttpServletRequest hreq = (HttpServletRequest) req;
       String uri = hreq.getRequestURI();
       if(allow(uri)){
         chain.doFilter(req, res);
       } else {
...........Send to Null
         // Do whatever: error page, redirect, etc.
       }
     } else {
       // Non-HTTP requests
       chain.doFilter(req, res);
     }
   }
     private boolean allow(String uri) {
     // Look up allowed urls in a DB, Collection, whatever
       SubstringTest = False;
    SubstringTest = string.indexOf("GET / HTTP/1.1") > 0;
     if(SubstringTest = True) return True;
     Do the same for the rest
     //GET / HTTP/1.0     //page1.jsp     //page2.jsp     //page3.jsp
//page4.jsp     //page5.jsp     //graphic1.gif     //graphic2.gif
     } }
Thanks,

Larry Nobs









Hi,
This is a trivial filter:
public class URLFilter implements Filter {
  ...
  public void doFilter(...) {
    if(req instance of HttpServletRequest) {
      HttpServletRequest hreq = (HttpServletRequest) req;
      String uri = hreq.getRequestURI();
      if(allow(uri)){
        chain.doFilter(req, res);
      } else {
        // Do whatever: error page, redirect, etc.
      }
    } else {
      // Non-HTTP requests
      chain.doFilter(req, res);
    }
  }
    private boolean allow(String uri) {
     // Look up allowed urls in a DB, Collection, whatever
    }
}
I omitted full prototype declarations above due to laziness.  It's the
javax.servlet.Filter interface.
Take a look at the balancer webapp that ships with tomcat 5.  The
URLStringMatchRule is pretty close to what you want, and can be easily
extended with a list of allow patterns and/or deny patterns.  Tomcat 
has
something similar as the base Valve for the RemoteAddr/RemoteHost
valves.

Yoav Shapira
Millennium Research Informatics

-----Original Message-----
From: lrnobs [mailto:[EMAIL PROTECTED]
Sent: Saturday, May 08, 2004 9:11 PM
To: Tomcat Users List
Subject: Filter on url example - Filter out hack attempts
I have had no luck Googling so far for an example on how to filter
based on
urls.

I thought I might put this in the AccessLogValve but will do whatever
works.
I have a limited number of jsp's and graphics on my site and would 
like
to
filter out all of the hack attempts that fill up my logs.

I would like to do something like this (in plain english)

Accept
GET / HTTP/1.1
GET / HTTP/1.0
*page1.jsp*
*page2.jsp*
*page3.jsp*
*page4.jsp*
*page5.jsp*
*graphic1.gif*
*graphic2.gif*
Drop All Other Requests - they are just hack attempts

Thanks,

Larry Nobs



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