Patch: FTP through HTTP-Proxy (Squid)

Marc Langheinrich (marclang@cs.washington.edu)
Tue, 15 Jun 1999 18:05:32 +0900 

Not sure if this is interesting enough to be included in the main
distribution, but it sure annoyed me enough to finally patch the LWP
library to support it.

My Intranet here only allows Internet access through an HTTP proxy server
("Squid"). Although I can freely "surf" the Web this way, none of my
standard ftp software (like "ftp", "ncftp" etc) works. However, when I
follow "ftp://" links through my browser, it seems to be no problem
accessing ftp sites. This is because HTTP proxies like Squid (don't know
much about any other, sorry) also support FTP requests (i.e. requests of
the form "GET ftp://ftp.redhat.com/ HTTP/1.0").

I attached a simplistic patch to "LWP/Protocol/ftp.pm" that checks for an
"http" proxy to be listed for the request (just set your "ftp_proxy"
environment variable to point to your HTTP proxy), and then simply
reblesses the LWP::Protocol::ftp object as an "LWP::Protocol::http" one.
This way LWP handles the request exactly as my Web browser does. This
allows me to use all of the standard LWP tools (i.e.  GET, lwp-rget,
lwp-mirror) for FTP requests through my HTTP firewall (well, at least with
Squid). 

I know it's a pretty ugly thing (i.e. morphing the request from ftp into
http), so it might not be appropriate to be in the standard LWP release,
but it works great for me and I sure don't want to miss it anymore...

Note: The patch doesn't check for allowed methods, but the proxy will most
likely complain with an HTTP error in case it doesn't support it (like POST
for ftp requests). 

PS: I _know_ that it's possible to use ftp through a firewall -- if it's
set up to do so, that is. However, my site isn't, so I have to resort to the
solution below. Your milage may vary.
 
-- 
Marc Langheinrich
marclang@cs.washington.edu


$ diff -c LWP/Protocol/ftp.pm.orig LWP/Protocol/ftp.pm
*** LWP/Protocol/ftp.pm.orig    Tue Jun 15 17:12:11 1999
--- LWP/Protocol/ftp.pm Tue Jun 15 17:17:46 1999
***************
*** 36,43 ****
--- 36,49 ----
      # check proxy
      if (defined $proxy)
      {
+       if ($proxy =~ /^http/i) {
+       require LWP::Protocol::http;
+       bless $self, LWP::Protocol::http;
+       return $self->request($request, $proxy, $arg, $size, $timeout);
+       } else {
        return HTTP::Response->new(&HTTP::Status::RC_BAD_REQUEST,
                                   'You can not proxy through the ftp');
+       }
      }
  
      my $url = $request->url;