#!/usr/bin/perl
#
#   CGIProxy 2.1beta15
#
#   nph-proxy.cgi-- CGIProxy 2.1: a proxy in the form of a CGI script.
#     Retrieves the resource at any HTTP or FTP URL, updating embedded URLs
#     in HTML and other resources to point back through this script.  By
#     default, no user info is sent to the server.  Options include
#     text-only proxying to save bandwidth, cookie filtering, ad filtering,
#     script removal, user-defined encoding of the target URL, and more.
#     Requires Perl 5.
#
#   Copyright (C) 1996, 1998-2006 by James Marshall, james@jmarshall.com
#   All rights reserved.  Free for non-commercial use; commercial use
#   requires a license.
#
#   For the latest, see http://www.jmarshall.com/tools/cgiproxy/
#
#
#   IMPORTANT NOTE ABOUT ANONYMOUS BROWSING:
#     CGIProxy was originally made for indirect browsing more than
#       anonymity, but since people are using it for anonymity, I've tried
#       to make it as anonymous as possible.  Suggestions welcome.  For best
#       anonymity, browse with JavaScript turned off.  In fact, that's the
#       only reliable way, in spite of what certain anonymity vendors claim.
#       That said, please notify me if you find any privacy holes, even when
#       using JavaScript.
#     Anonymity is good, but may not be bulletproof.  For example, if even
#       a single unchecked JavaScript statement can be run, your anonymity
#       can be compromised.  I've tried to handle JS in every place it can
#       exist, but please tell me if I missed any.  Also, browser plugins
#       or other executable extensions may be able to reveal you to a server.
#       Also, be aware that this script doesn't modify PDF files or other
#       third-party document formats that may contain linking ability, so
#       you will lose your anonymity if you follow links in such files.
#     If you find any other way your anonymity can be compromised, please let
#       me know.
#
#
#   CONFIGURATION:
#
#     None required in most situations.  On some servers, these might be
#       required (all in the "user configuration" section):
#       . If you're using another HTTP or SSL proxy, set $HTTP_PROXY,
#           $SSL_PROXY, and $NO_PROXY as needed.  If those proxies use
#           authentication, set $PROXY_AUTH and $SSL_PROXY_AUTH accordingly.
#       . If this is running on an SSL server that doesn't use port 443, set
#           $RUNNING_ON_SSL_SERVER=1 (otherwise, the default of '' is fine).
#
#     Options include:
#       . Set $TEXT_ONLY, $REMOVE_COOKIES, $REMOVE_SCRIPTS, $FILTER_ADS,
#           $HIDE_REFERER, and $INSERT_ENTRY_FORM as desired.  Set
#           $REMOVE_SCRIPTS if anonymity is important.
#       . To let the user choose all of those settings (except $TEXT_ONLY),
#           set $ALLOW_USER_CONFIG=1.
#       . To change the encoding format of the URL, modify the
#           proxy_encode() and proxy_decode() routines.  The default
#           routines are suitable for simple PATH_INFO compliance.
#       . To encode cookies, modify the cookie_encode() and cookie_decode()
#           routines.
#       . You can restrict which servers this proxy will access, with
#           @ALLOWED_SERVERS and @BANNED_SERVERS.
#       . Similarly, you can specify allowed and denied server lists for
#           both cookies and scripts.
#       . For security, you can ban access to private IP ranges, with
#           @BANNED_NETWORKS.
#       . If filtering ads, you can customize this with a few settings.
#       . To insert your own block of HTML into each page, set $INSERT_HTML
#           or $INSERT_FILE.
#       . As a last resort, if you really can't run this script as NPH,
#           you can try to run it as non-NPH by setting $NOT_RUNNING_AS_NPH=1.
#           BUT, read the notes and warnings above that line.  Caveat surfor.
#       . For crude load-balancing among a set of proxies, set @PROXY_GROUP.
#       . Other config is possible; see the user configuration section.
#       . If heavy use of this proxy puts a load on your server, see the
#           "NOTES ON PERFORMANCE" section below.
#
#     For more info, read the comments regarding any config options you set.
#
#     This script MUST be installed as a non-parsed header (NPH) script.
#       In Apache and many other servers, this is done by simply starting the
#       filename with "nph-".  It MAY be possible to fake it as a non-NPH
#       script, MOST of the time, by using the $NOT_RUNNING_AS_NPH feature.
#       This is not advised.  See the comments by that option for warnings.
#
#
#   TO USE:
#     Start a browsing session by calling the script with no parameters.
#       You can bookmark pages you browse to through the proxy, or link to
#       the URLs that are generated.
#
#
#   NOTES ON PERFORMANCE:
#     Unfortunately, this has gotten slower through the versions, mostly
#       because of optional new features.  Configured equally, version 1.3
#       takes 25% longer to run than 1.0 or 1.1 (based on *cough* highly
#       abbreviated testing).  Compiling takes about 50% longer.
#     Leaving $REMOVE_SCRIPTS=1 adds 25-50% to the running time.
#     Remember that we're talking about tenths of a second here.  Most of
#       the delay experienced by the user is from waiting on two network