Installing and Running CGI Proxy Python on Tomcat 7

Question

I want to set up a proxy running on tomcat for openlayers, so I followed these steps:

1. Downloaded the proxy.cgi file from the OpenLayers web site:

http://trac.osgeo.org/openlayers/browser/trunk/openlayers/examples/proxy.cgi

Here is the code:

#!c:/Python27/python.exe


"""This is a blind proxy that we use to get around browser
restrictions that prevent the Javascript from loading pages not on the
same server as the Javascript.  This has several problems: it's less
efficient, it might break some sites, and it's a security risk because
people can use this proxy to browse the web and possibly do bad stuff
with it.  It only loads pages via http and https, but it can load any
content type. It supports GET and POST requests."""

import urllib2
import cgi
import sys, os

# Designed to prevent Open Proxy type stuff.

allowedHosts = ['www.openlayers.org', 'openlayers.org', 
                'labs.metacarta.com', 'world.freemap.in', 
                'prototype.openmnnd.org', 'geo.openplans.org',
                'sigma.openplans.org', 'demo.opengeo.org',
                'www.openstreetmap.org', 'sample.azavea.com',
                'v2.suite.opengeo.org', 'v-swe.uni-muenster.de:8080', 
                'vmap0.tiles.osgeo.org', 'www.openrouteservice.org','localhost:6901']

method = os.environ["REQUEST_METHOD"]

if method == "POST":
    qs = os.environ["QUERY_STRING"]
    d = cgi.parse_qs(qs)
    if d.has_key("url"):
        url = d["url"][0]
    else:
        url = "http://www.openlayers.org"
else:
    fs = cgi.FieldStorage()
    url = fs.getvalue('url', "http://www.openlayers.org")

try:
    host = url.split("/")[2]
    if allowedHosts and not host in allowedHosts:
        print "Status: 502 Bad Gateway"
        print "Content-Type: text/plain"
        print
        print "This proxy does not allow you to access that location (%s)." % (host,)
        print
        print os.environ

    elif url.startswith("http://") or url.startswith("https://"):

        if method == "POST":
            length = int(os.environ["CONTENT_LENGTH"])
            headers = {"Content-Type": os.environ["CONTENT_TYPE"]}
            body = sys.stdin.read(length)
            r = urllib2.Request(url, body, headers)
            y = urllib2.urlopen(r)
        else:
            y = urllib2.urlopen(url)

        # print content type header
        i = y.info()
        if i.has_key("Content-Type"):
            print "Content-Type: %s" % (i["Content-Type"])
        else:
            print "Content-Type: text/plain"
        print

        print y.read()

        y.close()
    else:
        print "Content-Type: text/plain"
        print
        print "Illegal request."

except Exception, E:
    print "Status: 500 Unexpected Error"
    print "Content-Type: text/plain"
    print 
    print "Some unexpected error occurred. Error text was:", E

1. I have my tomcat at port 6901, so I modified the proxy.cgi file to include my domain in the allowedHosts list:

   allowedHosts = ['localhost:6901']

2. I copied the proxy.cgi file to the following folder:

   $TOMCAT_PATH$/webapps/myApp/WEB-INF/cgi/

3. Modified the file web.xml of the web app by adding the sections below the file at

   $TOMCAT_PATH$/webapps/myApp/WEB-INF/web.xml

<servlet> 
    <servlet-name>cgi</servlet-name> 
    <servlet-class>org.apache.catalina.servlets.CGIServlet</servlet-class> 
    <init-param> 
        <param-name>debug</param-name> 
        <param-value>0</param-value> 
    </init-param> 
    <init-param> 
        <param-name>cgiPathPrefix</param-name> 
        <param-value>WEB-INF/cgi</param-value> 
    </init-param> 
    <init-param> 
        <param-name>executable</param-name> 
        <param-value>c:\python25\python.exe</param-value> 
    </init-param> 
    <init-param> 
        <param-name>passShellEnvironment</param-name> 
        <param-value>true</param-value> 
    </init-param> 
    <load-on-startup>5</load-on-startup> 
</servlet> 

<servlet-mapping> 
<servlet-name>cgi</servlet-name> 
<url-pattern>/cgi-bin/*</url-pattern> 
</servlet-mapping>

Comment: the “param-value” for the “executable” parameter has to contain the path to your Pyhton installation. (it does!)

1. Modified the file context.xml of my web app by adding the element below, file at $TOMCAT_PATH$/webapps/myApp/META-INF/context.xml

2. Restarted Tomcat

3. To use the proxy with OpenLayers, included this single line into the code:

   OpenLayers.ProxyHost = "/yourWebApp/cgi-bin/proxy.cgi?url=";

But the proxy isn't working! When I try to use it like:

/myApp/cgi-bin/proxy.cgi?url=labs.metacarta.com 

I get this error:

Some unexpected error occurred. Error text was: list index out of range

I think it's related to os.environ["REQUEST_METHOD"], but I don't know how it's related.

Answer 1

The problem appears to be in your allowedHosts line. It should include the hosts that you want to connect to over the proxy (e.g. allowedHosts = ['labs.metacarta.com'])