[Twisted-Python] Twisted n00b question

Matt Goodall matt at pollenation.net
Mon Jan 23 18:55:40 EST 2006

> Hello -
> I'm completely new to Twisted and moderately (~1 year) experienced
> with Python, and I'm here because I need some help understanding how
> to set up a web proxy.
> My goal: an HTTP proxy living on my local machine (OS X) that will
> transparently serve up web pages  to myself, while allowing me to
> snoop & log connections I make to remote servers. I want the
> equivalent of an Attention Trust recorder (http://
> www.attentiontrust.org/services) without having to use Firefox.
> My first attempt: using the demonstration service.tac as a starting
> point, I wrote a new Resource that can view the request. I got far
> enough to look inside the request object passed to my resource's
> render() method, and return a meaningful response showing that I was
> seeing accurate request information. So in that render() method, I
> generate a new HTTPClientFactory object which *should* be able to
> make a request the intended server and return the results. I stopped
> when I realized the documentation showed examples using reactor.run
> (), while advising that I should never actually use reactor.run() in
> a real app. So I'm stuck trying to  generate a new http client
> request while inside an http server.
> My second attempt: I found the Proxy class in the twisted.web docs,
> which has this code snippet:
>     from twisted.protocols import http
>     f = http.HTTPFactory()
>     f.protocol = Proxy
> ...which is great, but I'm now I'm not sure what I need to do with
> the "f" object to make it work in a .tac/twistd context. It seems
> like should be able to add a callback in there someplace to intercept
> the proxied requests and pick them apart, but I'm a little stuck.

'f' is a protocol factory. It exists to create protocol instances
(proxy.Proxy) when something connects to a listening socket, typically a
TCP server.

Here's a complete .tac file that runs a proxy on port 8080.

from twisted.application import internet, service
from twisted.web import http, proxy

application = service.Application('proxy')

f = http.HTTPFactory()
f.protocol = proxy.Proxy
proxyService = internet.TCPServer(8080, f)

Hope that helps.

- Matt

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