Python Twisted proxy - how to intercept packets

Question

I'm trying to print out the body of a HTTP response using Python.

Here is my code sofar:

from twisted.web import proxy, http
from twisted.internet import reactor
from twisted.python import log
import sys

log.startLogging(sys.stdout)

class ProxyFactory(http.HTTPFactory):
  protocol=proxy.Proxy

reactor.listenTCP(8080, ProxyFactory())
reactor.run()

When I connect my browser to localhost:8080, I can see that all my requests are being directed through the Python proxy running locally. But how do I 1) print out response body and 2) edit the response body before sending it back to the browser?

I hope someone can point me in the right direction - please bear in mind that I'm very new to Python!

Nuncle

Answer 1

Override the dataReceived method of a protocol (proxy.Proxy in your case) and handle the data modification in that method:

from twisted.web import proxy, http
from twisted.internet import reactor
from twisted.python import log
import sys

log.startLogging(sys.stdout)

class MyProxy(proxy.Proxy):
    def dataReceived(self, data):

      # Modify the data here
      print data

      # perform the default functionality on modified data 
      return proxy.Proxy.dataReceived(self, data)

class ProxyFactory(http.HTTPFactory):
  protocol=MyProxy

factory = ProxyFactory()
reactor.listenTCP(8080, factory)
reactor.run()

Cytologist

Hey, many thanks for that reply. I got an exception - File "proxy4.py", line 15, in dataReceived return super(MyProxy,self).dataReceived(data) exceptions.TypeError: must be type, not classobj – Nuncle

Corrected the code. Can you check if it is still raising TypeError?. – Cytologist

you might mean: proxy.Proxy.dataReceived(self, data) instead of MyProxy.dataReceived(self, data) othewise it leads to stackoverflow. – Gladsome

Also dataReceived() sees only data send by client to server. Getting the data send by server to client might be more complicated – Gladsome

@J.F.Sebastian Tried the code using Chrome and Safari and received an Unhandled Error. Are you getting the same problem? – Inverter

@Nyxynyx: No. Are you trying to visit the proxy as a web server? You should not put the proxy url into the browser address bar. Configure network settings to use the proxy as a proxy instead. Note: only simple html pages will work if their content is uppercased (buffer.upper()) – Gladsome