Question

I have written a program that relies on a proxy to function. I now need a script that will check to see if the browser is set to use the right proxy, and if not, change it to use it. I need this implemented for as many browsers as possible, but is only required for Internet Explorer, Google Chrome, Mozilla Firefox, Safari and Opera. I am not even sure how to go about this, but it is for a project for work that will be due in a few days. If anyone can help or lend advice, I would greatly appreciate it!

I am programming on:

MS Windows XP
Python 2.6

Answer 1

The Windows stores its system wide proxy in the registry, look in the the HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings. You can use the Python _winreg module to change it (or just winreg if you use Python 3). Here is a sample code

import _winreg as winreg

INTERNET_SETTINGS = winreg.OpenKey(winreg.HKEY_CURRENT_USER,
    r'Software\Microsoft\Windows\CurrentVersion\Internet Settings',
    0, winreg.KEY_ALL_ACCESS)

def set_key(name, value):
    _, reg_type = winreg.QueryValueEx(INTERNET_SETTINGS, name)
    winreg.SetValueEx(INTERNET_SETTINGS, name, 0, reg_type, value)

set_key('ProxyEnable', 1)
set_key('ProxyOverride', u'*.local;<local>')  # Bypass the proxy for localhost
set_key('ProxyServer', u'X.X.X.X:8080')

To disable it you can just need to set ProxyEnable key to 0:

set_key('ProxyEnable', 0)

After the script runs the browsers will still have the old proxy stored in-memory, so you need to restart them so they can re-read the new proxy settings from the registry. I found this to be very annoying so I converted this snippet to Python.

import ctypes

INTERNET_OPTION_REFRESH = 37
INTERNET_OPTION_SETTINGS_CHANGED = 39

internet_set_option = ctypes.windll.Wininet.InternetSetOptionW

internet_set_option(0, self.INTERNET_OPTION_REFRESH, 0, 0)
internet_set_option(0, self.INTERNET_OPTION_SETTINGS_CHANGED, 0, 0)

This refreshes the Windows settings so all you have to do is hit F5 in your browser in order to it grab the new proxy settings.

I’ve written a small script to switch my proxy on or off, the source in on Bitbucket:
https://bitbucket.org/canassa/switch-proxy

This should work with any browser that uses the Windows system-wide proxy (e.g.: Chrome, IE). Some browsers like Firefox uses a internal proxy settings. If you want to change these you will have figure out where they store their settings and write code to change it.