Setting proxy settings in Windows with Python (using InternetSetOption)

I have written a little script that needs to be able to enable and disable proxy settings with Python. Right now I edit the registry to achieve this, but it doesn't seem to work on all versions of windows, so I would much rather use InternetSetOption. Information about the API is really scarce and most of the examples are in C, which I don't know: https://support.microsoft.com/en-us/kb/226473

It would probably look somewhat like this (this snippet is actually for refreshing the browser proxy settings):

import ctypes
INTERNET_OPTION_REFRESH = 37
INTERNET_OPTION_SETTINGS_CHANGED = 39

internet_set_option = ctypes.windll.Wininet.InternetSetOptionW
internet_set_option(0, 38, 0, 0)    
internet_set_option(0, INTERNET_OPTION_REFRESH, 0, 0)
internet_set_option(0, INTERNET_OPTION_SETTINGS_CHANGED, 0, 0)

Solution

I actually figured this out myself, through lots of trial and errors. Working example:

from ctypes import *
from ctypes.wintypes import *

LPWSTR = POINTER(WCHAR)
HINTERNET = LPVOID

INTERNET_PER_CONN_PROXY_SERVER = 2
INTERNET_OPTION_REFRESH = 37
INTERNET_OPTION_SETTINGS_CHANGED = 39
INTERNET_OPTION_PER_CONNECTION_OPTION = 75
INTERNET_PER_CONN_PROXY_BYPASS = 3
INTERNET_PER_CONN_FLAGS = 1

class INTERNET_PER_CONN_OPTION(Structure):
    class Value(Union):
        _fields_ = [
            ('dwValue', DWORD),
            ('pszValue', LPWSTR),
            ('ftValue', FILETIME),
        ]

    _fields_ = [
        ('dwOption', DWORD),
        ('Value', Value),
    ]

class INTERNET_PER_CONN_OPTION_LIST(Structure):
    _fields_ = [
        ('dwSize', DWORD),
        ('pszConnection', LPWSTR),
        ('dwOptionCount', DWORD),
        ('dwOptionError', DWORD),
        ('pOptions', POINTER(INTERNET_PER_CONN_OPTION)),
    ]

def set_proxy_settings(ip, port, on=True):
    if on:
        setting = create_unicode_buffer(ip+":"+str(port))
    else:
        setting = None

    InternetSetOption = windll.wininet.InternetSetOptionW
    InternetSetOption.argtypes = [HINTERNET, DWORD, LPVOID, DWORD]
    InternetSetOption.restype  = BOOL

    List = INTERNET_PER_CONN_OPTION_LIST()
    Option = (INTERNET_PER_CONN_OPTION * 3)()
    nSize = c_ulong(sizeof(INTERNET_PER_CONN_OPTION_LIST))

    Option[0].dwOption = INTERNET_PER_CONN_FLAGS
    Option[0].Value.dwValue = (2 if on else 1) # PROXY_TYPE_DIRECT Or 
    Option[1].dwOption = INTERNET_PER_CONN_PROXY_SERVER
    Option[1].Value.pszValue = setting
    Option[2].dwOption = INTERNET_PER_CONN_PROXY_BYPASS
    Option[2].Value.pszValue = create_unicode_buffer("localhost;127.*;10.*;172.16.*;172.17.*;172.18.*;172.19.*;172.20.*;172.21.*;172.22.*;172.23.*;172.24.*;172.25.*;172.26.*;172.27.*;172.28.*;172.29.*;172.30.*;172.31.*;172.32.*;192.168.*")

    List.dwSize = sizeof(INTERNET_PER_CONN_OPTION_LIST)
    List.pszConnection = None
    List.dwOptionCount = 3
    List.dwOptionError = 0
    List.pOptions = Option

    InternetSetOption(None, INTERNET_OPTION_PER_CONNECTION_OPTION, byref(List), nSize)
    InternetSetOption(None, INTERNET_OPTION_SETTINGS_CHANGED, None, 0)
    InternetSetOption(None, INTERNET_OPTION_REFRESH, None, 0)

set_proxy_settings("127.0.0.1", 52042)