Establish a socket connection through an HTTP proxy in Python.

http_proxy_connect.py

'''
Establish a socket connection through an HTTP proxy.

Author: Fredrik Østrem <frx.apps@gmail.com>

License:
  This code can be used, modified and distributed freely, as long as it is this note containing the original
  author, the source and this license, is put along with the source code.
'''

import socket
from base64 import b64encode

def http_proxy_connect(address, proxy = None, auth = None, headers = {}):
  """
  Establish a socket connection through an HTTP proxy.
  
  Arguments:
    address (required)     = The address of the target
    proxy (def: None)      = The address of the proxy server
    auth (def: None)       = A tuple of the username and password used for authentication
    headers (def: {})      = A set of headers that will be sent to the proxy
  
  Returns:
    A 3-tuple of the format:
      (socket, status_code, headers)
    Where `socket' is the socket object, `status_code` is the HTTP status code that the server
     returned and `headers` is a dict of headers that the server returned.
  """
  
  def valid_address(addr):
    """ Verify that an IP/port tuple is valid """
    return isinstance(addr, (list, tuple)) and len(addr) == 2 and isinstance(addr[0], str) and isinstance(addr[1], (int, long))
  
  if not valid_address(address):
    raise ValueError('Invalid target address')
  
  if proxy == None:
    s = socket.socket()
    s.connect(address)
    return s, 0, {}
  
  if not valid_address(proxy):
    raise ValueError('Invalid proxy address')
  
  headers = {
    'host': address[0]
  }
  
  if auth != None:
    if isinstance(auth, str):
      headers['proxy-authorization'] = auth
    elif auth and isinstance(auth, (tuple, list)) and len(auth) == 2:
      headers['proxy-authorization'] = 'Basic ' + b64encode('%s:%s' % auth)
    else:
      raise ValueError('Invalid authentication specification')
  
  s = socket.socket()
  s.connect(proxy)
  fp = s.makefile('r+')
  
  fp.write('CONNECT %s:%d HTTP/1.0\r\n' % address)
  fp.write('\r\n'.join('%s: %s' % (k, v) for (k, v) in headers.items()) + '\r\n\r\n')
  fp.flush()
  
  statusline = fp.readline().rstrip('\r\n')
  
  if statusline.count(' ') < 2:
    fp.close()
    s.close()
    raise IOError('Bad response')
  version, status, statusmsg = statusline.split(' ', 2)
  if not version in ('HTTP/1.0', 'HTTP/1.1'):
    fp.close()
    s.close()
    raise IOError('Unsupported HTTP version')
  try:
    status = int(status)
  except ValueError:
    fp.close()
    s.close()
    raise IOError('Bad response')
  
  response_headers = {}
  
  while True:
    tl = ''
    l = fp.readline().rstrip('\r\n')
    if l == '':
      break
    if not ':' in l:
      continue
    k, v = l.split(':', 1)
    response_headers[k.strip().lower()] = v.strip()
  
  fp.close()
  return (s, status, response_headers)