waybackproxy.py

#!/usr/bin/env python3
import base64, collections, datetime, json, re, socket, socketserver, string, sys, threading, time, traceback, urllib.parse
try:
	import urllib3
except ImportError:
	print('WaybackProxy now requires urllib3 to be installed. Follow setup step 3 on the readme to fix this.')
	sys.exit(1)
from config_handler import *

class ThreadingTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
	"""TCPServer with ThreadingMixIn added."""
	pass

# http://code.activestate.com/recipes/580644-lru-dictionary/
class LRUDict(collections.OrderedDict):
	'''An dict that can discard least-recently-used items, either by maximum capacity
	or by time to live.
	An item's ttl is refreshed (aka the item is considered "used") by direct access
	via [] or get() only, not via iterating over the whole collection with items()
	for example.
	Expired entries only get purged after insertions or changes. Either call purge()
	manually or check an item's ttl with ttl() if that's unacceptable.
	'''
	def __init__(self, *args, maxduration=None, maxsize=128, **kwargs):
		'''Same arguments as OrderedDict with these 2 additions:
		maxduration: number of seconds entries are kept. 0 or None means no timelimit.
		maxsize: maximum number of entries being kept.'''
		super().__init__(*args, **kwargs)
		self.maxduration = maxduration
		self.maxsize = maxsize
		self.purge()

	def purge(self):
		'''Removes expired or overflowing entries.'''
		if self.maxsize:
			# pop until maximum capacity is reached
			overflowing = max(0, len(self) - self.maxsize)
			for _ in range(overflowing):
				self.popitem(last=False)
		if self.maxduration:
			# expiration limit
			limit = time.time() - self.maxduration
			# as long as there are still items in the dictionary
			while self:
				# look at the oldest (front)
				_, lru = next(iter(super().values()))
				# if it is within the timelimit, we're fine
				if lru > limit:
					break
				# otherwise continue to pop the front
				self.popitem(last=False)

	def __getitem__(self, key):
		# retrieve item
		value = super().__getitem__(key)[0]
		# update lru time
		super().__setitem__(key, (value, time.time()))
		self.move_to_end(key)
		return value

	def get(self, key, default=None):
		try:
			return self[key]
		except KeyError:
			return default

	def ttl(self, key):
		'''Returns the number of seconds this item will live.
		The item might still be deleted if maxsize is reached.
		The time to live can be negative, as for expired items
		that have not been purged yet.'''
		if self.maxduration:
			lru = super().__getitem__(key)[1]
			return self.maxduration - (time.time() - lru)

	def __setitem__(self, key, value):
		super().__setitem__(key, (value, time.time()))
		self.purge()
		
	def items(self):
		# remove ttl from values
		return ((k, v) for k, (v, _) in super().items())
	
	def values(self):
		# remove ttl from values
		return (v for v, _ in super().values())

class SharedState:
	"""Class for storing shared state across instances of Handler."""

	def __init__(self):
		# Create urllib3 connection pool.
		self.http = urllib3.PoolManager(maxsize=4, block=True)
		urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)

		# Create internal LRU dictionary for preserving URLs on redirect.
		self.date_cache = LRUDict(maxduration=86400, maxsize=1024)

		# Create internal LRU dictionary for date availability.
		self.availability_cache = LRUDict(maxduration=86400, maxsize=1024)

		# Read domain whitelist file.
		try:
			with open('whitelist.txt', 'r') as f:
				self.whitelist = f.read().splitlines()
		except:
			self.whitelist = []

shared_state = SharedState()

class Handler(socketserver.BaseRequestHandler):
	"""Main request handler."""

	def setup(self, *args, **kwargs):
		"""Set up this instance of Handler."""
		super().setup(*args, **kwargs)

		# Store a local pointer to SharedState.
		self.shared_state = shared_state

	def handle(self):
		"""Handle a request."""

		# readline is pretty convenient
		f = self.request.makefile()

		# read request line
		reqline = line = f.readline()
		split = line.rstrip().split(' ')
		http_version = len(split) > 2 and split[2].upper() or 'HTTP/0.9'

		if len(split) < 2 or split[0].upper() != 'GET':
			# only GET is implemented
			return self.send_error_page(http_version, 501, 'Not Implemented', extra=split[0])

		# read out the headers
		request_host = None
		pac_host = '" + location.host + ":' + str(LISTEN_PORT) # may not actually work
		effective_date = DATE
		auth = None
		while line.strip() != '':
			line = f.readline()
			ll = line.lower()
			if ll[:6] == 'host: ':
				pac_host = request_host = line[6:].rstrip()
				if ':' not in pac_host: # explicitly specify port if running on port 80
					pac_host += ':80'
			elif ll[:21] == 'x-waybackproxy-date: ':
				# API for a personal project of mine
				effective_date = line[21:].rstrip()
			elif ll[:21] == 'authorization: basic ':
				# asset date code passed as username:password
				auth = base64.b64decode(ll[21:])

		# parse the URL
		pac_file_paths = ('/proxy.pac', '/wpad.dat', '/wpad.da')
		if split[1][0] == '/' and split[1] not in pac_file_paths:
			# just a path (not corresponding to a PAC file) => transparent proxy
			# Host header and therefore HTTP/1.1 are required
			if not request_host:
				return self.send_error_page(http_version, 400, 'Host header missing')
			archived_url = 'http://' + request_host + split[1]
		else:
			# full URL => explicit proxy
			archived_url = split[1]
		request_url = archived_url
		parsed = urllib.parse.urlparse(request_url)

		# make a path
		path = parsed.path
		if parsed.query:
			path += '?' + parsed.query
		elif path == '':
			path == '/'

		# get the hostname for later
		host = parsed.netloc.split(':')
		hostname = host[0]

		# get cached date for redirects, if available
		original_date = effective_date
		effective_date = self.shared_state.date_cache.get(str(effective_date) + '\x00' + str(archived_url), effective_date)

		# get date from username:password, if available
		if auth:
			effective_date = auth.replace(':', '')

		# Effectively handle the request.
		try:
			if path in pac_file_paths:
				# PAC file to bypass QUICK_IMAGES requests if WAYBACK_API is not enabled.
				pac  = http_version + ''' 200 OK\r\n'''
				pac += '''Content-Type: application/x-ns-proxy-autoconfig\r\n'''
				pac += '''\r\n'''
				pac += '''function FindProxyForURL(url, host)\r\n'''
				pac += '''{\r\n'''
				if not WAYBACK_API:
					pac += '''	if (shExpMatch(url, "http://web.archive.org/web/*") && !shExpMatch(url, "http://web.archive.org/web/??????????????if_/*"))\r\n'''
					pac += '''	{\r\n'''
					pac += '''		return "DIRECT";\r\n'''
					pac += '''	}\r\n'''
				pac += '''	return "PROXY ''' + pac_host + '''";\r\n'''
				pac += '''}\r\n'''
				self.request.sendall(pac.encode('ascii', 'ignore'))
				return
			elif hostname in self.shared_state.whitelist:
				_print('[>] [byp]', archived_url)
			elif hostname == 'web.archive.org':
				if path[:5] != '/web/':
					# Launch settings if enabled.
					if SETTINGS_PAGE:
						return self.handle_settings(parsed.query)
					else:
						return self.send_error_page(http_version, 404, 'Not Found')
				else:
					# Pass requests through to web.archive.org. Required for QUICK_IMAGES.
					split = request_url.split('/')
					effective_date = split[4]
					archived_url = '/'.join(split[5:])
					_print('[>] [QI]', archived_url)
			elif GEOCITIES_FIX and hostname == 'www.geocities.com':
				# Apply GEOCITIES_FIX and pass it through.
				_print('[>]', archived_url)

				split = archived_url.split('/')
				hostname = split[2] = 'www.oocities.org'
				request_url = '/'.join(split)
			else:
				# Get from the Wayback Machine.
				_print('[>]', archived_url)

				request_url = 'https://web.archive.org/web/{0}if_/{1}'.format(effective_date, archived_url)

			# Check Wayback Machine Availability API where applicable, to avoid archived 404 pages and other site errors.
			split = request_url.split('/')
			if split[2] == 'web.archive.org':
				# Remove extraneous :80 from URL.
				if ':' in split[5]:
					if split[7][-3:] == ':80':
						split[7] = split[7][:-3]
				elif split[5][-3:] == ':80':
					split[5] = split[5][:-3]

				# Check availability LRU cache.
				availability_url = '/'.join(split[5:])
				new_url = self.shared_state.availability_cache.get(availability_url, None)
				if new_url:
					# In cache => replace URL immediately.
					request_url = new_url
				elif WAYBACK_API:
					# Not in cache => contact API.
					try:
						availability_endpoint = 'https://archive.org/wayback/available?url=' + urllib.parse.quote_plus(availability_url) + '&timestamp=' + effective_date[:14]
						availability = json.loads(self.shared_state.http.request('GET', availability_endpoint, timeout=10, retries=1).data)
						closest = availability.get('archived_snapshots', {}).get('closest', {})
						new_date = closest.get('timestamp', None)
					except:
						_print('[!] Failed to fetch Wayback availability data')
						new_date = None

					if new_date and new_date != effective_date[:14]:
						# Returned date is different.
						new_url = closest['url']

						# Add asset tag to the date.
						split = new_url.split('/')
						if len(effective_date) > 14:
							split[4] += effective_date[14:]
						else:
							split[4] += 'if_'
						new_url = '/'.join(split)

						# Replace URL and add it to the availability cache.
						request_url = self.shared_state.availability_cache[availability_url] = new_url

			# Start fetching the URL.
			retry = urllib3.util.retry.Retry(total=10, connect=10, read=5, redirect=0, backoff_factor=1)
			while True:
				conn = self.shared_state.http.urlopen('GET', request_url, redirect=False, retries=retry, preload_content=False)

				# Check for redirects.
				destination = conn.get_redirect_location()
				if destination:
					self.drain_conn(conn)
					conn.release_conn()

					# Check if the redirect goes to a different Wayback URL.
					match = re.search('''(?:(?:https?:)?//web.archive.org)?/web/([^/]+/)(.+)''', destination)
					if match:
						archived_dest = self.sanitize_redirect(match.group(2))

						# Check if the archived URL is different.
						if archived_dest != archived_url:
							# Remove extraneous :80 from URL.
							archived_dest = re.sub('''^([^/]*//[^/]+):80''', '\\1', archived_dest)

							# Add destination to availability cache and redirect the client.
							_print('[r]', archived_dest)
							self.shared_state.availability_cache[archived_dest] = 'http://web.archive.org/web/' + match.group(1) + archived_dest
							return self.send_redirect_page(http_version, archived_dest, conn.status)

					# Not an archived URL or same URL, redirect ourselves.
					request_url = destination
					continue

				# Wayback will add its JavaScript to anything it thinks is JavaScript.
				# If this is detected, redirect ourselves through the raw asset interface.
				content_type = conn.headers.get('Content-Type')
				guessed_content_type = conn.headers.get('X-Archive-Guessed-Content-Type')
				if not guessed_content_type:
					guessed_content_type = content_type
				if 'javascript' in guessed_content_type:
					match = re.match('''(https?://web\\.archive\\.org/web/[0-9]+)([^/]*)(.+)''', request_url)
					if match and match.group(2) != 'im_':
						self.drain_conn(conn)
						conn.release_conn()
						request_url = match.group(1) + 'im_' + match.group(3)
						continue

				# This request can proceed.
				break
		except urllib3.exceptions.MaxRetryError as e:
			_print('[!] Fetch retries exceeded:', e.reason)
			return self.send_error_page(http_version, 504, 'Gateway Timeout')
		except:
			# Some other fetch exception has occurred.
			_print('[!] Fetch exception:')
			traceback.print_exc()
			return self.send_error_page(http_version, 502, 'Bad Gateway')

		# Check for HTTP errors.
		if conn.status != 200:
			if conn.status in (403, 404): # not found
				if self.guess_and_send_redirect(http_version, archived_url):
					self.drain_conn(conn)
					conn.release_conn()
					return
			#elif conn.status in (301, 302): # redirect loop detection currently unused
			#	self.drain_conn(conn)
			#	conn.release_conn()
			#	return self.send_error_page(http_version, 508, 'Infinite Redirect Loop')

			if conn.status != 412: # tolerance exceeded has its own error message above
				_print('[!]', conn.status, conn.reason)

			# If the memento Link header is present, this is a website error
			# instead of a Wayback error. Pass it along if that's the case.
			if 'Link' not in conn.headers:
				self.drain_conn(conn)
				conn.release_conn()
				return self.send_error_page(http_version, conn.status, conn.reason)

		# Adjust content type.
		if content_type == None:
			content_type = 'text/html'
		elif not CONTENT_TYPE_ENCODING:
			idx = content_type.find(';')
			if idx > -1:
				content_type = content_type[:idx]

		# Set the archive mode.
		if GEOCITIES_FIX and hostname in ('www.oocities.org', 'www.oocities.com'):
			mode = 1 # oocities
		else:
			mode = 0 # Wayback Machine

		# Check content type to determine if this is HTML we need to patch.
		# Wayback will add its HTML to anything it thinks is HTML.
		if 'text/html' in guessed_content_type:
			# Some dynamically-generated links may end up pointing to
			# web.archive.org. Correct that by redirecting the Wayback
			# portion of the URL away if it ends up being HTML consumed
			# through the QUICK_IMAGES interface.
			if hostname == 'web.archive.org':
				self.drain_conn(conn)
				conn.release_conn()
				archived_url = '/'.join(request_url.split('/')[5:])
				_print('[r] [QI]', archived_url)
				return self.send_redirect_page(http_version, archived_url, 301)

			# Check if the date is within tolerance.
			if DATE_TOLERANCE != None:
				match = re.search('''(?://web\\.archive\\.org|^)/web/([0-9]+)''', conn.geturl() or '')
				if match:
					requested_date = match.group(1)
					if self.wayback_to_datetime(requested_date) > self.wayback_to_datetime(original_date) + datetime.timedelta(int(DATE_TOLERANCE)):
						self.drain_conn(conn)
						conn.release_conn()
						_print('[!]', requested_date, 'is outside the configured tolerance of', DATE_TOLERANCE, 'days')
						if not self.guess_and_send_redirect(http_version, archived_url):
							self.send_error_page(http_version, 412, 'Snapshot ' + requested_date + ' not available')
						return

			# Consume all data.
			data = conn.read()
			conn.release_conn()

			# Patch the page.
			if mode == 0: # Wayback Machine
				# Check if this is a Wayback Machine page.
				if b'<title>Wayback Machine</title>' in data:
					# Check if this is an exclusion (robots.txt?) error page.
					if b'<p>This URL has been excluded from the Wayback Machine.</p>' in data:
						return self.send_error_page(http_version, 403, 'URL excluded')

					# Check if this is a media playback iframe page.
					# Some websites (especially ones that use frames)
					# inexplicably render inside a media playback iframe.
					# In that case, a simple redirect would result in a
					# redirect loop, so fetch and render the URL instead.
					match = re.search(b'''<iframe id="playback" src="((?:(?:https?:)?//web.archive.org)?/web/[^"]+)"''', data)
					if match:
						# Extract the content URL.
						request_url = match.group(1).decode('ascii', 'ignore')
						archived_url = '/'.join(request_url.split('/')[5:])

						# Start fetching the URL.
						_print('[f]', archived_url)
						conn = self.shared_state.http.urlopen('GET', request_url, retries=retry, preload_content=False)

						if conn.status != 200:
							_print('[!]', conn.status, conn.reason)

							# If the memento Link header is present, this is a website error
							# instead of a Wayback error. Pass it along if that's the case.
							if 'Link' not in conn.headers:
								self.drain_conn(conn)
								conn.release_conn()
								return self.send_error_page(http_version, conn.status, conn.reason)

						# Identify content type so we don't modify non-HTML content.
						content_type = conn.headers.get('Content-Type')
						if not CONTENT_TYPE_ENCODING:
							idx = content_type.find(';')
							if idx > -1:
								content_type = content_type[:idx]
						if 'text/html' in content_type:
							# Consume all data and proceed with patching the page.
							data = conn.read()
							conn.release_conn()
						else:
							# Pass non-HTML data through.
							return self.send_passthrough(conn, http_version, content_type, request_url)

				# Check if this is a Wayback Machine redirect page.
				if b'<title></title>' in data and b'<span class="label style-scope media-button"><!---->Wayback Machine<!----></span>' in data:
					match = re.search(b'''<p class="impatient"><a href="(?:(?:https?:)?//web\\.archive\\.org)?/web/([^/]+)/([^"]+)">Impatient\\?</a></p>''', data)
					if match:
						# Sanitize the URL.
						archived_url = self.sanitize_redirect(match.group(2).decode('ascii', 'ignore'))

						# Add URL to the date LRU cache.
						self.shared_state.date_cache[str(effective_date) + '\x00' + archived_url] = match.group(1).decode('ascii', 'ignore')

						# Get the original HTTP redirect code.
						match = re.search(b'''<p class="code shift red">Got an HTTP ([0-9]+)''', data)
						try:
							redirect_code = int(match.group(1))
						except:
							redirect_code = 302

						# Redirect client to the URL.
						_print('[r]', archived_url)
						return self.send_redirect_page(http_version, archived_url, redirect_code)

				# Remove pre-toolbar scripts and CSS.
				data = re.sub(b'''(?:<!-- is_embed=True -->\\r?\\n?)?<script (?:type="text/javascript" )?src="[^"]*/_static/js/.*<!-- End Wayback Rewrite JS Include -->\\r?\\n''', b'', data, count=1, flags=re.S)
				# Remove toolbar. The if_ asset tag serves no toolbar, but we remove it just in case.
				data = re.sub(b'''<!-- BEGIN WAYBACK TOOLBAR INSERT -->.*<!-- END WAYBACK TOOLBAR INSERT -->''', b'', data, count=1, flags=re.S)
				# Remove comments on footer.
				data = re.sub(b'''<!--\\r?\\n     FILE ARCHIVED .*$''', b'', data, flags=re.S)
				# Fix base tag.
				data = re.sub(b'''(<base\\s+[^>]*href=["']?)(?:(?:https?:)?//web.archive.org)?/web/[^/]+/(?:[^:/]+://)?''', b'\\1http://', data, flags=re.I + re.S)

				# Remove extraneous :80 from links.
				data = re.sub(b'((?:(?:https?:)?//web.archive.org)?/web/)([^/]+)/([^/:]+)://([^/:]+):80/', b'\\1\\2/\\3://\\4/', data)
				# Fix links.
				if QUICK_IMAGES:
					# QUICK_IMAGES works by intercepting asset URLs (those
					# with a date code ending in im_, js_...) and letting the
					# proxy pass them through. This may reduce load time
					# because Wayback doesn't have to hunt down the closest
					# copy of that asset to DATE, as those URLs have specific
					# date codes. This taints the HTML with web.archive.org
					# URLs. QUICK_IMAGES=2 uses the original URLs with an added
					# username:password, which taints less but is not supported
					# by all browsers - IE notably kills the whole page if it
					# sees an iframe pointing to an invalid URL.
					def filter_asset(match):
						if match.group(2) in (None, b'if_', b'fw_'): # non-asset URL
							return match.group(3) == b'https://' and b'http://' or match.group(3) # convert secure non-asset URLs to regular HTTP
						asset_type = match.group(2)
						if asset_type == b'js_': # cut down on the JavaScript detector's second request
							asset_type = b'im_'
						if QUICK_IMAGES == 2:
							return b'http://' + match.group(1) + b':' + asset_type + b'@'
						else:
							return b'http://web.archive.org/web/' + match.group(1) + asset_type + b'/' + match.group(3)
					data = re.sub(b'(?:(?:https?:)?//web.archive.org)?/web/([0-9]+)([a-z]+_)?/([^:/]+:(?://)?)', filter_asset, data)
				else:
					# Remove asset URLs while simultaneously adding them to the date LRU cache
					# with their respective date and converting secure URLs to regular HTTP.
					def add_to_date_cache(match):
						orig_url = match.group(2)
						if orig_url[:8] == b'https://':
							orig_url = b'http://' + orig_url[8:]
						self.shared_state.date_cache[str(effective_date) + '\x00' + orig_url.decode('ascii', 'ignore')] = match.group(1).decode('ascii', 'ignore').replace('js_', 'im_')
						return orig_url
					data = re.sub(b'''(?:(?:https?:)?//web.archive.org)?/web/([^/]+)/([^"\\'#<>]+)''', add_to_date_cache, data)
			elif mode == 1: # oocities
				# Remove viewport/cache-control/max-width code from the header.
				data = re.sub(b'''^.*?\n\n''', b'', data, flags=re.S)
				# Remove archive notice and tracking code from the footer.
				data = re.sub(b'''<style> \n.zoomout { -webkit-transition: .*$''', b'', data, flags=re.S)
				# Remove clearly labeled snippets from Geocities.
				data = re.sub(b'''^.*<\\!-- text above generated by server\\. PLEASE REMOVE -->''', b'', data, flags=re.S)
				data = re.sub(b'''<\\!-- following code added by server\\. PLEASE REMOVE -->.*<\!-- preceding code added by server\. PLEASE REMOVE -->''', b'', data, flags=re.S)
				data = re.sub(b'''<\\!-- text below generated by server\\. PLEASE REMOVE -->.*$''', b'', data, flags=re.S)

				# Fix links.
				data = re.sub(b'''//([^\\.]*\\.)?oocities\\.com/''', b'//\\1geocities.com/', data, flags=re.S)

			# Send patched page.
			self.send_response_headers(conn, http_version, content_type, request_url, content_length=len(data))
			self.request.sendall(data)
			self.request.close()
		else:
			# Pass non-HTML data through.
			self.send_passthrough(conn, http_version, content_type, request_url)

	def send_passthrough(self, conn, http_version, content_type, request_url):
		"""Pass data through to the client unmodified (save for our headers)."""
		self.send_response_headers(conn, http_version, content_type, request_url, content_length=True)
		for data in conn.stream(1024):
			self.request.sendall(data)
		conn.release_conn()
		self.request.close()

	def send_response_headers(self, conn, http_version, content_type, request_url, content_length=False):
		"""Generate and send the response headers."""

		# Pass the HTTP version, and error code if there is one.
		response = '{0} {1} {2}'.format(http_version, conn.status, conn.reason.replace('\n', ' '))

		# Add Content-Type, Content-Length and the caching ETag.
		response += '\r\nContent-Type: ' + content_type
		if type(content_length) == int:
			response += '\r\nContent-Length: ' + str(content_length)
			content_length = False # don't pass the original length through
		response += '\r\nETag: "' + request_url.replace('"', '') + '"'
		response += '\r\nConnection: close' # helps with IE6 trying to use proxy keep alive and holding half-open connections

		# Pass X-Archive-Orig-* (and Content-Length if requested) headers through.
		for header in conn.headers:
			if header.find('X-Archive-Orig-') == 0:
				orig_header = header[15:]
				# Skip headers which may affect client behavior.
				if orig_header.lower() not in ('connection', 'location', 'content-type', 'content-length', 'etag', 'authorization', 'set-cookie'):
					response += '\r\n' + orig_header + ': ' + conn.headers[header]
			elif content_length and header.lower() == 'content-length':
				response += '\r\n' + header + ': ' + conn.headers[header]

		# Finish and send the request.
		response += '\r\n\r\n'
		self.request.sendall(response.encode('utf8', 'ignore'))

	def send_error_page(self, http_version, code, reason, extra=''):
		"""Generate an error page."""

		# Get a description for this error code.
		if code in (404, 508): # page not archived or redirect loop
			description = 'This page may not be archived by the Wayback Machine.'
		elif code == 403: # not crawled due to exclusion
			description = 'This page was not archived due to a Wayback Machine exclusion.'
		elif code == 501: # method not implemented
			description = 'WaybackProxy only implements the GET method. Your browser sent a request with the {0} method.'.format(extra.upper())
		elif code == 502: # exception
			description = 'This page could not be fetched due to an unknown error.'
		elif code == 504: # timeout
			description = 'This page could not be fetched due to a Wayback Machine server error.'
		elif code == 412: # outside of tolerance
			description = 'The earliest snapshot for this page is outside of the configured tolerance interval.'
		elif code == 400 and reason == 'Host header missing': # no host header in transparent mode
			description = 'WaybackProxy\'s transparent mode requires an HTTP/1.1-compliant client.'
		else: # another error
			description = 'Unknown error. The Wayback Machine may be experiencing technical difficulties.'

		# Read error page file.
		try:
			with open('error.html', 'r', encoding='utf8', errors='ignore') as f:
				error_page = f.read()
		except:
			# Just send the code and reason as a backup.
			error_page = '${code} ${reason}'

		# Format error page template.
		signature = self.signature()
		error_page = string.Template(error_page).substitute(**locals())
		error_page_len = len(error_page)

		# Send formatted error page and stop.
		self.request.sendall(
			'{http_version} {code} {reason}\r\n'
			'Content-Type: text/html\r\n'
			'Content-Length: {error_page_len}\r\n'
			'\r\n'
			'{error_page}'
			.format(**locals()).encode('utf8', 'ignore')
		)
		self.request.close()

	def send_redirect_page(self, http_version, target, code=302):
		"""Generate a redirect page."""

		# make redirect page
		redirectpage  = '<html><head><title>Redirect</title><meta http-equiv="refresh" content="0;url='
		redirectpage += target
		redirectpage += '"></head><body><p>If you are not redirected, <a href="'
		redirectpage += target
		redirectpage += '">click here</a>.</p></body></html>'

		# send redirect page and stop
		self.request.sendall('{0} {1} Found\r\nLocation: {2}\r\nContent-Type: text/html\r\nContent-Length: {3}\r\n\r\n{4}'.format(http_version, code, target, len(redirectpage), redirectpage).encode('utf8', 'ignore'))
		self.request.close()

	def guess_and_send_redirect(self, http_version, guess_url):
		# Heuristically determine the static URL for some redirect scripts.
		parsed = urllib.parse.urlparse(guess_url)
		match = re.search('''(?:^|&)[^=]+=((?:https?(?:%3A|:)(?:%2F|/)|www[0-9]*\\.[^/%]+)?(?:%2F|/)[^&]+)''', parsed.query, re.I) # URL in query parameters
		if not match:
			full_path = parsed.path
			if parsed.query:
				full_path += '?' + parsed.query
			match = re.search('''((?:https?(?:%3A|:)(?:%2F|/)|www[0-9]*\\.[^/%]+)(?:(?:%2F|/).+|$))''', full_path, re.I) # URL in path or full query
		if match: # found URL
			# Decode and sanitize the URL.
			new_url = self.sanitize_redirect(urllib.parse.unquote_plus(match.group(1)))

			# Redirect client to the URL.
			_print('[r] [g]', new_url)
			self.send_redirect_page(http_version, new_url)
			return True
		return False

	def handle_settings(self, query):
		"""Generate the settings page."""

		global DATE, DATE_TOLERANCE, GEOCITIES_FIX, QUICK_IMAGES, WAYBACK_API, CONTENT_TYPE_ENCODING, SILENT, SETTINGS_PAGE

		if query != '': # handle any parameters that may have been sent
			parsed = urllib.parse.parse_qs(query)

			if 'date' in parsed and 'dateTolerance' in parsed:
				if DATE != parsed['date'][0]:
					DATE = parsed['date'][0]
					self.shared_state.date_cache.clear()
					self.shared_state.availability_cache.clear()
				if DATE_TOLERANCE != parsed['dateTolerance'][0]:
					DATE_TOLERANCE = parsed['dateTolerance'][0]
				GEOCITIES_FIX = 'gcFix' in parsed
				QUICK_IMAGES = 'quickImages' in parsed
				CONTENT_TYPE_ENCODING = 'ctEncoding' in parsed

		# send the page and stop
		settingspage  = 'HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n'
		settingspage += '<html><head><title>WaybackProxy Settings</title></head><body><p><b>'
		settingspage += self.signature()
		settingspage += '</b></p><form method="get" action="/">'
		settingspage += '<p>Date to get pages from: <input type="text" name="date" size="8" value="'
		settingspage += str(DATE)
		settingspage += '"><p>Date tolerance: <input type="text" name="dateTolerance" size="8" value="'
		settingspage += str(DATE_TOLERANCE)
		settingspage += '"> days<br><input type="checkbox" name="gcFix"'
		if GEOCITIES_FIX:
			settingspage += ' checked'
		settingspage += '> Geocities Fix<br><input type="checkbox" name="quickImages"'
		if QUICK_IMAGES:
			settingspage += ' checked'
		settingspage += '> Quick images<br><input type="checkbox" name="ctEncoding"'
		if CONTENT_TYPE_ENCODING:
			settingspage += ' checked'
		settingspage += '> Encoding in Content-Type</p><p><input type="submit" value="Save"></p></form></body></html>'
		self.request.send(settingspage.encode('utf8', 'ignore'))
		self.request.close()

	def sanitize_redirect(self, url):
		"""Sanitize an URL for client-side redirection."""
		if url[0] != '/' and '://' not in url:
			# Add protocol if the URL is absolute but missing a protocol.
			return 'http://' + url
		elif url[:8].lower() == 'https://':
			# Convert secure URLs to regular HTTP.
			return 'http://' + url[8:]
		else:
			# No changes required.
			return url

	def signature(self):
		"""Return the server signature."""
		return 'WaybackProxy on {0}'.format(socket.gethostname())

	def wayback_to_datetime(self, date):
		"""Convert a Wayback format date string to a datetime.datetime object."""
		date = str(date)
		fmt = '%Y%m%d%H%M%S'
		fmt_len = 14
		while fmt:
			try:
				return datetime.datetime.strptime(date[:fmt_len], fmt)
			except:
				fmt = fmt[:-2]
				fmt_len -= 2

	def drain_conn(self, conn):
		getattr(conn, 'drain_conn', conn.read)()

print_lock = threading.Lock()
def _print(*args, **kwargs):
	"""Logging function."""
	if SILENT:
		return
	with print_lock:
		print(*args, **kwargs, flush=True)

def main():
	"""Starts the server."""
	server = ThreadingTCPServer(('', LISTEN_PORT), Handler)
	_print('[-] Now listening on port', LISTEN_PORT)
	_print('[-] Date set to', DATE)
	try:
		server.serve_forever()
	except KeyboardInterrupt: # Ctrl+C to stop
		pass

if __name__ == '__main__':
	main()