#!/usr/bin/env python
#
# Copyright 2009 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
"""A class to serve pages from zip files and use memcache for performance.
This contains a class and a function to create an anonymous instance of the
class to serve HTTP GET requests. Memcache is used to increase response speed
and lower processing cycles used in serving. Credit to Guido van Rossum and
his implementation of zipserve which served as a reference as I wrote this.
MemcachedZipHandler: Class that serves request
create_handler: method to create instance of MemcachedZipHandler
"""
__author__ = 'jmatt@google.com (Justin Mattson)'
import email.Utils
import logging
import mimetypes
import time
import zipfile
from google.appengine.api import memcache
from google.appengine.ext import webapp
from google.appengine.ext.webapp import util
from time import localtime, strftime
def create_handler(zip_files, max_age=None, public=None):
"""Factory method to create a MemcachedZipHandler instance.
Args:
zip_files: A list of file names, or a list of lists of file name, first
member of file mappings. See MemcachedZipHandler documentation for
more information about using the list of lists format
max_age: The maximum client-side cache lifetime
public: Whether this should be declared public in the client-side cache
Returns:
A MemcachedZipHandler wrapped in a pretty, anonymous bow for use with App
Engine
Raises:
ValueError: if the zip_files argument is not a list
"""
# verify argument integrity. If the argument is passed in list format,
# convert it to list of lists format
if zip_files and type(zip_files).__name__ == 'list':
num_items = len(zip_files)
while num_items > 0:
if type(zip_files[num_items - 1]).__name__ != 'list':
zip_files[num_items - 1] = [zip_files[num_items-1]]
num_items -= 1
else:
raise ValueError('File name arguments must be a list')
class HandlerWrapper(MemcachedZipHandler):
"""Simple wrapper for an instance of MemcachedZipHandler.
I'm still not sure why this is needed
"""
def get(self, name):
self.zipfilenames = zip_files
self.TrueGet(name)
if max_age is not None:
MAX_AGE = max_age
if public is not None:
PUBLIC = public
return HandlerWrapper
class MemcachedZipHandler(webapp.RequestHandler):
"""Handles get requests for a given URL.
Serves a GET request from a series of zip files. As files are served they are
put into memcache, which is much faster than retreiving them from the zip
source file again. It also uses considerably fewer CPU cycles.
"""
zipfile_cache = {} # class cache of source zip files
MAX_AGE = 600 # max client-side cache lifetime
PUBLIC = True # public cache setting
CACHE_PREFIX = 'cache://' # memcache key prefix for actual URLs
NEG_CACHE_PREFIX = 'noncache://' # memcache key prefix for non-existant URL
intlString = 'intl/'
validLangs = ['en', 'de', 'es', 'fr','it','ja','zh-CN','zh-TW']
def TrueGet(self, reqUri):
"""The top-level entry point to serving requests.
Called 'True' get because it does the work when called from the wrapper
class' get method. Some logic is applied to the request to serve files
from an intl/<lang>/... directory or fall through to the default language.
Args:
name: URL requested
Returns:
None
"""
langName = 'en'
resetLangCookie = False
urlLangName = None
retry = False
isValidIntl = False
# Try to retrieve the user's lang pref from the cookie. If there is no
# lang pref cookie in the request, add set-cookie to the response with the
# default value of 'en'.
try:
langName = self.request.cookies['android_developer_pref_lang']
except KeyError:
resetLangCookie = True
#logging.info('==========================EXCEPTION: NO LANG COOKIE FOUND, USING [%s]', langName)
logging.info('==========================REQ INIT name [%s] langName [%s]', reqUri, langName)
# Preprocess the req url. If it references a directory or the domain itself,
# append '/index.html' to the url and 302 redirect. Otherwise, continue
# processing the request below.
name = self.PreprocessUrl(reqUri, langName)
if name:
# Do some prep for handling intl requests. Parse the url and validate
# the intl/lang substring, extract the url lang code (urlLangName) and the
# the uri that follows the intl/lang substring(contentUri)
sections = name.split("/", 2)
contentUri = 0
isIntl = len(sections) > 1 and (sections[0] == "intl")
if isIntl:
isValidIntl = sections[1] in self.validLangs
if isValidIntl:
urlLangName = sections[1]
contentUri = sections[2]
if (langName != urlLangName):
# if the lang code in the request is different from that in
# the cookie, reset the cookie to the url lang value.
langName = urlLangName
resetLangCookie = True
#logging.info('INTL PREP resetting langName to urlLangName [%s]', langName)
#else:
# logging.info('INTL PREP no need to reset langName')
# Send for processing
if self.isCleanUrl(name, langName, isValidIntl):
# handle a 'clean' request.
# Try to form a response using the actual request url.
if not self.CreateResponse(name, langName, isValidIntl, resetLangCookie):
# If CreateResponse returns False, there was no such document
# in the intl/lang tree. Before going to 404, see if there is an
# English-language version of the doc in the default
# default tree and return it, else go to 404.
self.CreateResponse(contentUri, langName, False, resetLangCookie)
elif isIntl:
# handle the case where we need to pass through an invalid intl req
# for processing (so as to get 404 as appropriate). This is needed
# because intl urls are passed through clean and retried in English,
# if necessary.
logging.info(' Handling an invalid intl request...')
self.CreateResponse(name, langName, isValidIntl, resetLangCookie)
else:
# handle the case where we have a non-clean url (usually a non-intl
# url) that we need to interpret in the context of any lang pref
# that is set. Prepend an intl/lang string to the request url and
# send it as a 302 redirect. After the redirect, the subsequent
# request will be handled as a clean url.
self.RedirToIntl(name, self.intlString, langName)
def isCleanUrl(self, name, langName, isValidIntl):
"""Determine whether to pass an incoming url straight to processing.
Args:
name: The incoming URL
Returns:
boolean: Whether the URL should be sent straight to processing
"""
if (langName == 'en') or isValidIntl or not ('.html' in name) or (not isValidIntl and not langName):
return True
def PreprocessUrl(self, name, langName):
"""Any preprocessing work on the URL when it comes in.
Put any work related to interpretting the incoming URL here. For example,
this is used to redirect requests for a directory to the index.html file
in that directory. Subclasses should override this method to do different
preprocessing.
Args:
name: The incoming URL
Returns:
False if the request was redirected to '/index.html', or
The processed URL, otherwise
"""
# determine if this is a request for a directory
final_path_segment = name
final_slash_offset = name.rfind('/')
if final_slash_offset != len(name) - 1:
final_path_segment = name[final_slash_offset + 1:]
if final_path_segment.find('.') == -1:
name = ''.join([name, '/'])
# if this is a directory or the domain itself, redirect to /index.html
if not name or (name[len(name) - 1:] == '/'):
uri = ''.join(['/', name, 'index.html'])
logging.info('--->PREPROCESSING REDIRECT [%s] to [%s] with langName [%s]', name, uri, langName)
self.redirect(uri, False)
return False
else:
return name
def RedirToIntl(self, name, intlString, langName):
"""Redirect an incoming request to the appropriate intl uri.
Builds the intl/lang string from a base (en) string
and redirects (302) the request to look for a version
of the file in the language that matches the client-
supplied cookie value.
Args:
name: The incoming, preprocessed URL
Returns:
The lang-specific URL
"""
builtIntlLangUri = ''.join([intlString, langName, '/', name, '?', self.request.query_string])
uri = ''.join(['/', builtIntlLangUri])
logging.info('-->>REDIRECTING %s to %s', name, uri)
self.redirect(uri, False)
return uri
def CreateResponse(self, name, langName, isValidIntl, resetLangCookie):
"""Process the url and form a response, if appropriate.
Attempts to retrieve the requested file (name) from cache,
negative cache, or store (zip) and form the response.
For intl requests that are not found (in the localized tree),
returns False rather than forming a response, so that
the request can be retried with the base url (this is the
fallthrough to default language).
For requests that are found, forms the headers and
adds the content to the response entity. If the request was
for an intl (localized) url, also resets the language cookie
to the language specified in the url if needed, to ensure that
the client language and response data remain harmonious.
Args:
name: The incoming, preprocessed URL
langName: The language id. Used as necessary to reset the
language cookie in the response.
isValidIntl: If present, indicates whether the request is
for a language-specific url
resetLangCookie: Whether the response should reset the
language cookie to 'langName'
Returns:
True: A response was successfully created for the request
False: No response was created.
"""
# see if we have the page in the memcache
logging.info('PROCESSING %s langName [%s] isValidIntl [%s] resetLang [%s]',
name, langName, isValidIntl, resetLangCookie)
resp_data = self.GetFromCache(name)
if resp_data is None:
logging.info(' Cache miss for %s', name)
resp_data = self.GetFromNegativeCache(name)
if resp_data is None:
resp_data = self.GetFromStore(name)
# IF we have the file, put it in the memcache
# ELSE put it in the negative cache
if resp_data is not None:
self.StoreOrUpdateInCache(name, resp_data)
elif isValidIntl:
# couldn't find the intl doc. Try to fall through to English.
#logging.info(' Retrying with base uri...')
return False
else:
logging.info(' Adding %s to negative cache, serving 404', name)
self.StoreInNegativeCache(name)
self.Write404Error()
return True
else:
# found it in negative cache
self.Write404Error()
return True
# found content from cache or store
logging.info('FOUND CLEAN')
if resetLangCookie:
logging.info(' Resetting android_developer_pref_lang cookie to [%s]',
langName)
expireDate = time.mktime(localtime()) + 60 * 60 * 24 * 365 * 10
self.response.headers.add_header('Set-Cookie',
'android_developer_pref_lang=%s; path=/; expires=%s' %
(langName, strftime("%a, %d %b %Y %H:%M:%S", localtime(expireDate))))
mustRevalidate = False
if ('.html' in name):
# revalidate html files -- workaround for cache inconsistencies for
# negotiated responses
mustRevalidate = True
logging.info(' Adding [Vary: Cookie] to response...')
self.response.headers.add_header('Vary', 'Cookie')
content_type, encoding = mimetypes.guess_type(name)
if content_type:
self.response.headers['Content-Type'] = content_type
self.SetCachingHeaders(mustRevalidate)
self.response.out.write(resp_data)
elif (name == 'favicon.ico'):
self.response.headers['Content-Type'] = 'image/x-icon'
self.SetCachingHeaders(mustRevalidate)
self.response.out.write(resp_data)
elif name.endswith('.psd'):
self.response.headers['Content-Type'] = 'application/octet-stream'
self.SetCachingHeaders(mustRevalidate)
self.response.out.write(resp_data)
return True
def GetFromStore(self, file_path):
"""Retrieve file from zip files.
Get the file from the source, it must not have been in the memcache. If
possible, we'll use the zip file index to quickly locate where the file
should be found. (See MapToFileArchive documentation for assumptions about
file ordering.) If we don't have an index or don't find the file where the
index says we should, look through all the zip files to find it.
Args:
file_path: the file that we're looking for
Returns:
The contents of the requested file
"""
resp_data = None
file_itr = iter(self.zipfilenames)
# check the index, if we have one, to see what archive the file is in
archive_name = self.MapFileToArchive(file_path)
if not archive_name:
archive_name = file_itr.next()[0]
while resp_data is None and archive_name:
zip_archive = self.LoadZipFile(archive_name)
if zip_archive:
# we expect some lookups will fail, and that's okay, 404s will deal
# with that
try:
resp_data = zip_archive.read(file_path)
except (KeyError, RuntimeError), err:
# no op
x = False
if resp_data is not None:
logging.info('%s read from %s', file_path, archive_name)
try:
archive_name = file_itr.next()[0]
except (StopIteration), err:
archive_name = False
return resp_data
def LoadZipFile(self, zipfilename):
"""Convenience method to load zip file.
Just a convenience method to load the zip file from the data store. This is
useful if we ever want to change data stores and also as a means of
dependency injection for testing. This method will look at our file cache
first, and then load and cache the file if there's a cache miss
Args:
zipfilename: the name of the zip file to load
Returns:
The zip file requested, or None if there is an I/O error
"""
zip_archive = None
zip_archive = self.zipfile_cache.get(zipfilename)
if zip_archive is None:
try:
zip_archive = zipfile.ZipFile(zipfilename)
self.zipfile_cache[zipfilename] = zip_archive
except (IOError, RuntimeError), err:
logging.error('Can\'t open zipfile %s, cause: %s' % (zipfilename,
err))
return zip_archive
def MapFileToArchive(self, file_path):
"""Given a file name, determine what archive it should be in.
This method makes two critical assumptions.
(1) The zip files passed as an argument to the handler, if concatenated
in that same order, would result in a total ordering
of all the files. See (2) for ordering type.
(2) Upper case letters before lower case letters. The traversal of a
directory tree is depth first. A parent directory's files are added
before the files of any child directories
Args:
file_path: the file to be mapped to an archive
Returns:
The name of the archive where we expect the file to be
"""
num_archives = len(self.zipfilenames)
while num_archives > 0:
target = self.zipfilenames[num_archives - 1]
if len(target) > 1:
if self.CompareFilenames(target[1], file_path) >= 0:
return target[0]
num_archives -= 1
return None
def CompareFilenames(self, file1, file2):
"""Determines whether file1 is lexigraphically 'before' file2.
WARNING: This method assumes that paths are output in a depth-first,
with parent directories' files stored before childs'
We say that file1 is lexigraphically before file2 if the last non-matching
path segment of file1 is alphabetically before file2.
Args:
file1: the first file path
file2: the second file path
Returns:
A positive number if file1 is before file2
A negative number if file2 is before file1
0 if filenames are the same
"""
f1_segments = file1.split('/')
f2_segments = file2.split('/')
segment_ptr = 0
while (segment_ptr < len(f1_segments) and
segment_ptr < len(f2_segments) and
f1_segments[segment_ptr] == f2_segments[segment_ptr]):
segment_ptr += 1
if len(f1_segments) == len(f2_segments):
# we fell off the end, the paths much be the same
if segment_ptr == len(f1_segments):
return 0
# we didn't fall of the end, compare the segments where they differ
if f1_segments[segment_ptr] < f2_segments[segment_ptr]:
return 1
elif f1_segments[segment_ptr] > f2_segments[segment_ptr]:
return -1
else:
return 0
# the number of segments differs, we either mismatched comparing
# directories, or comparing a file to a directory
else:
# IF we were looking at the last segment of one of the paths,
# the one with fewer segments is first because files come before
# directories
# ELSE we just need to compare directory names
if (segment_ptr + 1 == len(f1_segments) or
segment_ptr + 1 == len(f2_segments)):
return len(f2_segments) - len(f1_segments)
else:
if f1_segments[segment_ptr] < f2_segments[segment_ptr]:
return 1
elif f1_segments[segment_ptr] > f2_segments[segment_ptr]:
return -1
else:
return 0
def SetCachingHeaders(self, revalidate):
"""Set caching headers for the request."""
max_age = self.MAX_AGE
#self.response.headers['Expires'] = email.Utils.formatdate(
# time.time() + max_age, usegmt=True)
cache_control = []
if self.PUBLIC:
cache_control.append('public')
cache_control.append('max-age=%d' % max_age)
if revalidate:
cache_control.append('must-revalidate')
self.response.headers['Cache-Control'] = ', '.join(cache_control)
def GetFromCache(self, filename):
"""Get file from memcache, if available.
Args:
filename: The URL of the file to return
Returns:
The content of the file
"""
return memcache.get('%s%s' % (self.CACHE_PREFIX, filename))
def StoreOrUpdateInCache(self, filename, data):
"""Store data in the cache.
Store a piece of data in the memcache. Memcache has a maximum item size of
1*10^6 bytes. If the data is too large, fail, but log the failure. Future
work will consider compressing the data before storing or chunking it
Args:
filename: the name of the file to store
data: the data of the file
Returns:
None
"""
try:
if not memcache.add('%s%s' % (self.CACHE_PREFIX, filename), data):
memcache.replace('%s%s' % (self.CACHE_PREFIX, filename), data)
except (ValueError), err:
logging.warning('Data size too large to cache\n%s' % err)
def Write404Error(self):
"""Ouptut a simple 404 response."""
self.error(404)
self.response.out.write(
''.join(['<html><head><title>404: Not Found</title></head>',
'<body><b><h2>Error 404</h2><br/>',
'File not found</b></body></html>']))
def StoreInNegativeCache(self, filename):
"""If a non-existant URL is accessed, cache this result as well.
Future work should consider setting a maximum negative cache size to
prevent it from from negatively impacting the real cache.
Args:
filename: URL to add ot negative cache
Returns:
None
"""
memcache.add('%s%s' % (self.NEG_CACHE_PREFIX, filename), -1)
def GetFromNegativeCache(self, filename):
"""Retrieve from negative cache.
Args:
filename: URL to retreive
Returns:
The file contents if present in the negative cache.
"""
return memcache.get('%s%s' % (self.NEG_CACHE_PREFIX, filename))
def main():
application = webapp.WSGIApplication([('/([^/]+)/(.*)',
MemcachedZipHandler)])
util.run_wsgi_app(application)
if __name__ == '__main__':
main()