435 lines
15 KiB
Python
Executable file
435 lines
15 KiB
Python
Executable file
#!/usr/bin/env python
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#
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# Copyright 2008 Google Inc.
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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"""A class to serve pages from zip files and use memcache for performance.
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This contains a class and a function to create an anonymous instance of the
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class to serve HTTP GET requests. Memcache is used to increase response speed
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and lower processing cycles used in serving. Credit to Guido van Rossum and
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his implementation of zipserve which served as a reference as I wrote this.
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NOTE: THIS FILE WAS MODIFIED TO SUPPORT CLIENT CACHING
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MemcachedZipHandler: Class that serves request
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create_handler: method to create instance of MemcachedZipHandler
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"""
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__author__ = 'j.c@google.com (Justin Mattson)'
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import email.Utils
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import datetime
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import logging
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import mimetypes
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import os
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import time
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import zipfile
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from google.appengine.api import memcache
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from google.appengine.ext import webapp
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from google.appengine.ext.webapp import util
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from django.utils.hashcompat import md5_constructor
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def create_handler(zip_files, max_age=None, public=None, client_caching=None):
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"""Factory method to create a MemcachedZipHandler instance.
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Args:
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zip_files: A list of file names, or a list of lists of file name, first
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member of file mappings. See MemcachedZipHandler documentation for
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more information about using the list of lists format
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max_age: The maximum client-side cache lifetime
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public: Whether this should be declared public in the client-side cache
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Returns:
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A MemcachedZipHandler wrapped in a pretty, anonymous bow for use with App
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Engine
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Raises:
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ValueError: if the zip_files argument is not a list
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"""
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# verify argument integrity. If the argument is passed in list format,
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# convert it to list of lists format
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if zip_files and type(zip_files).__name__ == 'list':
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num_items = len(zip_files)
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while num_items > 0:
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if type(zip_files[num_items - 1]).__name__ != 'list':
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zip_files[num_items - 1] = [zip_files[num_items-1]]
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num_items -= 1
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else:
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raise ValueError('File name arguments must be a list')
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class HandlerWrapper(MemcachedZipHandler):
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"""Simple wrapper for an instance of MemcachedZipHandler.
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I'm still not sure why this is needed
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"""
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def get(self, name):
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self.zipfilenames = zip_files
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if max_age is not None:
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self.MAX_AGE = max_age
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if public is not None:
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self.PUBLIC = public
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if client_caching is not None:
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self.CLIENT_CACHING = client_caching
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self.TrueGet(name)
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return HandlerWrapper
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class CacheFile(object):
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pass
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class MemcachedZipHandler(webapp.RequestHandler):
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"""Handles get requests for a given URL.
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Serves a GET request from a series of zip files. As files are served they are
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put into memcache, which is much faster than retreiving them from the zip
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source file again. It also uses considerably fewer CPU cycles.
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"""
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zipfile_cache = {} # class cache of source zip files
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current_last_modified = None # where we save the current last modified datetime
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current_etag = None # the current ETag of a file served
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CLIENT_CACHING = True # is client caching enabled? (sending Last-Modified and ETag within response!)
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MAX_AGE = 600 # max client-side cache lifetime
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PUBLIC = True # public cache setting
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CACHE_PREFIX = "cache://" # memcache key prefix for actual URLs
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NEG_CACHE_PREFIX = "noncache://" # memcache key prefix for non-existant URL
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def TrueGet(self, name):
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"""The top-level entry point to serving requests.
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Called 'True' get because it does the work when called from the wrapper
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class' get method
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Args:
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name: URL requested
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Returns:
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None
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"""
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name = self.PreprocessUrl(name)
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# see if we have the page in the memcache
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resp_data = self.GetFromCache(name)
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if resp_data is None:
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logging.info('Cache miss for %s', name)
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resp_data = self.GetFromNegativeCache(name)
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if resp_data is None or resp_data == -1:
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resp_data = self.GetFromStore(name)
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# IF we have the file, put it in the memcache
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# ELSE put it in the negative cache
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if resp_data is not None:
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self.StoreOrUpdateInCache(name, resp_data)
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else:
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logging.info('Adding %s to negative cache, serving 404', name)
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self.StoreInNegativeCache(name)
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self.Write404Error()
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return
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else:
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self.Write404Error()
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return
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content_type, encoding = mimetypes.guess_type(name)
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if content_type:
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self.response.headers['Content-Type'] = content_type
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self.current_last_modified = resp_data.lastmod
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self.current_etag = resp_data.etag
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self.SetCachingHeaders()
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# if the received ETag matches
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if resp_data.etag == self.request.headers.get('If-None-Match'):
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self.error(304)
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return
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# if-modified-since was passed by the browser
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if self.request.headers.has_key('If-Modified-Since'):
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dt = self.request.headers.get('If-Modified-Since').split(';')[0]
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modsince = datetime.datetime.strptime(dt, "%a, %d %b %Y %H:%M:%S %Z")
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if modsince >= self.current_last_modified:
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# The file is older than the cached copy (or exactly the same)
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self.error(304)
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return
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self.response.out.write(resp_data.file)
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def PreprocessUrl(self, name):
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"""Any preprocessing work on the URL when it comes it.
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Put any work related to interpretting the incoming URL here. For example,
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this is used to redirect requests for a directory to the index.html file
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in that directory. Subclasses should override this method to do different
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preprocessing.
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Args:
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name: The incoming URL
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Returns:
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The processed URL
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"""
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if name[len(name) - 1:] == '/':
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return "%s%s" % (name, 'index.html')
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else:
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return name
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def GetFromStore(self, file_path):
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"""Retrieve file from zip files.
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Get the file from the source, it must not have been in the memcache. If
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possible, we'll use the zip file index to quickly locate where the file
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should be found. (See MapToFileArchive documentation for assumptions about
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file ordering.) If we don't have an index or don't find the file where the
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index says we should, look through all the zip files to find it.
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Args:
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file_path: the file that we're looking for
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Returns:
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The contents of the requested file
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"""
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resp_data = None
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file_itr = iter(self.zipfilenames)
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# check the index, if we have one, to see what archive the file is in
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archive_name = self.MapFileToArchive(file_path)
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if not archive_name:
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archive_name = file_itr.next()[0]
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while resp_data is None and archive_name:
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zip_archive = self.LoadZipFile(archive_name)
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if zip_archive:
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# we expect some lookups will fail, and that's okay, 404s will deal
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# with that
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try:
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resp_data = CacheFile()
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info = os.stat(archive_name)
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#lastmod = datetime.datetime.fromtimestamp(info[8])
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lastmod = datetime.datetime(*zip_archive.getinfo(file_path).date_time)
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resp_data.file = zip_archive.read(file_path)
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resp_data.lastmod = lastmod
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resp_data.etag = '"%s"' % md5_constructor(resp_data.file).hexdigest()
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except (KeyError, RuntimeError), err:
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# no op
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x = False
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resp_data = None
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if resp_data is not None:
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logging.info('%s read from %s', file_path, archive_name)
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try:
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archive_name = file_itr.next()[0]
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except (StopIteration), err:
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archive_name = False
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return resp_data
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def LoadZipFile(self, zipfilename):
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"""Convenience method to load zip file.
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Just a convenience method to load the zip file from the data store. This is
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useful if we ever want to change data stores and also as a means of
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dependency injection for testing. This method will look at our file cache
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first, and then load and cache the file if there's a cache miss
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Args:
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zipfilename: the name of the zip file to load
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Returns:
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The zip file requested, or None if there is an I/O error
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"""
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zip_archive = None
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zip_archive = self.zipfile_cache.get(zipfilename)
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if zip_archive is None:
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try:
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zip_archive = zipfile.ZipFile(zipfilename)
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self.zipfile_cache[zipfilename] = zip_archive
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except (IOError, RuntimeError), err:
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logging.error('Can\'t open zipfile %s, cause: %s' % (zipfilename,
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err))
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return zip_archive
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def MapFileToArchive(self, file_path):
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"""Given a file name, determine what archive it should be in.
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This method makes two critical assumptions.
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(1) The zip files passed as an argument to the handler, if concatenated
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in that same order, would result in a total ordering
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of all the files. See (2) for ordering type.
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(2) Upper case letters before lower case letters. The traversal of a
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directory tree is depth first. A parent directory's files are added
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before the files of any child directories
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Args:
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file_path: the file to be mapped to an archive
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Returns:
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The name of the archive where we expect the file to be
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"""
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num_archives = len(self.zipfilenames)
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while num_archives > 0:
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target = self.zipfilenames[num_archives - 1]
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if len(target) > 1:
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if self.CompareFilenames(target[1], file_path) >= 0:
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return target[0]
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num_archives -= 1
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return None
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def CompareFilenames(self, file1, file2):
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"""Determines whether file1 is lexigraphically 'before' file2.
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WARNING: This method assumes that paths are output in a depth-first,
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with parent directories' files stored before childs'
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We say that file1 is lexigraphically before file2 if the last non-matching
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path segment of file1 is alphabetically before file2.
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Args:
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file1: the first file path
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file2: the second file path
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Returns:
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A positive number if file1 is before file2
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A negative number if file2 is before file1
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0 if filenames are the same
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"""
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f1_segments = file1.split('/')
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f2_segments = file2.split('/')
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segment_ptr = 0
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while (segment_ptr < len(f1_segments) and
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segment_ptr < len(f2_segments) and
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f1_segments[segment_ptr] == f2_segments[segment_ptr]):
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segment_ptr += 1
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if len(f1_segments) == len(f2_segments):
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# we fell off the end, the paths much be the same
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if segment_ptr == len(f1_segments):
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return 0
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# we didn't fall of the end, compare the segments where they differ
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if f1_segments[segment_ptr] < f2_segments[segment_ptr]:
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return 1
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elif f1_segments[segment_ptr] > f2_segments[segment_ptr]:
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return -1
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else:
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return 0
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# the number of segments differs, we either mismatched comparing
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# directories, or comparing a file to a directory
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else:
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# IF we were looking at the last segment of one of the paths,
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# the one with fewer segments is first because files come before
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# directories
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# ELSE we just need to compare directory names
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if (segment_ptr + 1 == len(f1_segments) or
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segment_ptr + 1 == len(f2_segments)):
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return len(f2_segments) - len(f1_segments)
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else:
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if f1_segments[segment_ptr] < f2_segments[segment_ptr]:
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return 1
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elif f1_segments[segment_ptr] > f2_segments[segment_ptr]:
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return -1
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else:
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return 0
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def SetCachingHeaders(self):
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"""Set caching headers for the request."""
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max_age = self.MAX_AGE
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self.response.headers['Expires'] = email.Utils.formatdate(
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time.time() + max_age, usegmt=True)
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cache_control = []
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if self.PUBLIC:
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cache_control.append('public')
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cache_control.append('max-age=%d' % max_age)
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self.response.headers['Cache-Control'] = ', '.join(cache_control)
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# adding caching headers for the client
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if self.CLIENT_CACHING:
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if self.current_last_modified:
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self.response.headers['Last-Modified'] = self.current_last_modified.strftime("%a, %d %b %Y %H:%M:%S GMT")
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if self.current_etag:
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self.response.headers['ETag'] = self.current_etag
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def GetFromCache(self, filename):
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"""Get file from memcache, if available.
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Args:
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filename: The URL of the file to return
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Returns:
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The content of the file
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"""
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return memcache.get("%s%s" % (self.CACHE_PREFIX, filename))
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def StoreOrUpdateInCache(self, filename, data):
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"""Store data in the cache.
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Store a piece of data in the memcache. Memcache has a maximum item size of
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1*10^6 bytes. If the data is too large, fail, but log the failure. Future
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work will consider compressing the data before storing or chunking it
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Args:
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filename: the name of the file to store
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data: the data of the file
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Returns:
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None
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"""
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try:
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if not memcache.add("%s%s" % (self.CACHE_PREFIX, filename), data):
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memcache.replace("%s%s" % (self.CACHE_PREFIX, filename), data)
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except (ValueError), err:
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logging.warning("Data size too large to cache\n%s" % err)
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def Write404Error(self):
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"""Ouptut a simple 404 response."""
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self.error(404)
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self.response.out.write('Error 404, file not found')
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def StoreInNegativeCache(self, filename):
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"""If a non-existant URL is accessed, cache this result as well.
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Future work should consider setting a maximum negative cache size to
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prevent it from from negatively impacting the real cache.
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Args:
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filename: URL to add ot negative cache
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Returns:
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None
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"""
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memcache.add("%s%s" % (self.NEG_CACHE_PREFIX, filename), -1)
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def GetFromNegativeCache(self, filename):
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"""Retrieve from negative cache.
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Args:
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filename: URL to retreive
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Returns:
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The file contents if present in the negative cache.
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"""
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return memcache.get("%s%s" % (self.NEG_CACHE_PREFIX, filename))
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def main():
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application = webapp.WSGIApplication([('/([^/]+)/(.*)',
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MemcachedZipHandler)])
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util.run_wsgi_app(application)
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if __name__ == '__main__':
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main()
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