141 lines
4.9 KiB
Python
141 lines
4.9 KiB
Python
import flask; from flask import request
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import functools
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import time
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from voussoirkit import cacheclass
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import etiquette
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def cached_endpoint(max_age):
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'''
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The cached_endpoint decorator can be used on slow endpoints that don't need
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to be constantly updated or endpoints that produce large, static responses.
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WARNING: The return value of the endpoint is shared with all users.
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You should never use this cache on an endpoint that provides private
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or personalized data, and you should not try to pass other headers through
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the response.
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When the function is run, its return value is stored and a random etag is
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generated so that subsequent runs can respond with 304. This way, large
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response bodies do not need to be transmitted often.
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Given a nonzero max_age, the endpoint will only be run once per max_age
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seconds on a global basis (not per-user). This way, you can prevent a slow
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function from being run very often. In-between requests will just receive
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the previous return value (still using 200 or 304 as appropriate for the
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client's provided etag).
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An example use case would be large-sized data dumps that don't need to be
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precisely up to date every time.
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'''
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state = {
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'max_age': max_age,
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'stored_value': None,
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'stored_etag': None,
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'headers': {'ETag': None, 'Cache-Control': f'max-age={max_age}'},
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'last_run': 0,
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}
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def wrapper(function):
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@functools.wraps(function)
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def wrapped(*args, **kwargs):
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if (not state['max_age']) or (time.time() - state['last_run'] > state['max_age']):
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value = function(*args, **kwargs)
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if isinstance(value, flask.Response):
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value = value.response
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if value != state['stored_value']:
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state['stored_value'] = value
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state['stored_etag'] = etiquette.helpers.random_hex(20)
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state['headers']['ETag'] = state['stored_etag']
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state['last_run'] = time.time()
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else:
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value = state['stored_value']
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client_etag = request.headers.get('If-None-Match', None)
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if client_etag == state['stored_etag']:
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response = flask.Response(status=304, headers=state['headers'])
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else:
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response = flask.Response(value, status=200, headers=state['headers'])
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return response
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return wrapped
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return wrapper
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class FileCacheManager:
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'''
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The FileCacheManager serves ETag and Cache-Control headers for disk files.
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We consider the following cases:
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Client does not have the file (or has disabled their cache):
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Server sends file, provides ETag, tells client to save it for max-age.
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Client has the file, but it has been a long time, beyond the max-age:
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Client provides the old ETag. If it's still valid, Server responds with
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304 Not Modified and no data. Client keeps the old file.
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Client has the file, and it is within the max-age:
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Client does not make a request at all.
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We use the file's MD5 hash as the ETag, and will only recalculate it if the
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file's mtime has changed since the last request.
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'''
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def __init__(self, maxlen, max_age, max_filesize):
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self.cache = cacheclass.Cache(maxlen=maxlen)
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self.max_age = int(max_age)
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self.max_filesize = max(int(max_filesize), 0) or None
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def get(self, filepath):
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try:
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return self.cache[filepath]
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except KeyError:
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pass
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if (self.max_filesize is not None) and (filepath.size > self.max_filesize):
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return None
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cache_file = CacheFile(filepath, max_age=self.max_age)
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self.cache[filepath] = cache_file
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return cache_file
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def matches(self, request, filepath):
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client_etag = request.headers.get('If-None-Match', None)
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if client_etag is None:
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return False
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server_value = self.get(filepath)
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if server_value is None:
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return False
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server_etag = server_value.get_etag()
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if client_etag != server_etag:
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return False
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return server_value.get_headers()
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class CacheFile:
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def __init__(self, filepath, max_age):
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self.filepath = filepath
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self.max_age = int(max_age)
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self._stored_hash_time = None
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self._stored_hash_value = None
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def get_etag(self):
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mtime = self.filepath.stat.st_mtime
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do_refresh = (self._stored_hash_value is None) or (mtime > self._stored_hash_time)
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if do_refresh:
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self._stored_hash_time = mtime
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self._stored_hash_value = etiquette.helpers.hash_file_md5(self.filepath)
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return self._stored_hash_value
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def get_headers(self):
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headers = {
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'ETag': self.get_etag(),
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'Cache-Control': f'max-age={self.max_age}',
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}
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return headers
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