Add caching.cached_endpoint decorator for 304'ing any url.

frontends/etiquette_flask/etiquette_flask/caching.py

@@ -1,23 +1,6 @@
-'''
+import flask; from flask import request
-This file provides the FileCacheManager to serve ETag and Cache-Control headers
+import functools
-for files on disk.
+import hashlib
-
-We consider the following cases:
-
-Client does not have the file (or has disabled their cache, effectively same):
-    Server sends file, provides ETag, and tells client to save it for max-age.
-
-Client has the file, but it has been a long time, beyond the max-age:
-    Client provides the old ETag. If it's still valid, Server responds with
-    304 Not Modified and no data. Client keeps the file.
-
-Client has the file, and it is within the max-age:
-    Client does not make a request at all.
-
-This FileCacheManager uses the file's MD5 hash as the ETag, and will only
-recalculate it if the file's mtime has changed since the last request.
-'''
-
 import time
 
 import etiquette
@@ -25,42 +8,130 @@ import etiquette
 from voussoirkit import cacheclass
 from voussoirkit import pathclass
 
+
+def cached_endpoint(max_age):
+    '''
+    The cached_endpoint decorator can be used on slow endpoints that don't need
+    to be constantly updated or endpoints that produce large, static responses.
+
+    WARNING: The return value of the endpoint is shared with all users.
+    You should never use this cache on an endpoint that provides private
+    or personalized data, and you should not try to pass other headers through
+    the response.
+
+    When the function is run, its return value is stored and a random etag is
+    generated so that subsequent runs can respond with 304. This way, large
+    response bodies do not need to be transmitted often.
+
+    Given a nonzero max_age, the endpoint will only be run once per max_age
+    seconds on a global basis (not per-user). This way, you can prevent a slow
+    function from being run very often. In-between requests will just receive
+    the previous return value (still using 200 or 304 as appropriate for the
+    client's provided etag).
+
+    An example use case would be large-sized data dumps that don't need to be
+    precisely up to date every time.
+    '''
+    state = {
+        'max_age': max_age,
+        'stored_value': None,
+        'stored_etag': None,
+        'headers': {'ETag': None, 'Cache-Control': f'max-age={max_age}'},
+        'last_run': 0,
+    }
+
+    def wrapper(function):
+        @functools.wraps(function)
+        def wrapped(*args, **kwargs):
+            if (not state['max_age']) or (time.time() - state['last_run'] > state['max_age']):
+                value = function(*args, **kwargs)
+                if isinstance(value, flask.Response):
+                    value = value.response
+                if value != state['stored_value']:
+                    state['stored_value'] = value
+                    state['stored_etag'] = etiquette.helpers.random_hex(20)
+                    state['headers']['ETag'] = state['stored_etag']
+                state['last_run'] = time.time()
+            else:
+                value = state['stored_value']
+
+            client_etag = request.headers.get('If-None-Match', None)
+            if client_etag == state['stored_etag']:
+                response = flask.Response(status=304, headers=state['headers'])
+            else:
+                response = flask.Response(value, status=200, headers=state['headers'])
+
+            return response
+        return wrapped
+    return wrapper
+
+
 class FileCacheManager:
-    def __init__(self, maxlen, max_filesize, max_age):
+    '''
+    The FileCacheManager serves ETag and Cache-Control headers for disk files.
+
+    We consider the following cases:
+
+    Client does not have the file (or has disabled their cache):
+        Server sends file, provides ETag, tells client to save it for max-age.
+
+    Client has the file, but it has been a long time, beyond the max-age:
+        Client provides the old ETag. If it's still valid, Server responds with
+        304 Not Modified and no data. Client keeps the old file.
+
+    Client has the file, and it is within the max-age:
+        Client does not make a request at all.
+
+    We use the file's MD5 hash as the ETag, and will only recalculate it if the
+    file's mtime has changed since the last request.
+    '''
+    def __init__(self, maxlen, max_age, max_filesize):
         self.cache = cacheclass.Cache(maxlen=maxlen)
-        self.max_filesize = int(max_filesize)
         self.max_age = int(max_age)
+        self.max_filesize = max(int(max_filesize), 0) or None
 
     def get(self, filepath):
-        if (self.max_filesize is not None) and (filepath.size > self.max_filesize):
-            #print('I\'m not going to cache that!')
-            return None
-
         try:
             return self.cache[filepath]
         except KeyError:
             pass
+
+        if (self.max_filesize is not None) and (filepath.size > self.max_filesize):
+            return None
+
         cache_file = CacheFile(filepath, max_age=self.max_age)
         self.cache[filepath] = cache_file
         return cache_file
 
+    def matches(self, request, filepath):
+        client_etag = request.headers.get('If-None-Match', None)
+        if client_etag is None:
+            return False
+
+        server_value = self.get(filepath)
+        if server_value is None:
+            return False
+
+        server_etag = server_value.get_etag()
+        if client_etag != server_etag:
+            return False
+
+        return server_value.get_headers()
+
+
 class CacheFile:
     def __init__(self, filepath, max_age):
         self.filepath = filepath
-        self.max_age = max_age
+        self.max_age = int(max_age)
         self._stored_hash_time = None
         self._stored_hash_value = None
 
     def get_etag(self):
-        if self._stored_hash_value is None:
+        mtime = self.filepath.stat.st_mtime
-            refresh = True
+        do_refresh = (self._stored_hash_value is None) or (mtime > self._stored_hash_time)
-        elif self.filepath.stat.st_mtime > self._stored_hash_time:
-            refresh = True
-        else:
-            refresh = False
 
-        if refresh:
+        if do_refresh:
-            self._stored_hash_time = self.filepath.stat.st_mtime
+            self._stored_hash_time = mtime
             self._stored_hash_value = etiquette.helpers.hash_file_md5(self.filepath)
         return self._stored_hash_value
 

frontends/etiquette_flask/etiquette_flask/common.py

@@ -120,11 +120,9 @@ def send_file(filepath, override_mimetype=None):
     if not filepath.is_file:
         flask.abort(404)
 
-    cache_file = file_cache_manager.get(filepath)
+    headers = file_cache_manager.matches(request=request, filepath=filepath)
-    if cache_file is not None:
+    if headers:
-        client_etag = request.headers.get('If-None-Match', None)
+        response = flask.Response(status=304, headers=headers)
-        if client_etag and client_etag == cache_file.get_etag():
-            response = flask.Response(status=304, headers=cache_file.get_headers())
         return response
 
     outgoing_headers = {}
@@ -174,6 +172,7 @@ def send_file(filepath, override_mimetype=None):
 
     outgoing_headers['Accept-Ranges'] = 'bytes'
     outgoing_headers['Content-Length'] = (range_max - range_min) + 1
+    cache_file = file_cache_manager.get(filepath)
     if cache_file is not None:
         outgoing_headers.update(cache_file.get_headers())