Implement request caching in Redis so that we don't always have to fetch remote pages every time we want their mf2 items

lemoncurry/requests.py

@@ -0,0 +1,44 @@
+import requests
+from cachecontrol.wrapper import CacheControl
+from cachecontrol.cache import BaseCache
+from cachecontrol.heuristics import LastModified
+from datetime import datetime
+from django.core.cache import cache as django_cache
+from hashlib import sha256
+from mf2py import Parser
+
+
+class DjangoCache(BaseCache):
+    @classmethod
+    def key(cls, url):
+        return 'req:' + sha256(url.encode('utf-8')).hexdigest()
+
+    def get(self, url):
+        key = self.key(url)
+        return django_cache.get(key)
+
+    def set(self, url, value, expires=None):
+        key = self.key(url)
+        if expires:
+            lifetime = (expires - datetime.utcnow()).total_seconds()
+            django_cache.set(key, value, lifetime)
+        else:
+            django_cache.set(key, value)
+
+
+req = CacheControl(
+    requests.Session(),
+    cache=DjangoCache(),
+    heuristic=LastModified(),
+)
+
+
+def get(url):
+    r = req.get(url)
+    r.raise_for_status()
+    return r
+
+
+def mf2(url):
+    r = get(url)
+    return Parser(doc=r.text, url=url, html_parser='html5lib')