feat: cache rss feedgen for 5 minutes

The RSS feed should be perfectly fine even when caching them for 5
minutes. This should massively reduce the response times on the
endpoint.

Signed-off-by: Levente Polyak <anthraxx@archlinux.org>

aurweb/cache.py

@@ -1,6 +1,7 @@
 import pickle
 
 from sqlalchemy import orm
+from typing import Callable, Any
 
 from aurweb import config
 from aurweb.aur_redis import redis_connection
@@ -9,6 +10,22 @@ from aurweb.prometheus import SEARCH_REQUESTS
 _redis = redis_connection()
 
 
+def lambda_cache(key: str, value: Callable[[], Any], expire: int = None) -> list:
+    """Store and retrieve lambda results via redis cache.
+
+    :param key: Redis key
+    :param value: Lambda callable returning the value
+    :param expire: Optional expiration in seconds
+    :return: result of callable or cache
+    """
+    result = _redis.get(key)
+    if result is not None:
+        return pickle.loads(result)
+
+    _redis.set(key, (pickle.dumps(result := value())), ex=expire)
+    return result
+
+
 def db_count_cache(key: str, query: orm.Query, expire: int = None) -> int:
     """Store and retrieve a query.count() via redis cache.
 

aurweb/routers/rss.py

@@ -2,7 +2,8 @@ from fastapi import APIRouter, Request
 from fastapi.responses import Response
 from feedgen.feed import FeedGenerator
 
-from aurweb import db, filters
+from aurweb import config, db, filters
+from aurweb.cache import lambda_cache
 from aurweb.models import Package, PackageBase
 
 router = APIRouter()
@@ -56,9 +57,11 @@ async def rss(request: Request):
         )
     )
 
-    feed = make_rss_feed(request, packages)
-    response = Response(feed, media_type="application/rss+xml")
+    # we use redis for caching the results of the feedgen
+    cache_expire = config.getint("cache", "expiry_time_rss", 300)
+    feed = lambda_cache("rss", lambda: make_rss_feed(request, packages), cache_expire)
 
+    response = Response(feed, media_type="application/rss+xml")
     return response
 
 
@@ -76,7 +79,9 @@ async def rss_modified(request: Request):
         )
     )
 
-    feed = make_rss_feed(request, packages)
-    response = Response(feed, media_type="application/rss+xml")
+    # we use redis for caching the results of the feedgen
+    cache_expire = config.getint("cache", "expiry_time_rss", 300)
+    feed = lambda_cache("rss_modified", lambda: make_rss_feed(request, packages), cache_expire)
 
+    response = Response(feed, media_type="application/rss+xml")
     return response

conf/config.defaults

@@ -175,3 +175,5 @@ max_search_entries = 50000
 expiry_time_search = 600
 ; number of seconds after a cache entry for statistics queries expires, default is 5 minutes
 expiry_time_statistics = 300
+; number of seconds after a cache entry for rss queries expires, default is 5 minutes
+expiry_time_rss = 300