Cache url_for calls with lru_cache

This commit adds a caching_url_for using functools.lru_cache (currently
with maxsize at 4096 entries) and replaces flask.url_for with it, as
there is no harm in doing so.

This greatly improves template generation speed, from ~115ms to ~75ms on
the front page (using the simple benchmark introduced in the previous
commit).

nyaa/__init__.py

@@ -8,9 +8,15 @@
 from nyaa.api_handler import api_blueprint
 from nyaa.extensions import assets, cache, db, fix_paginate, toolbar
 from nyaa.template_utils import bp as template_utils_bp
+from nyaa.template_utils import caching_url_for
 from nyaa.utils import random_string
 from nyaa.views import register_views
 
+# Replace the Flask url_for with our cached version, since there's no real harm in doing so
+# (caching_url_for has stored a reference to the OG url_for, so we won't recurse)
+# Touching globals like this is a bit dirty, but nicer than replacing every url_for usage
+flask.url_for = caching_url_for
+
 
 def create_app(config):
     """ Nyaa app factory """
@@ -86,6 +92,10 @@ def internal_error(exception):
     app.jinja_env.lstrip_blocks = True
     app.jinja_env.trim_blocks = True
 
+    # The default jinja_env has the OG Flask url_for (from before we replaced it),
+    # so update the globals with our version
+    app.jinja_env.globals['url_for'] = flask.url_for
+
     # Database
     fix_paginate()  # This has to be before the database is initialized
     app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

nyaa/template_utils.py

@@ -1,3 +1,4 @@
+import functools
 import os.path
 import re
 from datetime import datetime
@@ -25,6 +26,28 @@ def create_magnet_from_es_torrent():
 
 # ######################### TEMPLATE GLOBALS #########################
 
+flask_url_for = flask.url_for
+
+
+@functools.lru_cache(maxsize=1024*4)
+def _caching_url_for(endpoint, **values):
+    return flask_url_for(endpoint, **values)
+
+
+@bp.app_template_global()
+def caching_url_for(*args, **kwargs):
+    try:
+        # lru_cache requires the arguments to be hashable.
+        # Majority of the time, they are! But there are some small edge-cases,
+        # like our copypasted pagination, parameters can be lists.
+        # Attempt caching first:
+        return _caching_url_for(*args, **kwargs)
+    except TypeError:
+        # Then fall back to the original url_for.
+        # We could convert the lists to tuples, but the savings are marginal.
+        return flask_url_for(*args, **kwargs)
+
+
 @bp.app_template_global()
 def static_cachebuster(filename):
     """ Adds a ?t=<mtime> cachebuster to the given path, if the file exists.