Try to do memoization without Flask-Caching

Flask-Caching is Python 3 only, and we need Python 2 support.

mailman_api/mailman.py

@@ -5,9 +5,7 @@ import re
 import ssl
 import subprocess
 import sys
-from functools import wraps
 from flask import Flask, request, abort, make_response, jsonify, g
-from flask_caching import Cache
 
 from .sso_api import sso_api_auth_required, init_sso
 from .tls_auth import tls_auth, init_tls_auth, PeerCertWSGIRequestHandler
@@ -23,8 +21,6 @@ app.config['TLS_AUTH_ACLS'] = [
     ('/', 'client'),
 ]
 
-cache = Cache(config={'CACHE_TYPE': 'SimpleCache'})
-
 # Set up environment for Mailman processes: if we don't explicitly
 # control LANG, we're going to get locale setup errors.
 mm_env = dict(os.environ)
@@ -133,10 +129,24 @@ def regenerate_archives():
 
 ### Instrumentation.
 
+def cache(timeout):
+    _store = {'deadline': 0, 'value': None}
+    def _cache_wrapper(fn):
+        @wraps(fn)
+        def _cache(*args, **kwargs):
+            now = time.time()
+            if now > _store['deadline']:
+                _store['value'] = fn(*args, **kwargs)
+                _store['deadline'] = now + timeout
+            return _store['value']
+        return _cache
+    return _cache_wrapper
+
+
 @app.route('/metrics')
-@cache.cached(timeout=900)
+@cache(900)
 def metrics():
-    def _dump_metrics():
+    out = []
     list_names = Utils.list_names()
     for list_name in list_names:
         try:
@@ -147,10 +157,10 @@ def metrics():
 
         num_rmembers = len(mlist.getRegularMemberKeys())
         num_dmembers = len(mlist.getDigestMemberKeys())
-            yield 'mailman_subscribers{list="%s"} %d\n' % (
-                list_name.lower(), num_rmembers + num_dmembers)
+        out.append('mailman_subscribers{list="%s"} %d\n' % (
+            list_name.lower(), num_rmembers + num_dmembers))
 
-    return app.response_class(_dump_metrics(), mimetype='text/plain')
+    return app.response_class(''.join(out), mimetype='text/plain')
 
 
 ### SSL server with the right parameters.
@@ -182,7 +192,6 @@ def main():
         parser.error('Too many arguments')
 
     app.config.from_pyfile(opts.config)
-    cache.init_app(app)
     init_sso(app)
     init_tls_auth(app)
     serve_ssl(app, host=opts.addr, port=opts.port)

requirements.txt

 git+https://git.autistici.org/ai/sso.git#egg=sso&subdirectory=src/python
 Flask
-Flask-Caching

setup.py

@@ -11,7 +11,6 @@ setup(
     author_email="info@autistici.org",
     url="https://git.autistici.org/ai3/python-mailman-api",
     install_requires=["Flask",
-                      "Flask-Caching",
                       "sso"],
     packages=find_packages(),
     entry_points={