push_notifications: Use lru_cache decorator.

This does the same thing in a simpler way.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/push_notifications.py

@@ -4,6 +4,7 @@ import base64
 import logging
 import re
 import time
+from functools import lru_cache
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, Sequence, Tuple, Union
 
 import gcm
@@ -59,26 +60,20 @@ def hex_to_b64(data: str) -> str:
 # Sending to APNs, for iOS
 #
 
-_apns_client: Optional["APNsClient"] = None
-_apns_client_initialized = False
-
 
+@lru_cache(maxsize=None)
 def get_apns_client() -> "Optional[APNsClient]":
     # We lazily do this import as part of optimizing Zulip's base
     # import time.
     from apns2.client import APNsClient
 
-    global _apns_client, _apns_client_initialized
-    if not _apns_client_initialized:
-        # NB if called concurrently, this will make excess connections.
-        # That's a little sloppy, but harmless unless a server gets
-        # hammered with a ton of these all at once after startup.
-        if settings.APNS_CERT_FILE is not None:
-            _apns_client = APNsClient(
-                credentials=settings.APNS_CERT_FILE, use_sandbox=settings.APNS_SANDBOX
-            )
-        _apns_client_initialized = True
-    return _apns_client
+    if settings.APNS_CERT_FILE is None:
+        return None
+
+    # NB if called concurrently, this will make excess connections.
+    # That's a little sloppy, but harmless unless a server gets
+    # hammered with a ton of these all at once after startup.
+    return APNsClient(credentials=settings.APNS_CERT_FILE, use_sandbox=settings.APNS_SANDBOX)
 
 
 def apns_enabled() -> bool:

zerver/tests/test_push_notifications.py

@@ -1313,7 +1313,7 @@ class TestAPNs(PushNotificationTest):
         """
         import zerver.lib.push_notifications
 
-        zerver.lib.push_notifications._apns_client_initialized = False
+        zerver.lib.push_notifications.get_apns_client.cache_clear()
         try:
             with self.settings(APNS_CERT_FILE="/foo.pem"), mock.patch(
                 "apns2.client.APNsClient"
@@ -1321,10 +1321,9 @@ class TestAPNs(PushNotificationTest):
                 client = get_apns_client()
                 self.assertEqual(mock_client.return_value, client)
         finally:
-            # Reset the values set by `get_apns_client` so that we don't
+            # Reset the cache for `get_apns_client` so that we don't
             # leak changes to the rest of the world.
-            zerver.lib.push_notifications._apns_client_initialized = False
-            zerver.lib.push_notifications._apns_client = None
+            zerver.lib.push_notifications.get_apns_client.cache_clear()
 
     def test_not_configured(self) -> None:
         self.setup_apns_tokens()