Prevent duplicate entries in uri_keys lists (#63)

This prevents duplicate entries in the `uri_keys` lists for the items in the keyring.

Author: aweakley

testproject/home/tests.py

@@ -1,3 +1,5 @@
+import time
+
 from django.contrib.auth.models import User
 from django.contrib.contenttypes.models import ContentType
 from django.core.cache import caches
@@ -490,6 +492,23 @@ def test_cache_keyring(self):
         # Compare Keys
         self.assertEqual(key, url)
 
+    @override_settings(WAGTAIL_CACHE_BACKEND="one_second")
+    def test_cache_keyring_no_uri_key_duplication(self):
+        # First get to populate keyring
+        self.get_miss(self.page_cachedpage.get_url())
+        # Wait a short time
+        time.sleep(0.5)
+        # Fetch a different page
+        self.get_miss(self.page_wagtailpage.get_url())
+        # Wait until the first page is expired, but not the keyring
+        time.sleep(0.6)
+        # Fetch the first page again
+        self.get_miss(self.page_cachedpage.get_url())
+        # Check the keyring does not contain duplicate uri_keys
+        url = "http://%s%s" % ("testserver", self.page_cachedpage.get_url())
+        keyring = self.cache.get("keyring")
+        self.assertEqual(len(keyring.get(url, [])), 1)
+
     def test_clear_cache(self):
         # First get should miss cache.
         self.get_miss(self.page_cachedpage.get_url())

testproject/testproject/settings.py

@@ -133,6 +133,10 @@
         "BACKEND": "django.core.cache.backends.locmem.LocMemCache",
         "TIMEOUT": 90061,  # 1 day, 1 hour, 1 minute, 1 second.
     },
+    "one_second": {
+        "BACKEND": "django.core.cache.backends.locmem.LocMemCache",
+        "TIMEOUT": 1,
+    },
     "zero": {
         "BACKEND": "django.core.cache.backends.locmem.LocMemCache",
         "TIMEOUT": 0,

wagtailcache/cache.py

@@ -308,9 +308,10 @@ def process_response(
             # Get current cache keys belonging to this URI.
             # This should be a list of keys.
             uri_keys: List[str] = keyring.get(uri, [])
-            # Append the key to this list and save.
-            uri_keys.append(cache_key)
-            keyring[uri] = uri_keys
+            # Append the key to this list if not already present and save.
+            if cache_key not in uri_keys:
+                uri_keys.append(cache_key)
+                keyring[uri] = uri_keys
             self._wagcache.set("keyring", keyring)
 
             if isinstance(response, SimpleTemplateResponse):