feat: status on cache are now actually ephemeral (#105)

Author: corp-0

src/baby_serverlist/models.py

@@ -6,9 +6,10 @@
 from django.db import models
 
 from accounts.models import Account
-from commons.cache import get_baby_server_heartbeat
+from commons.cache import BABY_SERVER_HEARTBEAT_TTL_SECONDS, get_baby_server_heartbeat
 
 SERVERLIST_TOKEN_SALT = "baby_serverlist.serverlist_token"
+LIVE_HEARTBEAT_GRACE_SECONDS = 2
 
 
 class BabyServer(models.Model):
@@ -40,7 +41,7 @@ def generate_serverlist_token(self) -> str:
         return signing.dumps(payload, salt=SERVERLIST_TOKEN_SALT)
 
     def is_live(self) -> bool:
-        """Return True when the server has reported within the last 12 seconds."""
+        """Return True when the server has reported within the heartbeat TTL window."""
         heartbeat_iso = get_baby_server_heartbeat(str(self.id))
         if not heartbeat_iso:
             return False
@@ -50,4 +51,7 @@ def is_live(self) -> bool:
             return False
         if heartbeat_time.tzinfo is None:
             heartbeat_time = heartbeat_time.replace(tzinfo=UTC)
-        return datetime.now(tz=UTC) - heartbeat_time <= timedelta(seconds=12)
+
+        # live if last heartbeat within the cache TTL plus a small grace buffer
+        ttl_with_grace = BABY_SERVER_HEARTBEAT_TTL_SECONDS + LIVE_HEARTBEAT_GRACE_SECONDS
+        return datetime.now(tz=UTC) - heartbeat_time <= timedelta(seconds=ttl_with_grace)

src/commons/cache.py

@@ -3,6 +3,9 @@
 
 from django.core.cache import cache
 
+BABY_SERVER_STATUS_TTL_SECONDS = 10
+BABY_SERVER_HEARTBEAT_TTL_SECONDS = 10
+
 SERVER_STATUS_KEY_PREFIX = "baby_server_status:"
 SERVER_HEARTBEAT_KEY_PREFIX = "baby_server_heartbeat:"
 
@@ -19,7 +22,7 @@ def _heartbeat_key(server_id: str) -> str:
 
 def set_baby_server_status(server_id: str, status: dict[str, Any]) -> None:
     """Persist the latest status payload for a server."""
-    cache.set(_status_key(server_id), status)
+    cache.set(_status_key(server_id), status, timeout=BABY_SERVER_STATUS_TTL_SECONDS)
 
 
 def get_baby_server_status(server_id: str) -> dict[str, Any] | None:
@@ -39,7 +42,7 @@ def get_many_baby_server_statuses(server_ids: Iterable[str]) -> dict[str, dict[s
 
 def set_baby_server_heartbeat(server_id: str, timestamp: str) -> None:
     """Persist the last-reported timestamp for a server."""
-    cache.set(_heartbeat_key(server_id), timestamp)
+    cache.set(_heartbeat_key(server_id), timestamp, timeout=BABY_SERVER_HEARTBEAT_TTL_SECONDS)
 
 
 def get_baby_server_heartbeat(server_id: str) -> str | None:

src/tests/baby_serverlist/test_api.py

@@ -7,8 +7,9 @@
 from rest_framework.test import APITestCase
 
 from accounts.models import Account
-from baby_serverlist.models import BabyServer
+from baby_serverlist.models import LIVE_HEARTBEAT_GRACE_SECONDS, BabyServer
 from commons.cache import (
+    BABY_SERVER_HEARTBEAT_TTL_SECONDS,
     get_baby_server_heartbeat,
     get_baby_server_status,
     set_baby_server_heartbeat,
@@ -154,7 +155,9 @@ def test_list_owned_baby_servers_live_flag(self) -> None:
         response = self.client.get(reverse("baby_serverlist:list-owned"))
         self.assertTrue(response.json()[0]["live"])
 
-        stale_time = datetime.now(tz=UTC) - timedelta(seconds=13)
+        stale_time = datetime.now(tz=UTC) - timedelta(
+            seconds=BABY_SERVER_HEARTBEAT_TTL_SECONDS + LIVE_HEARTBEAT_GRACE_SECONDS + 1
+        )
         set_baby_server_heartbeat(str(baby_server.id), stale_time.isoformat())
 
         response = self.client.get(reverse("baby_serverlist:list-owned"))
@@ -184,3 +187,20 @@ def test_list_baby_servers_ignores_non_whitelisted(self) -> None:
 
         self.assertEqual(response.status_code, status.HTTP_200_OK)
         self.assertEqual(response.json(), {"servers": []})
+
+    def test_baby_server_is_live_respects_heartbeat_ttl(self) -> None:
+        baby_server = BabyServer.objects.create(owner=self.user)
+
+        fresh_time = datetime.now(tz=UTC) - timedelta(
+            seconds=BABY_SERVER_HEARTBEAT_TTL_SECONDS + LIVE_HEARTBEAT_GRACE_SECONDS - 1
+        )
+        set_baby_server_heartbeat(str(baby_server.id), fresh_time.isoformat())
+        self.assertTrue(baby_server.is_live())
+
+        stale_time = datetime.now(tz=UTC) - timedelta(
+            seconds=BABY_SERVER_HEARTBEAT_TTL_SECONDS + LIVE_HEARTBEAT_GRACE_SECONDS + 1
+        )
+        set_baby_server_heartbeat(str(baby_server.id), stale_time.isoformat())
+        stored = get_baby_server_heartbeat(str(baby_server.id))
+        self.assertEqual(stored, stale_time.isoformat())
+        self.assertFalse(baby_server.is_live())

src/tests/commons/__init__.py

@@ -0,0 +1 @@
+

src/tests/commons/test_cache.py

@@ -0,0 +1,33 @@
+from unittest.mock import patch
+
+from django.test import SimpleTestCase
+
+from commons import cache as cache_module
+
+
+class CommonsCacheTests(SimpleTestCase):
+    def test_set_baby_server_status_uses_ephemeral_timeout(self) -> None:
+        payload = {"ServerName": "test"}
+        server_id = "server-123"
+
+        with patch.object(cache_module, "cache") as fake_cache:
+            cache_module.set_baby_server_status(server_id, payload)
+
+        fake_cache.set.assert_called_once_with(
+            f"{cache_module.SERVER_STATUS_KEY_PREFIX}{server_id}",
+            payload,
+            timeout=cache_module.BABY_SERVER_STATUS_TTL_SECONDS,
+        )
+
+    def test_set_baby_server_heartbeat_uses_ephemeral_timeout(self) -> None:
+        timestamp = "2024-01-01T00:00:00+00:00"
+        server_id = "server-456"
+
+        with patch.object(cache_module, "cache") as fake_cache:
+            cache_module.set_baby_server_heartbeat(server_id, timestamp)
+
+        fake_cache.set.assert_called_once_with(
+            f"{cache_module.SERVER_HEARTBEAT_KEY_PREFIX}{server_id}",
+            timestamp,
+            timeout=cache_module.BABY_SERVER_HEARTBEAT_TTL_SECONDS,
+        )