Keep sessions marked as deleted

Keep sessions marked as deleted for an hour before purging them from
the Redis store. This change is to allow the client to recover from a
session deletion when the user navigates back to the page.

CHANGELOG.md

@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## UNRELEASED
+
+- Kept sessions marked as deleted for an hour before purging them from the Redis store. This change is to allow the client to recover from a session deletion when the user navigates back to the page.
+
 ## 1.10.0 (2024-01-25)
 
 - Added CancelRendering() exception. The exception makes it possible to cancel the command execution and return an empty string instead of a half-rendered component or an exception.

livecomponents/manager/stores.py

@@ -106,7 +106,26 @@ def clear_all_sessions(self) -> None:
 
 
 class RedisStateStore(IStateStore):
-    """Redis-based state store."""
+    """Redis-based state store.
+
+    Args:
+        redis_url: URL of the Redis server.
+        state_prefix: Prefix for keys that store component states.
+        context_prefix: Prefix for keys that store component contexts.
+        templates_prefix: Prefix for keys that store component templates.
+        template_cache_prefix: Prefix for keys that store cached component templates.
+        ttl: Time-to-live for session keys. Each time the session is accessed, the TTL
+            is reset. If the session is not accessed for this time, it is deleted, and
+            subsequent accesses will result in a "Session not found" error and a 410
+            status code in the response. How this status is handled is up to the
+            client. There is no default behavior, but the client can choose to reload
+            the page, for example.
+        ttl_gc: Time-to-live for garbage collection. This TTL is lower than the session
+            TTL, and it's set for sessions scheduled for deletion in response to
+            a "clear_session" call. We don't delete the session immediately in case the
+            client decides to access the page again when clicking the back button,
+            for example.
+    """
 
     def __init__(
         self,
@@ -116,13 +135,15 @@ def __init__(
         templates_prefix: str = "lc:templates:",
         template_cache_prefix: str = "lc:template_cache:",
         ttl: datetime.timedelta = datetime.timedelta(days=1),
+        ttl_gc: datetime.timedelta = datetime.timedelta(hours=1),
     ):
         self.client = Redis.from_url(redis_url)  # type: ignore
         self.key_prefix = state_prefix
         self.context_prefix = context_prefix
         self.templates_prefix = templates_prefix
         self.template_cache_prefix = template_cache_prefix
         self.ttl = ttl
+        self.ttl_gc = ttl_gc
 
     def session_exists(self, session_id: str) -> bool:
         key_name = self._get_key_name(self.key_prefix, session_id)
@@ -195,8 +216,11 @@ def restore_component_template(self, state_addr: StateAddress) -> bytes | None:
 
     def clear_session(self, session_id: str) -> None:
         with self.client.pipeline() as pipe:
-            pipe.delete(self._get_key_name(self.key_prefix, session_id))
-            pipe.delete(self._get_key_name(self.templates_prefix, session_id))
+            # Instead of deleting the keys, we set a TTL for garbage collection.
+            pipe.expire(self._get_key_name(self.key_prefix, session_id), self.ttl_gc)
+            pipe.expire(
+                self._get_key_name(self.templates_prefix, session_id), self.ttl_gc
+            )
             pipe.execute()
 
     def clear_all_sessions(self) -> None:

tests/conftest.py

@@ -3,6 +3,7 @@
 import pytest
 
 from livecomponents.manager import get_state_manager
+from livecomponents.manager.stores import RedisStateStore
 
 # Playwright runs the async loop which makes Django raising a SynchronousOnlyOperation
 # exception. This is a workaround to allow async code in tests.
@@ -16,3 +17,11 @@ def state_manager():
     state_manager = get_state_manager()
     state_manager.store.clear_all_sessions()
     return state_manager
+
+
+@pytest.fixture
+def redis_state_store():
+    redis_url = os.environ.get("REDIS_URL")
+    if not redis_url:
+        pytest.skip("Redis URL not provided")
+    return RedisStateStore(redis_url=redis_url)

tests/test_redis_state_store.py

@@ -0,0 +1,51 @@
+from livecomponents.types import StateAddress
+
+
+def test_save_state_sets_ttl(redis_state_store):
+    state_addr = StateAddress(session_id="session_id", component_id="|root:0")
+    state = b"state"
+    redis_state_store.save_state(state_addr, state)
+
+    # A bit less than ttl
+    state_key = get_state_key(redis_state_store, state_addr)
+    assert (
+        redis_state_store.client.ttl(state_key)
+        > redis_state_store.ttl.total_seconds() - 10
+    )
+
+
+def test_clear_session_sets_ttl_gc(redis_state_store):
+    session_id = "session_id"
+    state_addr = StateAddress(session_id=session_id, component_id="|root:0")
+    state = b"state"
+    redis_state_store.save_state(state_addr, state)
+
+    # A bit less than ttl_gc
+    redis_state_store.clear_session(session_id)
+    state_key = get_state_key(redis_state_store, state_addr)
+    assert (
+        redis_state_store.client.ttl(state_key)
+        <= redis_state_store.ttl_gc.total_seconds()
+    )
+
+
+def test_clear_session_and_then_save_state_recovers_ttl(redis_state_store):
+    session_id = "session_id"
+    state_addr = StateAddress(session_id=session_id, component_id="|root:0")
+    state = b"state"
+    redis_state_store.save_state(state_addr, state)
+    redis_state_store.clear_session(session_id)
+    redis_state_store.save_state(state_addr, state)
+
+    # A bit less than ttl again
+    state_key = get_state_key(redis_state_store, state_addr)
+    assert (
+        redis_state_store.client.ttl(state_key)
+        > redis_state_store.ttl.total_seconds() - 10
+    )
+
+
+def get_state_key(redis_state_store, state_addr):
+    return redis_state_store._get_key_name(
+        redis_state_store.key_prefix, state_addr.session_id
+    )