feat(server): implement Redis-based event queue manager

- Add RedisQueueManager class to handle event queues using Redis
- Implement core functionalities: add, get, tap, close, create_or_tap
- Add unit tests for RedisQueueManager
- Update .gitignore to exclude spec.json and .idea
- Refactor event type definition in event_queue.py
- Add fakeredis dependency in pyproject.toml

Author: long.qul

.gitignore

@@ -8,4 +8,5 @@ __pycache__
 .venv
 coverage.xml
 .nox
-spec.json
+spec.json
+.idea

pyproject.toml

@@ -21,6 +21,7 @@ dependencies = [
   "grpcio-tools>=1.60",
   "grpcio_reflection>=1.7.0",
   "protobuf==5.29.5",
+  "fakeredis>=2.30.1",
 ]
 
 classifiers = [

src/a2a/server/events/event_queue.py

@@ -1,6 +1,9 @@
 import asyncio
 import logging
 import sys
+from typing import Union, Annotated
+
+from pydantic import Field
 
 from a2a.types import (
     Message,
@@ -14,7 +17,7 @@
 logger = logging.getLogger(__name__)
 
 
-Event = Message | Task | TaskStatusUpdateEvent | TaskArtifactUpdateEvent
+Event = Annotated[Union[Message, Task ,TaskStatusUpdateEvent, TaskArtifactUpdateEvent], Field(discriminator="kind")]
 """Type alias for events that can be enqueued."""
 
 DEFAULT_MAX_QUEUE_SIZE = 1024

src/a2a/server/events/redis_queue_manager.py

@@ -0,0 +1,134 @@
+import asyncio
+from asyncio import Task
+from functools import partial
+from typing import Dict
+
+from redis.asyncio import Redis
+
+from a2a.server.events import QueueManager, EventQueue, TaskQueueExists, Event, EventConsumer, NoTaskQueue
+
+
+class RedisQueueManager(QueueManager):
+    """
+    This implements the `QueueManager` interface using Redis for event
+    queues. Primary jobs:
+    1. Broadcast local events to proxy queues in other processes using redis pubsub
+    2. Subscribe event messages from redis pubsub and replay to local proxy queues
+    """
+
+    def __init__(self, redis_client: Redis,
+                 relay_channel_key_prefix: str = "a2a.event.relay.",
+                 task_registry_key: str = "a2a.event.registry"
+                 ):
+        self._redis = redis_client
+        self._local_queue: dict[str, EventQueue] = {}
+        self._proxy_queue: dict[str, EventQueue] = {}
+        self._lock = asyncio.Lock()
+        self._pubsub = redis_client.pubsub()
+        self._relay_channel_name = relay_channel_key_prefix
+        self._background_tasks: Dict[str, Task] = {}
+        self._task_registry_name = task_registry_key
+
+    async def _listen_and_relay(self, task_id: str):
+        c = EventConsumer(self._local_queue[task_id])
+        async for event in c.consume_all():
+            await self._redis.publish(self._task_channel_name(task_id), event.model_dump_json(exclude_none=True))
+
+    def _task_channel_name(self, task_id: str):
+        return self._relay_channel_name + task_id
+
+    async def _has_task_id(self, task_id: str):
+        ret = await self._redis.sismember(self._task_registry_name, task_id)
+        return ret
+
+    async def _register_task_id(self, task_id: str):
+        await self._redis.sadd(self._task_registry_name, task_id)
+        self._background_tasks[task_id] = asyncio.create_task(self._listen_and_relay(task_id))
+
+    async def _remove_task_id(self, task_id: str):
+        if task_id in self._background_tasks:
+            self._background_tasks[task_id].cancel("task_id is closed: " + task_id)
+        return await self._redis.srem(self._task_registry_name, task_id)
+
+    async def _subscribe_remote_task_events(self, task_id: str):
+        await self._pubsub.subscribe(**{
+            self._task_channel_name(task_id):  partial(self._relay_remote_events, task_id)
+        })
+
+    def _unsubscribe_remote_task_events(self, task_id: str):
+        self._pubsub.unsubscribe(self._task_channel_name(task_id))
+
+    def _relay_remote_events(self, task_id: str , event_json: str):
+        if task_id in self._proxy_queue:
+            event = Event.model_validate_json(event_json)
+            self._proxy_queue[task_id].enqueue_event(event)
+
+    async def add(self, task_id: str, queue: EventQueue) -> None:
+        async with self._lock:
+            if await self._has_task_id(task_id):
+                raise TaskQueueExists()
+            self._local_queue[task_id] = queue
+            await self._register_task_id(task_id)
+
+    async def get(self, task_id: str) -> EventQueue | None:
+        async with self._lock:
+            # lookup locally
+            if task_id in self._local_queue:
+                return self._local_queue[task_id]
+            # lookup globally
+            if await self._has_task_id(task_id):
+                if task_id not in self._proxy_queue:
+                    queue = EventQueue()
+                    self._proxy_queue[task_id] = queue
+                    await self._subscribe_remote_task_events(task_id)
+                return self._proxy_queue[task_id]
+            return None
+
+    async def tap(self, task_id: str) -> EventQueue | None:
+        event_queue = await self.get(task_id)
+        if event_queue:
+            return event_queue.tap()
+        return None
+
+    async def close(self, task_id: str) -> None:
+        async with self._lock:
+            if task_id in self._local_queue:
+                # close locally
+                queue = self._local_queue.pop(task_id)
+                await queue.close()
+                # remove from global registry if a local queue is closed
+                await self._remove_task_id(task_id)
+                return  None
+
+            if task_id in self._proxy_queue:
+                # close proxy queue
+                queue = self._proxy_queue.pop(task_id)
+                await queue.close()
+                # unsubscribe from remote, but don't remove from global registry
+                self._unsubscribe_remote_task_events(task_id)
+                return None
+
+            raise NoTaskQueue()
+
+    async def create_or_tap(self, task_id: str) -> EventQueue:
+        async with self._lock:
+            if await self._has_task_id(task_id):
+                # if it's a local queue, tap directly
+                if task_id in self._local_queue:
+                    return self._local_queue[task_id].tap()
+
+                # if it's a proxy queue, tap the proxy
+                if task_id in self._proxy_queue:
+                    return self._proxy_queue[task_id].tap()
+
+                # if the proxy is not created, create the proxy and return
+                queue = EventQueue()
+                self._proxy_queue[task_id] = queue
+                await self._subscribe_remote_task_events(task_id)
+                return self._proxy_queue[task_id]
+            else:
+                # the task doesn't exist before, create a local queue
+                queue = EventQueue()
+                self._local_queue[task_id] = queue
+                await self._register_task_id(task_id)
+                return queue

tests/server/events/test_redis_queue_manager.py

@@ -0,0 +1,127 @@
+import asyncio
+from unittest.mock import MagicMock
+
+import pytest
+from fakeredis import FakeAsyncRedis
+
+from a2a.server.events import EventQueue, TaskQueueExists
+from a2a.server.events.redis_queue_manager import RedisQueueManager
+
+
+class TestRedisQueueManager:
+    @pytest.fixture
+    def redis(self):
+        return FakeAsyncRedis()
+
+    @pytest.fixture
+    def queue_manager(self, redis):
+        return RedisQueueManager(redis)
+
+    @pytest.fixture
+    def event_queue(self):
+        queue = MagicMock(spec=EventQueue)
+        # Mock the tap method to return itself
+        queue.tap.return_value = queue
+        return queue
+
+    @pytest.mark.asyncio
+    async def test_init(self, queue_manager):
+        assert queue_manager._local_queue == {}
+        assert queue_manager._proxy_queue == {}
+        assert isinstance(queue_manager._lock, asyncio.Lock)
+
+
+    @pytest.mark.asyncio
+    async def test_add_new_queue(self, queue_manager, event_queue):
+        """Test adding a new queue to the manager."""
+        task_id = 'test_task_id'
+        await queue_manager.add(task_id, event_queue)
+        assert queue_manager._local_queue[task_id] == event_queue
+
+    @pytest.mark.asyncio
+    async def test_add_existing_queue(self, queue_manager, event_queue):
+        task_id = 'test_task_id'
+        await queue_manager.add(task_id, event_queue)
+
+        with pytest.raises(TaskQueueExists):
+            await queue_manager.add(task_id, event_queue)
+
+    @pytest.mark.asyncio
+    async def test_get_existing_queue(self, queue_manager, event_queue):
+        task_id = 'test_task_id'
+        await queue_manager.add(task_id, event_queue)
+
+        result = await queue_manager.get(task_id)
+        assert result == event_queue
+
+    @pytest.mark.asyncio
+    async def test_get_nonexistent_queue(self, queue_manager):
+        result = await queue_manager.get('nonexistent_task_id')
+        assert result is None
+
+
+    @pytest.mark.asyncio
+    async def test_tap_existing_queue(self, queue_manager, event_queue):
+        task_id = 'test_task_id'
+        await queue_manager.add(task_id, event_queue)
+
+        result = await queue_manager.tap(task_id)
+        assert result == event_queue
+        event_queue.tap.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_tap_nonexistent_queue(self, queue_manager):
+        result = await queue_manager.tap('nonexistent_task_id')
+        assert result is None
+
+    @pytest.mark.asyncio
+    async def test_close_existing_queue(self, queue_manager, event_queue):
+        task_id = 'test_task_id'
+        await queue_manager.add(task_id, event_queue)
+
+        await queue_manager.close(task_id)
+        assert task_id not in queue_manager._local_queue
+
+
+    @pytest.mark.asyncio
+    async def test_create_or_tap_existing_queue(
+        self, queue_manager, event_queue
+    ):
+        task_id = 'test_task_id'
+        await queue_manager.add(task_id, event_queue)
+
+        result = await queue_manager.create_or_tap(task_id)
+
+        assert result == event_queue
+        event_queue.tap.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_concurrency(self, queue_manager):
+        async def add_task(task_id):
+            queue = EventQueue()
+            await queue_manager.add(task_id, queue)
+            return task_id
+
+        async def get_task(task_id):
+            return await queue_manager.get(task_id)
+
+        # Create 10 different task IDs
+        task_ids = [f'task_{i}' for i in range(10)]
+
+        # Add tasks concurrently
+        add_tasks = [add_task(task_id) for task_id in task_ids]
+        added_task_ids = await asyncio.gather(*add_tasks)
+
+        # Verify all tasks were added
+        assert set(added_task_ids) == set(task_ids)
+
+        # Get tasks concurrently
+        get_tasks = [get_task(task_id) for task_id in task_ids]
+        queues = await asyncio.gather(*get_tasks)
+
+        # Verify all queues are not None
+        assert all(queue is not None for queue in queues)
+
+        # Verify all tasks are in the manager
+        for task_id in task_ids:
+            assert task_id in queue_manager._local_queue