feat: Add push notification support

examples/langgraph/__main__.py

@@ -2,14 +2,15 @@
 import sys
 
 import click
+import httpx
 
 from agent import CurrencyAgent
 from agent_executor import CurrencyAgentExecutor
 from dotenv import load_dotenv
 
 from a2a.server.apps import A2AStarletteApplication
 from a2a.server.request_handlers import DefaultRequestHandler
-from a2a.server.tasks import InMemoryTaskStore
+from a2a.server.tasks import InMemoryPushNotifier, InMemoryTaskStore
 from a2a.types import (
     AgentAuthentication,
     AgentCapabilities,
@@ -29,9 +30,11 @@ def main(host: str, port: int):
         print('GOOGLE_API_KEY environment variable not set.')
         sys.exit(1)
 
+    client = httpx.AsyncClient()
     request_handler = DefaultRequestHandler(
         agent_executor=CurrencyAgentExecutor(),
         task_store=InMemoryTaskStore(),
+        push_notifier=InMemoryPushNotifier(client),
     )
 
     server = A2AStarletteApplication(

src/a2a/server/request_handlers/default_request_handler.py

@@ -14,7 +14,12 @@
     TaskQueueExists,
 )
 from a2a.server.request_handlers.request_handler import RequestHandler
-from a2a.server.tasks import ResultAggregator, TaskManager, TaskStore
+from a2a.server.tasks import (
+    PushNotifier,
+    ResultAggregator,
+    TaskManager,
+    TaskStore,
+)
 from a2a.types import (
     InternalError,
     Message,
@@ -42,10 +47,12 @@ def __init__(
         agent_executor: AgentExecutor,
         task_store: TaskStore,
         queue_manager: QueueManager | None = None,
+        push_notifier: PushNotifier | None = None,
     ) -> None:
         self.agent_executor = agent_executor
         self.task_store = task_store
         self._queue_manager = queue_manager or InMemoryQueueManager()
+        self._push_notifier = push_notifier
         # TODO: Likely want an interface for managing this, like AgentExecutionManager.
         self._running_agents = {}
         self._running_agents_lock = asyncio.Lock()
@@ -116,6 +123,15 @@ async def on_message_send(
         task: Task | None = await task_manager.get_task()
         if task:
             task = task_manager.update_with_message(params.message, task)
+            if (
+                self._push_notifier
+                and params.configuration
+                and params.configuration.pushNotificationConfig
+                and not params.configuration.blocking
+            ):
+                await self._push_notifier.set_info(
+                    task.id, params.configuration.pushNotificationConfig
+                )
         request_context = RequestContext(
             params,
             task.id if task else None,
@@ -174,6 +190,16 @@ async def on_message_send_stream(
         if task:
             task = task_manager.update_with_message(params.message, task)
 
+            if (
+                self._push_notifier
+                and params.configuration
+                and params.configuration.pushNotificationConfig
+            ):
+                await self._push_notifier.set_info(
+                    task.id, params.configuration.pushNotificationConfig
+                )
+        else:
+            queue = EventQueue()
         result_aggregator = ResultAggregator(task_manager)
         request_context = RequestContext(
             params,
@@ -198,12 +224,26 @@ async def on_message_send_stream(
                 # Now we know we have a Task, register the queue
                 if isinstance(event, Task):
                     try:
-                        await self._queue_manager.add(event.id, queue)
-                        task_id = event.id
+                        created_task: Task = event
+                        await self._queue_manager.add(created_task.id, queue)
+                        task_id = created_task.id
                     except TaskQueueExists:
                         logging.info(
                             'Multiple Task objects created in event stream.'
                         )
+                    if (
+                        self._push_notifier
+                        and params.configuration
+                        and params.configuration.pushNotificationConfig
+                    ):
+                        await self._push_notifier.set_info(
+                            created_task.id,
+                            params.configuration.pushNotificationConfig,
+                        )
+                if self._push_notifier and task_id:
+                    latest_task = await result_aggregator.current_result
+                    if isinstance(latest_task, Task):
+                        await self._push_notifier.send_notification(latest_task)
                 yield event
         finally:
             await self._cleanup_producer(producer_task, task_id)
@@ -222,13 +262,38 @@ async def on_set_task_push_notification_config(
         self, params: TaskPushNotificationConfig
     ) -> TaskPushNotificationConfig:
         """Default handler for 'tasks/pushNotificationConfig/set'."""
-        raise ServerError(error=UnsupportedOperationError())
+        if not self._push_notifier:
+            raise ServerError(error=UnsupportedOperationError())
+
+        task: Task | None = await self.task_store.get(params.taskId)
+        if not task:
+            raise ServerError(error=TaskNotFoundError())
+
+        await self._push_notifier.set_info(
+            params.taskId,
+            params.pushNotificationConfig,
+        )
+
+        return params
 
     async def on_get_task_push_notification_config(
         self, params: TaskIdParams
     ) -> TaskPushNotificationConfig:
         """Default handler for 'tasks/pushNotificationConfig/get'."""
-        raise ServerError(error=UnsupportedOperationError())
+        if not self._push_notifier:
+            raise ServerError(error=UnsupportedOperationError())
+
+        task: Task | None = await self.task_store.get(params.id)
+        if not task:
+            raise ServerError(error=TaskNotFoundError())
+
+        push_notification_config = await self._push_notifier.get_info(params.id)
+        if not push_notification_config:
+            raise ServerError(error=InternalError())
+
+        return TaskPushNotificationConfig(
+            taskId=params.id, pushNotificationConfig=push_notification_config
+        )
 
     async def on_resubscribe_to_task(
         self, params: TaskIdParams

src/a2a/server/tasks/__init__.py

@@ -1,12 +1,16 @@
+from a2a.server.tasks.inmemory_push_notifier import InMemoryPushNotifier
 from a2a.server.tasks.inmemory_task_store import InMemoryTaskStore
+from a2a.server.tasks.push_notifier import PushNotifier
 from a2a.server.tasks.result_aggregator import ResultAggregator
 from a2a.server.tasks.task_manager import TaskManager
 from a2a.server.tasks.task_store import TaskStore
 from a2a.server.tasks.task_updater import TaskUpdater
 
 
 __all__ = [
+    'InMemoryPushNotifier',
     'InMemoryTaskStore',
+    'PushNotifier',
     'ResultAggregator',
     'TaskManager',
     'TaskStore',

src/a2a/server/tasks/inmemory_push_notifier.py

@@ -0,0 +1,49 @@
+import asyncio
+import logging
+
+import httpx
+
+from a2a.server.tasks.push_notifier import PushNotifier
+from a2a.types import PushNotificationConfig, Task
+
+
+logger = logging.getLogger(__name__)
+
+
+class InMemoryPushNotifier(PushNotifier):
+    """In-memory implementation of PushNotifier interface."""
+
+    def __init__(self, httpx_client: httpx.AsyncClient) -> None:
+        self._client = httpx_client
+        self.lock = asyncio.Lock()
+        self._push_notification_infos: dict[str, PushNotificationConfig] = {}
+
+    async def set_info(
+        self, task_id: str, notification_config: PushNotificationConfig
+    ):
+        async with self.lock:
+            self._push_notification_infos[task_id] = notification_config
+
+    async def get_info(self, task_id: str) -> PushNotificationConfig | None:
+        async with self.lock:
+            return self._push_notification_infos.get(task_id)
+
+    async def delete_info(self, task_id: str):
+        async with self.lock:
+            if task_id in self._push_notification_infos:
+                del self._push_notification_infos[task_id]
+
+    async def send_notification(self, task: Task):
+        push_info = await self.get_info(task.id)
+        if not push_info:
+            return
+        url = push_info.url
+
+        try:
+            response = await self._client.post(
+                url, json=task.model_dump(mode='json', exclude_none=True)
+            )
+            response.raise_for_status()
+            logger.info(f'Push-notification sent for URL: {url}')
+        except Exception as e:
+            logger.error(f'Error sending push-notification: {e}')

src/a2a/server/tasks/push_notifier.py

@@ -0,0 +1,25 @@
+from abc import ABC, abstractmethod
+
+from a2a.types import PushNotificationConfig, Task
+
+
+class PushNotifier(ABC):
+    """PushNotifier interface to store, retrieve push notification for tasks and send push notifications."""
+
+    @abstractmethod
+    async def set_info(
+        self, task_id: str, notification_config: PushNotificationConfig
+    ):
+        pass
+
+    @abstractmethod
+    async def get_info(self, task_id: str) -> PushNotificationConfig | None:
+        pass
+
+    @abstractmethod
+    async def delete_info(self, task_id: str):
+        pass
+
+    @abstractmethod
+    async def send_notification(self, task: Task):
+        pass