Python: feat: Add Agent Framework to A2A bridge support

python/packages/a2a/AGENTS.md

@@ -4,20 +4,48 @@ Agent-to-Agent (A2A) protocol support for inter-agent communication.
 
 ## Main Classes
 
-- **`A2AAgent`** - Agent wrapper that exposes an agent via the A2A protocol
+- **`A2AAgent`** - Client to connect to remote A2A-compliant agents.
+- **`A2AExecutor`** - Bridge to expose Agent Framework agents via the A2A protocol.
 
 ## Usage
 
+### A2AAgent (Client)
+
 ```python
 from agent_framework.a2a import A2AAgent
 
-a2a_agent = A2AAgent(agent=my_agent)
+# Connect to a remote A2A agent
+a2a_agent = A2AAgent(url="http://remote-agent/a2a")
+response = await a2a_agent.run("Hello!")
+```
+
+### A2AExecutor (Server/Bridge)
+
+```python
+from agent_framework.a2a import A2AExecutor
+from a2a.server.apps import A2AStarletteApplication
+from a2a.server.request_handlers import DefaultRequestHandler
+from a2a.server.tasks import InMemoryTaskStore
+
+# Create an A2A executor for your agent
+executor = A2AExecutor(agent=my_agent)
+
+# Set up the request handler and server application
+request_handler = DefaultRequestHandler(
+    agent_executor=executor,
+    task_store=InMemoryTaskStore(),
+)
+
+app = A2AStarletteApplication(
+    agent_card=my_agent_card,
+    http_handler=request_handler,
+).build()
 ```
 
 ## Import Path
 
 ```python
-from agent_framework.a2a import A2AAgent
+from agent_framework.a2a import A2AAgent, A2AExecutor
 # or directly:
-from agent_framework_a2a import A2AAgent
+from agent_framework_a2a import A2AAgent, A2AExecutor
 ```

python/packages/a2a/README.md

@@ -10,11 +10,49 @@ pip install agent-framework-a2a --pre
 
 The A2A agent integration enables communication with remote A2A-compliant agents using the standardized A2A protocol. This allows your Agent Framework applications to connect to agents running on different platforms, languages, or services.
 
+### A2AAgent (Client)
+
+The `A2AAgent` class is a client that wraps an A2A Client to connect the Agent Framework with external A2A-compliant agents.
+
+```python
+from agent_framework.a2a import A2AAgent
+
+# Connect to a remote A2A agent
+a2a_agent = A2AAgent(url="http://remote-agent/a2a")
+response = await a2a_agent.run("Hello!")
+```
+
+### A2AExecutor (Hosting)
+
+The `A2AExecutor` class bridges local AI agents built with the `agent_framework` library to the A2A protocol, allowing them to be hosted and accessed by other A2A-compliant clients.
+
+```python
+from agent_framework.a2a import A2AExecutor
+from a2a.server.apps import A2AStarletteApplication
+from a2a.server.request_handlers import DefaultRequestHandler
+from a2a.server.tasks import InMemoryTaskStore
+
+# Create an A2A executor for your agent
+executor = A2AExecutor(agent=my_agent)
+
+# Set up the request handler and server application
+request_handler = DefaultRequestHandler(
+    agent_executor=executor,
+    task_store=InMemoryTaskStore(),
+)
+
+app = A2AStarletteApplication(
+    agent_card=my_agent_card,
+    http_handler=request_handler,
+).build()
+```
+
 ### Basic Usage Example
 
 See the [A2A agent examples](../../samples/04-hosting/a2a/) which demonstrate:
 
 - Connecting to remote A2A agents
+- Hosting local agents via A2A protocol
 - Sending messages and receiving responses
 - Handling different content types (text, files, data)
 - Streaming responses and real-time interaction

python/packages/a2a/agent_framework_a2a/__init__.py

@@ -2,6 +2,7 @@
 
 import importlib.metadata
 
+from ._a2a_executor import A2AExecutor
 from ._agent import A2AAgent, A2AContinuationToken
 
 try:
@@ -12,5 +13,6 @@
 __all__ = [
     "A2AAgent",
     "A2AContinuationToken",
+    "A2AExecutor",
     "__version__",
 ]

python/packages/a2a/agent_framework_a2a/_a2a_executor.py

@@ -0,0 +1,275 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+import logging
+from asyncio import CancelledError
+from collections.abc import Mapping
+from functools import partial
+from typing import Any
+
+from a2a.server.agent_execution import AgentExecutor, RequestContext
+from a2a.server.events import EventQueue
+from a2a.server.tasks import TaskUpdater
+from a2a.types import FilePart, FileWithBytes, FileWithUri, Part, TaskState, TextPart
+from a2a.utils import new_task
+from agent_framework import (
+    AgentResponseUpdate,
+    AgentSession,
+    Message,
+    SupportsAgentRun,
+)
+from typing_extensions import override
+
+from agent_framework_a2a._utils import get_uri_data
+
+logger = logging.getLogger("agent_framework.a2a")
+
+
+class A2AExecutor(AgentExecutor):
+    """Execute AI agents using the A2A (Agent-to-Agent) protocol.
+
+    The A2AExecutor bridges AI agents built with the agent_framework library and the A2A protocol,
+    enabling structured agent execution with event-driven communication. It handles execution
+    contexts, delegates history management to the agent's session, and converts agent
+    responses into A2A protocol events.
+
+    The executor supports executing an Agent or WorkflowAgent. It provides comprehensive
+    error handling with task status updates and supports various content types including text,
+    binary data, and URI-based content.
+
+    Example:
+        .. code-block:: python
+
+            from a2a.server.apps import A2AStarletteApplication
+            from a2a.server.request_handlers import DefaultRequestHandler
+            from a2a.server.tasks import InMemoryTaskStore
+            from a2a.types import AgentCapabilities, AgentCard
+            from agent_framework.a2a import A2AExecutor
+            from agent_framework.openai import OpenAIResponsesClient
+
+            public_agent_card = AgentCard(
+                name="Food Agent",
+                description="A simple agent that provides food-related information.",
+                url="http://localhost:9999/",
+                version="1.0.0",
+                defaultInputModes=["text"],
+                defaultOutputModes=["text"],
+                capabilities=AgentCapabilities(streaming=True),
+                skills=[],
+            )
+
+            # Create an agent
+            agent = OpenAIResponsesClient().as_agent(
+                name="Food Agent",
+                instructions="A simple agent that provides food-related information.",
+            )
+
+            # Set up the A2A server with the A2AExecutor enabled for streaming
+            # and passing custom keyword arguments to the agent's run method.
+            request_handler = DefaultRequestHandler(
+                agent_executor=A2AExecutor(agent, stream=True, run_kwargs={"client_kwargs": {"max_tokens": 500}}),
+                task_store=InMemoryTaskStore(),
+            )
+
+            server = A2AStarletteApplication(
+                agent_card=public_agent_card,
+                http_handler=request_handler,
+            ).build()
+
+    Args:
+        agent: The AI agent to execute.
+        stream: Whether to stream the agent response. Defaults to False.
+        run_kwargs: Additional keyword arguments to pass to the agent's run method.
+    """
+
+    def __init__(self, agent: SupportsAgentRun, stream: bool = False, run_kwargs: Mapping[str, Any] | None = None):
+        """Initialize the A2AExecutor with the specified agent.
+
+        Args:
+            agent: The AI agent or workflow to execute.
+            stream: Whether to stream the agent response. Defaults to False.
+            run_kwargs: Additional keyword arguments to pass to the agent's run method.
+                Cannot contain 'session' or 'stream' as these are managed by the executor.
+
+        Raises:
+            ValueError: If run_kwargs contains 'session' or 'stream'.
+        """
+        super().__init__()
+        self._agent: SupportsAgentRun = agent
+        self._stream: bool = stream
+        if run_kwargs:
+            if "session" in run_kwargs:
+                raise ValueError("run_kwargs cannot contain 'session' as it is managed by the executor.")
+            if "stream" in run_kwargs:
+                raise ValueError("run_kwargs cannot contain 'stream' as it is managed by the executor.")
+        self._run_kwargs: Mapping[str, Any] = run_kwargs or {}
+
+    @override
+    async def cancel(self, context: RequestContext, event_queue: EventQueue) -> None:
+        """Cancel agent execution for the given request context.
+
+        Uses a TaskUpdater to send a cancellation event through the provided event queue.
+
+        Args:
+            context: The request context identifying the task to cancel.
+            event_queue: The event queue to publish the cancellation event to.
+
+        Raises:
+            ValueError: If context_id is not provided in the RequestContext.
+        """
+        if context.context_id is None:
+            raise ValueError("Context ID must be provided in the RequestContext")
+
+        updater = TaskUpdater(
+            event_queue=event_queue,
+            task_id=context.task_id or "",
+            context_id=context.context_id,
+        )
+
+        await updater.cancel()
+
+    @override
+    async def execute(self, context: RequestContext, event_queue: EventQueue) -> None:
+        """Execute the agent with the given context and event queue.
+
+        Orchestrates the agent execution process: sets up the agent session,
+        executes the agent, processes response messages, and handles errors with appropriate task status updates.
+        """
+        if context.context_id is None:
+            raise ValueError("Context ID must be provided in the RequestContext")
+        if context.message is None:
+            raise ValueError("Message must be provided in the RequestContext")
+
+        query = context.get_user_input()
+        task = context.current_task
+
+        if not task:
+            task = new_task(context.message)
+            await event_queue.enqueue_event(task)
+
+        updater = TaskUpdater(event_queue, task.id, context.context_id)
+        await updater.submit()
+
+        try:
+            await updater.start_work()
+
+            session = self._agent.create_session(session_id=task.context_id)
+
+            if self._stream:
+                await self._run_stream(query, session, updater)
+            else:
+                await self._run(query, session, updater)
+
+            # Mark as complete
+            await updater.complete()
+        except CancelledError:
+            await updater.update_status(state=TaskState.canceled, final=True)
+        except Exception as e:
+            logger.exception("A2AExecutor encountered an error during execution.", exc_info=e)
+            await updater.update_status(
+                state=TaskState.failed,
+                final=True,
+                message=updater.new_agent_message([Part(root=TextPart(text=str(e)))]),
+            )
+
+    async def _run_stream(self, query: Any, session: AgentSession, updater: TaskUpdater) -> None:
+        """Run the agent in streaming mode and publish updates to the task updater."""
+        response_stream = self._agent.run(query, session=session, stream=True, **self._run_kwargs)
+        streamed_artifact_ids: set[str] = set()
+        await (
+            response_stream.with_transform_hook(
+                partial(self.handle_events, updater=updater, streamed_artifact_ids=streamed_artifact_ids)
+            )
+        ).get_final_response()
+
+    async def _run(self, query: Any, session: AgentSession, updater: TaskUpdater) -> None:
+        """Run the agent in non-streaming mode and publish messages to the task updater."""
+        response = await self._agent.run(query, session=session, stream=False, **self._run_kwargs)
+        response_messages = response.messages
+
+        if not isinstance(response_messages, list):
+            response_messages = [response_messages]
+
+        for message in response_messages:
+            await self.handle_events(message, updater)
+
+    async def handle_events(
+        self, item: Message | AgentResponseUpdate, updater: TaskUpdater, streamed_artifact_ids: set[str] | None = None
+    ) -> None:
+        """Convert agent response items (Messages or Updates) to A2A protocol events.
+
+        Processes Message or AgentResponseUpdate objects and converts them into A2A protocol format.
+        Handles text, data, and URI content. USER role messages are skipped.
+
+        Users can override this method in a subclass to implement custom transformations
+        from their agent's output format to A2A protocol events.
+
+        Args:
+            item: The agent response item (Message or AgentResponseUpdate) to process.
+            updater: The task updater to publish events to.
+            streamed_artifact_ids: A set of artifact IDs that have already been streamed.
+                Used to prevent duplicate updates for the same artifact.
+
+        Example:
+            .. code-block:: python
+
+                class CustomA2AExecutor(A2AExecutor):
+                    async def handle_events(
+                        self,
+                        item: Message | AgentResponseUpdate,
+                        updater: TaskUpdater,
+                        streamed_artifact_ids: set[str] | None = None,
+                    ) -> None:
+                        # Custom logic to transform item contents
+                        if item.role == "assistant" and item.contents:
+                            parts = [Part(root=TextPart(text=f"Custom: {item.contents[0].text}"))]
+                            await updater.update_status(
+                                state=TaskState.working,
+                                message=updater.new_agent_message(parts=parts),
+                            )
+                        else:
+                            await super().handle_events(item, updater)
+        """
+        role = getattr(item, "role", None)
+        if role == "user":
+            # This is a user message, we can ignore it in the context of task updates
+            return
+
+        parts: list[Part] = []
+        metadata = getattr(item, "additional_properties", None)
+
+        # AgentResponseUpdate uses 'contents', Message uses 'contents'
+        contents = getattr(item, "contents", [])
+
+        for content in contents:
+            if content.type == "text" and content.text:
+                parts.append(Part(root=TextPart(text=content.text)))
+            elif content.type == "data" and content.uri:
+                base64_str = get_uri_data(content.uri)
+                parts.append(Part(root=FilePart(file=FileWithBytes(bytes=base64_str, mime_type=content.media_type))))
+            elif content.type == "uri" and content.uri:
+                parts.append(Part(root=FilePart(file=FileWithUri(uri=content.uri, mime_type=content.media_type))))
+            else:
+                # Silently skip unsupported content types
+                logger.warning("A2AExecutor does not yet support content type: %s. Omitted.", content.type)
+
+        if parts:
+            if isinstance(item, AgentResponseUpdate):
+                # For streaming updates, we send TaskArtifactUpdateEvent via add_artifact
+                await updater.add_artifact(
+                    parts=parts,
+                    artifact_id=item.message_id,
+                    metadata=metadata,
+                    append=(
+                        True
+                        if streamed_artifact_ids is not None and item.message_id in (streamed_artifact_ids or set())
+                        else None
+                    ),
+                )
+                if item.message_id and streamed_artifact_ids is not None:
+                    streamed_artifact_ids.add(item.message_id)
+            else:
+                # For final messages, we send TaskStatusUpdateEvent with 'working' state
+                await updater.update_status(
+                    state=TaskState.working,
+                    message=updater.new_agent_message(parts=parts, metadata=metadata),
+                )