feat: add metadata to send message request (#532)

Extended `client.send_message` to take `metadata` parameter which gets
attached to `MessageSendParams`.

Author: yarolegovich

src/a2a/client/base_client.py

@@ -1,4 +1,5 @@
 from collections.abc import AsyncIterator
+from typing import Any
 
 from a2a.client.client import (
     Client,
@@ -47,6 +48,7 @@ async def send_message(
         request: Message,
         *,
         context: ClientCallContext | None = None,
+        request_metadata: dict[str, Any] | None = None,
     ) -> AsyncIterator[ClientEvent | Message]:
         """Sends a message to the agent.
 
@@ -57,6 +59,7 @@ async def send_message(
         Args:
             request: The message to send to the agent.
             context: The client call context.
+            request_metadata: Extensions Metadata attached to the request.
 
         Yields:
             An async iterator of `ClientEvent` or a final `Message` response.
@@ -70,7 +73,9 @@ async def send_message(
                 else None
             ),
         )
-        params = MessageSendParams(message=request, configuration=config)
+        params = MessageSendParams(
+            message=request, configuration=config, metadata=request_metadata
+        )
 
         if not self._config.streaming or not self._card.capabilities.streaming:
             response = await self._transport.send_message(

src/a2a/client/client.py

@@ -110,6 +110,7 @@ async def send_message(
         request: Message,
         *,
         context: ClientCallContext | None = None,
+        request_metadata: dict[str, Any] | None = None,
     ) -> AsyncIterator[ClientEvent | Message]:
         """Sends a message to the server.
 

tests/client/test_base_client.py

@@ -73,9 +73,14 @@ async def create_stream(*args, **kwargs):
 
     mock_transport.send_message_streaming.return_value = create_stream()
 
-    events = [event async for event in base_client.send_message(sample_message)]
+    meta = {'test': 1}
+    stream = base_client.send_message(sample_message, request_metadata=meta)
+    events = [event async for event in stream]
 
     mock_transport.send_message_streaming.assert_called_once()
+    assert (
+        mock_transport.send_message_streaming.call_args[0][0].metadata == meta
+    )
     assert not mock_transport.send_message.called
     assert len(events) == 1
     assert events[0][0].id == 'task-123'
@@ -92,9 +97,12 @@ async def test_send_message_non_streaming(
         status=TaskStatus(state=TaskState.completed),
     )
 
-    events = [event async for event in base_client.send_message(sample_message)]
+    meta = {'test': 1}
+    stream = base_client.send_message(sample_message, request_metadata=meta)
+    events = [event async for event in stream]
 
     mock_transport.send_message.assert_called_once()
+    assert mock_transport.send_message.call_args[0][0].metadata == meta
     assert not mock_transport.send_message_streaming.called
     assert len(events) == 1
     assert events[0][0].id == 'task-456'