feat(client): allow specifying history_length via call-site MessageSendConfiguration in BaseClient.send_message

src/a2a/client/base_client.py

@@ -46,6 +46,7 @@ async def send_message(
         self,
         request: Message,
         *,
+        configuration: MessageSendConfiguration | None = None,
         context: ClientCallContext | None = None,
     ) -> AsyncIterator[ClientEvent | Message]:
         """Sends a message to the agent.
@@ -56,12 +57,13 @@ async def send_message(
 
         Args:
             request: The message to send to the agent.
+            configuration: Optional per-call overrides for message sending behavior.
             context: The client call context.
 
         Yields:
             An async iterator of `ClientEvent` or a final `Message` response.
         """
-        config = MessageSendConfiguration(
+        base_config = MessageSendConfiguration(
             accepted_output_modes=self._config.accepted_output_modes,
             blocking=not self._config.polling,
             push_notification_config=(
@@ -70,6 +72,16 @@ async def send_message(
                 else None
             ),
         )
+        if configuration is not None:
+            overrides = configuration.model_dump(
+                exclude_unset=True,
+                exclude_none=True,
+                by_alias=False,
+            )
+            config = base_config.model_copy(update=overrides)
+        else:
+            config = base_config
+
         params = MessageSendParams(message=request, configuration=config)
 
         if not self._config.streaming or not self._card.capabilities.streaming:

tests/client/test_base_client.py

@@ -9,6 +9,7 @@
     AgentCapabilities,
     AgentCard,
     Message,
+    MessageSendConfiguration,
     Part,
     Role,
     Task,
@@ -115,3 +116,109 @@ async def test_send_message_non_streaming_agent_capability_false(
     assert not mock_transport.send_message_streaming.called
     assert len(events) == 1
     assert events[0][0].id == 'task-789'
+
+
+@pytest.mark.asyncio
+async def test_send_message_uses_callsite_configuration_partial_override_non_streaming(
+    base_client: BaseClient, mock_transport: MagicMock, sample_message: Message
+):
+    base_client._config.streaming = False
+    mock_transport.send_message.return_value = Task(
+        id='task-cfg-ns-1',
+        context_id='ctx-cfg-ns-1',
+        status=TaskStatus(state=TaskState.completed),
+    )
+
+    cfg = MessageSendConfiguration(history_length=2)
+    events = [
+        ev
+        async for ev in base_client.send_message(
+            sample_message, configuration=cfg
+        )
+    ]
+
+    mock_transport.send_message.assert_called_once()
+    assert not mock_transport.send_message_streaming.called
+    assert len(events) == 1
+    task, _ = events[0]
+    assert task.id == 'task-cfg-ns-1'
+
+    params = mock_transport.send_message.await_args.args[0]
+    assert params.configuration.history_length == 2
+    assert params.configuration.blocking == (not base_client._config.polling)
+    assert (
+        params.configuration.accepted_output_modes
+        == base_client._config.accepted_output_modes
+    )
+
+
+@pytest.mark.asyncio
+async def test_send_message_ignores_none_fields_in_callsite_configuration_non_streaming(
+    base_client: BaseClient, mock_transport: MagicMock, sample_message: Message
+):
+    base_client._config.streaming = False
+    mock_transport.send_message.return_value = Task(
+        id='task-cfg-ns-2',
+        context_id='ctx-cfg-ns-2',
+        status=TaskStatus(state=TaskState.completed),
+    )
+
+    cfg = MessageSendConfiguration(history_length=None, blocking=None)
+    events = [
+        ev
+        async for ev in base_client.send_message(
+            sample_message, configuration=cfg
+        )
+    ]
+
+    mock_transport.send_message.assert_called_once()
+    assert len(events) == 1
+    task, _ = events[0]
+    assert task.id == 'task-cfg-ns-2'
+
+    params = mock_transport.send_message.await_args.args[0]
+    assert params.configuration.history_length is None
+    assert params.configuration.blocking == (not base_client._config.polling)
+    assert (
+        params.configuration.accepted_output_modes
+        == base_client._config.accepted_output_modes
+    )
+
+
+@pytest.mark.asyncio
+async def test_send_message_uses_callsite_configuration_partial_override_streaming(
+    base_client: BaseClient, mock_transport: MagicMock, sample_message: Message
+):
+    base_client._config.streaming = True
+    base_client._card.capabilities.streaming = True
+
+    async def create_stream(*args, **kwargs):
+        yield Task(
+            id='task-cfg-s-1',
+            context_id='ctx-cfg-s-1',
+            status=TaskStatus(state=TaskState.completed),
+        )
+
+    mock_transport.send_message_streaming.return_value = create_stream()
+
+    cfg = MessageSendConfiguration(history_length=0)
+    events = [
+        ev
+        async for ev in base_client.send_message(
+            sample_message, configuration=cfg
+        )
+    ]
+
+    mock_transport.send_message_streaming.assert_called_once()
+    assert not mock_transport.send_message.called
+    assert len(events) == 1
+    task, _ = events[0]
+    assert task.id == 'task-cfg-s-1'
+
+    params = mock_transport.send_message_streaming.call_args.args[0]
+    assert params.configuration.history_length == 0
+    assert params.configuration.blocking == (not base_client._config.polling)
+    assert (
+        params.configuration.accepted_output_modes
+        == base_client._config.accepted_output_modes
+    )