feat: Add progressive streaming for run_async via ProgressiveTool (partial progress + final result)

src/google/adk/flows/llm_flows/base_llm_flow.py

@@ -647,14 +647,26 @@ async def _postprocess_handle_function_calls_async(
       function_call_event: Event,
       llm_request: LlmRequest,
   ) -> AsyncGenerator[Event, None]:
-    if function_response_event := await functions.handle_function_calls_async(
-        invocation_context, function_call_event, llm_request.tools_dict
-    ):
-      auth_event = functions.generate_auth_event(
-          invocation_context, function_response_event
+    # First, stream progressive tools if present (partial events + final event)
+    final_event_from_progressive = None
+    async with Aclosing(
+        functions.iter_progressive_function_calls_async(
+            invocation_context, function_call_event, llm_request.tools_dict
+        )
+    ) as agen:
+      async for event in agen:
+        final_event_from_progressive = event
+        yield event
+
+    # If progressive produced a final event, continue with it; otherwise fallback
+    # to the default async handler (non-progressive tools and parallel merge)
+    function_response_event = final_event_from_progressive
+    if not function_response_event:
+      function_response_event = await functions.handle_function_calls_async(
+          invocation_context, function_call_event, llm_request.tools_dict
       )
-      if auth_event:
-        yield auth_event
+      if not function_response_event:
+        return
 
       tool_confirmation_event = functions.generate_request_confirmation_event(
           invocation_context, function_call_event, function_response_event
@@ -665,25 +677,28 @@ async def _postprocess_handle_function_calls_async(
       # Always yield the function response event first
       yield function_response_event
 
-      # Check if this is a set_model_response function response
-      if json_response := _output_schema_processor.get_structured_model_response(
-          function_response_event
-      ):
-        # Create and yield a final model response event
-        final_event = (
-            _output_schema_processor.create_final_model_response_event(
-                invocation_context, json_response
-            )
-        )
-        yield final_event
-      transfer_to_agent = function_response_event.actions.transfer_to_agent
-      if transfer_to_agent:
-        agent_to_run = self._get_agent_to_run(
-            invocation_context, transfer_to_agent
-        )
-        async with Aclosing(agent_to_run.run_async(invocation_context)) as agen:
-          async for event in agen:
-            yield event
+    # Common path: auth event, structured response, agent transfer
+    auth_event = functions.generate_auth_event(
+        invocation_context, function_response_event
+    )
+    if auth_event:
+      yield auth_event
+
+    if json_response := _output_schema_processor.get_structured_model_response(
+        function_response_event
+    ):
+      final_event = _output_schema_processor.create_final_model_response_event(
+          invocation_context, json_response
+      )
+      yield final_event
+    transfer_to_agent = function_response_event.actions.transfer_to_agent
+    if transfer_to_agent:
+      agent_to_run = self._get_agent_to_run(
+          invocation_context, transfer_to_agent
+      )
+      async with Aclosing(agent_to_run.run_async(invocation_context)) as agen:
+        async for event in agen:
+          yield event
 
   def _get_agent_to_run(
       self, invocation_context: InvocationContext, agent_name: str

src/google/adk/flows/llm_flows/functions.py

@@ -40,6 +40,7 @@
 from ...telemetry.tracing import tracer
 from ...tools.base_tool import BaseTool
 from ...tools.tool_confirmation import ToolConfirmation
+from ...tools.progressive_function_tool import ProgressiveFunctionTool
 from ...tools.tool_context import ToolContext
 from ...utils.context_utils import Aclosing
 
@@ -267,6 +268,79 @@ async def handle_function_call_list_async(
   return merged_event
 
 
+async def iter_progressive_function_calls_async(
+    invocation_context: InvocationContext,
+    function_call_event: Event,
+    tools_dict: dict[str, BaseTool],
+) -> AsyncGenerator[Event, None]:
+  """Streams progress for ProgressiveFunctionTool, then yields final result.
+
+  This is async-run only and independent of LiveRequestQueue.
+  For each function call that maps to a ProgressiveFunctionTool:
+    - yield partial Events for each progress update
+    - then run the tool's run_async for the final result and yield a final Event
+  Non-progressive tools are ignored by this iterator.
+  """
+  function_calls = function_call_event.get_function_calls()
+  if not function_calls:
+    return
+
+  for function_call in function_calls:
+    name = function_call.name
+    if name not in tools_dict:
+      continue
+    tool = tools_dict[name]
+    if not isinstance(tool, ProgressiveFunctionTool):
+      continue
+
+    tool_context = ToolContext(
+        invocation_context=invocation_context,
+        function_call_id=function_call.id,
+    )
+    function_args = (
+        copy.deepcopy(function_call.args) if function_call.args else {}
+    )
+
+    # Progress stream
+    try:
+      async with Aclosing(
+          tool.progress_stream(args=function_args, tool_context=tool_context)
+      ) as agen:
+        async for progress in agen:
+          partial_event = __build_response_event(
+              tool, progress, tool_context, invocation_context
+          )
+          partial_event.partial = True
+          yield partial_event
+    except Exception as tool_error:
+      # Let on_tool_error callbacks decide if they want to convert error to result
+      error_response = (
+          await invocation_context.plugin_manager.run_on_tool_error_callback(
+              tool=tool,
+              tool_args=function_args,
+              tool_context=tool_context,
+              error=tool_error,
+          )
+      )
+      if error_response is None:
+        raise
+      # Treat handled error as final function response
+      final_event = __build_response_event(
+          tool, error_response, tool_context, invocation_context
+      )
+      yield final_event
+      continue
+
+    # Final result for the model
+    final_result = await __call_tool_async(
+        tool, args=function_args, tool_context=tool_context
+    )
+    final_event = __build_response_event(
+        tool, final_result, tool_context, invocation_context
+    )
+    yield final_event
+
+
 async def _execute_single_function_call_async(
     invocation_context: InvocationContext,
     function_call: types.FunctionCall,

src/google/adk/tools/__init__.py

@@ -30,6 +30,7 @@
 from .load_memory_tool import load_memory_tool as load_memory
 from .long_running_tool import LongRunningFunctionTool
 from .preload_memory_tool import preload_memory_tool as preload_memory
+from .progressive_tool import ProgressiveTool
 from .tool_context import ToolContext
 from .transfer_to_agent_tool import transfer_to_agent
 from .url_context_tool import url_context
@@ -49,6 +50,7 @@
     'ExampleTool',
     'exit_loop',
     'FunctionTool',
+    'ProgressiveTool',
     'get_user_choice',
     'load_artifacts',
     'load_memory',

src/google/adk/tools/progressive_function_tool.py

@@ -0,0 +1,45 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import annotations
+
+from typing import Any
+from typing import AsyncGenerator
+
+from .function_tool import FunctionTool
+from .tool_context import ToolContext
+
+
+class ProgressiveFunctionTool(FunctionTool):
+  """A FunctionTool that can stream progress updates during run_async.
+
+  Implement `progress_stream` to yield intermediate progress payloads.
+  The final result for model consumption must be returned by `run_async`.
+  """
+
+  async def progress_stream(
+      self,
+      *,
+      args: dict[str, Any],
+      tool_context: ToolContext,
+  ) -> AsyncGenerator[Any, None]:
+    """Yields progress updates while the tool is executing.
+
+    Subclasses should override this method to emit progress objects. The last
+    item yielded here does not need to be the final result; the final result
+    should be returned by `run_async`.
+    """
+    raise NotImplementedError(
+        f"{type(self).__name__}.progress_stream is not implemented"
+    )

src/google/adk/tools/progressive_tool.py

@@ -0,0 +1,152 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import annotations
+
+import asyncio
+import inspect
+from typing import Any
+from typing import Optional
+
+from ..utils.context_utils import Aclosing
+from .function_tool import FunctionTool
+from .progressive_function_tool import ProgressiveFunctionTool
+from .tool_context import ToolContext
+
+
+class ProgressiveTool(ProgressiveFunctionTool):
+  """Wraps a regular async function to emit progress during run_async.
+
+  Usage:
+    from google.adk.tools.progressive_tool import ProgressiveTool
+    ProgressiveTool(my_async_function)
+
+  Supported function shapes:
+    - async generator function: yields are treated as progress; last yielded
+      value is treated as the final result.
+    - async function with optional `progress` or `progress_callback` parameter:
+      the wrapper injects a reporter callable that streams progress; the return
+      value of the function is treated as the final result.
+    - async function without any progress parameter: no progress is emitted; the
+      return value is treated as the final result.
+  """
+
+  def __init__(self, func):
+    # Initialize as FunctionTool to extract name/description and signature logic
+    FunctionTool.__init__(self, func)
+    self._results_by_call_id: dict[str, Any] = {}
+    # Hide internal progress params from function declaration so the model is
+    # never prompted for them and schema parsing doesn't fail.
+    try:
+      ignore_list = list(getattr(self, '_ignore_params', []))
+    except Exception:
+      ignore_list = []
+    for p in ('progress', 'progress_callback'):
+      if p not in ignore_list:
+        ignore_list.append(p)
+    self._ignore_params = ignore_list
+
+  async def progress_stream(
+      self,
+      *,
+      args: dict[str, Any],
+      tool_context: ToolContext,
+  ) -> asyncio.AsyncGenerator[Any, None]:
+    signature = inspect.signature(self.func)
+    valid_params = {param for param in signature.parameters}
+
+    # Build args for the wrapped function
+    args_to_call = {k: v for k, v in args.items() if k in valid_params}
+    if 'tool_context' in valid_params:
+      args_to_call['tool_context'] = tool_context
+
+    call_id: Optional[str] = tool_context.function_call_id
+
+    # Async generator function: yield directly and capture last item
+    if inspect.isasyncgenfunction(self.func):
+      last: Any = None
+      async with Aclosing(self.func(**args_to_call)) as agen:
+        async for item in agen:
+          last = item
+          yield item
+      if call_id:
+        self._results_by_call_id[call_id] = last
+      return
+
+    # Coroutine function: run in background, capture progress via callback
+    # Determine which progress parameter to use if present
+    progress_param: Optional[str] = None
+    if 'progress' in valid_params:
+      progress_param = 'progress'
+    elif 'progress_callback' in valid_params:
+      progress_param = 'progress_callback'
+
+    queue: asyncio.Queue[Any] = asyncio.Queue()
+
+    async def _report_progress(payload: Any):
+      await queue.put(payload)
+
+    if progress_param:
+      args_to_call[progress_param] = _report_progress
+
+    result_box: dict[str, Any] = {}
+
+    async def _run_and_capture():
+      result_box['value'] = await self.func(**args_to_call)
+
+    task = asyncio.create_task(_run_and_capture())
+
+    # Drain progress while task runs
+    try:
+      while True:
+        if task.done() and queue.empty():
+          break
+        try:
+          item = await asyncio.wait_for(queue.get(), timeout=0.1)
+          yield item
+        except asyncio.TimeoutError:
+          await asyncio.sleep(0)
+          continue
+    finally:
+      # Ensure task completion / propagate exception
+      await task
+
+    if call_id:
+      self._results_by_call_id[call_id] = result_box.get('value')
+
+  async def run_async(
+      self, *, args: dict[str, Any], tool_context: ToolContext
+  ) -> Any:
+    """Return final result. If progress_stream already ran, use captured value."""
+    call_id: Optional[str] = tool_context.function_call_id
+    if call_id and call_id in self._results_by_call_id:
+      return self._results_by_call_id.pop(call_id)
+
+    # Fallback: invoke function directly if progress_stream wasn't used
+    signature = inspect.signature(self.func)
+    valid_params = {param for param in signature.parameters}
+    args_to_call = {k: v for k, v in args.items() if k in valid_params}
+    if 'tool_context' in valid_params:
+      args_to_call['tool_context'] = tool_context
+
+    if inspect.isasyncgenfunction(self.func):
+      # Consume generator fully; return last item
+      last: Any = None
+      async with Aclosing(self.func(**args_to_call)) as agen:
+        async for item in agen:
+          last = item
+      return last
+
+    # Coroutine function
+    return await self.func(**args_to_call)