feat: Allow toolset to process llm_request before tools returned by it

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

@@ -42,6 +42,7 @@
 from ...telemetry import trace_call_llm
 from ...telemetry import trace_send_data
 from ...telemetry import tracer
+from ...tools.base_toolset import BaseToolset
 from ...tools.tool_context import ToolContext
 
 if TYPE_CHECKING:
@@ -341,13 +342,25 @@ async def _preprocess_async(
         yield event
 
     # Run processors for tools.
-    for tool in await agent.canonical_tools(
-        ReadonlyContext(invocation_context)
-    ):
+    for tool_union in agent.tools:
       tool_context = ToolContext(invocation_context)
-      await tool.process_llm_request(
-          tool_context=tool_context, llm_request=llm_request
+
+      # If it's a toolset, process it first
+      if isinstance(tool_union, BaseToolset):
+        await tool_union.process_llm_request(
+            tool_context=tool_context, llm_request=llm_request
+        )
+
+      from ...agents.llm_agent import _convert_tool_union_to_tools
+
+      # Then process all tools from this tool union
+      tools = await _convert_tool_union_to_tools(
+          tool_union, ReadonlyContext(invocation_context)
       )
+      for tool in tools:
+        await tool.process_llm_request(
+            tool_context=tool_context, llm_request=llm_request
+        )
 
   async def _postprocess_async(
       self,

src/google/adk/tools/base_toolset.py

@@ -20,11 +20,16 @@
 from typing import Optional
 from typing import Protocol
 from typing import runtime_checkable
+from typing import TYPE_CHECKING
 from typing import Union
 
 from ..agents.readonly_context import ReadonlyContext
 from .base_tool import BaseTool
 
+if TYPE_CHECKING:
+  from ..models.llm_request import LlmRequest
+  from .tool_context import ToolContext
+
 
 @runtime_checkable
 class ToolPredicate(Protocol):
@@ -96,3 +101,20 @@ def _is_tool_selected(
       return tool.name in self.tool_filter
 
     return False
+
+  async def process_llm_request(
+      self, *, tool_context: ToolContext, llm_request: LlmRequest
+  ) -> None:
+    """Processes the outgoing LLM request for this toolset. This method will be
+    called before each tool processes the llm request.
+
+    Use cases:
+    - Instead of let each tool process the llm request, we can let the toolset
+      process the llm request. e.g. ComputerUseToolset can add computer use
+      tool to the llm request.
+
+    Args:
+      tool_context: The context of the tool.
+      llm_request: The outgoing LLM request, mutable this method.
+    """
+    pass

tests/unittests/flows/llm_flows/test_base_llm_flow.py

@@ -0,0 +1,150 @@
+# 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.
+
+"""Unit tests for BaseLlmFlow toolset integration."""
+
+from unittest.mock import AsyncMock
+
+from google.adk.agents import Agent
+from google.adk.flows.llm_flows.base_llm_flow import BaseLlmFlow
+from google.adk.models.llm_request import LlmRequest
+from google.adk.models.llm_response import LlmResponse
+from google.adk.tools.base_toolset import BaseToolset
+from google.genai import types
+import pytest
+
+from ... import testing_utils
+
+
+class BaseLlmFlowForTesting(BaseLlmFlow):
+  """Test implementation of BaseLlmFlow for testing purposes."""
+
+  pass
+
+
+@pytest.mark.asyncio
+async def test_preprocess_calls_toolset_process_llm_request():
+  """Test that _preprocess_async calls process_llm_request on toolsets."""
+
+  # Create a mock toolset that tracks if process_llm_request was called
+  class _MockToolset(BaseToolset):
+
+    def __init__(self):
+      super().__init__()
+      self.process_llm_request_called = False
+      self.process_llm_request = AsyncMock(side_effect=self._track_call)
+
+    async def _track_call(self, **kwargs):
+      self.process_llm_request_called = True
+
+    async def get_tools(self, readonly_context=None):
+      return []
+
+    async def close(self):
+      pass
+
+  mock_toolset = _MockToolset()
+
+  # Create a mock model that returns a simple response
+  mock_response = LlmResponse(
+      content=types.Content(
+          role='model', parts=[types.Part.from_text(text='Test response')]
+      ),
+      partial=False,
+  )
+
+  mock_model = testing_utils.MockModel.create(responses=[mock_response])
+
+  # Create agent with the mock toolset
+  agent = Agent(name='test_agent', model=mock_model, tools=[mock_toolset])
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent, user_content='test message'
+  )
+
+  flow = BaseLlmFlowForTesting()
+
+  # Call _preprocess_async
+  llm_request = LlmRequest()
+  events = []
+  async for event in flow._preprocess_async(invocation_context, llm_request):
+    events.append(event)
+
+  # Verify that process_llm_request was called on the toolset
+  assert mock_toolset.process_llm_request_called
+
+
+@pytest.mark.asyncio
+async def test_preprocess_handles_mixed_tools_and_toolsets():
+  """Test that _preprocess_async properly handles both tools and toolsets."""
+  from google.adk.tools.base_tool import BaseTool
+  from google.adk.tools.function_tool import FunctionTool
+
+  # Create a mock tool
+  class _MockTool(BaseTool):
+
+    def __init__(self):
+      super().__init__(name='mock_tool', description='Mock tool')
+      self.process_llm_request_called = False
+      self.process_llm_request = AsyncMock(side_effect=self._track_call)
+
+    async def _track_call(self, **kwargs):
+      self.process_llm_request_called = True
+
+    async def call(self, **kwargs):
+      return 'mock result'
+
+  # Create a mock toolset
+  class _MockToolset(BaseToolset):
+
+    def __init__(self):
+      super().__init__()
+      self.process_llm_request_called = False
+      self.process_llm_request = AsyncMock(side_effect=self._track_call)
+
+    async def _track_call(self, **kwargs):
+      self.process_llm_request_called = True
+
+    async def get_tools(self, readonly_context=None):
+      return []
+
+    async def close(self):
+      pass
+
+  def _test_function():
+    """Test function tool."""
+    return 'function result'
+
+  mock_tool = _MockTool()
+  mock_toolset = _MockToolset()
+
+  # Create agent with mixed tools and toolsets
+  agent = Agent(
+      name='test_agent', tools=[mock_tool, _test_function, mock_toolset]
+  )
+
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent, user_content='test message'
+  )
+
+  flow = BaseLlmFlowForTesting()
+
+  # Call _preprocess_async
+  llm_request = LlmRequest()
+  events = []
+  async for event in flow._preprocess_async(invocation_context, llm_request):
+    events.append(event)
+
+  # Verify that process_llm_request was called on both tools and toolsets
+  assert mock_tool.process_llm_request_called
+  assert mock_toolset.process_llm_request_called

tests/unittests/tools/test_base_toolset.py

@@ -0,0 +1,109 @@
+# 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.
+
+"""Unit tests for BaseToolset."""
+
+from typing import Optional
+
+from google.adk.agents.invocation_context import InvocationContext
+from google.adk.agents.readonly_context import ReadonlyContext
+from google.adk.agents.sequential_agent import SequentialAgent
+from google.adk.models.llm_request import LlmRequest
+from google.adk.sessions.in_memory_session_service import InMemorySessionService
+from google.adk.tools.base_tool import BaseTool
+from google.adk.tools.base_toolset import BaseToolset
+from google.adk.tools.tool_context import ToolContext
+import pytest
+
+
+class _TestingToolset(BaseToolset):
+  """A test implementation of BaseToolset."""
+
+  async def get_tools(
+      self, readonly_context: Optional[ReadonlyContext] = None
+  ) -> list[BaseTool]:
+    return []
+
+  async def close(self) -> None:
+    pass
+
+
+@pytest.mark.asyncio
+async def test_process_llm_request_default_implementation():
+  """Test that the default process_llm_request implementation does nothing."""
+  toolset = _TestingToolset()
+
+  # Create test objects
+  session_service = InMemorySessionService()
+  session = await session_service.create_session(
+      app_name='test_app', user_id='test_user'
+  )
+  agent = SequentialAgent(name='test_agent')
+  invocation_context = InvocationContext(
+      invocation_id='test_id',
+      agent=agent,
+      session=session,
+      session_service=session_service,
+  )
+  tool_context = ToolContext(invocation_context)
+  llm_request = LlmRequest()
+
+  # The default implementation should not modify the request
+  original_request = LlmRequest.model_validate(llm_request.model_dump())
+
+  await toolset.process_llm_request(
+      tool_context=tool_context, llm_request=llm_request
+  )
+
+  # Verify the request was not modified
+  assert llm_request.model_dump() == original_request.model_dump()
+
+
+@pytest.mark.asyncio
+async def test_process_llm_request_can_be_overridden():
+  """Test that process_llm_request can be overridden by subclasses."""
+
+  class _CustomToolset(_TestingToolset):
+
+    async def process_llm_request(
+        self, *, tool_context: ToolContext, llm_request: LlmRequest
+    ) -> None:
+      # Add some custom processing
+      if not llm_request.contents:
+        llm_request.contents = []
+      llm_request.contents.append('Custom processing applied')
+
+  toolset = _CustomToolset()
+
+  # Create test objects
+  session_service = InMemorySessionService()
+  session = await session_service.create_session(
+      app_name='test_app', user_id='test_user'
+  )
+  agent = SequentialAgent(name='test_agent')
+  invocation_context = InvocationContext(
+      invocation_id='test_id',
+      agent=agent,
+      session=session,
+      session_service=session_service,
+  )
+  tool_context = ToolContext(invocation_context)
+  llm_request = LlmRequest()
+
+  await toolset.process_llm_request(
+      tool_context=tool_context, llm_request=llm_request
+  )
+
+  # Verify the custom processing was applied
+  assert llm_request.contents == ['Custom processing applied']