From b6e2934f7b3c1e62e4241dee7f13ee21712e38a4 Mon Sep 17 00:00:00 2001 From: Ben Browning Date: Fri, 26 Sep 2025 12:09:48 -0400 Subject: [PATCH] fix: Gracefully handle errors when listing MCP tools (#2544) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit # What does this PR do? When listing (and lazily indexing) tools, it's possible for an error to get thrown by individual toolgroups if for example an MCP toolgroup is unable to connect to its `mcp_endpoint`. This logs a warning in the server when that happens, logs a full stack trace of the error if debug logging is enabled, and just returns the list of tools from all working toolgroups instead of throwing an error to the client when a single toolgroup is temporarily or permanently misbehaving. The exception to the above is authentication errors, which we specifically send all the way back to the client as that's how we indicate to the client that it needs to provide authentication data for the remote MCP servers. Closes #2540 ## Test Plan A new unit test was added to test this exception handling, which is run as part of our regular test suite but also manually run to specifically verify this fix via: ``` uv run pytest -sv --asyncio-mode=auto \ tests/unit/distribution/routers/test_routing_tables.py ``` To verify the additional debug logging is printing properly: ``` LLAMA_STACK_LOGGING=core=debug \ uv run pytest -sv --asyncio-mode=auto \ tests/unit/distribution/routers/test_routing_tables.py ``` The mcp integration tests were run as below (and by CI): ``` ollama run llama3.2:3b ENABLE_OLLAMA="ollama" \ OLLAMA_INFERENCE_MODEL="meta-llama/Llama-3.2-3B-Instruct" \ LLAMA_STACK_CONFIG=starter \ uv run pytest -sv tests/integration/tool_runtime/test_mcp.py \ --text-model meta-llama/Llama-3.2-3B-Instruct ``` --------- Signed-off-by: Ben Browning Signed-off-by: Sébastien Han Co-authored-by: Sébastien Han --- llama_stack/core/routing_tables/toolgroups.py | 15 ++++++++++-- .../routers/test_routing_tables.py | 23 +++++++++++++++++++ 2 files changed, 36 insertions(+), 2 deletions(-) diff --git a/llama_stack/core/routing_tables/toolgroups.py b/llama_stack/core/routing_tables/toolgroups.py index eeea406c1..8172b9b5f 100644 --- a/llama_stack/core/routing_tables/toolgroups.py +++ b/llama_stack/core/routing_tables/toolgroups.py @@ -9,7 +9,7 @@ from typing import Any from llama_stack.apis.common.content_types import URL from llama_stack.apis.common.errors import ToolGroupNotFoundError from llama_stack.apis.tools import ListToolGroupsResponse, ListToolsResponse, Tool, ToolGroup, ToolGroups -from llama_stack.core.datatypes import ToolGroupWithOwner +from llama_stack.core.datatypes import AuthenticationRequiredError, ToolGroupWithOwner from llama_stack.log import get_logger from .common import CommonRoutingTableImpl @@ -54,7 +54,18 @@ class ToolGroupsRoutingTable(CommonRoutingTableImpl, ToolGroups): all_tools = [] for toolgroup in toolgroups: if toolgroup.identifier not in self.toolgroups_to_tools: - await self._index_tools(toolgroup) + try: + await self._index_tools(toolgroup) + except AuthenticationRequiredError: + # Send authentication errors back to the client so it knows + # that it needs to supply credentials for remote MCP servers. + raise + except Exception as e: + # Other errors that the client cannot fix are logged and + # those specific toolgroups are skipped. + logger.warning(f"Error listing tools for toolgroup {toolgroup.identifier}: {e}") + logger.debug(e, exc_info=True) + continue all_tools.extend(self.toolgroups_to_tools[toolgroup.identifier]) return ListToolsResponse(data=all_tools) diff --git a/tests/unit/distribution/routers/test_routing_tables.py b/tests/unit/distribution/routers/test_routing_tables.py index bbfea3f46..456a5d041 100644 --- a/tests/unit/distribution/routers/test_routing_tables.py +++ b/tests/unit/distribution/routers/test_routing_tables.py @@ -10,6 +10,7 @@ from unittest.mock import AsyncMock import pytest +from llama_stack.apis.common.content_types import URL from llama_stack.apis.common.type_system import NumberType from llama_stack.apis.datasets.datasets import Dataset, DatasetPurpose, URIDataSource from llama_stack.apis.datatypes import Api @@ -645,3 +646,25 @@ async def test_models_source_interaction_cleanup_provider_models(cached_disk_dis # Cleanup await table.shutdown() + + +async def test_tool_groups_routing_table_exception_handling(cached_disk_dist_registry): + """Test that the tool group routing table handles exceptions when listing tools, like if an MCP server is unreachable.""" + + exception_throwing_tool_groups_impl = ToolGroupsImpl() + exception_throwing_tool_groups_impl.list_runtime_tools = AsyncMock(side_effect=Exception("Test exception")) + + table = ToolGroupsRoutingTable( + {"test_provider": exception_throwing_tool_groups_impl}, cached_disk_dist_registry, {} + ) + await table.initialize() + + await table.register_tool_group( + toolgroup_id="test-toolgroup-exceptions", + provider_id="test_provider", + mcp_endpoint=URL(uri="http://localhost:8479/foo/bar"), + ) + + tools = await table.list_tools(toolgroup_id="test-toolgroup-exceptions") + + assert len(tools.data) == 0