fix mcp list result parsing

litellm/experimental_mcp_client/client.py

@@ -18,6 +18,7 @@ from typing import (
     Union,
 )
 import httpx
+import mcp.types as types
 from mcp import ClientSession, ReadResourceResult, Resource, StdioServerParameters
 from mcp.client.sse import sse_client
 from mcp.client.stdio import stdio_client
@@ -41,7 +42,7 @@ from mcp.types import (
     TextContent,
 )
 from mcp.types import Tool as MCPTool
-from pydantic import AnyUrl
+from pydantic import AnyUrl, Field
 from litellm._logging import verbose_logger
 from litellm.constants import MCP_CLIENT_TIMEOUT, MCP_NPM_CACHE_DIR
 from litellm.llms.custom_httpx.http_handler import get_ssl_configuration
@@ -81,6 +82,14 @@ def _first_non_cancelled_cause(exc: BaseException) -> Optional[BaseException]:
     return None
 
 
+class _LenientListPromptsResult(types.ListPromptsResult):
+    prompts: List[Prompt] = Field(default_factory=list)
+
+
+class _LenientListResourcesResult(types.ListResourcesResult):
+    resources: List[Resource] = Field(default_factory=list)
+
+
 TSessionResult = TypeVar("TSessionResult")
 
 
@@ -628,7 +637,10 @@ class MCPClient:
         )
 
         async def _list_prompts_operation(session: ClientSession):
-            return await session.list_prompts()
+            return await session.send_request(
+                types.ClientRequest(types.ListPromptsRequest(params=None)),
+                _LenientListPromptsResult,
+            )
 
         try:
             result = await self.run_with_session(_list_prompts_operation)
@@ -713,7 +725,10 @@ class MCPClient:
         )
 
         async def _list_resources_operation(session: ClientSession):
-            return await session.list_resources()
+            return await session.send_request(
+                types.ClientRequest(types.ListResourcesRequest(params=None)),
+                _LenientListResourcesResult,
+            )
 
         try:
             result = await self.run_with_session(_list_resources_operation)

tests/test_litellm/experimental_mcp_client/test_mcp_client.py

@@ -542,6 +542,44 @@ class TestExecuteSessionOperationSurfacesTransportError:
         result = await client._execute_session_operation(transport_ctx, _op)
         assert result == "done"
 
+    @pytest.mark.asyncio
+    async def test_list_resources_tolerates_missing_resources_field(self):
+        client = MCPClient(server_url="http://example.com/mcp", transport_type="http")
+        session = AsyncMock()
+
+        async def send_request(_request, result_type):
+            assert result_type is mcp_client_module._LenientListResourcesResult
+            return result_type.model_validate({})
+
+        session.send_request = AsyncMock(side_effect=send_request)
+
+        async def run_with_session(operation):
+            return await operation(session)
+
+        client.run_with_session = AsyncMock(side_effect=run_with_session)
+
+        assert await client.list_resources() == []
+        session.send_request.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    async def test_list_prompts_tolerates_missing_prompts_field(self):
+        client = MCPClient(server_url="http://example.com/mcp", transport_type="http")
+        session = AsyncMock()
+
+        async def send_request(_request, result_type):
+            assert result_type is mcp_client_module._LenientListPromptsResult
+            return result_type.model_validate({})
+
+        session.send_request = AsyncMock(side_effect=send_request)
+
+        async def run_with_session(operation):
+            return await operation(session)
+
+        client.run_with_session = AsyncMock(side_effect=run_with_session)
+
+        assert await client.list_prompts() == []
+        session.send_request.assert_awaited_once()
+
 
 if __name__ == "__main__":
     pytest.main([__file__])