test simple middleware / no statefulness changes

langchain_mcp_adapters/middleware.py

@@ -0,0 +1,47 @@
+"""Agent middleware for LangChain."""
+
+import asyncio
+from concurrent.futures import ThreadPoolExecutor
+from typing import TYPE_CHECKING
+
+from langchain.agents.middleware import AgentMiddleware
+
+from langchain_mcp_adapters.client import MultiServerMCPClient
+from langchain_mcp_adapters.sessions import (
+    StreamableHttpConnection,
+)
+from langchain_core.tools import BaseTool
+
+
+def _sync_await(coro):
+    """Run an async coroutine from sync code, even if a loop is already running."""
+    try:
+        asyncio.get_running_loop()
+    except RuntimeError:
+        # No running loop in this thread: just run it.
+        return asyncio.run(coro)
+    with ThreadPoolExecutor(max_workers=1) as ex:
+        return ex.submit(lambda: asyncio.run(coro)).result()
+
+
+class MCPMiddleware(AgentMiddleware):
+    """MCP Middleware to register tools for use in an agent."""
+
+    def __init__(self, connections: dict[str, StreamableHttpConnection]) -> None:
+        """Initialize the middleware."""
+        self.server_to_connection = connections
+        for connection in connections.values():
+            assert connection["transport"] == "streamable_http"
+            # Check how it looks if we only support stateless connections
+            # assert connection["is_stateful"] == False
+        self._client = MultiServerMCPClient(connections)
+        self._tools = None
+
+    # Do we want to make tools a property? Or support an async method?
+    @property
+    def tools(self) -> list[BaseTool]:
+        """No additional tools"""
+        if self._tools is not None:
+            return self._tools
+        self._tools = _sync_await(self._client.get_tools())
+        return self._tools

pyproject.toml

@@ -14,7 +14,9 @@ repository = "https://www.github.com/langchain-ai/langchain-mcp-adapters"
 readme = "README.md"
 requires-python = ">=3.10"
 dependencies = [
+    "langchain",
     "langchain-core>=0.3.36,<0.4",
+    "langchain-openai>=0.3.33",
     "mcp>=1.9.2",
     "typing-extensions>=4.14.0",
 ]
@@ -66,6 +68,9 @@ warn_unused_configs = true
 disallow_untyped_defs = true
 check_untyped_defs = true
 
+[tool.uv.sources]
+langchain = { path = "../langchain/libs/langchain_v1" }
+
 [tool.ruff.lint.extend-per-file-ignores]
 "tests/**/*.py" = [
     # at least this three should be fine in tests: