From 4f6aefed7a249cd6a8d42bdc4e7c98fbc7bdd39d Mon Sep 17 00:00:00 2001
From: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>
Date: Mon, 7 Apr 2025 11:23:29 -0400
Subject: [PATCH] add in memory client

---
 src/fastmcp/client/__init__.py | 11 +++++--
 src/fastmcp/client/memory.py   | 54 ++++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+), 2 deletions(-)
 create mode 100644 src/fastmcp/client/memory.py

diff --git a/src/fastmcp/client/__init__.py b/src/fastmcp/client/__init__.py
index ceb3f12a0..2a07f0fdb 100644
--- a/src/fastmcp/client/__init__.py
+++ b/src/fastmcp/client/__init__.py
@@ -1,5 +1,12 @@
 from .websocket import WebSocketClient
 from .sse import SSEClient
-from .stdio import StdioClient
+from .stdio import StdioClient, UvxClient
+from .memory import InMemoryClient
 
-__all__ = ["StdioClient", "SSEClient", "WebSocketClient"]
+__all__ = [
+    "StdioClient",
+    "SSEClient",
+    "WebSocketClient",
+    "UvxClient",
+    "InMemoryClient",
+]
diff --git a/src/fastmcp/client/memory.py b/src/fastmcp/client/memory.py
new file mode 100644
index 000000000..59c65995b
--- /dev/null
+++ b/src/fastmcp/client/memory.py
@@ -0,0 +1,54 @@
+import contextlib
+from typing import Any, TypeVar
+
+from mcp.server import Server
+from mcp.shared.memory import create_connected_server_and_client_session
+from typing_extensions import Unpack
+
+from fastmcp.client.base import BaseClient, ClientKwargs
+
+T = TypeVar("T")
+
+
+class InMemoryClient(BaseClient):
+    """Client that connects to an in-memory MCP server.
+
+    This client creates and manages an in-memory connection to a server,
+    without using any external processes or network connections.
+    """
+
+    def __init__(
+        self,
+        server: Server[Any],
+        raise_exceptions: bool = False,
+        **kwargs: Unpack[ClientKwargs],
+    ):
+        """Initialize an InMemoryClient that connects to an in-memory MCP server.
+
+        Args:
+            server: The MCP server instance to connect to
+            raise_exceptions: Whether to raise exceptions from the server
+            **kwargs: Additional arguments for BaseClient
+        """
+        super().__init__(**kwargs)
+        self.server = server
+        self.raise_exceptions = raise_exceptions
+        self._cm_session = None
+
+    @contextlib.asynccontextmanager
+    async def _connect(self):
+        """Set up in-memory connection and session"""
+        self._cm_session = create_connected_server_and_client_session(
+            server=self.server,
+            read_timeout_seconds=self._read_timeout_seconds,
+            sampling_callback=self._sampling_callback,
+            list_roots_callback=self._list_roots_callback,
+            logging_callback=self._logging_callback,
+            message_handler=self._message_handler,
+            raise_exceptions=self.raise_exceptions,
+        )
+
+        async with self._cm_session as session:
+            # No need to call initialize as create_connected_server_and_client_session already does
+            async with self._set_session((None, None), session):
+                yield self