Merge pull request #460 from jlowin/update-proxy-example

docs/servers/proxy.mdx

@@ -89,7 +89,7 @@ proxy = FastMCP.from_client(client, name="SSE to Stdio Proxy")
 You can also proxy an in-memory `FastMCP` instance, which is useful for adjusting the configuration or behavior of a server you don't completely control.
 
 ```python
-from fastmcp import FastMCP
+from fastmcp import FastMCP, Client
 
 # Original server
 original_server = FastMCP(name="Original")
@@ -98,9 +98,12 @@ original_server = FastMCP(name="Original")
 def tool_a() -> str: 
     return "A"
 
-# Create a proxy of the original server
+# To proxy an in-memory server, first create a Client to it.
+client_to_original = Client(original_server)
+
+# Create a proxy of the original server using the client.
 proxy = FastMCP.from_client(
-    original_server,
+    client_to_original,
     name="Proxy Server"
 )
 

examples/in_memory_proxy_example.py

@@ -0,0 +1,89 @@
+"""
+This example demonstrates how to set up and use an in-memory FastMCP proxy.
+
+It illustrates the pattern:
+1. Create an original FastMCP server with some tools.
+2. Create a Client that connects to this original server (in-memory).
+3. Create a proxy FastMCP server using FastMCP.from_client(), passing it the client from step 2.
+4. Use another Client to connect to the proxy server (in-memory) and interact with the original server's tools through the proxy.
+"""
+
+import asyncio
+
+from mcp.types import TextContent
+
+from fastmcp import FastMCP
+from fastmcp.client import Client
+
+
+class EchoService:
+    """A simple service to demonstrate with"""
+
+    def echo(self, message: str) -> str:
+        return f"Original server echoes: {message}"
+
+
+async def main():
+    print("--- In-Memory FastMCP Proxy Example ---")
+    print("This example will walk through setting up an in-memory proxy.")
+    print("-----------------------------------------")
+
+    # 1. Original Server Setup
+    print(
+        "\nStep 1: Setting up the Original Server (OriginalEchoServer) with an 'echo' tool..."
+    )
+    original_server = FastMCP("OriginalEchoServer")
+    original_server.add_tool(EchoService().echo)
+    print(f"   -> Original Server '{original_server.name}' created.")
+
+    # 2. Client for Proxy
+    print("\nStep 2: Creating a Client to connect to the Original Server...")
+    print("          (This client will be used internally by the proxy server)")
+    client_to_original = Client(original_server)
+    print(f"   -> Client for proxy created, targeting '{original_server.name}'.")
+
+    # 3. Proxy Server Creation
+    print("\nStep 3: Creating the Proxy Server (InMemoryProxy)...")
+    print(
+        f"          (Using FastMCP.from_client, passing it the client from Step 2 that targets '{original_server.name}')"
+    )
+    proxy_server = FastMCP.from_client(client_to_original, name="InMemoryProxy")
+    print(
+        f"   -> Proxy Server '{proxy_server.name}' created, proxying '{original_server.name}'."
+    )
+
+    # 4. Interacting via Proxy
+    print("\nStep 4: Using a new Client to connect to the Proxy Server and interact...")
+    async with Client(proxy_server) as final_client:
+        print(f"   -> Successfully connected to proxy '{proxy_server.name}'.")
+
+        print("\n   Listing tools available via proxy...")
+        tools = await final_client.list_tools()
+        if tools:
+            print("      Available Tools:")
+            for tool in tools:
+                print(
+                    f"        - {tool.name} (Description: {tool.description or 'N/A'})"
+                )
+        else:
+            print("      No tools found via proxy.")
+
+        message_to_echo = "Hello, simplified proxied world!"
+        print(f"\n   Calling 'echo' tool via proxy with message: '{message_to_echo}'")
+        try:
+            result = await final_client.call_tool("echo", {"message": message_to_echo})
+            if result and isinstance(result[0], TextContent):
+                print(f"      Result from proxied 'echo' call: '{result[0].text}'")
+            else:
+                print(
+                    f"      Error: Unexpected result format from proxied 'echo' call: {result}"
+                )
+        except Exception as e:
+            print(f"      Error calling 'echo' tool via proxy: {e}")
+
+    print("\n-----------------------------------------")
+    print("--- In-Memory Proxy Example Finished ---")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())