WIP - move tool call handler registration away from mount function

fastapi_mcp/mcp_tools.py

@@ -7,7 +7,8 @@ without the intermediate step of dynamically generating Python functions.
 
 import json
 import logging
-from typing import Any, Dict, List, Optional, Union, Tuple
+from typing import Any, Dict, List, Optional, Union, Tuple, AsyncIterator
+from contextlib import asynccontextmanager
 
 import httpx
 from fastapi import FastAPI
@@ -349,6 +350,7 @@ def create_mcp_server(
     app: FastAPI,
     name: Optional[str] = None,
     description: Optional[str] = None,
+    base_url: Optional[str] = None,
     describe_all_responses: bool = False,
     describe_full_response_schema: bool = False,
 ) -> tuple[Server, Dict[str, Dict[str, Any]]]:
@@ -359,6 +361,7 @@ def create_mcp_server(
         app: The FastAPI application
         name: Name for the MCP server (defaults to app.title)
         description: Description for the MCP server (defaults to app.description)
+        base_url: Base URL for API requests (defaults to http://localhost:$PORT)
         describe_all_responses: Whether to include all possible response schemas in tool descriptions
         describe_full_response_schema: Whether to include full response schema in tool descriptions
 
@@ -387,15 +390,57 @@ def create_mcp_server(
         describe_full_response_schema=describe_full_response_schema,
     )
 
+    # Determine base URL if not provided
+    if not base_url:
+        # Try to determine the base URL from FastAPI config
+        if hasattr(app, "root_path") and app.root_path:
+            base_url = app.root_path
+        else:
+            # Default to localhost with FastAPI default port
+            port = 8000
+            for route in app.routes:
+                if hasattr(route, "app") and hasattr(route.app, "port"):
+                    port = route.app.port
+                    break
+            base_url = f"http://localhost:{port}"
+
+    # Normalize base URL
+    if base_url.endswith("/"):
+        base_url = base_url[:-1]
+
     # Create the MCP server
     mcp_server: Server = Server(server_name, server_description)
 
+    # Create a lifespan context manager to store the base_url and operation_map
+    @asynccontextmanager
+    async def server_lifespan(server) -> AsyncIterator[Dict[str, Any]]:
+        # Store context data that will be available to all server handlers
+        context = {"base_url": base_url, "operation_map": operation_map}
+        yield context
+
+    # Use our custom lifespan
+    mcp_server.lifespan = server_lifespan
+
     # Register handlers for tools
     @mcp_server.list_tools()
     async def handle_list_tools() -> List[types.Tool]:
         """Handler for the tools/list request"""
         return tools
 
+    # Register the tool call handler
+    @mcp_server.call_tool()
+    async def handle_call_tool(
+        name: str, arguments: Dict[str, Any]
+    ) -> List[Union[types.TextContent, types.ImageContent, types.EmbeddedResource]]:
+        """Handler for the tools/call request"""
+        # Get context from server lifespan
+        ctx = mcp_server.request_context
+        base_url = ctx.lifespan_context["base_url"]
+        operation_map = ctx.lifespan_context["operation_map"]
+
+        # Execute the tool
+        return await execute_http_tool(base_url, name, arguments, operation_map)
+
     return mcp_server, operation_map
 
 
@@ -422,35 +467,6 @@ def mount_mcp_server(
     if mount_path.endswith("/"):
         mount_path = mount_path[:-1]
 
-    # Determine base URL if not provided
-    if not base_url:
-        # Try to determine the base URL from FastAPI config
-        if hasattr(app, "root_path") and app.root_path:
-            base_url = app.root_path
-        else:
-            # Default to localhost with FastAPI default port
-            port = 8000
-            for route in app.routes:
-                if hasattr(route, "app") and hasattr(route.app, "port"):
-                    port = route.app.port
-                    break
-            base_url = f"http://localhost:{port}"
-
-    # Normalize base URL
-    if base_url.endswith("/"):
-        base_url = base_url[:-1]
-
-    # Create final base URL to use for HTTP requests
-    final_base_url = base_url
-
-    # Register the tool call handler
-    @mcp_server.call_tool()
-    async def handle_call_tool(
-        name: str, arguments: Dict[str, Any]
-    ) -> List[Union[types.TextContent, types.ImageContent, types.EmbeddedResource]]:
-        """Handler for the tools/call request"""
-        return await execute_http_tool(final_base_url, name, arguments, operation_map)
-
     # Create SSE transport for MCP messages
     from mcp.server.sse import SseServerTransport
     from fastapi import Request
@@ -500,6 +516,7 @@ def add_mcp_server(
         app,
         name,
         description,
+        base_url,
         describe_all_responses=describe_all_responses,
         describe_full_response_schema=describe_full_response_schema,
     )

fastapi_mcp/server.py

@@ -19,6 +19,7 @@ def create_mcp_server(
     name: Optional[str] = None,
     description: Optional[str] = None,
     capabilities: Optional[Dict[str, Any]] = None,
+    base_url: Optional[str] = None,
     describe_all_responses: bool = False,
     describe_full_response_schema: bool = False,
 ) -> Server:
@@ -30,6 +31,7 @@ def create_mcp_server(
         name: Name for the MCP server (defaults to app.title)
         description: Description for the MCP server (defaults to app.description)
         capabilities: Optional capabilities for the MCP server (ignored in direct conversion)
+        base_url: Base URL for API requests (defaults to http://localhost:$PORT)
         describe_all_responses: Whether to include all possible response schemas in tool descriptions. Recommended to keep False, as the LLM will probably derive if there is an error.
         describe_full_response_schema: Whether to include full json schema for responses in tool descriptions. Recommended to keep False, as examples are more LLM friendly, and save tokens.
 
@@ -41,6 +43,7 @@ def create_mcp_server(
         app,
         name,
         description,
+        base_url,
         describe_all_responses=describe_all_responses,
         describe_full_response_schema=describe_full_response_schema,
     )
@@ -53,8 +56,6 @@ def mount_mcp_server(
     mcp_server: Server,
     mount_path: str = "/mcp",
     base_url: Optional[str] = None,
-    describe_all_responses: bool = False,
-    describe_full_response_schema: bool = False,
 ) -> None:
     """
     Mount an MCP server to a FastAPI app.
@@ -64,8 +65,6 @@ def mount_mcp_server(
         mcp_server: The MCP server to mount
         mount_path: Path where the MCP server will be mounted
         base_url: Base URL for API requests
-        describe_all_responses: Whether to include all possible response schemas in tool descriptions. Recommended to keep False, as the LLM will probably derive if there is an error.
-        describe_full_response_schema: Whether to include full json schema for responses in tool descriptions. Recommended to keep False, as examples are more LLM friendly, and save tokens.
     """
     # Get OpenAPI schema from FastAPI app for operation mapping
     from fastapi.openapi.utils import get_openapi
@@ -81,11 +80,7 @@ def mount_mcp_server(
 
     # Extract operation map for HTTP calls
     # The function returns a tuple (tools, operation_map)
-    result = convert_openapi_to_mcp_tools(
-        openapi_schema,
-        describe_all_responses=describe_all_responses,
-        describe_full_response_schema=describe_full_response_schema,
-    )
+    result = convert_openapi_to_mcp_tools(openapi_schema)
     operation_map = result[1]
 
     # Mount using the direct approach