add stateless http transport support

Author: Edison-A-N

fastapi_mcp/server.py

@@ -330,6 +330,16 @@ def mount_http(
                 """
             ),
         ] = "/mcp",
+        stateless: Annotated[
+            bool,
+            Doc(
+                """
+                Whether to force stateless transport. When True, the MCP server will ignore
+                the mcp-session-id header and treat all requests as stateless.
+                Defaults to False.
+                """
+            ),
+        ] = False,
     ) -> None:
         """
         Mount the MCP server with HTTP transport to **any** FastAPI app or APIRouter.
@@ -348,7 +358,7 @@ def mount_http(
 
         assert isinstance(router, (FastAPI, APIRouter)), f"Invalid router type: {type(router)}"
 
-        http_transport = FastApiHttpSessionManager(mcp_server=self.server)
+        http_transport = FastApiHttpSessionManager(mcp_server=self.server, stateless=stateless)
         dependencies = self._auth_config.dependencies if self._auth_config else None
 
         self._register_mcp_endpoints_http(router, http_transport, mount_path, dependencies)

fastapi_mcp/transport/http.py

@@ -20,11 +20,13 @@ def __init__(
         event_store: EventStore | None = None,
         json_response: bool = True,  # Default to JSON for HTTP transport
         security_settings: TransportSecuritySettings | None = None,
+        stateless: bool = False,
     ):
         self.mcp_server = mcp_server
         self.event_store = event_store
         self.json_response = json_response
         self.security_settings = security_settings
+        self.stateless = stateless
         self._session_manager: StreamableHTTPSessionManager | None = None
         self._manager_task: asyncio.Task | None = None
         self._manager_started = False
@@ -47,13 +49,12 @@ async def _ensure_session_manager_started(self) -> None:
             logger.debug("Starting StreamableHTTP session manager")
 
             # Create the session manager
-            # Note: We don't use stateless=True because we want to support sessions
-            # but sessions are optional as per the MCP spec
+            # Use stateless flag to determine whether to support sessions
             self._session_manager = StreamableHTTPSessionManager(
                 app=self.mcp_server,
                 event_store=self.event_store,
                 json_response=self.json_response,
-                stateless=False,  # Always support sessions, but they're optional
+                stateless=self.stateless,  # Use the stateless flag
                 security_settings=self.security_settings,
             )