fix: update response status code for invalid session ID in StreamableHTTPSessionManager

BUMshakalaka · BUMshakalaka · commit 52c63c53e223 · 2025-09-24T15:13:17.000+02:00
Changed the status code from BAD_REQUEST to NOT_FOUND and added MCP_SESSION_ID_HEADER to the response headers if available. This behaviour is align with MCP spec https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#session-management
diff --git a/src/mcp/server/streamable_http_manager.py b/src/mcp/server/streamable_http_manager.py
@@ -274,6 +274,7 @@ async def run_server(*, task_status: TaskStatus[None] = anyio.TASK_STATUS_IGNORE
             # Invalid session ID
             response = Response(
                 "Bad Request: No valid session ID provided",
-                status_code=HTTPStatus.BAD_REQUEST,
+                status_code=HTTPStatus.NOT_FOUND,
+                headers={MCP_SESSION_ID_HEADER: request_mcp_session_id} if request_mcp_session_id else {},
             )
             await response(scope, receive, send)

Original file line number	Diff line number	Diff line change
`@@ -274,6 +274,7 @@ async def run_server(*, task_status: TaskStatus[None] = anyio.TASK_STATUS_IGNORE`
`274`	`274`	`# Invalid session ID`
`275`	`275`	`response = Response(`
`276`	`276`	`"Bad Request: No valid session ID provided",`
`277`		`- status_code=HTTPStatus.BAD_REQUEST,`
	`277`	`+ status_code=HTTPStatus.NOT_FOUND,`
	`278`	`+ headers={MCP_SESSION_ID_HEADER: request_mcp_session_id} if request_mcp_session_id else {},`
`278`	`279`	`)`
`279`	`280`	`await response(scope, receive, send)`