feat(MCP Server Trigger Node): Terminate sessions on DELETE request (#16550)

packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpServer.ts

@@ -219,6 +219,30 @@ export class McpServerManager {
 		return wasToolCall(req.rawBody.toString());
 	}
 
+	async handleDeleteRequest(req: express.Request, resp: CompressionResponse) {
+		const sessionId = this.getSessionId(req);
+
+		if (!sessionId) {
+			resp.status(400).send('No sessionId provided');
+			return;
+		}
+
+		const transport = this.getTransport(sessionId);
+
+		if (transport) {
+			if (transport instanceof FlushingStreamableHTTPTransport) {
+				await transport.handleRequest(req, resp);
+				return;
+			} else {
+				// For SSE transport, we don't support DELETE requests
+				resp.status(405).send('Method Not Allowed');
+				return;
+			}
+		}
+
+		resp.status(404).send('Session not found');
+	}
+
 	setUpHandlers(server: Server) {
 		server.setRequestHandler(
 			ListToolsRequestSchema,

packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpTrigger.node.ts

@@ -125,6 +125,16 @@ export class McpTrigger extends Node {
 				ndvHideMethod: true,
 				ndvHideUrl: true,
 			},
+			{
+				name: 'default',
+				httpMethod: 'DELETE',
+				responseMode: 'onReceived',
+				isFullPath: true,
+				path: '={{$parameter["path"]}}',
+				nodeType: 'mcp',
+				ndvHideMethod: true,
+				ndvHideUrl: true,
+			},
 		],
 	};
 
@@ -162,22 +172,30 @@ export class McpTrigger extends Node {
 
 			return { noWebhookResponse: true };
 		} else if (webhookName === 'default') {
-			// Here we handle POST requests. These can be either
+			// Here we handle POST and DELETE requests.
+			// POST can be either:
 			// 1) Client calls in an established session using the SSE transport, or
 			// 2) Client calls in an established session using the StreamableHTTPServerTransport
 			// 3) Session setup requests using the StreamableHTTPServerTransport
+			// DELETE is used to terminate the session using the StreamableHTTPServerTransport
 
-			// Check if there is a session and a transport is already established
-			const sessionId = mcpServerManager.getSessionId(req);
-			if (sessionId && mcpServerManager.getTransport(sessionId)) {
-				const connectedTools = await getConnectedTools(context, true);
-				const wasToolCall = await mcpServerManager.handlePostMessage(req, resp, connectedTools);
-				if (wasToolCall) return { noWebhookResponse: true, workflowData: [[{ json: {} }]] };
+			if (req.method === 'DELETE') {
+				await mcpServerManager.handleDeleteRequest(req, resp);
 			} else {
-				// If no session is established, this is a setup request
-				// for the StreamableHTTPServerTransport, so we create a new transport
-				await mcpServerManager.createServerWithStreamableHTTPTransport(serverName, resp, req);
+				// Check if there is a session and a transport is already established
+				const sessionId = mcpServerManager.getSessionId(req);
+
+				if (sessionId && mcpServerManager.getTransport(sessionId)) {
+					const connectedTools = await getConnectedTools(context, true);
+					const wasToolCall = await mcpServerManager.handlePostMessage(req, resp, connectedTools);
+					if (wasToolCall) return { noWebhookResponse: true, workflowData: [[{ json: {} }]] };
+				} else {
+					// If no session is established, this is a setup request
+					// for the StreamableHTTPServerTransport, so we create a new transport
+					await mcpServerManager.createServerWithStreamableHTTPTransport(serverName, resp, req);
+				}
 			}
+
 			return { noWebhookResponse: true };
 		}
 

packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/__test__/McpServer.test.ts

@@ -445,4 +445,88 @@ describe('McpServer', () => {
 			expect(result2).toBe(mockTransport2);
 		});
 	});
+
+	describe('handleDeleteRequest', () => {
+		beforeEach(() => {
+			// Clear transports and servers before each test
+			mcpServerManager.transports = {};
+			mcpServerManager.servers = {};
+		});
+
+		it('should handle DELETE request for StreamableHTTP transport', async () => {
+			const deleteSessionId = 'delete-session-id';
+			const mockDeleteRequest = mock<Request>({
+				headers: { 'mcp-session-id': deleteSessionId },
+			});
+			const mockDeleteResponse = mock<CompressionResponse>();
+			mockDeleteResponse.status.mockReturnThis();
+
+			// Create a mock transport that passes instanceof check
+			const mockHttpTransport = Object.create(FlushingStreamableHTTPTransport.prototype);
+			mockHttpTransport.handleRequest = jest.fn();
+
+			// Set up the transport
+			mcpServerManager.transports[deleteSessionId] = mockHttpTransport;
+
+			// Call handleDeleteRequest
+			await mcpServerManager.handleDeleteRequest(mockDeleteRequest, mockDeleteResponse);
+
+			// Verify transport.handleRequest was called
+			expect(mockHttpTransport.handleRequest).toHaveBeenCalledWith(
+				mockDeleteRequest,
+				mockDeleteResponse,
+			);
+		});
+
+		it('should return 400 when no sessionId provided', async () => {
+			const mockDeleteRequest = mock<Request>({
+				query: {},
+				headers: {},
+			});
+			const mockDeleteResponse = mock<CompressionResponse>();
+			mockDeleteResponse.status.mockReturnThis();
+
+			// Mock getSessionId to return undefined
+			jest.spyOn(mcpServerManager, 'getSessionId').mockReturnValueOnce(undefined);
+
+			// Call handleDeleteRequest without sessionId
+			await mcpServerManager.handleDeleteRequest(mockDeleteRequest, mockDeleteResponse);
+
+			// Verify 400 response
+			expect(mockDeleteResponse.status).toHaveBeenCalledWith(400);
+		});
+
+		it('should return 404 for non-existent session', async () => {
+			const mockDeleteRequest = mock<Request>({
+				headers: { 'mcp-session-id': 'non-existent-session' },
+			});
+			const mockDeleteResponse = mock<CompressionResponse>();
+			mockDeleteResponse.status.mockReturnThis();
+
+			// Call handleDeleteRequest with non-existent sessionId
+			await mcpServerManager.handleDeleteRequest(mockDeleteRequest, mockDeleteResponse);
+
+			// Verify 404 response (session not found)
+			expect(mockDeleteResponse.status).toHaveBeenCalledWith(404);
+		});
+
+		it('should return 405 for SSE transport session', async () => {
+			const sseSessionId = 'sse-session-id';
+			const mockDeleteRequest = mock<Request>({
+				query: { sessionId: sseSessionId },
+			});
+			const mockDeleteResponse = mock<CompressionResponse>();
+			mockDeleteResponse.status.mockReturnThis();
+			const mockSSETransport = mock<FlushingSSEServerTransport>();
+
+			// Set up SSE transport
+			mcpServerManager.transports[sseSessionId] = mockSSETransport;
+
+			// Call handleDeleteRequest
+			await mcpServerManager.handleDeleteRequest(mockDeleteRequest, mockDeleteResponse);
+
+			// Verify 405 response (DELETE not supported for SSE)
+			expect(mockDeleteResponse.status).toHaveBeenCalledWith(405);
+		});
+	});
 });

packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/__test__/McpTrigger.node.test.ts

@@ -5,7 +5,10 @@ import type { INode, IWebhookFunctions } from 'n8n-workflow';
 
 import * as helpers from '@utils/helpers';
 
-import type { FlushingSSEServerTransport } from '../FlushingTransport';
+import type {
+	FlushingSSEServerTransport,
+	FlushingStreamableHTTPTransport,
+} from '../FlushingTransport';
 import type { McpServerManager } from '../McpServer';
 import { McpTrigger } from '../McpTrigger.node';
 
@@ -137,5 +140,32 @@ describe('McpTrigger Node', () => {
 				mockResponse,
 			);
 		});
+
+		it('should handle DELETE webhook for StreamableHTTP session termination', async () => {
+			// Configure the context for DELETE webhook
+			mockContext.getWebhookName.mockReturnValue('default');
+			const mockDeleteRequest = mock<Request>({
+				method: 'DELETE',
+				headers: { 'mcp-session-id': sessionId },
+				path: '/custom-path',
+			});
+			mockContext.getRequestObject.mockReturnValueOnce(mockDeleteRequest);
+
+			// Mock existing StreamableHTTP transport
+			mockServerManager.getSessionId.mockReturnValue(sessionId);
+			mockServerManager.getTransport.mockReturnValue(mock<FlushingStreamableHTTPTransport>({}));
+
+			// Call the webhook method
+			const result = await mcpTrigger.webhook(mockContext);
+
+			// Verify that handleDeleteRequest was called
+			expect(mockServerManager.handleDeleteRequest).toHaveBeenCalledWith(
+				mockDeleteRequest,
+				mockResponse,
+			);
+
+			// Verify the returned result
+			expect(result).toEqual({ noWebhookResponse: true });
+		});
 	});
 });