feat(MCP Server Trigger Node): Support for Streamable HTTP transport in MCP Server (#15833)

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

@@ -0,0 +1,61 @@
+import { SSEServerTransport } from '@modelcontextprotocol/sdk/server/sse.js';
+import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
+import type { StreamableHTTPServerTransportOptions } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
+import type { JSONRPCMessage } from '@modelcontextprotocol/sdk/types.js';
+import type { Response } from 'express';
+import type { IncomingMessage, ServerResponse } from 'http';
+
+export type CompressionResponse = Response & {
+	/**
+	 * `flush()` is defined in the compression middleware.
+	 * This is necessary because the compression middleware sometimes waits
+	 * for a certain amount of data before sending the data to the client
+	 */
+	flush: () => void;
+};
+
+export class FlushingSSEServerTransport extends SSEServerTransport {
+	constructor(
+		_endpoint: string,
+		private response: CompressionResponse,
+	) {
+		super(_endpoint, response);
+	}
+
+	async send(message: JSONRPCMessage): Promise<void> {
+		await super.send(message);
+		this.response.flush();
+	}
+
+	async handleRequest(
+		req: IncomingMessage,
+		resp: ServerResponse,
+		message: IncomingMessage,
+	): Promise<void> {
+		await super.handlePostMessage(req, resp, message);
+		this.response.flush();
+	}
+}
+
+export class FlushingStreamableHTTPTransport extends StreamableHTTPServerTransport {
+	private response: CompressionResponse;
+
+	constructor(options: StreamableHTTPServerTransportOptions, response: CompressionResponse) {
+		super(options);
+		this.response = response;
+	}
+
+	async send(message: JSONRPCMessage): Promise<void> {
+		await super.send(message);
+		this.response.flush();
+	}
+
+	async handleRequest(
+		req: IncomingMessage,
+		resp: ServerResponse,
+		parsedBody?: unknown,
+	): Promise<void> {
+		await super.handleRequest(req, resp, parsedBody);
+		this.response.flush();
+	}
+}