feat: add streamable HTTP transport support

package.json

@@ -1,6 +1,6 @@
 {
   "name": "fred-mcp-server",
-  "version": "1.0.2",
+  "version": "1.1.0",
   "description": "Federal Reserve Economic Data (FRED) MCP Server - Access all 800,000+ economic time series with search, browse, and data retrieval capabilities",
   "main": "build/index.js",
   "keywords": [
@@ -49,10 +49,12 @@
   "license": "AGPL-3.0",
   "dependencies": {
     "@modelcontextprotocol/sdk": "^1.11.2",
+    "express": "^4.21.2",
     "zod": "^3.24.4"
   },
   "devDependencies": {
     "@jest/globals": "^29.7.0",
+    "@types/express": "^4.17.25",
     "@types/jest": "^29.5.14",
     "@types/node": "^22.15.17",
     "jest": "^29.7.0",

src/http-server.ts

@@ -0,0 +1,64 @@
+import express from 'express';
+import { randomUUID } from 'node:crypto';
+import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
+import { createServer } from './index.js';
+
+const DEFAULT_PORT = 3000;
+const DEFAULT_HOST = '0.0.0.0';
+const ENV_PORT = 'PORT';
+const ENV_HOST = 'HOST';
+
+export interface HttpServerOptions {
+  port?: number;
+  host?: string;
+}
+
+export async function startHttpServer(options: HttpServerOptions = {}) {
+  const port = options.port ?? parseInt(process.env[ENV_PORT] ?? String(DEFAULT_PORT), 10);
+  const host = options.host ?? process.env[ENV_HOST] ?? DEFAULT_HOST;
+
+  const app = express();
+  app.use(express.json());
+
+  const transports = new Map<string, StreamableHTTPServerTransport>();
+
+  app.all('/mcp', async (req, res) => {
+    try {
+      const sessionId = req.headers['mcp-session-id'] as string | undefined;
+
+      if (sessionId && transports.has(sessionId)) {
+        await transports.get(sessionId)!.handleRequest(req, res, req.body);
+      } else if (!sessionId) {
+        const transport = new StreamableHTTPServerTransport({
+          sessionIdGenerator: () => randomUUID(),
+          onsessioninitialized: (id) => transports.set(id, transport)
+        });
+
+        transport.onclose = () => {
+          if (transport.sessionId) transports.delete(transport.sessionId);
+        };
+
+        const server = createServer();
+        await server.connect(transport);
+        await transport.handleRequest(req, res, req.body);
+      } else {
+        res.status(404).json({ error: 'Session not found' });
+      }
+    } catch (error) {
+      console.error('Error in /mcp handler:', error);
+      if (!res.headersSent) {
+        res.status(500).json({ error: 'Internal server error' });
+      }
+    }
+  });
+
+  app.get('/health', (_req, res) => {
+    res.json({ status: 'ok', sessions: transports.size });
+  });
+
+  app.listen(port, host, () => {
+    console.error(`FRED MCP Server: http://${host}:${port}/mcp`);
+  });
+
+  return new Promise<void>(() => {});
+}

src/index.ts

@@ -5,6 +5,7 @@ import { registerFREDTools } from "./fred/tools.js";
 import { readFileSync } from "fs";
 import { fileURLToPath } from "url";
 import { dirname, join } from "path";
+import { startHttpServer } from "./http-server.js";
 
 /**
  * Create and configure a new FRED MCP server
@@ -18,7 +19,7 @@ export function createServer() {
 
   /**
    * Main FRED MCP Server
-   * 
+   *
    * Provides access to Federal Reserve Economic Data through the
    * Model Context Protocol
    */
@@ -35,7 +36,7 @@ export function createServer() {
 }
 
 /**
- * Connect and start the MCP server
+ * Connect and start the MCP server with stdio transport
  */
 export async function startServer(server: McpServer, transport: StdioServerTransport) {
   console.error("FRED MCP Server starting...");
@@ -49,24 +50,63 @@ export async function startServer(server: McpServer, transport: StdioServerTrans
       console.error("Server shutting down...");
       process.exit(0);
     });
-    
+
     return true;
   } catch (error) {
     console.error("Failed to start server:", error);
     return false;
   }
 }
 
-/**
- * Main entry point
- */
+const TRANSPORT_STDIO = 'stdio' as const;
+const TRANSPORT_STREAMABLE_HTTP = 'streamable-http' as const;
+
+const CLI_FLAG_STREAMABLE_HTTP = '--streamable-http';
+const CLI_FLAG_PORT = '--port=';
+const CLI_FLAG_HOST = '--host=';
+
+const ENV_TRANSPORT = 'FRED_MCP_TRANSPORT';
+const ENV_PORT = 'PORT';
+const ENV_HOST = 'HOST';
+
+const DEFAULT_PORT = 3000;
+const DEFAULT_HOST = '0.0.0.0';
+
+type TransportType = typeof TRANSPORT_STDIO | typeof TRANSPORT_STREAMABLE_HTTP;
+
+interface ServerConfig {
+  transport: TransportType;
+  port?: number;
+  host?: string;
+}
+
+function parseConfig(): ServerConfig {
+  const args = process.argv.slice(2);
+
+  const getArgValue = (prefix: string) =>
+    args.find(arg => arg.startsWith(prefix))?.split('=')[1];
+
+  const useStreamableHttp =
+    args.includes(CLI_FLAG_STREAMABLE_HTTP) ||
+    process.env[ENV_TRANSPORT] === TRANSPORT_STREAMABLE_HTTP;
+
+  return {
+    transport: useStreamableHttp ? TRANSPORT_STREAMABLE_HTTP : TRANSPORT_STDIO,
+    port: getArgValue(CLI_FLAG_PORT) ? parseInt(getArgValue(CLI_FLAG_PORT)!, 10) : undefined,
+    host: getArgValue(CLI_FLAG_HOST)
+  };
+}
+
 async function main() {
-  const server = createServer();
-  const transport = new StdioServerTransport();
-
-  const success = await startServer(server, transport);
-  if (!success) {
-    process.exit(1);
+  const config = parseConfig();
+
+  if (config.transport === TRANSPORT_STREAMABLE_HTTP) {
+    await startHttpServer({ port: config.port, host: config.host });
+  } else {
+    const server = createServer();
+    const transport = new StdioServerTransport();
+    const success = await startServer(server, transport);
+    if (!success) process.exit(1);
   }
 }