mcp-hub-004: Sample MCP backend with echo tool

sample-mcp/index.js

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+'use strict';
+
+const WebSocket = require('ws');
+
+const HUB_URL = 'wss://mcp.arik.work/ws/register';
+const HUB_URL_FALLBACK = 'ws://mcp.arik.work/ws/register';
+const SERVICE_ID = 'sample-mcp';
+const SECRET = 'dev-secret';
+
+let reconnectDelay = 1000;
+let ws = null;
+let useTLS = true;
+
+function getHubUrl() {
+  return useTLS ? HUB_URL : HUB_URL_FALLBACK;
+}
+
+function connect() {
+  const url = getHubUrl();
+  console.log(`[sample-mcp] Connecting to hub at ${url}`);
+  ws = new WebSocket(url);
+
+  ws.on('open', () => {
+    reconnectDelay = 1000;
+    console.log('[sample-mcp] Connected to hub');
+    const registerMsg = { type: 'register', serviceId: SERVICE_ID, secret: SECRET };
+    ws.send(JSON.stringify(registerMsg));
+    console.log(`[sample-mcp] Sent register: serviceId=${SERVICE_ID}`);
+  });
+
+  ws.on('message', (data) => {
+    let envelope;
+    try {
+      envelope = JSON.parse(data);
+    } catch (err) {
+      console.error('[sample-mcp] Failed to parse message:', err.message);
+      return;
+    }
+
+    if (envelope.type !== 'mcp-request') {
+      console.log(`[sample-mcp] Ignoring message type: ${envelope.type}`);
+      return;
+    }
+
+    const { requestId, clientSessionId, payload } = envelope;
+    console.log(`[sample-mcp] Request received: requestId=${requestId} method=${payload && payload.method}`);
+
+    const method = payload && payload.method;
+
+    // Notifications have no id and need no response
+    if (method === 'notifications/initialized') {
+      console.log('[sample-mcp] Got notifications/initialized, no response needed');
+      return;
+    }
+
+    let result;
+    switch (method) {
+      case 'initialize':
+        result = {
+          protocolVersion: '2024-11-05',
+          capabilities: { tools: {} },
+          serverInfo: { name: 'sample-mcp', version: '1.0.0' },
+        };
+        break;
+
+      case 'tools/list':
+        result = {
+          tools: [
+            {
+              name: 'echo',
+              description: 'Echoes back the input',
+              inputSchema: {
+                type: 'object',
+                properties: { message: { type: 'string' } },
+                required: ['message'],
+              },
+            },
+          ],
+        };
+        break;
+
+      case 'tools/call': {
+        const toolName = payload.params && payload.params.name;
+        const args = (payload.params && payload.params.arguments) || {};
+        if (toolName === 'echo') {
+          result = {
+            content: [{ type: 'text', text: `Echo: ${args.message}` }],
+          };
+        } else {
+          const errorResponse = {
+            jsonrpc: '2.0',
+            id: payload.id,
+            error: { code: -32601, message: `Unknown tool: ${toolName}` },
+          };
+          sendResponse(requestId, clientSessionId, errorResponse);
+          return;
+        }
+        break;
+      }
+
+      default:
+        console.warn(`[sample-mcp] Unknown method: ${method}`);
+        const errorResponse = {
+          jsonrpc: '2.0',
+          id: payload.id,
+          error: { code: -32601, message: `Method not found: ${method}` },
+        };
+        sendResponse(requestId, clientSessionId, errorResponse);
+        return;
+    }
+
+    const jsonrpcResponse = { jsonrpc: '2.0', id: payload.id, result };
+    sendResponse(requestId, clientSessionId, jsonrpcResponse);
+  });
+
+  ws.on('close', (code, reason) => {
+    console.log(`[sample-mcp] Disconnected (code=${code} reason=${reason}), reconnecting in ${reconnectDelay}ms`);
+    scheduleReconnect();
+  });
+
+  ws.on('error', (err) => {
+    console.error(`[sample-mcp] WebSocket error: ${err.message}`);
+    if (useTLS && err.message && (err.message.includes('ECONNREFUSED') || err.message.includes('certificate') || err.message.includes('connect'))) {
+      console.log('[sample-mcp] TLS connection failed, will try ws:// on next attempt');
+      useTLS = false;
+    }
+  });
+}
+
+function sendResponse(requestId, clientSessionId, jsonrpcPayload) {
+  if (!ws || ws.readyState !== WebSocket.OPEN) {
+    console.error('[sample-mcp] Cannot send response: not connected');
+    return;
+  }
+  const envelope = {
+    type: 'mcp-response',
+    requestId,
+    clientSessionId,
+    payload: jsonrpcPayload,
+  };
+  ws.send(JSON.stringify(envelope));
+  console.log(`[sample-mcp] Response sent: requestId=${requestId} method=${jsonrpcPayload.result ? 'ok' : 'error'}`);
+}
+
+function scheduleReconnect() {
+  setTimeout(() => {
+    connect();
+    reconnectDelay = Math.min(reconnectDelay * 2, 30000);
+  }, reconnectDelay);
+}
+
+connect();

sample-mcp/package-lock.json

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+{
+  "name": "sample-mcp",
+  "version": "1.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "sample-mcp",
+      "version": "1.0.0",
+      "dependencies": {
+        "ws": "^8.19.0"
+      }
+    },
+    "node_modules/ws": {
+      "version": "8.19.0",
+      "resolved": "https://registry.npmjs.org/ws/-/ws-8.19.0.tgz",
+      "integrity": "sha512-blAT2mjOEIi0ZzruJfIhb3nps74PRWTCz1IjglWEEpQl5XS/UNama6u2/rjFkDDouqr4L67ry+1aGIALViWjDg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=10.0.0"
+      },
+      "peerDependencies": {
+        "bufferutil": "^4.0.1",
+        "utf-8-validate": ">=5.0.2"
+      },
+      "peerDependenciesMeta": {
+        "bufferutil": {
+          "optional": true
+        },
+        "utf-8-validate": {
+          "optional": true
+        }
+      }
+    }
+  }
+}

sample-mcp/package.json

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+{
+  "name": "sample-mcp",
+  "version": "1.0.0",
+  "description": "Sample MCP backend for testing hub relay",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js"
+  },
+  "dependencies": {
+    "ws": "^8.19.0"
+  }
+}