Adding prometheus middleware (#10)

* feat: adding prometheus middleware

Author: jkyberneees

demos/prometheus.ts

@@ -0,0 +1,279 @@
+import http from '../index'
+import {createPrometheusIntegration} from '../lib/middleware/prometheus'
+
+// Create Prometheus integration with custom options
+const prometheus = createPrometheusIntegration({
+  // Collect default Node.js metrics (memory, CPU, etc.)
+  collectDefaultMetrics: true,
+
+  // Exclude certain paths from metrics
+  excludePaths: ['/health', '/favicon.ico'],
+
+  // Skip metrics for certain HTTP methods
+  skipMethods: ['OPTIONS'],
+
+  // Custom route normalization
+  normalizeRoute: (req) => {
+    const url = new URL(req.url, 'http://localhost')
+    let pathname = url.pathname
+
+    // Custom patterns for this demo
+    pathname = pathname
+      .replace(/\/users\/\d+/, '/users/:id')
+      .replace(/\/products\/[a-zA-Z0-9-]+/, '/products/:slug')
+      .replace(/\/api\/v\d+/, '/api/:version')
+
+    return pathname
+  },
+
+  // Add custom labels to metrics
+  extractLabels: (req, response) => {
+    const labels: Record<string, string> = {}
+
+    // Add user agent category
+    const userAgent = req.headers.get('user-agent') || ''
+    if (userAgent.includes('curl')) {
+      labels.client_type = 'curl'
+    } else if (userAgent.includes('Chrome')) {
+      labels.client_type = 'browser'
+    } else {
+      labels.client_type = 'other'
+    }
+
+    // Add response type
+    const contentType = response?.headers?.get('content-type') || ''
+    if (contentType.includes('json')) {
+      labels.response_type = 'json'
+    } else if (contentType.includes('html')) {
+      labels.response_type = 'html'
+    } else {
+      labels.response_type = 'other'
+    }
+
+    return labels
+  },
+})
+
+// Create custom metrics for business logic
+const {promClient} = prometheus
+
+const orderCounter = new promClient.Counter({
+  name: 'orders_total',
+  help: 'Total number of orders processed',
+  labelNames: ['status', 'payment_method'],
+})
+
+const orderValue = new promClient.Histogram({
+  name: 'order_value_dollars',
+  help: 'Value of orders in dollars',
+  labelNames: ['payment_method'],
+  buckets: [10, 50, 100, 500, 1000, 5000],
+})
+
+const activeUsers = new promClient.Gauge({
+  name: 'active_users',
+  help: 'Number of currently active users',
+})
+
+// Simulate some active users
+let userCount = 0
+setInterval(() => {
+  userCount = Math.floor(Math.random() * 100) + 50
+  activeUsers.set(userCount)
+}, 5000)
+
+// Configure the server
+const {router} = http({})
+
+// Apply Prometheus middleware
+router.use(prometheus.middleware)
+
+// Health check endpoint (excluded from metrics)
+router.get('/health', () => {
+  return new Response(
+    JSON.stringify({
+      status: 'healthy',
+      timestamp: new Date().toISOString(),
+      uptime: process.uptime(),
+    }),
+    {
+      headers: {'Content-Type': 'application/json'},
+    },
+  )
+})
+
+// User endpoints
+router.get('/users/:id', (req) => {
+  const id = req.params?.id
+  return new Response(
+    JSON.stringify({
+      id: parseInt(id),
+      name: `User ${id}`,
+      email: `user${id}@example.com`,
+      created_at: new Date().toISOString(),
+    }),
+    {
+      headers: {'Content-Type': 'application/json'},
+    },
+  )
+})
+
+router.post('/users', async (req) => {
+  const body = await req.json()
+  const user = {
+    id: Math.floor(Math.random() * 1000),
+    name: body.name || 'Anonymous',
+    email: body.email || `user${Date.now()}@example.com`,
+    created_at: new Date().toISOString(),
+  }
+
+  return new Response(JSON.stringify(user), {
+    status: 201,
+    headers: {'Content-Type': 'application/json'},
+  })
+})
+
+// Product endpoints
+router.get('/products/:slug', (req) => {
+  const slug = req.params?.slug
+  return new Response(
+    JSON.stringify({
+      slug,
+      name: slug
+        .split('-')
+        .map((word) => word.charAt(0).toUpperCase() + word.slice(1))
+        .join(' '),
+      price: Math.floor(Math.random() * 500) + 10,
+      in_stock: Math.random() > 0.2,
+    }),
+    {
+      headers: {'Content-Type': 'application/json'},
+    },
+  )
+})
+
+// Order endpoint with custom metrics
+router.post('/orders', async (req) => {
+  try {
+    const body = await req.json()
+    const amount = body.amount || 0
+    const method = body.method || 'unknown'
+
+    // Simulate order processing
+    const success = Math.random() > 0.1 // 90% success rate
+    const status = success ? 'completed' : 'failed'
+
+    // Record custom metrics
+    orderCounter.inc({status, payment_method: method})
+
+    if (success && amount > 0) {
+      orderValue.observe({payment_method: method}, amount)
+    }
+
+    const order = {
+      id: `order_${Date.now()}`,
+      amount,
+      payment_method: method,
+      status,
+      created_at: new Date().toISOString(),
+    }
+
+    return new Response(JSON.stringify(order), {
+      status: success ? 201 : 402,
+      headers: {'Content-Type': 'application/json'},
+    })
+  } catch (error) {
+    return new Response(
+      JSON.stringify({
+        error: 'Invalid JSON body',
+      }),
+      {
+        status: 400,
+        headers: {'Content-Type': 'application/json'},
+      },
+    )
+  }
+})
+
+// Slow endpoint for testing duration metrics
+router.get('/slow', async () => {
+  // Random delay between 1-3 seconds
+  const delay = Math.floor(Math.random() * 2000) + 1000
+  await new Promise((resolve) => setTimeout(resolve, delay))
+
+  return new Response(
+    JSON.stringify({
+      message: `Processed after ${delay}ms`,
+      timestamp: new Date().toISOString(),
+    }),
+    {
+      headers: {'Content-Type': 'application/json'},
+    },
+  )
+})
+
+// Error endpoint for testing error metrics
+router.get('/error', () => {
+  // Randomly throw different types of errors
+  const errorType = Math.floor(Math.random() * 3)
+
+  switch (errorType) {
+    case 0:
+      return new Response('Not Found', {status: 404})
+    case 1:
+      return new Response('Internal Server Error', {status: 500})
+    case 2:
+      throw new Error('Unhandled error for testing')
+    default:
+      return new Response('Bad Request', {status: 400})
+  }
+})
+
+// Versioned API endpoint
+router.get('/api/:version/data', (req) => {
+  const version = req.params?.version
+  return new Response(
+    JSON.stringify({
+      api_version: version,
+      data: {message: 'Hello from versioned API'},
+      timestamp: new Date().toISOString(),
+    }),
+    {
+      headers: {'Content-Type': 'application/json'},
+    },
+  )
+})
+
+// Metrics endpoint - this should be added last
+router.get('/metrics', prometheus.metricsHandler)
+
+// Server startup logic
+const port = process.env.PORT || 3003
+
+console.log('🚀 Starting Prometheus Demo Server')
+console.log('=====================================')
+console.log(`📊 Metrics endpoint: http://localhost:${port}/metrics`)
+console.log(`🏠 Demo page: http://localhost:${port}/`)
+console.log(`� Health check: http://localhost:${port}/health`)
+console.log(`🔧 Port: ${port}`)
+console.log('=====================================')
+console.log('')
+console.log('Try these commands to generate metrics:')
+console.log('curl http://localhost:' + port + '/metrics')
+console.log('curl http://localhost:' + port + '/users/123')
+console.log('curl http://localhost:' + port + '/products/awesome-widget')
+console.log(
+  'curl -X POST http://localhost:' +
+    port +
+    '/orders -H \'Content-Type: application/json\' -d \'{"amount": 99.99, "method": "card"}\'',
+)
+console.log('curl http://localhost:' + port + '/slow')
+console.log('curl http://localhost:' + port + '/error')
+console.log('')
+
+console.log(`✅ Server running at http://localhost:${port}/`)
+
+export default {
+  port,
+  fetch: router.fetch.bind(router),
+}