feat: Add OpenTelemetry OTLP HTTP receiver

- Add POST /v1/traces endpoint for OTLP JSON trace ingestion
- Convert OTLP spans to internal format and save to PostgreSQL
- Manual JSON parsing (no Go 1.24 dependencies)
- Add Node.js instrumentation example with Express
- Add Python instrumentation example with Flask
- Auto-instrumentation support for both languages

examples/otel-nodejs/app.js

@@ -0,0 +1,160 @@
+// ═══════════════════════════════════════════════════════════
+// 📱 Example Express App with OpenTelemetry
+// ═══════════════════════════════════════════════════════════
+//
+// Run with: npm run trace
+// Or: node --require ./tracing.js app.js
+
+const express = require('express');
+const { trace, SpanStatusCode } = require('@opentelemetry/api');
+
+const app = express();
+const PORT = process.env.PORT || 3000;
+
+// Get a tracer for manual instrumentation
+const tracer = trace.getTracer('example-app');
+
+// Simulated database
+const users = [
+  { id: 1, name: 'Alice', email: 'alice@example.com' },
+  { id: 2, name: 'Bob', email: 'bob@example.com' },
+  { id: 3, name: 'Charlie', email: 'charlie@example.com' },
+];
+
+// Middleware to add request tracing
+app.use((req, res, next) => {
+  const span = trace.getActiveSpan();
+  if (span) {
+    span.setAttribute('http.user_agent', req.get('user-agent') || 'unknown');
+  }
+  next();
+});
+
+// Health check
+app.get('/health', (req, res) => {
+  res.json({ status: 'healthy', service: 'nodejs-example' });
+});
+
+// Get all users (with manual span)
+app.get('/users', async (req, res) => {
+  // Create a custom span for database operation
+  const span = tracer.startSpan('db.query.users');
+  span.setAttribute('db.system', 'memory');
+  span.setAttribute('db.operation', 'SELECT');
+  
+  try {
+    // Simulate database latency
+    await sleep(Math.random() * 100);
+    
+    span.setAttribute('db.row_count', users.length);
+    span.setStatus({ code: SpanStatusCode.OK });
+    
+    res.json({ users });
+  } catch (error) {
+    span.setStatus({
+      code: SpanStatusCode.ERROR,
+      message: error.message,
+    });
+    span.recordException(error);
+    res.status(500).json({ error: error.message });
+  } finally {
+    span.end();
+  }
+});
+
+// Get user by ID
+app.get('/users/:id', async (req, res) => {
+  const userId = parseInt(req.params.id);
+  
+  const span = tracer.startSpan('db.query.user_by_id');
+  span.setAttribute('db.system', 'memory');
+  span.setAttribute('db.operation', 'SELECT');
+  span.setAttribute('user.id', userId);
+  
+  try {
+    await sleep(Math.random() * 50);
+    
+    const user = users.find(u => u.id === userId);
+    
+    if (!user) {
+      span.setStatus({ code: SpanStatusCode.ERROR, message: 'User not found' });
+      res.status(404).json({ error: 'User not found' });
+    } else {
+      span.setStatus({ code: SpanStatusCode.OK });
+      res.json({ user });
+    }
+  } finally {
+    span.end();
+  }
+});
+
+// Create order (simulates complex operation with nested spans)
+app.post('/orders', express.json(), async (req, res) => {
+  const parentSpan = tracer.startSpan('order.create');
+  
+  try {
+    // Step 1: Validate inventory
+    const inventorySpan = tracer.startSpan('inventory.check', {
+      attributes: { 'order.items': req.body.items?.length || 0 },
+    });
+    await sleep(Math.random() * 100);
+    inventorySpan.setStatus({ code: SpanStatusCode.OK });
+    inventorySpan.end();
+    
+    // Step 2: Process payment
+    const paymentSpan = tracer.startSpan('payment.process', {
+      attributes: { 'payment.method': 'credit_card' },
+    });
+    await sleep(Math.random() * 200);
+    paymentSpan.setStatus({ code: SpanStatusCode.OK });
+    paymentSpan.end();
+    
+    // Step 3: Create order record
+    const createSpan = tracer.startSpan('db.insert.order');
+    await sleep(Math.random() * 50);
+    const orderId = Date.now().toString(36);
+    createSpan.setAttribute('order.id', orderId);
+    createSpan.setStatus({ code: SpanStatusCode.OK });
+    createSpan.end();
+    
+    parentSpan.setStatus({ code: SpanStatusCode.OK });
+    res.json({ orderId, status: 'created' });
+    
+  } catch (error) {
+    parentSpan.setStatus({ code: SpanStatusCode.ERROR, message: error.message });
+    parentSpan.recordException(error);
+    res.status(500).json({ error: error.message });
+  } finally {
+    parentSpan.end();
+  }
+});
+
+// Simulate error endpoint (for testing error traces)
+app.get('/error', (req, res) => {
+  const span = trace.getActiveSpan();
+  const error = new Error('Simulated error for testing');
+  
+  if (span) {
+    span.recordException(error);
+    span.setStatus({ code: SpanStatusCode.ERROR, message: error.message });
+  }
+  
+  res.status(500).json({ error: error.message });
+});
+
+// Helper
+function sleep(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+// Start server
+app.listen(PORT, () => {
+  console.log(`🚀 Example app listening on http://localhost:${PORT}`);
+  console.log('');
+  console.log('Try these endpoints:');
+  console.log(`  GET  http://localhost:${PORT}/health`);
+  console.log(`  GET  http://localhost:${PORT}/users`);
+  console.log(`  GET  http://localhost:${PORT}/users/1`);
+  console.log(`  POST http://localhost:${PORT}/orders`);
+  console.log(`  GET  http://localhost:${PORT}/error`);
+});