@tailchi/express

Express middleware for tailchi. Traces incoming HTTP requests and handles frontend event flush.

Installation

npm install @tailchi/core @tailchi/express

Usage

import express from 'express';
import { houndMiddleware } from '@tailchi/express';

const app = express();

// Add middleware (handles tracing + frontend event flush)
app.use(houndMiddleware());

app.get('/api/hello', (req, res) => {
  res.json({ message: 'Hello' });
});

app.listen(4000);

What It Does

1. Extracts or creates flow ID from incoming requests
2. Emits events: http.received (start) and http.responded (end)
3. Propagates flow ID via response header
4. Handles /__hound/events endpoint for frontend event flush

Events Emitted

• http.received - Request received (with method, path)
• http.responded - Response sent (with status, duration)

Frontend Integration

The middleware automatically handles POST requests to /__hound/events, allowing the frontend to flush events through the backend:

// Frontend config
configureHounddog({
  service: 'web',
  sink: {
    kind: 'http',
    endpoint: 'http://localhost:4000/__hound/events',
  },
});

Example Output

│ 📥 in.http.received GET path=/api/users +0ms
│ 📤 out.http.responded 200 (15ms) +15ms