Hono Middleware Patterns

Overview

Hono provides a powerful middleware system with an "onion" execution model. Middleware processes requests before handlers and responses after handlers, enabling cross-cutting concerns like authentication, logging, and CORS.

Key Features:

• Onion-style execution order
• Type-safe middleware creation with createMiddleware
• 25+ built-in middleware
• Context variable passing between middleware
• Async/await support throughout

When to Use This Skill

Use Hono middleware when:

• Adding authentication/authorization
• Implementing CORS for cross-origin requests
• Adding request logging or timing
• Compressing responses
• Rate limiting API endpoints
• Validating requests before handlers

Middleware Basics

Inline Middleware

import { Hono } from 'hono'

const app = new Hono()

// Simple logging middleware
app.use('*', async (c, next) => {
  console.log(`[${c.req.method}] ${c.req.url}`)
  await next()
})

// Path-specific middleware
app.use('/api/*', async (c, next) => {
  const start = Date.now()
  await next()
  const ms = Date.now() - start
  c.header('X-Response-Time', `${ms}ms`)
})

Execution Order (Onion Model)

app.use(async (c, next) => {
  console.log('1. Before (first in)')
  await next()
  console.log('6. After (first out)')
})

app.use(async (c, next) => {
  console.log('2. Before (second in)')
  await next()
  console.log('5. After (second out)')
})

app.use(async (c, next) => {
  console.log('3. Before (third in)')
  await next()
  console.log('4. After (third out)')
})

app.get('/', (c) => {
  console.log('Handler')
  return c.text('Hello!')
})

// Output:
// 1. Before (first in)
// 2. Before (second in)
// 3. Before (third in)
// Handler
// 4. After (third out)
// 5. After (second out)
// 6. After (first out)

Creating Reusable Middleware

import { createMiddleware } from 'hono/factory'

// Type-safe reusable middleware
const logger = createMiddleware(async (c, next) => {
  console.log(`[${new Date().toISOString()}] ${c.req.method} ${c.req.path}`)
  await next()
})

// Middleware with options
const timing = (headerName = 'X-Response-Time') => {
  return createMiddleware(async (c, next) => {
    const start = Date.now()
    await next()
    c.header(headerName, `${Date.now() - start}ms`)
  })
}

app.use(logger)
app.use(timing('X-Duration'))

Context Variables

Passing Data Between Middleware

import { createMiddleware } from 'hono/factory'

// Define variable types
type Variables = {
  user: { id: string; email: string; role: string }
  requestId: string
}

const app = new Hono<{ Variables: Variables }>()

// Auth middleware sets user
const auth = createMiddleware<{ Variables: Variables }>(async (c, next) => {
  const token = c.req.header('Authorization')?.replace('Bearer ', '')

  if (!token) {
    return c.json({ error: 'Unauthorized' }, 401)
  }

  const user = await verifyToken(token)
  c.set('user', user)  // Type-safe!
  await next()
})

// Request ID middleware
const requestId = createMiddleware<{ Variables: Variables }>(async (c, next) => {
  c.set('requestId', crypto.randomUUID())