Middleware #

Middleware works after/before Handler. We can get Request before dispatching or manipulate Response after dispatching.

Definition of Middleware #

Handler - should return Response object. Only one handler will be called.
Middleware - should return nothing, will be proceeded to next middleware with await next()

The user can register middleware using app.use or using app.HTTP_METHOD as well as the handlers. For this feature, it’s easy to specify the path and the method.

// match any method, all routes
app.use('*', logger())

// specify path
app.use('/posts/*', cors())

// specify method and path
app.post('/posts/*', basicAuth())

If the handler returns Response, it will be used for the end-user, and stopping the processing.

app.post('/posts', (c) => c.text('Created!', 201))

In this case, four middleware are processed before dispatching like this:

logger() -> cors() -> basicAuth() -> *handler*

Built-in Middleware #

Hono has built-in middleware.

import { Hono } from 'hono'
import { poweredBy } from 'hono/powered-by'
import { logger } from 'hono/logger'
import { basicAuth } from 'hono/basicAuth'

const app = new Hono()

app.use('*', poweredBy())
app.use('*', logger())

app.use(
  '/auth/*',
  basicAuth({
    username: 'hono',
    password: 'acoolproject',
  })
)

Available built-in middleware is listed on the middleware section.

Custom Middleware #

You can write your own middleware.

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

// Add a custom header
app.use('/message/*', async (c, next) => {
  await next()
  c.header('x-message', 'This is middleware!')
})

app.get('/message/hello', (c) => c.text('Hello Middleware!'))

Third-party Middleware #

Built-in middleware does not depend on external modules, but third-party middleware can depend on third-party libraries. So with them, we may make more complex application.

For example, we are planning to release “graphql-server” middleware and “firebase-auth” middleware.