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Version: v5.3.x

Middleware

Middleware​

Starting with Fastify v3.0.0, middleware is not supported out of the box and requires an external plugin such as @fastify/express or @fastify/middie.

An example of registering the @fastify/express plugin to use Express middleware:

await fastify.register(require('@fastify/express'))
fastify.use(require('cors')())
fastify.use(require('dns-prefetch-control')())
fastify.use(require('frameguard')())
fastify.use(require('hsts')())
fastify.use(require('ienoopen')())
fastify.use(require('x-xss-protection')())

@fastify/middie can also be used, which provides support for simple Express-style middleware with improved performance:

await fastify.register(require('@fastify/middie'))
fastify.use(require('cors')())

Middleware can be encapsulated, allowing control over where it runs using register as explained in the plugins guide.

Fastify middleware does not expose the send method or other methods specific to the Fastify Reply instance. This is because Fastify wraps the incoming req and res Node instances using the Request and Reply objects internally, but this is done after the middleware phase. To create middleware, use the Node req and res instances. Alternatively, use the preHandler hook that already has the Fastify Request and Reply instances. For more information, see Hooks.

Restrict middleware execution to certain paths​

To run middleware under certain paths, pass the path as the first parameter to use.

🛈 Note: This does not support routes with parameters (e.g. /user/:id/comments) and wildcards are not supported in multiple paths.

const path = require('node:path')
const serveStatic = require('serve-static')

// Single path
fastify.use('/css', serveStatic(path.join(__dirname, '/assets')))

// Wildcard path
fastify.use('/css/(.*)', serveStatic(path.join(__dirname, '/assets')))

// Multiple paths
fastify.use(['/css', '/js'], serveStatic(path.join(__dirname, '/assets')))

Alternatives​

Fastify offers alternatives to commonly used middleware, such as @fastify/helmet for helmet, @fastify/cors for cors, and @fastify/static for serve-static.