For help with understanding when middleware is executed, take a look at the lifecycle page.
Fastify middleware don't support the full syntax
middleware(err, req, res, next), because error handling is done inside Fastify. Furthermore, methods added by Express and Restify to the enhanced versions of
res are not supported in Fastify middlewares.
Also, if you are using middleware that bundles different, smaller middleware, such as helmet, we recommend using the single modules for better performance.
fastify.use(require('cors')()) fastify.use(require('dns-prefetch-control')()) fastify.use(require('frameguard')()) fastify.use(require('hide-powered-by')()) fastify.use(require('hsts')()) fastify.use(require('ienoopen')()) fastify.use(require('x-xss-protection')())
const fastify = require('fastify')() const helmet = require('fastify-helmet') fastify.register(helmet)
Remember that middleware can be encapsulated, this means that you can decide where your middleware should run by using
register as explained in the plugins guide.
Fastify middleware also do not expose the
send method or other methods specific to the Fastify Reply instance. This is because Fastify wraps the incoming
res Node instances using the Request and Reply objects internally, but this is done after the middleware phase. If you need to create middleware, you have to use the Node
res instances. Otherwise, you can use the
preHandler hook which already has the Request and Reply Fastify instances. For more information, see Hooks.
Restrict middleware execution to a certain path(s)
If you need to run a middleware only under certain path(s), just pass the path as first parameter to
use and you are done!
Note that this does not support routes with parameters, (eg:
/user/:id/comments) and wildcards are not supported in multiple paths.
const path = require('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')))
Express middleware compatibility
Express modifies the prototype of the node core Request and Response objects heavily so Fastify cannot guarantee full middleware compatibility. Express specific functionality such as
express.Router() instances will not work with Fastify. For example, cors is compatible while passport is not.