[Hapi.js] Extending the request with lifecycle events

Posted 2020-06-17

Instead of using middlware, hapi provides a number of points during the lifecycle of a request that you can hook-in to provide additional functionality, called "extension events". This lesson will give you an introduction to using extension events, and show how they can be used to manipulate the request or response in-flight.

 

const Hapi = require( ‘hapi‘ )
const Boom = require( ‘boom‘ )
const server = new Hapi.Server()
server.connection( { port: 8000 } )

server.ext( ‘onRequest‘, ( request, reply ) => {
    request.setUrl( ‘/‘ )
    request.setMethod( ‘GET‘ )
    // need to call continue, the same as Express‘s next()
    reply.continue()
} )

/**
 * After the request has gone through the router, it needs to be authenticated. OnPreAuth runs before authentication, and onPostAuth runs after.
 */
server.ext( ‘onRequest‘, ( request, reply ) => {
    console.log( ‘onRequest‘ )
    reply.continue()
} )

/**
 * After the request has gone through the router, it needs to be authenticated. OnPreAuth runs before authentication, and onPostAuth runs after.
 */
server.ext( ‘onPreAuth‘, ( request, reply ) => {
    console.log( ‘onPreAuth‘ )
    reply.continue()
} )

server.ext( ‘onPostAuth‘, ( request, reply ) => {
    console.log( ‘onPostAuth‘ )
    reply.continue()
} )

/**
 * Validation is handled next. OnPreHandler runs, then, the route itself.
 */
server.ext( ‘onPreHandler‘, ( request, reply ) => {
    console.log( ‘onPreHandler‘ )
    reply.continue()
} )

/**
 * OnPostHandler runs after the handler.
 */
server.ext( ‘onPostHandler‘, ( request, reply ) => {
    console.log( ‘onPostHandler‘ )
    reply.continue()
} )

/**
 * Then, the response payload is validated on pre-response runs, and the response is sent to the client.
 */
server.ext( ‘onPreResponse‘, ( request, reply ) => {
    console.log( ‘onPreResponse‘ )
    reply.continue()
} )

server.route( {
    method: ‘GET‘,
    path: ‘/‘,
    handler: function ( request, reply ) {
        console.log( ‘handler‘ )
        reply( ‘hello world‘ )
    }
} )

server.start( () => {
} )

 

What are these extensions good for? Each extension can be used to manipulate the request or response at any point in the lifecycle. For example, in onRequest, I can force all requests to be interpreted as GETs to the route path.

To do so, I‘ll use request.seturl, pass in the string/, and pass the string GET to request.setmethod. Now, when I make a post request to /foo, it still hits my defined route.