Boilerplate code for our web performance modifications to the page.
// set the site we are modifying | |
const site = 'www.example.com'; | |
// do this on a fetch | |
addEventListener('fetch', event => { | |
const request = event.request | |
event.respondWith(handleRequest(request)) | |
}); | |
async function handleRequest(request) { | |
// store the URL | |
const url = new URL(request.url); | |
// disallow crawlers (write a robots.txt file) | |
if(url.pathname === "/robots.txt") { | |
return new Response('User-agent: *\nDisallow: /', {status: 200}); | |
} | |
// when overrideHost is used in a WPT script, WPT sets x-host to original host i.e. site we want to proxy | |
// store the value of x-host | |
const xhost = request.headers.get('x-host'); | |
// If the `x-host` header is missing, abort and tell us | |
if(!xhost) { | |
return new Response('x-host header missing', {status: 403}); | |
} | |
// set our hostname to that listed in the x-host header | |
url.hostname = xhost; | |
// look for header that allows us to bypass the transform entirely | |
const bypassTransform = request.headers.get('x-bypass-transform'); | |
// get the accept header to allow us to examine the type of request it is | |
const acceptHeader = request.headers.get('accept'); | |
// check that the x-host header matches what is contained in the site | |
// make sure we aren't wanting to bypass the transformations | |
if(xhost === site && (!bypassTransform || (bypassTransform && bypassTransform.indexOf('true') === -1))){ | |
// check for an accept header and what it contains | |
if(acceptHeader && acceptHeader.indexOf('text/html') >= 0){ | |
// store this particular HTML response for modification | |
let oldResponse = await fetch(url.toString(), request) | |
// create a new response | |
let newResponse = new HTMLRewriter() | |
/** | |
* Our modifications to the HTML go in here using the HTMLRewriter API | |
* https://developers.cloudflare.com/workers/runtime-apis/html-rewriter | |
*/ | |
.transform(oldResponse) | |
// return the modified page | |
return newResponse | |
} | |
} | |
// otherwise just proxy the request unmodified | |
return fetch(url.toString(), request); | |
} |
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