create-cloudflare
Version:
A CLI for creating and deploying new applications to Cloudflare.
42 lines (35 loc) • 1.95 kB
text/typescript
const ORIGIN_URL = 'https://example.com';
const EXPERIMENTS = [
{ name: 'big-button', threshold: 0.5 }, // enable the Big Button experiment for 50% of users
{ name: 'new-brand', threshold: 0.1 }, // enable the New Brand experiment for 10% of users
{ name: 'new-layout', threshold: 0.02 }, // enable the New Layout experiment for 2% of users
];
export default {
async fetch(request, env, ctx): Promise<Response> {
const fingerprint = [request.headers.get('cf-connecting-ip'), request.cf?.postalCode]; // add any values you want considered as a fingerprint
const activeExperiments = await getActiveExperiments(fingerprint, EXPERIMENTS);
// add a data-experiments attribute to the <body> tag
// which can be styled in CSS with a wildcard selector like [data-experiments*="big-button"]
const rewriter = new HTMLRewriter().on('body', {
element(element: Element) {
element.setAttribute('data-experiments', activeExperiments.join(' '));
},
});
const res = await fetch(ORIGIN_URL, request);
return rewriter.transform(res);
},
} satisfies ExportedHandler<Env>;
// Get active experiments by hashing a fingerprint
async function getActiveExperiments(fingerprint: unknown, experiments: Array<{ name: string; threshold: number }>) {
const fingerprintHash: Uint8Array = await hash('SHA-1', JSON.stringify(fingerprint));
const MAX_UINT8 = 255;
const activeExperiments = experiments.filter((exp, i) => fingerprintHash[i] <= exp.threshold * MAX_UINT8);
return activeExperiments.map((exp) => exp.name);
}
// Hash a string using the Web Crypto API
async function hash(algorithm: 'SHA-1' | 'SHA-256' | 'SHA-512', message: string): Promise<Uint8Array> {
const msgUint8 = new TextEncoder().encode(message); // encode as (utf-8) Uint8Array
const hashBuffer = await crypto.subtle.digest(algorithm, msgUint8); // hash the message
const hashArray = new Uint8Array(hashBuffer); // convert buffer to byte array
return hashArray;
}