unleash.unleash/src/lib/util/load-index-html.ts

import fs from 'fs';
import { IUnleashConfig } from '../server-impl';
import { rewriteHTML } from './rewriteHTML';
import path from 'path';
import fetch from 'make-fetch-happen';

export async function loadIndexHTML(
    config: IUnleashConfig,
    publicFolder: string,
): Promise<string> {
    const { cdnPrefix, baseUriPath = '' } = config.server;
    const uiFlags = JSON.stringify(config.ui.flags);

    let indexHTML: string;
    if (cdnPrefix) {
        const res = await fetch(`${cdnPrefix}/index.html`);
        indexHTML = await res.text();
    } else {
        indexHTML = fs
            .readFileSync(path.join(publicFolder, 'index.html'))
            .toString();
    }

    return rewriteHTML(indexHTML, baseUriPath, cdnPrefix, uiFlags);
}