copy-assets.js

const fs = require('fs').promises;
const path = require('path');
const staticSrcPath = path.join(__dirname, '.next/static');
const staticDestPath = path.join(__dirname, '.next/standalone/.next/static');
const publicSrcPath = path.join(__dirname, 'public');
const publicDestPath = path.join(__dirname, '.next/standalone/public');

function copyAssets(src, dest, destRoot = dest) {
    return fs.mkdir(dest, { recursive: true })
        .then(() => fs.readdir(src, { withFileTypes: true }))
        .then(items => {
            const promises = items.map(item => {
                const srcPath = path.join(src, item.name);
                const destPath = path.join(dest, item.name);

                // Resolve the real absolute paths to prevent traversal
                const resolvedDest = path.resolve(destPath);
                const resolvedRoot = path.resolve(destRoot);

                if (!resolvedDest.startsWith(resolvedRoot + path.sep) &&
                    resolvedDest !== resolvedRoot) {
                    throw new Error(
                        `Path traversal detected: "${item.name}" resolves outside destination root`
                    );
                }

                if (item.isDirectory()) {
                    return copyAssets(srcPath, destPath, destRoot);
                } else {
                    return fs.copyFile(srcPath, destPath);
                }
            });
            return Promise.all(promises);
        })
        .catch(err => {
            console.error(`Error: ${err}`);
            throw err;
        });
}

const greenTick = `\x1b[32m\u2713\x1b[0m`;
const redCross =  `\x1b[31m\u274C\x1b[0m`;

copyAssets(staticSrcPath, staticDestPath)
    .then(() => copyAssets(publicSrcPath, publicDestPath))
    .then(() => console.log(`${greenTick} Assets copied successfully`))
    .catch(err => console.error(`${redCross} Failed to copy assets: ${err}`));