backfill missing wordpress uploads from a live website to a development copy

mu-plugin-backfill-missing-uploads.php

<?php
// Backfill missing uploads

// build your dev copy using plugins, theme and database
// don't download all uploads
// access an image on it, for example /wp-content/uploads/2021/10/some-image.png
// (of course, just loading a page with images on it will do)
// you will get 404s on all images
// place this file in mu-plugins folder
// try to access the url/page again
// this will download all missing images from the configured remote
// and redirect the image urls to load and show them

add_action('pre_handle_404', function() {
	$backfill_remote_base = 'https://YOUR-SOURCE-WEBSITE-DOMAIN-HERE.com'; // <------------- this is the source domain

	$path = wp_upload_dir()['basedir'];
	$url = wp_upload_dir()['baseurl'];
	$rel_url = parse_url($url, PHP_URL_PATH);
	$remote_url = trim($backfill_remote_base, '/') . $rel_url;
	
	if ( 0 === strpos($_SERVER['REQUEST_URI'], $rel_url) ) { // only handle uploads folder
		$_SERVER['REQUEST_URI'] = rtrim($_SERVER['REQUEST_URI'], '/'); // remove the WordPress-added trailing slash
		$file = str_replace($rel_url, $path, $_SERVER['REQUEST_URI']);
		$dirs = str_replace($rel_url, '', dirname($_SERVER['REQUEST_URI']));
		if (!is_file($file)) {
			// create directories, if not exist
			$dirs = explode('/', trim($dirs, './'));
			$make_dir = $path;

			foreach ($dirs as $dir) {
				$make_dir = $make_dir .'/'. $dir;
				if (!is_dir($make_dir)) {
					mkdir($make_dir);
				}
			}

			$local_full_url = remove_query_arg('');
			$remote_full_url = trim($backfill_remote_base, '/') . $local_full_url;

			$result = wp_remote_get( $remote_full_url, ['sslverify' => false ] ); // my local install has SSL issues
			$file_data = wp_remote_retrieve_body( $result );
			file_put_contents($make_dir .'/'. basename($file), $file_data ); 
			$local_full_url = add_query_arg('_', microtime(true), $local_full_url);
			wp_redirect($local_full_url, 307, basename(__FILE__));
			exit;
		}
	}
});