Download xls file via REST

rest-download-xls.php

<?php

add_action(
	'rest_api_init',
	static function () {
		$namespace = 'myplugin/v1';
		$route     = '/file';
		$params    = [
			[
				'methods'  => 'GET',
				'callback' => 'my_callback',
			],
		];

		register_rest_route( $namespace, $route, $params );
	}
);

function my_callback( WP_REST_Request $request ) {

	my_download_file( site_url( 'test.xlsx' ) );
}

/**
 * Download file.
 *
 * @param string $url file url.
 */
function my_download_file( string $url ): void {
	if ( ! $url ) {
		return;
	}

	$file_path = realpath( untrailingslashit( ABSPATH ) . wp_make_link_relative( $url ) );

	if ( ! $file_path ) {
		return;
	}

	$file_name = rawurlencode( pathinfo( $file_path, PATHINFO_FILENAME ) );

	$file_extension = rawurlencode( pathinfo( $file_path, PATHINFO_EXTENSION ) );

	$file_size = filesize( $file_path );

	$known_content_types = [
		'html' => 'text/html',
		'htm'  => 'text/html',
		'txt'  => 'text/plain',
		'jpg'  => 'image/jpg',
		'jpeg' => 'image/jpg',
		'png'  => 'image/png',
		'gif'  => 'image/gif',
		'tiff' => 'image/tiff',
		'pdf'  => 'application/pdf',
		'doc'  => 'application/msword',
		'docx' => 'application/msword',
		'xls'  => 'application/vnd.ms-excel',
		'xlsx' => 'application/vnd.ms-excel',
		'ppt'  => 'application/vnd.ms-powerpoint',
		'pptx' => 'application/vnd.ms-powerpoint',
		'php'  => 'text/plain',
		'exe'  => 'application/octet-stream',
		'zip'  => 'application/zip',
	];

	$content_type = 'application/force-download';

	if ( array_key_exists( $file_extension, $known_content_types ) ) {
		$content_type = $known_content_types[ $file_extension ];
	}

	header( 'Expires: 0' );
	header( 'Cache-Control: no-cache, no-store, must-revalidate' );
	header( 'Cache-Control: pre-check=0, post-check=0, max-age=0', false );
	header( 'Pragma: no-cache' );
	header( "Content-type: {$content_type}" );
	header( "Content-Disposition:attachment; filename={$file_name}.{$file_extension}" );
	header( 'Content-Transfer-Encoding: binary' );
	header( "Content-Length: {$file_size}" );

	// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_read_readfile
	readfile( $file_path );
	exit();
}