svg-utils.php

<?php

function iti_get_svg_markup( $svg_id = 0 ) {
	// get the file name of the svg
	$svg_id = absint( $svg_id );
	$svg_file = get_post_meta( $svg_id, '_wp_attached_file', true );

	// locate the file on disk
	$upload_dir = wp_upload_dir();
	$upload_basedir = trailingslashit( $upload_dir['basedir'] );

	$svg_markup = iti_get_svg_content( $upload_basedir . $svg_file );

	return $svg_markup;
}

function iti_get_svg_content( $svg_file = '' ) {

	// prep the filesystem
	global $wp_filesystem;
	include_once ABSPATH . 'wp-admin/includes/file.php';
	WP_Filesystem();

	// make sure at least the extension is proper
	if ( '.svg' !== strtolower( substr( $svg_file, -4 ) ) ) {
		return '';
	}

	if ( ! file_exists( $svg_file ) ) {
		return '';
	}

	// retrieve the markup
	$svg_markup = $wp_filesystem->get_contents( $svg_file );

	// filter the markup
	$allowed = array(
		'svg' => array(
			'width' => array(),
			'height' => array(),
			'viewbox' => array(),
			'version' => array(),
			'xmlns' => array(),
			'xmlns:xlink' => array(),
		),
		'g' => array(
			'stroke' => array(),
			'stroke-width' => array(),
			// 'fill' => array(),
			'fill-rule' => array(),
		),
		'path' => array(
			'd' => array(),
			'id' => array(),
		),
	);

	return wp_kses( $svg_markup, $allowed );
}