remove http and https from links

force-protocol-less-url.php

<?php
//code from https://wordpress.org/plugins/cloudflare/
/**
 * remove http and https from links, save in mu-plugins
 */


if (true !== function_exists('cloudflare_buffer_wrapup')) {
	function cloudflare_buffer_wrapup($buffer) {
	    // Check for a Content-Type header. Currently only apply rewriting to "text/html" or undefined
	    $headers = headers_list();
	    $content_type = null;

	    foreach ($headers as $header) {
	        if (strpos(strtolower($header), 'content-type:') === 0) {
	            $pieces = explode(':', strtolower($header));
	            $content_type = trim($pieces[1]);
	            break;
	        }
	    }

	    if (is_null($content_type) || substr($content_type, 0, 9) === 'text/html') {
	        // replace href or src attributes within script, link, base, and img tags with just "//" for protocol
	        $re     = "/(<(script|link|base|img|form)([^>]*)(href|src|action)=[\"'])https?:\\/\\//i";
	        $subst  = "$1//";
	        $return = preg_replace($re, $subst, $buffer);

	        // on regex error, skip overwriting buffer
	        if ($return) {
	            $buffer = $return;
	        }
	    }
	    return $buffer;
	}

	function cloudflare_buffer_init() {
	    // load just the single option, defaulting to on
	    //$cloudflare_protocol_rewrite = load_protocol_rewrite();
	    //if ($cloudflare_protocol_rewrite == 1) {
	        ob_start('cloudflare_buffer_wrapup');
	    //}
	}

	add_action('plugins_loaded', 'cloudflare_buffer_init');
}