Added related function for url sanitization

src/functions.php

@@ -0,0 +1,157 @@
+<?php
+
+/**
+ * Deep replace of strings in an array or string.
+ *
+ * @since 0.0.2
+ *
+ * @param string $subject
+ * @param string $search
+ *
+ * @return string The processed string.
+ */
+function _deep_replace($subject, $search)
+{
+    $subject = (string) $subject;
+
+    $count = 1;
+    while ($count) {
+        $subject = str_replace($search, '', $subject, $count);
+    }
+
+    return $subject;
+}
+
+/**
+ * A wrapper for PHP's parse_url() function that handles consistency in the return
+ * values across PHP versions.
+ *
+ * PHP 5.4.7 expanded parse_url()'s ability to handle non-absolute url's, including
+ * schemeless and relative url's with :// in the path. This function works around
+ * those limitations providing a standard output on PHP 5.2~5.4+.
+ *
+ * Secondly, across various PHP versions, schemeless URLs starting containing a ":"
+ * in the query are being handled inconsistently. This function works around those
+ * differences as well.
+ *
+ * @since 4.4.0
+ * @since 4.7.0 The `$component` parameter was added for parity with PHP's `parse_url()`.
+ *
+ * @link https://www.php.net/manual/en/function.parse-url.php
+ *
+ * @param string $url       The URL to parse.
+ * @param int    $component The specific component to retrieve. Use one of the PHP
+ *                          predefined constants to specify which one.
+ *                          Defaults to -1 (= return all parts as an array).
+ * @return mixed False on parse failure; Array of URL components on success;
+ *               When a specific component has been requested: null if the component
+ *               doesn't exist in the given URL; a string or - in the case of
+ *               PHP_URL_PORT - integer when it does. See parse_url()'s return values.
+ */
+function parse_url_string($url, $component = -1)
+{
+    $to_unset = array();
+    $url      = (string) $url;
+
+    if ('//' === substr($url, 0, 2)) {
+        $to_unset[] = 'scheme';
+        $url        = 'placeholder:' . $url;
+    } elseif ('/' === substr($url, 0, 1)) {
+        $to_unset[] = 'scheme';
+        $to_unset[] = 'host';
+        $url        = 'placeholder://placeholder' . $url;
+    }
+
+    $parts = parse_url($url);
+
+    if (false === $parts) {
+        // Parsing failure.
+        return $parts;
+    }
+
+    // Remove the placeholder values.
+    foreach ($to_unset as $key) {
+        unset($parts[$key]);
+    }
+
+    return _get_component_from_parsed_url($parts, $component);
+}
+
+/**
+ * Retrieve a specific component from a parsed URL array.
+ *
+ * @internal
+ *
+ * @since 0.0.2
+ * @access private
+ *
+ * @link https://www.php.net/manual/en/function.parse-url.php
+ *
+ * @param array|false $url_parts The parsed URL. Can be false if the URL failed to parse.
+ * @param int         $component The specific component to retrieve. Use one of the PHP
+ *                               predefined constants to specify which one.
+ *                               Defaults to -1 (= return all parts as an array).
+ * @return mixed False on parse failure; Array of URL components on success;
+ *               When a specific component has been requested: null if the component
+ *               doesn't exist in the given URL; a string or - in the case of
+ *               PHP_URL_PORT - integer when it does. See parse_url()'s return values.
+ */
+function _get_component_from_parsed_url($url_parts, $component = -1)
+{
+    if (-1 === $component) {
+        return $url_parts;
+    }
+
+    $key = _translate_php_url_constant_to_key($component);
+
+    if (false !== $key && is_array($url_parts) && isset($url_parts[$key])) {
+        return $url_parts[$key];
+    } else {
+        return null;
+    }
+}
+
+/**
+ * Translate a PHP_URL_* constant to the named array keys PHP uses.
+ *
+ * @internal
+ *
+ * @since 0.0.2
+ * @access private
+ *
+ * @link https://www.php.net/manual/en/url.constants.php
+ *
+ * @param int $constant PHP_URL_* constant.
+ * @return string|false The named key or false.
+ */
+function _translate_php_url_constant_to_key($constant)
+{
+    $translation = array(
+        PHP_URL_SCHEME   => 'scheme',
+        PHP_URL_HOST     => 'host',
+        PHP_URL_PORT     => 'port',
+        PHP_URL_USER     => 'user',
+        PHP_URL_PASS     => 'pass',
+        PHP_URL_PATH     => 'path',
+        PHP_URL_QUERY    => 'query',
+        PHP_URL_FRAGMENT => 'fragment',
+    );
+
+    if (isset($translation[$constant])) {
+        return $translation[$constant];
+    } else {
+        return false;
+    }
+}
+
+/**
+ * Get allowed protocols for URLs.
+ *
+ * @since 0.0.2
+ *
+ * @return array Array of allowed protocols.
+ */
+function get_allowed_protocols()
+{
+    return array('http', 'https', 'ftp', 'ftps', 'mailto', 'news', 'irc', 'irc6', 'ircs', 'gopher', 'nntp', 'feed', 'telnet', 'mms', 'rtsp', 'sms', 'svn', 'tel', 'fax', 'xmpp', 'webcal', 'urn');
+}