Add output helpers

[MAILPOET-1891]

lib/Newsletter/Renderer/EscapeHelper.php

@@ -0,0 +1,28 @@
+<?php
+namespace MailPoet\Newsletter\Renderer;
+
+class EscapeHelper {
+  static function escapeHtmlText($string) {
+    return htmlspecialchars((string)$string, ENT_NOQUOTES, 'UTF-8');
+  }
+
+  static function escapeHtmlAttr($string) {
+    return htmlspecialchars((string)$string, ENT_QUOTES, 'UTF-8', true);
+  }
+
+  static function escapeHtmlStyleAttr($string) {
+    return htmlspecialchars((string)$string, ENT_COMPAT, 'UTF-8', true);
+  }
+
+  static function unescapeHtmlStyleAttr($string) {
+    return htmlspecialchars_decode((string)$string, ENT_COMPAT);
+  }
+
+  static function escapeHtmlLinkAttr($string) {
+    $string = self::escapeHtmlAttr($string);
+    if (preg_match('~^javascript:|^data:text|^data:application~i', $string) === 1) {
+      return '';
+    }
+    return $string;
+  }
+}