Fix issue 618 by returning the input unaltered in case PCRE still fails

to evaluate it with the expanded backtrack limit.

src/IDF/Template.php

@@ -0,0 +1,51 @@
+<?php
+/* -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+# ***** BEGIN LICENSE BLOCK *****
+# This file is part of InDefero, an open source project management application.
+# Copyright (C) 2011 Céondo Ltd and contributors.
+#
+# InDefero is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# InDefero is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#
+# ***** END LICENSE BLOCK ***** */
+
+/**
+ * PHP sets the backtrack limit quite low, so some (harder to analyze) regexes may fail
+ * unexpectedly on large inputs or weird cornercases (see issue 618). Unfortunately this
+ * fix does not always work and the execution time gets bigger the bigger we set the limit,
+ * so in case PCRE fails to analyze the input string and preg_replace(_callback) returns NULL,
+ * we at least return the input string unaltered.
+ *
+ * @param $pattern  The pattern
+ * @param $mixed    Callback or replacement string
+ * @param $input    The input
+ * @return The output
+ */
+function IDF_Template_safePregReplace($pattern, $mixed, $input)
+{
+    $pcre_backtrack_limit = ini_get('pcre.backtrack_limit');
+    ini_set('pcre.backtrack_limit', 10000000);
+   
+    if (is_string($mixed) && !function_exists($mixed))
+        $output = preg_replace($pattern, $mixed, $input);
+    else
+        $output = preg_replace_callback($pattern, $mixed, $input);
+
+    if ($output === null)
+        $output = $input;
+
+    ini_set('pcre.backtrack_limit', $pcre_backtrack_limit);
+    return $output;
+}