+
+/**
+ * Checks if a string represents a valid date
+ *
+ * @param string a string-formatted date
+ * @param format the expected DateTime format of the string
+ * @return whether the string is a valid date
+ * @see http://php.net/manual/en/class.datetime.php
+ * @see http://php.net/manual/en/datetime.createfromformat.php
+ */
+function checkDateFormat($format, $string)
+{
+ $date = DateTime::createFromFormat($format, $string);
+ return $date && $date->format($string) == $string;
+}
+
+/**
+ * Generate a header location from HTTP_REFERER.
+ * Make sure the referer is Shaarli itself and prevent redirection loop.
+ *
+ * @param string $referer - HTTP_REFERER.
+ * @param string $host - Server HOST.
+ * @param array $loopTerms - Contains list of term to prevent redirection loop.
+ *
+ * @return string $referer - final referer.
+ */
+function generateLocation($referer, $host, $loopTerms = array())
+{
+ $final_referer = '?';
+
+ // No referer if it contains any value in $loopCriteria.
+ foreach ($loopTerms as $value) {
+ if (strpos($referer, $value) !== false) {
+ return $final_referer;
+ }
+ }
+
+ // Remove port from HTTP_HOST
+ if ($pos = strpos($host, ':')) {
+ $host = substr($host, 0, $pos);
+ }
+
+ if (!empty($referer) && strpos(parse_url($referer, PHP_URL_HOST), $host) !== false) {
+ $final_referer = $referer;
+ }
+
+ return $final_referer;
+}
+
+/**
+ * Checks the PHP version to ensure Shaarli can run
+ *
+ * @param string $minVersion minimum PHP required version
+ * @param string $curVersion current PHP version (use PHP_VERSION)
+ *
+ * @throws Exception the PHP version is not supported
+ */
+function checkPHPVersion($minVersion, $curVersion)
+{
+ if (version_compare($curVersion, $minVersion) < 0) {
+ throw new Exception(
+ 'Your PHP version is obsolete!'
+ .' Shaarli requires at least PHP '.$minVersion.', and thus cannot run.'
+ .' Your PHP version has known security vulnerabilities and should be'
+ .' updated as soon as possible.'
+ );
+ }
+}
+
+/**
+ * Validate session ID to prevent Full Path Disclosure.
+ * See #298.
+ *
+ * @param string $sessionId Session ID
+ *
+ * @return true if valid, false otherwise.
+ */
+function is_session_id_valid($sessionId)
+{
+ if (empty($sessionId)) {
+ return false;
+ }
+
+ if (!$sessionId) {
+ return false;
+ }
+
+ if (!preg_match('/^[a-z0-9]{2,32}$/', $sessionId)) {
+ return false;
+ }
+
+ return true;
+}