Customisable constants.local.php (#1725)

https://github.com/FreshRSS/FreshRSS/issues/1562
https://github.com/FreshRSS/FreshRSS/issues/1607
https://github.com/FreshRSS/FreshRSS/pull/1656
https://github.com/FreshRSS/FreshRSS/issues/1705
https://github.com/FreshRSS/FreshRSS/pull/1712

.gitignore

@@ -0,0 +1 @@
+constants.local.php

constants.php

@@ -1,35 +1,50 @@
 <?php
+//NB: Do not edit; use ./constants.local.php instead.
+
+//<Not customisable>
 define('FRESHRSS_VERSION', '1.8.1-dev');
 define('FRESHRSS_WEBSITE', 'https://freshrss.org');
 define('FRESHRSS_WIKI', 'https://freshrss.github.io/FreshRSS/');
 
-define('FRESHRSS_USERAGENT', 'FreshRSS/' . FRESHRSS_VERSION . ' (' . PHP_OS . '; ' . FRESHRSS_WEBSITE . ')');
+define('FRESHRSS_PATH', __DIR__);
+define('PUBLIC_PATH', FRESHRSS_PATH . '/p');
+define('PUBLIC_TO_INDEX_PATH', '/i');
+define('INDEX_PATH', PUBLIC_PATH . PUBLIC_TO_INDEX_PATH);
+define('PUBLIC_RELATIVE', '..');
+define('LIB_PATH', FRESHRSS_PATH . '/lib');
+define('APP_PATH', FRESHRSS_PATH . '/app');
+define('EXTENSIONS_PATH', FRESHRSS_PATH . '/extensions');
+//</Not customisable>
+
+function safe_define($name, $value) {
+	if (!defined($name)) {
+		return define($name, $value);
+	}
+}
+
+if (file_exists(__DIR__ . '/constants.local.php')) {
+	//Include custom / local settings:
+	include(__DIR__ . '/constants.local.php');
+}
+
+safe_define('FRESHRSS_USERAGENT', 'FreshRSS/' . FRESHRSS_VERSION . ' (' . PHP_OS . '; ' . FRESHRSS_WEBSITE . ')');
 
 // PHP text output compression http://php.net/ob_gzhandler (better to do it at Web server level)
-define('PHP_COMPRESSION', false);
+safe_define('PHP_COMPRESSION', false);
 
 // Maximum log file size in Bytes, before it will be divided by two
-define('MAX_LOG_SIZE', 1048576);
-
-// Constantes de chemins
-define('FRESHRSS_PATH', dirname(__FILE__));
-
-	define('PUBLIC_PATH', FRESHRSS_PATH . '/p');
-		define('PUBLIC_TO_INDEX_PATH', '/i');
-		define('INDEX_PATH', PUBLIC_PATH . PUBLIC_TO_INDEX_PATH);
-		define('PUBLIC_RELATIVE', '..');
-
-	define('DATA_PATH', FRESHRSS_PATH . '/data');
-		define('UPDATE_FILENAME', DATA_PATH . '/update.php');
-		define('USERS_PATH', DATA_PATH . '/users');
-		define('ADMIN_LOG', USERS_PATH . '/_/log.txt');
-		define('API_LOG', USERS_PATH . '/_/log_api.txt');
-		define('CACHE_PATH', DATA_PATH . '/cache');
-		define('PSHB_LOG', USERS_PATH . '/_/log_pshb.txt');
-		define('PSHB_PATH', DATA_PATH . '/PubSubHubbub');
-
-	define('LIB_PATH', FRESHRSS_PATH . '/lib');
-	define('APP_PATH', FRESHRSS_PATH . '/app');
-	define('EXTENSIONS_PATH', FRESHRSS_PATH . '/extensions');
-
-define('TMP_PATH', sys_get_temp_dir());
+safe_define('MAX_LOG_SIZE', 1048576);
+
+//This directory must be writable
+safe_define('DATA_PATH', FRESHRSS_PATH . '/data');
+
+safe_define('UPDATE_FILENAME', DATA_PATH . '/update.php');
+safe_define('USERS_PATH', DATA_PATH . '/users');
+safe_define('ADMIN_LOG', USERS_PATH . '/_/log.txt');
+safe_define('API_LOG', USERS_PATH . '/_/log_api.txt');
+safe_define('CACHE_PATH', DATA_PATH . '/cache');
+safe_define('PSHB_LOG', USERS_PATH . '/_/log_pshb.txt');
+safe_define('PSHB_PATH', DATA_PATH . '/PubSubHubbub');
+
+//Directory used for feed mutex with *.freshrss.lock files. Must be writable.
+safe_define('TMP_PATH', sys_get_temp_dir());