Add optional timezoneOffset config for appenders

Example:
    log4js.configure({
        appenders: [{type: 'console', timezoneOffset: -540}],
        replaceConsole: true
    });

The expected value is the equivalent of (new Date).getTimezoneOffset()
In this example, -540 is the value for JST.
This allows machines members of world-wide-spread cluster to all report
log time-stamps using the same timezone (or adapt the timezone to a
local different from the system)

lib/appenders/console.js

@@ -2,10 +2,10 @@
 var layouts = require('../layouts')
 , consoleLog = console.log.bind(console);
 
-function consoleAppender (layout) {
+function consoleAppender (layout, timezoneOffset) {
   layout = layout || layouts.colouredLayout;
   return function(loggingEvent) {
-    consoleLog(layout(loggingEvent));
+    consoleLog(layout(loggingEvent, timezoneOffset));
   };
 }
 
@@ -14,7 +14,7 @@ function configure(config) {
   if (config.layout) {
     layout = layouts.layout(config.layout.type, config.layout);
   }
-  return consoleAppender(layout);
+  return consoleAppender(layout, config.timezoneOffset);
 }
 
 exports.appender = consoleAppender;

lib/appenders/dateFile.js

@@ -20,8 +20,9 @@ process.on('exit', function() {
  * @pattern the format that will be added to the end of filename when rolling,
  *          also used to check when to roll files - defaults to '.yyyy-MM-dd'
  * @layout layout function for log messages - defaults to basicLayout
+ * @timezoneOffset optional timezone offset in minutes - defaults to system local
  */
-function appender(filename, pattern, alwaysIncludePattern, layout) {
+function appender(filename, pattern, alwaysIncludePattern, layout, timezoneOffset) {
   layout = layout || layouts.basicLayout;
 
   var logFile = new streams.DateRollingFileStream(
@@ -32,7 +33,7 @@ function appender(filename, pattern, alwaysIncludePattern, layout) {
   openFiles.push(logFile);
 
   return function(logEvent) {
-    logFile.write(layout(logEvent) + eol, "utf8");
+    logFile.write(layout(logEvent, timezoneOffset) + eol, "utf8");
   };
 
 }
@@ -52,7 +53,7 @@ function configure(config, options) {
     config.filename = path.join(options.cwd, config.filename);
   }
 
-  return appender(config.filename, config.pattern, config.alwaysIncludePattern, layout);
+  return appender(config.filename, config.pattern, config.alwaysIncludePattern, layout, config.timezoneOffset);
 }
 
 function shutdown(cb) {

lib/appenders/file.js

@@ -26,8 +26,10 @@ process.on('exit', function() {
  *   if not provided then logs won't be rotated.
  * @param numBackups - the number of log files to keep after logSize 
  *   has been reached (default 5)
+ * @param compress - flag that controls log file compression
+ * @param timezoneOffset - optional timezone offset in minutes (default system local)
  */
-function fileAppender (file, layout, logSize, numBackups, compress) {
+function fileAppender (file, layout, logSize, numBackups, compress, timezoneOffset) {
   var bytesWritten = 0;
   file = path.normalize(file);
   layout = layout || layouts.basicLayout;
@@ -64,7 +66,7 @@ function fileAppender (file, layout, logSize, numBackups, compress) {
   openFiles.push(logFile);
 
   return function(loggingEvent) {
-    logFile.write(layout(loggingEvent) + eol, "utf8");
+    logFile.write(layout(loggingEvent, timezoneOffset) + eol, "utf8");
   };
 
 }
@@ -79,7 +81,7 @@ function configure(config, options) {
     config.filename = path.join(options.cwd, config.filename);
   }
 
-  return fileAppender(config.filename, layout, config.maxLogSize, config.backups, config.compress);
+  return fileAppender(config.filename, layout, config.maxLogSize, config.backups, config.compress, config.timezoneOffset);
 }
 
 function shutdown(cb) {

lib/appenders/fileSync.js

@@ -127,8 +127,10 @@ RollingFileSync.prototype.write = function(chunk, encoding) {
  *   if not provided then logs won't be rotated.
  * @param numBackups - the number of log files to keep after logSize 
  *   has been reached (default 5)
+ * @param timezoneOffset - optional timezone offset in minutes
+ *   (default system local)
  */
-function fileAppender (file, layout, logSize, numBackups) {
+function fileAppender (file, layout, logSize, numBackups, timezoneOffset) {
   debug("fileSync appender created");
   var bytesWritten = 0;
   file = path.normalize(file);
@@ -166,7 +168,7 @@ function fileAppender (file, layout, logSize, numBackups) {
   var logFile = openTheStream(file, logSize, numBackups);
   
   return function(loggingEvent) {
-    logFile.write(layout(loggingEvent) + eol);
+    logFile.write(layout(loggingEvent, timezoneOffset) + eol);
   };
 }
 
@@ -180,7 +182,7 @@ function configure(config, options) {
     config.filename = path.join(options.cwd, config.filename);
   }
 
-  return fileAppender(config.filename, layout, config.maxLogSize, config.backups);
+  return fileAppender(config.filename, layout, config.maxLogSize, config.backups, config.timezoneOffset);
 }
 
 exports.appender = fileAppender;

lib/appenders/smtp.js

@@ -28,7 +28,7 @@ function smtpAppender(config, layout) {
       var firstEvent = logEventBuffer[0];
       var body = "";
       while (logEventBuffer.length > 0) {
-        body += layout(logEventBuffer.shift()) + "\n";
+        body += layout(logEventBuffer.shift(), config.timezoneOffset) + "\n";
       }
 
       var msg = {

lib/date_format.js

@@ -21,9 +21,9 @@ function addZero(vNumber) {
  * Thanks to http://www.svendtofte.com/code/date_format/
  * @private
  */
-function offset(date) {
+function offset(timezoneOffset) {
   // Difference to Greenwich time (GMT) in hours
-  var os = Math.abs(date.getTimezoneOffset());
+  var os = Math.abs(timezoneOffset);
   var h = String(Math.floor(os/60));
   var m = String(os%60);
   if (h.length == 1) {
@@ -32,26 +32,31 @@ function offset(date) {
   if (m.length == 1) {
     m = "0" + m;
   }
-  return date.getTimezoneOffset() < 0 ? "+"+h+m : "-"+h+m;
+  return timezoneOffset < 0 ? "+"+h+m : "-"+h+m;
 }
 
-exports.asString = function(/*format,*/ date) {
+exports.asString = function(/*format,*/ date, timezoneOffset) {
   var format = exports.ISO8601_FORMAT;
   if (typeof(date) === "string") {
     format = arguments[0];
     date = arguments[1];
+    timezoneOffset = arguments[2];
   }
-
-  var vDay = addZero(date.getDate());
-  var vMonth = addZero(date.getMonth()+1);
-  var vYearLong = addZero(date.getFullYear());
-  var vYearShort = addZero(date.getFullYear().toString().substring(2,4));
+  // make the date independent of the system timezone by working with UTC
+  if (timezoneOffset === undefined) {
+      timezoneOffset = date.getTimezoneOffset();
+  }
+  date.setUTCMinutes(date.getUTCMinutes() - timezoneOffset);
+  var vDay = addZero(date.getUTCDate());
+  var vMonth = addZero(date.getUTCMonth()+1);
+  var vYearLong = addZero(date.getUTCFullYear());
+  var vYearShort = addZero(date.getUTCFullYear().toString().substring(2,4));
   var vYear = (format.indexOf("yyyy") > -1 ? vYearLong : vYearShort);
-  var vHour  = addZero(date.getHours());
-  var vMinute = addZero(date.getMinutes());
-  var vSecond = addZero(date.getSeconds());
-  var vMillisecond = padWithZeros(date.getMilliseconds(), 3);
-  var vTimeZone = offset(date);
+  var vHour  = addZero(date.getUTCHours());
+  var vMinute = addZero(date.getUTCMinutes());
+  var vSecond = addZero(date.getUTCSeconds());
+  var vMillisecond = padWithZeros(date.getUTCMilliseconds(), 3);
+  var vTimeZone = offset(timezoneOffset);
   var formatted = format
     .replace(/dd/g, vDay)
     .replace(/MM/g, vMonth)

lib/layouts.js

@@ -71,11 +71,11 @@ function colorize (str, style) {
   return colorizeStart(style) + str + colorizeEnd(style);
 }
 
-function timestampLevelAndCategory(loggingEvent, colour) {
+function timestampLevelAndCategory(loggingEvent, colour, timezoneOffest) {
   var output = colorize(
     formatLogData(
       '[%s] [%s] %s - '
-      , dateFormat.asString(loggingEvent.startTime)
+      , dateFormat.asString(loggingEvent.startTime, timezoneOffest)
       , loggingEvent.level
       , loggingEvent.categoryName
     )
@@ -93,18 +93,19 @@ function timestampLevelAndCategory(loggingEvent, colour) {
  *
  * @author Stephan Strittmatter
  */
-function basicLayout (loggingEvent) {
-  return timestampLevelAndCategory(loggingEvent) + formatLogData(loggingEvent.data);
+function basicLayout (loggingEvent, timezoneOffset) {
+  return timestampLevelAndCategory(loggingEvent, undefined, timezoneOffset) + formatLogData(loggingEvent.data);
 }
 
 /**
  * colouredLayout - taken from masylum's fork.
  * same as basicLayout, but with colours.
  */
-function colouredLayout (loggingEvent) {
+function colouredLayout (loggingEvent, timezoneOffset) {
   return timestampLevelAndCategory(
     loggingEvent,
-    colours[loggingEvent.level.toString()]
+    colours[loggingEvent.level.toString()],
+    timezoneOffset
   ) + formatLogData(loggingEvent.data);
 }