added a log rolling function to file appender

lib/log4js.js

@@ -342,22 +342,69 @@ module.exports = function (fileSystem, standardOutput, configPaths) {
     }
 
     /**
-     * File Appender writing the logs to a text file.
+     * File Appender writing the logs to a text file. Supports rolling of logs by size.
      * 
      * @param file file log messages will be written to
      * @param layout a function that takes a logevent and returns a string (defaults to basicLayout).
+     * @param logSize - the maximum size (in bytes) for a log file, 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 filePollInterval - the time in seconds between file size checks (default 30s)
      */
-    function fileAppender (file, layout) {
+    function fileAppender (file, layout, logSize, numBackups, filePollInterval) {
 	layout = layout || basicLayout;	
 	//syncs are generally bad, but we need 
 	//the file to be open before we start doing any writing.
 	var logFile = fs.openSync(file, 'a', 0644);
 
+        if (logSize > 0) {
+            setupLogRolling(logFile, file, logSize, numBackups || 5, (filePollInterval * 1000) || 30000);
+        }
+	
 	return function(loggingEvent) {
 	    fs.write(logFile, layout(loggingEvent)+'\n', null, "utf8");
 	};
     }
 
+    function setupLogRolling (logFile, filename, logSize, numBackups, filePollInterval) {
+        fs.watchFile(filename, 
+                     { 
+                         persistent: false, 
+                         interval: filePollInterval 
+                     },
+                     function (curr, prev) {
+                         if (curr.size >= logSize) {
+                             rollThatLog(logFile, filename, numBackups);
+                         }
+                     }
+                    );
+    }
+
+    function rollThatLog (logFile, filename, numBackups) {
+        //first close the current one.
+        fs.closeSync(logFile);
+        //roll the backups (rename file.n-1 to file.n, where n <= numBackups)
+        for (var i=numBackups; i > 0; i--) {
+            if (i > 1) {
+                if (fileExists(filename + '.' + (i-1))) {
+                    fs.renameSync(filename+'.'+(i-1), filename+'.'+i);
+                }
+            } else {
+                fs.renameSync(filename, filename+'.1');
+            }
+        }
+        //open it up again
+        logFile = fs.openSync(filename, 'a', 0644);
+    }
+
+    function fileExists (filename) {
+        try {
+            fs.statSync(filename);
+            return true;
+        } catch (e) {
+            return false;
+        }
+    }
+
     function logLevelFilter (levelString, appender) {
 	var level = Level.toLevel(levelString);
 	return function(logEvent) {

test/logging.js

@@ -61,6 +61,9 @@ vows.describe('log4js').addBatch({
 		    assert.isNull(arguments[2]);
 		    assert.equal(arguments[3], "utf8");
 		    logmessages.push(arguments[1]);
+		},
+                watchFile: function() {
+                    throw new Error("watchFile should not be called if logSize is not defined");
                 }
 	    },
 	    log4js = require('../lib/log4js')(fakeFS);
@@ -91,7 +94,8 @@ vows.describe('log4js').addBatch({
             log4js = require('../lib/log4js')({
                 watchFile: function(file, options, callback) {
                     assert.equal(file, 'tests.log');
-                    assert.deepEqual(options, { persistent: true, interval: 30000 });
+                    assert.equal(options.persistent, false);
+                    assert.equal(options.interval, 30000);
                     assert.isFunction(callback);
                     watchCb = callback;
                 },
@@ -146,10 +150,10 @@ vows.describe('log4js').addBatch({
             assert.length(filesClosed, 2);
             //it should have renamed both the old log file, and the previous '.1' file
             assert.length(filesRenamed, 3);
-            assert.deepEqual(filesRenamed, ['tests.log', 'tests.log', 'tests.log.1' ]);
+            assert.deepEqual(filesRenamed, ['tests.log', 'tests.log.1', 'tests.log' ]);
             //it should have renamed 2 more file
-            assert.length(existingFiles, 2);
-            assert.deepEqual(existingFiles, ['tests.log', 'tests.log.2', 'tests.log.1']);
+            assert.length(existingFiles, 4);
+            assert.deepEqual(existingFiles, ['tests.log', 'tests.log.1', 'tests.log.2', 'tests.log.1']);
             //and opened a new log file
             assert.length(filesOpened, 3);
 
@@ -159,10 +163,10 @@ vows.describe('log4js').addBatch({
             assert.length(filesClosed, 3);
             //it should have renamed the old log file and the 2 backups, with the last one being overwritten.
             assert.length(filesRenamed, 5);
-            assert.deepEqual(filesRenamed, ['tests.log', 'tests.log', 'tests.log.1', 'tests.log', 'tests.log.1' ]);
+            assert.deepEqual(filesRenamed, ['tests.log', 'tests.log.1', 'tests.log', 'tests.log.1', 'tests.log' ]);
             //it should have renamed 2 more files
-            assert.length(existingFiles, 5);
-            assert.deepEqual(existingFiles, ['tests.log', 'tests.log.2', 'tests.log.1', 'tests.log.2', 'tests.log.1']);
+            assert.length(existingFiles, 6);
+            assert.deepEqual(existingFiles, ['tests.log', 'tests.log.1', 'tests.log.2', 'tests.log.1', 'tests.log.2', 'tests.log.1']);
             //and opened a new log file
             assert.length(filesOpened, 4);
         }