log4js-node/lib/streams/RollingFileStream.js

var BaseRollingFileStream = require('./BaseRollingFileStream'),
    util = require('util'),
    path = require('path'),
    fs = require('fs'),
    async = require('async');

function debug() {
//    util.debug(message);
//  console.log.apply(console, arguments);
}

module.exports = RollingFileStream;

function RollingFileStream (filename, size, backups, options) {
    this.size = size;
    this.backups = backups || 1;

    function throwErrorIfArgumentsAreNotValid() {
        if (!filename || !size || size <= 0) {
            throw new Error("You must specify a filename and file size");
        }
    }

    throwErrorIfArgumentsAreNotValid();

    RollingFileStream.super_.call(this, filename, options);
}
util.inherits(RollingFileStream, BaseRollingFileStream);

RollingFileStream.prototype.shouldRoll = function() {
  debug("should roll with current size %d, and max size %d", this.currentSize, this.size);
    return this.currentSize >= this.size;
};

RollingFileStream.prototype.roll = function(filename, callback) {
    var that = this,
        nameMatcher = new RegExp('^' + path.basename(filename));

    function justTheseFiles (item) {
        return nameMatcher.test(item);
    }

    function index(filename_) {
        return parseInt(filename_.substring((path.basename(filename) + '.').length), 10) || 0;
    }

    function byIndex(a, b) {
        if (index(a) > index(b)) {
            return 1;
        } else if (index(a) < index(b) ) {
            return -1;
        } else {
            return 0;
        }
    }

    function increaseFileIndex (fileToRename, cb) {
        var idx = index(fileToRename);
        debug('Index of ' + fileToRename + ' is ' + idx);
        if (idx < that.backups) {
            //on windows, you can get a EEXIST error if you rename a file to an existing file
            //so, we'll try to delete the file we're renaming to first
            fs.unlink(filename + '.' + (idx+1), function (err) {
                //ignore err: if we could not delete, it's most likely that it doesn't exist
                debug('Renaming ' + fileToRename + ' -> ' + filename + '.' + (idx+1));
                fs.rename(path.join(path.dirname(filename), fileToRename), filename + '.' + (idx + 1), cb);
            });
        } else {
            cb();
        }
    }

    function renameTheFiles(cb) {
        //roll the backups (rename file.n to file.n+1, where n <= numBackups)
        debug("Renaming the old files");
        fs.readdir(path.dirname(filename), function (err, files) {
            async.forEachSeries(
                files.filter(justTheseFiles).sort(byIndex).reverse(),
                increaseFileIndex,
                cb
            );
        });
    }

  debug("Rolling, rolling, rolling");
  async.series([
    this.closeTheStream.bind(this),
    renameTheFiles,
    this.openTheStream.bind(this)
  ], callback);

};