A simple Nodejs File server that streams non-requested resources to the client and loads already requested resources from a simple cache

server.js

/*
 * Before executing this script
 *
 * 1. Create a dir named content
 * 2. With an index.html that requests for files e.g css
 *
 * This simple server will automatically stream the 
 * requested resource from the content directory to the client
 *
 * author: Evander Tino
 *
 */

var http = require('http');
var fs = require('fs');
var path = require('path');

var mimeTypes = {
  '.js' : 'text/javascript',
  '.html': 'text/html',
  '.css' : 'text/css'
};

var cache = {
  store: {},
  maxSize: 26214400, //(bytes) 25mb
  maxAge: 5400 * 1000, //(ms) 1 and a half hours
  cleanAfter: 7200 * 1000,//(ms) two hours
  cleanedAt: 0, //to be set dynamically
  clean: function(now) {
    if (now - this.cleanAfter > this.cleanedAt) {
      this.cleanedAt = now;
      that = this;
      Object.keys(this.store).forEach(function (file) {
        if (now > that.store[file].timestamp + that.maxAge) {
          delete that.store[file];
        }
      });
    }
  }
};

http.createServer(function (request, response) {
  var lookup = path.basename(decodeURI(request.url)) || 'index.html';
  var f = 'content/' + lookup;
  fs.exists(f, function (exists) {
    if (exists) {
      var headers = {'Content-Type': mimeTypes[path.extname(f)]};
      if (cache.store[f]) {
        response.writeHead(200, headers);
        response.end(cache.store[f].content);
        console.log('loading ' + f + ' from the cache');
        return;
      }
      var s = fs.createReadStream(f).once('open', function() {
        response.writeHead(200, headers);
        this.pipe(response);
        console.log('streaming ' + f + ' from disk');
      }).once('error', function(e) {
        console.log(e);
        response.writeHead(500);
        response.end('Server Error!');
      });
      fs.stat(f, function(err, stats) {
        if (stats.size < cache.maxSize) {
          var bufferOffset = 0;
          cache.store[f] = {content: new Buffer(stats.size), timestamp: Date.now() };
          s.on('data', function(data) {
            data.copy(cache.store[f].content, bufferOffset);
            bufferOffset += data.length;
          });
        }
      });
    } else {
      response.writeHead(404);
      response.end('Page Not Found');
    }
  });
  cache.clean(Date.now());
}).listen(8080);

Hello EvaderTino
I have been reading about node and your code is interesting, i am a beginner and I do not understand somethings, Could you answer me some question please:

Is cache a global variable?...
Are maxSize, cleanAfter Default attributes for this variable?
where can I find out about this in the node page i have not find it...

thanks