node cache practise

gistfile1.txt

//app.js
var PORT=3000;
var http=require('http');
var url=require('url');
var fs=require('fs');
var path=require('path');
var mime=require('./mime').types;
var config=require('./config');

var server=http.createServer(function(request,response){
    var pathname=url.parse(request.url).pathname;
    var realPath='publice'+pathname;
    var ext=path.extname(realPath);
    ext=ext?ext.slice(1):'unknown';
    var contentType=mime[ext]||'text/plain';

    //Cache-Control
    if(ext.match(config.Expires.fileMatch)){
        var expires=new Date();
        expires.setTime(expires.getTime()+config.Expires.maxAge*1000);
        response.setHeader('Expires',expires.toUTCString());
        response.setHeader('Cache-Control','max-age='+config.Expires.maxAge);
    }

    //Last-Modified
    fs.stat(realPath,function(err,stat){
        var lastModified=stat.mtime.toUTCString();
        response.setHeader('Last-Modified',lastModified);
        if(request.headers['if-modified-since'] && lastModified==request.headers['if-modified-since']){
            response.writeHead(304,'Not Modified');
            response.end();
        }else{
            fs.exists(realPath,function(exists){
                if(!exists){
                    response.writeHead(404,{
                        'Content-Type':'text/plain'
                    });
                    response.write('This URL'+pathname+'not found');
                    response.end();
                }else{
                    fs.readFile(realPath,'binary',function(err,file){
                        if(err){
                            response.writeHead(500,{
                                'Content-Type':'text/plain'
                            });
                            response.end();
                        }else{
                            response.writeHead(200,{
                                'Content-Type':contentType
                            });
                            response.write(file,'binary');
                            response.end();
                        }
                    })
                }
            })
        }        
    })
});

server.listen(PORT);
console.log('port:'+PORT);

gistfile2.txt

//config.js
exports.Expires={
    fileMatch:/^(png|gif|jpg|js|css)$/ig,
    maxAge:60*60*24*365
}

gistfile3.txt

//mime.js
exports.types={
    'jpg':'image/jpeg',
    'json':'application/json'
}