Node.js: Reads a file in the server and writes its contents to the response. Nested non-blocking calls

readFile-response with node.js

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

http.createServer(function(request, response) {
  response.writeHead(200);  // 1.
  
  var callback = function(err, contents){
    response.write(contents);   // 3.
  	response.end();             // 4.
  }
  
  fs.readFile('index.html',callback)  // 2.
  
}).listen(8080);