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Server-side JavaScript

Prof. Cesare Pautasso
http://www.pautasso.info
[email protected]
@pautasso

Dynamic Web

Where are we?

Web Architecture

Apps and Web Servers

Hello World on the Server

var http = require('http');


function onrequest(request, response) {
  response.writeHead(200);
  response.end("Hello World\n");
}

var server = http.createServer(onrequest);
server.listen(8000);


console.log("Listening on http://127.0.0.1:8000/");

Server Programming

  1. The server should always be ready for handling client requests
  2. Requests should be answered as quickly as possible
  3. One server should handle many types of requests coming from multiple clients at the same time

Web Server Architecture

Web Server in JavaScript

var http = require("http");
var url = require("url");
function onrequest(request, response) { 

var pathname = url.parse(request.url).pathname;
 if (typeof rh[pathname] === 'function') { 
   rh[pathname](request, response); 
 } else { 
   response.writeHead(404); 
   response.end(); 
 }
}
http.createServer(onrequest).listen(8888);

Routing Request Handlers

//Request Handlers
var root = function(request, response) { … }
var hello = function(request, response) {

  response.writeHead(200,
              {"Content-Type": "text/html"}); 
  response.write("…"); //body
  response.end();
}

//Routing Table (Map URL -> Request Handler)
rh["/"] = root;
rh["/hello"] = hello;

Working with requests

request.url
request.method
request.headers

Working with URLs

var url = require(‘url’);
var p_url = url.parse('/status?name=cp', true);
p_url = {
  href: '/status?name=cp',
  search: '?name=cp',
  query: { name: ‘cp' }, 
  pathname: '/status'
}

Working with responses

response.writeHead(statusCode, [msg], [headers]);
response.write(body);
response.end();

Explicit Headers

response.setHeader(key, value);
response.getHeader(key);
response.statusCode
response.write(body);
response.end();

Implicit Headers

Concurrency - Threads

Concurrency - Events

Events

  • Pro: No synchronization needed, there is only one thread that reads/write variables shared between different request handlers
  • Con: A slow request handler will block the entire server. All I/O operations need to be non-blocking

Threads

  • Con: Shared variables between thread need to be protected from concurrent access
  • Pro: Threads run in parallel, if one is slow/blocked, it will not delay all other pending requests (unless there is a shared lock)

Non-blocking callbacks

//blocking function
function(arguments)
var y = f(x);
...

Blocking functions return their result when they finish

//non-blocking function
function(arguments, callback)
f(x, function(y) { ... });

Non-blocking functions return immediately and use callbacks to pass the results later when it's ready

Composing callbacks

var y = f(x);
var z = g(y);
var z = g(f(x));
console.log(z);

Compose two non-blocking functions f and g and log the result in the console

Request Events

var postData = "";
request.setEncoding("utf8");
request.on("data", 
  function(chunk) { postData += chunk; });
request.on("end", 
  function() { 
    console.log ("received" + postData); 
  });

Read the body of a post request

Tools

References

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