HTTP Module

The HTTP core module is a key module to Node networking.

It has following properties

METHODS
STATUS_CODES
globalAgent

It has following methods

createServer()
request()
get()

It has following classes

Agent
ClientRequest
Server
ServerResponse
IncomingMessage

It can be included using – const http = require(‘http’)

The module provides some properties and methods, and some classes.

http.METHODS

This property lists all the HTTP methods supported:

> require(‘http’).METHODS

[ ‘ACL’,

‘BIND’,

‘CHECKOUT’,

‘CONNECT’,

‘COPY’,

‘DELETE’,

‘GET’,

‘HEAD’,

‘LINK’,

‘LOCK’,

‘M-SEARCH’,

‘MERGE’,

‘MKACTIVITY’,

‘MKCALENDAR’,

‘MKCOL’,

‘MOVE’,

‘NOTIFY’,

‘OPTIONS’,

‘PATCH’,

‘POST’,

‘PROPFIND’,

‘PROPPATCH’,

‘PURGE’,

‘PUT’,

‘REBIND’,

‘REPORT’,

‘SEARCH’,

‘SUBSCRIBE’,

‘TRACE’,

‘UNBIND’,

‘UNLINK’,

‘UNLOCK’,

‘UNSUBSCRIBE’ ]

http.STATUS_CODES

This property lists all the HTTP status codes and their description:

> require(‘http’).STATUS_CODES

{ ‘100’: ‘Continue’,

‘101’: ‘Switching Protocols’,

‘102’: ‘Processing’,

‘200’: ‘OK’,

‘201’: ‘Created’,

‘202’: ‘Accepted’,

‘203’: ‘Non-Authoritative Information’,

‘204’: ‘No Content’,

‘205’: ‘Reset Content’,

‘206’: ‘Partial Content’,

‘207’: ‘Multi-Status’,

‘208’: ‘Already Reported’,

‘226’: ‘IM Used’,

‘300’: ‘Multiple Choices’,

‘301’: ‘Moved Permanently’,

‘302’: ‘Found’,

‘303’: ‘See Other’,

‘304’: ‘Not Modified’,

‘305’: ‘Use Proxy’,

‘307’: ‘Temporary Redirect’,

‘308’: ‘Permanent Redirect’,

‘400’: ‘Bad Request’,

‘401’: ‘Unauthorized’,

‘402’: ‘Payment Required’,

‘403’: ‘Forbidden’,

‘404’: ‘Not Found’,

‘405’: ‘Method Not Allowed’,

‘406’: ‘Not Acceptable’,

‘407’: ‘Proxy Authentication Required’,

‘408’: ‘Request Timeout’,

‘409’: ‘Conflict’,

‘410’: ‘Gone’,

‘411’: ‘Length Required’,

‘412’: ‘Precondition Failed’,

‘413’: ‘Payload Too Large’,

‘414’: ‘URI Too Long’,

‘415’: ‘Unsupported Media Type’,

‘416’: ‘Range Not Satisfiable’,

‘417’: ‘Expectation Failed’,

‘418’: ‘I\’m a teapot’,

‘421’: ‘Misdirected Request’,

‘422’: ‘Unprocessable Entity’,

‘423’: ‘Locked’,

‘424’: ‘Failed Dependency’,

‘425’: ‘Unordered Collection’,

‘426’: ‘Upgrade Required’,

‘428’: ‘Precondition Required’,

‘429’: ‘Too Many Requests’,

‘431’: ‘Request Header Fields Too Large’,

‘451’: ‘Unavailable For Legal Reasons’,

‘500’: ‘Internal Server Error’,

‘501’: ‘Not Implemented’,

‘502’: ‘Bad Gateway’,

‘503’: ‘Service Unavailable’,

‘504’: ‘Gateway Timeout’,

‘505’: ‘HTTP Version Not Supported’,

‘506’: ‘Variant Also Negotiates’,

‘507’: ‘Insufficient Storage’,

‘508’: ‘Loop Detected’,

‘509’: ‘Bandwidth Limit Exceeded’,

‘510’: ‘Not Extended’,

‘511’: ‘Network Authentication Required’ }

http.globalAgent

Points to the global instance of the Agent object, which is an instance of the http.Agent class. It’s used to manage connections persistance and reuse for HTTP clients, and it’s a key component of Node HTTP networking.

http.createServer()

It returns a new instance of the http.Server class.

Usage:

const server = http.createServer((req, res) => {

//handle every single request with this callback

})

http.request()

Makes an HTTP request to a server, creating an instance of the http.ClientRequest class.

http.get()

Similar to http.request(), but automatically sets the HTTP method to GET, and calls req.end() automatically.

Classes

The HTTP module provides 5 classes:

Agent
ClientRequest
Server
ServerResponse
IncomingMessage

http.Agent

Node creates a global instance of the http.Agent class to manage connections persistance and reuse for HTTP clients, a key component of Node HTTP networking. This object makes sure that every request made to a server is queued and a single socket is reused. It also maintains a pool of sockets. This is key for performance reasons.

http.ClientRequest

An http.ClientRequest object is created when http.request() or http.get() is called.

When a response is received, the response event is called with the response, with an http.IncomingMessage instance as argument.

The returned data of a response can be read in 2 ways:

you can call the response.read() method
in the response event handler you can setup an event listener for the data event, so you can listen for the data streamed into.

http.Server

This class is commonly instantiated and returned when creating a new server using http.createServer().

Once you have a server object, you have access to its methods:

close() stops the server from accepting new connections
listen() starts the HTTP server and listens for connections

http.ServerResponse

Created by an http.Server and passed as the second parameter to the request event it fires. Commonly known and used in code as res:

const server = http.createServer((req, res) => {

//res is an http.ServerResponse object

})

The method you’ll always call in the handler is end(), which closes the response, the message is complete and the server can send it to the client. It must be called on each response.

These methods are used to interact with HTTP headers:

getHeaderNames() get the list of the names of the HTTP headers already set
getHeaders() get a copy of the HTTP headers already set
setHeader(‘headername’, value) sets an HTTP header value
getHeader(‘headername’) gets an HTTP header already set
removeHeader(‘headername’) removes an HTTP header already set
hasHeader(‘headername’) return true if the response has that header set
headersSent() return true if the headers have already been sent to the client

After processing the headers you can send them to the client by calling response.writeHead(), which accepts the statusCode as the first parameter, the optional status message, and the headers object.

To send data to the client in the response body, you use write(). It will send buffered data to the HTTP response stream.

If the headers were not sent yet using response.writeHead(), it will send the headers first, with the status code and message that’s set in the request, which you can edit by setting the statusCode and statusMessage properties values:

response.statusCode = 500

response.statusMessage = ‘Internal Server Error’

http.IncomingMessage

An http.IncomingMessage object is created by:

Server when listening to the request event
ClientRequest when listening to the response event

It can be used to access the response:

status using its statusCode and statusMessage methods
headers using its headers method or rawHeaders
HTTP method using its method method
HTTP version using the httpVersion method
URL using the url method
underlying socket using the socket method

The data is accessed using streams, since http.IncomingMessage implements the Readable Stream interface.

Add an HTTP Header

If the response from the HTTP server is supposed to be displayed as HTML, you should include an HTTP header with the correct content type:

Example

var http = require(‘http’);

http.createServer(function (req, res) {

res.writeHead(200, {‘Content-Type’: ‘text/html’});

res.write(‘Hello World!’);

res.end();

}).listen(8080);

The first argument of the res.writeHead() method is the status code, 200 means that all is OK, the second argument is an object containing the response headers.

Read the Query String

The function passed into the http.createServer() has a req argument that represents the request from the client, as an object (http.IncomingMessage object). This object has a property called “url” which holds the part of the url that comes after the domain name:

demo_http_url.js

var http = require(‘http’);

http.createServer(function (req, res) {

res.writeHead(200, {‘Content-Type’: ‘text/html’});

res.write(req.url);

res.end();

}).listen(8080);

Save the code above in a file called “demo_http_url.js” and initiate the file:

Initiate demo_http_url.js:

C:\Users\Your Name>node demo_http_url.js

If you have followed the same steps on your computer, you should see two different results when opening these two addresses: http://localhost:8080/summer , will produce this result: /summer

http://localhost:8080/winter , will produce this result: /winter