Node.js response.addTrailers() Method

The response.addTrailers() (Added in v0.3.0) method is an inbuilt application programming interface of the ‘http‘ module which adds HTTP trailing headers (a header but at the end of the message) to the response. Trailers will only be emitted if the chunked encoding is used for the response; if it is not (e.g. if the request was HTTP/1.0), they will be silently discarded. HTTP requires the Trailer header to be sent in order to emit trailers, with a list of the header fields in its value.

When headers have been set with response.setHeader(), they will be merged with any headers passed to response.writeHead(), with the headers passed to response.writeHead() given precedence.

In order to get a response and a proper result, we need to import ‘http’ module.

Syntax:

const http = require('http');

Syntax:

response.addTrailers(headers);

Parameters: This property accepts a single parameter as mentioned above and described below:

• headers<String>: It accepts the name of the HTTP trailing headers (a header but at the end of the message) to the response.

Return Value: It does not return any value, instead sets a header as described below.

The below example illustrates the use of response.addTrailers() property in Node.js.

Example 1: Filename: index.js

// Node.js program to demonstrate the
// response.addTrailers() Method

// Importing http module
var http = require('http');

// Setting up PORT
const PORT = process.env.PORT || 3000;

// Creating http Server
var httpServer = http.createServer(
       function(request, response) {

  // Setting up Headers
  response.setHeader('Alfa', 'Beta');

  response.writeHead(200, {
    'Content-Type': 'text/plain',
    'Trailer': 'Content-MD5'
  });
  response.addTrailers({'Content-MD5':
    '7895bf4b8828b55ceaf47747b4bca667'});

  console.log(response.getHeaders());
  response.end('Trailer Added, ok');
});

// Listening to http Server
httpServer.listen(PORT, () => {
    console.log(
      "Server is running at port 3000...");
});

Now run http://localhost:3000/ in the browser.

Output: In Console

>> Server is running at port 3000…

>> [Object: null prototype] {

    alfa:’Beta’,

    ‘content-type’:’text/plain’,

    trailer: ‘Content-MD5’}

Output: In Browser

Trailer Added, ok

Example 2: Filename: index.js

Javascript

// Node.js program to demonstrate the
// response.addTrailers() Method

// Importing http module
var http = require('http');

// Setting up PORT
const PORT = process.env.PORT || 3000;

// Creating http Server
var httpServer = http.createServer(
          function(req, response) {

  // Setting up Headers
  response.setHeader('Alfa1', '');
  response.setHeader('Cookie-Setup',
       ['Alfa=Beta', 'Beta=Romeo']);

  response.writeHead(200, {
    'Content-Type': 'text/plain',
    'Trailer': 'Content-MD5'
  });

  // addTrailers Content-MD5
  response.addTrailers({'Content-MD5':
    '7895bf4b8828b55ceaf47747b4bca667'});

  // Adding Cookie-Setup as trailer
  // ( Not gets added as trailer )
  response.addTrailers({ 'Cookie-Setup':
       ['Alfa=Beta', 'Beta=Romeo'] });

  // Checking and printing the headers
  console.log("Calling trailer by getHeader :",
  response.getHeader('Content-MD5'));

  // console.log("Calling trailer by getHeader :",
  response);

  // Getting the set Headers
  const headers = response.getHeaders();

  // Printing those headers
  // Header
  console.log("Printing _header: ", response._header);

  // Trailer
  console.log("Printing _trailer: ", response._trailer);

  // All headers
  console.log("Printing All headers: ", headers);

  var Output = "Hello Geeksforgeeks..., "
    + "Available headers and trailers are:"
    + JSON.stringify(headers);

  // Prints Output on the browser in response
  response.write(Output);
  response.end('ok');
});

// Listening to http Server
httpServer.listen(PORT, () => {
    console.log("Server is running at port 3000...");
});

Run index.js file using the following command:

node index.js

Output:

In Console

Server is running at port 3000…

>> Calling trailer by getHeader : undefined

>> Printing _header: HTTP/1.1 200 OK

    Alfa1:

    Cookie-Setup: Alfa=Beta

    Cookie-Setup: Beta=Romeo

    Content-Type: text/plain

    Trailer: Content-MD5

    Date: Wed, 09 Sep 2020 06:03:32 GMT

    Connection: keep-alive

    Transfer-Encoding: chunked

>> Printing _trailer: Cookie-Setup: Alfa=Beta, Beta=Romeo

>> Printing All headers: [Object: null prototype] {

     alfa1: ”,

     ‘cookie-setup’: [ ‘Alfa=Beta’, ‘Beta=Romeo’ ],

     ‘content-type’: ‘text/plain’,

     trailer: ‘Content-MD5’}

Now run http://localhost:3000/ in the browser.

Output: In Browser

Hello Geeksforgeeks…, Available headers and trailers are:{“alfa1″:””, “cookie-setup”:[“Alfa=Beta”, “Beta=Romeo”],

“content-type”:”text/plain”, “trailer”:”Content-MD5″}ok

Reference: https://nodejs.org/api/http.html#http_response_addtrailers_headers