finalhandler

What is finalhandler?

The finalhandler npm package is a Node.js module designed to ensure that the final response is sent to the client. It acts as a final step in the request-response cycle, handling any remaining tasks such as sending a 404 response if no middleware has handled the request, or handling errors that may have occurred during the request processing.

What are finalhandler's main functionalities?

Error Handling

This code demonstrates how finalhandler can be used to handle errors that occur during the request processing. If an error is thrown, finalhandler will ensure that an appropriate HTTP error response is sent to the client.

const finalhandler = require('finalhandler');
const http = require('http');

http.createServer(function (req, res) {
  const done = finalhandler(req, res);
  throw new Error('Something went wrong!');
}).listen(3000);

Uncaught Exception Handling

This code sample shows how finalhandler can handle exceptions that are not caught within the context of the request. It ensures that the server remains operational and sends an error response to the client.

const finalhandler = require('finalhandler');
const http = require('http');

http.createServer(function (req, res) {
  const done = finalhandler(req, res);
  process.nextTick(function () {
    throw new Error('Async error!');
  });
  done();
}).listen(3000);

404 Not Found Response

This example illustrates how finalhandler can be used to send a 404 Not Found response when no middleware or routes have handled the request.

const finalhandler = require('finalhandler');
const http = require('http');

http.createServer(function (req, res) {
  const done = finalhandler(req, res);
  // No routes or middleware respond
  done();
}).listen(3000);

Other packages similar to finalhandler

on-finished

The 'on-finished' package is similar to finalhandler in that it is used to execute a callback when a HTTP response is finished or when an error occurs. It is a lower-level utility than finalhandler and does not handle the response itself, but rather provides a way to detect when the response has been completed.

connect

Connect is an extensible HTTP server framework for node, which uses 'middleware' to enhance Node.js features. While not a direct alternative to finalhandler, it includes similar error handling and final response capabilities within its middleware stack.

README

finalhandler

Node.js function to invoke as the final step to respond to HTTP request.

Installation

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install finalhandler

API

var finalhandler = require('finalhandler')

finalhandler(req, res, [options])

Returns function to be invoked as the final step for the given req and res. This function is to be invoked as fn(err). If err is falsy, the handler will write out a 404 response to the res. If it is truthy, an error response will be written out to the res or res will be terminated if a response has already started.

When an error is written, the following information is added to the response:

• The res.statusCode is set from err.status (or err.statusCode). If this value is outside the 4xx or 5xx range, it will be set to 500.
• The res.statusMessage is set according to the status code.
• The body will be the HTML of the status code message if env is 'production', otherwise will be err.stack.
• Any headers specified in an err.headers object.

The final handler will also unpipe anything from req when it is invoked.

options.env

By default, the environment is determined by NODE_ENV variable, but it can be overridden by this option.

options.onerror

Provide a function to be called with the err when it exists. Can be used for writing errors to a central location without excessive function generation. Called as onerror(err, req, res).

Examples

always 404

var finalhandler = require('finalhandler')
var http = require('http')

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res)
  done()
})

server.listen(3000)

perform simple action

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

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res)

  fs.readFile('index.html', function (err, buf) {
    if (err) return done(err)
    res.setHeader('Content-Type', 'text/html')
    res.end(buf)
  })
})

server.listen(3000)

use with middleware-style functions

var finalhandler = require('finalhandler')
var http = require('http')
var serveStatic = require('serve-static')

var serve = serveStatic('public')

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res)
  serve(req, res, done)
})

server.listen(3000)

keep log of all errors

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

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res, { onerror: logerror })

  fs.readFile('index.html', function (err, buf) {
    if (err) return done(err)
    res.setHeader('Content-Type', 'text/html')
    res.end(buf)
  })
})

server.listen(3000)

function logerror (err) {
  console.error(err.stack || err.toString())
}

License

MIT