DEV Community: Aditya Kresna

[NodeJS] Simple Express Response Hijack/Interceptor Library

Aditya Kresna — Thu, 27 May 2021 12:13:34 +0000

So this is a short introduction about my express-multi-hijack library that I just published a few minutes ago. express-multi-hijack is a simple express middleware for hijacking or intercept Your HTTP or API responses.

It's based on my experience when I want to intercept JSON Api response. This library might be useful for your use-case with your NodeJS or Typescript project (yes, it is typescript friendly) when it needs an interception on response body

Installation

npm i express-multi-hijack

How It Works

This library works by overriding res.end function, still maintaining the original one once all of the "hijack" functions are executed.
So it is safe to use with Your own custom res.end implementation.

Some Examples

Simple Tracing Response Body

const Express = require('express');
const { Hijack } = require('express-multi-hijack');

const app = Express()

app.use(Hijack({
  json: true,
  handler: (body, req, res, next) => {
    console.info('got response body', body) // { "foo": "bar" }
  }
}))

app.get('/bar', (req, res, next) => {
  res.json({
    bar: 'foo',
  })
})

app.get('/foo', (req, res, next) => {
  res.json({
    foo: 'bar',
  })
})

app.listen(8080)

Based on the example above, the hijack handler will print { "foo": "bar" } on request to localhost:8080/foo and { "bar": "foo" } when requesting to localhost:8080/bar.

Intercept / Hijack Response Body

const Express = require('express')
const { Hijack } = require('../dist')

const app = Express()

app.use(Hijack({
  json: true,
  handler: (body, _, res) => {
    console.info('body:', body)
    res.json({ message: 'Today is the bad day' })
  }
}))

app.get('/', (_, res) => {
  return res.json({ message: 'Today is a Great Day!' })
})

app.listen(8080)

The code above will change the response message from 'Today is a Great Day!' to 'Today is the bad day'

Multiple Hijack, early hijack function got highest priority

const Express = require('express')
const { Hijack } = require('../dist')

const app = Express()

// hijack on monday
app.use(Hijack({
  json: true,
  handler: (body, _, res) => {
    if (body.today === 'Monday') {
      res.json({
        ...body,
        message: 'What a lazy day'
      })
    }
  }
}))

// hijack on friday
app.use(Hijack({
  json: true,
  handler: (body, req, res) => {
    if (req.path === '/friday') {
      res.json({
        ...body,
        message: 'What a wondeful day'
      })
    }
  }
}))

app.get('/', (_, res) => res.json({ message: 'No Hijack' }))

app.get('/monday', (_, res) => {
  return res.status(200).json({ today: 'Monday', message: 'Today is a Great Day!' })
})

app.get('/friday', (_, res) => {
  return res.status(200).json({ message: 'Today is a Great Day!' })
})

app.listen(8080)

The code above will intercept and change response for localhost:8080/monday to {today: 'Moday', message: 'What a lazy day'}, and localhost:8080/friday to {message: 'What a wondeful day'}

That's all, thank you for reading my post, for more code examples You can visit the example directory.

This post originally published here

How Your Company moving from using the existing (legacy) application architecture to a new one?

Aditya Kresna — Sat, 16 Nov 2019 17:29:43 +0000

Have you thinking about your current running system is needed to rebuild? The same situation is happen to us, as the current application is majority supporting almost all of our business process.

Short Story

The story began when our system is highly developed to support our customers in a short period of time. This kind of process unfortunately ignores the process of designing scalable application, actually we design it to scale, but, at that time the insights are very limited to us to make our system is stable longer.

Our system is based on RESTful and divided into more than 5 microservices, which each microservices are tightly tied to one service that act like an API Gateway.

The "API Gateway" service is not like another(Kong, Ambassador, etc), it is a NodeJs application which also holds a logic composition when the "request" is coming and pointed to another service for the specific operation. It also responsible for Authentication with the outside world which adds more complexity when we try to excluding it from the service.

Need Help!

Is that situation ever happened to you? if yes, how to deal with that?
Is there any best practice about step-by-step to move seamlessly into a brand new system?
Because we use Functional paradigm, please comment if you do know about refactoring recipes in functional programming, any experience or advice will be appreciated.
How to make a decoupled microservices, when between microservices needed an authorization and (eventually) depends on one Auth (like) service to verify the request?

Write Semi-Advanced Timer Component in Vue

Aditya Kresna — Wed, 30 Oct 2019 05:09:32 +0000

I thought it was hard to build a semi-advanced timer based on the VueJs component. Turns out the result is quite good to use on my project, maybe in yours too.