Introducing

 

 

 

 

 

 

The stylish Node.js middleware engine

for AWS Lambda

npm install middy
const middy = require('middy')
const { urlEncodedBodyParser, validator, httpErrorHandler } = require('middy/middlewares')

const processPaymentHandler = (event, context, callback) => {
  const { 
    creditCardNumber,
    expiryMonth,
    expiryYear,
    cvc,
    nameOnCard,
    amount
  } = event.body
  
  // do stuff with this data ...
  
  return callback(null,
    { result: 'success', message: 'payment processed correctly'}
  )
}

const inputSchema = {
 // define validation schema here ...
}

const handler = middy(processPaymentHandler)
  .use(urlEncodedBodyParser())
  .use(validator(inputSchema))
  .use(httpErrorHandler())

module.exports = { handler }

Handler

Attach middlewares

Export enhanced handler

Why?

  • Simplify code
  • Reusability
    • input parsing
    • input & output validation
    • output serialization
    • error handling
    • ...
  • Focus MORE on business logic

Usage

const middy = require('middy')
const { middleware1, middleware2, middleware3 } = require('middy/middlewares')

const originalHandler = (event, context, callback) => {
  /* your business logic */
}

const handler = middy(originalHandler)

handler
  .use(middleware1())
  .use(middleware2())
  .use(middleware3())

module.exports = { handler }

1. define handler

2. "middify" handler

3. attach middlewares

4. export "middyfied" handler

How it works

Execution order

  1. middleware1 (before)
  2. middleware2 (before)
  3. middleware3 (before)
  4. handler
  5. middleware3 (after)
  6. middleware2 (after)
  7. middleware1 (after)

When an error happens...

  • Flow is stopped
  • First middleware implementing `onError` gets control
  • It can choose to handle the error, or delegate it to the next handler
  • If the error is handler a response is returned
  • If the error is not handled the execution fails reporting the unhandled error

Writing a middleware

const myMiddleware = (config) => {
  
  // might set default options in config
  
  return ({
    before: (handler, next) => {
      // might read options from `config`
    },
    after: (handler, next) => {
      // might read options from `config`
    },
    onError: (handler, next) => {
      // might read options from `config`
    }
  })
}

module.exports = myMiddleware

Inline middlewares

const middy = require('middy')

const handler = middy((event, context, callback) => {
  // do stuff
})

handler.before((handler, next) => {
  // do something in the before phase
  next()
})

handler.after((handler, next) => {
  // do something in the after phase
  next()
})

handler.onError((handler, next) => {
  // do something in the on error phase
  next()
})

module.exports = { handler }

Currently availble middlewares

Json Body Parser

Url Encoded Body Parser

Validator

HTTP Error Handler

In development

That's all folks

(for now!)

Introducing Middy

By Luciano Mammino

Introducing Middy

Introducing Middy: 🛵 The stylish Node.js middleware engine for AWS Lambda

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