aws-lambda-middleware

aws-lambda-middleware

AWS Lambda Middleware

You can simply apply Middleware in Lambda. 
Clean code split is possible, and it includes a simple and extensible Parameter PropTypes validater.

 

Install

npm i aws-lambda-middleware

 

Quick setting

const { Middleware, PropTypes } = require('aws-lambda-middleware')


exports.handler = new Middleware().add({
	queryStringParameters: {
		username: PropTypes.string.isRequired,
		age: PropTypes.integer
	}
}).add(async (event, context, prevData) => {
	const query = event.queryStringParameters

	//your code

	return {
		statusCode: 200,
		body: JSON.stringify({
			message: 'success'
		})
	}
})

 

Options

You can set global options and cluster options.
Setting priority is globalOption < clusterOption < callbackResult

callbackData: {Object} Common data applied during callback

const { Middleware, PropTypes } = require('aws-lambda-middleware')

Middleware.globalOption({
	callbackData: {
		headers: { 'Access-Control-Allow-Origin': '*' }
	}
})

Cluster option can be applied to each middleware.

const { Middleware, PropTypes } = require('aws-lambda-middleware')

exports.handler = new Middleware({
	callbackData: {
		headers: { 'Access-Control-Allow-Origin': '*' }
	}
})

 

Middleware

Middleware

constructor

Param	Type	Description
clusterOption	Object	middleware options

add(handler) : {Middleware}

Add Flow handler & ProType rules

Param	Type	Description
handler	Function	@param {Object} event Lambda event (converted data type) @param {Object} context Lambda context @param {Object} prevData Previous handler return data
handler	Object	PropTypes rules

exports.handler = new Middleware().add(async (event, context, prevData) => {
	if (event.source === 'serverless-plugin-warmup') {
		//If Promise.reject() is returned, execute Lambda handler callback(null, rejectValue) without executing next handler
		return Promise.reject('Lambda is warm!')
	}
}).add({
	//PropTypes do not need to be added as a first flow
	body: {
		username: PropTypes.string.isRequired
	}
}).add(async (event, context, prevData) => {
	//code

	return {
		statusCode: 200,
		body: JSON.stringify({
			message: 'success'
		})
	}
})

Example

exports.handler = new Middleware().add({
	queryStringParameters: {
		age: PropTypes.integer.isRequired
	},
	pathParameters: {
		groupId: PropTypes.integer.isRequired
	}
}).add(async (event, context, prevData) => {
	const query = event.queryStringParameters

	if (query.age > 20) {
		return {
			myName: 'jone'
		}
	} else {
		return Promise.reject({
			statusCode: 404,
			body: JSON.stringify({
				message: 'not found'
			})
		})
	}
}).add(async (event, context, prevData) => {
	const pathParam = event.pathParameters

	console.log(prevData.myName) // 'jone'

	return {
		statusCode: 200,
		body: JSON.stringify({
			message: 'success'
		})
	}
})

 

PropTypes

Parameter PropTypes validater

Support Types

Type	Description
string	String
number	Number or Numberic string
integer	Integer or Integeric string
bool	Boolean or Boolean string
array	Array, isRequired = array.length > 0

exports.handler = new Middleware().add({
	//Validate child property of Lambda event (queryStringParameters, body, pathParameters ...)
	queryStringParameters: {
		//Type + Required
		username: PropTypes.string.isRequired,
		//Only Type (Do not check when there is empty value)
		age: PropTypes.integer
	}
})

addRules(rules)

In addition to the basic rules, new rules can be added.
Adding with the same type name overrides the existing rule.
This setting is applied globally.

Param	Type	Description
rules	Object	-

const { Middleware, PropTypes } = require('aws-lambda-middleware')

PropTypes.addRules({
	//It overrides the existing string rule.
	get string () {
		return PropTypes.makeRule({
			//Valid function to check data type
			validType: (value) => {
				return typeof value === 'string'
			},
			//Valid function to check if it is required
			validRequired: (value) => {
				return value.length > 0
			},
			//A function that converts the value of Paramers when it is incorrectly converted to a string. (Set only when necessary)
			convert: (value) => {
				return String(value)
			}
		})
	},

	//Multiple settings are possible at once
	get number () {
		return PropTypes.makeRule({
			validType: (value) => {
				return ...
			},
			validRequired: (value) => {
				return ...
			},
			convert: (value) => {
				return ...
			}
		})
	}
})

 

Node Version Compatibility

Node.js ^8.3.0