Lambda-Stream

This library adds types and local support for AWS Lambda Response Streaming. Locally, it'll buffer and return the entire response.

In AWS Lambda, it'll simply use the global awslambda.streamifyResponse.

This library exposes a ResponseStream class, the streamifyResponse method, and isInAWS method. Types are also included.

Why?

AWS added Lambda Response Streaming directly into the NodeJS runtime as a global method, instead of providing it with the AWS-SDK.

This makes functions leveraging Lambda Response Streaming difficult to test, run locally, or even write Lambda functions using a typical editor. Magic, runtime-only methods are a drag on developer experience!

So I wrote this library to fill that gap

End of Life

This library shouldn't exist.

If or when AWS decides to release and support a library which makes AWS Lambda Streaming Responses usable and testable locally, I'll happily archive this project.

Examples

Works like this:

import { APIGatewayProxyEvent } from 'aws-lambda'
import { streamifyResponse, ResponseStream } from 'lambda-stream'

export const handler = streamifyResponse(myHandler)

async function myHandler(
  event: APIGatewayProxyEvent,
  responseStream: ResponseStream
): Promise<void> {
  console.log('Handler got event:', event)
  responseStream.setContentType('text/plain')
  responseStream.write('Hello, world!')
  responseStream.end()
}

Or in commonjs:

'use strict'
const { streamifyResponse } = require('lambda-stream')

module.exports.hello = streamifyResponse(
  async (event, responseStream, context) => {
    responseStream.setContentType('text/plain')
    responseStream.write('Hello, world!')
    responseStream.end()
  }
)

Pipelining is also supported:

const pipeline = require('util').promisify(require('stream').pipeline)
const { Readable } = require('stream')
const { streamifyResponse } = require('lambda-stream')

const handler = async (event, responseStream, _context) => {
  // As an example, convert event to a readable stream.
  requestStream = Readable.from(Buffer.from(JSON.stringify({ hello: 'world' })))

  await pipeline(requestStream, zlib.createGzip(), responseStream)
}

module.exports.gzip = streamifyResponse(handler)