scandium/entrypoint.js

> Easily deploy any Node.js web server to AWS Lambda.

import net from 'node:net'
import url from 'node:url'
import http from 'node:http'
import stream from 'node:stream'

const kChunks = Symbol('chunks')
const kCallback = Symbol('callback')
const kFromLoadBalancer = Symbol('loadBalancer')

function shouldBase64Encode (headers) {
  /* Every other content-encoding than "identity" is higlhy likely to be binary */
  if ((headers['content-encoding'] || 'identity') !== 'identity') {
    return true
  }

  /* Common text based formats doesn't need to be encoded */
  if (
    /^text\//.exec(headers['content-type']) ||
    /^application\/(dart|(java|ecma|post)script)/.exec(headers['content-type']) ||
    /^application\/(.+\+)?(json|xml)/.exec(headers['content-type'])
  ) {
    return false
  }

  /* Fallback to do the encoding */
  return true
}

function createMultipleHeaderValues (headers) {
  const result = Object.create(null)

  for (const key in headers) {
    if (headers[key] instanceof Array) {
      result[key] = headers[key].map(value => String(value))
    } else {
      result[key] = [String(headers[key])]
    }
  }

  return result
}

function extractMultipleHeaderValues (headers) {
  const result = Object.create(null)

  for (const key in headers) {
    if (headers[key] instanceof Array) {
      result[key] = headers[key]
      delete headers[key]
    }
  }

  return result
}

function extractQueryParameters (event) {
  const result = Object.create(null)

  if (event.multiValueQueryStringParameters) {
    for (const key in event.multiValueQueryStringParameters) {
      // Application Load Balancer doesn't decode query parameters
      result[key] = event.multiValueQueryStringParameters[key].map(value => decodeURIComponent(value))
    }
  } else if (event.queryStringParameters) {
    for (const key in event.queryStringParameters) {
      // API Gateway does decode query parameters
      result[key] = [event.queryStringParameters[key]]
    }
  }

  return result
}

class LambdaSocket extends stream.Duplex {
  constructor (event) {
    super()

    this[kFromLoadBalancer] = (event.requestContext.elb != null)

    const sourceIp = event.requestContext.identity?.sourceIp ?? '127.0.0.1'
    const sourceFamily = net.isIPv6(sourceIp) ? 'IPv6' : 'IPv4'

    this.bufferSize = 0
    this.bytesRead = 0
    this.bytesWritten = 0
    this.connecting = false
    this.destroyed = false
    this.encrypted = true
    this.localAddress = '127.0.0.1'
    this.localPort = 80
    this.readable = false
    this.remoteAddress = sourceIp
    this.remoteFamily = sourceFamily
    this.remotePort = 80
  }

  address () {
    return { port: this.localPort, family: 'IPv4', address: this.localAddress }
  }

  connect () {
    throw new Error('Cannot connect this socket')
  }

  // Nothing to destroy
  destroy () {}

  // Discard all data, it's handled elsewhere
  _write (chunk, encoding, next) { next() }

  // This stream will start ended
  _read () {}
}

class LambdaRequest extends http.IncomingMessage {
  constructor (socket, event) {
    super(socket)

    const rawHeaders = []

    if (event.multiValueHeaders) {
      for (const key of Object.keys(event.multiValueHeaders)) {
        for (const value of event.multiValueHeaders[key]) {
          rawHeaders.push(key)
          rawHeaders.push(value)
        }
      }
    } else if (event.headers) {
      for (const key of Object.keys(event.headers)) {
        rawHeaders.push(key)
        rawHeaders.push(event.headers[key])
      }
    }

    this._addHeaderLines(rawHeaders, rawHeaders.length)

    this.httpVersionMajor = '1'
    this.httpVersionMinor = '1'
    this.httpVersion = '1.1'
    this.complete = true

    this.url = event.rawPath
      ? event.rawPath + (event.rawQueryString ? '?' + event.rawQueryString : '')
      : url.format({ pathname: event.path, query: extractQueryParameters(event) })

    this.method = event.httpMethod ?? event.requestContext?.http?.method

    const body = event.body ? Buffer.from(event.body, event.isBase64Encoded ? 'base64' : 'utf8') : ''

    if (body) {
      if (!('content-length' in this.headers)) {
        this.headers['content-length'] = String(body.byteLength)
      }

      this.push(body)
    }

    this.push(null)
  }
}

class LambdaResponse extends http.ServerResponse {
  constructor (socket, request, cb) {
    super(request)

    this[kChunks] = []
    this[kCallback] = cb

    this.assignSocket(socket)

    this.write = LambdaResponse.prototype.write
    this.end = LambdaResponse.prototype.end
  }

  write (chunk) {
    if (typeof chunk === 'string') {
      chunk = Buffer.from(chunk)
    }

    if (!Buffer.isBuffer(chunk)) {
      throw new TypeError('Invalid non-string/buffer chunk')
    }

    this[kChunks].push(chunk)
  }

  end (chunk) {
    if (chunk) this.write(chunk)

    const headers = this.getHeaders()
    const base64Encode = shouldBase64Encode(headers)
    const body = Buffer.concat(this[kChunks]).toString(base64Encode ? 'base64' : 'utf8')

    let result
    if (this.socket[kFromLoadBalancer]) {
      const multiValueHeaders = createMultipleHeaderValues(headers)

      result = {
        isBase64Encoded: base64Encode,
        statusCode: this.statusCode,
        statusDescription: `${this.statusCode} ${this.statusMessage}`,
        multiValueHeaders,
        body
      }
    } else {
      const multiValueHeaders = extractMultipleHeaderValues(headers)

      result = {
        isBase64Encoded: base64Encode,
        statusCode: this.statusCode,
        headers,
        multiValueHeaders,
        body
      }
    }

    this.emit('finish')

    this[kCallback](null, result)
  }
}

const serverPromise = new Promise((resolve) => {
  let listenCalled = false

  http.Server.prototype.listen = function listen () {
    if (listenCalled) {
      throw new Error('`.listen()` can only be called once when running on Lambda')
    }

    listenCalled = true

    resolve(this)
  }
})

export function handler (event, context, cb) {
  // Lambda will try and wait for the event loop to exhaust. In a web server
  // that typically won't happen because of connection pools to the database,
  // open connections to external services, etc. Tell Lambda to complete the
  // function anyways.
  context.callbackWaitsForEmptyEventLoop = false

  if (event.scandiumInvokeHook) {
    Promise.resolve()
      .then(() => import('./' + event.scandiumInvokeHook.file))
      .then((hooks) => hooks[event.scandiumInvokeHook.hook]())
      .then(() => cb(null), (err) => cb(err))

    return
  }

  const socket = new LambdaSocket(event)
  const request = new LambdaRequest(socket, event)
  const response = new LambdaResponse(socket, request, cb)

  serverPromise.then((server) => server.emit('request', request, response))
}

// Start the actual app
await import('{{MAIN_FILE}}')