fix(adapter): handle multi value headers in AWS Lambda

[exoego]

Fixes #2493
Fixes #2495

Fixes for #2493

The current implementation assumes headers are always defined, which is incorrect
headers can be undefined if multiValueHeaders exists,, and vice-versa, sinceheaders and multiValueHeaders are mutually exclusive.

aws-lambda type definition in DefinitelyTyped also does so:

export interface ALBEvent {
   requestContext: ALBEventRequestContext;
   httpMethod: string;
   path: string;
   queryStringParameters?: ALBEventQueryStringParameters | undefined; // URL encoded
   headers?: ALBEventHeaders | undefined;
   multiValueQueryStringParameters?: ALBEventMultiValueQueryStringParameters | undefined; // URL encoded
   multiValueHeaders?: ALBEventMultiValueHeaders | undefined;
   body: string | null;
   isBase64Encoded: boolean;
}

Fixes for #2495

This PR also fixes a conversion from Lambda Event to Request for all event types (ALB, API GW V1/V2).
The current implementation does not extract values from multi-value headers.
The new impl. extract values and delegates those to Request objects, using Header#append.

Author should do the followings, if applicable

• Add tests
• Run tests
• yarn denoify to generate files for Deno

[yusukebe]

Hi @exoego

Thank you for the PR. Looks good to me. But I'd like @watany-dev to review it. @watany-dev Can you do it?

[watany-dev]

It is complicated, but it seems better to maintain runtime_tests/lambda instead of here.

[exoego]

Moved to d51f022
And added tests for APIGW V1 and V2 as well.

[watany-dev]

What is your rationale for this? The documentation does not appear to include multiValueHeaders in ver 2.0. https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-develop-integrations-lambda.html

[exoego]

It simplifies code in my opinion.

It allows

event.multiValueHeaders?.['host']?.[0]

instead of

'multiValueHeaders' in event
      ? event.multiValueHeaders.['host']?.[0]
      : undefined

and it also allows

} else if (event.multiValueHeaders) {
  for (const [k, values] of
    Object.entries(event.multiValueHeaders)) {

instead of

 } else if ('multiValueHeaders' in event) {
  for (const [k, values] of
    Object.entries(event.multiValueHeaders || {})) {

[watany-dev]

Thank you. The implementation is clean, and I think this is good.

---

Note.

Below is a note for when the need arises to completely remove 'multiValueHeaders'.

const createRequest = (event: LambdaEvent) => {
  const queryString = extractQueryString(event)
  const domainName =
    event.requestContext && 'domainName' in event.requestContext
      ? event.requestContext.domainName
      : getHostFromEvent(event)

  const path = isProxyEventV2(event) ? event.rawPath : event.path
  const urlPath = `https://${domainName}${path}`
  const url = queryString ? `${urlPath}?${queryString}` : urlPath

  const headers = new Headers()
  getCookies(event, headers)
  if (event.headers) {
    for (const [k, v] of Object.entries(event.headers)) {
      if (v) {
        headers.set(k, v)
      }
    }
  }
  if (isAPIGatewayProxyEvent(event) && event.multiValueHeaders) {
    for (const [k, values] of Object.entries(event.multiValueHeaders)) {
      if (values) {
        values.forEach((v) => headers.append(k, v))
      }
    }
  }

  const method = isProxyEventV2(event) ? event.requestContext.http.method : event.httpMethod
  const requestInit: RequestInit = {
    headers,
    method,
  }

  if (event.body) {
    requestInit.body = event.isBase64Encoded ? Buffer.from(event.body, 'base64') : event.body
  }

  return new Request(url, requestInit)
}

const getHostFromEvent = (event: LambdaEvent): string => {
  if (!event.headers) {
    return 'localhost'
  }

  if (isAPIGatewayProxyEvent(event)) {
    return event.headers['host'] ?? event.multiValueHeaders?.['host']?.[0] ?? 'localhost'
  } else {
    return event.headers['host'] ?? 'localhost'
  }
}

const isAPIGatewayProxyEvent = (event: LambdaEvent): event is APIGatewayProxyEvent => {
  return 'multiValueHeaders' in event
}

[watany-dev]

Note:
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/lambda-functions.html#multi-value-headers

[watany-dev]

@exoego
Thanks for fixing it. I made a couple of comments, can I ask you to check them out?

[exoego]

@watany-dev Please take a look 🙇

[yusukebe]

Hey @watany-dev, Can you see this?

[watany-dev]

@exoego @yusukebe
Sorry to keep you waiting. I think it's good.

[exoego]

Note) This is not } else if because headers are not optional, at least in type definition in this repo.
It means that we need to take care of headers and multiValueHeaders in tests.

[yusukebe]

@watany-dev Thanks!

I also think it looks good. @exoego Can I merge this now?

[exoego]

@yusukebe Yessss, it's ready to be merged

[yusukebe]

@exoego

Okay! Let's go!