connexion and mangum

[AviranAbady]

I'm trying to deploy connexion using serverless AWS lambda using mangum, post requests with a body payload will fail due to BadRequestProblem("RequestBody is required")

The request body is stored in key "properties" and not in "default" making the validation code miss the body, any idea how to mitigate that?
mangum supports starlette ASGI but I cant get pass the validation.

/connexion/validators/abstract.py

# Handle missing bodies
headers = Headers(scope=scope)
if not int(headers.get("content-length", 0)):
    body = self._schema.get("default")
    if body is None and self._required:
        raise BadRequestProblem("RequestBody is required")
    # The default body is encoded as a `receive` channel to mimic an incoming body
    receive, scope = self._insert_body(receive, body=body, scope=scope)

[FelixSchwarz]

Sorry to be that guy but can you reproduce the issue with a standalone connexion app locally (not running serverless)? If so, could you post a minimal working example and a curl call so we can reproduce the issue?
In exchange for this annoying work, I promise to take 20-30 minutes looking into the problem. Probably that won't help much but at least I can write something here. My hope is that this makes it easier for one of the maintainers to give his opinion (bug, misunderstanding, unsupported, ...).

[AviranAbady]

Hey @FelixSchwarz

Here's a repo reproducing the issue, just run microservice.py, it will run locally, processing input event as if being executed by aws lambda. mangum wraps the wsgi/asgi app and call the API handler for a specific HTTP request according the the input event.

https://github.com/AviranAbady/connexion-mangum-issue

[FelixSchwarz]

Thank you for the nice reproducer. I believe the problem is that you are not sending a Content-Length header. Once I add that to the JSON payload, the handler functions receives the expected body:

def post(body=None):
    print(body)
    return "hello world", 200

Btw: The relevant connexion code can be found in connexion/validators/abstract.py / wrap_receive()

[FelixSchwarz]

btw: #2020 seems to be relevant as well.

[AviranAbady]

Hey @FelixSchwarz , thanks for the quick reply.

I've double checked, it seems that AWS API Gateway strips the content length header, not sure why, using the default configuration for lambda proxy.

it is possible to configure a mapping template in API GW when not using the proxy pass through configuration, I doubt it's the better solution in this case.

Also possible to 'inject' that content length header in the lambda handler itself using event['headers']['content-length'] = len(event['body']).

I understand why you want to avoid consuming the stream ahead of time, but I think that in the case of AWS Serverless this puts connexion at a disadvantage.

[AviranAbady]

I would suggest contacting the mangum maintainers to resolve this issue at runtime through injecting the content-length header with a specific ConnexionAdapter

[FelixSchwarz]

@AviranAbady please note that I'm (mostly) just a Connexion user :-)
If you want specific adaptations for mangum, I guess your best bet is submitting something for mangum. Alternatively try to come up with an Connexion implementation so the header is not strictly required anymore (see #2020).