Binary output/response?

[repi]

When using lambda_runtime it seems to be hardcoded that one's lambda handler will take JSON as input and output in JSON and it serialises the structures using serde_json. Is it possible to configure this and esp. be able to return binary data with a specified mime type instead of "application/json"?

This would be most useful for lambdas for example responding with image/png, image/jpg and other binary types.

I also tested using lambda-runtime-client directly as then I have control over the deserialising of the request and are able to directly output a binary blob as the response. But the header for the response is fixed to use const API_CONTENT_TYPE: &str = "application/json";.

Have there been any thoughts of how to support and handle binary responses with other mime types?

[sapessi]

Hey @repi - the Lambda runtime API only supports JSON, so one way or another we'll have to translate to JSON. For example, API Gateway handles binary data for lambda by base64 encoding it on the way in and expecting a base64 encoded blob out from Lambda - API Gateway takes care of decoding it before shipping it back as a binary response.

Having said all this, we are working on a refactor of the runtime (#63) that exposes a new crate called lambda-runtime-core. The core runtime implements the "main loop" and expects a handler interface that receives a Vec<u8> and returns a Result<Vec<u8>, StdError + Display + LambdaErrorExt>. Hopefully this will be merged and go out over the next few days.

[repi]

Ok thanks. If one have has a Vec<u8> response/output from a lambda_runtime handler, do you know if there are some attributes one can use on that field to make it base64 encoded?

Because today it looks like it just turned into a json text giant number array which is of course very inefficient for a large binary :)

[repi]

For now I manually specify that the Vec<u8> fields in my input & outputs for the lambda should be base64 encoded/decoded using same technique as described here: serde-rs/json#360

[davidbarsky]

@repi:

Hi Johan! Sorry about the delay.

For now I manually specify that the Vec fields in my input & outputs for the lambda should be base64 encoded/decoded using same technique as described here: serde-rs/json#360

I think that's a reasonable workaround for now!

[repi]

Thanks!

[softprops]

@repi it's unreleased but the lambda-http module handles this automatically for you. I can it's not easy to find because there hasn't been a release published yet but take a look at the body response formats supported https://github.com/awslabs/aws-lambda-rust-runtime/blob/master/lambda-http/src/body.rs. I'll put together a example soon

[repi]

@softprops ah that looks good, thanks!

[sapessi]

Resolving since 0.1 of the lambda-http crate is being pushed now.