Is there a way to control errorType in an error response?

[kikuomax]

I would like to handle specific errors from a Lambda handler with a Retry field in a StepFunctions state machine. To capture errors, I have to specify exact names (errorTypes) to ErrorEquals parameter.

As far as I read the code, lambda_runtime uses std::any::type_name_of_val std::any::type_name to produce errorType in error responses, which we should avoid using to affect program behavior.
https://github.com/awslabs/aws-lambda-rust-runtime/blob/a4aa23ecd1d98fdba8f5a671f0959ad743bfe138/lambda-runtime/src/lib.rs#L252-L261

Is there any more reliable way to specify errorType in error responses?

[calavera]

We could introduce some kind of error casting. We could check for it, using type_name_of_val as a fallback. That's just an idea, but if you have any other idea, or want to try to implement it, feel free to open a PR.

[kikuomax]

@calavera Thanks for answering the question. I will give it a shot!

[kikuomax]

• Allow error response customization #828

[evbo]

@kikuomax In your example how do you define main?:
https://github.com/awslabs/aws-lambda-rust-runtime/pull/828/files#diff-ea9f9e8a3273dae249b71b478e9026be91d1ee33c280edec3d1aa25077f7bd11R28

And did you use Cow types for any particular reason? There's no real performance penalty in this case, whereas you might want to use Cow for a function that may or may not returned a borrow of the original input, presuming the input argument is big and expensive to clone.

[evbo]

also, what about Error and Diagnostic being behind a "types" feaure flag?

That way some other crate can be responsible for transforming custom error types into Diagnostic that can be reused by multiple lambdas (without a huge compile footprint)

[kikuomax]

@evbo Custom error response does not matter to main definition. It may be as simple as:

#[tokio::main]
async fn main() -> Result<(), lambda_runtime::Error> {
    lambda_runtime::tracing::init_default_subscriber();
    let func = lambda_runtime::service_fn(my_handler);
    lambda_runtime::run(function_handler).await?;
    Ok(())
}

[kikuomax]

I should have included it in the example.