feat: support multiple error headers

[DanielBauman88]

Issue

smithy-lang/smithy#1170

Description

This change adds support for multiple values in the x-amzn-errortype header. The reason for this is that API-Gateway always adds its own x-amzn-errortype header on gateway responses. This header that APIG adds and does not let the customer configure will almost never match the specific errors that customers model for their API. As an aside, I have logged a feature request for APIG to support configuration of this header - however this is unlikely to be delivered any time soon.

Anyone using this package today to generate clients of their own therefore cannot use gateway responses and have a functioning SDK for their errors. It isn't possible to avoid gateway responses for things like auth/throttling when those are configured on the apig.

This change takes the first header value from x-amzn-errortype if multiple headers are provided. It has no effect when a single header is provided.

An example curl output for a response that this works for:

HTTP/2 401
date: Tue, 09 Aug 2022 21:24:20 GMT
content-type: application/json
content-length: 92
x-amzn-requestid: xxxx
access-control-allow-origin: *
x-amzn-errortype: UnauthorizedError <- set by customer
x-amzn-errortype: UnauthorizedException <- set by API Gateway
x-amz-apigw-id: xxxx
x-amzn-trace-id: Root=xxxx

In this instance this code will select the first header value.

Testing

I built and inspected the codegen/generic-client-test/build/smithyprojections/generic-client-test/echo-service/typescript-codegen/src/protocols/Aws_restJson1.ts file.

Contents is as expected:

        const sanitizeErrorCode = (rawValue: string | number): string => {
            let cleanValue = rawValue;
            if (typeof cleanValue === "number") {
                cleanValue = cleanValue.toString();
            }
            if (cleanValue.indexOf(",") >= 0) {
                cleanValue = cleanValue.split(",")[0];
            }
            if (cleanValue.indexOf(":") >= 0) {
                cleanValue = cleanValue.split(":")[0];
            }

I didn't find tests exercising this client in the repository.

Additional context

There are a few other things that can be considered here

Do we need to support commas in header values, data.code or data["__type"]

I suspect not. A comma isn't valid in a fully qualified structure name for smithy/openapi.
There's code to split on a ":". I don't know what that is for and if we'd ever expect commas before that colon.

Alternatives

I've considered a few alternatives which I'll enumerate below and would be happy to implement.

1. Fetch the x-amzn-errortype string via the service provider interface. Implement a default interface that returns x-amzn-errortype if no provider is specified. This is entirely backwards compatible and allows for customers to use a different header which I think is a net benefit for eventually extracting functionality from the sdk package into the generic smithy implementation. This is actually my ideal solution but it requires a little more code. If you like this please let me know and I'll make this into a PR. See example code here https://github.com/aws/aws-sdk-js-v3/pull/3853/files
2. Check data.code before the headers. I have no idea if this would be a backwards compatible change for the SDKs and I suspect not - but listing for completeness. It would be easy to implement. This would work for our use-case because the body is entirely under our control - apig doesn't insert things like it does in the headers.

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[kuhe]

• run codegen for clients

I can do that and merge when able

[DanielBauman88]

• run codegen for clients

I can do that and merge when able

Hey @kuhe, did you request changes with this comment? Trying to understand if I'm missing something in the ui.

[kuhe]

merging to run codegen on my own branch. I think the build errors are due to smithy being out of date on this branch, and will override.

[kuhe]

#3904

[github-actions]

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