Use a bespoke version of Either

[hlbarber]

Motivation and Context

https://docs.rs/tower/latest/tower/util/enum.Either.html

Both services must be of the same request, response, and error types.

This is not the case, the error types are not required to be the same - as seen in the actual Service implementation. The tower::util::Either instead takes either error and converts it to Box<dyn Error> which is not the intended behavior and conflicts with the contract of Smithy which wants either Infallible in the case of a HTTP middleware and Op::Error in the case of a model middleware.

Description

• Roll bespoke version of Either which preserves error.
• Add Plugin implementation for Plugin.
• Use bespoke Either for FilterByOperationName.

[github-actions]

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• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
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[hlbarber]

I think I should probably pull Either into this module actually, rather than pub mod.

[jjant]

I think I would put Either in its own util module like tower does (given that Either is not just a Plugin, but a Service/Layer/Plugin combinator).

[hlbarber]

Yeah that could work except all these Plugins are kinda utils though?

• Stack
• FilterByOperationName
• OperationNameFn

The only non-util Plugin in this repo is the InstrumentPlugin which lives in a different module - src/instrument/plugin.rs.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python

A new doc preview is ready to view.

[jjant]

The current (tower 0.4.13) behaviour of tower's Either seems to be unintended, see this PR that changes it. It looks like we could use their type after that fix is released in 0.5 or 1.0, so let's keep an eye on that.

I think this is fine to merge in the meantime.

[jjant]

I think I would put Either in its own util module like tower does (given that Either is not just a Plugin, but a Service/Layer/Plugin combinator).

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python

A new doc preview is ready to view.