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Server/Router type signatures are not grok-able #874

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iitalics opened this issue Dec 28, 2021 · 2 comments
Closed

Server/Router type signatures are not grok-able #874

iitalics opened this issue Dec 28, 2021 · 2 comments

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@iitalics
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Bug Report

Version

0.6.2

Platform

any

Crates

tonic

Description

The type signatures in the Server/Router builders are convoluted and reference private types, which makes them completely un-understandable to users.

For example, from tonic::transport::server::Router:

pub async fn serve<ResBody>(self, addr: SocketAddr) -> Result<(), Error> where
    L: Layer<Routes<A, B, Request<Body>>>,
    L::Service: Service<Request<Body>, Response = Response<ResBody>> + Clone + Send + 'static,
    <<L as Layer<Routes<A, B, Request<Body>>>>::Service as Service<Request<Body>>>::Future: Send + 'static,
    <<L as Layer<Routes<A, B, Request<Body>>>>::Service as Service<Request<Body>>>::Error: Into<Box<dyn Error + Send + Sync>> + Send,
    ResBody: Body<Data = Bytes> + Send + 'static,
    ResBody::Error: Into<Box<dyn Error + Send + Sync>>,

Besides this just being an incredibly complex type signature, users can't derive any information out of it because the type Routes is private. In particular, you can't figure out what the associated types mean (or what the constraints imply) without going to the source code.
@davidpdrsn
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What specific questions do you have?

The trait bounds are not intentionally complicated but exist to enable other features. You're welcome to make suggestions on how to simplify them.

The Routes type is private because users shouldn't have to use it. That'll be changed in #830 which makes the routing simpler, including simplifying some types.

@LucioFranco
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The compiler errors produced from these bounds are what is important. Most of these bounds just add send requirements and in reality can be mostly ignored. Once rust gets proper trait aliases we can consider using those to reduce it. Going to close this but feel free to reopen it if you have any more questions!

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3 participants
@davidpdrsn @iitalics @LucioFranco