h2 crate still pulled in after disabling "http2" feature

[w-flo]

• I have looked for existing issues (including closed) about this

Bug Report

Version

├── axum v0.7.1
│   ├── axum-core v0.4.0
├── axum-extra v0.9.0
│   ├── axum v0.7.1 (*)
│   ├── axum-core v0.4.0 (*)

Platform

Linux [..] 6.2.0-36-generic #37-Ubuntu SMP PREEMPT_DYNAMIC Wed Oct 4 10:14:28 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

Description

The issue title says it all: After disabling the "http2" feature in axum, the h2 crate is still getting built in in the cargo build process if the "tokio" feature is enabled. I use these (and no hyper dep):

axum = { version = "0.7", default-features = false, features = ["http1", "tokio"] }
axum-extra = { version = "0.9", features = ["cookie"] }

Suspected cause

The reason for this unexpected behavior appears to be that hyper's "http2" feature is still enabled through the optional hyper-util dependency with the "server-auto" feature enabled, which is enabled in axum when enabling the "tokio" feature.

[jplatte]

Can confirm the suspected cause. I think this should likely be considered a bug in hyper-util (though unfortunately fixing it will be a breaking change).

[davidpdrsn]

Moving issue to hyper-util (hyperium/hyper#3493) since we can't do anything about it from axum's side.

[w-flo]

If I understand hyperium/hyper-util#80 correctly, hyper-util now supports enabling just the server feature with http1, which would still make the auto builder available without http2 support.

So if I got that right, axum could now drop the server-auto feature in hyper-util. I think the http1 and http2 features in axum would then need to enable hyper-util?/http1 and hyper-util?/http2, respectively.

[davidpdrsn]

Yes it should be possible to fix now!