Usability nits

[tgeoghegan]

I want to note a grab bag of minor usability nits to see whether the maintainer(s) care about them and/or agree with my suggestions. These would involve changing or adding to public API so there are meaningful maintainability considerations here.

• making clients import both bhttp and ohttp is a chore. Is anyone ever going to use ohttp without bhttp? In particular, this is annoying because I wind up having to define separate enum variants in my error type for ohttp::Error and bhttp::Error, as does glean/Viaduct.
• bhttp has its own bhttp::StatusCode which is an alias for u16. What if this was http::StatusCode instead? Or perhaps there's a good reason that bhttp/ohttp avoid depending on crate http.
• Continuing from that, it'd be nice to have adapters from things like bhttp::Message to things like http::Response or http::Request. These would be easy to gate behind a feature if there's a concern about dragging http into everyone's Cargo.lock.
• decapsulating responses requires unnecessary ceremony in the common case where the response is small and I have the whole thing in memory. See glean/Viaduct: you already have the whole encapsulated response in memory, so it'd be nice to have a one-shot call on ClientResponse that does the Cursor dance for you and spits out a [Message] (or, in the context of Handling ControlData::Request when decapsulating responses is awkward #66, a more specific response type).

[martinthomson]

In general, I'm trying to avoid pulling in a whole lot of dependencies, which the http-related changes would. An adapter (or From/Into implementations) would be OK with a feature gate.

As for ohttp vs. bhttp, the two are completely independent from a code perspective. The convenience functions you are talking about adding might end that, so we can maybe wrap one error in the other for those functions.

I don't have a ton of spare time for doing this work, but I'd be happy to help out with reviews and whatnot.

[DanGould]

What if this was http::StatusCode instead? Or perhaps there's a good reason that bhttp/ohttp avoid depending on crate http.

While avoiding a dependency on http is noble and admirable, I can't think of any environment where bhttp/ohttp would be used without a dependency on http somewhere in the tree.

[martinthomson]

Our use of this crate in Firefox is an example of exactly that, as it happens. Pulling in http would mean a much bigger binary. I'm OK with these conveniences being present, but they would need to be optional, I think.