A type to represent a valid HeaderValue and String

[seanmonstar]

A HeaderValue may not always be a valid UTF-8 String, and so there is a to_str(&self) -> Result<&str, ToStrError> method that validates the bytes first. To create a String, one could instead do String::from_utf8(value.as_bytes()), but once you have that String, you'll need to re-validate it to turn it back into a HeaderValue.

It would be useful to have a type that represents being both a valid HeaderValue and a valid String at the same time. This type would have a free as_str() method, since it's already been validated, and conversely a free into_value() method (again, because it's already validated).

[seanmonstar]

Naming is hard, but to keep it simple, it could just be HeaderValueString...

[carllerche]

Could you provide examples in which HeaderValueString would be helpful?

[seanmonstar]

As I work on typed headers, a few types are most useful as strings (such as UserAgent). It'd be useful to allow UserAgent::as_str() for free, while still being to able to encode its inner value as a HeaderValue for free.

Other types, while having more specific semantics, still essentially need just a string underneath (like Authorization, Cookie, Server, Referer, and likely others).

[carllerche]

At what point would the UTF-8 check happen?

[seanmonstar]

I'd expect the UTF-8 check to happen when parsing to a typed version, so if it weren't valid UTF-8, the typed version would not parse.

// essentially `struct UserAgent(HeaderValueString)`
let ua = req.headers().typed_get::<UserAgent>();
println!("user-agent: {}", ua.as_str());

[jplatte]

Naming is hard, but to keep it simple, it could just be HeaderValueString...

Another possibility would be Utf8HeaderValue or HeaderValueUtf8. Would make it a little easier to guess what it's about IMHO.

[carllerche]

Another option would be for you to use the String type from the string crate. It would be a private dependency and would not require adding a new type.

You would do String.

[seanmonstar]

Indeed, for now, I've implemented a HeaderValueString externally, it just requires some unsafe blocks. They could be removed if the type were part of http, but it may not be worth it. I'll continue on externally for now.

[hh9527]

SafeHeaderString or HeaderSafeString ?