Stringly-typed HeaderValue?

[srijs]

Hi!

Hyper made the design decision to having properly-typed header values, and cites good reasons for it: https://docs.rs/hyper/0.11.6/hyper/header/index.html

I was wondering if it was an explicit design decision in http to not do this, and if so, could someone go into the reasons?

I'm genuinely curious if this could be a nice addition to http, especially since it seems hyper is planning to move to http-provided types in a future version, or whether there are strong reasons against it.

[steveklabnik]

For a quick answer: https://www.reddit.com/r/rust/comments/6qr9mf/announcing_the_http_crate/dkzqcmq/

[srijs]

Cool, thanks @steveklabnik! @seanmonstar, what does this mean for hyper specifically? Will hyper continue to provide the typed header abstraction on top of http?

[seanmonstar]

hyper will eventually replace its usage of Request and Response for those in http (and thus, the associated types like method, status, headers, etc). It needs to do this to in order to allow hyper to be used with frameworks who don't specifically use hyper, but just http.

The typed headers will be moved a separate crate, I imagine. Related hyper issue.

[carllerche]

I have some thoughts re: typed headers (for outside the http crate), but I haven't explored them fully.

[mikeyhew]

@seanmonstar from reddit, linked above

While I still feel that typed headers are a fantastic thing that Rust can provide, they don't fit in http. Some people want them, some people hate them and just use headers.set_raw and headers.get_raw. And, the typed headers do have an overhead to them (it's very minimal, but it's not free).

Can you explain the overhead, and is there a longer explanation why it was decided that typed headers don't fit into the http crate? I feel that since http is supposed to be the standard HTTP crate that the community uses, it is important that a decision like this be explained in detail.

[sagebind]

Just to chime in pseudo-randomly, I personally prefer the "stringly-typed" header values how they are in this crate. Maybe I just have a bad "get off my lawn" attitude, but I know the HTTP headers and generally how they should be written. This crate should worry about the basic HTTP types needed for interoperability, and not whether I'm reading or writing the right content in my HTTP messages. Moreover, I think a big use case is to translate headers from "raw" sources (HTTP parsers, (Fast)CGI, etc.) where typed header values are of little use anyway.

It's also a lot easier to put a typed abstraction on a string-based approach than the other way around.

[vorot93]

Typed headers got lost in transition to Hyper 0.12 after all. What a shame! Now downstream has to take extra care every time a Request or Response is crafted not to screw up.

[sfackler]

@vorot93 https://crates.io/crates/hyperx is one option for typed headers.

[fdubois1]

Is there an easy way to rebuild the typed headers from the HeaderValue ? Because from what I understood, now, the HeaderMap::get(key) will return a HeaderValue.

For example, I used to write something like this :
req.headers().get::()

But now, the get is defined like this :
pub fn get(&self, key: K) -> Option<&T>

The key, if I understand correctly is http::header::IF_MATCH. So I should do something like this :
headers().get(::http::header::IF_MATCH) and this will return a HeaderValue. How can I build the IfMatch type from that ?

Thanks

[saghm]

Hi @fdubois1! I've just run into the same issue myself, and I think I can provide at least a partial solution. Assuming you know which header you want, you can use HeaderMap::get to obtain the HeaderValue that you want, using either a static string or the constant provided by the library (e.g. for the Link header, you can either pass the actual string "link" or this constant). HeaderValue has a to_str method, which lets you get the raw string value of the header, which you can then use to construct the header by using its FromStr implementation. All together, it would look something like this (with the caveat that I haven't compiled or run this snippet):

let header_value = headers.get(::http::header::LINK);
let raw_string = header_value.to_str()?;
let link_header = ::hyperx::header::Link::from_str(raw_string)?;

Converting the entire HeaderMap into a list of hyperx::Header values would be a bit more work, but hopefully this is sufficient for what you need!

[carllerche]

There is ongoing work to provide a crate that includes typed headers.

[seanmonstar]

As stated, work has been happening around this. See #264 for thoughts on where the API should "live".