How can I implement a custom typed header for use with Hyper?

Question

I'd prefer to take advantage of the type safety of Hyper's hyper::header::Headers#get method instead of using get_raw with a &str.

What is the best way to accomplish this?

Answer 1

Digging through the hyper::header::Headers source code, I found that there is a neat macro for generating the code: header!. You will need some incantation to make it useful, though:

#[macro_use]
extern crate hyper;

use hyper::{Body, Method, Request, Response};
use std::fmt::{self, Display};
use std::str::FromStr;
use std::num::ParseIntError;

// For a header that looks like this:
//    x-arbitrary-header-with-an-integer: 8

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ArbitraryNumber(i8);

impl Display for ArbitraryNumber {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Arbitrary Protocol v{}", self.0)
    }
}

impl FromStr for ArbitraryNumber {
    type Err = ParseIntError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        s.parse::<i8>().map(|int| ArbitraryNumber(int))
    }
}

//impl Header for ArbitraryNumberHeader
header! { (ArbitraryNumberHeader, "x-arbitrary-header-with-an-integer") => [ArbitraryNumber] }

Once you've got a Response named res in scope, you can access this header like so:

let arbitrary_header: AribitraryNumber = res.headers().get::<ArbitraryNumberHeader>().unwrap();