How to extract custom Header

[woile]

Hello people, thanks for this awesome framework. I've been struggling to extract a custom header. I'm trying to parse a git webhook with header X-Event-Key. I created an enum EventKey and I implemented the FromStr. I realize somewhere I need to provide the name of the X-Event-Key but I just don't understand where or how. I started digging a bit and TypeHeader seems to be what I need, but my enum is missing some implementation, from the error I get I don't understand what am I missing. I went into a rabbit hole reading the headers crate, but still I couldn't make it work. It's Friday evening so maybe I'm a bit tired already haha.

#[derive(Deserialize, Debug, Clone)]
enum EventKey {
    RepoPush,
}

impl FromStr for EventKey {
    type Err = AppError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "repo:push" => Ok(Self::RepoPush),
            _ => Err(AppError::InvalidHeader),
        }
    }
}

async fn webhook_handler(event_type: TypedHeader<EventKey>) -> Response {
    println!("{event_type:?}");
    return (StatusCode::OK, String::from("Ok")).into_response();
}

The error I get:

---- ^^^^^^^^^^^^^^^ the trait `Handler<_, _, _>` is not implemented for `fn(TypedHeader<EventKey>) -> impl Future<Output = Response<http_body::combinators::box_body::UnsyncBoxBody<axum::body::Bytes, axum::Error>>> {webhook_handler}`
    |                     |
    |                     required by a bound introduced by this call

I'm now trying to implement the Header trait, but it requires a reference to a HeaderName, which I don't know how to implement 😅

Thanks in advance!!

[davidpdrsn]

Don't bother with TypedHeader for something like this. Either write your own FromRequest implementation or extract HeaderMap directly.

[woile]

Thanks! I'll give it a try. So TypedHeader is mostly for standardize headers?

[davidpdrsn]

It is for headers defined in this crate https://docs.rs/headers/0.3.8/headers/

[woile]

Thanks David! Using HeaderMap worked 👍🏻 , I ended up implementing FromStr in my enum and now it looks something like:

async fn webhook_handler(event_type: HeaderMap) {
    let event_key = event_type
        .get(EVENT_KEY_HEADER)
        .ok_or(AppError::HeaderNotFound(EVENT_KEY_HEADER.into()))?
        .to_str()
        .map_err(|_| AppError::InvalidHeader)?
        .parse::<EventKey>()?;
    println!("{event_key:?}");

[vlad-ivanov-name]

for anyone stumbling upon this in 2025 (and probably later?), here's how you can define a custom string header that works with axum extractors:

macro_rules! define_string_header {
    ($type_name:ident, $header_str:expr) => {
        pub struct $type_name {
            value: String,
        }

        impl ::headers::Header for $type_name {
            fn name() -> &'static ::axum::http::HeaderName {
                static HEADER_NAME: ::axum::http::HeaderName =
                    ::axum::http::HeaderName::from_static($header_str);
                &HEADER_NAME
            }

            fn decode<'i, I>(values: &mut I) -> Result<Self, ::headers::Error>
            where
                Self: Sized,
                I: Iterator<Item = &'i ::axum::http::HeaderValue>,
            {
                let value = values
                    .next()
                    .ok_or_else(::headers::Error::invalid)?
                    .to_str()
                    .map_err(|_| ::headers::Error::invalid())?
                    .to_string();

                Ok(Self { value })
            }

            fn encode<E: Extend<axum::http::HeaderValue>>(&self, values: &mut E) {
                values.extend(std::iter::once(
                    self.value.parse().expect("failed to encode header"),
                ));
            }
        }

        impl std::fmt::Display for $type_name {
            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
                write!(f, "{}", self.value)
            }
        }
    };
}

define_string_header!(MyHeader, "x-my-header");