Header names with capital letters are not deserialized

[JuliDi]

Headers with (renamed) names that include capital letters fail to deserialize.

For example:

#[derive(Serialize, Deserialize, JsonSchema)]
pub struct MyHeaders {
    header_a: String,
    #[serde(rename = "X-Header-B")]
    header_b: String,
}

#[endpoint {
    method = GET,
    path = "/test",
}]
pub async fn get_test(
    rqctx: RequestContext<AppContext>,
    header_params: Header<MyHeaders>,
) -> Result<HttpResponseOk<()>, HttpError> {
    info!("rqctx headers: {:?}", rqctx.request.headers());
    let headers = header_params.into_inner();
    info!("Headers: {:?}, {:?}", headers.header_a, headers.header_b);

    Ok(HttpResponseOk(()))
}

Using the following request

causes the following error:

thread 'tokio-runtime-worker' panicked at /home/user/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/dropshot-0.16.2/src/extractor/header.rs:53:44:
called `Result::unwrap()` on an `Err` value: "missing field `X-Header-B`"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Jul 18 08:31:05.526 ERRO handler panicked; propogating panic, uri: /test, method: GET, req_id: 921b5a49-668e-4a6a-9e48-284ff37f91cb, remote_addr: 127.0.0.1:60506, local_addr: 127.0.0.1:8020

Removing the #[serde(rename = "X-Header-B")] reveals in the logs:

rqctx headers: {"accept": "application/json, text/plain, */*", "user-agent": "bruno-runtime/2.7.0", "header_a": "header_a value", "x-header-b": "header_b value", "header_b": "header_b value", "request-start-time": "1752827600143", "accept-encoding": "gzip, compress, deflate, br", "host": "localhost:8020", "connection": "keep-alive"}

So the error seems to be caused by "X-Header-B" being renamed to "x-header-b" in the request context. Since HTTP headers are not case-sensitive, I think deserialization should generally not be case sensitive either.

If someone could tell me where to best introduce this change, I am happy to make a PR for this.

As a workaround, it seems like it's sufficient to specify an alias, e.g. #[serde(rename = "X-Header-B", alias = "x-header-b")]

[davepacheco]

Yikes -- sorry about that. It's definitely a problem that Dropshot panicked when it failed to deserialize the header for the extractor. I've filed #1380 for that because it's separate from the question here of how to support headers with a different case.

I am less clear about what to do with the question of case. As you said, HTTP headers are supposed to be case-insensitive. It's the underlying crates here (like http) that "normalize[s headers] to lower case" and I think that's a pretty standard and reasonable way to deal with case-insensitivity (i.e., treat them as all lowercase within the program). And since usually people are extracting these into Rust field names, which also tend to be lowercase, this usually works without people having to think about it. I gather you ran into this because you explicitly renamed the field with some capital letters, right? And if I'm understanding right, it's not that you want capital letters there, but rather you renamed the field (presumably to put the x- prefix in), happened to use a capital letter, and it seemed like it should work. Is that right? That would be consistent with the behavior in the docs I linked to that "when creating a HeaderName with a string, even if upper case characters are included, when getting a string representation of the HeaderName, it will be all lower case." I can see how it would make sense if we could make this work.

I'm not positive about how to do this, but I wonder if it might be as simple as adding .to_lowercase() in the from_map() deserializer -- namely, here, after key:

dropshot/dropshot/src/from_map.rs

Line 382 in 1272cb4

let mut deserializer = MapDeserializer::Value(key);

CC @ahl

[JuliDi]

I gather you ran into this because you explicitly renamed the field with some capital letters, right? And if I'm understanding right, it's not that you want capital letters there, but rather you renamed the field (presumably to put the x- prefix in), happened to use a capital letter, and it seemed like it should work. Is that right?

Exactly, I wanted to add the "x-" prefix and typed it as a capital "X-" for no particular reason.
I expected that it would only make a difference documentation-wise, so the openapi.json would document the header as "key: X-Header-B", and dropshot would deserialize the header regardless of any capitalization.

If it is not possible to fix this without major rewrites, I think some documentation for the Header struct would already be helpful. I could draft a PR for this, once we know whether there is a solution or not.