Currently the typical way to insert a single header into a RequestBuilder is something like (e.g., Range header):

let request = client
    .get(file_url)
    .header(RANGE, format!("bytes={offset}-"));

let mut response = request.send().await?;

I recently discovered the awesome headers crate and wanted to replace the string formatting with something strongly typed. However, there doesn't currently exist a direct way to plug something that implements Header.

One workaround is to construct a HeaderMap, for which headers::HeaderMapExt::typed_insert exists:

use headers::HeaderMapExt;

let request = client
    .get(file_url);

let header_map = {
    let mut header_map = headers::HeaderMap::new();
    let range_header = headers::Range::bytes(offset..).unwrap()
    header_map.typed_insert(range_header);
    header_map
};

let request = request.headers(header_map);

let mut response = request.send().await?;

But to me, the intermediate steps start to diminish the utility of RequestBuilder (at least, since there's only one custom header to insert). Another workaround would be to build the Request, and then add to its internal HeaderMap:

use headers::HeaderMapExt;

let mut request = client
    .get(file_url)
    .build()?;

let header_map = request.headers_mut();
let range_header = headers::Range::bytes(offset..).unwrap()
header_map.typed_insert(range_header);

let mut response = client.execute(request).await?;

but this somewhat feels like Request is doing the job really meant for RequestBuilder.

Ideally, reqwest provides a RequestBuilder::typed_header to directly insert a impl Header instance. Alternatively, headers could expose something like RequestBuilderExt, similar to HeaderMapExt. Although, that might well go beyond the intended scope of headers.

Are there any other solutions that I may have missed? I'm happy to submit a PR for what ever path is most agreeable.

Thank you for reqwest (and headers)!