How to append response headers to ServeFile?

[wbenny]

I went through various questions here, I spent hours in axum and tower code, and all I can conclude is that I can't simply modify response headers with ServeFile (e.g. add Content-Disposition, like with actix NamedFile::set_content_disposition).

Please tell me that I'm wrong and that I'm overlooking something, because I refuse to believe such fundamental functionality wouldn't be included.

Please, don't tell me to open the file manually and convert it to StreamBody, because that loses all the goodies ServeFile offers (like handling of range headers).

There's a similar discussion here: #608 however that discussion ends exactly at the point where I'm picking this up.

I'm becoming quite hopeless. Is there a way how to do it, without reimplementing the whole ServeFile?

[davidpdrsn]

You can use https://docs.rs/tower-http/0.3.5/tower_http/set_header/response/index.html or https://docs.rs/tower/0.4.13/tower/trait.ServiceExt.html#method.map_response to add additional headers to a response.

[wbenny]

This doesn't work either :/

    let download = download.map_response(
        |record| {
        record
            .headers_mut()
            .insert(
                header::CONTENT_DISPOSITION,
                HeaderValue::from_static("attachment; filename=override.mkv")
            );
        record
    });

[davidpdrsn]

Please elaborate. "Doesn't work" how?

[wbenny]

It doesn't compile. Usage:

    let app = Router::new()
        .route("/download", download);
/* mismatched types expected struct `MethodRouter<Arc<AppState>, _>`
   found struct `tower::util::MapResponse<MethodRouter<(), _> */

[davidpdrsn]

Use .route_service(...) instead of .route(...)

[wbenny]

Thanks a lot! Got it working now :)

[kreibaum]

Thanks for posting this question and answer, it was a great starting point.

The answer from 2023-01-08 not work for me anymore on axum 0.7.2. I ran into Send/Sync issues.
I found a different solution that works 2024-05-12.

Here is the static file where I need to add a header:

.nest_service(
    "/js/lib_worker.min.js",
    ServeFile::new("../target/js/lib_worker.min.js").precompressed_br(),
)

I first define a function to add the header to the response:

async fn credentialless<B>(mut response: Response<B>) -> Response<B> {
    response.headers_mut().insert("cross-origin-embedder-policy", "credentialless".parse().unwrap());
    response
}

Now I can do a similar trick as above, first putting the download service in a variable and then layering a map_response on top of it to add the header:

See: https://docs.rs/axum/latest/axum/middleware/fn.map_response.html

let download: routing::MethodRouter = routing::get_service(
    ServeFile::new("../target/js/lib_worker.min.js").precompressed_br()
).layer(map_response(credentialless));

Finally, I can nest the download service in the router:

.route_service(
    "/js/lib_worker.min.js",
    download,
)

If anyone is curious about the "off topic" bits in the example:

• precompressed_br() - See https://docs.rs/tower-http/latest/tower_http/services/struct.ServeFile.html#method.precompressed_br
• "cross-origin-embedder-policy" - Required for Browsers to activate some performance features.