Axum middleware to rewrite a request such that a version prefix is added to the path. This is based on a set of API versions and an optional "x-api-version" custom HTTP header: if no such header is present, the highest version is used. Yet this only applies to requests the URIs of which pass a filter; others are not rewritten. Also, paths starting with a valid/existing version prefix, e.g. "/v0", are not rewritten.
struct ReadyFilter;
impl ApiVersionFilter for ReadyFilter {
    type Error = Infallible;
    async fn should_rewrite(&self, uri: &Uri) -> Result<bool, Self::Error> {
        Ok(uri.path() != "/")
    }
}
let app = Router::new()
    .route("/", get(ready))
    .route("/v0/test", get(ok_0))
    .route("/v1/test", get(ok_1));
const API_VERSIONS: ApiVersions<2> = ApiVersions::new([0, 1]);
let app = ApiVersionLayer::new(API_VERSIONS, ReadyFilter).layer(app);This code is open source software licensed under the Apache 2.0 License.