Accessing response extensions

[darrell-roberts]

Hi,

I can use AddExtensionLayer with my routes and access the type from a custom extractor and of course the handler functions. I was under the impression that the extensions() from the Response would also have the same extensions accessible to the Request. It seems that this is not the case.

For example:

Router::new()
    .route(
      "/user/:id",
      get(handlers::get_user).layer(AndThenLayer::new(middleware::hash_user)),
    )
...
  .layer(AddExtensionLayer::new(Arc::new(app_config)))

middleware.rs

fn get_hash_prefix(response: &Response<BoxBody>) -> &str {
  response
    .extensions()
    .get::<Arc<AppConfig>>()
    .map(|config| config.hash_prefix.as_str())
    .unwrap_or("default_prefix")
}

pub async fn hash_user(
  response: Response<BoxBody>,
) -> Result<Response<BoxBody>, Infallible> {
  let prefix = get_hash_prefix(&response).to_owned();

  event!(target: FRAMEWORK_TARGET, Level::DEBUG, "Using hash prefix: {prefix}");

  if response.status().is_success() {
    let result = response.map(move |body| {
      boxed(body.map_data(move |bytes| {
        match serde_json::from_slice(&bytes)
          .map(|b: User| b.hash(&prefix))
          .ok()
        {
          Some(hashed) => Bytes::from(serde_json::to_vec(&hashed).unwrap()),
          None => bytes,
        }
      }))
    });
    Ok(result)
  } else {
    Ok(response)
  }
}

The get_hash_prefix always returns the "default_prefix". The Arc<AppConfig> does not appear to be stored in the Response extensions.

[davidpdrsn]

Extensions on the request aren't automatically copied to the response. You have to do that manually for the necessary extensions.

[darrell-roberts]

Ok. That's what I thought. In this case I opted to create middleware via layer_fn. This way I can source the extensions from the request. It's more code then using the AndThenLayer but it works.