feat: delta filtering and etag handling

[sjaanus]

This PR handles 2 things

1. Etag handling, so we know what etag we receiving and what to send back
2. Filtering features based on etag and query params

Next PR

1. Automatic tests for client API.
2. Connect to delta cache manager, which is also being developed currently.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

OpenSSF Scorecard

Package	Version	Score	Details
cargo/actix-middleware-etag	0.4.4	Unknown	Unknown
cargo/actix-middleware-etag	>= 0.4.4, < 0.5.0	Unknown	Unknown

Scanned Files

• Cargo.lock
• server/Cargo.toml

[sjaanus]

Get etag from sdk

[sjaanus]

This is moved to delta_filters

[sjaanus]

This is based on filters.rs, which is for filtering old features.

[sighphyre]

What's 100 here? Is the max or something? Hard to know what this is without context, can we put it in a well named const?

[sjaanus]

Thanks, this was oversight actually. fixed.

[sighphyre]

I think the return type of Option<Result> is making your life much harder than it needs to be around error handling here and it makes semantic understanding of the function challenging. Usually this is expressed as Result<Option> for this reason. I also don't think this function has any business converting things to Json, based on its name, that's a higher level responsibility if we can possibly help it. We can also move the check for the feature refresher earlier where it can act as a guard clause before we need to do any work for the building of fiilters. This can all be expressed as

async fn resolve_delta(
    edge_token: EdgeToken,
    token_cache: Data<DashMap<String, EdgeToken>>,
    filter_query: Query<FeatureFilters>,
    requested_revision_id: u32,
    req: HttpRequest,
) -> EdgeResult<Option<ClientFeaturesDelta>> {
    let Some(refresher) = req.app_data::<Data<FeatureRefresher>>() else {
        return Err(EdgeError::ClientHydrationFailed(
            "FeatureRefresher is missing - cannot resolve delta in offline mode".to_string(),
        ));
    };
    let (validated_token, filter_set, ..) =
        get_feature_filter(&edge_token, &token_cache, filter_query.clone())?;
    let delta_filter_set = get_delta_filter(&edge_token, &token_cache, filter_query.clone())?;

    let current_sdk_revision_id = requested_revision_id + 1; // TODO: get from delta manager
    if requested_revision_id >= current_sdk_revision_id {
        return Ok(None);
    }

    let delta = refresher
        .delta_events_for_filter(
            validated_token.clone(),
            &filter_set,
            &delta_filter_set,
            requested_revision_id,
        )
        .await?;

    if !delta.events.is_empty() {
        Ok(Some(delta))
    } else {
        Ok(None)
    }
}

[sjaanus]

Regarding JSON, this is following existing pattern.

unleash-edge/server/src/client_api.rs

Line 163 in 9a26011

Ok(Json(ClientFeatures {

[sjaanus]

Also, Reworked the Option as you suggested. Now it is inside instead. I think its better now.

[sighphyre]

Regarding JSON, this is following existing pattern.

unleash-edge/server/src/client_api.rs

Line 163 in 9a26011

Ok(Json(ClientFeatures {

Yeah but that doesn't work so well with Options, which is why I suggested not using that. I think what you've done is okay though

[sighphyre]

Sure