Statum/src/StatumDirectives.vala

using Invercargill;
using Invercargill.DataStructures;
using Astralis;

namespace Statum {

    /**
     * Helpers for rendering Statum directive responses.
     */
    public class StatumDirectives : Object {

        /** The content type that distinguishes a Statum directive response. */
        public const string CONTENT_TYPE = "application/vnd.statum+json";

        /**
         * Builds the short-circuit response an endpoint returns when the request
         * carried slots the server does not have in memory: a `transmit(retry)`
         * per missing key (plus an `invalidate` per untrustworthy frame
         * signature). The client re-sends the frames to the slot post endpoint,
         * drops any that fail verification, then re-issues the original request.
         */
        public static HttpResult transmit_result(Lot<string> transmit_keys, Lot<string>? invalid_signatures = null) throws GLib.Error {
            var directives = new Series<Model.DirectiveDto>();
            foreach (var key in transmit_keys) {
                directives.add(new Model.TransmitDirectiveDto.with(key, true));
            }
            return to_result(directives, invalid_signatures);
        }

        /**
         * Renders a lot of directives as the JSON array response served by every
         * directive-returning endpoint, with the Statum content type and
         * `Cache-Control: no-store`.
         *
         * Any invalid frame `signature`s are appended as `invalidate` directives
         * so the client drops slots whose frames the server could not trust.
         * Stale slot keys are auto-signed and appended as `set` directives so the
         * client refreshes outdated snapshots.
         */
        public static HttpResult to_result(
                Lot<Model.DirectiveDto> directives,
                Lot<string>? invalid_signatures = null,
                StateService? state_service = null,
                Lot<string>? stale_keys = null) throws GLib.Error {
            var rendered = new Series<Model.DirectiveDto>();
            foreach (var directive in directives) {
                rendered.add(directive);
            }
            if (invalid_signatures != null) {
                foreach (var signature in (!)invalid_signatures) {
                    rendered.add(new Model.InvalidateDirectiveDto.with_signature(signature));
                }
            }
            if (state_service != null && stale_keys != null) {
                foreach (var key in (!)stale_keys) {
                    var frame = state_service.sign_slot(key);
                    if (frame != null) {
                        rendered.add(new Model.SetDirectiveDto.with_frame((!)frame));
                    }
                }
            }

            var json = Model.DirectiveDto.serialize_array(rendered);
            var result = new HttpStringResult(json.stringify());
            result.set_header("Content-Type", CONTENT_TYPE);
            result.set_header("Cache-Control", "no-store");
            return result;
        }

    }

}