Support inverted observations for gRPC - #5302
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Closes #DS-3867
Description
Fixes a high-severity bug in the streams-adapter Go runtime: gRPC subscribers to an inverse pair (e.g. a client requesting
TRY/USDagainst a provider that only publishesUSD/TRY) received the un-inverted, reciprocal price — off by a factor matching the pair's magnitude (measured ~2,156x in one case) — delivered under the correct request's payload hash, with no error, flag, or other signal that the denomination was reversed.The HTTP transport already handled this correctly:
respondWithObservationreads each cache item'sRequiresInverseflag and inverts before responding. The gRPC fan-out path inredcon.go'shandleEval, however, published the raw provider observation to every subscriber of a transformed key regardless of that flag, so a client polling over HTTP and a client streaming the same request over gRPC would see different — reciprocal — values for the same underlying cache state.Changes
redcon/redcon.go: thehandleEvalpublish loop now looks up each subscriber's ownRequiresInverseflag (per raw key, since a single provider feed can serve both a direct and an inverse subscriber) before publishing, inverting the observation for inverse subscribers. If inversion fails, that subscriber's update is skipped rather than falling back to publishing the raw (wrong) value.helpers/inversion.go(new):InvertObservationand its private helpers, moved out ofserverso the HTTP and gRPC transports share a single implementation instead of duplicating (and risking diverging on) the reciprocal logic.server/server.go: updated to callhelpers.InvertObservation.