fix: backtracking when fallback is enabled #166
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leviramsey
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pvlugter
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core/src/main/scala/akka/persistence/dynamodb/internal/QueryDao.scala
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pvlugter
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core/src/main/scala/akka/persistence/dynamodb/internal/QueryDao.scala
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The
QueryDaoNPEs when backtracking over fallback breadcrumb items, as it expects theEventSerIdattribute to be set, when it's not.Fix is to use a
dummyzero serializer ID for breadcrumb items when backtracking. Since the only query for events which backtracks is theeventsBySlicequery which only uses the serializer ID to:FilteredPayloadserializer ID to mark the resulting envelope as filteredany serializer ID would do; zero is chosen as it's Akka-reserved but otherwise unused
but (for the absolute avoidance of confusion), this fix selects (on encountering the first fallback breadcrumb while backtracking) a serializer ID which is not bound to a serializer (since there are 4 billion legal serializer IDs (assuming negative IDs are allowed) and it's unlikely that a real system has even 4 thousand serializers (thus the chances are likely better than 999,999 in a million that any guess finds an unbound ID), it should be quick to find such an ID). Since the by-slice queries emit event envelopes and envelopes from backtracking leave the event empty, this dummy serializer ID doesn't get exposed to the user.