https://docs.cloud.google.com/java/docs/reference/gax/latest/com.google.api.gax.rpc.OperationCallSettings.Builder.html
Class OperationCallSettings.BuilderRequestT,ResponseT,MetadataT (2.80.0) | Java client libraries...
java clientclass
https://sq.wikipedia.org/wiki/Metadatat
Metadatat - Wikipedia
wikipedia