Report came from Gitter -- in a Spring Cloud Stream application, HeaderMapper fields are not customizable in the adapters. In a Processor SCS application, if the Pub/Sub message received from one subscription is passed as-is to a topic, the message will be rejected with:

com.google.api.gax.rpc.InvalidArgumentException: io.grpc.StatusRuntimeException: INVALID_ARGUMENT: The request contains an attribute key that is not valid (key=googclient_deliveryattempt). Attribute keys must be non-empty and must not begin with 'goog' (case-insensitive).

To prevent this issue, PubSubHeaderMapper.outboundHeaderPatterns needs to include "!goog_* by default.