Cross-cutting logic around gRPC service calls, such as authentication, logging or metrics.

The interceptor runs before the request is unmarshalled. It can reject the call by returning a failed CompletionStage, for example with a akka.grpc.GrpcServiceException, which is turned into a gRPC error response using the default exception mapping of GrpcExceptionHandler. It can pass information to a Power API service implementation by adding request attributes, which are then available through Metadata.getAttribute. It can also wrap the response to observe the outcome of the call.

The interceptor is called from the server stream and must not block. The request entity is a stream that can only be consumed once, so an interceptor that reads it must not pass the same request to next.

Errors in streamed responses happen after the response headers are sent and are not visible to interceptors.