share trailers through matval

[laglangyue]

motivation

close #302
share trailers through matval

how

• remove usage of val trailerPromise = Promise[Metadata]()
• use pekko metadata instead of grpc-java metadata
• will throw class GrpcServiceException(val status: Status, val metadata: Metadata) extends StatusRuntimeException(status, metadata.raw.orNull) instead of StatusRuntimeException (grpc-java)

[Roiocam]

It seems that you missed the deletion of FIXME comment.

[laglangyue]

It seems that you missed the deletion of FIXME comment.

you mean it in title and description? I have removed it.

[Roiocam]

you mean it in title and description? I have removed it.

In the code mentioned in your ISSUE

pekko-grpc/runtime/src/main/scala/org/apache/pekko/grpc/internal/PekkoNettyGrpcClientGraphStage.scala

Lines 169 to 176 in 83bdd04

	def onCallClosed(status: Status, trailers: Metadata): Unit = {
	if (status.isOk()) {
	// FIXME share trailers through matval
	completeStage()
	} else {
	failStage(status.asRuntimeException(trailers))
	}
	call = null