server: handle context errors returned by service handler

[menghanl]

fixes #5155

RELEASE NOTES:

• server: convert context errors returned by service handlers to status with the correct status code (Canceled or DeadlineExceeded), instead of Unknown

[easwars]

Can we avoid underscores in these error message. They make them really hard to read and add no value. I know this is the way many existing tests report errors, but do we need to continue doing it.

[menghanl]

Are you suggesting deleting _,?

[easwars]

Yes, thanks :)

[dfawley]

add no value

I have to disagree on this a bit. They show the parameter/return signature of the function being called accurately. If a function accepts 3 values and returns 3, but you only show 1 or 2 of each of them, how do you know what the values represent?

If you want to remove them here then don't imply the function only returns one value. Do something like this instead:

t.Fatalf("ss.Client.EmptyCall() got error %v; want status with Code()=DeadlineExceeded", err)

[menghanl]

Done

[dfawley]

Please update the docstrings here:

grpc-go/stream.go

Lines 48 to 52 in 14c1138

	// StreamHandler defines the handler called by gRPC server to complete the
	// execution of a streaming RPC. If a StreamHandler returns an error, it
	// should be produced by the status package, or else gRPC will use
	// codes.Unknown as the status code and err.Error() as the status message
	// of the RPC.

and here:

grpc-go/interceptor.go

Lines 74 to 77 in 14c1138

	// UnaryHandler defines the handler invoked by UnaryServerInterceptor to complete the normal
	// execution of a unary RPC. If a UnaryHandler returns an error, it should be produced by the
	// status package, or else gRPC will use codes.Unknown as the status code and err.Error() as
	// the status message of the RPC.

[menghanl]

Done