CodeFromError convert the error into XCode interface to response to user client.

ErrHandler is a DIY error process http handler for recognize the XCode ErrHandler is used by applet-api http server as a router middware Hope that http response always is http.statusok and any include the real err.

in this grpc logic, some return error is XCode format , before return to grpc Client, must convert the err (which is XCode format) into gRPC status.

FromProto convert proto message (in gstatus deatils) to XCode ().

GrpcStatusToXCode take out the details(protomessage) in gstatus,and convert it into XCode.

NewCode returns a new Code include all function of XCode.

NewStatus return a new Status generate by Code and it has all method of XCode interface.

Code is athe real implementation of XCode.

XCode is a DIY Error interface.