[C++] Custom error_message for grpc::Status::OK

[tnkh...@gmail.com]

Sometimes, I want to return a Status::OK but with a custom message in error_message(). I cannot extract the error_message in a Status::OK from client. I have to change the server to return some random error like UNKNOWN, OUT_OF_RANGE to read error_message() from the server. 

tldr; How can I extract error_message() from a StatusCode::OK in client?

[Menghan Li]

OK status is not designed to include error messages.

Other options are:

 - Send it in the response

 - Send RPC trailer metadata (example: https://github.com/grpc/grpc/tree/master/examples/cpp/metadata)