Add InvokeMethod with CB

[MelamudMichael]

Suggestion for API -

UStatus invokeMethod(const uprotocol::v1::UUri &topic, const uprotocol::utransport::UPayload &payload, const uprotocol::v1::CallOptions &options const uprotocol::utransport::UListener &callback) = 0;

[tamarafischer]

struct RpcResponse { uprotocol::v1::UStatus status; uprotocol::utransport::UMessage message; };

IMHO the response should be a UPayload

Why would a client asking for RPC be interested in anything else? IMHO, keeping it simple and returning the status and the payload has advantages over a UMessage whose purpose in life is to provide state changes.

[stevenhartley]

@MelamudMichael can you please provide documentation/description of to the justifications for the requested API? Is this for C++ only or in the specification for all programming languages?

@tamarafischer are you requesting we go back to UPayload in lieu of returning UMessage? It was a mistake to use UMessage for RpcClient, that I will admit and willing to move back for 1.5.8 to UPayload.

[tamarafischer]

@tamarafischer are you requesting we go back to UPayload in lieu of returning UMessage? It was a mistake to use UMessage for RpcClient, that I will admit and willing to move back for 1.5.8 to UPayload.

No. I am suggesting something new. Not UMessage and Not UPayload.

A new structure that @MelamudMichael provided, with a small change The Struct is called RpcResponseUMessage and contains 2 parts: UStatus - success or failure of the RPC request UPayload - the response from the desination in the case the message was successfully delivered.

Yes going back to using UPayload but adding the Status - @MelamudMichael explained the why

Michael coded his part, I can code the Java and it goes in core and can be a proto message the same way UMessage is. I am also good with a simple interface :)

[stevenhartley]

Closing as duplicate of #82 , moving the proposal to that issue.