`BackendClient.sendCommand` method's rejection callback is not invoked

[YegorUdovchenko]

The BackendClient.sendCommand() currently provides the functionality of sending commands with an acknowledgment of a successful delivery and errors occurrence:

• The parameterless successListener is called if no transport errors occurred and the command message meets the validation requirements.
• The errorCallback is called on transport errors, command message validation errors and server runtime errors.

The rejectionCallback that can be passed to sendCommand as a parameter is not invoked currently though.

This issue is to complete/fix the BackendClient.sendCommand() method's functionality so that a rejection callback works as designed.

[armiol]

@dmitrykuzmin please have a look. I think this issue is either obsolete or done.

[dmitrykuzmin]

The ability to pass this callback is still present in the new Client API.

In theory, it can be invoked - when the client app implements a custom filter which rejects the command not with Error but with a RejectionMessage. But I don't really know if it's a valid use case. Standard Spine filters never do that.

This issue, I guess, was originally about callback not being invoked after command leads to a rejection. As we can now observe the events/rejections produced by a command, it's better, in my opinion, to drop the support of this callback altogether.

[armiol]

@dmitrykuzmin let's schedule the removal of this callback and stick with the observation only.