ANNOUNCE error codes

[vasilvv]

We currently don't have any specific error codes specified for announce. We should either define some, or merge the space with subscribe errors.

The ones I have in mind are "Internal error", "Announce not supported" (aka this is a delivery-only endpoint), "Permission denied".

[fluffy]

+1

What does the sender do with an "internal Error" ?

[kixelated]

+1

Most of these errors are solely informative since we don't have a REASON string. At a minimum we need "unauthorized" which could be automatically handled by the publisher, but more often will just be presented to the user.

[vasilvv]

What does the sender do with an "internal Error" ?

Probably the same thing one would do in HTTP when you receive a 500 error (which is typically tell the user their operation cannot be finished because the server is broken).

[ianswett]

ANNOUNCE_CANCEL now has error codes as well (#522), so ideally we should fix those at the same time.