Remove PendingUpgrade in favor of DeniedUpgrade

[thomaseizinger]

Description

In #2785, we added a PendingUpgrade implementation that is essentially equivalent to DeniedUpgrade apart from also needing a protocol. @mxinden was this on purpose or an oversight? DeniedUpgrade has quite some usage throughout the codebase but I think I prefer the name PendingUpgrade as it reflects the use of futures::pending. At the same time, passing a protocol to PendingUpgrade is unnecessary IMO.

What do people think of removing

Motivation

Having two upgrades with the same functionality is unnecessary.

Current Implementation

Are you planning to do it yourself in a pull request?

Maybe.

[mxinden]

In #2785, we added a PendingUpgrade implementation that is essentially equivalent to DeniedUpgrade apart from also needing a protocol. @mxinden was this on purpose or an oversight?

They serve two different purposes. PendingUpgrade provides a protocol name during multistream-select negotiation, but never proceeds once the protocol has been negotiated. DeniedUpgrade provides no protocol name during multistream-select negotiation, thereby the multistream-select negotiation fails.

I can not think of a use-case for PendingUpgrade beyond testing, though I think that is enough to justify its existence.

Does the above make sense?

[thomaseizinger]

Does make sense, thanks for the explanation!