This patch changes separates the business logic of fetching from the process of
fetching itself. It does this through a sans-IO approach, where a `Fetcher`
provides the necessary state to help drive a fetch forward, without performing
any of the IO itself.
What the `Fetcher` cares about is:
- What nodes are going to be attempted to be fetched from
- In what order should they be attempted
- When should the fetching process be considered finished
The `Fetcher` is then used in `radicle-cli` to drive forward the `sync::fetch`
function, allowing it to only care about the IO.
The `no quorum found` error can be opaque and lead to a lot of confusion. It is
better to give more information for this error so that it leads to easier
debugging, since it can be quite a common warning/error.
Instead of a single error, there are two cases provided: `NoCandidates` and
`Diverging`, to capture the two different variants of errors that can occur.
`Display` implementations are provided for both to provide more information.
The failure to set a HEAD ref, due to quourum, during a fetch should not fail
the fetch entirely.
Instead, log the success and failure, or return an error in other cases.
In fact, any failure to set the head could have resulted in notifications not
being sent, nor caching to occur.
The rules for checking the quorum of the remote helper, when pushing to the
canonical branch, can prevent the operator from even attempting to try converge
to a state of agreeance.
Instead, the checking of the quorum rules are relaxed. It is still the case that
if the peer is pushing a diverging commit while in a working state they are
warned and the push does not go through. However, there are two cases where it
is fine to force push a change:
1. When pushing a new tip, as a delegate, there is still a canonical tip and the
new tip still converges with the history, i.e. it is equal to, behind, or
ahead of another delegate tip.
2. If there is no quorum in the current state, for example there were multiple
concurrent pushes, then the peer is free to continue to push to their default
branch in attempt to converge with the other peers.
The example tests ensure that these cases are covered, while also preserving the
old behaviour.
Signed-off-by: Fintan Halpenny <fintan.halpenny@gmail.com>
X-Clacks-Overhead: GNU Terry Pratchett
If a delegate is in a diverged state from the canonical head, ensure
that they can easily reset to another delegate's head to converge
again.
Signed-off-by: Fintan Halpenny <fintan.halpenny@gmail.com>
X-Clacks-Overhead: GNU Terry Pratchett
Fintan Halpenny
Lorenz Leutgeb