This PR improves `TestBlockSync` so that it also tests the finality
update validation.
Note: to this date four long and complex (at least partly AI generated)
PRs arrived that did something related to testing finality but honestly
we do not need a bloated "comprehensive" test to test a trivial feature
because maintaining these tests can also be a pain over the long term.
This PR adds some sufficient sanity checks to detect if finality ever
gets broken by a future change.
This PR adds an extra mechanism to sync.HeadSync that tries to retrieve the latest finality update from every server each time it sends an optimistic update in a new epoch (unless we already have a validated finality update attested in the same epoch).
Note that this is not necessary and does not happen if the new finality update is delivered before the optimistic update. The spec only mandates light_client_finality_update events when a new epoch is finalized. If the chain does not finalize for a while then we might need an explicit request that returns a finality proof that proves the same finality epoch from the latest attested epoch.
This adds support for the Deneb beacon chain fork, and fork handling
in general, to the beacon chain light client implementation.
Co-authored-by: Zsolt Felfoldi <zsfelfoldi@gmail.com>
Here we add a beacon chain light client for use by geth.
Geth can now be configured to run against a beacon chain API endpoint,
without pointing a CL to it. To set this up, use the `--beacon.api` flag. Information
provided by the beacon chain is verified, i.e. geth does not blindly trust the beacon
API endpoint in this mode. The root of trust are the beacon chain 'sync committees'.
The configured beacon API endpoint must provide light client data. At this time, only
Lodestar and Nimbus provide the necessary APIs.
There is also a standalone tool, cmd/blsync, which uses the beacon chain light client
to drive any EL implementation via its engine API.
---------
Co-authored-by: Felix Lange <fjl@twurst.com>
