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.
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Co-authored-by: Felix Lange <fjl@twurst.com>
This change implements CommitteeChain which is a key component of the beacon light client. It is a passive data structure that can validate, hold and update a chain of beacon light sync committees and updates, starting from a checkpoint that proves the starting committee through a beacon block hash, header and corresponding state. Once synced to the current sync period, CommitteeChain can also validate signed beacon headers.
