Known duty broadcasted

[dB2510]

Problem to be solved

While testing with multiple beacon client implementations when we use same beacon node endpoint for each charon node, it has been found that when a peer broadcasts duty data from core/bcast component it gets an error somewhat similar to PriorAttestationKnown. This happens because some peer in the cluster has sent the duty data (attestation/block) first and when other peers send the same data they get this error. Following is a case where it happens with Lighthouse beacon node on prater:


In first screenshot we can see that node2 has successfully broadcasted its attestation to lighthouse Beacon Node while other 3 nodes failed to do so.
Second screenshot is from Lighthouse logs, where you all can see that it gives error showing reason as: PriorAttestationKnown

Proposed solution

These types of errors should be handled in core/bcast from different implementations of beacon nodes. Since attestation is broadcasted successfully to beacon chain, this shouldn't be an error. Solution may look like:

err = b.eth2Cl.SubmitAttestations(ctx, []*eth2p0.Attestation{&att.Attestation})
if isKnownAttestationError(err) {
    // Assume this is a race with a peer in the cluster.
    err = nil
}
if err == nil {
    log.Info(ctx, "Attestation successfully submitted to beacon node",
        z.Any("delay", b.delayFunc(duty.Slot)),
    )
}