When aggregates are propagated through the network, it is often the case
that a better aggregate has already been seen - in particular, this
happens when an aggregator has not been able to include itself in the
mesh and therefore publishes an aggregate with only its own
attestations.
This new ignore rule allows dropping all aggregates that are
(non-strict) subsets of aggregates that have already been seen on the
network. In particular, it does not mandate dropping aggregates where a
union of previous aggregates would cause it to become a subset).
The logic for allowing this is based on the premise that any aggregate
that has already been seen by a peer will also have been seen by its
neighbours - a subset aggregate (strict or not) brings no new value to
the aggregation algorithm, except in the extreme edge case where you
could combine several such sparse aggregates into a single, more dense
"combined" aggregate and thus use less block space.
Further, as a small benefit, computing the `hash_tree_root` of the full
aggregate is generally not done -however, `hash_tree_root(data)` is
already done for other purposes as this is used as index in the beacon
API.
When nodes are syncing but have not yet reached the canonical `head`,
they cannot determine whether nodes they are connected to serve a valid
history or are making bogus claims in their `Status` advertisement.
Thus, the best course of action that a client can take is to vote for
its "current" best synced head, regardless of whether it's connected to
peers that claim to have other heads or not.
However, in the p2p spec, we penalize such peers with a `REJECT` - this
should be an `IGNORE` instead because this vote is correct per the spec,
albeit "late" according to the validating clients' view of the chain.
The spec reserves the libp2p error code range `[3, 127]` for future use
but actually defines error code `3` as `ResourceUnavailable`. This patch
updates the reserved range to `[4, 127]`.
When a light client updates its `finalized_header` using a forced update
because of the timeout, and the new header was not signed by enough sync
committee participants to pass `get_safety_threshold(store)`, it may
occur that `store.finalized_header.slot > store.optimistic_header.slot`.
This patch ensures that the `optimistic_header` is updated to the latest
`finalized_header` if that happens, so that it always indicates the
latest known and accepted head.
There were a couple instances where a division was used on an epoch
to derive the corresponding sync committee period instead of calling the
`compute_sync_committee_period` function.
These instances were changed to also use the function.
In the light client docs a mentioning of a function trigger is lacking
the `genesis_validators_root` argument. This patch adds that argument
to the documentation to match the real function signature. It also
slightly improves the grammar.
This renames the `sync_committee_aggregate` field of `LightClientUpdate`
to `sync_aggregate` for consistency with the terminology in the rest of
the spec.
Jacek Sieka
Danny Ryan
Mikhail Kalinin
Hsiao-Wei Wang
Etan Kissling
Dustin Brody
Alex Stokes
Paul Hauner
vbuterin