* Ignore subset aggregates
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.
* add subset ignore rule to sync contributions as well
* typo
As the sync committee signs the previous block, the situation arises at
every sync committee period boundary, that the new sync committee signs
a block in the previous sync committee period. The light client cannot
reliably detect this condition (e.g., assume that this is the case when
it is currently on the last slot of a sync committee period), because
the last couple slots of a sync committee period may not have a block.
For example, when receiving a `LightClientUpdate` that is constructed
as in the following illustration, it is unknown whether `sync_aggregate`
was signed by the current or next sync committee at `attested_header`.
```
slot N N + 1 | N + 2 (slot not sent!)
|
+-----------------+ \ / | +----------------+
| attested_header | <--- X ----|---- | sync_aggregate |
+-----------------+ / \ | +----------------+
missed |
|
sync committee
period boundary
```
This patch addresses this edge case by including the slot at which the
`sync_aggregate` was created into the `LightClientUpdate` object.
Note that the `signature_slot` cannot be trusted beyond the purpose of
signature verification, as it could be manipulated to any other slot
within the same sync committee period and fork version, without making
the `sync_aggregate` invalid.
Documentation on how to call `prepare_execution_payload` had the params
for `safe_block_hash` and `finalized_block` hash flipped compared to the
function definition. Also updated tests for consistency.
Jacek Sieka
Alex Stokes
Danny Ryan
ChihChengLiang
terencechain
Mikhail Kalinin
Hsiao-Wei Wang
Justin Traglia
Caspar Schwarz-Schilling
Michael Sproul
Etan Kissling
Dmitrii Shmatko
Ben Edgington