status-im
/
eth2.0-specs
mirror of https://github.com/status-im/eth2.0-specs.git
2
0
Fork 0
Code Issues Projects Releases Wiki Activity

Merge pull request #2746 from ethereum/vbuterin-patch-12 

Simplify sync protocol and update to calculate optimistic heads
This commit is contained in:
Hsiao-Wei Wang 2021-12-16 00:12:36 +08:00 committed by GitHub
parent 4cd2334bdd de892382db
commit 2fa396f67d
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
5 changed files with 197 additions and 123 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
presets/mainnet/altair.yaml
View File

@ -22,3 +22,5 @@ EPOCHS_PER_SYNC_COMMITTEE_PERIOD: 256
# ---------------------------------------------------------------
# 1
MIN_SYNC_COMMITTEE_PARTICIPANTS: 1
# SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD (= 32 * 256)
UPDATE_TIMEOUT: 8192

2
presets/minimal/altair.yaml
View File

@ -22,3 +22,5 @@ EPOCHS_PER_SYNC_COMMITTEE_PERIOD: 8
# ---------------------------------------------------------------
# 1
MIN_SYNC_COMMITTEE_PARTICIPANTS: 1
# SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD (= 8 * 8)
UPDATE_TIMEOUT: 64

1
setup.py
View File

@ -683,6 +683,7 @@ ignored_dependencies = [
'uint8', 'uint16', 'uint32', 'uint64', 'uint128', 'uint256',
'bytes', 'byte', 'ByteList', 'ByteVector',
'Dict', 'dict', 'field', 'ceillog2', 'floorlog2', 'Set',
'Optional',
]

199
specs/altair/sync-protocol.md
View File

@ -13,12 +13,14 @@
- [Preset](#preset)
- [Misc](#misc)
- [Containers](#containers)
- [`LightClientSnapshot`](#lightclientsnapshot)
- [`LightClientUpdate`](#lightclientupdate)
- [`LightClientStore`](#lightclientstore)
- [Helper functions](#helper-functions)
- [`get_subtree_index`](#get_subtree_index)
- [`get_active_header`](#get_active_header)
- [`get_safety_threshold`](#get_safety_threshold)
- [Light client state updates](#light-client-state-updates)
- [`process_slot_for_light_client_store`](#process_slot_for_light_client_store)
- [`validate_light_client_update`](#validate_light_client_update)
- [`apply_light_client_update`](#apply_light_client_update)
- [`process_light_client_update`](#process_light_client_update)
@ -47,38 +49,27 @@ uses sync committees introduced in [this beacon chain extension](./beacon-chain.
### Misc
| Name | Value |
| - | - |
| `MIN_SYNC_COMMITTEE_PARTICIPANTS` | `1` |
| Name | Value | Notes |
| - | - | - |
| `MIN_SYNC_COMMITTEE_PARTICIPANTS` | `1` | |
| `UPDATE_TIMEOUT` | `SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD` | ~27.3 hours |
## Containers
### `LightClientSnapshot`
```python
class LightClientSnapshot(Container):
# Beacon block header
header: BeaconBlockHeader
# Sync committees corresponding to the header
current_sync_committee: SyncCommittee
next_sync_committee: SyncCommittee
```
### `LightClientUpdate`
```python
class LightClientUpdate(Container):
# Update beacon block header
header: BeaconBlockHeader
# Next sync committee corresponding to the header
# The beacon block header that is attested to by the sync committee
attested_header: BeaconBlockHeader
# Next sync committee corresponding to the active header
next_sync_committee: SyncCommittee
next_sync_committee_branch: Vector[Bytes32, floorlog2(NEXT_SYNC_COMMITTEE_INDEX)]
# Finality proof for the update header
finality_header: BeaconBlockHeader
# The finalized beacon block header attested to by Merkle branch
finalized_header: BeaconBlockHeader
finality_branch: Vector[Bytes32, floorlog2(FINALIZED_ROOT_INDEX)]
# Sync committee aggregate signature
sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE]
sync_committee_signature: BLSSignature
sync_committee_aggregate: SyncAggregate
# Fork version for the aggregate signature
fork_version: Version
```
@ -88,8 +79,18 @@ class LightClientUpdate(Container):
```python
@dataclass
class LightClientStore(object):
snapshot: LightClientSnapshot
valid_updates: Set[LightClientUpdate]
# Beacon block header that is finalized
finalized_header: BeaconBlockHeader
# Sync committees corresponding to the header
current_sync_committee: SyncCommittee
next_sync_committee: SyncCommittee
# Best available header to switch finalized head to if we see nothing else
best_valid_update: Optional[LightClientUpdate]
# Most recent available reasonably-safe header
optimistic_header: BeaconBlockHeader
# Max number of active participants in a sync committee (used to calculate safety threshold)
previous_max_active_participants: uint64
current_max_active_participants: uint64
```
## Helper functions
@ -101,95 +102,157 @@ def get_subtree_index(generalized_index: GeneralizedIndex) -> uint64:
return uint64(generalized_index % 2**(floorlog2(generalized_index)))
```
### `get_active_header`
```python
def get_active_header(update: LightClientUpdate) -> BeaconBlockHeader:
# The "active header" is the header that the update is trying to convince us
# to accept. If a finalized header is present, it's the finalized header,
# otherwise it's the attested header
if update.finalized_header != BeaconBlockHeader():
return update.finalized_header
else:
return update.attested_header
```
### `get_safety_threshold`
```python
def get_safety_threshold(store: LightClientStore) -> uint64:
return max(
store.previous_max_active_participants,
store.current_max_active_participants,
) // 2
```
## Light client state updates
A light client maintains its state in a `store` object of type `LightClientStore` and receives `update` objects of type `LightClientUpdate`. Every `update` triggers `process_light_client_update(store, update, current_slot)` where `current_slot` is the current slot based on some local clock.
A light client maintains its state in a `store` object of type `LightClientStore` and receives `update` objects of type `LightClientUpdate`. Every `update` triggers `process_light_client_update(store, update, current_slot)` where `current_slot` is the current slot based on some local clock. `process_slot_for_light_client_store` is processed every time the current slot increments.
#### `process_slot_for_light_client_store`
```python
def process_slot_for_light_client_store(store: LightClientStore, current_slot: Slot) -> None:
if current_slot % UPDATE_TIMEOUT == 0:
store.previous_max_active_participants = store.current_max_active_participants
store.current_max_active_participants = 0
if (
current_slot > store.finalized_header.slot + UPDATE_TIMEOUT
and store.best_valid_update is not None
):
# Forced best update when the update timeout has elapsed
apply_light_client_update(store, store.best_valid_update)
store.best_valid_update = None
```
#### `validate_light_client_update`
```python
def validate_light_client_update(snapshot: LightClientSnapshot,
def validate_light_client_update(store: LightClientStore,
update: LightClientUpdate,
current_slot: Slot,
genesis_validators_root: Root) -> None:
# Verify update slot is larger than snapshot slot
assert update.header.slot > snapshot.header.slot
# Verify update slot is larger than slot of current best finalized header
active_header = get_active_header(update)
assert current_slot >= active_header.slot > store.finalized_header.slot
# Verify update does not skip a sync committee period
snapshot_period = compute_epoch_at_slot(snapshot.header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
update_period = compute_epoch_at_slot(update.header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
assert update_period in (snapshot_period, snapshot_period + 1)
finalized_period = compute_epoch_at_slot(store.finalized_header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
update_period = compute_epoch_at_slot(active_header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
assert update_period in (finalized_period, finalized_period + 1)
# Verify update header root is the finalized root of the finality header, if specified
if update.finality_header == BeaconBlockHeader():
signed_header = update.header
# Verify that the `finalized_header`, if present, actually is the finalized header saved in the
# state of the `attested header`
if update.finalized_header == BeaconBlockHeader():
assert update.finality_branch == [Bytes32() for _ in range(floorlog2(FINALIZED_ROOT_INDEX))]
else:
signed_header = update.finality_header
assert is_valid_merkle_branch(
leaf=hash_tree_root(update.header),
leaf=hash_tree_root(update.finalized_header),
branch=update.finality_branch,
depth=floorlog2(FINALIZED_ROOT_INDEX),
index=get_subtree_index(FINALIZED_ROOT_INDEX),
root=update.finality_header.state_root,
root=update.attested_header.state_root,
)
# Verify update next sync committee if the update period incremented
if update_period == snapshot_period:
sync_committee = snapshot.current_sync_committee
if update_period == finalized_period:
sync_committee = store.current_sync_committee
assert update.next_sync_committee_branch == [Bytes32() for _ in range(floorlog2(NEXT_SYNC_COMMITTEE_INDEX))]
else:
sync_committee = snapshot.next_sync_committee
sync_committee = store.next_sync_committee
assert is_valid_merkle_branch(
leaf=hash_tree_root(update.next_sync_committee),
branch=update.next_sync_committee_branch,
depth=floorlog2(NEXT_SYNC_COMMITTEE_INDEX),
index=get_subtree_index(NEXT_SYNC_COMMITTEE_INDEX),
root=update.header.state_root,
root=active_header.state_root,
)
sync_aggregate = update.sync_committee_aggregate
# Verify sync committee has sufficient participants
assert sum(update.sync_committee_bits) >= MIN_SYNC_COMMITTEE_PARTICIPANTS
assert sum(sync_aggregate.sync_committee_bits) >= MIN_SYNC_COMMITTEE_PARTICIPANTS
# Verify sync committee aggregate signature
participant_pubkeys = [pubkey for (bit, pubkey) in zip(update.sync_committee_bits, sync_committee.pubkeys) if bit]
participant_pubkeys = [
pubkey for (bit, pubkey) in zip(sync_aggregate.sync_committee_bits, sync_committee.pubkeys)
if bit
]
domain = compute_domain(DOMAIN_SYNC_COMMITTEE, update.fork_version, genesis_validators_root)
signing_root = compute_signing_root(signed_header, domain)
assert bls.FastAggregateVerify(participant_pubkeys, signing_root, update.sync_committee_signature)
signing_root = compute_signing_root(update.attested_header, domain)
assert bls.FastAggregateVerify(participant_pubkeys, signing_root, sync_aggregate.sync_committee_signature)
```
#### `apply_light_client_update`
```python
def apply_light_client_update(snapshot: LightClientSnapshot, update: LightClientUpdate) -> None:
snapshot_period = compute_epoch_at_slot(snapshot.header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
update_period = compute_epoch_at_slot(update.header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
if update_period == snapshot_period + 1:
snapshot.current_sync_committee = snapshot.next_sync_committee
snapshot.next_sync_committee = update.next_sync_committee
snapshot.header = update.header
def apply_light_client_update(store: LightClientStore, update: LightClientUpdate) -> None:
active_header = get_active_header(update)
finalized_period = compute_epoch_at_slot(store.finalized_header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
update_period = compute_epoch_at_slot(active_header.slot) // EPOCHS_PER_SYNC_COMMITTEE_PERIOD
if update_period == finalized_period + 1:
store.current_sync_committee = store.next_sync_committee
store.next_sync_committee = update.next_sync_committee
store.finalized_header = active_header
```
#### `process_light_client_update`
```python
def process_light_client_update(store: LightClientStore, update: LightClientUpdate, current_slot: Slot,
def process_light_client_update(store: LightClientStore,
update: LightClientUpdate,
current_slot: Slot,
genesis_validators_root: Root) -> None:
validate_light_client_update(store.snapshot, update, genesis_validators_root)
store.valid_updates.add(update)
validate_light_client_update(store, update, current_slot, genesis_validators_root)
update_timeout = SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD
sync_committee_bits = update.sync_committee_aggregate.sync_committee_bits
# Update the best update in case we have to force-update to it if the timeout elapses
if (
sum(update.sync_committee_bits) * 3 >= len(update.sync_committee_bits) * 2
and update.finality_header != BeaconBlockHeader()
store.best_valid_update is None
or sum(sync_committee_bits) > sum(store.best_valid_update.sync_committee_aggregate.sync_committee_bits)
):
# Apply update if (1) 2/3 quorum is reached and (2) we have a finality proof.
# Note that (2) means that the current light client design needs finality.
# It may be changed to re-organizable light client design. See the on-going issue consensus-specs#2182.
apply_light_client_update(store.snapshot, update)
store.valid_updates = set()
elif current_slot > store.snapshot.header.slot + update_timeout:
# Forced best update when the update timeout has elapsed
apply_light_client_update(store.snapshot,
max(store.valid_updates, key=lambda update: sum(update.sync_committee_bits)))
store.valid_updates = set()
store.best_valid_update = update
# Track the maximum number of active participants in the committee signatures
store.current_max_active_participants = max(
store.current_max_active_participants,
sum(sync_committee_bits),
)
# Update the optimistic header
if (
sum(sync_committee_bits) > get_safety_threshold(store)
and update.attested_header.slot > store.optimistic_header.slot
):
store.optimistic_header = update.attested_header
# Update finalized header
if (
sum(sync_committee_bits) * 3 >= len(sync_committee_bits) * 2
and update.finalized_header != BeaconBlockHeader()
):
# Normal update through 2/3 threshold
apply_light_client_update(store, update)
store.best_valid_update = None
```

116
tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py
View File

@ -1,3 +1,5 @@
from copy import deepcopy
from eth2spec.test.context import (
spec_state_test,
with_presets,
@ -19,20 +21,24 @@ from eth2spec.test.helpers.sync_committee import (
from eth2spec.test.helpers.merkle import build_proof
@with_altair_and_later
@spec_state_test
def test_process_light_client_update_not_updated(spec, state):
pre_snapshot = spec.LightClientSnapshot(
header=spec.BeaconBlockHeader(),
def _initialize_light_client_store(spec, state):
return spec.LightClientStore(
finalized_header=spec.BeaconBlockHeader(),
current_sync_committee=state.current_sync_committee,
next_sync_committee=state.next_sync_committee,
)
store = spec.LightClientStore(
snapshot=pre_snapshot,
valid_updates=set(),
best_valid_update=None,
optimistic_header=spec.BeaconBlockHeader(),
previous_max_active_participants=0,
current_max_active_participants=0,
)
# Block at slot 1 doesn't increase sync committee period, so it won't update snapshot
@with_altair_and_later
@spec_state_test
def test_process_light_client_update_not_timeout(spec, state):
store = _initialize_light_client_store(spec, state)
# Block at slot 1 doesn't increase sync committee period, so it won't force update store.finalized_header
block = build_empty_block_for_next_slot(spec, state)
signed_block = state_transition_and_sign_block(spec, state, block)
block_header = spec.BeaconBlockHeader(
@ -52,6 +58,10 @@ def test_process_light_client_update_not_updated(spec, state):
block_header.slot,
committee,
)
sync_committee_aggregate = spec.SyncAggregate(
sync_committee_bits=sync_committee_bits,
sync_committee_signature=sync_committee_signature,
)
next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
# Ensure that finality checkpoint is genesis
@ -61,40 +71,34 @@ def test_process_light_client_update_not_updated(spec, state):
finality_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.FINALIZED_ROOT_INDEX))]
update = spec.LightClientUpdate(
header=block_header,
attested_header=block_header,
next_sync_committee=state.next_sync_committee,
next_sync_committee_branch=next_sync_committee_branch,
finality_header=finality_header,
finalized_header=finality_header,
finality_branch=finality_branch,
sync_committee_bits=sync_committee_bits,
sync_committee_signature=sync_committee_signature,
sync_committee_aggregate=sync_committee_aggregate,
fork_version=state.fork.current_version,
)
pre_store = deepcopy(store)
spec.process_light_client_update(store, update, state.slot, state.genesis_validators_root)
assert len(store.valid_updates) == 1
assert store.valid_updates.pop() == update
assert store.snapshot == pre_snapshot
assert store.current_max_active_participants > 0
assert store.optimistic_header == update.attested_header
assert store.finalized_header == pre_store.finalized_header
assert store.best_valid_update == update
@with_altair_and_later
@spec_state_test
@with_presets([MINIMAL], reason="too slow")
def test_process_light_client_update_timeout(spec, state):
pre_snapshot = spec.LightClientSnapshot(
header=spec.BeaconBlockHeader(),
current_sync_committee=state.current_sync_committee,
next_sync_committee=state.next_sync_committee,
)
store = spec.LightClientStore(
snapshot=pre_snapshot,
valid_updates=set(),
)
store = _initialize_light_client_store(spec, state)
# Forward to next sync committee period
next_slots(spec, state, spec.SLOTS_PER_EPOCH * (spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD))
snapshot_period = spec.compute_epoch_at_slot(pre_snapshot.header.slot) // spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD
next_slots(spec, state, spec.UPDATE_TIMEOUT)
snapshot_period = spec.compute_epoch_at_slot(store.optimistic_header.slot) // spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD
update_period = spec.compute_epoch_at_slot(state.slot) // spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD
assert snapshot_period + 1 == update_period
@ -119,6 +123,10 @@ def test_process_light_client_update_timeout(spec, state):
committee,
block_root=spec.Root(block_header.hash_tree_root()),
)
sync_committee_aggregate = spec.SyncAggregate(
sync_committee_bits=sync_committee_bits,
sync_committee_signature=sync_committee_signature,
)
# Sync committee is updated
next_sync_committee_branch = build_proof(state.get_backing(), spec.NEXT_SYNC_COMMITTEE_INDEX)
@ -127,36 +135,30 @@ def test_process_light_client_update_timeout(spec, state):
finality_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.FINALIZED_ROOT_INDEX))]
update = spec.LightClientUpdate(
header=block_header,
attested_header=block_header,
next_sync_committee=state.next_sync_committee,
next_sync_committee_branch=next_sync_committee_branch,
finality_header=finality_header,
finalized_header=finality_header,
finality_branch=finality_branch,
sync_committee_bits=sync_committee_bits,
sync_committee_signature=sync_committee_signature,
sync_committee_aggregate=sync_committee_aggregate,
fork_version=state.fork.current_version,
)
pre_store = deepcopy(store)
spec.process_light_client_update(store, update, state.slot, state.genesis_validators_root)
# snapshot has been updated
assert len(store.valid_updates) == 0
assert store.snapshot.header == update.header
assert store.current_max_active_participants > 0
assert store.optimistic_header == update.attested_header
assert store.best_valid_update == update
assert store.finalized_header == pre_store.finalized_header
@with_altair_and_later
@spec_state_test
@with_presets([MINIMAL], reason="too slow")
def test_process_light_client_update_finality_updated(spec, state):
pre_snapshot = spec.LightClientSnapshot(
header=spec.BeaconBlockHeader(),
current_sync_committee=state.current_sync_committee,
next_sync_committee=state.next_sync_committee,
)
store = spec.LightClientStore(
snapshot=pre_snapshot,
valid_updates=set(),
)
store = _initialize_light_client_store(spec, state)
# Change finality
blocks = []
@ -167,7 +169,7 @@ def test_process_light_client_update_finality_updated(spec, state):
# Ensure that finality checkpoint has changed
assert state.finalized_checkpoint.epoch == 3
# Ensure that it's same period
snapshot_period = spec.compute_epoch_at_slot(pre_snapshot.header.slot) // spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD
snapshot_period = spec.compute_epoch_at_slot(store.optimistic_header.slot) // spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD
update_period = spec.compute_epoch_at_slot(state.slot) // spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD
assert snapshot_period == update_period
@ -199,20 +201,24 @@ def test_process_light_client_update_finality_updated(spec, state):
committee,
block_root=spec.Root(block_header.hash_tree_root()),
)
update = spec.LightClientUpdate(
header=finalized_block_header,
next_sync_committee=state.next_sync_committee,
next_sync_committee_branch=next_sync_committee_branch,
finality_header=block_header, # block_header is the signed header
finality_branch=finality_branch,
sync_committee_aggregate = spec.SyncAggregate(
sync_committee_bits=sync_committee_bits,
sync_committee_signature=sync_committee_signature,
)
update = spec.LightClientUpdate(
attested_header=block_header,
next_sync_committee=state.next_sync_committee,
next_sync_committee_branch=next_sync_committee_branch,
finalized_header=finalized_block_header,
finality_branch=finality_branch,
sync_committee_aggregate=sync_committee_aggregate,
fork_version=state.fork.current_version,
)
spec.process_light_client_update(store, update, state.slot, state.genesis_validators_root)
# snapshot has been updated
assert len(store.valid_updates) == 0
assert store.snapshot.header == update.header
assert store.current_max_active_participants > 0
assert store.optimistic_header == update.attested_header
assert store.finalized_header == update.finalized_header
assert store.best_valid_update is None