Merge pull request #2927 from etan-status/lc-redundantnext

Allow passing redundant `next_sync_committee`
ethereum · Jun 30, 2022 · abcacca · abcacca
2 parents f810b67 + f5f3031
commit abcacca
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Showing 2 changed files with 23 additions and 7 deletions.
diff --git a/specs/altair/sync-protocol.md b/specs/altair/sync-protocol.md
@@ -16,6 +16,7 @@
   - [`LightClientUpdate`](#lightclientupdate)
   - [`LightClientStore`](#lightclientstore)
 - [Helper functions](#helper-functions)
+  - [`is_sync_committee_update`](#is_sync_committee_update)
   - [`is_finality_update`](#is_finality_update)
   - [`get_subtree_index`](#get_subtree_index)
   - [`get_active_header`](#get_active_header)
@@ -96,6 +97,13 @@ class LightClientStore(object):
 
 ## Helper functions
 
+### `is_sync_committee_update`
+
+```python
+def is_sync_committee_update(update: LightClientUpdate) -> bool:
+    return update.next_sync_committee_branch != [Bytes32() for _ in range(floorlog2(NEXT_SYNC_COMMITTEE_INDEX))]
+```
+
 ### `is_finality_update`
 
 ```python
@@ -189,10 +197,14 @@ def validate_light_client_update(store: LightClientStore,
             root=update.attested_header.state_root,
         )
 
-    # Verify update next sync committee if the update period incremented
-    if update_period == finalized_period:
-        assert update.next_sync_committee_branch == [Bytes32() for _ in range(floorlog2(NEXT_SYNC_COMMITTEE_INDEX))]
+    # Verify that the `next_sync_committee`, if present, actually is the next sync committee saved in the
+    # state of the `active_header`
+    if not is_sync_committee_update(update):
+        assert update_period == finalized_period
+        assert update.next_sync_committee == SyncCommittee()
     else:
+        if update_period == finalized_period:
+            assert update.next_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,

diff --git a/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py b/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py
@@ -42,6 +42,7 @@ def test_process_light_client_update_not_timeout(spec, state):
 
     # Sync committee signing the block_header
     sync_aggregate, signature_slot = get_sync_aggregate(spec, state, block_header)
+    next_sync_committee = spec.SyncCommittee()
     next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
 
     # Ensure that finality checkpoint is genesis
@@ -52,7 +53,7 @@ def test_process_light_client_update_not_timeout(spec, state):
 
     update = spec.LightClientUpdate(
         attested_header=block_header,
-        next_sync_committee=state.next_sync_committee,
+        next_sync_committee=next_sync_committee,
         next_sync_committee_branch=next_sync_committee_branch,
         finalized_header=finality_header,
         finality_branch=finality_branch,
@@ -94,6 +95,7 @@ def test_process_light_client_update_at_period_boundary(spec, state):
 
     # Sync committee signing the block_header
     sync_aggregate, signature_slot = get_sync_aggregate(spec, state, block_header)
+    next_sync_committee = spec.SyncCommittee()
     next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
 
     # Finality is unchanged
@@ -102,7 +104,7 @@ def test_process_light_client_update_at_period_boundary(spec, state):
 
     update = spec.LightClientUpdate(
         attested_header=block_header,
-        next_sync_committee=state.next_sync_committee,
+        next_sync_committee=next_sync_committee,
         next_sync_committee_branch=next_sync_committee_branch,
         finalized_header=finality_header,
         finality_branch=finality_branch,
@@ -146,14 +148,15 @@ def test_process_light_client_update_timeout(spec, state):
     sync_aggregate, signature_slot = get_sync_aggregate(spec, state, block_header)
 
     # Sync committee is updated
+    next_sync_committee = state.next_sync_committee
     next_sync_committee_branch = build_proof(state.get_backing(), spec.NEXT_SYNC_COMMITTEE_INDEX)
     # Finality is unchanged
     finality_header = spec.BeaconBlockHeader()
     finality_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.FINALIZED_ROOT_INDEX))]
 
     update = spec.LightClientUpdate(
         attested_header=block_header,
-        next_sync_committee=state.next_sync_committee,
+        next_sync_committee=next_sync_committee,
         next_sync_committee_branch=next_sync_committee_branch,
         finalized_header=finality_header,
         finality_branch=finality_branch,
@@ -191,6 +194,7 @@ def test_process_light_client_update_finality_updated(spec, state):
     assert snapshot_period == update_period
 
     # Updated sync_committee and finality
+    next_sync_committee = spec.SyncCommittee()
     next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
     finalized_block_header = blocks[spec.SLOTS_PER_EPOCH - 1].message
     assert finalized_block_header.slot == spec.compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)
@@ -212,7 +216,7 @@ def test_process_light_client_update_finality_updated(spec, state):
 
     update = spec.LightClientUpdate(
         attested_header=block_header,
-        next_sync_committee=state.next_sync_committee,
+        next_sync_committee=next_sync_committee,
         next_sync_committee_branch=next_sync_committee_branch,
         finalized_header=finalized_block_header,
         finality_branch=finality_branch,