Implement process_ejections

eth2/beacon/state_machines/forks/serenity/epoch_processing.py

@@ -56,6 +56,9 @@
     get_randao_mix,
     slot_to_epoch,
 )
+from eth2.beacon.validator_status_helpers import (
+    exit_validator,
+)
 from eth2.beacon._utils.hash import (
     hash_eth2,
 )
@@ -784,6 +787,30 @@ def process_rewards_and_penalties(state: BeaconState, config: BeaconConfig) -> B
     return state
 
 
+#
+# Ejections
+#
+def process_ejections(state: BeaconState,
+                      config: BeaconConfig) -> BeaconState:
+    """
+    Iterate through the validator registry and eject active validators
+    with balance below ``EJECTION_BALANCE``.
+    """
+    active_validator_indices = get_active_validator_indices(
+        state.validator_registry,
+        state.current_epoch(config.SLOTS_PER_EPOCH),
+    )
+    for index in set(active_validator_indices):
+        if state.validator_balances[index] < config.EJECTION_BALANCE:
+            state = exit_validator(
+                state,
+                index,
+                slots_per_epoch=config.SLOTS_PER_EPOCH,
+                activation_exit_delay=config.ACTIVATION_EXIT_DELAY,
+            )
+    return state
+
+
 #
 # Validator registry and shuffling seed data
 #

eth2/beacon/state_machines/forks/serenity/state_transitions.py

@@ -20,6 +20,7 @@
 from .epoch_processing import (
     process_justification,
     process_crosslinks,
+    process_ejections,
     process_final_updates,
     process_rewards_and_penalties,
     process_validator_registry,
@@ -90,7 +91,7 @@ def per_epoch_transition(self, state: BeaconState, block: BaseBeaconBlock) -> Be
         state = process_justification(state, self.config)
         state = process_crosslinks(state, self.config)
         state = process_rewards_and_penalties(state, self.config)
-        # TODO: state = process_ejections(state, self.config)
+        state = process_ejections(state, self.config)
         state = process_validator_registry(state, self.config)
         state = process_final_updates(state, self.config)
 

tests/eth2/beacon/state_machines/forks/test_serenity_epoch_processing.py

@@ -29,10 +29,14 @@
 from eth2.beacon.configs import (
     CommitteeConfig,
 )
+from eth2.beacon.constants import (
+    FAR_FUTURE_EPOCH,
+)
 from eth2.beacon.helpers import (
     get_active_validator_indices,
     get_block_root,
     get_epoch_start_slot,
+    get_delayed_activation_exit_epoch,
     get_randao_mix,
     slot_to_epoch,
 )
@@ -50,16 +54,17 @@
 from eth2.beacon.types.pending_attestation_records import PendingAttestationRecord
 from eth2.beacon.state_machines.forks.serenity.epoch_processing import (
     _check_if_update_validator_registry,
-    _update_latest_active_index_roots,
-    process_crosslinks,
-    process_final_updates,
+    _current_previous_epochs_justifiable,
+    _get_finalized_epoch,
     _process_rewards_and_penalties_for_attestation_inclusion,
     _process_rewards_and_penalties_for_crosslinks,
     _process_rewards_and_penalties_for_finality,
-    process_validator_registry,
-    _current_previous_epochs_justifiable,
-    _get_finalized_epoch,
+    _update_latest_active_index_roots,
+    process_crosslinks,
+    process_ejections,
+    process_final_updates,
     process_justification,
+    process_validator_registry,
 )
 
 from eth2.beacon.types.states import BeaconState
@@ -838,6 +843,41 @@ def test_process_rewards_and_penalties_for_crosslinks(
         assert rewards_received[index] == expected_rewards_received[index]
 
 
+#
+# Ejections
+#
+def test_process_ejections(genesis_state, config, activation_exit_delay):
+    current_epoch = 8
+    state = genesis_state.copy(
+        slot=get_epoch_start_slot(current_epoch, config.SLOTS_PER_EPOCH),
+    )
+    delayed_activation_exit_epoch = get_delayed_activation_exit_epoch(
+        current_epoch,
+        activation_exit_delay,
+    )
+
+    ejecting_validator_index = 0
+    validator = state.validator_registry[ejecting_validator_index]
+    assert validator.is_active(current_epoch)
+    assert validator.exit_epoch > delayed_activation_exit_epoch
+
+    state = state.update_validator_balance(
+        validator_index=ejecting_validator_index,
+        balance=config.EJECTION_BALANCE - 1,
+    )
+    result_state = process_ejections(state, config)
+    result_validator = result_state.validator_registry[ejecting_validator_index]
+    assert result_validator.is_active(current_epoch)
+    assert result_validator.exit_epoch == delayed_activation_exit_epoch
+    # The ejecting validator will be inactive at the exit_epoch
+    assert not result_validator.is_active(result_validator.exit_epoch)
+    # Other validators are not ejected
+    assert (
+        result_state.validator_registry[ejecting_validator_index + 1].exit_epoch ==
+        FAR_FUTURE_EPOCH
+    )
+
+
 #
 # Validator registry and shuffling seed data
 #