Fix ethereum#413

eth2/beacon/configs.py

@@ -52,6 +52,7 @@
         ('ACTIVATION_EXIT_DELAY', int),
         ('EPOCHS_PER_ETH1_VOTING_PERIOD', int),
         ('MIN_VALIDATOR_WITHDRAWABILITY_DELAY', int),
+        ('PERSISTENT_COMMITTEE_PERIOD', int),
         # Reward and penalty quotients
         ('BASE_REWARD_QUOTIENT', int),
         ('WHISTLEBLOWER_REWARD_QUOTIENT', int),

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

@@ -714,7 +714,7 @@ def validate_slashable_attestation(state: 'BeaconState',
 def validate_voluntary_exit(state: 'BeaconState',
                             voluntary_exit: 'VoluntaryExit',
                             slots_per_epoch: int,
-                            activation_exit_delay: int) -> None:
+                            persistent_committee_period: int) -> None:
     validator = state.validator_registry[voluntary_exit.validator_index]
     current_epoch = state.current_epoch(slots_per_epoch)
 
@@ -724,6 +724,8 @@ def validate_voluntary_exit(state: 'BeaconState',
 
     validate_voluntary_exit_epoch(voluntary_exit, current_epoch)
 
+    validate_voluntary_exit_persistent(validator, current_epoch, persistent_committee_period)
+
     validate_voluntary_exit_signature(state, voluntary_exit, validator)
 
 
@@ -760,6 +762,20 @@ def validate_voluntary_exit_epoch(voluntary_exit: 'VoluntaryExit',
         )
 
 
+def validate_voluntary_exit_persistent(validator: 'ValidatorRecord',
+                                       current_epoch: Epoch,
+                                       persistent_committee_period: int) -> None:
+    """
+    # Must have been in the validator set long enough
+    """
+    if current_epoch - validator.activation_epoch < persistent_committee_period:
+        raise ValidationError(
+            "current_epoch - validator.activation_epoch "
+            f"({current_epoch} - {validator.activation_epoch}) should be greater than or equal to "
+            f"PERSISTENT_COMMITTEE_PERIOD ({persistent_committee_period})"
+        )
+
+
 def validate_voluntary_exit_signature(state: 'BeaconState',
                                       voluntary_exit: 'VoluntaryExit',
                                       validator: 'ValidatorRecord') -> None:

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

@@ -52,6 +52,7 @@
     ACTIVATION_EXIT_DELAY=2**2,  # (= 4) epochs
     EPOCHS_PER_ETH1_VOTING_PERIOD=2**4,  # (= 16) epochs
     MIN_VALIDATOR_WITHDRAWABILITY_DELAY=2**8,  # (= 256) epochs
+    PERSISTENT_COMMITTEE_PERIOD=2**11,  # (= 2,048) epochs
     # Reward and penalty quotients
     BASE_REWARD_QUOTIENT=2**10,  # (= 1,024)
     WHISTLEBLOWER_REWARD_QUOTIENT=2**9,  # (= 512)

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

@@ -162,7 +162,7 @@ def process_voluntary_exits(state: BeaconState,
             state,
             voluntary_exit,
             config.SLOTS_PER_EPOCH,
-            config.ACTIVATION_EXIT_DELAY,
+            config.PERSISTENT_COMMITTEE_PERIOD,
         )
         # Run the exit
         state = initiate_validator_exit(state, voluntary_exit.validator_index)

tests/eth2/beacon/conftest.py

@@ -550,6 +550,11 @@ def min_validator_withdrawability_delay():
     return SERENITY_CONFIG.MIN_VALIDATOR_WITHDRAWABILITY_DELAY
 
 
+@pytest.fixture
+def persistent_committee_period():
+    return SERENITY_CONFIG.PERSISTENT_COMMITTEE_PERIOD
+
+
 @pytest.fixture
 def base_reward_quotient():
     return SERENITY_CONFIG.BASE_REWARD_QUOTIENT
@@ -718,6 +723,7 @@ def config(
         activation_exit_delay,
         epochs_per_eth1_voting_period,
         min_validator_withdrawability_delay,
+        persistent_committee_period,
         base_reward_quotient,
         whistleblower_reward_quotient,
         attestation_inclusion_reward_quotient,
@@ -759,6 +765,7 @@ def config(
         ACTIVATION_EXIT_DELAY=activation_exit_delay,
         EPOCHS_PER_ETH1_VOTING_PERIOD=epochs_per_eth1_voting_period,
         MIN_VALIDATOR_WITHDRAWABILITY_DELAY=min_validator_withdrawability_delay,
+        PERSISTENT_COMMITTEE_PERIOD=persistent_committee_period,
         BASE_REWARD_QUOTIENT=base_reward_quotient,
         WHISTLEBLOWER_REWARD_QUOTIENT=whistleblower_reward_quotient,
         ATTESTATION_INCLUSION_REWARD_QUOTIENT=attestation_inclusion_reward_quotient,

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

@@ -15,6 +15,7 @@
     validate_voluntary_exit,
     validate_voluntary_exit_epoch,
     validate_voluntary_exit_initiated_exit,
+    validate_voluntary_exit_persistent,
     validate_voluntary_exit_signature,
     validate_voluntary_exit_validator_exit_epoch,
 )
@@ -29,26 +30,41 @@
         'slots_per_epoch',
         'target_committee_size',
         'activation_exit_delay',
+        'persistent_committee_period',
     ),
     [
-        (40, 2, 2, 2),
+        (40, 2, 2, 2, 16),
     ]
 )
 def test_validate_voluntary_exit(
         genesis_state,
         keymap,
         slots_per_epoch,
-        activation_exit_delay,
+        persistent_committee_period,
         config):
-    state = genesis_state
+    state = genesis_state.copy(
+        slot=get_epoch_start_slot(
+            config.GENESIS_EPOCH + persistent_committee_period,
+            slots_per_epoch
+        ),
+    )
     validator_index = 0
+    validator = state.validator_registry[validator_index].copy(
+        activation_epoch=config.GENESIS_EPOCH,
+    )
+    state = state.update_validator_registry(validator_index, validator)
     valid_voluntary_exit = create_mock_voluntary_exit(
         state,
         config,
         keymap,
         validator_index,
     )
-    validate_voluntary_exit(state, valid_voluntary_exit, slots_per_epoch, activation_exit_delay)
+    validate_voluntary_exit(
+        state,
+        valid_voluntary_exit,
+        slots_per_epoch,
+        persistent_committee_period,
+    )
 
 
 @pytest.mark.parametrize(
@@ -172,6 +188,55 @@ def test_validate_voluntary_exit_epoch(
             validate_voluntary_exit_epoch(voluntary_exit, state.current_epoch(slots_per_epoch))
 
 
+@pytest.mark.parametrize(
+    (
+        'current_epoch',
+        'persistent_committee_period',
+        'activation_epoch',
+        'success',
+    ),
+    [
+        (16, 4, 16 - 4, True),
+        (16, 4, 16 - 4 + 1, False),
+    ]
+)
+def test_validate_voluntary_exit_persistent(
+        genesis_state,
+        keymap,
+        current_epoch,
+        activation_epoch,
+        slots_per_epoch,
+        persistent_committee_period,
+        success):
+    state = genesis_state.copy(
+        slot=get_epoch_start_slot(
+            current_epoch,
+            slots_per_epoch
+        ),
+    )
+    validator_index = 0
+    validator = state.validator_registry[validator_index].copy(
+        activation_epoch=activation_epoch,
+    )
+    state = state.update_validator_registry(validator_index, validator)
+
+    validator_index = 0
+
+    if success:
+        validate_voluntary_exit_persistent(
+            validator,
+            state.current_epoch(slots_per_epoch),
+            persistent_committee_period,
+        )
+    else:
+        with pytest.raises(ValidationError):
+            validate_voluntary_exit_persistent(
+                validator,
+                state.current_epoch(slots_per_epoch),
+                persistent_committee_period,
+            )
+
+
 @pytest.mark.parametrize(
     (
         'num_validators',