Capella

Author: MegaRedHand

spec/fork.md

@@ -30,6 +30,8 @@ Warning: this configuration is not definitive.
 | `ALTAIR_FORK_EPOCH` | `Epoch(74240)` (Oct 27, 2021, 10:56:23am UTC) |
 | `BELLATRIX_FORK_VERSION` | `Version('0x02000000')` |
 | `BELLATRIX_FORK_EPOCH` | `Epoch(144896)` (Sept 6, 2022, 11:34:47am UTC) |
+| `CAPELLA_FORK_VERSION` | `Version('0x03000000')` |
+| `CAPELLA_FORK_EPOCH` | `Epoch(194048)` (April 12, 2023, 10:27:35pm UTC) |
 
 ## Helper functions
 
@@ -42,6 +44,8 @@ def compute_fork_version(epoch: Epoch) -> Version:
     """
     Return the fork version at the given ``epoch``.
     """
+    if epoch >= CAPELLA_FORK_EPOCH:
+        return CAPELLA_FORK_VERSION
     if epoch >= BELLATRIX_FORK_EPOCH:
         return BELLATRIX_FORK_VERSION
     if epoch >= ALTAIR_FORK_EPOCH:
@@ -196,3 +200,91 @@ def upgrade_to_bellatrix(pre: altair.BeaconState) -> BeaconState:
 
     return post
 ```
+
+## Fork to Capella
+
+### Fork trigger
+
+The fork is triggered at epoch `CAPELLA_FORK_EPOCH`.
+
+Note that for the pure Capella networks, we don't apply `upgrade_to_capella` since it starts with Capella version logic.
+
+### Upgrading the state
+
+If `state.slot % SLOTS_PER_EPOCH == 0` and `compute_epoch_at_slot(state.slot) == CAPELLA_FORK_EPOCH`,
+an irregular state change is made to upgrade to Capella.
+
+The upgrade occurs after the completion of the inner loop of `process_slots` that sets `state.slot` equal to `CAPELLA_FORK_EPOCH * SLOTS_PER_EPOCH`.
+Care must be taken when transitioning through the fork boundary as implementations will need a modified [state transition function](../phase0/beacon-chain.md#beacon-chain-state-transition-function) that deviates from the Phase 0 document.
+In particular, the outer `state_transition` function defined in the Phase 0 document will not expose the precise fork slot to execute the upgrade in the presence of skipped slots at the fork boundary. Instead, the logic must be within `process_slots`.
+
+```python
+def upgrade_to_capella(pre: bellatrix.BeaconState) -> BeaconState:
+    epoch = bellatrix.get_current_epoch(pre)
+    latest_execution_payload_header = ExecutionPayloadHeader(
+        parent_hash=pre.latest_execution_payload_header.parent_hash,
+        fee_recipient=pre.latest_execution_payload_header.fee_recipient,
+        state_root=pre.latest_execution_payload_header.state_root,
+        receipts_root=pre.latest_execution_payload_header.receipts_root,
+        logs_bloom=pre.latest_execution_payload_header.logs_bloom,
+        prev_randao=pre.latest_execution_payload_header.prev_randao,
+        block_number=pre.latest_execution_payload_header.block_number,
+        gas_limit=pre.latest_execution_payload_header.gas_limit,
+        gas_used=pre.latest_execution_payload_header.gas_used,
+        timestamp=pre.latest_execution_payload_header.timestamp,
+        extra_data=pre.latest_execution_payload_header.extra_data,
+        base_fee_per_gas=pre.latest_execution_payload_header.base_fee_per_gas,
+        block_hash=pre.latest_execution_payload_header.block_hash,
+        transactions_root=pre.latest_execution_payload_header.transactions_root,
+        withdrawals_root=Root(),  # [New in Capella]
+    )
+    post = BeaconState(
+        # Versioning
+        genesis_time=pre.genesis_time,
+        genesis_validators_root=pre.genesis_validators_root,
+        slot=pre.slot,
+        fork=Fork(
+            previous_version=pre.fork.current_version,
+            current_version=CAPELLA_FORK_VERSION,
+            epoch=epoch,
+        ),
+        # History
+        latest_block_header=pre.latest_block_header,
+        block_roots=pre.block_roots,
+        state_roots=pre.state_roots,
+        historical_roots=pre.historical_roots,
+        # Eth1
+        eth1_data=pre.eth1_data,
+        eth1_data_votes=pre.eth1_data_votes,
+        eth1_deposit_index=pre.eth1_deposit_index,
+        # Registry
+        validators=pre.validators,
+        balances=pre.balances,
+        # Randomness
+        randao_mixes=pre.randao_mixes,
+        # Slashings
+        slashings=pre.slashings,
+        # Participation
+        previous_epoch_participation=pre.previous_epoch_participation,
+        current_epoch_participation=pre.current_epoch_participation,
+        # Finality
+        justification_bits=pre.justification_bits,
+        previous_justified_checkpoint=pre.previous_justified_checkpoint,
+        current_justified_checkpoint=pre.current_justified_checkpoint,
+        finalized_checkpoint=pre.finalized_checkpoint,
+        # Inactivity
+        inactivity_scores=pre.inactivity_scores,
+        # Sync
+        current_sync_committee=pre.current_sync_committee,
+        next_sync_committee=pre.next_sync_committee,
+        # Execution-layer
+        latest_execution_payload_header=latest_execution_payload_header,
+        # Withdrawals
+        next_withdrawal_index=WithdrawalIndex(0),  # [New in Capella]
+        next_withdrawal_validator_index=ValidatorIndex(0),  # [New in Capella]
+        # Deep history valid from Capella onwards
+        historical_summaries=List[HistoricalSummary, HISTORICAL_ROOTS_LIMIT]([]),  # [New in Capella]
+    )
+
+    return post
+```