eth2.0-specs/specs/bellatrix/fork.md

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# Bellatrix -- Fork Logic
## Table of contents
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- [Introduction](#introduction)
- [Configuration](#configuration)
- [Helper functions](#helper-functions)
- [Misc](#misc)
- [Modified `compute_fork_version`](#modified-compute_fork_version)
- [Fork to Bellatrix](#fork-to-bellatrix)
- [Fork trigger](#fork-trigger)
- [Upgrading the state](#upgrading-the-state)
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## Introduction
This document describes the process of Bellatrix upgrade.
## Configuration
| Name | Value |
| - | - |
| `BELLATRIX_FORK_VERSION` | `Version('0x02000000')` |
| `BELLATRIX_FORK_EPOCH` | `Epoch(144896)` (Sept 6, 2022, 11:34:47am UTC) |
## Helper functions
### Misc
#### Modified `compute_fork_version`
```python
def compute_fork_version(epoch: Epoch) -> Version:
"""
Return the fork version at the given ``epoch``.
"""
if epoch >= BELLATRIX_FORK_EPOCH:
return BELLATRIX_FORK_VERSION
if epoch >= ALTAIR_FORK_EPOCH:
return ALTAIR_FORK_VERSION
return GENESIS_FORK_VERSION
```
## Fork to Bellatrix
### Fork trigger
TBD. Social consensus, along with state conditions such as epoch boundary, finality, deposits, active validator count, etc. may be part of the decision process to trigger the fork. For now we assume the condition will be triggered at epoch `BELLATRIX_FORK_EPOCH`.
Note that for the pure Bellatrix networks, we don't apply `upgrade_to_bellatrix` since it starts with Bellatrix version logic.
### Upgrading the state
As with the Phase0-to-Altair upgrade, the `state_transition` is modified to upgrade the `BeaconState`.
The `BeaconState` upgrade runs as part of `process_slots`, slots with missing block proposals do not affect the upgrade time.
If `state.slot % SLOTS_PER_EPOCH == 0` and `compute_epoch_at_slot(state.slot) == BELLATRIX_FORK_EPOCH`, an irregular state change is made to upgrade to Bellatrix.
The upgrade occurs after the completion of the inner loop of `process_slots` that sets `state.slot` equal to `BELLATRIX_FORK_EPOCH * SLOTS_PER_EPOCH`.
When multiple upgrades are scheduled for the same epoch (common for test-networks),
all the upgrades run in sequence before resuming the regular state transition.
```python
def upgrade_to_bellatrix(pre: altair.BeaconState) -> BeaconState:
epoch = altair.get_current_epoch(pre)
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=BELLATRIX_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=ExecutionPayloadHeader(),
)
return post
```