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eth2.0-specs
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Make phase 0 fork choice more modular to more easily adopt for slight modifications in phase 1

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Danny Ryan 2020-01-15 16:03:07 -07:00
parent 8d0e1bda6e
commit 3c07b2c954
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5 changed files with 133 additions and 40 deletions
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2
Makefile
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@ -107,7 +107,7 @@ $(PY_SPEC_PHASE_0_TARGETS): $(PY_SPEC_PHASE_0_DEPS)
python3 $(SCRIPT_DIR)/build_spec.py -p0 $(PHASE0_SPEC_DIR)/beacon-chain.md $(PHASE0_SPEC_DIR)/fork-choice.md $(PHASE0_SPEC_DIR)/validator.md $@
$(PY_SPEC_DIR)/eth2spec/phase1/spec.py: $(PY_SPEC_PHASE_1_DEPS)
python3 $(SCRIPT_DIR)/build_spec.py -p1 $(PHASE0_SPEC_DIR)/beacon-chain.md $(PHASE0_SPEC_DIR)/fork-choice.md $(PHASE1_SPEC_DIR)/custody-game.md $(PHASE1_SPEC_DIR)/beacon-chain.md $(PHASE1_SPEC_DIR)/fraud-proofs.md $(PHASE1_SPEC_DIR)/phase1-fork.md $@
python3 $(SCRIPT_DIR)/build_spec.py -p1 $(PHASE0_SPEC_DIR)/beacon-chain.md $(PHASE0_SPEC_DIR)/fork-choice.md $(PHASE1_SPEC_DIR)/custody-game.md $(PHASE1_SPEC_DIR)/beacon-chain.md $(PHASE1_SPEC_DIR)/fraud-proofs.md $(PHASE1_SPEC_DIR)/fork-choice.md $(PHASE1_SPEC_DIR)/phase1-fork.md $@
# TODO: also build validator spec and light-client-sync

11
scripts/build_spec.py
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@ -230,6 +230,7 @@ def build_phase1_spec(phase0_beacon_sourcefile: str,
phase1_custody_sourcefile: str,
phase1_beacon_sourcefile: str,
phase1_fraud_sourcefile: str,
phase1_fork_choice_sourcefile: str,
phase1_fork_sourcefile: str,
outfile: str=None) -> Optional[str]:
all_sourcefiles = (
@ -238,6 +239,7 @@ def build_phase1_spec(phase0_beacon_sourcefile: str,
phase1_custody_sourcefile,
phase1_beacon_sourcefile,
phase1_fraud_sourcefile,
phase1_fork_choice_sourcefile,
phase1_fork_sourcefile,
)
all_spescs = [get_spec(spec) for spec in all_sourcefiles]
@ -267,8 +269,9 @@ If building phase 1:
3rd argument is input phase1/custody-game.md
4th argument is input phase1/beacon-chain.md
5th argument is input phase1/fraud-proofs.md
6th argument is input phase1/phase1-fork.md
7th argument is output spec.py
6th argument is input phase1/fork-choice.md
7th argument is input phase1/phase1-fork.md
8th argument is output spec.py
'''
parser = ArgumentParser(description=description)
parser.add_argument("-p", "--phase", dest="phase", type=int, default=0, help="Build for phase #")
@ -281,13 +284,13 @@ If building phase 1:
else:
print(" Phase 0 requires spec, forkchoice, and v-guide inputs as well as an output file.")
elif args.phase == 1:
if len(args.files) == 7:
if len(args.files) == 8:
build_phase1_spec(*args.files)
else:
print(
" Phase 1 requires input files as well as an output file:\n"
"\t phase0: (beacon-chain.md, fork-choice.md)\n"
"\t phase1: (custody-game.md, beacon-chain.md, fraud-proofs.md, phase1-fork.md)\n"
"\t phase1: (custody-game.md, beacon-chain.md, fraud-proofs.md, fork-choice.md, phase1-fork.md)\n"
"\t and output.py"
)
else:

97
specs/phase0/fork-choice.md
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@ -24,6 +24,10 @@
- [`get_filtered_block_tree`](#get_filtered_block_tree)
- [`get_head`](#get_head)
- [`should_update_justified_checkpoint`](#should_update_justified_checkpoint)
- [`on_attestation` helpers](#on_attestation-helpers)
- [`validate_on_attestation`](#validate_on_attestation)
- [`store_target_checkpoint_state`](#store_target_checkpoint_state)
- [`update_latest_messages`](#update_latest_messages)
- [Handlers](#handlers)
- [`on_tick`](#on_tick)
- [`on_block`](#on_block)
@ -257,6 +261,59 @@ def should_update_justified_checkpoint(store: Store, new_justified_checkpoint: C
return True
```
#### `on_attestation` helpers
##### `validate_on_attestation`
```python
def validate_on_attestation(store: Store, attestation: Attestation) -> None:
target = attestation.data.target
# Attestations must be from the current or previous epoch
current_epoch = compute_epoch_at_slot(get_current_slot(store))
# Use GENESIS_EPOCH for previous when genesis to avoid underflow
previous_epoch = current_epoch - 1 if current_epoch > GENESIS_EPOCH else GENESIS_EPOCH
assert target.epoch in [current_epoch, previous_epoch]
assert target.epoch == compute_epoch_at_slot(attestation.data.slot)
# Attestations target be for a known block. If target block is unknown, delay consideration until the block is found
assert target.root in store.blocks
# Attestations cannot be from future epochs. If they are, delay consideration until the epoch arrives
assert get_current_slot(store) >= compute_start_slot_at_epoch(target.epoch)
# Attestations must be for a known block. If block is unknown, delay consideration until the block is found
assert attestation.data.beacon_block_root in store.blocks
# Attestations must not be for blocks in the future. If not, the attestation should not be considered
assert store.blocks[attestation.data.beacon_block_root].slot <= attestation.data.slot
# Attestations can only affect the fork choice of subsequent slots.
# Delay consideration in the fork choice until their slot is in the past.
assert get_current_slot(store) >= attestation.data.slot + 1
```
##### `store_target_checkpoint_state`
```python
def store_target_checkpoint_state(store: Store, target: Checkpoint) -> None:
# Store target checkpoint state if not yet seen
if target not in store.checkpoint_states:
base_state = store.block_states[target.root].copy()
process_slots(base_state, compute_start_slot_at_epoch(target.epoch))
store.checkpoint_states[target] = base_state
```
##### `update_latest_messages`
```python
def update_latest_messages(store: Store, attesting_indices: Sequence[ValidatorIndex], attestation: Attestation) -> None:
target = attestation.data.target
beacon_block_root = attestation.data.beacon_block_root
for i in attesting_indices:
if i not in store.latest_messages or target.epoch > store.latest_messages[i].epoch:
store.latest_messages[i] = LatestMessage(epoch=target.epoch, root=beacon_block_root)
```
### Handlers
#### `on_tick`
@ -323,42 +380,14 @@ def on_attestation(store: Store, attestation: Attestation) -> None:
An ``attestation`` that is asserted as invalid may be valid at a later time,
consider scheduling it for later processing in such case.
"""
target = attestation.data.target
validate_on_attestation(store, attestation)
store_target_checkpoint_state(store, attestation.data.target)
# Attestations must be from the current or previous epoch
current_epoch = compute_epoch_at_slot(get_current_slot(store))
# Use GENESIS_EPOCH for previous when genesis to avoid underflow
previous_epoch = current_epoch - 1 if current_epoch > GENESIS_EPOCH else GENESIS_EPOCH
assert target.epoch in [current_epoch, previous_epoch]
assert target.epoch == compute_epoch_at_slot(attestation.data.slot)
# Attestations target be for a known block. If target block is unknown, delay consideration until the block is found
assert target.root in store.blocks
# Attestations cannot be from future epochs. If they are, delay consideration until the epoch arrives
base_state = store.block_states[target.root].copy()
assert get_current_slot(store) >= compute_start_slot_at_epoch(target.epoch)
# Attestations must be for a known block. If block is unknown, delay consideration until the block is found
assert attestation.data.beacon_block_root in store.blocks
# Attestations must not be for blocks in the future. If not, the attestation should not be considered
assert store.blocks[attestation.data.beacon_block_root].slot <= attestation.data.slot
# Store target checkpoint state if not yet seen
if target not in store.checkpoint_states:
process_slots(base_state, compute_start_slot_at_epoch(target.epoch))
store.checkpoint_states[target] = base_state
target_state = store.checkpoint_states[target]
# Attestations can only affect the fork choice of subsequent slots.
# Delay consideration in the fork choice until their slot is in the past.
assert get_current_slot(store) >= attestation.data.slot + 1
# Get state at the `target` to validate attestation and calculate the committees
# Get state at the `target` to fully validate attestation
target_state = store.checkpoint_states[attestation.data.target]
indexed_attestation = get_indexed_attestation(target_state, attestation)
assert is_valid_indexed_attestation(target_state, indexed_attestation)
# Update latest messages
for i in indexed_attestation.attesting_indices:
if i not in store.latest_messages or target.epoch > store.latest_messages[i].epoch:
store.latest_messages[i] = LatestMessage(epoch=target.epoch, root=attestation.data.beacon_block_root)
# Update latest messages for attesting indices
update_latest_messages(store, indexed_attestation.attesting_indices, attestation)
```

52
specs/phase1/fork-choice.md Normal file
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@ -0,0 +1,52 @@
# Ethereum 2.0 Phase 1 -- Beacon Chain Fork Choice
**Notice**: This document is a work-in-progress for researchers and implementers.
## Table of contents
<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
- [Introduction](#introduction)
- [Fork choice](#fork-choice)
- [Handlers](#handlers)
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
<!-- /TOC -->
## Introduction
This document is the beacon chain fork choice spec for part of Ethereum 2.0 Phase 1.
## Fork choice
Due to the changes in the structure of `IndexedAttestation` in Phase 1, `on_attestation` must be re-specified to handle this. The bulk of `on_attestation` has been moved out into a few helpers to reduce code duplication where possible.
The rest of the fork choice remains stable.
### Handlers
```python
def on_attestation(store: Store, attestation: Attestation) -> None:
"""
Run ``on_attestation`` upon receiving a new ``attestation`` from either within a block or directly on the wire.
An ``attestation`` that is asserted as invalid may be valid at a later time,
consider scheduling it for later processing in such case.
"""
validate_on_attestation(store, attestation)
store_target_checkpoint_state(store, attestation.data.target)
# Get state at the `target` to fully validate attestation
target_state = store.checkpoint_states[attestation.data.target]
indexed_attestation = get_indexed_attestation(target_state, attestation)
assert is_valid_indexed_attestation(target_state, indexed_attestation)
# Update latest messages for attesting indices
attesting_indices = [
index for i, index in enumerate(indexed_attestation.committee)
if attestation.aggregation_bits[i]
]
update_latest_messages(store, attesting_indices, attestation)
```

11
tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
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@ -15,8 +15,17 @@ def run_on_attestation(spec, state, store, attestation, valid=True):
indexed_attestation = spec.get_indexed_attestation(state, attestation)
spec.on_attestation(store, attestation)
if spec.version == 'phase0':
sample_index = indexed_attestation.attesting_indices[0]
else:
attesting_indices = [
index for i, index in enumerate(indexed_attestation.committee)
if attestation.aggregation_bits[i]
]
sample_index = attesting_indices[0]
assert (
store.latest_messages[indexed_attestation.attesting_indices[0]] ==
store.latest_messages[sample_index] ==
spec.LatestMessage(
epoch=attestation.data.target.epoch,
root=attestation.data.beacon_block_root,