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cleanup per slot processing

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Danny Ryan 2018-12-05 12:40:08 -06:00
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specs/core/0_beacon-chain.md
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@ -360,7 +360,6 @@ Unless otherwise indicated, code appearing in `this style` is to be interpreted
# Recent state
'latest_crosslinks': [CrosslinkRecord],
'latest_state_recalculation_slot': 'uint64',
'latest_block_hashes': ['hash32'], # Needed to process attestations, older to newer
'latest_penalized_exit_balances': ['uint64'], # Balances penalized at every withdrawal period
'latest_attestations': [PendingAttestationRecord],
@ -682,7 +681,7 @@ We now define the state transition function. At a high level the state transitio
1. The per-slot transitions, which happens every slot, and only affects a parts of the `state`.
2. The per-epoch transitions, which happens at every epoch boundary (i.e. `state.slot % EPOCH_LENGTH == 0`), and affects the entire `state`.
The per-epoch transitions focus on the [validator](#dfn-validator) registry, including adjusting balances and activating and exiting [validators](#dfn-validator), as well as processing crosslinks and managing block justification/finalization. The per-slot transitions generally focuses on verifying aggregate signatures and saving temporary records relating to the per-slot activity in the `BeaconState`.
The per-slot transitions generally focus on verifying aggregate signatures and saving temporary records relating to the per-slot activity in the `BeaconState`. The per-epoch transitions focus on the [validator](#dfn-validator) registry, including adjusting balances and activating and exiting [validators](#dfn-validator), as well as processing crosslinks and managing block justification/finalization.
### Helper functions
@ -835,7 +834,7 @@ def get_shard_committees_at_slot(state: BeaconState,
"""
Returns the ``ShardCommittee`` for the ``slot``.
"""
earliest_slot_in_array = state.latest_state_recalculation_slot - EPOCH_LENGTH
earliest_slot_in_array = state.slot - (state.slot % EPOCH_LENGTH) - EPOCH_LENGTH
assert earliest_slot_in_array <= slot < earliest_slot_in_array + EPOCH_LENGTH * 2
return state.shard_committees_at_slots[slot - earliest_slot_in_array]
```
@ -844,22 +843,22 @@ def get_shard_committees_at_slot(state: BeaconState,
```python
def get_block_hash(state: BeaconState,
current_block: BeaconBlock,
slot: int) -> Hash32:
"""
Returns the block hash at a recent ``slot``.
"""
earliest_slot_in_array = current_block.slot - len(state.latest_block_hashes)
assert earliest_slot_in_array <= slot < current_block.slot
earliest_slot_in_array = state.slot - len(state.latest_block_hashes)
assert earliest_slot_in_array <= slot < state.slot
return state.latest_block_hashes[slot - earliest_slot_in_array]
```
`get_block_hash(_, _, s)` should always return the block hash in the beacon chain at slot `s`, and `get_shard_committees_at_slot(_, s)` should not change unless the [validator](#dfn-validator) registry changes.
`get_block_hash(_, s)` should always return the block hash in the beacon chain at slot `s`, and `get_shard_committees_at_slot(_, s)` should not change unless the [validator](#dfn-validator) registry changes.
#### `get_beacon_proposer_index`
```python
def get_beacon_proposer_index(state:BeaconState, slot: int) -> int:
def get_beacon_proposer_index(state:BeaconState,
slot: int) -> int:
"""
Returns the beacon proposer index for the ``slot``.
"""
@ -1013,7 +1012,6 @@ def on_startup(initial_validator_entries: List[Any],
# Recent state
latest_crosslinks=[CrosslinkRecord(slot=INITIAL_SLOT_NUMBER, shard_block_hash=ZERO_HASH) for _ in range(SHARD_COUNT)],
latest_state_recalculation_slot=INITIAL_SLOT_NUMBER,
latest_block_hashes=[ZERO_HASH for _ in range(EPOCH_LENGTH * 2)],
latest_penalized_exit_balances=[],
latest_attestations=[],
@ -1105,6 +1103,7 @@ def get_new_validators(validators: List[ValidatorRecord],
return validators_copy, index
```
`BLSVerify` is a function for verifying a BLS12-381 signature, defined in the [BLS12-381 spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_verify.md).
Now, to add a [validator](#dfn-validator) or top up an existing [validator](#dfn-validator)'s balance:
@ -1185,46 +1184,51 @@ def exit_validator(index: int,
## Per-slot processing
Below are the processing steps that happen at every slot. If there is no block from the proposer for a given slot a "skip block" is inserted into the beacon chain. The skip block is a `BeaconBlock` where the non-zero fields are:
Below are the processing steps that happen at every slot.
* `parent_hash`: the hash of the previous block (which may itself be a skip block)
* `slot`: the current slot
* `state_root`: the state root at the current slot
First we define the following helpers.
```python
```
Denote by `block` the associated block, possibly a skip block.
* Let `parent_hash` be the hash of the immediate previous beacon slot (i.e. equal to `block.ancestor_hashes[0]`).
* Let `parent` be the beacon slot with the hash `parent_hash`.
First, set `state.latest_block_hashes` to the output of the following:
```python
def append_to_recent_block_hashes(old_block_hashes: List[Hash32],
parent_slot: int,
current_slot: int,
def get_updated_ancestor_hashes(parent: BeaconBlock,
parent_hash: Hash32) -> List[Hash32]:
d = current_slot - parent_slot
return old_block_hashes + [parent_hash] * d
```
The output of `get_block_hash` should not change, except that it will no longer throw for `current_slot - 1`. Also, check that the block's `ancestor_hashes` array was correctly updated, using the following algorithm:
```python
def update_ancestor_hashes(parent_ancestor_hashes: List[Hash32],
parent_slot: int,
parent_hash: Hash32) -> List[Hash32]:
new_ancestor_hashes = copy.copy(parent_ancestor_hashes)
new_ancestor_hashes = copy.copy(parent.ancestor_hashes)
for i in range(32):
if parent_slot % 2**i == 0:
if parent.slot % 2**i == 0:
new_ancestor_hashes[i] = parent_hash
return new_ancestor_hashes
def get_skip_block(slot: int,
parent: BeaconBlock,
parent_hash: Hash32) -> BeaconBlock:
return BeaconBlock(
slot=state.slot,
randao_reveal=ZERO_HASH,
candidate_pow_receipt_root=ZERO_HASH,
ancestor_hashes=get_updated_ancestor_hashes(parent, parent_hash),
state_root=ZERO_HASH, # filled in with post-state-transition root
attestations=[],
specials=[],
proposer_signature=[0, 0]
)
```
* Let `parent_hash` be the hash of the beacon block at the immediate previous slot.
* Let `parent` be the `BeaconBlock` with the hash `parent_hash`.
If there is a block from the proposer for `state.slot`, we process that incoming block:
* Let `block` be that associated incoming block.
If there is not a block from the proposer for `state.slot`, a "skip block" is inserted into the beacon chain:
* Let `block` be a skip block defined by `get_skip_block(state.slot, parent, parent_hash)`.
Set `state.latest_block_hashes` to `state.latest_block_hashes + [parent_hash]`. (The output of `get_block_hash` should not change, except that it will no longer throw for `state.slot - 1`.)
Also, check that the `block.ancestor_hashes` equals `get_updated_ancestor_hashes(parent, parent_hash)`.
### Proposer signature
If `block` is not a skip block:
* Let `block_hash_without_sig` be the hash of `block` where `proposer_signature` is set to `[0, 0]`.
* Let `proposal_hash = hash(ProposalSignedData(state.slot, BEACON_CHAIN_SHARD_NUMBER, block_hash_without_sig))`.
* Verify that `BLSVerify(pubkey=state.validator_registry[get_beacon_proposer_index(state, state.slot)].pubkey, data=proposal_hash, sig=block.proposer_signature, domain=get_domain(state.fork_data, state.slot, DOMAIN_PROPOSAL))`.
@ -1237,7 +1241,7 @@ For each `attestation` in `block.attestations`:
* Verify that `attestation.data.slot <= state.slot - MIN_ATTESTATION_INCLUSION_DELAY`.
* Verify that `attestation.data.slot >= max(parent.slot - EPOCH_LENGTH + 1, 0)`.
* Verify that `attestation.data.justified_slot` is equal to `state.justified_slot if attestation.data.slot >= state.latest_state_recalculation_slot else state.previous_justified_slot`.
* Verify that `attestation.data.justified_slot` is equal to `state.justified_slot if attestation.data.slot >= state.slot - (state.slot % EPOCH_LENGTH) else state.previous_justified_slot`.
* Verify that `attestation.data.justified_block_hash` is equal to `get_block_hash(state, block, attestation.data.justified_slot)`.
* Verify that either `attestation.data.latest_crosslink_hash` or `attestation.data.shard_block_hash` equals `state.crosslinks[shard].shard_block_hash`.
* `aggregate_signature` verification:
@ -1264,7 +1268,10 @@ If `block` is not a skip block:
### PoW receipt root
If `block.candidate_pow_receipt_root` is `x.candidate_pow_receipt_root` for some `x` in `state.candidate_pow_receipt_roots`, set `x.votes += 1`. Otherwise, append to `state.candidate_pow_receipt_roots` a new `CandidatePoWReceiptRootRecord(candidate_pow_receipt_root=block.candidate_pow_receipt_root, votes=1)`.
If `block` is not a skip block:
* If `block.candidate_pow_receipt_root` is `x.candidate_pow_receipt_root` for some `x` in `state.candidate_pow_receipt_roots`, set `x.votes += 1`.
* Otherwise, append to `state.candidate_pow_receipt_roots` a new `CandidatePoWReceiptRootRecord(candidate_pow_receipt_root=block.candidate_pow_receipt_root, votes=1)`.
### Special objects