Add comments to block_processing code

This commit is contained in:
Paul Hauner 2019-03-06 16:24:56 +11:00
parent 40f74c9b26
commit 599948b26b
No known key found for this signature in database
GPG Key ID: D362883A9218FCC6
9 changed files with 258 additions and 81 deletions

View File

@ -1,4 +1,4 @@
use types::BeaconStateError;
use types::*;
macro_rules! impl_from_beacon_state_error {
($type: ident) => {
@ -39,23 +39,31 @@ macro_rules! impl_into_with_index_without_beacon_error {
};
}
/// A conversion that consumes `self` and adds an `index` variable to resulting struct.
///
/// Used here to allow converting an error into an upstream error that points to the object that
/// caused the error. For example, pointing to the index of an attestation that caused the
/// `AttestationInvalid` error.
pub trait IntoWithIndex<T>: Sized {
fn into_with_index(self, i: usize) -> T;
fn into_with_index(self, index: usize) -> T;
}
/*
* Block Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum BlockProcessingError {
/// The `BeaconBlock` is invalid.
/// Validation completed successfully and the object is invalid.
Invalid(BlockInvalid),
/// Encountered a `BeaconStateError` whilst attempting to determine validity.
BeaconStateError(BeaconStateError),
}
impl_from_beacon_state_error!(BlockProcessingError);
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum BlockInvalid {
StateSlotMismatch,
@ -87,28 +95,61 @@ impl Into<BlockProcessingError> for BlockInvalid {
* Attestation Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum AttestationValidationError {
/// The `Attestation` is invalid.
/// Validation completed successfully and the object is invalid.
Invalid(AttestationInvalid),
/// Encountered a `BeaconStateError` whilst attempting to determine validity.
BeaconStateError(BeaconStateError),
}
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum AttestationInvalid {
PreGenesis,
IncludedTooEarly,
IncludedTooLate,
WrongJustifiedSlot,
WrongJustifiedRoot,
/// Attestation references a pre-genesis slot.
///
/// (genesis_slot, attestation_slot)
PreGenesis(Slot, Slot),
/// Attestation included before the inclusion delay.
///
/// (state_slot, inclusion_delay, attestation_slot)
IncludedTooEarly(Slot, u64, Slot),
/// Attestation slot is too far in the past to be included in a block.
///
/// (state_slot, attestation_slot)
IncludedTooLate(Slot, Slot),
/// Attestation justified epoch does not match the states current or previous justified epoch.
///
/// (attestation_justified_epoch, state_epoch, used_previous_epoch)
WrongJustifiedEpoch(Epoch, Epoch, bool),
/// Attestation justified epoch root does not match root known to the state.
///
/// (state_justified_root, attestation_justified_root)
WrongJustifiedRoot(Hash256, Hash256),
/// Attestation crosslink root does not match the state crosslink root for the attestations
/// slot.
BadLatestCrosslinkRoot,
/// The custody bitfield has some bits set `true`. This is not allowed in phase 0.
CustodyBitfieldHasSetBits,
/// There are no set bits on the attestation -- an attestation must be signed by at least one
/// validator.
AggregationBitfieldIsEmpty,
BadAggregationBitfieldLength,
BadCustodyBitfieldLength,
NoCommitteeForShard,
/// The custody bitfield length is not the smallest possible size to represent the committee.
///
/// (committee_len, bitfield_len)
BadCustodyBitfieldLength(usize, usize),
/// The aggregation bitfield length is not the smallest possible size to represent the committee.
///
/// (committee_len, bitfield_len)
BadAggregationBitfieldLength(usize, usize),
/// There was no known committee for the given shard in the given slot.
///
/// (attestation_data_shard, attestation_data_slot)
NoCommitteeForShard(u64, Slot),
/// The attestation signature verification failed.
BadSignature,
/// The shard block root was not set to zero. This is a phase 0 requirement.
ShardBlockRootNotZero,
}
@ -119,21 +160,29 @@ impl_into_with_index_with_beacon_error!(AttestationValidationError, AttestationI
* `AttesterSlashing` Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum AttesterSlashingValidationError {
/// The `SlashableAttestation` is invalid.
/// Validation completed successfully and the object is invalid.
Invalid(AttesterSlashingInvalid),
/// Encountered a `BeaconStateError` whilst attempting to determine validity.
BeaconStateError(BeaconStateError),
}
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum AttesterSlashingInvalid {
/// The attestation data is identical, an attestation cannot conflict with itself.
AttestationDataIdentical,
/// The attestations were not in conflict.
NotSlashable,
/// The first `SlashableAttestation` was invalid.
SlashableAttestation1Invalid(SlashableAttestationInvalid),
/// The second `SlashableAttestation` was invalid.
SlashableAttestation2Invalid(SlashableAttestationInvalid),
UnknownValidator,
/// The validator index is unknown. One cannot slash one who does not exist.
UnknownValidator(u64),
/// There were no indices able to be slashed.
NoSlashableIndices,
}
@ -144,19 +193,35 @@ impl_into_with_index_with_beacon_error!(AttesterSlashingValidationError, Atteste
* `SlashableAttestation` Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum SlashableAttestationValidationError {
/// Validation completed successfully and the object is invalid.
Invalid(SlashableAttestationInvalid),
}
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum SlashableAttestationInvalid {
/// The custody bitfield has some bits set `true`. This is not allowed in phase 0.
CustodyBitfieldHasSetBits,
/// No validator indices were specified.
NoValidatorIndices,
BadValidatorIndicesOrdering,
BadCustodyBitfieldLength,
MaxIndicesExceed,
UnknownValidator,
/// The validator indices were not in increasing order.
///
/// The error occured between the given `index` and `index + 1`
BadValidatorIndicesOrdering(usize),
/// The custody bitfield length is not the smallest possible size to represent the validators.
///
/// (validators_len, bitfield_len)
BadCustodyBitfieldLength(usize, usize),
/// The number of slashable indices exceed the global maximum.
///
/// (max_indices, indices_given)
MaxIndicesExceed(usize, usize),
/// The validator index is unknown. One cannot slash one who does not exist.
UnknownValidator(u64),
/// The slashable attestation aggregate signature was not valid.
BadSignature,
}
@ -172,19 +237,35 @@ impl Into<SlashableAttestationInvalid> for SlashableAttestationValidationError {
* `ProposerSlashing` Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum ProposerSlashingValidationError {
/// Validation completed successfully and the object is invalid.
Invalid(ProposerSlashingInvalid),
}
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum ProposerSlashingInvalid {
ProposerUnknown,
ProposalSlotMismatch,
ProposalShardMismatch,
ProposalBlockRootMismatch,
/// The proposer index is not a known validator.
ProposerUnknown(u64),
/// The two proposal have different slots.
///
/// (proposal_1_slot, proposal_2_slot)
ProposalSlotMismatch(Slot, Slot),
/// The two proposal have different shards.
///
/// (proposal_1_shard, proposal_2_shard)
ProposalShardMismatch(u64, u64),
/// The two proposal have different block roots.
///
/// (proposal_1_root, proposal_2_root)
ProposalBlockRootMismatch(Hash256, Hash256),
/// The specified proposer has already been slashed.
ProposerAlreadySlashed,
/// The first proposal signature was invalid.
BadProposal1Signature,
/// The second proposal signature was invalid.
BadProposal2Signature,
}
@ -197,14 +278,20 @@ impl_into_with_index_without_beacon_error!(
* `Deposit` Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum DepositValidationError {
/// Validation completed successfully and the object is invalid.
Invalid(DepositInvalid),
}
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum DepositInvalid {
BadIndex,
/// The deposit index does not match the state index.
///
/// (state_index, deposit_index)
BadIndex(u64, u64),
}
impl_into_with_index_without_beacon_error!(DepositValidationError, DepositInvalid);
@ -213,16 +300,24 @@ impl_into_with_index_without_beacon_error!(DepositValidationError, DepositInvali
* `Exit` Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum ExitValidationError {
/// Validation completed successfully and the object is invalid.
Invalid(ExitInvalid),
}
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum ExitInvalid {
ValidatorUnknown,
/// The specified validator is not in the state's validator registry.
ValidatorUnknown(u64),
AlreadyExited,
FutureEpoch,
/// The exit is for a future epoch.
///
/// (state_epoch, exit_epoch)
FutureEpoch(Epoch, Epoch),
/// The exit signature was not signed by the validator.
BadSignature,
}
@ -232,11 +327,14 @@ impl_into_with_index_without_beacon_error!(ExitValidationError, ExitInvalid);
* `Transfer` Validation
*/
/// The object is invalid or validation failed.
#[derive(Debug, PartialEq)]
pub enum TransferValidationError {
/// Validation completed successfully and the object is invalid.
Invalid(TransferInvalid),
}
/// Describes why an object is invalid.
#[derive(Debug, PartialEq)]
pub enum TransferInvalid {}

View File

@ -19,6 +19,12 @@ mod verify_proposer_slashing;
mod verify_slashable_attestation;
mod verify_transfer;
/// Updates the state for a new block, whilst validating that the block is valid.
///
/// Returns `Ok(())` if the block is valid and the state was successfully updated. Otherwise
/// returns an error describing why the block was invalid or how the function failed to execute.
///
/// Spec v0.4.0
pub fn per_block_processing(
state: &mut BeaconState,
block: &BeaconBlock,
@ -27,6 +33,13 @@ pub fn per_block_processing(
per_block_processing_signature_optional(state, block, true, spec)
}
/// Updates the state for a new block, whilst validating that the block is valid, without actually
/// checking the block proposer signature.
///
/// Returns `Ok(())` if the block is valid and the state was successfully updated. Otherwise
/// returns an error describing why the block was invalid or how the function failed to execute.
///
/// Spec v0.4.0
pub fn per_block_processing_without_verifying_block_signature(
state: &mut BeaconState,
block: &BeaconBlock,
@ -35,6 +48,13 @@ pub fn per_block_processing_without_verifying_block_signature(
per_block_processing_signature_optional(state, block, false, spec)
}
/// Updates the state for a new block, whilst validating that the block is valid, optionally
/// checking the block proposer signature.
///
/// Returns `Ok(())` if the block is valid and the state was successfully updated. Otherwise
/// returns an error describing why the block was invalid or how the function failed to execute.
///
/// Spec v0.4.0
fn per_block_processing_signature_optional(
mut state: &mut BeaconState,
block: &BeaconBlock,

View File

@ -3,7 +3,10 @@ use ssz::TreeHash;
use types::beacon_state::helpers::*;
use types::*;
/// Validate an attestation, checking the aggregate signature.
/// Indicates if an `Attestation` is valid to be included in a block in the current epoch of the
/// given state.
///
/// Returns `Ok(())` if the `Attestation` is valid, otherwise indicates the reason for invalidity.
///
/// Spec v0.4.0
pub fn validate_attestation(
@ -14,7 +17,10 @@ pub fn validate_attestation(
validate_attestation_signature_optional(state, attestation, spec, true)
}
/// Validate an attestation, without checking the aggregate signature.
/// Indicates if an `Attestation` is valid to be included in a block in the current epoch of the
/// given state, without validating the aggregate signature.
///
/// Returns `Ok(())` if the `Attestation` is valid, otherwise indicates the reason for invalidity.
///
/// Spec v0.4.0
pub fn validate_attestation_without_signature(
@ -25,7 +31,9 @@ pub fn validate_attestation_without_signature(
validate_attestation_signature_optional(state, attestation, spec, false)
}
/// Validate an attestation, optionally checking the aggregate signature.
/// Indicates if an `Attestation` is valid to be included in a block in the current epoch of the
/// given state, optionally validating the aggregate signature.
///
///
/// Spec v0.4.0
fn validate_attestation_signature_optional(
@ -37,19 +45,23 @@ fn validate_attestation_signature_optional(
// Verify that `attestation.data.slot >= GENESIS_SLOT`.
verify!(
attestation.data.slot >= spec.genesis_slot,
Invalid::PreGenesis
Invalid::PreGenesis(spec.genesis_slot, attestation.data.slot)
);
// Verify that `attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot`.
verify!(
attestation.data.slot + spec.min_attestation_inclusion_delay <= state.slot,
Invalid::IncludedTooEarly
Invalid::IncludedTooEarly(
state.slot,
spec.min_attestation_inclusion_delay,
attestation.data.slot
)
);
// Verify that `state.slot < attestation.data.slot + SLOTS_PER_EPOCH`.
verify!(
state.slot < attestation.data.slot + spec.slots_per_epoch,
Invalid::IncludedTooLate
Invalid::IncludedTooLate(state.slot, attestation.data.slot)
);
// Verify that `attestation.data.justified_epoch` is equal to `state.justified_epoch` if
@ -58,29 +70,37 @@ fn validate_attestation_signature_optional(
if (attestation.data.slot + 1).epoch(spec.slots_per_epoch) >= state.current_epoch(spec) {
verify!(
attestation.data.justified_epoch == state.justified_epoch,
Invalid::WrongJustifiedSlot
Invalid::WrongJustifiedEpoch(
attestation.data.justified_epoch,
state.justified_epoch,
false
)
);
} else {
verify!(
attestation.data.justified_epoch == state.previous_justified_epoch,
Invalid::WrongJustifiedSlot
Invalid::WrongJustifiedEpoch(
attestation.data.justified_epoch,
state.previous_justified_epoch,
true
)
);
}
// Verify that `attestation.data.justified_block_root` is equal to `get_block_root(state,
// get_epoch_start_slot(attestation.data.justified_epoch))`.
let justified_block_root = *state
.get_block_root(
attestation
.data
.justified_epoch
.start_slot(spec.slots_per_epoch),
&spec,
)
.ok_or(BeaconStateError::InsufficientBlockRoots)?;
verify!(
attestation.data.justified_block_root
== *state
.get_block_root(
attestation
.data
.justified_epoch
.start_slot(spec.slots_per_epoch),
&spec
)
.ok_or(BeaconStateError::InsufficientBlockRoots)?,
Invalid::WrongJustifiedRoot
attestation.data.justified_block_root == justified_block_root,
Invalid::WrongJustifiedRoot(justified_block_root, attestation.data.justified_block_root)
);
// Verify that either:
@ -106,7 +126,12 @@ fn validate_attestation_signature_optional(
.get_crosslink_committees_at_slot(attestation.data.slot, spec)?
.iter()
.find(|(_committee, shard)| *shard == attestation.data.shard)
.ok_or_else(|| Error::Invalid(Invalid::NoCommitteeForShard))?;
.ok_or_else(|| {
Error::Invalid(Invalid::NoCommitteeForShard(
attestation.data.shard,
attestation.data.slot,
))
})?;
// Custody bitfield is all zeros (phase 0 requirement).
verify!(
@ -115,8 +140,8 @@ fn validate_attestation_signature_optional(
);
// Custody bitfield length is correct.
verify!(
verify_bitfield_length(&attestation.aggregation_bitfield, committee.len()),
Invalid::BadCustodyBitfieldLength
verify_bitfield_length(&attestation.custody_bitfield, committee.len()),
Invalid::BadCustodyBitfieldLength(committee.len(), attestation.custody_bitfield.len())
);
// Aggregation bitfield isn't empty.
verify!(
@ -126,7 +151,10 @@ fn validate_attestation_signature_optional(
// Aggregation bitfield length is correct.
verify!(
verify_bitfield_length(&attestation.aggregation_bitfield, committee.len()),
Invalid::BadAggregationBitfieldLength
Invalid::BadAggregationBitfieldLength(
committee.len(),
attestation.aggregation_bitfield.len()
)
);
if verify_signature {

View File

@ -2,10 +2,10 @@ use super::verify_slashable_attestation::verify_slashable_attestation;
use crate::errors::{AttesterSlashingInvalid as Invalid, AttesterSlashingValidationError as Error};
use types::*;
/// Returns `Ok(())` if some `AttesterSlashing` is valid to be included in some `BeaconState`,
/// otherwise returns an `Err`.
/// Indicates if an `AttesterSlashing` is valid to be included in a block in the current epoch of the given
/// state.
///
/// Returns the slashable indices from the `AttesterSlashing`.
/// Returns `Ok(())` if the `AttesterSlashing` is valid, otherwise indicates the reason for invalidity.
///
/// Spec v0.4.0
pub fn verify_attester_slashing(
@ -36,7 +36,7 @@ pub fn verify_attester_slashing(
let validator = state
.validator_registry
.get(*i as usize)
.ok_or_else(|| Error::Invalid(Invalid::UnknownValidator))?;
.ok_or_else(|| Error::Invalid(Invalid::UnknownValidator(*i)))?;
if slashable_attestation_1.validator_indices.contains(&i) & !validator.slashed {
slashable_indices.push(*i);

View File

@ -1,22 +1,26 @@
use crate::errors::{DepositInvalid as Invalid, DepositValidationError as Error};
use ssz::TreeHash;
use types::beacon_state::helpers::verify_bitfield_length;
use types::*;
/// Verify validity of ``slashable_attestation`` fields.
/// Indicates if a `Deposit` is valid to be included in a block in the current epoch of the given
/// state.
///
/// Returns `Ok(())` if all fields are valid.
/// Returns `Ok(())` if the `Deposit` is valid, otherwise indicates the reason for invalidity.
///
/// Note: this function is incomplete.
///
/// Spec v0.4.0
pub fn verify_deposit(
state: &BeaconState,
deposit: &Deposit,
spec: &ChainSpec,
_spec: &ChainSpec,
) -> Result<(), Error> {
// TODO: verify serialized deposit data.
// TODO: verify deposit index.
verify!(deposit.index == state.deposit_index, Invalid::BadIndex);
verify!(
deposit.index == state.deposit_index,
Invalid::BadIndex(state.deposit_index, deposit.index)
);
// TODO: verify merkle branch.

View File

@ -2,9 +2,10 @@ use crate::errors::{ExitInvalid as Invalid, ExitValidationError as Error};
use ssz::SignedRoot;
use types::*;
/// Verify validity of ``slashable_attestation`` fields.
/// Indicates if an `Exit` is valid to be included in a block in the current epoch of the given
/// state.
///
/// Returns `Ok(())` if all fields are valid.
/// Returns `Ok(())` if the `Exit` is valid, otherwise indicates the reason for invalidity.
///
/// Spec v0.4.0
pub fn verify_exit(
@ -15,7 +16,9 @@ pub fn verify_exit(
let validator = state
.validator_registry
.get(exit.validator_index as usize)
.ok_or(Error::Invalid(Invalid::ValidatorUnknown))?;
.ok_or(Error::Invalid(Invalid::ValidatorUnknown(
exit.validator_index,
)))?;
verify!(
validator.exit_epoch
@ -25,7 +28,7 @@ pub fn verify_exit(
verify!(
state.current_epoch(spec) >= exit.epoch,
Invalid::FutureEpoch
Invalid::FutureEpoch(state.current_epoch(spec), exit.epoch)
);
let message = exit.signed_root();

View File

@ -2,8 +2,10 @@ use crate::errors::{ProposerSlashingInvalid as Invalid, ProposerSlashingValidati
use ssz::SignedRoot;
use types::*;
/// Returns `Ok(())` if some `ProposerSlashing` is valid to be included in some `BeaconState`,
/// otherwise returns an `Err`.
/// Indicates if a `ProposerSlashing` is valid to be included in a block in the current epoch of the given
/// state.
///
/// Returns `Ok(())` if the `ProposerSlashing` is valid, otherwise indicates the reason for invalidity.
///
/// Spec v0.4.0
pub fn verify_proposer_slashing(
@ -14,21 +16,32 @@ pub fn verify_proposer_slashing(
let proposer = state
.validator_registry
.get(proposer_slashing.proposer_index as usize)
.ok_or(Error::Invalid(Invalid::ProposerUnknown))?;
.ok_or(Error::Invalid(Invalid::ProposerUnknown(
proposer_slashing.proposer_index,
)))?;
verify!(
proposer_slashing.proposal_1.slot == proposer_slashing.proposal_2.slot,
Invalid::ProposalSlotMismatch
Invalid::ProposalSlotMismatch(
proposer_slashing.proposal_1.slot,
proposer_slashing.proposal_2.slot
)
);
verify!(
proposer_slashing.proposal_1.shard == proposer_slashing.proposal_2.shard,
Invalid::ProposalShardMismatch
Invalid::ProposalShardMismatch(
proposer_slashing.proposal_1.shard,
proposer_slashing.proposal_2.shard
)
);
verify!(
proposer_slashing.proposal_1.block_root != proposer_slashing.proposal_2.block_root,
Invalid::ProposalBlockRootMismatch
Invalid::ProposalBlockRootMismatch(
proposer_slashing.proposal_1.block_root,
proposer_slashing.proposal_2.block_root
)
);
verify!(!proposer.slashed, Invalid::ProposerAlreadySlashed);
@ -55,6 +68,9 @@ pub fn verify_proposer_slashing(
Ok(())
}
/// Verifies the signature of a proposal.
///
/// Returns `true` if the signature is valid.
fn verify_proposal_signature(
proposal: &Proposal,
pubkey: &PublicKey,

View File

@ -5,9 +5,10 @@ use ssz::TreeHash;
use types::beacon_state::helpers::verify_bitfield_length;
use types::*;
/// Verify validity of ``slashable_attestation`` fields.
/// Indicates if a `SlashableAttestation` is valid to be included in a block in the current epoch of the given
/// state.
///
/// Returns `Ok(())` if all fields are valid.
/// Returns `Ok(())` if the `SlashableAttestation` is valid, otherwise indicates the reason for invalidity.
///
/// Spec v0.4.0
pub fn verify_slashable_attestation(
@ -27,7 +28,7 @@ pub fn verify_slashable_attestation(
if slashable_attestation.validator_indices[i]
>= slashable_attestation.validator_indices[i + 1]
{
invalid!(Invalid::BadValidatorIndicesOrdering);
invalid!(Invalid::BadValidatorIndicesOrdering(i));
}
}
@ -35,12 +36,18 @@ pub fn verify_slashable_attestation(
&slashable_attestation.custody_bitfield,
slashable_attestation.validator_indices.len(),
) {
invalid!(Invalid::BadCustodyBitfieldLength);
invalid!(Invalid::BadCustodyBitfieldLength(
slashable_attestation.validator_indices.len(),
slashable_attestation.custody_bitfield.len()
));
}
if slashable_attestation.validator_indices.len() > spec.max_indices_per_slashable_vote as usize
{
invalid!(Invalid::MaxIndicesExceed);
invalid!(Invalid::MaxIndicesExceed(
spec.max_indices_per_slashable_vote as usize,
slashable_attestation.validator_indices.len()
));
}
// TODO: this signature verification could likely be replaced with:
@ -62,7 +69,7 @@ pub fn verify_slashable_attestation(
Some(validator) => {
aggregate_pubs[custody_bit as usize].add(&validator.pubkey);
}
None => invalid!(Invalid::UnknownValidator),
None => invalid!(Invalid::UnknownValidator(*v)),
};
}

View File

@ -1,17 +1,18 @@
use crate::errors::{TransferInvalid as Invalid, TransferValidationError as Error};
use ssz::TreeHash;
use types::beacon_state::helpers::verify_bitfield_length;
use types::*;
/// Verify validity of ``slashable_attestation`` fields.
/// Indicates if a `Transfer` is valid to be included in a block in the current epoch of the given
/// state.
///
/// Returns `Ok(())` if all fields are valid.
/// Returns `Ok(())` if the `Transfer` is valid, otherwise indicates the reason for invalidity.
///
/// Note: this function is incomplete.
///
/// Spec v0.4.0
pub fn verify_transfer(
state: &BeaconState,
transfer: &Transfer,
spec: &ChainSpec,
_state: &BeaconState,
_transfer: &Transfer,
_spec: &ChainSpec,
) -> Result<(), Error> {
// TODO: verify transfer.