SubstrateMessagesTarget {
/// Create new Substrate headers target.
pub fn new(
target_client: Client,
source_client: Client,
lane_id: LaneId,
relayer_id_at_source: AccountIdOf,
transaction_params: TransactionParams>,
metric_values: StandaloneMessagesMetrics,
source_to_target_headers_relay: Option<
Arc>>,
>,
) -> Self {
SubstrateMessagesTarget {
target_client,
source_client,
lane_id,
relayer_id_at_source,
transaction_params,
metric_values,
source_to_target_headers_relay,
}
}
/// Read inbound lane state from the on-chain storage at given block.
async fn inbound_lane_data(
&self,
id: TargetHeaderIdOf>,
) -> Result>>, SubstrateError> {
self.target_client
.storage_value(
inbound_lane_data_key(
P::SourceChain::WITH_CHAIN_MESSAGES_PALLET_NAME,
&self.lane_id,
),
Some(id.1),
)
.await
}
/// Ensure that the messages pallet at target chain is active.
async fn ensure_pallet_active(&self) -> Result<(), SubstrateError> {
ensure_messages_pallet_active::(&self.target_client).await
}
}
impl Clone for SubstrateMessagesTarget {
fn clone(&self) -> Self {
Self {
target_client: self.target_client.clone(),
source_client: self.source_client.clone(),
lane_id: self.lane_id,
relayer_id_at_source: self.relayer_id_at_source.clone(),
transaction_params: self.transaction_params.clone(),
metric_values: self.metric_values.clone(),
source_to_target_headers_relay: self.source_to_target_headers_relay.clone(),
}
}
}
#[async_trait]
impl RelayClient for SubstrateMessagesTarget {
type Error = SubstrateError;
async fn reconnect(&mut self) -> Result<(), SubstrateError> {
self.target_client.reconnect().await?;
self.source_client.reconnect().await
}
}
#[async_trait]
impl TargetClient> for SubstrateMessagesTarget
where
AccountIdOf:
From< as Pair>::Public>,
P::TargetTransactionSignScheme: TransactionSignScheme,
BalanceOf: TryFrom>,
{
async fn state(&self) -> Result>, SubstrateError> {
// we can't continue to deliver confirmations if source node is out of sync, because
// it may have already received confirmations that we're going to deliver
//
// we can't continue to deliver messages if target node is out of sync, because
// it may have already received (some of) messages that we're going to deliver
self.source_client.ensure_synced().await?;
self.target_client.ensure_synced().await?;
// we can't relay messages if messages pallet at target chain is halted
self.ensure_pallet_active().await?;
read_client_state(
&self.target_client,
Some(&self.source_client),
P::SourceChain::BEST_FINALIZED_HEADER_ID_METHOD,
)
.await
}
async fn latest_received_nonce(
&self,
id: TargetHeaderIdOf>,
) -> Result<(TargetHeaderIdOf>, MessageNonce), SubstrateError> {
// lane data missing from the storage is fine until first message is received
let latest_received_nonce = self
.inbound_lane_data(id)
.await?
.map(|data| data.last_delivered_nonce())
.unwrap_or(0);
Ok((id, latest_received_nonce))
}
async fn latest_confirmed_received_nonce(
&self,
id: TargetHeaderIdOf>,
) -> Result<(TargetHeaderIdOf>, MessageNonce), SubstrateError> {
// lane data missing from the storage is fine until first message is received
let last_confirmed_nonce = self
.inbound_lane_data(id)
.await?
.map(|data| data.last_confirmed_nonce)
.unwrap_or(0);
Ok((id, last_confirmed_nonce))
}
async fn unrewarded_relayers_state(
&self,
id: TargetHeaderIdOf>,
) -> Result<(TargetHeaderIdOf>, UnrewardedRelayersState), SubstrateError>
{
let inbound_lane_data = self.inbound_lane_data(id).await?;
let last_delivered_nonce =
inbound_lane_data.as_ref().map(|data| data.last_delivered_nonce()).unwrap_or(0);
let relayers = inbound_lane_data.map(|data| data.relayers).unwrap_or_else(VecDeque::new);
let unrewarded_relayers_state = bp_messages::UnrewardedRelayersState {
unrewarded_relayer_entries: relayers.len() as _,
messages_in_oldest_entry: relayers
.front()
.map(|entry| 1 + entry.messages.end - entry.messages.begin)
.unwrap_or(0),
total_messages: total_unrewarded_messages(&relayers).unwrap_or(MessageNonce::MAX),
last_delivered_nonce,
};
Ok((id, unrewarded_relayers_state))
}
async fn prove_messages_receiving(
&self,
id: TargetHeaderIdOf>,
) -> Result<
(
TargetHeaderIdOf>,
as MessageLane>::MessagesReceivingProof,
),
SubstrateError,
> {
let (id, relayers_state) = self.unrewarded_relayers_state(id).await?;
let inbound_data_key = bp_messages::storage_keys::inbound_lane_data_key(
P::SourceChain::WITH_CHAIN_MESSAGES_PALLET_NAME,
&self.lane_id,
);
let proof = self
.target_client
.prove_storage(vec![inbound_data_key], id.1)
.await?
.iter_nodes()
.collect();
let proof = FromBridgedChainMessagesDeliveryProof {
bridged_header_hash: id.1,
storage_proof: proof,
lane: self.lane_id,
};
Ok((id, (relayers_state, proof)))
}
async fn submit_messages_proof(
&self,
_generated_at_header: SourceHeaderIdOf>,
nonces: RangeInclusive,
proof: as MessageLane>::MessagesProof,
) -> Result, SubstrateError> {
let genesis_hash = *self.target_client.genesis_hash();
let transaction_params = self.transaction_params.clone();
let relayer_id_at_source = self.relayer_id_at_source.clone();
let nonces_clone = nonces.clone();
let (spec_version, transaction_version) =
self.target_client.simple_runtime_version().await?;
self.target_client
.submit_signed_extrinsic(
self.transaction_params.signer.public().into(),
SignParam:: {
spec_version,
transaction_version,
genesis_hash,
signer: self.transaction_params.signer.clone(),
},
move |best_block_id, transaction_nonce| {
make_messages_delivery_transaction::(
&transaction_params,
best_block_id,
transaction_nonce,
relayer_id_at_source,
nonces_clone,
proof,
true,
)
},
)
.await?;
Ok(nonces)
}
async fn require_source_header_on_target(&self, id: SourceHeaderIdOf>) {
if let Some(ref source_to_target_headers_relay) = self.source_to_target_headers_relay {
source_to_target_headers_relay.require_more_headers(id.0).await;
}
}
async fn estimate_delivery_transaction_in_source_tokens(
&self,
nonces: RangeInclusive,
total_prepaid_nonces: MessageNonce,
total_dispatch_weight: Weight,
total_size: u32,
) -> Result< as MessageLane>::SourceChainBalance, SubstrateError> {
let conversion_rate =
self.metric_values.target_to_source_conversion_rate().await.ok_or_else(|| {
SubstrateError::Custom(format!(
"Failed to compute conversion rate from {} to {}",
P::TargetChain::NAME,
P::SourceChain::NAME,
))
})?;
let (spec_version, transaction_version) =
self.target_client.simple_runtime_version().await?;
// Prepare 'dummy' delivery transaction - we only care about its length and dispatch weight.
let delivery_tx = P::TargetTransactionSignScheme::sign_transaction(
SignParam {
spec_version,
transaction_version,
genesis_hash: Default::default(),
signer: self.transaction_params.signer.clone(),
},
make_messages_delivery_transaction::(
&self.transaction_params,
HeaderId(Default::default(), Default::default()),
Zero::zero(),
self.relayer_id_at_source.clone(),
nonces.clone(),
prepare_dummy_messages_proof::(
nonces.clone(),
total_dispatch_weight,
total_size,
),
false,
)?,
)?
.encode();
let delivery_tx_fee = self.target_client.estimate_extrinsic_fee(Bytes(delivery_tx)).await?;
let inclusion_fee_in_target_tokens = delivery_tx_fee.inclusion_fee();
// The pre-dispatch cost of delivery transaction includes additional fee to cover dispatch
// fee payment (Currency::transfer in regular deployment). But if message dispatch has
// already been paid at the Source chain, the delivery transaction will refund relayer with
// this additional cost. But `estimate_extrinsic_fee` obviously just returns pre-dispatch
// cost of the transaction. So if transaction delivers prepaid message, then it may happen
// that pre-dispatch cost is larger than reward and `Rational` relayer will refuse to
// deliver this message.
//
// The most obvious solution would be to deduct total weight of dispatch fee payments from
// the `total_dispatch_weight` and use regular `estimate_extrinsic_fee` call. But what if
// `total_dispatch_weight` is less than total dispatch fee payments weight? Weight is
// strictly positive, so we can't use this option.
//
// Instead we'll be directly using `WeightToFee` and `NextFeeMultiplier` of the Target
// chain. This requires more knowledge of the Target chain, but seems there's no better way
// to solve this now.
let expected_refund_in_target_tokens = if total_prepaid_nonces != 0 {
const WEIGHT_DIFFERENCE: Weight = 100;
let (spec_version, transaction_version) =
self.target_client.simple_runtime_version().await?;
let larger_dispatch_weight = total_dispatch_weight.saturating_add(WEIGHT_DIFFERENCE);
let dummy_tx = P::TargetTransactionSignScheme::sign_transaction(
SignParam {
spec_version,
transaction_version,
genesis_hash: Default::default(),
signer: self.transaction_params.signer.clone(),
},
make_messages_delivery_transaction::(
&self.transaction_params,
HeaderId(Default::default(), Default::default()),
Zero::zero(),
self.relayer_id_at_source.clone(),
nonces.clone(),
prepare_dummy_messages_proof::(
nonces.clone(),
larger_dispatch_weight,
total_size,
),
false,
)?,
)?
.encode();
let larger_delivery_tx_fee =
self.target_client.estimate_extrinsic_fee(Bytes(dummy_tx)).await?;
compute_prepaid_messages_refund::(
total_prepaid_nonces,
compute_fee_multiplier::(
delivery_tx_fee.adjusted_weight_fee,
total_dispatch_weight,
larger_delivery_tx_fee.adjusted_weight_fee,
larger_dispatch_weight,
),
)
} else {
Zero::zero()
};
let delivery_fee_in_source_tokens =
convert_target_tokens_to_source_tokens::(
FixedU128::from_float(conversion_rate),
inclusion_fee_in_target_tokens.saturating_sub(expected_refund_in_target_tokens),
);
log::trace!(
target: "bridge",
"Estimated {} -> {} messages delivery transaction.\n\t\
Total nonces: {:?}\n\t\
Prepaid messages: {}\n\t\
Total messages size: {}\n\t\
Total messages dispatch weight: {}\n\t\
Inclusion fee (in {1} tokens): {:?}\n\t\
Expected refund (in {1} tokens): {:?}\n\t\
{1} -> {0} conversion rate: {:?}\n\t\
Expected delivery tx fee (in {0} tokens): {:?}",
P::SourceChain::NAME,
P::TargetChain::NAME,
nonces,
total_prepaid_nonces,
total_size,
total_dispatch_weight,
inclusion_fee_in_target_tokens,
expected_refund_in_target_tokens,
conversion_rate,
delivery_fee_in_source_tokens,
);
Ok(delivery_fee_in_source_tokens)
}
}
/// Make messages delivery transaction from given proof.
fn make_messages_delivery_transaction(
target_transaction_params: &TransactionParams>,
target_best_block_id: HeaderIdOf,
transaction_nonce: IndexOf,
relayer_id_at_source: AccountIdOf,
nonces: RangeInclusive,
proof: SubstrateMessagesProof,
trace_call: bool,
) -> Result, SubstrateError>
where
P::TargetTransactionSignScheme: TransactionSignScheme,
{
let messages_count = nonces.end() - nonces.start() + 1;
let dispatch_weight = proof.0;
let call = P::ReceiveMessagesProofCallBuilder::build_receive_messages_proof_call(
relayer_id_at_source,
proof,
messages_count as _,
dispatch_weight,
trace_call,
);
Ok(UnsignedTransaction::new(call.into(), transaction_nonce)
.era(TransactionEra::new(target_best_block_id, target_transaction_params.mortality)))
}
/// Prepare 'dummy' messages proof that will compose the delivery transaction.
///
/// We don't care about proof actually being the valid proof, because its validity doesn't
/// affect the call weight - we only care about its size.
fn prepare_dummy_messages_proof(
nonces: RangeInclusive,
total_dispatch_weight: Weight,
total_size: u32,
) -> SubstrateMessagesProof {
(
total_dispatch_weight,
FromBridgedChainMessagesProof {
bridged_header_hash: Default::default(),
storage_proof: vec![vec![
0;
SC::STORAGE_PROOF_OVERHEAD.saturating_add(total_size) as usize
]],
lane: Default::default(),
nonces_start: *nonces.start(),
nonces_end: *nonces.end(),
},
)
}
/// Given delivery transaction fee in target chain tokens and conversion rate to the source
/// chain tokens, compute transaction cost in source chain tokens.
fn convert_target_tokens_to_source_tokens(
target_to_source_conversion_rate: FixedU128,
target_transaction_fee: TC::Balance,
) -> SC::Balance
where
SC::Balance: TryFrom,
{
SC::Balance::try_from(
target_to_source_conversion_rate.saturating_mul_int(target_transaction_fee),
)
.unwrap_or_else(|_| SC::Balance::max_value())
}
/// Compute fee multiplier that is used by the chain, given a couple of fees for transactions
/// that are only differ in dispatch weights.
///
/// This function assumes that standard transaction payment pallet is used by the chain.
/// The only fee component that depends on dispatch weight is the `adjusted_weight_fee`.
///
/// **WARNING**: this functions will only be accurate if weight-to-fee conversion function
/// is linear. For non-linear polynomials the error will grow with `weight_difference` growth.
/// So better to use smaller differences.
fn compute_fee_multiplier(
smaller_adjusted_weight_fee: BalanceOf,
smaller_tx_weight: Weight,
larger_adjusted_weight_fee: BalanceOf,
larger_tx_weight: Weight,
) -> FixedU128 {
let adjusted_weight_fee_difference =
larger_adjusted_weight_fee.saturating_sub(smaller_adjusted_weight_fee);
let smaller_tx_unadjusted_weight_fee = WeightToFeeOf::::calc(&smaller_tx_weight);
let larger_tx_unadjusted_weight_fee = WeightToFeeOf::::calc(&larger_tx_weight);
FixedU128::saturating_from_rational(
adjusted_weight_fee_difference,
larger_tx_unadjusted_weight_fee.saturating_sub(smaller_tx_unadjusted_weight_fee),
)
}
/// Compute fee that will be refunded to the relayer because dispatch of `total_prepaid_nonces`
/// messages has been paid at the source chain.
fn compute_prepaid_messages_refund(
total_prepaid_nonces: MessageNonce,
fee_multiplier: FixedU128,
) -> BalanceOf {
fee_multiplier.saturating_mul_int(WeightToFeeOf::::calc(
&C::PAY_INBOUND_DISPATCH_FEE_WEIGHT_AT_CHAIN.saturating_mul(total_prepaid_nonces),
))
}
#[cfg(test)]
mod tests {
use super::*;
use relay_rialto_client::Rialto;
use relay_rococo_client::Rococo;
use relay_wococo_client::Wococo;
#[test]
fn prepare_dummy_messages_proof_works() {
const DISPATCH_WEIGHT: Weight = 1_000_000;
const SIZE: u32 = 1_000;
let dummy_proof = prepare_dummy_messages_proof::(1..=10, DISPATCH_WEIGHT, SIZE);
assert_eq!(dummy_proof.0, DISPATCH_WEIGHT);
assert!(
dummy_proof.1.encode().len() as u32 > SIZE,
"Expected proof size at least {}. Got: {}",
SIZE,
dummy_proof.1.encode().len(),
);
}
#[test]
fn convert_target_tokens_to_source_tokens_works() {
assert_eq!(
convert_target_tokens_to_source_tokens::((150, 100).into(), 1_000),
1_500
);
assert_eq!(
convert_target_tokens_to_source_tokens::((50, 100).into(), 1_000),
500
);
assert_eq!(
convert_target_tokens_to_source_tokens::((100, 100).into(), 1_000),
1_000
);
}
#[test]
fn compute_fee_multiplier_returns_sane_results() {
let multiplier = FixedU128::saturating_from_rational(1, 1000);
let smaller_weight = 1_000_000;
let smaller_adjusted_weight_fee =
multiplier.saturating_mul_int(WeightToFeeOf::::calc(&smaller_weight));
let larger_weight = smaller_weight + 200_000;
let larger_adjusted_weight_fee =
multiplier.saturating_mul_int(WeightToFeeOf::::calc(&larger_weight));
assert_eq!(
compute_fee_multiplier::(
smaller_adjusted_weight_fee,
smaller_weight,
larger_adjusted_weight_fee,
larger_weight,
),
multiplier,
);
}
#[test]
fn compute_prepaid_messages_refund_returns_sane_results() {
assert!(
compute_prepaid_messages_refund::(
10,
FixedU128::saturating_from_rational(110, 100),
) > (10 * Rialto::PAY_INBOUND_DISPATCH_FEE_WEIGHT_AT_CHAIN).into()
);
}
}