message_lane_loop.rs

// Copyright 2019-2021 Parity Technologies (UK) Ltd.
// This file is part of Parity Bridges Common.

// Parity Bridges Common is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity Bridges Common is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.

//! Message delivery loop. Designed to work with messages pallet.
//!
//! Single relay instance delivers messages of single lane in single direction.
//! To serve two-way lane, you would need two instances of relay.
//! To serve N two-way lanes, you would need N*2 instances of relay.
//!
//! Please keep in mind that the best header in this file is actually best
//! finalized header. I.e. when talking about headers in lane context, we
//! only care about finalized headers.

use std::{collections::BTreeMap, fmt::Debug, future::Future, ops::RangeInclusive, time::Duration};

use async_trait::async_trait;
use futures::{channel::mpsc::unbounded, future::FutureExt, stream::StreamExt};

use bp_messages::{LaneId, MessageNonce, UnrewardedRelayersState, Weight};
use bp_runtime::messages::DispatchFeePayment;
use relay_utils::{
	interval, metrics::MetricsParams, process_future_result, relay_loop::Client as RelayClient,
	retry_backoff, FailedClient, TransactionTracker,
};

use crate::{
	message_lane::{MessageLane, SourceHeaderIdOf, TargetHeaderIdOf},
	message_race_delivery::run as run_message_delivery_race,
	message_race_receiving::run as run_message_receiving_race,
	metrics::MessageLaneLoopMetrics,
	relay_strategy::RelayStrategy,
};

/// Message lane loop configuration params.
#[derive(Debug, Clone)]
pub struct Params<Strategy: RelayStrategy> {
	/// Id of lane this loop is servicing.
	pub lane: LaneId,
	/// Interval at which we ask target node about its updates.
	pub source_tick: Duration,
	/// Interval at which we ask target node about its updates.
	pub target_tick: Duration,
	/// Delay between moments when connection error happens and our reconnect attempt.
	pub reconnect_delay: Duration,
	/// Message delivery race parameters.
	pub delivery_params: MessageDeliveryParams<Strategy>,
}

/// Relayer operating mode.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RelayerMode {
	/// The relayer doesn't care about rewards.
	Altruistic,
	/// The relayer will deliver all messages and confirmations as long as he's not losing any
	/// funds.
	Rational,
}

/// Message delivery race parameters.
#[derive(Debug, Clone)]
pub struct MessageDeliveryParams<Strategy: RelayStrategy> {
	/// Maximal number of unconfirmed relayer entries at the inbound lane. If there's that number
	/// of entries in the `InboundLaneData::relayers` set, all new messages will be rejected until
	/// reward payment will be proved (by including outbound lane state to the message delivery
	/// transaction).
	pub max_unrewarded_relayer_entries_at_target: MessageNonce,
	/// Message delivery race will stop delivering messages if there are
	/// `max_unconfirmed_nonces_at_target` unconfirmed nonces on the target node. The race would
	/// continue once they're confirmed by the receiving race.
	pub max_unconfirmed_nonces_at_target: MessageNonce,
	/// Maximal number of relayed messages in single delivery transaction.
	pub max_messages_in_single_batch: MessageNonce,
	/// Maximal cumulative dispatch weight of relayed messages in single delivery transaction.
	pub max_messages_weight_in_single_batch: Weight,
	/// Maximal cumulative size of relayed messages in single delivery transaction.
	pub max_messages_size_in_single_batch: u32,
	/// Relay strategy
	pub relay_strategy: Strategy,
}

/// Message details.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct MessageDetails<SourceChainBalance> {
	/// Message dispatch weight.
	pub dispatch_weight: Weight,
	/// Message size (number of bytes in encoded payload).
	pub size: u32,
	/// The relayer reward paid in the source chain tokens.
	pub reward: SourceChainBalance,
	/// Where the fee for dispatching message is paid?
	pub dispatch_fee_payment: DispatchFeePayment,
}

/// Messages details map.
pub type MessageDetailsMap<SourceChainBalance> =
	BTreeMap<MessageNonce, MessageDetails<SourceChainBalance>>;

/// Message delivery race proof parameters.
#[derive(Debug, PartialEq, Eq)]
pub struct MessageProofParameters {
	/// Include outbound lane state proof?
	pub outbound_state_proof_required: bool,
	/// Cumulative dispatch weight of messages that we're building proof for.
	pub dispatch_weight: Weight,
}

/// Artifacts of submitting nonces proof.
pub struct NoncesSubmitArtifacts<T> {
	/// Submitted nonces range.
	pub nonces: RangeInclusive<MessageNonce>,
	/// Submitted transaction tracker.
	pub tx_tracker: T,
}

/// Source client trait.
#[async_trait]
pub trait SourceClient<P: MessageLane>: RelayClient {
	/// Transaction tracker to track submitted transactions.
	type TransactionTracker: TransactionTracker<HeaderId = SourceHeaderIdOf<P>>;

	/// Returns state of the client.
	async fn state(&self) -> Result<SourceClientState<P>, Self::Error>;

	/// Get nonce of instance of latest generated message.
	async fn latest_generated_nonce(
		&self,
		id: SourceHeaderIdOf<P>,
	) -> Result<(SourceHeaderIdOf<P>, MessageNonce), Self::Error>;

	/// Get nonce of the latest message, which receiving has been confirmed by the target chain.
	async fn latest_confirmed_received_nonce(
		&self,
		id: SourceHeaderIdOf<P>,
	) -> Result<(SourceHeaderIdOf<P>, MessageNonce), Self::Error>;

	/// Returns mapping of message nonces, generated on this client, to their weights.
	///
	/// Some messages may be missing from returned map, if corresponding messages were pruned at
	/// the source chain.
	async fn generated_message_details(
		&self,
		id: SourceHeaderIdOf<P>,
		nonces: RangeInclusive<MessageNonce>,
	) -> Result<MessageDetailsMap<P::SourceChainBalance>, Self::Error>;

	/// Prove messages in inclusive range [begin; end].
	async fn prove_messages(
		&self,
		id: SourceHeaderIdOf<P>,
		nonces: RangeInclusive<MessageNonce>,
		proof_parameters: MessageProofParameters,
	) -> Result<(SourceHeaderIdOf<P>, RangeInclusive<MessageNonce>, P::MessagesProof), Self::Error>;

	/// Submit messages receiving proof.
	async fn submit_messages_receiving_proof(
		&self,
		generated_at_block: TargetHeaderIdOf<P>,
		proof: P::MessagesReceivingProof,
	) -> Result<Self::TransactionTracker, Self::Error>;

	/// We need given finalized target header on source to continue synchronization.
	async fn require_target_header_on_source(&self, id: TargetHeaderIdOf<P>);

	/// Estimate cost of single message confirmation transaction in source chain tokens.
	async fn estimate_confirmation_transaction(&self) -> P::SourceChainBalance;
}

/// Target client trait.
#[async_trait]
pub trait TargetClient<P: MessageLane>: RelayClient {
	/// Transaction tracker to track submitted transactions.
	type TransactionTracker: TransactionTracker<HeaderId = TargetHeaderIdOf<P>>;

	/// Returns state of the client.
	async fn state(&self) -> Result<TargetClientState<P>, Self::Error>;

	/// Get nonce of latest received message.
	async fn latest_received_nonce(
		&self,
		id: TargetHeaderIdOf<P>,
	) -> Result<(TargetHeaderIdOf<P>, MessageNonce), Self::Error>;

	/// Get nonce of the latest confirmed message.
	async fn latest_confirmed_received_nonce(
		&self,
		id: TargetHeaderIdOf<P>,
	) -> Result<(TargetHeaderIdOf<P>, MessageNonce), Self::Error>;