Relay basic single-bit message dispatch results back to the source chain (#935)

* relay dispatch result flags back to the source chain

* OnMessagesDelivered callback

* add lane id to OnDeliveredMessages callback

* fix benchmarks && upate weights

* clippy

* clippy

* clipy another try

* OnMessagesDelivered -> OnDeliveryConfirmed

* Update primitives/messages/src/source_chain.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

bridges/primitives/messages/Cargo.toml

@@ -7,7 +7,9 @@ edition = "2018"
 license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
 
 [dependencies]
-codec = { package = "parity-scale-codec", version = "2.0.0", default-features = false, features = ["derive"] }
+bitvec = { version = "0.20", default-features = false, features = ["alloc"] }
+codec = { package = "parity-scale-codec", version = "2.0.0", default-features = false, features = ["derive", "bit-vec"] }
+impl-trait-for-tuples = "0.2"
 serde = { version = "1.0.101", optional = true, features = ["derive"] }
 
 # Bridge dependencies

bridges/primitives/messages/src/lib.rs

@@ -22,6 +22,7 @@
 // Generated by `DecodeLimit::decode_with_depth_limit`
 #![allow(clippy::unnecessary_mut_passed)]
 
+use bitvec::prelude::*;
 use codec::{Decode, Encode};
 use frame_support::RuntimeDebug;
 use sp_std::{collections::vec_deque::VecDeque, prelude::*};
@@ -120,7 +121,7 @@ pub struct InboundLaneData<RelayerId> {
 	/// When a relayer sends a single message, both of MessageNonces are the same.
 	/// When relayer sends messages in a batch, the first arg is the lowest nonce, second arg the highest nonce.
 	/// Multiple dispatches from the same relayer are allowed.
-	pub relayers: VecDeque<(MessageNonce, MessageNonce, RelayerId)>,
+	pub relayers: VecDeque<UnrewardedRelayer<RelayerId>>,
 
 	/// Nonce of the last message that
 	/// a) has been delivered to the target (this) chain and
@@ -147,18 +148,22 @@ impl<RelayerId> InboundLaneData<RelayerId> {
 	/// size of each entry.
 	///
 	/// Returns `None` if size overflows `u32` limits.
-	pub fn encoded_size_hint(relayer_id_encoded_size: u32, relayers_entries: u32) -> Option<u32> {
+	pub fn encoded_size_hint(relayer_id_encoded_size: u32, relayers_entries: u32, messages_count: u32) -> Option<u32> {
 		let message_nonce_size = 8;
 		let relayers_entry_size = relayer_id_encoded_size.checked_add(2 * message_nonce_size)?;
 		let relayers_size = relayers_entries.checked_mul(relayers_entry_size)?;
-		relayers_size.checked_add(message_nonce_size)
+		let dispatch_results_per_byte = 8;
+		let dispatch_result_size = sp_std::cmp::max(relayers_entries, messages_count / dispatch_results_per_byte);
+		relayers_size
+			.checked_add(message_nonce_size)
+			.and_then(|result| result.checked_add(dispatch_result_size))
 	}
 
 	/// Nonce of the last message that has been delivered to this (target) chain.
 	pub fn last_delivered_nonce(&self) -> MessageNonce {
 		self.relayers
 			.back()
-			.map(|(_, last_nonce, _)| *last_nonce)
+			.map(|entry| entry.messages.end)
 			.unwrap_or(self.last_confirmed_nonce)
 	}
 }
@@ -176,6 +181,71 @@ pub struct MessageDetails<OutboundMessageFee> {
 	pub delivery_and_dispatch_fee: OutboundMessageFee,
 }
 
+/// Bit vector of message dispatch results.
+pub type DispatchResultsBitVec = BitVec<Msb0, u8>;
+
+/// Unrewarded relayer entry stored in the inbound lane data.
+///
+/// This struct represents a continuous range of messages that have been delivered by the same relayer
+/// and whose confirmations are still pending.
+#[derive(Encode, Decode, Clone, RuntimeDebug, PartialEq, Eq)]
+pub struct UnrewardedRelayer<RelayerId> {
+	/// Identifier of the relayer.
+	pub relayer: RelayerId,
+	/// Messages range, delivered by this relayer.
+	pub messages: DeliveredMessages,
+}
+
+/// Delivered messages with their dispatch result.
+#[derive(Clone, Default, Encode, Decode, RuntimeDebug, PartialEq, Eq)]
+pub struct DeliveredMessages {
+	/// Nonce of the first message that has been delivered (inclusive).
+	pub begin: MessageNonce,
+	/// Nonce of the last message that has been delivered (inclusive).
+	pub end: MessageNonce,
+	/// Dispatch result (`false`/`true`), returned by the message dispatcher for every
+	/// message in the `[begin; end]` range. See `dispatch_result` field of the
+	/// `bp_runtime::messages::MessageDispatchResult` structure for more information.
+	pub dispatch_results: DispatchResultsBitVec,
+}
+
+impl DeliveredMessages {
+	/// Create new `DeliveredMessages` struct that confirms delivery of single nonce with given dispatch result.
+	pub fn new(nonce: MessageNonce, dispatch_result: bool) -> Self {
+		DeliveredMessages {
+			begin: nonce,
+			end: nonce,
+			dispatch_results: bitvec![Msb0, u8; if dispatch_result { 1 } else { 0 }],
+		}
+	}
+
+	/// Note new dispatched message.
+	pub fn note_dispatched_message(&mut self, dispatch_result: bool) {
+		self.end += 1;
+		self.dispatch_results.push(dispatch_result);
+	}
+
+	/// Returns true if delivered messages contain message with given nonce.
+	pub fn contains_message(&self, nonce: MessageNonce) -> bool {
+		(self.begin..=self.end).contains(&nonce)
+	}
+
+	/// Get dispatch result flag by message nonce.
+	///
+	/// Dispatch result flag must be interpreted using the knowledge of dispatch mechanism
+	/// at the target chain. See `dispatch_result` field of the
+	/// `bp_runtime::messages::MessageDispatchResult` structure for more information.
+	///
+	/// Panics if message nonce is not in the `begin..=end` range. Typically you'll first
+	/// check if message is within the range by calling `contains_message`.
+	pub fn message_dispatch_result(&self, nonce: MessageNonce) -> bool {
+		const INVALID_NONCE: &str = "Invalid nonce used to index dispatch_results";
+
+		let index = nonce.checked_sub(self.begin).expect(INVALID_NONCE) as usize;
+		*self.dispatch_results.get(index).expect(INVALID_NONCE)
+	}
+}
+
 /// Gist of `InboundLaneData::relayers` field used by runtime APIs.
 #[derive(Clone, Default, Encode, Decode, RuntimeDebug, PartialEq, Eq)]
 pub struct UnrewardedRelayersState {
@@ -214,12 +284,10 @@ impl Default for OutboundLaneData {
 /// Returns total number of messages in the `InboundLaneData::relayers` vector.
 ///
 /// Returns `None` if there are more messages that `MessageNonce` may fit (i.e. `MessageNonce + 1`).
-pub fn total_unrewarded_messages<RelayerId>(
-	relayers: &VecDeque<(MessageNonce, MessageNonce, RelayerId)>,
-) -> Option<MessageNonce> {
+pub fn total_unrewarded_messages<RelayerId>(relayers: &VecDeque<UnrewardedRelayer<RelayerId>>) -> Option<MessageNonce> {
 	match (relayers.front(), relayers.back()) {
-		(Some((begin, _, _)), Some((_, end, _))) => {
-			if let Some(difference) = end.checked_sub(*begin) {
+		(Some(front), Some(back)) => {
+			if let Some(difference) = back.messages.end.checked_sub(front.messages.begin) {
 				difference.checked_add(1)
 			} else {
 				Some(0)
@@ -237,9 +305,18 @@ mod tests {
 	fn total_unrewarded_messages_does_not_overflow() {
 		assert_eq!(
 			total_unrewarded_messages(
-				&vec![(0, 0, 1), (MessageNonce::MAX, MessageNonce::MAX, 2)]
-					.into_iter()
-					.collect()
+				&vec![
+					UnrewardedRelayer {
+						relayer: 1,
+						messages: DeliveredMessages::new(0, true)
+					},
+					UnrewardedRelayer {
+						relayer: 2,
+						messages: DeliveredMessages::new(MessageNonce::MAX, true)
+					},
+				]
+				.into_iter()
+				.collect()
 			),
 			None,
 		);
@@ -247,19 +324,60 @@ mod tests {
 
 	#[test]
 	fn inbound_lane_data_returns_correct_hint() {
-		let expected_size = InboundLaneData::<u8>::encoded_size_hint(1, 13);
-		let actual_size = InboundLaneData {
-			relayers: (1u8..=13u8).map(|i| (i as _, i as _, i)).collect(),
-			last_confirmed_nonce: 13,
+		let test_cases = vec![
+			// single relayer, multiple messages
+			(1, 128u8),
+			// multiple relayers, single message per relayer
+			(128u8, 128u8),
+			// several messages per relayer
+			(13u8, 128u8),
+		];
+		for (relayer_entries, messages_count) in test_cases {
+			let expected_size = InboundLaneData::<u8>::encoded_size_hint(1, relayer_entries as _, messages_count as _);
+			let actual_size = InboundLaneData {
+				relayers: (1u8..=relayer_entries)
+					.map(|i| {
+						let mut entry = UnrewardedRelayer {
+							relayer: i,
+							messages: DeliveredMessages::new(i as _, true),
+						};
+						entry.messages.dispatch_results = bitvec![
+							Msb0, u8;
+							1;
+							(messages_count / relayer_entries) as _
+						];
+						entry
+					})
+					.collect(),
+				last_confirmed_nonce: messages_count as _,
+			}
+			.encode()
+			.len();
+			let difference = (expected_size.unwrap() as f64 - actual_size as f64).abs();
+			assert!(
+				difference / (std::cmp::min(actual_size, expected_size.unwrap() as usize) as f64) < 0.1,
+				"Too large difference between actual ({}) and expected ({:?}) inbound lane data size. Test case: {}+{}",
+				actual_size,
+				expected_size,
+				relayer_entries,
+				messages_count,
+			);
 		}
-		.encode()
-		.len();
-		let difference = (expected_size.unwrap() as f64 - actual_size as f64).abs();
-		assert!(
-			difference / (std::cmp::min(actual_size, expected_size.unwrap() as usize) as f64) < 0.1,
-			"Too large difference between actual ({}) and expected ({:?}) inbound lane data size",
-			actual_size,
-			expected_size,
-		);
+	}
+
+	#[test]
+	fn message_dispatch_result_works() {
+		let delivered_messages = DeliveredMessages {
+			begin: 100,
+			end: 150,
+			dispatch_results: bitvec![Msb0, u8; 1; 151],
+		};
+
+		assert!(!delivered_messages.contains_message(99));
+		assert!(delivered_messages.contains_message(100));
+		assert!(delivered_messages.contains_message(150));
+		assert!(!delivered_messages.contains_message(151));
+
+		assert!(delivered_messages.message_dispatch_result(125));
 	}
 }

bridges/primitives/messages/src/source_chain.rs

@@ -16,7 +16,7 @@
 
 //! Primitives of messages module, that are used on the source chain.
 
-use crate::{InboundLaneData, LaneId, MessageNonce, OutboundLaneData};
+use crate::{DeliveredMessages, InboundLaneData, LaneId, MessageNonce, OutboundLaneData};
 
 use bp_runtime::Size;
 use frame_support::{Parameter, RuntimeDebug};
@@ -135,6 +135,15 @@ pub trait MessageDeliveryAndDispatchPayment<AccountId, Balance> {
 	}
 }
 
+/// Handler for messages delivery confirmation.
+#[impl_trait_for_tuples::impl_for_tuples(30)]
+pub trait OnDeliveryConfirmed {
+	/// Called when we receive confirmation that our messages have been delivered to the
+	/// target chain. The confirmation also has single bit dispatch result for every
+	/// confirmed message (see `DeliveredMessages` for details).
+	fn on_messages_delivered(_lane: &LaneId, _messages: &DeliveredMessages) {}
+}
+
 /// Structure that may be used in place of `TargetHeaderChain`, `LaneMessageVerifier` and
 /// `MessageDeliveryAndDispatchPayment` on chains, where outbound messages are forbidden.
 pub struct ForbidOutboundMessages;

bridges/primitives/messages/src/target_chain.rs

@@ -164,6 +164,7 @@ impl<AccountId, Fee> MessageDispatch<AccountId, Fee> for ForbidInboundMessages {
 
 	fn dispatch(_: &AccountId, _: DispatchMessage<Self::DispatchPayload, Fee>) -> MessageDispatchResult {
 		MessageDispatchResult {
+			dispatch_result: false,
 			unspent_weight: 0,
 			dispatch_fee_paid_during_dispatch: false,
 		}