Ignore reward when funds unavailable

bridges/snowbridge/Cargo.toml

@@ -52,3 +52,16 @@ derivable_impls = { level = "allow", priority = 2 }                  # false pos
 stable_sort_primitive = { level = "allow", priority = 2 }            # prefer stable sort
 extra-unused-type-parameters = { level = "allow", priority = 2 }     # stylistic
 default_constructed_unit_structs = { level = "allow", priority = 2 } # stylistic
+
+[workspace.dependencies]
+polkavm-linker = "0.8.2"
+polkavm-derive = "0.8.0"
+log = { version = "0.4.20", default-features = false }
+quote = { version = "1.0.33" }
+serde = { version = "1.0.197", default-features = false }
+serde-big-array = { version = "0.3.2" }
+serde_derive = { version = "1.0.117" }
+serde_json = { version = "1.0.114", default-features = false }
+serde_yaml = { version = "0.9" }
+syn = { version = "2.0.50" }
+thiserror = { version = "1.0.48" }

bridges/snowbridge/pallets/inbound-queue/src/lib.rs

@@ -44,14 +44,15 @@ use envelope::Envelope;
 use frame_support::{
 	traits::{
 		fungible::{Inspect, Mutate},
-		tokens::Preservation,
+		tokens::{Fortitude, Preservation},
 	},
 	weights::WeightToFee,
 	PalletError,
 };
 use frame_system::ensure_signed;
 use scale_info::TypeInfo;
 use sp_core::{H160, H256};
+use sp_runtime::traits::Zero;
 use sp_std::{convert::TryFrom, vec};
 use xcm::prelude::{
 	send_xcm, Instruction::SetTopic, Junction::*, Location, SendError as XcmpSendError, SendXcm,
@@ -261,11 +262,19 @@ pub mod pallet {
 				}
 			})?;
 
-			// Reward relayer from the sovereign account of the destination parachain
-			// Expected to fail if sovereign account has no funds
+			// Reward relayer from the sovereign account of the destination parachain, only if funds
+			// are available
 			let sovereign_account = sibling_sovereign_account::<T>(channel.para_id);
 			let delivery_cost = Self::calculate_delivery_cost(message.encode().len() as u32);
-			T::Token::transfer(&sovereign_account, &who, delivery_cost, Preservation::Preserve)?;
+			let amount = T::Token::reducible_balance(
+				&sovereign_account,
+				Preservation::Preserve,
+				Fortitude::Polite,
+			)
+			.min(delivery_cost);
+			if amount > BalanceOf::<T>::zero() {
+				T::Token::transfer(&sovereign_account, &who, amount, Preservation::Preserve)?;
+			}
 
 			// Decode message into XCM
 			let (xcm, fee) =

bridges/snowbridge/pallets/inbound-queue/src/mock.rs

@@ -4,7 +4,7 @@ use super::*;
 
 use frame_support::{
 	parameter_types,
-	traits::{ConstU128, ConstU32, Everything},
+	traits::{ConstU32, Everything},
 	weights::IdentityFee,
 };
 use hex_literal::hex;
@@ -74,14 +74,18 @@ impl frame_system::Config for Test {
 	type Block = Block;
 }
 
+parameter_types! {
+	pub const ExistentialDeposit: u128 = 1;
+}
+
 impl pallet_balances::Config for Test {
 	type MaxLocks = ();
 	type MaxReserves = ();
 	type ReserveIdentifier = [u8; 8];
 	type Balance = Balance;
 	type RuntimeEvent = RuntimeEvent;
 	type DustRemoval = ();
-	type ExistentialDeposit = ConstU128<1>;
+	type ExistentialDeposit = ExistentialDeposit;
 	type AccountStore = System;
 	type WeightInfo = ();
 	type FreezeIdentifier = ();

bridges/snowbridge/pallets/inbound-queue/src/test.rs

@@ -6,7 +6,7 @@ use frame_support::{assert_noop, assert_ok};
 use hex_literal::hex;
 use snowbridge_core::{inbound::Proof, ChannelId};
 use sp_keyring::AccountKeyring as Keyring;
-use sp_runtime::{DispatchError, TokenError};
+use sp_runtime::DispatchError;
 use sp_std::convert::From;
 
 use crate::{Error, Event as InboundQueueEvent};
@@ -150,12 +150,12 @@ fn test_submit_with_invalid_nonce() {
 }
 
 #[test]
-fn test_submit_no_funds_to_reward_relayers() {
+fn test_submit_no_funds_to_reward_relayers_just_ignore() {
 	new_tester().execute_with(|| {
 		let relayer: AccountId = Keyring::Bob.into();
 		let origin = RuntimeOrigin::signed(relayer);
 
-		// Reset balance of sovereign_account to zero so to trigger the FundsUnavailable error
+		// Reset balance of sovereign_account to zero first
 		let sovereign_account = sibling_sovereign_account::<Test>(ASSET_HUB_PARAID.into());
 		Balances::set_balance(&sovereign_account, 0);
 
@@ -168,10 +168,8 @@ fn test_submit_no_funds_to_reward_relayers() {
 				data: Default::default(),
 			},
 		};
-		assert_noop!(
-			InboundQueue::submit(origin.clone(), message.clone()),
-			TokenError::FundsUnavailable
-		);
+		// Check submit successfully in case no funds available
+		assert_ok!(InboundQueue::submit(origin.clone(), message.clone()));
 	});
 }
 
@@ -210,3 +208,46 @@ fn test_set_operating_mode_root_only() {
 		);
 	});
 }
+
+#[test]
+fn test_submit_no_funds_to_reward_relayers_and_ed_preserved() {
+	new_tester().execute_with(|| {
+		let relayer: AccountId = Keyring::Bob.into();
+		let origin = RuntimeOrigin::signed(relayer);
+
+		// Reset balance of sovereign account to (ED+1) first
+		let sovereign_account = sibling_sovereign_account::<Test>(ASSET_HUB_PARAID.into());
+		Balances::set_balance(&sovereign_account, ExistentialDeposit::get() + 1);
+
+		// Submit message successfully
+		let message = Message {
+			event_log: mock_event_log(),
+			proof: Proof {
+				block_hash: Default::default(),
+				tx_index: Default::default(),
+				data: Default::default(),
+			},
+		};
+		assert_ok!(InboundQueue::submit(origin.clone(), message.clone()));
+
+		// Check balance of sovereign account to ED
+		let amount = Balances::balance(&sovereign_account);
+		assert_eq!(amount, ExistentialDeposit::get());
+
+		// Submit another message with nonce set as 2
+		let mut event_log = mock_event_log();
+		event_log.data[31] = 2;
+		let message = Message {
+			event_log,
+			proof: Proof {
+				block_hash: Default::default(),
+				tx_index: Default::default(),
+				data: Default::default(),
+			},
+		};
+		assert_ok!(InboundQueue::submit(origin.clone(), message.clone()));
+		// Check balance of sovereign account as ED does not change
+		let amount = Balances::balance(&sovereign_account);
+		assert_eq!(amount, ExistentialDeposit::get());
+	});
+}

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/tests/snowbridge.rs

@@ -29,7 +29,7 @@ use snowbridge_pallet_inbound_queue_fixtures::{
 use snowbridge_pallet_system;
 use snowbridge_router_primitives::inbound::GlobalConsensusEthereumConvertsFor;
 use sp_core::H256;
-use sp_runtime::{ArithmeticError::Underflow, DispatchError::Arithmetic};
+use sp_runtime::{DispatchError::Token, TokenError::FundsUnavailable};
 use testnet_parachains_constants::rococo::snowbridge::EthereumNetwork;
 
 const INITIAL_FUND: u128 = 5_000_000_000 * ROCOCO_ED;
@@ -532,6 +532,6 @@ fn send_token_from_ethereum_to_asset_hub_fail_for_insufficient_fund() {
 	BridgeHubRococo::fund_para_sovereign(AssetHubRococo::para_id().into(), 1_000);
 
 	BridgeHubRococo::execute_with(|| {
-		assert_err!(send_inbound_message(make_register_token_message()), Arithmetic(Underflow));
+		assert_err!(send_inbound_message(make_register_token_message()), Token(FundsUnavailable));
 	});
 }