Ignore rewarding 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(do the payment
+			// only if funds 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/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};
@@ -150,7 +150,7 @@ 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);
@@ -168,10 +168,7 @@ fn test_submit_no_funds_to_reward_relayers() {
 				data: Default::default(),
 			},
 		};
-		assert_noop!(
-			InboundQueue::submit(origin.clone(), message.clone()),
-			TokenError::FundsUnavailable
-		);
+		assert_ok!(InboundQueue::submit(origin.clone(), message.clone()));
 	});
 }