feat: check all restricted balances are above minimum when redeeming

state-chain/pallets/cf-funding/src/lib.rs

@@ -243,6 +243,9 @@ pub mod pallet {
 		/// When requesting a redemption, you must not have an amount below the minimum.
 		BelowMinimumFunding,
 
+		/// When requesting a redemption, all restricted balances must be above the minimum.
+		RestrictedBalanceBelowMinimumFunding,
+
 		/// There are not enough unrestricted funds to process the redemption.
 		InsufficientUnrestrictedFunds,
 
@@ -407,6 +410,13 @@ pub mod pallet {
 				// Use the full debit amount here - fees are paid by restricted funds by default.
 				total_restricted_balance = *restricted_balance;
 				restricted_balance.saturating_reduce(debit_amount);
+				// ensure that the remaining restricted balance is zero or above MinimumFunding
+				ensure!(
+					restricted_balance.is_zero() ||
+						*restricted_balance >= MinimumFunding::<T>::get(),
+					Error::<T>::RestrictedBalanceBelowMinimumFunding
+				);
+
 				if restricted_balance.is_zero() {
 					restricted_balances.remove(&address);
 				}

state-chain/pallets/cf-funding/src/tests.rs

@@ -527,9 +527,11 @@ fn redemption_expiry_removes_redemption() {
 		);
 
 		// Success, can request redemption again since the last one expired.
+		// Note that restricted balance is REDEMPTION_TAX less after refund, so adjust the
+		// TO_REDEEM accordingly to make sure restricted balance is above minimum
 		assert_ok!(Funding::redeem(
 			RuntimeOrigin::signed(ALICE),
-			TO_REDEEM.into(),
+			(TO_REDEEM - REDEMPTION_TAX).into(),
 			RESTRICTED_ADDRESS,
 			Default::default()
 		));
@@ -600,8 +602,8 @@ fn restore_restricted_balance_when_redemption_expires() {
 	do_test(RedemptionAmount::Exact(RESTRICTED_AMOUNT));
 	// Redeem a little less than the restricted balance.
 	do_test(RedemptionAmount::Exact(RESTRICTED_AMOUNT - 1));
-	// Redeem signficantly less than the restricted balance.
-	do_test(RedemptionAmount::Exact(RESTRICTED_AMOUNT - REDEMPTION_TAX * 2));
+	// Redeem significantly less than the restricted balance. Make sure rest is above minimum
+	do_test(RedemptionAmount::Exact(RESTRICTED_AMOUNT - REDEMPTION_TAX * 3));
 }
 
 #[test]
@@ -1160,6 +1162,24 @@ mod test_restricted_balances {
 			None::<Error<Test>>
 		),
 	];
+	test_restricted_balances![
+		restricted_balances_can_only_be_zero_or_above_minimum_after_redeeming,
+		NO_BOND,
+		// Succeed, with restricted balance1 = 0
+		(RedemptionAmount::Exact(RESTRICTED_BALANCE_1), RESTRICTED_ADDRESS_1, None::<Error<Test>>),
+		// Succeed, with restricted balance1 = MIN_FUNDING
+		(
+			RedemptionAmount::Exact(RESTRICTED_BALANCE_1 - MIN_FUNDING - REDEMPTION_TAX),
+			RESTRICTED_ADDRESS_1,
+			None::<Error<Test>>
+		),
+		// Fails, because restricted balance1 would have been < MIN_FUNDING
+		(
+			RedemptionAmount::Exact(RESTRICTED_BALANCE_1 - MIN_FUNDING - REDEMPTION_TAX + 1),
+			RESTRICTED_ADDRESS_1,
+			Some(Error::<Test>::RestrictedBalanceBelowMinimumFunding)
+		),
+	];
 	test_restricted_balances![
 		higher_than_restricted_amount_1_can_only_be_redeemed_to_restricted_address_2,
 		NO_BOND,