[#1107] Using DefaultBaseFeePerGas * T::Threshold::ideal() as base_fee floor value.

client/rpc/src/eth/fee.rs

@@ -72,7 +72,9 @@ where
 		.await?
 		{
 			let Ok(number) = self.client.expect_block_number_from_id(&id) else {
-				return Err(internal_err(format!("Failed to retrieve block number at {id}")));
+				return Err(internal_err(format!(
+					"Failed to retrieve block number at {id}"
+				)));
 			};
 			// Highest and lowest block number within the requested range.
 			let highest = UniqueSaturatedInto::<u64>::unique_saturated_into(number);

frame/base-fee/src/lib.rs

@@ -177,7 +177,18 @@ pub mod pallet {
 						let decrease = scaled_basefee
 							.checked_div(U256::from(1_000_000))
 							.unwrap_or_else(U256::zero);
-						*bf = bf.saturating_sub(decrease);
+						let default_base_fee = T::DefaultBaseFeePerGas::get();
+						// lowest fee is norm(DefaultBaseFeePerGas * Threshold::ideal()):
+						let lowest_base_fee = default_base_fee
+							.checked_mul(U256::from(T::Threshold::ideal().deconstruct()))
+							.unwrap_or(default_base_fee)
+							.checked_div(U256::from(1_000_000))
+							.unwrap_or(default_base_fee);
+						if bf.saturating_sub(decrease) >= lowest_base_fee {
+							*bf = bf.saturating_sub(decrease);
+						} else {
+							*bf = lowest_base_fee;
+						}
 					} else {
 						Self::deposit_event(Event::BaseFeeOverflow);
 					}

frame/base-fee/src/tests.rs

@@ -33,6 +33,7 @@ use sp_runtime::{
 
 use super::*;
 use crate as pallet_base_fee;
+use crate::BaseFeeThreshold as BaseFeeThresholdT;
 
 type UncheckedExtrinsic = frame_system::mocking::MockUncheckedExtrinsic<Test>;
 type Block = frame_system::mocking::MockBlock<Test>;
@@ -75,7 +76,7 @@ parameter_types! {
 }
 
 pub struct BaseFeeThreshold;
-impl pallet_base_fee::BaseFeeThreshold for BaseFeeThreshold {
+impl BaseFeeThresholdT for BaseFeeThreshold {
 	fn lower() -> Permill {
 		Permill::zero()
 	}
@@ -132,6 +133,15 @@ pub fn new_test_ext(base_fee: Option<U256>, elasticity: Option<Permill>) -> Test
 	TestExternalities::new(t)
 }
 
+pub fn get_lowest_base_fee() -> U256 {
+	let default_base_fee = DefaultBaseFeePerGas::get();
+	default_base_fee
+		.checked_mul(U256::from(BaseFeeThreshold::ideal().deconstruct()))
+		.unwrap_or(default_base_fee)
+		.checked_div(U256::from(1_000_000))
+		.unwrap_or(default_base_fee)
+}
+
 #[test]
 fn should_default() {
 	new_test_ext(None, None).execute_with(|| {
@@ -158,12 +168,11 @@ fn should_not_overflow_u256() {
 }
 
 #[test]
-fn should_handle_zero() {
+fn should_fallback_to_default_value() {
 	let base_fee = U256::zero();
 	new_test_ext(Some(base_fee), None).execute_with(|| {
-		let init = BaseFeePerGas::<Test>::get();
 		BaseFee::on_finalize(System::block_number());
-		assert_eq!(BaseFeePerGas::<Test>::get(), init);
+		assert_eq!(BaseFeePerGas::<Test>::get(), get_lowest_base_fee());
 	});
 }
 
@@ -175,11 +184,7 @@ fn should_handle_consecutive_empty_blocks() {
 			BaseFee::on_finalize(System::block_number());
 			System::set_block_number(System::block_number() + 1);
 		}
-		assert_eq!(
-			BaseFeePerGas::<Test>::get(),
-			// 8 is the lowest number which's 12.5% is >= 1.
-			U256::from(7)
-		);
+		assert_eq!(BaseFeePerGas::<Test>::get(), get_lowest_base_fee());
 	});
 	let zero_elasticity = Permill::zero();
 	new_test_ext(Some(base_fee), Some(zero_elasticity)).execute_with(|| {