Add 'lending_currentInterestRate' RPC method (#959)

* Add 'current_interest_rate' RPC endpoint in pallet-lending

* Fix remarks

* Add tests

Author: andor0

frame/lending/rpc/Cargo.toml

@@ -0,0 +1,31 @@
+[package]
+authors = ["Composable Developers"]
+edition = "2021"
+homepage = "https://composable.finance"
+name = "lending-rpc"
+rust-version = "1.56"
+version = "0.0.1"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+# substrate primitives
+sp-api = { git = "https://github.com/paritytech/substrate", branch = "polkadot-v0.9.18" }
+sp-blockchain = { git = "https://github.com/paritytech/substrate", branch = "polkadot-v0.9.18" }
+sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "polkadot-v0.9.18" }
+sp-std = { git = "https://github.com/paritytech/substrate", branch = "polkadot-v0.9.18" }
+
+# local
+composable-support = { path = "../../composable-support" }
+composable-traits = { path = "../../composable-traits" }
+lending-runtime-api = { path = "../runtime-api" }
+
+# SCALE
+codec = { default-features = false, features = [ "derive" ], package = "parity-scale-codec", version = "3.0.0" }
+scale-info = { version = "2.1.1", default-features = false, features = [ "derive" ] }
+
+# rpc
+jsonrpc-core = "18.0.0"
+jsonrpc-core-client = "18.0.0"
+jsonrpc-derive = "18.0.0"

frame/lending/rpc/src/lib.rs

@@ -0,0 +1,66 @@
+use codec::Codec;
+use composable_support::rpc_helpers::SafeRpcWrapper;
+use composable_traits::defi::Rate;
+use core::{fmt::Display, str::FromStr};
+use jsonrpc_core::{Error as RpcError, ErrorCode, Result as RpcResult};
+use jsonrpc_derive::rpc;
+use lending_runtime_api::LendingRuntimeApi;
+use sp_api::ProvideRuntimeApi;
+use sp_blockchain::HeaderBackend;
+use sp_runtime::{generic::BlockId, traits::Block as BlockT};
+use sp_std::sync::Arc;
+
+#[rpc]
+pub trait LendingApi<BlockHash, MarketId>
+where
+	MarketId: FromStr + Display,
+{
+	#[rpc(name = "lending_currentInterestRate")]
+	fn current_interest_rate(
+		&self,
+		market_id: SafeRpcWrapper<MarketId>,
+		at: Option<BlockHash>,
+	) -> RpcResult<SafeRpcWrapper<Rate>>;
+}
+
+pub struct Lending<C, Block> {
+	client: Arc<C>,
+	_marker: sp_std::marker::PhantomData<Block>,
+}
+
+impl<C, M> Lending<C, M> {
+	pub fn new(client: Arc<C>) -> Self {
+		Self { client, _marker: Default::default() }
+	}
+}
+
+impl<C, Block, MarketId> LendingApi<<Block as BlockT>::Hash, MarketId>
+	for Lending<C, (Block, MarketId)>
+where
+	Block: BlockT,
+	MarketId: Send + Sync + 'static + Codec + FromStr + Display,
+	C: Send + Sync + 'static,
+	C: ProvideRuntimeApi<Block>,
+	C: HeaderBackend<Block>,
+	C::Api: LendingRuntimeApi<Block, MarketId>,
+{
+	fn current_interest_rate(
+		&self,
+		market_id: SafeRpcWrapper<MarketId>,
+		at: Option<<Block as BlockT>::Hash>,
+	) -> RpcResult<SafeRpcWrapper<Rate>> {
+		let api = self.client.runtime_api();
+
+		let at = BlockId::hash(at.unwrap_or_else(|| self.client.info().best_hash));
+
+		// calling ../../runtime-api
+		let runtime_api_result = api.current_interest_rate(&at, market_id.0);
+		runtime_api_result.map_err(|e| {
+			RpcError {
+				code: ErrorCode::ServerError(9876), // No real reason for this value
+				message: "Something wrong".into(),
+				data: Some(format!("{:?}", e).into()),
+			}
+		})
+	}
+}

frame/lending/runtime-api/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+authors = ["Composable Developers"]
+edition = "2021"
+homepage = "https://composable.finance"
+name = "lending-runtime-api"
+rust-version = "1.56"
+version = "0.0.1"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+codec = { default-features = false, features = [ "derive" ], package = "parity-scale-codec", version = "3.0.0" }
+composable-support = { path = "../../composable-support", default-features = false }
+composable-traits = { path = "../../composable-traits", default-features = false }
+sp-api = { default-features = false, git = "https://github.com/paritytech/substrate", branch = "polkadot-v0.9.18" }
+
+[features]
+default = ["std"]
+std = ["sp-api/std", "composable-support/std"]

frame/lending/runtime-api/src/lib.rs

@@ -0,0 +1,17 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use codec::Codec;
+use composable_support::rpc_helpers::SafeRpcWrapper;
+use composable_traits::defi::Rate;
+
+// Lending Runtime API declaration. Implemented for each runtime at
+// `runtime/<runtime-name>/src/lib.rs`.
+sp_api::decl_runtime_apis! {
+	pub trait LendingRuntimeApi<MarketId>
+	where
+		MarketId: Codec,
+	{
+		/// Retrieve the current interest rate for the given `market_id`.
+		fn current_interest_rate(market_id: MarketId) -> SafeRpcWrapper<Rate>;
+	}
+}

frame/lending/src/lib.rs

@@ -116,14 +116,16 @@ pub mod pallet {
 		<T as Config>::LiquidationStrategyId,
 	>;
 
+	pub type MarketId = u32;
+
 	// REVIEW: Maybe move this to `models::market_index`?
 	// TODO: Rename to `MarketId`.
 	#[derive(Default, Debug, Copy, Clone, Encode, Decode, PartialEq, MaxEncodedLen, TypeInfo)]
 	#[repr(transparent)]
 	pub struct MarketIndex(
 		#[cfg(test)] // to allow pattern matching in tests outside of this crate
-		pub u32,
-		#[cfg(not(test))] pub(crate) u32,
+		pub MarketId,
+		#[cfg(not(test))] pub(crate) MarketId,
 	);
 
 	impl MarketIndex {
@@ -1773,4 +1775,24 @@ pub mod pallet {
 		pub(crate) accrued_increment: T::Balance,
 		pub(crate) new_borrow_index: FixedU128,
 	}
+
+	/// Retrieve the current interest rate for the given `market_id`.
+	pub fn current_interest_rate<T: Config>(market_id: MarketId) -> Result<Rate, DispatchError> {
+		let market_id = MarketIndex::new(market_id);
+		let total_borrowed_from_market_excluding_interest =
+			Pallet::<T>::total_borrowed_from_market_excluding_interest(&market_id)?;
+		let total_available_to_be_borrowed =
+			Pallet::<T>::total_available_to_be_borrowed(&market_id)?;
+		let utilization_ratio = Pallet::<T>::calculate_utilization_ratio(
+			total_available_to_be_borrowed,
+			total_borrowed_from_market_excluding_interest,
+		)?;
+
+		Markets::<T>::try_get(market_id)
+			.map_err(|_| Error::<T>::MarketDoesNotExist)?
+			.interest_rate_model
+			.get_borrow_rate(utilization_ratio)
+			.ok_or(Error::<T>::BorrowRateDoesNotExist)
+			.map_err(Into::into)
+	}
 }

frame/lending/src/tests.rs

@@ -1039,6 +1039,38 @@ fn test_warn_soon_under_collateralized() {
 	});
 }
 
+#[test]
+fn current_interest_rate_test() {
+	new_test_ext().execute_with(|| {
+		System::set_block_number(1);
+		let manager = *ALICE;
+		// Create a market
+		let ((market_id, _), _) = create_simple_vaulted_market(BTC::instance(), manager);
+
+		assert_eq!(
+			crate::current_interest_rate::<Runtime>(market_id.0).unwrap(),
+			FixedU128::saturating_from_rational(2, 100)
+		);
+
+		// Update the market
+		let market = crate::Markets::<Runtime>::get(market_id).unwrap();
+		let update_input = UpdateInput {
+			collateral_factor: market.collateral_factor,
+			under_collateralized_warn_percent: market.under_collateralized_warn_percent,
+			liquidators: market.liquidators,
+			interest_rate_model: InterestRateModel::Curve(
+				CurveModel::new(CurveModel::MAX_BASE_RATE).unwrap(),
+			),
+		};
+		assert_ok!(Lending::update_market(Origin::signed(manager), market_id, update_input));
+
+		assert_eq!(
+			crate::current_interest_rate::<Runtime>(market_id.0).unwrap(),
+			FixedU128::saturating_from_rational(1, 10)
+		);
+	})
+}
+
 prop_compose! {
 	fn valid_amount_without_overflow()
 		(x in MINIMUM_BALANCE..u64::MAX as Balance) -> Balance {