program: add buffer to calculating max perp if fee (#635)

* program: add buffer to calculating max perp if fee

* update comments

* CHANGELOG

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Features
 
+- program: add buffer to calculating max perp if fee ([#635](https://github.com/drift-labs/protocol-v2/pull/635))
 - sdk: remove getMakerLimitBids/Asks ([#632](https://github.com/drift-labs/protocol-v2/pull/632))
 - program: add ix to transfer protocol if shares ([#612](https://github.com/drift-labs/protocol-v2/pull/612))
 

programs/drift/src/controller/liquidation/tests.rs

@@ -1929,8 +1929,136 @@ pub mod liquidate_perp {
         .unwrap();
 
         let market_after = perp_market_map.get_ref(&0).unwrap();
-        // .5% * 100 =$0.5
-        assert_eq!(market_after.amm.total_liquidation_fee, QUOTE_PRECISION / 2);
+        // .5% * 100 * .95 =$0.475
+        assert_eq!(market_after.amm.total_liquidation_fee, 475000);
+    }
+
+    #[test]
+    pub fn successful_liquidation_portion_of_if_fee() {
+        let now = 0_i64;
+        let slot = 0_u64;
+
+        let mut oracle_price = get_hardcoded_pyth_price(23244136, 6);
+        let oracle_price_key =
+            Pubkey::from_str("J83w4HKfqxwcq3BEMMkPFSppX3gqekLyLJBexebFVkix").unwrap();
+        let pyth_program = crate::ids::pyth_program::id();
+        create_account_info!(
+            oracle_price,
+            &oracle_price_key,
+            &pyth_program,
+            oracle_account_info
+        );
+        let mut oracle_map = OracleMap::load_one(&oracle_account_info, slot, None).unwrap();
+
+        let mut market = PerpMarket {
+            amm: AMM {
+                base_asset_reserve: 100 * AMM_RESERVE_PRECISION,
+                quote_asset_reserve: 100 * AMM_RESERVE_PRECISION,
+                bid_base_asset_reserve: 101 * AMM_RESERVE_PRECISION,
+                bid_quote_asset_reserve: 99 * AMM_RESERVE_PRECISION,
+                ask_base_asset_reserve: 99 * AMM_RESERVE_PRECISION,
+                ask_quote_asset_reserve: 101 * AMM_RESERVE_PRECISION,
+                sqrt_k: 100 * AMM_RESERVE_PRECISION,
+                peg_multiplier: 100 * PEG_PRECISION,
+                max_slippage_ratio: 50,
+                max_fill_reserve_fraction: 100,
+                order_step_size: 10000000,
+                quote_asset_amount: 50 * QUOTE_PRECISION_I128,
+                base_asset_amount_with_amm: BASE_PRECISION_I128,
+                oracle: oracle_price_key,
+                historical_oracle_data: HistoricalOracleData::default_price(oracle_price.agg.price),
+                funding_period: 3600,
+                ..AMM::default()
+            },
+            margin_ratio_initial: 1000,
+            margin_ratio_maintenance: 500,
+            number_of_users_with_base: 1,
+            number_of_users: 1,
+            status: MarketStatus::Initialized,
+            liquidator_fee: LIQUIDATION_FEE_PRECISION / 100,
+            if_liquidation_fee: LIQUIDATION_FEE_PRECISION / 100,
+            ..PerpMarket::default()
+        };
+        create_anchor_account_info!(market, PerpMarket, market_account_info);
+        let perp_market_map = PerpMarketMap::load_one(&market_account_info, true).unwrap();
+
+        let mut spot_market = SpotMarket {
+            market_index: 0,
+            oracle_source: OracleSource::QuoteAsset,
+            cumulative_deposit_interest: SPOT_CUMULATIVE_INTEREST_PRECISION,
+            decimals: 6,
+            initial_asset_weight: SPOT_WEIGHT_PRECISION,
+            historical_oracle_data: HistoricalOracleData {
+                last_oracle_price_twap: PRICE_PRECISION_I64,
+                last_oracle_price_twap_5min: PRICE_PRECISION_I64,
+                ..HistoricalOracleData::default()
+            },
+            ..SpotMarket::default()
+        };
+        create_anchor_account_info!(spot_market, SpotMarket, spot_market_account_info);
+        let spot_market_map = SpotMarketMap::load_one(&spot_market_account_info, true).unwrap();
+
+        let mut user = User {
+            perp_positions: get_positions(PerpPosition {
+                market_index: 0,
+                base_asset_amount: -299400000000,
+                quote_asset_amount: 6959294318,
+                quote_entry_amount: 6959294318,
+                quote_break_even_amount: 6959294318,
+                ..PerpPosition::default()
+            }),
+            spot_positions: get_spot_positions(SpotPosition {
+                market_index: 0,
+                balance_type: SpotBalanceType::Deposit,
+                scaled_balance: 113838792 * 1000,
+                ..SpotPosition::default()
+            }),
+            ..User::default()
+        };
+
+        let mut liquidator = User {
+            spot_positions: get_spot_positions(SpotPosition {
+                market_index: 0,
+                balance_type: SpotBalanceType::Deposit,
+                scaled_balance: 50000 * SPOT_BALANCE_PRECISION_U64,
+                ..SpotPosition::default()
+            }),
+            ..User::default()
+        };
+
+        let user_key = Pubkey::default();
+        let liquidator_key = Pubkey::default();
+
+        let mut user_stats = UserStats::default();
+        let mut liquidator_stats = UserStats::default();
+        let state = State {
+            liquidation_margin_buffer_ratio: 200,
+            initial_pct_to_liquidate: LIQUIDATION_PCT_PRECISION as u16,
+            liquidation_duration: 150,
+            ..Default::default()
+        };
+        liquidate_perp(
+            0,
+            300 * BASE_PRECISION_U64,
+            None,
+            &mut user,
+            &user_key,
+            &mut user_stats,
+            &mut liquidator,
+            &liquidator_key,
+            &mut liquidator_stats,
+            &perp_market_map,
+            &spot_market_map,
+            &mut oracle_map,
+            slot,
+            now,
+            &state,
+        )
+        .unwrap();
+
+        let market_after = perp_market_map.get_ref(&0).unwrap();
+        assert!(!user.is_being_liquidated());
+        assert_eq!(market_after.amm.total_liquidation_fee, 41787043);
     }
 }
 

programs/drift/src/math/liquidation.rs

@@ -379,15 +379,21 @@ pub fn calculate_perp_if_fee(
         .safe_div(PRICE_PRECISION)?;
 
     // margin ratio - liquidator fee - (margin shortage / (user base asset amount * price))
-    let implied_if_fee = margin_ratio.saturating_sub(liquidator_fee).saturating_sub(
-        margin_shortage
-            .safe_mul(BASE_PRECISION)?
-            .safe_div(user_base_asset_amount.cast()?)?
-            .safe_mul(PRICE_PRECISION)?
-            .safe_div(price)?
-            .cast::<u32>()
-            .unwrap_or(u32::MAX),
-    );
+    let implied_if_fee = margin_ratio
+        .saturating_sub(liquidator_fee)
+        .saturating_sub(
+            margin_shortage
+                .safe_mul(BASE_PRECISION)?
+                .safe_div(user_base_asset_amount.cast()?)?
+                .safe_mul(PRICE_PRECISION)?
+                .safe_div(price)?
+                .cast::<u32>()
+                .unwrap_or(u32::MAX),
+        )
+        // multiply by 95% to avoid situation where fee leads to deposits == negative pnl
+        // leading to bankruptcy
+        .safe_mul(19)?
+        .safe_div(20)?;
 
     Ok(max_if_liquidation_fee.min(implied_if_fee))
 }

programs/drift/src/math/liquidation/tests.rs

@@ -560,7 +560,7 @@ mod calculate_perp_if_fee {
         )
         .unwrap();
 
-        assert_eq!(fee, LIQUIDATION_FEE_PRECISION / 50); // 2%
+        assert_eq!(fee, 19000); // 2% * .95
 
         let tiny_margin_shortage = QUOTE_PRECISION;
         let fee = calculate_perp_if_fee(
@@ -574,7 +574,7 @@ mod calculate_perp_if_fee {
         )
         .unwrap();
 
-        assert_eq!(fee, 39000); // 3.9%
+        assert_eq!(fee, 37050); // 3.9% * .95
 
         let huge_margin_shortage = 1000 * QUOTE_PRECISION;
         let fee = calculate_perp_if_fee(