stake-pool: Ceiling all fee calculations (HAL-01) (#6153)

stake-pool: Ceiling all fee calculations

Author: joncinque

stake-pool/program/src/state.rs

@@ -942,9 +942,13 @@ impl Fee {
         if self.denominator == 0 {
             return Some(0);
         }
-        (amt as u128)
-            .checked_mul(self.numerator as u128)?
-            .checked_div(self.denominator as u128)
+        let numerator = (amt as u128).checked_mul(self.numerator as u128)?;
+        // ceiling the calculation by adding (denominator - 1) to the numerator
+        let denominator = self.denominator as u128;
+        numerator
+            .checked_add(denominator)?
+            .checked_sub(1)?
+            .checked_div(denominator)
     }
 
     /// Withdrawal fees have some additional restrictions,

stake-pool/program/tests/helpers/mod.rs

@@ -897,15 +897,17 @@ impl StakePoolAccounts {
     }
 
     pub fn calculate_fee(&self, amount: u64) -> u64 {
-        amount * self.epoch_fee.numerator / self.epoch_fee.denominator
+        (amount * self.epoch_fee.numerator + self.epoch_fee.denominator - 1)
+            / self.epoch_fee.denominator
     }
 
     pub fn calculate_withdrawal_fee(&self, pool_tokens: u64) -> u64 {
-        pool_tokens * self.withdrawal_fee.numerator / self.withdrawal_fee.denominator
+        (pool_tokens * self.withdrawal_fee.numerator + self.withdrawal_fee.denominator - 1)
+            / self.withdrawal_fee.denominator
     }
 
     pub fn calculate_inverse_withdrawal_fee(&self, pool_tokens: u64) -> u64 {
-        pool_tokens * self.withdrawal_fee.denominator
+        (pool_tokens * self.withdrawal_fee.denominator + self.withdrawal_fee.denominator - 1)
             / (self.withdrawal_fee.denominator - self.withdrawal_fee.numerator)
     }
 
@@ -914,7 +916,8 @@ impl StakePoolAccounts {
     }
 
     pub fn calculate_sol_deposit_fee(&self, pool_tokens: u64) -> u64 {
-        pool_tokens * self.sol_deposit_fee.numerator / self.sol_deposit_fee.denominator
+        (pool_tokens * self.sol_deposit_fee.numerator + self.sol_deposit_fee.denominator - 1)
+            / self.sol_deposit_fee.denominator
     }
 
     pub fn calculate_sol_referral_fee(&self, deposit_fee_collected: u64) -> u64 {

stake-pool/program/tests/withdraw_sol.rs

@@ -214,15 +214,15 @@ async fn fail_overdraw_reserve() {
         .await;
     assert!(error.is_none(), "{:?}", error);
 
-    // try to withdraw one lamport, will overdraw
+    // try to withdraw one lamport after fees, will overdraw
     let error = stake_pool_accounts
         .withdraw_sol(
             &mut context.banks_client,
             &context.payer,
             &context.last_blockhash,
             &user,
             &pool_token_account,
-            1,
+            2,
             None,
         )
         .await

stake-pool/program/tests/withdraw_with_fee.rs

@@ -6,10 +6,10 @@ mod helpers;
 use {
     bincode::deserialize,
     helpers::*,
-    solana_program::{borsh0_10::try_from_slice_unchecked, pubkey::Pubkey, stake},
+    solana_program::{pubkey::Pubkey, stake},
     solana_program_test::*,
     solana_sdk::signature::{Keypair, Signer},
-    spl_stake_pool::{minimum_stake_lamports, state},
+    spl_stake_pool::minimum_stake_lamports,
 };
 
 #[tokio::test]
@@ -183,20 +183,8 @@ async fn success_empty_out_stake_with_fee() {
             .await;
     let lamports_to_withdraw =
         validator_stake_account.lamports - minimum_stake_lamports(&meta, stake_minimum_delegation);
-    let stake_pool_account = get_account(
-        &mut context.banks_client,
-        &stake_pool_accounts.stake_pool.pubkey(),
-    )
-    .await;
-    let stake_pool =
-        try_from_slice_unchecked::<state::StakePool>(stake_pool_account.data.as_slice()).unwrap();
-    let fee = stake_pool.stake_withdrawal_fee;
-    let inverse_fee = state::Fee {
-        numerator: fee.denominator - fee.numerator,
-        denominator: fee.denominator,
-    };
     let pool_tokens_to_withdraw =
-        lamports_to_withdraw * inverse_fee.denominator / inverse_fee.numerator;
+        stake_pool_accounts.calculate_inverse_withdrawal_fee(lamports_to_withdraw);
 
     let last_blockhash = context
         .banks_client