quote

Author: billythedummy

core/src/lib.rs

@@ -4,11 +4,13 @@ mod instructions;
 mod internal_utils;
 mod keys;
 mod pda;
+mod quote;
 mod state;
 mod typedefs;
 
 pub use instructions::*;
 pub use keys::*;
 pub use pda::*;
+pub use quote::*;
 pub use state::*;
 pub use typedefs::*;

core/src/quote.rs

@@ -0,0 +1,23 @@
+/// Given the total lamports of a validator stake account (includes rent-exemption),
+/// return the maximum active stake lamports that the program will allow to be withdrawn from it.
+///
+/// Returns `None` on arithmetic failure.
+///
+/// When quoting with [`crate::ExchangeRate::quote_withdraw_stake`], make sure its returned
+/// amount does not exceed this amount for the largest validator stake account in the pool.
+#[inline]
+pub const fn max_withdraw_lamports(stake_acc_total_lamports: u64) -> Option<u64> {
+    const MINIMUM_STAKE_ACCOUNT_BALANCE: u64 = 1_002_282_880;
+    const TEN_SOL: u64 = 10_000_000_000;
+
+    let ten_pct_plus_10 = match (stake_acc_total_lamports / 10).checked_add(TEN_SOL) {
+        Some(r) => r,
+        None => return None,
+    };
+    let exhaustion = stake_acc_total_lamports.saturating_sub(MINIMUM_STAKE_ACCOUNT_BALANCE);
+    Some(if ten_pct_plus_10 < exhaustion {
+        ten_pct_plus_10
+    } else {
+        exhaustion
+    })
+}

core/src/typedefs/exchange_rate.rs

@@ -7,6 +7,24 @@ pub struct ExchangeRate {
     pub sol_balance: u64,
 }
 
+impl ExchangeRate {
+    /// Returns the staked lamports that will be split
+    /// from the active stake account upon burning `stsol_amount` stSOL
+    ///
+    /// Returns None on arithmetic failure
+    #[inline]
+    pub fn quote_withdraw_stake(&self, stsol_amount: u64) -> Option<u64> {
+        if self.st_sol_supply == 0 {
+            return None;
+        }
+        // unchecked mul: 2 u64s will not overflow u128
+        // unchecked div: nonzero denom checked above
+        let res = (u128::from(stsol_amount) * u128::from(self.sol_balance))
+            / u128::from(self.st_sol_supply);
+        res.try_into().ok()
+    }
+}
+
 impl ExchangeRate {
     inherent_borsh_serde!();
 }

core/tests/tests/instructions/withdraw_v2.rs

@@ -6,7 +6,7 @@ use solana_account::Account;
 use solana_instruction::Instruction;
 use solana_pubkey::Pubkey;
 use solido_legacy_core::{
-    ValidatorList, WithdrawV2IxData, WithdrawV2IxKeysOwned, PROGRAM_ID, STAKE_PROGRAM,
+    Lido, ValidatorList, WithdrawV2IxData, WithdrawV2IxKeysOwned, PROGRAM_ID, STAKE_PROGRAM,
     WITHDRAW_V2_IX_IS_SIGNER, WITHDRAW_V2_IX_IS_WRITER,
 };
 
@@ -61,8 +61,12 @@ fn withdraw_v2_fixture() {
     const AMOUNT: u64 = 1_000_000_000;
 
     let account = KeyedUiAccount::from_test_fixtures_file("validator-list");
-    let data = account.account_data();
-    let val_list = ValidatorList::deserialize(data.as_slice()).unwrap();
+    let val_list_data = account.account_data();
+    let val_list = ValidatorList::deserialize(val_list_data.as_slice()).unwrap();
+
+    let account = KeyedUiAccount::from_test_fixtures_file("lido");
+    let lido = Lido::borsh_de(account.account_data().as_slice()).unwrap();
+    let quoted_stake_lamports = lido.exchange_rate.quote_withdraw_stake(AMOUNT).unwrap();
 
     let [user, burn_stsol_from, split_stake_to] = core::array::from_fn(|_i| Pubkey::new_unique());
     let mollusk = mollusk_lido_prog();
@@ -86,7 +90,23 @@ fn withdraw_v2_fixture() {
         ])
         .collect();
 
-    let InstructionResult { raw_result, .. } = mollusk.process_instruction_chain(ixs, &accounts);
+    let InstructionResult {
+        raw_result,
+        resulting_accounts,
+        ..
+    } = mollusk.process_instruction_chain(ixs, &accounts);
 
     raw_result.unwrap();
+
+    let split_stake_to_lamports = resulting_accounts
+        .iter()
+        .find(|(pk, _a)| *pk == split_stake_to)
+        .unwrap()
+        .1
+        .lamports;
+
+    assert_eq!(
+        split_stake_to_lamports,
+        quoted_stake_lamports + STAKE_ACC_RENT_EXEMPT_LAMPORTS
+    );
 }