audit-fix: Swap and Flashloan Fees Not Accumulated

[elrakabawi]

Swap and Flashloan Fees Not Accumulated

• Severity: Medium
• Target: Smart Contract
• Category: Logic Error
• Status: Pending

Description

During swaps, the total_fee and the futarchy_fee are calculated as follows:

    let total_fee = (amount_in as u128)
        .checked_mul(pair.swap_fee_bps as u128)
        .ok_or(ErrorCode::FeeMathOverflow)?
        .checked_div(BPS_DENOMINATOR as u128)
        .ok_or(ErrorCode::FeeMathOverflow)? as u64;

    // Calculate futarchy fee portion of the total fee
    let futarchy_fee = (total_fee as u128)
        .checked_mul(futarchy_authority.revenue_share.swap_bps as u128)
        .ok_or(ErrorCode::FeeMathOverflow)?
        .checked_div(BPS_DENOMINATOR as u128)
        .ok_or(ErrorCode::FeeMathOverflow)? as u64;

However, the remaining portion of the fee (total_fee - futarchy_fee) is ignored, it is neither transferred out nor recorded in internal accounting.

A similar issue exists in the flashloan logic:

      let fee0 = (amount0 as u128)
          .checked_mul(FLASHLOAN_FEE_BPS as u128)
          .unwrap()
          .checked_div(BPS_DENOMINATOR as u128)
          .unwrap() as u64;
      
      let fee1 = (amount1 as u128)
          .checked_mul(FLASHLOAN_FEE_BPS as u128)
          .unwrap()
          .checked_div(BPS_DENOMINATOR as u128)
          .unwrap() as u64;

These fees are not accumulated into the pool reserves or protocol revenue.

Impact

The protocol and liquidity providers may earn less revenue than expected because a portion of the fees is never credited.

Recommendation

Add the logic to accumulate the fees.

Fix

• Added swap LP fee to reserves
• Added flashloan LP fee to reserves