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| function flash(
address recipient, // 借贷方地址，用于调用回调函数
uint256 amount0, // 借贷的 token0 的数量
uint256 amount1, // 借贷的 token1 的数量
bytes calldata data //回调函数的参数
) external override lock noDelegateCall {
uint128 _liquidity = liquidity;
require(_liquidity > 0, 'L');
// 计算借贷所需要扣除的手续费
uint256 fee0 = FullMath.mulDivRoundingUp(amount0, fee, 1e6);
uint256 fee1 = FullMath.mulDivRoundingUp(amount1, fee, 1e6);
// 记录下当前的余额
uint256 balance0Before = balance0();
uint256 balance1Before = balance1();
// 将所需 token 发送给借贷方
if (amount0 > 0) TransferHelper.safeTransfer(token0, recipient, amount0);
if (amount1 > 0) TransferHelper.safeTransfer(token1, recipient, amount1);
// 调用借贷方地址的回调函数，将函数用户传入的 data 参数传给这个回调函数
IUniswapV3FlashCallback(msg.sender).uniswapV3FlashCallback(fee0, fee1, data);
// 记录调用完成后的余额
uint256 balance0After = balance0();
uint256 balance1After = balance1();
// 比对借出代币前和回调函数调用完成后余额的数量，对于每个 token，余额只能多不能少
require(balance0Before.add(fee0) <= balance0After, 'F0');
require(balance1Before.add(fee1) <= balance1After, 'F1');
// sub is safe because we know balanceAfter is gt balanceBefore by at least fee
// 手续费相关的计算
uint256 paid0 = balance0After - balance0Before;
uint256 paid1 = balance1After - balance1Before;
if (paid0 > 0) {
uint8 feeProtocol0 = slot0.feeProtocol % 16;
uint256 fees0 = feeProtocol0 == 0 ? 0 : paid0 / feeProtocol0;
if (uint128(fees0) > 0) protocolFees.token0 += uint128(fees0);
feeGrowthGlobal0X128 += FullMath.mulDiv(paid0 - fees0, FixedPoint128.Q128, _liquidity);
}
if (paid1 > 0) {
uint8 feeProtocol1 = slot0.feeProtocol >> 4;
uint256 fees1 = feeProtocol1 == 0 ? 0 : paid1 / feeProtocol1;
if (uint128(fees1) > 0) protocolFees.token1 += uint128(fees1);
feeGrowthGlobal1X128 += FullMath.mulDiv(paid1 - fees1, FixedPoint128.Q128, _liquidity);
}
emit Flash(msg.sender, recipient, amount0, amount1, paid0, paid1);
}
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