Payment.cpp

#include <xrpl/tx/transactors/payment/Payment.h>
 
#include <xrpl/basics/Log.h>
#include <xrpl/beast/utility/Zero.h>
#include <xrpl/beast/utility/instrumentation.h>
#include <xrpl/core/ServiceRegistry.h>
#include <xrpl/ledger/PaymentSandbox.h>
#include <xrpl/ledger/ReadView.h>
#include <xrpl/ledger/helpers/AccountRootHelpers.h>
#include <xrpl/ledger/helpers/CredentialHelpers.h>
#include <xrpl/ledger/helpers/MPTokenHelpers.h>
#include <xrpl/ledger/helpers/PermissionedDEXHelpers.h>
#include <xrpl/ledger/helpers/TokenHelpers.h>
#include <xrpl/protocol/AccountID.h>
#include <xrpl/protocol/Asset.h>
#include <xrpl/protocol/Feature.h>
#include <xrpl/protocol/Indexes.h>
#include <xrpl/protocol/Issue.h>
#include <xrpl/protocol/LedgerFormats.h>
#include <xrpl/protocol/MPTIssue.h>
#include <xrpl/protocol/Permissions.h>
#include <xrpl/protocol/Quality.h>
#include <xrpl/protocol/Rate.h>
#include <xrpl/protocol/SField.h>
#include <xrpl/protocol/STAmount.h>
#include <xrpl/protocol/STLedgerEntry.h>
#include <xrpl/protocol/STPathSet.h>
#include <xrpl/protocol/STTx.h>
#include <xrpl/protocol/TER.h>
#include <xrpl/protocol/TxFlags.h>
#include <xrpl/protocol/UintTypes.h>
#include <xrpl/protocol/XRPAmount.h>
#include <xrpl/protocol/jss.h>
#include <xrpl/tx/Transactor.h>
#include <xrpl/tx/applySteps.h>
#include <xrpl/tx/paths/RippleCalc.h>
 
#include <algorithm>
#include <cstdint>
#include <memory>
#include <optional>
#include <unordered_set>
 
namespace xrpl {
 
TxConsequences
Payment::makeTxConsequences(PreflightContext const& ctx)
{
    auto calculateMaxXRPSpend = [](STTx const& tx) -> XRPAmount {
        STAmount const maxAmount = tx.isFieldPresent(sfSendMax) ? tx[sfSendMax] : tx[sfAmount];
 
        // If there's no sfSendMax in XRP, and the sfAmount isn't
        // in XRP, then the transaction does not spend XRP.
        return maxAmount.native() ? maxAmount.xrp() : beast::kZero;
    };
 
    return TxConsequences{ctx.tx, calculateMaxXRPSpend(ctx.tx)};
}
 
STAmount
getMaxSourceAmount(
    AccountID const& account,
    STAmount const& dstAmount,
    std::optional<STAmount> const& sendMax)
{
    if (sendMax)
    {
        return *sendMax;
    }
    return dstAmount.asset().visit(
        [&](MPTIssue const& issue) { return dstAmount; },
        [&](Issue const& issue) {
            if (issue.native())
                return dstAmount;
            return STAmount(
                Issue{issue.currency, account},
                dstAmount.mantissa(),
                dstAmount.exponent(),
                dstAmount < beast::kZero);
        });
}
 
bool
Payment::checkExtraFeatures(PreflightContext const& ctx)
{
    if (ctx.tx.isFieldPresent(sfCredentialIDs) && !ctx.rules.enabled(featureCredentials))
        return false;
    if (ctx.tx.isFieldPresent(sfDomainID) && !ctx.rules.enabled(featurePermissionedDEX))
        return false;
 
    return true;
}
 
std::uint32_t
Payment::getFlagsMask(PreflightContext const& ctx)
{
    auto& tx = ctx.tx;
 
    STAmount const dstAmount(tx.getFieldAmount(sfAmount));
    bool const isDstMPT = dstAmount.holds<MPTIssue>();
    bool const mpTokensV2 = ctx.rules.enabled(featureMPTokensV2);
 
    static constexpr std::uint32_t kTfMptPaymentMaskV1 = ~(tfUniversal | tfPartialPayment);
    std::uint32_t const paymentMask =
        (isDstMPT && !mpTokensV2) ? kTfMptPaymentMaskV1 : tfPaymentMask;
 
    return paymentMask;
}
 
NotTEC
Payment::preflight(PreflightContext const& ctx)
{
    auto& tx = ctx.tx;
    auto& j = ctx.j;
 
    STAmount const dstAmount(tx.getFieldAmount(sfAmount));
    bool const isDstMPT = dstAmount.holds<MPTIssue>();
    bool const mpTokensV2 = ctx.rules.enabled(featureMPTokensV2);
 
    if (!ctx.rules.enabled(featureMPTokensV1) && isDstMPT)
        return temDISABLED;
 
    if (!mpTokensV2 && isDstMPT && ctx.tx.isFieldPresent(sfPaths))
        return temMALFORMED;
 
    // A zero DomainID is invalid for a PermissionedDomain ledger entry because
    // keylet::permissionedDomain(uint256) uses the DomainID as the ledger key.
    if (auto const domainID = tx[~sfDomainID];
        ctx.rules.enabled(fixCleanup3_2_0) && domainID && *domainID == beast::kZero)
        return temMALFORMED;
 
    bool const partialPaymentAllowed = tx.isFlag(tfPartialPayment);
    bool const limitQuality = tx.isFlag(tfLimitQuality);
    bool const defaultPathsAllowed = !tx.isFlag(tfNoRippleDirect);
    bool const hasPaths = tx.isFieldPresent(sfPaths);
    bool const hasMax = tx.isFieldPresent(sfSendMax);
 
    auto const deliverMin = tx[~sfDeliverMin];
 
    auto const account = tx.getAccountID(sfAccount);
    STAmount const maxSourceAmount = getMaxSourceAmount(account, dstAmount, tx[~sfSendMax]);
 
    if (!mpTokensV2 &&
        ((isDstMPT && dstAmount.asset() != maxSourceAmount.asset()) ||
         (!isDstMPT && maxSourceAmount.holds<MPTIssue>())))
    {
        JLOG(j.trace()) << "Malformed transaction: inconsistent issues: " << dstAmount.getFullText()
                        << " " << maxSourceAmount.getFullText() << " "
                        << deliverMin.value_or(STAmount{}).getFullText();
        return temMALFORMED;
    }
 
    auto const& srcAsset = maxSourceAmount.asset();
    auto const& dstAsset = dstAmount.asset();
 
    bool const xrpDirect = srcAsset.native() && dstAsset.native();
 
    if (!isLegalNet(dstAmount) || !isLegalNet(maxSourceAmount))
        return temBAD_AMOUNT;
 
    auto const dstAccountID = tx.getAccountID(sfDestination);
 
    if (!dstAccountID)
    {
        JLOG(j.trace()) << "Malformed transaction: "
                        << "Payment destination account not specified.";
        return temDST_NEEDED;
    }
    if (hasMax && maxSourceAmount <= beast::kZero)
    {
        JLOG(j.trace()) << "Malformed transaction: bad max amount: "
                        << maxSourceAmount.getFullText();
        return temBAD_AMOUNT;
    }
    if (dstAmount <= beast::kZero)
    {
        JLOG(j.trace()) << "Malformed transaction: bad dst amount: " << dstAmount.getFullText();
        return temBAD_AMOUNT;
    }
    auto bad = [&](auto const& asset) {
        if (ctx.rules.enabled(featureMPTokensV2))
            return badAsset() == asset;
        return badCurrency() == asset;
    };
    if (bad(srcAsset) || bad(dstAsset))
    {
        JLOG(j.trace()) << "Malformed transaction: Bad currency.";
        return temBAD_CURRENCY;
    }
    if (account == dstAccountID && equalTokens(srcAsset, dstAsset) && !hasPaths)
    {
        // You're signing yourself a payment.
        // If hasPaths is true, you might be trying some arbitrage.
        JLOG(j.trace()) << "Malformed transaction: "
                        << "Redundant payment from " << to_string(account)
                        << " to self without path for " << to_string(dstAsset);
        return temREDUNDANT;
    }
    if (xrpDirect && hasMax)
    {
        // Consistent but redundant transaction.
        JLOG(j.trace()) << "Malformed transaction: "
                        << "SendMax specified for XRP to XRP.";
        return temBAD_SEND_XRP_MAX;
    }
    if ((xrpDirect || (!mpTokensV2 && isDstMPT)) && hasPaths)
    {
        // XRP is sent without paths.
        JLOG(j.trace()) << "Malformed transaction: "
                        << "Paths specified for XRP to XRP or MPT to MPT.";
        return temBAD_SEND_XRP_PATHS;
    }
    if (xrpDirect && partialPaymentAllowed)
    {
        // Consistent but redundant transaction.
        JLOG(j.trace()) << "Malformed transaction: "
                        << "Partial payment specified for XRP to XRP.";
        return temBAD_SEND_XRP_PARTIAL;
    }
    if ((xrpDirect || (!mpTokensV2 && isDstMPT)) && limitQuality)
    {
        // Consistent but redundant transaction.
        JLOG(j.trace()) << "Malformed transaction: "
                        << "Limit quality specified for XRP to XRP or MPT to MPT.";
        return temBAD_SEND_XRP_LIMIT;
    }
    if ((xrpDirect || (!mpTokensV2 && isDstMPT)) && !defaultPathsAllowed)
    {
        // Consistent but redundant transaction.
        JLOG(j.trace()) << "Malformed transaction: "
                        << "No ripple direct specified for XRP to XRP or MPT to MPT.";
        return temBAD_SEND_XRP_NO_DIRECT;
    }
 
    if (deliverMin)
    {
        if (!partialPaymentAllowed)
        {
            JLOG(j.trace()) << "Malformed transaction: Partial payment not "
                               "specified for "
                            << jss::DeliverMin.cStr() << ".";
            return temBAD_AMOUNT;
        }
 
        auto const dMin = *deliverMin;
        if (!isLegalNet(dMin) || dMin <= beast::kZero)
        {
            JLOG(j.trace()) << "Malformed transaction: Invalid " << jss::DeliverMin.cStr()
                            << " amount. " << dMin.getFullText();
            return temBAD_AMOUNT;
        }
        if (dMin.asset() != dstAmount.asset())
        {
            JLOG(j.trace()) << "Malformed transaction: Dst issue differs "
                               "from "
                            << jss::DeliverMin.cStr() << ". " << dMin.getFullText();
            return temBAD_AMOUNT;
        }
        if (dMin > dstAmount)
        {
            JLOG(j.trace()) << "Malformed transaction: Dst amount less than "
                            << jss::DeliverMin.cStr() << ". " << dMin.getFullText();
            return temBAD_AMOUNT;
        }
    }
 
    if (auto const err = credentials::checkFields(ctx.tx, ctx.j); !isTesSuccess(err))
        return err;
 
    return tesSUCCESS;
}
 
NotTEC
Payment::checkGranularSemantics(
    ReadView const& view,
    STTx const& tx,
    std::unordered_set<GranularPermissionType> const& heldGranularPermissions)
{
    auto const& dstAmount = tx.getFieldAmount(sfAmount);
    auto const& amountAsset = dstAmount.asset();
 
    // Granular permissions are only valid for direct payments.
    if (tx.isFieldPresent(sfSendMax) && tx[sfSendMax].asset() != amountAsset)
        return terNO_DELEGATE_PERMISSION;
 
    if (isXRP(amountAsset))
        return terNO_DELEGATE_PERMISSION;
 
    return amountAsset.visit(
        [&](MPTIssue const& mptIssue) -> NotTEC {
            // For MPT payments, the MPTokenIssuanceID encodes the issuer unambiguously,
            // unlike IOU, there is no endpoint aliasing where either side of the
            // trustline can appear as the issuer.
            if (heldGranularPermissions.contains(PaymentMint) &&
                mptIssue.getIssuer() == tx[sfAccount])
                return tesSUCCESS;
            if (heldGranularPermissions.contains(PaymentBurn) &&
                mptIssue.getIssuer() == tx[sfDestination])
                return tesSUCCESS;
            return terNO_DELEGATE_PERMISSION;
        },
        [&](Issue const& issue) -> NotTEC {
            // For IOU payments, either endpoint may be encoded as the issuer in
            // sfAmount. PaySteps normalizes those endpoint aliases, so sfAmount.issuer
            // alone does not reliably identify whether the transaction issues or redeems
            // IOUs. We determine PaymentMint vs PaymentBurn from the trustline balance
            // direction instead.
            auto const account = tx[sfAccount];
            auto const destination = tx[sfDestination];
 
            // Reject if neither endpoint is the issuer.
            if (issue.getIssuer() != account && issue.getIssuer() != destination)
                return terNO_DELEGATE_PERMISSION;
 
            auto const sle = view.read(keylet::trustLine(account, destination, issue.currency));
            if (!sle)
                return terNO_DELEGATE_PERMISSION;
 
            bool const accountIsLow = (account < destination);
            auto const destLimit = sle->getFieldAmount(accountIsLow ? sfHighLimit : sfLowLimit);
            auto const rawBalance = sle->getFieldAmount(sfBalance);
            bool const accountIsHolder =
                accountIsLow ? rawBalance > beast::kZero : rawBalance < beast::kZero;
 
            // PaymentMint requires the destination to be the holder and the account to be the
            // issuer. destLimit > 0: destination is willing to hold account's IOUs (account is the
            // issuer). !accountIsHolder: DirectStepI will issue, not redeem.
            if (heldGranularPermissions.contains(PaymentMint) && destLimit > beast::kZero &&
                !accountIsHolder)
                return tesSUCCESS;
 
            // PaymentBurn requires the source account to be the holder and the destination to be
            // the issuer. accountIsHolder: DirectStepI will redeem, not issue.
            if (heldGranularPermissions.contains(PaymentBurn) && accountIsHolder)
                return tesSUCCESS;
 
            return terNO_DELEGATE_PERMISSION;
        });
}
 
TER
Payment::preclaim(PreclaimContext const& ctx)
{
    // Ripple if source or destination is non-native or if there are paths.
    bool const partialPaymentAllowed = ctx.tx.isFlag(tfPartialPayment);
    auto const hasPaths = ctx.tx.isFieldPresent(sfPaths);
    auto const sendMax = ctx.tx[~sfSendMax];
 
    AccountID const dstAccountID(ctx.tx[sfDestination]);
    STAmount const dstAmount(ctx.tx[sfAmount]);
 
    auto const k = keylet::account(dstAccountID);
    auto const sleDst = ctx.view.read(k);
 
    if (!sleDst)
    {
        // Destination account does not exist.
        if (!dstAmount.native())
        {
            JLOG(ctx.j.trace()) << "Delay transaction: Destination account does not exist.";
 
            // Another transaction could create the account and then this
            // transaction would succeed.
            return tecNO_DST;
        }
        if (ctx.view.open() && partialPaymentAllowed)
        {
            // You cannot fund an account with a partial payment.
            // Make retry work smaller, by rejecting this.
            JLOG(ctx.j.trace()) << "Delay transaction: Partial payment not "
                                   "allowed to create account.";
 
            // Another transaction could create the account and then this
            // transaction would succeed.
            return telNO_DST_PARTIAL;
        }
        if (dstAmount < STAmount(ctx.view.fees().reserve))
        {
            // accountReserve is the minimum amount that an account can have.
            // Reserve is not scaled by load.
            JLOG(ctx.j.trace()) << "Delay transaction: Destination account does not exist. "
                                << "Insufficent payment to create account.";
 
            // TODO: de-dupe
            // Another transaction could create the account and then this
            // transaction would succeed.
            return tecNO_DST_INSUF_XRP;
        }
    }
    else if (sleDst->isFlag(lsfRequireDestTag) && !ctx.tx.isFieldPresent(sfDestinationTag))
    {
        // The tag is basically account-specific information we don't
        // understand, but we can require someone to fill it in.
 
        // We didn't make this test for a newly-formed account because there's
        // no way for this field to be set.
        JLOG(ctx.j.trace()) << "Malformed transaction: DestinationTag required.";
 
        return tecDST_TAG_NEEDED;
    }
 
    // Payment with at least one intermediate step and uses transitive balances.
    if ((hasPaths || sendMax || !dstAmount.native()) && ctx.view.open())
    {
        STPathSet const& paths = ctx.tx.getFieldPathSet(sfPaths);
 
        if (paths.size() > kMaxPathSize || std::ranges::any_of(paths, [](STPath const& path) {
                return path.size() > kMaxPathLength;
            }))
        {
            return telBAD_PATH_COUNT;
        }
    }
 
    if (auto const err = credentials::valid(ctx.tx, ctx.view, ctx.tx[sfAccount], ctx.j);
        !isTesSuccess(err))
        return err;
 
    if (ctx.tx.isFieldPresent(sfDomainID))
    {
        if (!permissioned_dex::accountInDomain(ctx.view, ctx.tx[sfAccount], ctx.tx[sfDomainID]))
            return tecNO_PERMISSION;
 
        if (!permissioned_dex::accountInDomain(ctx.view, ctx.tx[sfDestination], ctx.tx[sfDomainID]))
            return tecNO_PERMISSION;
    }
 
    return tesSUCCESS;
}
 
TER
Payment::doApply()
{
    auto const deliverMin = ctx_.tx[~sfDeliverMin];
 
    // Ripple if source or destination is non-native or if there are paths.
    bool const partialPaymentAllowed = ctx_.tx.isFlag(tfPartialPayment);
    bool const limitQuality = ctx_.tx.isFlag(tfLimitQuality);
    bool const defaultPathsAllowed = !ctx_.tx.isFlag(tfNoRippleDirect);
    auto const hasPaths = ctx_.tx.isFieldPresent(sfPaths);
    auto const sendMax = ctx_.tx[~sfSendMax];
 
    AccountID const dstAccountID(ctx_.tx.getAccountID(sfDestination));
    STAmount const dstAmount(ctx_.tx.getFieldAmount(sfAmount));
    bool const isDstMPT = dstAmount.holds<MPTIssue>();
    STAmount const maxSourceAmount = getMaxSourceAmount(accountID_, dstAmount, sendMax);
 
    JLOG(j_.trace()) << "maxSourceAmount=" << maxSourceAmount.getFullText()
                     << " dstAmount=" << dstAmount.getFullText();
 
    // Open a ledger for editing.
    auto const k = keylet::account(dstAccountID);
    SLE::pointer sleDst = view().peek(k);
 
    if (!sleDst)
    {
        // Create the account.
        sleDst = std::make_shared<SLE>(k);
        sleDst->setAccountID(sfAccount, dstAccountID);
        sleDst->setFieldU32(sfSequence, view().seq());
        sleDst->setFieldAmount(sfBalance, XRPAmount(beast::kZero));
 
        view().insert(sleDst);
    }
    else
    {
        // Tell the engine that we are intending to change the destination
        // account.  The source account gets always charged a fee so it's always
        // marked as modified.
        view().update(sleDst);
    }
 
    bool const mpTokensV2 = view().rules().enabled(featureMPTokensV2);
 
    // Direct MPT payment is handled by payment engine if MPTokensV2 is enabled
    bool const ripple = (hasPaths || sendMax || !dstAmount.native()) && (!isDstMPT || mpTokensV2);
 
    if (ripple)
    {
        // XRPL payment with at least one intermediate step and uses
        // transitive balances.
 
        // An account that requires authorization has two ways to get an
        // IOU Payment in:
        //  1. If Account == Destination, or
        //  2. If Account is deposit preauthorized by destination.
 
        if (auto err = verifyDepositPreauth(
                ctx_.tx, ctx_.view(), accountID_, dstAccountID, sleDst, ctx_.journal);
            !isTesSuccess(err))
            return err;
 
        path::RippleCalc::Input rcInput;
        rcInput.partialPaymentAllowed = partialPaymentAllowed;
        rcInput.defaultPathsAllowed = defaultPathsAllowed;
        rcInput.limitQuality = limitQuality;
        rcInput.isLedgerOpen = view().open();
 
        path::RippleCalc::Output rc;
        {
            PaymentSandbox pv(&view());
            JLOG(j_.debug()) << "Entering RippleCalc in payment: " << ctx_.tx.getTransactionID();
            rc = path::RippleCalc::rippleCalculate(
                pv,
                maxSourceAmount,
                dstAmount,
                dstAccountID,
                accountID_,
                ctx_.tx.getFieldPathSet(sfPaths),
                ctx_.tx[~sfDomainID],
                ctx_.registry,
                &rcInput);
            // VFALCO NOTE We might not need to apply, depending
            //             on the TER. But always applying *should*
            //             be safe.
            pv.apply(ctx_.rawView());
        }
 
        // TODO: is this right?  If the amount is the correct amount, was
        // the delivered amount previously set?
        if (isTesSuccess(rc.result()) && rc.actualAmountOut != dstAmount)
        {
            if (deliverMin && rc.actualAmountOut < *deliverMin)
            {
                rc.setResult(tecPATH_PARTIAL);
            }
            else
            {
                ctx_.deliver(rc.actualAmountOut);
            }
        }
 
        auto terResult = rc.result();
 
        // Because of its overhead, if RippleCalc
        // fails with a retry code, claim a fee
        // instead. Maybe the user will be more
        // careful with their path spec next time.
        if (isTerRetry(terResult))
            terResult = tecPATH_DRY;
        return terResult;
    }
    if (isDstMPT)
    {
        JLOG(j_.trace()) << " dstAmount=" << dstAmount.getFullText();
        auto const& mptIssue = dstAmount.get<MPTIssue>();
 
        if (auto const ter = requireAuth(view(), mptIssue, accountID_); !isTesSuccess(ter))
            return ter;
 
        if (auto const ter = requireAuth(view(), mptIssue, dstAccountID); !isTesSuccess(ter))
            return ter;
 
        if (auto const ter = canTransfer(view(), mptIssue, accountID_, dstAccountID);
            !isTesSuccess(ter))
            return ter;
 
        if (auto err = verifyDepositPreauth(
                ctx_.tx, ctx_.view(), accountID_, dstAccountID, sleDst, ctx_.journal);
            !isTesSuccess(err))
            return err;
 
        auto const& issuer = mptIssue.getIssuer();
 
        // Transfer rate
        Rate rate{QUALITY_ONE};
        // Payment between the holders
        if (accountID_ != issuer && dstAccountID != issuer)
        {
            // If globally/individually locked then
            //   - can't send between holders
            //   - holder can send back to issuer
            //   - issuer can send to holder
            if (isAnyFrozen(view(), {accountID_, dstAccountID}, mptIssue))
                return tecLOCKED;
 
            // Get the rate for a payment between the holders.
            rate = transferRate(view(), mptIssue.getMptID());
        }
 
        // Amount to deliver.
        STAmount amountDeliver = dstAmount;
        // Factor in the transfer rate.
        // No rounding. It'll change once MPT integrated into DEX.
        STAmount requiredMaxSourceAmount = multiply(dstAmount, rate);
 
        // Send more than the account wants to pay or less than
        // the account wants to deliver (if no SendMax).
        // Adjust the amount to deliver.
        if (partialPaymentAllowed && requiredMaxSourceAmount > maxSourceAmount)
        {
            requiredMaxSourceAmount = maxSourceAmount;
            // No rounding. It'll change once MPT integrated into DEX.
            amountDeliver = divide(maxSourceAmount, rate);
        }
 
        if (requiredMaxSourceAmount > maxSourceAmount ||
            (deliverMin && amountDeliver < *deliverMin))
            return tecPATH_PARTIAL;
 
        PaymentSandbox pv(&view());
        auto res = accountSend(pv, accountID_, dstAccountID, amountDeliver, ctx_.journal);
        if (isTesSuccess(res))
        {
            pv.apply(ctx_.rawView());
 
            // If the actual amount delivered is different from the original
            // amount due to partial payment or transfer fee, we need to update
            // DeliveredAmount using the actual delivered amount
            if (view().rules().enabled(fixMPTDeliveredAmount) && amountDeliver != dstAmount)
                ctx_.deliver(amountDeliver);
        }
        else if (res == tecINSUFFICIENT_FUNDS || res == tecPATH_DRY)
        {
            res = tecPATH_PARTIAL;
        }
 
        return res;
    }
 
    XRPL_ASSERT(dstAmount.native(), "xrpl::Payment::doApply : amount is XRP");
 
    // Direct XRP payment.
 
    auto const sleSrc = view().peek(keylet::account(accountID_));
    if (!sleSrc)
        return tefINTERNAL;  // LCOV_EXCL_LINE
 
    // ownerCount is the number of entries in this ledger for this
    // account that require a reserve.
    auto const ownerCount = sleSrc->getFieldU32(sfOwnerCount);
 
    // This is the total reserve in drops.
    auto const reserve = view().fees().accountReserve(ownerCount);
 
    // In a delegated payment, the fee payer is the delegated account,
    // not the source account (accountID_).
    bool const accountIsPayer = (ctx_.tx.getFeePayer() == accountID_);
 
    // preFeeBalance_ is the balance on the source account (accountID_) BEFORE the fees
    // were charged. If source account is the fee payer, it must also cover the fee.
    // The final spend may use the reserve to cover fees.
    auto const minRequiredFunds =
        accountIsPayer ? std::max(reserve, ctx_.tx.getFieldAmount(sfFee).xrp()) : reserve;
 
    if (preFeeBalance_ < dstAmount.xrp() + minRequiredFunds)
    {
        // Vote no. However the transaction might succeed, if applied in
        // a different order.
        JLOG(j_.trace()) << "Delay transaction: Insufficient funds: " << to_string(preFeeBalance_)
                         << " / " << to_string(dstAmount.xrp() + minRequiredFunds) << " ("
                         << to_string(reserve) << ")";
 
        return tecUNFUNDED_PAYMENT;
    }
 
    // Pseudo-accounts cannot receive payments, other than these native to
    // their underlying ledger object - implemented in their respective
    // transaction types. Note, this is not amendment-gated because all writes
    // to pseudo-account discriminator fields **are** amendment gated, hence the
    // behaviour of this check will always match the active amendments.
    if (isPseudoAccount(sleDst))
        return tecNO_PERMISSION;
 
    // The source account does have enough money.  Make sure the
    // source account has authority to deposit to the destination.
    // An account that requires authorization has three ways to get an XRP
    // Payment in:
    //  1. If Account == Destination, or
    //  2. If Account is deposit preauthorized by destination, or
    //  3. If the destination's XRP balance is
    //    a. less than or equal to the base reserve and
    //    b. the deposit amount is less than or equal to the base reserve,
    // then we allow the deposit.
    //
    // Rule 3 is designed to keep an account from getting wedged
    // in an unusable state if it sets the lsfDepositAuth flag and
    // then consumes all of its XRP.  Without the rule if an
    // account with lsfDepositAuth set spent all of its XRP, it
    // would be unable to acquire more XRP required to pay fees.
    //
    // We choose the base reserve as our bound because it is
    // a small number that seldom changes but is always sufficient
    // to get the account un-wedged.
 
    // Get the base reserve.
    XRPAmount const dstReserve{view().fees().reserve};
 
    if (dstAmount > dstReserve || sleDst->getFieldAmount(sfBalance) > dstReserve)
    {
        if (auto err = verifyDepositPreauth(
                ctx_.tx, ctx_.view(), accountID_, dstAccountID, sleDst, ctx_.journal);
            !isTesSuccess(err))
            return err;
    }
 
    // Do the arithmetic for the transfer and make the ledger change.
    sleSrc->setFieldAmount(sfBalance, sleSrc->getFieldAmount(sfBalance) - dstAmount);
    sleDst->setFieldAmount(sfBalance, sleDst->getFieldAmount(sfBalance) + dstAmount);
 
    // Re-arm the password change fee if we can and need to.
    if (sleDst->isFlag(lsfPasswordSpent))
        sleDst->clearFlag(lsfPasswordSpent);
 
    return tesSUCCESS;
}
 
void
Payment::visitInvariantEntry(bool, SLE::const_ref, SLE::const_ref)
{
    // No transaction-specific invariants yet (future work).
}
 
bool
Payment::finalizeInvariants(STTx const&, TER, XRPAmount, ReadView const&, beast::Journal const&)
{
    // No transaction-specific invariants yet (future work).
    return true;
}
 
}  // namespace xrpl