PaymentSandbox.cpp

#include <xrpl/beast/utility/instrumentation.h>
#include <xrpl/ledger/PaymentSandbox.h>
#include <xrpl/ledger/View.h>
#include <xrpl/protocol/SField.h>
 
namespace xrpl {
 
namespace detail {
 
auto
DeferredCredits::makeKey(AccountID const& a1, AccountID const& a2, Currency const& c) -> Key
{
    if (a1 < a2)
    {
        return std::make_tuple(a1, a2, c);
    }
 
    return std::make_tuple(a2, a1, c);
}
 
void
DeferredCredits::credit(
    AccountID const& sender,
    AccountID const& receiver,
    STAmount const& amount,
    STAmount const& preCreditSenderBalance)
{
    XRPL_ASSERT(
        sender != receiver, "xrpl::detail::DeferredCredits::credit : sender is not receiver");
    XRPL_ASSERT(!amount.negative(), "xrpl::detail::DeferredCredits::credit : positive amount");
 
    auto const k = makeKey(sender, receiver, amount.getCurrency());
    auto i = credits_.find(k);
    if (i == credits_.end())
    {
        Value v;
 
        if (sender < receiver)
        {
            v.highAcctCredits = amount;
            v.lowAcctCredits = amount.zeroed();
            v.lowAcctOrigBalance = preCreditSenderBalance;
        }
        else
        {
            v.highAcctCredits = amount.zeroed();
            v.lowAcctCredits = amount;
            v.lowAcctOrigBalance = -preCreditSenderBalance;
        }
 
        credits_[k] = v;
    }
    else
    {
        // only record the balance the first time, do not record it here
        auto& v = i->second;
        if (sender < receiver)
        {
            v.highAcctCredits += amount;
        }
        else
        {
            v.lowAcctCredits += amount;
        }
    }
}
 
void
DeferredCredits::ownerCount(AccountID const& id, std::uint32_t cur, std::uint32_t next)
{
    auto const v = std::max(cur, next);
    auto r = ownerCounts_.emplace(std::make_pair(id, v));
    if (!r.second)
    {
        auto& mapVal = r.first->second;
        mapVal = std::max(v, mapVal);
    }
}
 
std::optional<std::uint32_t>
DeferredCredits::ownerCount(AccountID const& id) const
{
    auto i = ownerCounts_.find(id);
    if (i != ownerCounts_.end())
        return i->second;
    return std::nullopt;
}
 
// Get the adjustments for the balance between main and other.
auto
DeferredCredits::adjustments(
    AccountID const& main,
    AccountID const& other,
    Currency const& currency) const -> std::optional<Adjustment>
{
    std::optional<Adjustment> result;
 
    Key const k = makeKey(main, other, currency);
    auto i = credits_.find(k);
    if (i == credits_.end())
        return result;
 
    auto const& v = i->second;
 
    if (main < other)
    {
        result.emplace(v.highAcctCredits, v.lowAcctCredits, v.lowAcctOrigBalance);
        return result;
    }
 
    result.emplace(v.lowAcctCredits, v.highAcctCredits, -v.lowAcctOrigBalance);
    return result;
}
 
void
DeferredCredits::apply(DeferredCredits& to)
{
    for (auto const& i : credits_)
    {
        auto r = to.credits_.emplace(i);
        if (!r.second)
        {
            auto& toVal = r.first->second;
            auto const& fromVal = i.second;
            toVal.lowAcctCredits += fromVal.lowAcctCredits;
            toVal.highAcctCredits += fromVal.highAcctCredits;
            // Do not update the orig balance, it's already correct
        }
    }
 
    for (auto const& i : ownerCounts_)
    {
        auto r = to.ownerCounts_.emplace(i);
        if (!r.second)
        {
            auto& toVal = r.first->second;
            auto const& fromVal = i.second;
            toVal = std::max(toVal, fromVal);
        }
    }
}
 
}  // namespace detail
 
STAmount
PaymentSandbox::balanceHook(
    AccountID const& account,
    AccountID const& issuer,
    STAmount const& amount) const
{
    /*
    There are two algorithms here. The pre-switchover algorithm takes the
    current amount and subtracts the recorded credits. The post-switchover
    algorithm remembers the original balance, and subtracts the debits. The
    post-switchover algorithm should be more numerically stable. Consider a
    large credit with a small initial balance. The pre-switchover algorithm
    computes (B+C)-C (where B+C will the amount passed in). The
    post-switchover algorithm returns B. When B and C differ by large
    magnitudes, (B+C)-C may not equal B.
    */
 
    auto const currency = amount.getCurrency();
 
    auto delta = amount.zeroed();
    auto lastBal = amount;
    auto minBal = amount;
    for (auto curSB = this; curSB != nullptr; curSB = curSB->ps_)
    {
        if (auto adj = curSB->tab_.adjustments(account, issuer, currency))
        {
            delta += adj->debits;
            lastBal = adj->origBalance;
            if (lastBal < minBal)
                minBal = lastBal;
        }
    }
 
    // The adjusted amount should never be larger than the balance. In
    // some circumstances, it is possible for the deferred credits table
    // to compute usable balance just slightly above what the ledger
    // calculates (but always less than the actual balance).
    auto adjustedAmt = std::min({amount, lastBal - delta, minBal});
    adjustedAmt.setIssuer(amount.getIssuer());
 
    if (isXRP(issuer) && adjustedAmt < beast::zero)
    {
        // A calculated negative XRP balance is not an error case. Consider a
        // payment snippet that credits a large XRP amount and then debits the
        // same amount. The credit can't be used but we subtract the debit and
        // calculate a negative value. It's not an error case.
        adjustedAmt.clear();
    }
 
    return adjustedAmt;
}
 
std::uint32_t
PaymentSandbox::ownerCountHook(AccountID const& account, std::uint32_t count) const
{
    std::uint32_t result = count;
    for (auto curSB = this; curSB != nullptr; curSB = curSB->ps_)
    {
        if (auto adj = curSB->tab_.ownerCount(account))
            result = std::max(result, *adj);
    }
    return result;
}
 
void
PaymentSandbox::creditHook(
    AccountID const& from,
    AccountID const& to,
    STAmount const& amount,
    STAmount const& preCreditBalance)
{
    tab_.credit(from, to, amount, preCreditBalance);
}
 
void
PaymentSandbox::adjustOwnerCountHook(
    AccountID const& account,
    std::uint32_t cur,
    std::uint32_t next)
{
    tab_.ownerCount(account, cur, next);
}
 
void
PaymentSandbox::apply(RawView& to)
{
    XRPL_ASSERT(!ps_, "xrpl::PaymentSandbox::apply : non-null sandbox");
    items_.apply(to);
}
 
void
PaymentSandbox::apply(PaymentSandbox& to)
{
    XRPL_ASSERT(ps_ == &to, "xrpl::PaymentSandbox::apply : matching sandbox");
    items_.apply(to);
    tab_.apply(to.tab_);
}
 
std::map<std::tuple<AccountID, AccountID, Currency>, STAmount>
PaymentSandbox::balanceChanges(ReadView const& view) const
{
    using key_t = std::tuple<AccountID, AccountID, Currency>;
    // Map of delta trust lines. As a special case, when both ends of the trust
    // line are the same currency, then it's delta currency for that issuer. To
    // get the change in XRP balance, Account == root, issuer == root, currency
    // == XRP
    std::map<key_t, STAmount> result;
 
    // populate a dictionary with low/high/currency/delta. This can be
    // compared with the other versions payment code.
    auto each = [&result](
                    uint256 const& key,
                    bool isDelete,
                    std::shared_ptr<SLE const> const& before,
                    std::shared_ptr<SLE const> const& after) {
        STAmount oldBalance;
        STAmount newBalance;
        AccountID lowID;
        AccountID highID;
 
        // before is read from prev view
        if (isDelete)
        {
            if (!before)
                return;
 
            auto const bt = before->getType();
            switch (bt)
            {
                case ltACCOUNT_ROOT:
                    lowID = xrpAccount();
                    highID = (*before)[sfAccount];
                    oldBalance = (*before)[sfBalance];
                    newBalance = oldBalance.zeroed();
                    break;
                case ltRIPPLE_STATE:
                    lowID = (*before)[sfLowLimit].getIssuer();
                    highID = (*before)[sfHighLimit].getIssuer();
                    oldBalance = (*before)[sfBalance];
                    newBalance = oldBalance.zeroed();
                    break;
                case ltOFFER:
                    // TBD
                    break;
                default:
                    break;
            }
        }
        else if (!before)
        {
            // insert
            auto const at = after->getType();
            switch (at)
            {
                case ltACCOUNT_ROOT:
                    lowID = xrpAccount();
                    highID = (*after)[sfAccount];
                    newBalance = (*after)[sfBalance];
                    oldBalance = newBalance.zeroed();
                    break;
                case ltRIPPLE_STATE:
                    lowID = (*after)[sfLowLimit].getIssuer();
                    highID = (*after)[sfHighLimit].getIssuer();
                    newBalance = (*after)[sfBalance];
                    oldBalance = newBalance.zeroed();
                    break;
                case ltOFFER:
                    // TBD
                    break;
                default:
                    break;
            }
        }
        else
        {
            // modify
            auto const at = after->getType();
            XRPL_ASSERT(
                at == before->getType(),
                "xrpl::PaymentSandbox::balanceChanges : after and before "
                "types matching");
            switch (at)
            {
                case ltACCOUNT_ROOT:
                    lowID = xrpAccount();
                    highID = (*after)[sfAccount];
                    oldBalance = (*before)[sfBalance];
                    newBalance = (*after)[sfBalance];
                    break;
                case ltRIPPLE_STATE:
                    lowID = (*after)[sfLowLimit].getIssuer();
                    highID = (*after)[sfHighLimit].getIssuer();
                    oldBalance = (*before)[sfBalance];
                    newBalance = (*after)[sfBalance];
                    break;
                case ltOFFER:
                    // TBD
                    break;
                default:
                    break;
            }
        }
        // The following are now set, put them in the map
        auto delta = newBalance - oldBalance;
        auto const cur = newBalance.getCurrency();
        result[std::make_tuple(lowID, highID, cur)] = delta;
        auto r = result.emplace(std::make_tuple(lowID, lowID, cur), delta);
        if (r.second)
        {
            r.first->second += delta;
        }
 
        delta.negate();
        r = result.emplace(std::make_tuple(highID, highID, cur), delta);
        if (r.second)
        {
            r.first->second += delta;
        }
    };
    items_.visit(view, each);
    return result;
}
 
XRPAmount
PaymentSandbox::xrpDestroyed() const
{
    return items_.dropsDestroyed();
}
 
}  // namespace xrpl