OfferStream.cpp

#include <xrpl/basics/Log.h>
#include <xrpl/ledger/View.h>
#include <xrpl/protocol/Feature.h>
#include <xrpl/protocol/LedgerFormats.h>
#include <xrpl/tx/paths/OfferStream.h>
#include <xrpl/tx/transactors/PermissionedDEXHelpers.h>
 
namespace xrpl {
 
namespace {
bool
checkIssuers(ReadView const& view, Book const& book)
{
    auto issuerExists = [](ReadView const& view, Issue const& iss) -> bool {
        return isXRP(iss.account) || view.read(keylet::account(iss.account));
    };
    return issuerExists(view, book.in) && issuerExists(view, book.out);
}
}  // namespace
 
template <class TIn, class TOut>
TOfferStreamBase<TIn, TOut>::TOfferStreamBase(
    ApplyView& view,
    ApplyView& cancelView,
    Book const& book,
    NetClock::time_point when,
    StepCounter& counter,
    beast::Journal journal)
    : j_(journal)
    , view_(view)
    , cancelView_(cancelView)
    , book_(book)
    , validBook_(checkIssuers(view, book))
    , expire_(when)
    , tip_(view, book_)
    , counter_(counter)
{
    XRPL_ASSERT(validBook_, "xrpl::TOfferStreamBase::TOfferStreamBase : valid book");
}
 
// Handle the case where a directory item with no corresponding ledger entry
// is found. This shouldn't happen but if it does we clean it up.
template <class TIn, class TOut>
void
TOfferStreamBase<TIn, TOut>::erase(ApplyView& view)
{
    // NIKB NOTE This should be using ApplyView::dirRemove, which would
    //           correctly remove the directory if its the last entry.
    //           Unfortunately this is a protocol breaking change.
 
    auto p = view.peek(keylet::page(tip_.dir()));
 
    if (p == nullptr)
    {
        JLOG(j_.error()) << "Missing directory " << tip_.dir() << " for offer " << tip_.index();
        return;
    }
 
    auto v(p->getFieldV256(sfIndexes));
    auto it(std::find(v.begin(), v.end(), tip_.index()));
 
    if (it == v.end())
    {
        JLOG(j_.error()) << "Missing offer " << tip_.index() << " for directory " << tip_.dir();
        return;
    }
 
    v.erase(it);
    p->setFieldV256(sfIndexes, v);
    view.update(p);
 
    JLOG(j_.trace()) << "Missing offer " << tip_.index() << " removed from directory "
                     << tip_.dir();
}
 
static STAmount
accountFundsHelper(
    ReadView const& view,
    AccountID const& id,
    STAmount const& saDefault,
    Issue const&,
    FreezeHandling freezeHandling,
    beast::Journal j)
{
    return accountFunds(view, id, saDefault, freezeHandling, j);
}
 
static IOUAmount
accountFundsHelper(
    ReadView const& view,
    AccountID const& id,
    IOUAmount const& amtDefault,
    Issue const& issue,
    FreezeHandling freezeHandling,
    beast::Journal j)
{
    if (issue.account == id)
        // self funded
        return amtDefault;
 
    return toAmount<IOUAmount>(
        accountHolds(view, id, issue.currency, issue.account, freezeHandling, j));
}
 
static XRPAmount
accountFundsHelper(
    ReadView const& view,
    AccountID const& id,
    XRPAmount const& amtDefault,
    Issue const& issue,
    FreezeHandling freezeHandling,
    beast::Journal j)
{
    return toAmount<XRPAmount>(
        accountHolds(view, id, issue.currency, issue.account, freezeHandling, j));
}
 
template <class TIn, class TOut>
template <class TTakerPays, class TTakerGets>
bool
TOfferStreamBase<TIn, TOut>::shouldRmSmallIncreasedQOffer() const
{
    static_assert(
        std::is_same_v<TTakerPays, IOUAmount> || std::is_same_v<TTakerPays, XRPAmount>,
        "STAmount is not supported");
 
    static_assert(
        std::is_same_v<TTakerGets, IOUAmount> || std::is_same_v<TTakerGets, XRPAmount>,
        "STAmount is not supported");
 
    static_assert(
        !std::is_same_v<TTakerPays, XRPAmount> || !std::is_same_v<TTakerGets, XRPAmount>,
        "Cannot have XRP/XRP offers");
 
    // Consider removing the offer if:
    //  o `TakerPays` is XRP (because of XRP drops granularity) or
    //  o `TakerPays` and `TakerGets` are both IOU and `TakerPays`<`TakerGets`
    constexpr bool const inIsXRP = std::is_same_v<TTakerPays, XRPAmount>;
    constexpr bool const outIsXRP = std::is_same_v<TTakerGets, XRPAmount>;
 
    if constexpr (outIsXRP)
    {
        // If `TakerGets` is XRP, the worst this offer's quality can change is
        // to about 10^-81 `TakerPays` and 1 drop `TakerGets`. This will be
        // remarkably good quality for any realistic asset, so these offers
        // don't need this extra check.
        return false;
    }
 
    TAmounts<TTakerPays, TTakerGets> const ofrAmts{
        toAmount<TTakerPays>(offer_.amount().in), toAmount<TTakerGets>(offer_.amount().out)};
 
    if constexpr (!inIsXRP && !outIsXRP)
    {
        if (ofrAmts.in >= ofrAmts.out)
            return false;
    }
 
    TTakerGets const ownerFunds = toAmount<TTakerGets>(*ownerFunds_);
 
    auto const effectiveAmounts = [&] {
        if (offer_.owner() != offer_.issueOut().account && ownerFunds < ofrAmts.out)
        {
            // adjust the amounts by owner funds.
            //
            // It turns out we can prevent order book blocking by rounding down
            // the ceil_out() result.
            return offer_.quality().ceil_out_strict(ofrAmts, ownerFunds, /* roundUp */ false);
        }
        return ofrAmts;
    }();
 
    // If either the effective in or out are zero then remove the offer.
    if (effectiveAmounts.in.signum() <= 0 || effectiveAmounts.out.signum() <= 0)
        return true;
 
    if (effectiveAmounts.in > TTakerPays::minPositiveAmount())
        return false;
 
    Quality const effectiveQuality{effectiveAmounts};
    return effectiveQuality < offer_.quality();
}
 
template <class TIn, class TOut>
bool
TOfferStreamBase<TIn, TOut>::step()
{
    // Modifying the order or logic of these
    // operations causes a protocol breaking change.
 
    if (!validBook_)
        return false;
 
    for (;;)
    {
        ownerFunds_ = std::nullopt;
        // BookTip::step deletes the current offer from the view before
        // advancing to the next (unless the ledger entry is missing).
        if (!tip_.step(j_))
            return false;
 
        std::shared_ptr<SLE> entry = tip_.entry();
 
        // If we exceed the maximum number of allowed steps, we're done.
        if (!counter_.step())
            return false;
 
        // Remove if missing
        if (!entry)
        {
            erase(view_);
            erase(cancelView_);
            continue;
        }
 
        // Remove if expired
        using d = NetClock::duration;
        using tp = NetClock::time_point;
        if (entry->isFieldPresent(sfExpiration) && tp{d{(*entry)[sfExpiration]}} <= expire_)
        {
            JLOG(j_.trace()) << "Removing expired offer " << entry->key();
            permRmOffer(entry->key());
            continue;
        }
 
        offer_ = TOffer<TIn, TOut>(entry, tip_.quality());
 
        auto const amount(offer_.amount());
 
        // Remove if either amount is zero
        if (amount.empty())
        {
            JLOG(j_.warn()) << "Removing bad offer " << entry->key();
            permRmOffer(entry->key());
            offer_ = TOffer<TIn, TOut>{};
            continue;
        }
 
        bool const deepFrozen = isDeepFrozen(
            view_, offer_.owner(), offer_.issueIn().currency, offer_.issueIn().account);
        if (deepFrozen)
        {
            JLOG(j_.trace()) << "Removing deep frozen unfunded offer " << entry->key();
            permRmOffer(entry->key());
            offer_ = TOffer<TIn, TOut>{};
            continue;
        }
 
        if (entry->isFieldPresent(sfDomainID) &&
            !permissioned_dex::offerInDomain(
                view_, entry->key(), entry->getFieldH256(sfDomainID), j_))
        {
            JLOG(j_.trace()) << "Removing offer no longer in domain " << entry->key();
            permRmOffer(entry->key());
            offer_ = TOffer<TIn, TOut>{};
            continue;
        }
 
        // Calculate owner funds
        ownerFunds_ = accountFundsHelper(
            view_, offer_.owner(), amount.out, offer_.issueOut(), fhZERO_IF_FROZEN, j_);
 
        // Check for unfunded offer
        if (*ownerFunds_ <= beast::zero)
        {
            // If the owner's balance in the pristine view is the same,
            // we haven't modified the balance and therefore the
            // offer is "found unfunded" versus "became unfunded"
            auto const original_funds = accountFundsHelper(
                cancelView_, offer_.owner(), amount.out, offer_.issueOut(), fhZERO_IF_FROZEN, j_);
 
            if (original_funds == *ownerFunds_)
            {
                permRmOffer(entry->key());
                JLOG(j_.trace()) << "Removing unfunded offer " << entry->key();
            }
            else
            {
                JLOG(j_.trace()) << "Removing became unfunded offer " << entry->key();
            }
            offer_ = TOffer<TIn, TOut>{};
            // See comment at top of loop for how the offer is removed
            continue;
        }
 
        bool const rmSmallIncreasedQOffer = [&] {
            bool const inIsXRP = isXRP(offer_.issueIn());
            bool const outIsXRP = isXRP(offer_.issueOut());
            if (inIsXRP && !outIsXRP)
            {
                // Without the `if constexpr`, the
                // `shouldRmSmallIncreasedQOffer` template will be instantiated
                // even if it is never used. This can cause compiler errors in
                // some cases, hence the `if constexpr` guard.
                // Note that TIn can be XRPAmount or STAmount, and TOut can be
                // IOUAmount or STAmount.
                if constexpr (!(std::is_same_v<TIn, IOUAmount> || std::is_same_v<TOut, XRPAmount>))
                    return shouldRmSmallIncreasedQOffer<XRPAmount, IOUAmount>();
            }
            if (!inIsXRP && outIsXRP)
            {
                // See comment above for `if constexpr` rationale
                if constexpr (!(std::is_same_v<TIn, XRPAmount> || std::is_same_v<TOut, IOUAmount>))
                    return shouldRmSmallIncreasedQOffer<IOUAmount, XRPAmount>();
            }
            if (!inIsXRP && !outIsXRP)
            {
                // See comment above for `if constexpr` rationale
                if constexpr (!(std::is_same_v<TIn, XRPAmount> || std::is_same_v<TOut, XRPAmount>))
                    return shouldRmSmallIncreasedQOffer<IOUAmount, IOUAmount>();
            }
            // LCOV_EXCL_START
            UNREACHABLE(
                "xrpl::TOfferStreamBase::step::rmSmallIncreasedQOffer : XRP "
                "vs XRP offer");
            return false;
            // LCOV_EXCL_STOP
        }();
 
        if (rmSmallIncreasedQOffer)
        {
            auto const original_funds = accountFundsHelper(
                cancelView_, offer_.owner(), amount.out, offer_.issueOut(), fhZERO_IF_FROZEN, j_);
 
            if (original_funds == *ownerFunds_)
            {
                permRmOffer(entry->key());
                JLOG(j_.trace()) << "Removing tiny offer due to reduced quality " << entry->key();
            }
            else
            {
                JLOG(j_.trace()) << "Removing tiny offer that became tiny due "
                                    "to reduced quality "
                                 << entry->key();
            }
            offer_ = TOffer<TIn, TOut>{};
            // See comment at top of loop for how the offer is removed
            continue;
        }
 
        break;
    }
 
    return true;
}
 
void
OfferStream::permRmOffer(uint256 const& offerIndex)
{
    offerDelete(cancelView_, cancelView_.peek(keylet::offer(offerIndex)), j_);
}
 
template <class TIn, class TOut>
void
FlowOfferStream<TIn, TOut>::permRmOffer(uint256 const& offerIndex)
{
    permToRemove_.insert(offerIndex);
}
 
template class FlowOfferStream<STAmount, STAmount>;
template class FlowOfferStream<IOUAmount, IOUAmount>;
template class FlowOfferStream<XRPAmount, IOUAmount>;
template class FlowOfferStream<IOUAmount, XRPAmount>;
 
template class TOfferStreamBase<STAmount, STAmount>;
template class TOfferStreamBase<IOUAmount, IOUAmount>;
template class TOfferStreamBase<XRPAmount, IOUAmount>;
template class TOfferStreamBase<IOUAmount, XRPAmount>;
}  // namespace xrpl