NFTokenUtils.cpp

#include <xrpl/basics/algorithm.h>
#include <xrpl/ledger/Dir.h>
#include <xrpl/ledger/View.h>
#include <xrpl/protocol/Feature.h>
#include <xrpl/protocol/STArray.h>
#include <xrpl/protocol/TxFlags.h>
#include <xrpl/protocol/nftPageMask.h>
#include <xrpl/tx/transactors/NFT/NFTokenUtils.h>
 
#include <functional>
#include <memory>
 
namespace xrpl {
 
namespace nft {
 
static std::shared_ptr<SLE const>
locatePage(ReadView const& view, AccountID const& owner, uint256 const& id)
{
    auto const first = keylet::nftpage(keylet::nftpage_min(owner), id);
    auto const last = keylet::nftpage_max(owner);
 
    // This NFT can only be found in the first page with a key that's strictly
    // greater than `first`, so look for that, up until the maximum possible
    // page.
    return view.read(
        Keylet(ltNFTOKEN_PAGE, view.succ(first.key, last.key.next()).value_or(last.key)));
}
 
static std::shared_ptr<SLE>
locatePage(ApplyView& view, AccountID const& owner, uint256 const& id)
{
    auto const first = keylet::nftpage(keylet::nftpage_min(owner), id);
    auto const last = keylet::nftpage_max(owner);
 
    // This NFT can only be found in the first page with a key that's strictly
    // greater than `first`, so look for that, up until the maximum possible
    // page.
    return view.peek(
        Keylet(ltNFTOKEN_PAGE, view.succ(first.key, last.key.next()).value_or(last.key)));
}
 
static std::shared_ptr<SLE>
getPageForToken(
    ApplyView& view,
    AccountID const& owner,
    uint256 const& id,
    std::function<void(ApplyView&, AccountID const&)> const& createCallback)
{
    auto const base = keylet::nftpage_min(owner);
    auto const first = keylet::nftpage(base, id);
    auto const last = keylet::nftpage_max(owner);
 
    // This NFT can only be found in the first page with a key that's strictly
    // greater than `first`, so look for that, up until the maximum possible
    // page.
    auto cp =
        view.peek(Keylet(ltNFTOKEN_PAGE, view.succ(first.key, last.key.next()).value_or(last.key)));
 
    // A suitable page doesn't exist; we'll have to create one.
    if (!cp)
    {
        STArray arr;
        cp = std::make_shared<SLE>(last);
        cp->setFieldArray(sfNFTokens, arr);
        view.insert(cp);
        createCallback(view, owner);
        return cp;
    }
 
    STArray narr = cp->getFieldArray(sfNFTokens);
 
    // The right page still has space: we're good.
    if (narr.size() != dirMaxTokensPerPage)
        return cp;
 
    // We need to split the page in two: the first half of the items in this
    // page will go into the new page; the rest will stay with the existing
    // page.
    //
    // Note we can't always split the page exactly in half.  All equivalent
    // NFTs must be kept on the same page.  So when the page contains
    // equivalent NFTs, the split may be lopsided in order to keep equivalent
    // NFTs on the same page.
    STArray carr;
    {
        // We prefer to keep equivalent NFTs on a page boundary.  That gives
        // any additional equivalent NFTs maximum room for expansion.
        // Round up the boundary until there's a non-equivalent entry.
        uint256 const cmp =
            narr[(dirMaxTokensPerPage / 2) - 1].getFieldH256(sfNFTokenID) & nft::pageMask;
 
        // Note that the calls to find_if_not() and (later) find_if()
        // rely on the fact that narr is kept in sorted order.
        auto splitIter = std::find_if_not(
            narr.begin() + (dirMaxTokensPerPage / 2), narr.end(), [&cmp](STObject const& obj) {
                return (obj.getFieldH256(sfNFTokenID) & nft::pageMask) == cmp;
            });
 
        // If we get all the way from the middle to the end with only
        // equivalent NFTokens then check the front of the page for a
        // place to make the split.
        if (splitIter == narr.end())
            splitIter = std::find_if(narr.begin(), narr.end(), [&cmp](STObject const& obj) {
                return (obj.getFieldH256(sfNFTokenID) & nft::pageMask) == cmp;
            });
 
        // There should be no circumstance when splitIter == end(), but if it
        // were to happen we should bail out because something is confused.
        if (splitIter == narr.end())
            return nullptr;
 
        // If splitIter == begin(), then the entire page is filled with
        // equivalent tokens.  This requires special handling.
        if (splitIter == narr.begin())
        {
            auto const relation{(id & nft::pageMask) <=> cmp};
            if (relation == 0)
            {
                // If the passed in id belongs exactly on this (full) page
                // this account simply cannot store the NFT.
                return nullptr;
            }
 
            if (relation > 0)
            {
                // We need to leave the entire contents of this page in
                // narr so carr stays empty.  The new NFT will be
                // inserted in carr.  This keeps the NFTs that must be
                // together all on their own page.
                splitIter = narr.end();
            }
 
            // If neither of those conditions apply then put all of
            // narr into carr and produce an empty narr where the new NFT
            // will be inserted.  Leave the split at narr.begin().
        }
 
        // Split narr at splitIter.
        STArray newCarr(std::make_move_iterator(splitIter), std::make_move_iterator(narr.end()));
        narr.erase(splitIter, narr.end());
        std::swap(carr, newCarr);
    }
 
    // Determine the ID for the page index.
    //
    // Note that we use uint256::next() because there's a subtlety in the way
    // NFT pages are structured.  The low 96-bits of NFT ID must be strictly
    // less than the low 96-bits of the enclosing page's index.  In order to
    // accommodate that requirement we use an index one higher than the
    // largest NFT in the page.
    uint256 const tokenIDForNewPage = narr.size() == dirMaxTokensPerPage
        ? narr[dirMaxTokensPerPage - 1].getFieldH256(sfNFTokenID).next()
        : carr[0].getFieldH256(sfNFTokenID);
 
    auto np = std::make_shared<SLE>(keylet::nftpage(base, tokenIDForNewPage));
    XRPL_ASSERT(np->key() > base.key, "xrpl::nft::getPageForToken : valid NFT page index");
    np->setFieldArray(sfNFTokens, narr);
    np->setFieldH256(sfNextPageMin, cp->key());
 
    if (auto ppm = (*cp)[~sfPreviousPageMin])
    {
        np->setFieldH256(sfPreviousPageMin, *ppm);
 
        if (auto p3 = view.peek(Keylet(ltNFTOKEN_PAGE, *ppm)))
        {
            p3->setFieldH256(sfNextPageMin, np->key());
            view.update(p3);
        }
    }
 
    view.insert(np);
 
    cp->setFieldArray(sfNFTokens, carr);
    cp->setFieldH256(sfPreviousPageMin, np->key());
    view.update(cp);
 
    createCallback(view, owner);
 
    return (first.key < np->key()) ? np : cp;
}
 
bool
compareTokens(uint256 const& a, uint256 const& b)
{
    // The sort of NFTokens needs to be fully deterministic, but the sort
    // is weird because we sort on the low 96-bits first. But if the low
    // 96-bits are identical we still need a fully deterministic sort.
    // So we sort on the low 96-bits first. If those are equal we sort on
    // the whole thing.
    if (auto const lowBitsCmp{(a & nft::pageMask) <=> (b & nft::pageMask)}; lowBitsCmp != 0)
        return lowBitsCmp < 0;
 
    return a < b;
}
 
TER
changeTokenURI(
    ApplyView& view,
    AccountID const& owner,
    uint256 const& nftokenID,
    std::optional<xrpl::Slice> const& uri)
{
    std::shared_ptr<SLE> const page = locatePage(view, owner, nftokenID);
 
    // If the page couldn't be found, the given NFT isn't owned by this account
    if (!page)
        return tecINTERNAL;  // LCOV_EXCL_LINE
 
    // Locate the NFT in the page
    STArray& arr = page->peekFieldArray(sfNFTokens);
 
    auto const nftIter = std::find_if(arr.begin(), arr.end(), [&nftokenID](STObject const& obj) {
        return (obj[sfNFTokenID] == nftokenID);
    });
 
    if (nftIter == arr.end())
        return tecINTERNAL;  // LCOV_EXCL_LINE
 
    if (uri)
        nftIter->setFieldVL(sfURI, *uri);
    else if (nftIter->isFieldPresent(sfURI))
        nftIter->makeFieldAbsent(sfURI);
 
    view.update(page);
    return tesSUCCESS;
}
 
TER
insertToken(ApplyView& view, AccountID owner, STObject&& nft)
{
    XRPL_ASSERT(nft.isFieldPresent(sfNFTokenID), "xrpl::nft::insertToken : has NFT token");
 
    // First, we need to locate the page the NFT belongs to, creating it
    // if necessary. This operation may fail if it is impossible to insert
    // the NFT.
    std::shared_ptr<SLE> page =
        getPageForToken(view, owner, nft[sfNFTokenID], [](ApplyView& view, AccountID const& owner) {
            adjustOwnerCount(
                view,
                view.peek(keylet::account(owner)),
                1,
                beast::Journal{beast::Journal::getNullSink()});
        });
 
    if (!page)
        return tecNO_SUITABLE_NFTOKEN_PAGE;
 
    {
        auto arr = page->getFieldArray(sfNFTokens);
        arr.push_back(std::move(nft));
 
        arr.sort([](STObject const& o1, STObject const& o2) {
            return compareTokens(o1.getFieldH256(sfNFTokenID), o2.getFieldH256(sfNFTokenID));
        });
 
        page->setFieldArray(sfNFTokens, arr);
    }
 
    view.update(page);
 
    return tesSUCCESS;
}
 
static bool
mergePages(ApplyView& view, std::shared_ptr<SLE> const& p1, std::shared_ptr<SLE> const& p2)
{
    if (p1->key() >= p2->key())
        Throw<std::runtime_error>("mergePages: pages passed in out of order!");
 
    if ((*p1)[~sfNextPageMin] != p2->key())
        Throw<std::runtime_error>("mergePages: next link broken!");
 
    if ((*p2)[~sfPreviousPageMin] != p1->key())
        Throw<std::runtime_error>("mergePages: previous link broken!");
 
    auto const p1arr = p1->getFieldArray(sfNFTokens);
    auto const p2arr = p2->getFieldArray(sfNFTokens);
 
    // Now check whether to merge the two pages; it only makes sense to do
    // this it would mean that one of them can be deleted as a result of
    // the merge.
 
    if (p1arr.size() + p2arr.size() > dirMaxTokensPerPage)
        return false;
 
    STArray x(p1arr.size() + p2arr.size());
 
    std::merge(
        p1arr.begin(),
        p1arr.end(),
        p2arr.begin(),
        p2arr.end(),
        std::back_inserter(x),
        [](STObject const& a, STObject const& b) {
            return compareTokens(a.getFieldH256(sfNFTokenID), b.getFieldH256(sfNFTokenID));
        });
 
    p2->setFieldArray(sfNFTokens, x);
 
    // So, at this point we need to unlink "p1" (since we just emptied it) but
    // we need to first relink the directory: if p1 has a previous page (p0),
    // load it, point it to p2 and point p2 to it.
 
    p2->makeFieldAbsent(sfPreviousPageMin);
 
    if (auto const ppm = (*p1)[~sfPreviousPageMin])
    {
        auto p0 = view.peek(Keylet(ltNFTOKEN_PAGE, *ppm));
 
        if (!p0)
            Throw<std::runtime_error>("mergePages: p0 can't be located!");
 
        p0->setFieldH256(sfNextPageMin, p2->key());
        view.update(p0);
 
        p2->setFieldH256(sfPreviousPageMin, *ppm);
    }
 
    view.update(p2);
    view.erase(p1);
 
    return true;
}
 
TER
removeToken(ApplyView& view, AccountID const& owner, uint256 const& nftokenID)
{
    std::shared_ptr<SLE> page = locatePage(view, owner, nftokenID);
 
    // If the page couldn't be found, the given NFT isn't owned by this account
    if (!page)
        return tecNO_ENTRY;
 
    return removeToken(view, owner, nftokenID, std::move(page));
}
 
TER
removeToken(
    ApplyView& view,
    AccountID const& owner,
    uint256 const& nftokenID,
    std::shared_ptr<SLE>&& curr)
{
    // We found a page, but the given NFT may not be in it.
    auto arr = curr->getFieldArray(sfNFTokens);
 
    {
        auto x = std::find_if(arr.begin(), arr.end(), [&nftokenID](STObject const& obj) {
            return (obj[sfNFTokenID] == nftokenID);
        });
 
        if (x == arr.end())
            return tecNO_ENTRY;
 
        arr.erase(x);
    }
 
    // Page management:
    auto const loadPage = [&view](std::shared_ptr<SLE> const& page1, SF_UINT256 const& field) {
        std::shared_ptr<SLE> page2;
 
        if (auto const id = (*page1)[~field])
        {
            page2 = view.peek(Keylet(ltNFTOKEN_PAGE, *id));
 
            if (!page2)
                Throw<std::runtime_error>(
                    "page " + to_string(page1->key()) + " has a broken " + field.getName() +
                    " field pointing to " + to_string(*id));
        }
 
        return page2;
    };
 
    auto const prev = loadPage(curr, sfPreviousPageMin);
    auto const next = loadPage(curr, sfNextPageMin);
 
    if (!arr.empty())
    {
        // The current page isn't empty. Update it and then try to consolidate
        // pages. Note that this consolidation attempt may actually merge three
        // pages into one!
        curr->setFieldArray(sfNFTokens, arr);
        view.update(curr);
 
        int cnt = 0;
 
        if (prev && mergePages(view, prev, curr))
            cnt--;
 
        if (next && mergePages(view, curr, next))
            cnt--;
 
        if (cnt != 0)
            adjustOwnerCount(
                view,
                view.peek(keylet::account(owner)),
                cnt,
                beast::Journal{beast::Journal::getNullSink()});
 
        return tesSUCCESS;
    }
 
    if (prev)
    {
        // With fixNFTokenPageLinks...
        // The page is empty and there is a prev.  If the last page of the
        // directory is empty then we need to:
        //  1. Move the contents of the previous page into the last page.
        //  2. Fix up the link from prev's previous page.
        //  3. Fix up the owner count.
        //  4. Erase the previous page.
        if (view.rules().enabled(fixNFTokenPageLinks) &&
            ((curr->key() & nft::pageMask) == pageMask))
        {
            // Copy all relevant information from prev to curr.
            curr->peekFieldArray(sfNFTokens) = prev->peekFieldArray(sfNFTokens);
 
            if (auto const prevLink = prev->at(~sfPreviousPageMin))
            {
                curr->at(sfPreviousPageMin) = *prevLink;
 
                // Also fix up the NextPageMin link in the new Previous.
                auto const newPrev = loadPage(curr, sfPreviousPageMin);
                newPrev->at(sfNextPageMin) = curr->key();
                view.update(newPrev);
            }
            else
            {
                curr->makeFieldAbsent(sfPreviousPageMin);
            }
 
            adjustOwnerCount(
                view,
                view.peek(keylet::account(owner)),
                -1,
                beast::Journal{beast::Journal::getNullSink()});
 
            view.update(curr);
            view.erase(prev);
            return tesSUCCESS;
        }
 
        // The page is empty and not the last page, so we can just unlink it
        // and then remove it.
        if (next)
            prev->setFieldH256(sfNextPageMin, next->key());
        else
            prev->makeFieldAbsent(sfNextPageMin);
 
        view.update(prev);
    }
 
    if (next)
    {
        // Make our next page point to our previous page:
        if (prev)
            next->setFieldH256(sfPreviousPageMin, prev->key());
        else
            next->makeFieldAbsent(sfPreviousPageMin);
 
        view.update(next);
    }
 
    view.erase(curr);
 
    int cnt = 1;
 
    // Since we're here, try to consolidate the previous and current pages
    // of the page we removed (if any) into one.  mergePages() _should_
    // always return false.  Since tokens are burned one at a time, there
    // should never be a page containing one token sitting between two pages
    // that have few enough tokens that they can be merged.
    //
    // But, in case that analysis is wrong, it's good to leave this code here
    // just in case.
    if (prev && next &&
        mergePages(
            view,
            view.peek(Keylet(ltNFTOKEN_PAGE, prev->key())),
            view.peek(Keylet(ltNFTOKEN_PAGE, next->key()))))
        cnt++;
 
    adjustOwnerCount(
        view,
        view.peek(keylet::account(owner)),
        -1 * cnt,
        beast::Journal{beast::Journal::getNullSink()});
 
    return tesSUCCESS;
}
 
std::optional<STObject>
findToken(ReadView const& view, AccountID const& owner, uint256 const& nftokenID)
{
    std::shared_ptr<SLE const> page = locatePage(view, owner, nftokenID);
 
    // If the page couldn't be found, the given NFT isn't owned by this account
    if (!page)
        return std::nullopt;
 
    // We found a candidate page, but the given NFT may not be in it.
    for (auto const& t : page->getFieldArray(sfNFTokens))
    {
        if (t[sfNFTokenID] == nftokenID)
            return t;
    }
 
    return std::nullopt;
}
 
std::optional<TokenAndPage>
findTokenAndPage(ApplyView& view, AccountID const& owner, uint256 const& nftokenID)
{
    std::shared_ptr<SLE> page = locatePage(view, owner, nftokenID);
 
    // If the page couldn't be found, the given NFT isn't owned by this account
    if (!page)
        return std::nullopt;
 
    // We found a candidate page, but the given NFT may not be in it.
    for (auto const& t : page->getFieldArray(sfNFTokens))
    {
        if (t[sfNFTokenID] == nftokenID)
            // This std::optional constructor is explicit, so it is spelled out.
            return std::optional<TokenAndPage>(std::in_place, t, std::move(page));
    }
    return std::nullopt;
}
 
std::size_t
removeTokenOffersWithLimit(ApplyView& view, Keylet const& directory, std::size_t maxDeletableOffers)
{
    if (maxDeletableOffers == 0)
        return 0;
 
    std::optional<std::uint64_t> pageIndex{0};
    std::size_t deletedOffersCount = 0;
 
    do
    {
        auto const page = view.peek(keylet::page(directory, *pageIndex));
        if (!page)
            break;
 
        // We get the index of the next page in case the current
        // page is deleted after all of its entries have been removed
        pageIndex = (*page)[~sfIndexNext];
 
        auto offerIndexes = page->getFieldV256(sfIndexes);
 
        // We reverse-iterate the offer directory page to delete all entries.
        // Deleting an entry in a NFTokenOffer directory page won't cause
        // entries from other pages to move to the current, so, it is safe to
        // delete entries one by one in the page. It is required to iterate
        // backwards to handle iterator invalidation for vector, as we are
        // deleting during iteration.
        for (int i = offerIndexes.size() - 1; i >= 0; --i)
        {
            if (auto const offer = view.peek(keylet::nftoffer(offerIndexes[i])))
            {
                if (deleteTokenOffer(view, offer))
                    ++deletedOffersCount;
                else
                    Throw<std::runtime_error>(
                        "Offer " + to_string(offerIndexes[i]) + " cannot be deleted!");
            }
 
            if (maxDeletableOffers == deletedOffersCount)
                break;
        }
    } while (pageIndex.value_or(0) && maxDeletableOffers != deletedOffersCount);
 
    return deletedOffersCount;
}
 
TER
notTooManyOffers(ReadView const& view, uint256 const& nftokenID)
{
    std::size_t totalOffers = 0;
 
    {
        Dir buys(view, keylet::nft_buys(nftokenID));
        for (auto iter = buys.begin(); iter != buys.end(); iter.next_page())
        {
            totalOffers += iter.page_size();
            if (totalOffers > maxDeletableTokenOfferEntries)
                return tefTOO_BIG;
        }
    }
 
    {
        Dir sells(view, keylet::nft_sells(nftokenID));
        for (auto iter = sells.begin(); iter != sells.end(); iter.next_page())
        {
            totalOffers += iter.page_size();
            if (totalOffers > maxDeletableTokenOfferEntries)
                return tefTOO_BIG;
        }
    }
    return tesSUCCESS;
}
 
bool
deleteTokenOffer(ApplyView& view, std::shared_ptr<SLE> const& offer)
{
    if (offer->getType() != ltNFTOKEN_OFFER)
        return false;
 
    auto const owner = (*offer)[sfOwner];
 
    if (!view.dirRemove(keylet::ownerDir(owner), (*offer)[sfOwnerNode], offer->key(), false))
        return false;
 
    auto const nftokenID = (*offer)[sfNFTokenID];
 
    if (!view.dirRemove(
            ((*offer)[sfFlags] & tfSellNFToken) ? keylet::nft_sells(nftokenID)
                                                : keylet::nft_buys(nftokenID),
            (*offer)[sfNFTokenOfferNode],
            offer->key(),
            false))
        return false;
 
    adjustOwnerCount(
        view, view.peek(keylet::account(owner)), -1, beast::Journal{beast::Journal::getNullSink()});
 
    view.erase(offer);
    return true;
}
 
bool
repairNFTokenDirectoryLinks(ApplyView& view, AccountID const& owner)
{
    bool didRepair = false;
 
    auto const last = keylet::nftpage_max(owner);
 
    std::shared_ptr<SLE> page = view.peek(Keylet(
        ltNFTOKEN_PAGE,
        view.succ(keylet::nftpage_min(owner).key, last.key.next()).value_or(last.key)));
 
    if (!page)
        return didRepair;
 
    if (page->key() == last.key)
    {
        // There's only one page in this entire directory.  There should be
        // no links on that page.
        bool const nextPresent = page->isFieldPresent(sfNextPageMin);
        bool const prevPresent = page->isFieldPresent(sfPreviousPageMin);
        if (nextPresent || prevPresent)
        {
            didRepair = true;
            if (prevPresent)
                page->makeFieldAbsent(sfPreviousPageMin);
            if (nextPresent)
                page->makeFieldAbsent(sfNextPageMin);
            view.update(page);
        }
        return didRepair;
    }
 
    // First page is not the same as last page.  The first page should not
    // contain a previous link.
    if (page->isFieldPresent(sfPreviousPageMin))
    {
        didRepair = true;
        page->makeFieldAbsent(sfPreviousPageMin);
        view.update(page);
    }
 
    std::shared_ptr<SLE> nextPage;
    while (
        (nextPage = view.peek(Keylet(
             ltNFTOKEN_PAGE, view.succ(page->key().next(), last.key.next()).value_or(last.key)))))
    {
        if (!page->isFieldPresent(sfNextPageMin) ||
            page->getFieldH256(sfNextPageMin) != nextPage->key())
        {
            didRepair = true;
            page->setFieldH256(sfNextPageMin, nextPage->key());
            view.update(page);
        }
 
        if (!nextPage->isFieldPresent(sfPreviousPageMin) ||
            nextPage->getFieldH256(sfPreviousPageMin) != page->key())
        {
            didRepair = true;
            nextPage->setFieldH256(sfPreviousPageMin, page->key());
            view.update(nextPage);
        }
 
        if (nextPage->key() == last.key)
            // We need special handling for the last page.
            break;
 
        page = nextPage;
    }
 
    // When we arrive here, nextPage should have the same index as last.
    // If not, then that's something we need to fix.
    if (!nextPage)
    {
        // It turns out that page is the last page for this owner, but
        // that last page does not have the expected final index.  We need
        // to move the contents of the current last page into a page with the
        // correct index.
        //
        // The owner count does not need to change because, even though
        // we're adding a page, we'll also remove the page that used to be
        // last.
        didRepair = true;
        nextPage = std::make_shared<SLE>(last);
 
        // Copy all relevant information from prev to curr.
        nextPage->peekFieldArray(sfNFTokens) = page->peekFieldArray(sfNFTokens);
 
        if (auto const prevLink = page->at(~sfPreviousPageMin))
        {
            nextPage->at(sfPreviousPageMin) = *prevLink;
 
            // Also fix up the NextPageMin link in the new Previous.
            auto const newPrev = view.peek(Keylet(ltNFTOKEN_PAGE, *prevLink));
            if (!newPrev)
                Throw<std::runtime_error>(
                    "NFTokenPage directory for " + to_string(owner) +
                    " cannot be repaired.  Unexpected link problem.");
            newPrev->at(sfNextPageMin) = nextPage->key();
            view.update(newPrev);
        }
        view.erase(page);
        view.insert(nextPage);
        return didRepair;
    }
 
    XRPL_ASSERT(nextPage, "xrpl::nft::repairNFTokenDirectoryLinks : next page is available");
    if (nextPage->isFieldPresent(sfNextPageMin))
    {
        didRepair = true;
        nextPage->makeFieldAbsent(sfNextPageMin);
        view.update(nextPage);
    }
    return didRepair;
}
 
NotTEC
tokenOfferCreatePreflight(
    AccountID const& acctID,
    STAmount const& amount,
    std::optional<AccountID> const& dest,
    std::optional<std::uint32_t> const& expiration,
    std::uint16_t nftFlags,
    Rules const& rules,
    std::optional<AccountID> const& owner,
    std::uint32_t txFlags)
{
    if (amount.negative())
        // An offer for a negative amount makes no sense.
        return temBAD_AMOUNT;
 
    if (!isXRP(amount))
    {
        if (nftFlags & nft::flagOnlyXRP)
            return temBAD_AMOUNT;
 
        if (!amount)
            return temBAD_AMOUNT;
    }
 
    // If this is an offer to buy, you must offer something; if it's an
    // offer to sell, you can ask for nothing.
    bool const isSellOffer = txFlags & tfSellNFToken;
    if (!isSellOffer && !amount)
        return temBAD_AMOUNT;
 
    if (expiration.has_value() && expiration.value() == 0)
        return temBAD_EXPIRATION;
 
    // The 'Owner' field must be present when offering to buy, but can't
    // be present when selling (it's implicit):
    if (owner.has_value() == isSellOffer)
        return temMALFORMED;
 
    if (owner && owner == acctID)
        return temMALFORMED;
 
    // The destination can't be the account executing the transaction.
    if (dest && dest == acctID)
    {
        return temMALFORMED;
    }
    return tesSUCCESS;
}
 
TER
tokenOfferCreatePreclaim(
    ReadView const& view,
    AccountID const& acctID,
    AccountID const& nftIssuer,
    STAmount const& amount,
    std::optional<AccountID> const& dest,
    std::uint16_t nftFlags,
    std::uint16_t xferFee,
    beast::Journal j,
    std::optional<AccountID> const& owner,
    std::uint32_t txFlags)
{
    if (!(nftFlags & nft::flagCreateTrustLines) && !amount.native() && xferFee)
    {
        if (!view.exists(keylet::account(nftIssuer)))
            return tecNO_ISSUER;
 
        // If the IOU issuer and the NFToken issuer are the same, then that
        // issuer does not need a trust line to accept their fee.
        if (view.rules().enabled(featureNFTokenMintOffer))
        {
            if (nftIssuer != amount.getIssuer() &&
                !view.read(keylet::line(nftIssuer, amount.issue())))
                return tecNO_LINE;
        }
        else if (!view.exists(keylet::line(nftIssuer, amount.issue())))
        {
            return tecNO_LINE;
        }
 
        if (isFrozen(view, nftIssuer, amount.getCurrency(), amount.getIssuer()))
            return tecFROZEN;
    }
 
    if (nftIssuer != acctID && !(nftFlags & nft::flagTransferable))
    {
        auto const root = view.read(keylet::account(nftIssuer));
        XRPL_ASSERT(root, "xrpl::nft::tokenOfferCreatePreclaim : non-null account");
 
        if (auto minter = (*root)[~sfNFTokenMinter]; minter != acctID)
            return tefNFTOKEN_IS_NOT_TRANSFERABLE;
    }
 
    if (isFrozen(view, acctID, amount.getCurrency(), amount.getIssuer()))
        return tecFROZEN;
 
    // If this is an offer to buy the token, the account must have the
    // needed funds at hand; but note that funds aren't reserved and the
    // offer may later become unfunded.
    if ((txFlags & tfSellNFToken) == 0)
    {
        // We allow an IOU issuer to make a buy offer
        // using their own currency.
        if (accountFunds(view, acctID, amount, FreezeHandling::fhZERO_IF_FROZEN, j).signum() <= 0)
            return tecUNFUNDED_OFFER;
    }
 
    if (dest)
    {
        // If a destination is specified, the destination must already be in
        // the ledger.
        auto const sleDst = view.read(keylet::account(*dest));
 
        if (!sleDst)
            return tecNO_DST;
 
        // check if the destination has disallowed incoming offers
        if (sleDst->getFlags() & lsfDisallowIncomingNFTokenOffer)
            return tecNO_PERMISSION;
    }
 
    if (owner)
    {
        auto const sleOwner = view.read(keylet::account(*owner));
 
        // defensively check
        // it should not be possible to specify owner that doesn't exist
        if (!sleOwner)
            return tecNO_TARGET;
 
        if (sleOwner->getFlags() & lsfDisallowIncomingNFTokenOffer)
            return tecNO_PERMISSION;
    }
 
    if (view.rules().enabled(fixEnforceNFTokenTrustlineV2) && !amount.native())
    {
        // If this is a sell offer, check that the account is allowed to
        // receive IOUs. If this is a buy offer, we have to check that trustline
        // is authorized, even though we previously checked it's balance via
        // accountHolds. This is due to a possibility of existence of
        // unauthorized trustlines with balance
        auto const res =
            nft::checkTrustlineAuthorized(view, acctID, j, amount.asset().get<Issue>());
        if (res != tesSUCCESS)
            return res;
    }
    return tesSUCCESS;
}
 
TER
tokenOfferCreateApply(
    ApplyView& view,
    AccountID const& acctID,
    STAmount const& amount,
    std::optional<AccountID> const& dest,
    std::optional<std::uint32_t> const& expiration,
    SeqProxy seqProxy,
    uint256 const& nftokenID,
    XRPAmount const& priorBalance,
    beast::Journal j,
    std::uint32_t txFlags)
{
    Keylet const acctKeylet = keylet::account(acctID);
    if (auto const acct = view.read(acctKeylet);
        priorBalance < view.fees().accountReserve((*acct)[sfOwnerCount] + 1))
        return tecINSUFFICIENT_RESERVE;
 
    auto const offerID = keylet::nftoffer(acctID, seqProxy.value());
 
    // Create the offer:
    {
        // Token offers are always added to the owner's owner directory:
        auto const ownerNode =
            view.dirInsert(keylet::ownerDir(acctID), offerID, describeOwnerDir(acctID));
 
        if (!ownerNode)
            return tecDIR_FULL;  // LCOV_EXCL_LINE
 
        bool const isSellOffer = txFlags & tfSellNFToken;
 
        // Token offers are also added to the token's buy or sell offer
        // directory
        auto const offerNode = view.dirInsert(
            isSellOffer ? keylet::nft_sells(nftokenID) : keylet::nft_buys(nftokenID),
            offerID,
            [&nftokenID, isSellOffer](std::shared_ptr<SLE> const& sle) {
                (*sle)[sfFlags] = isSellOffer ? lsfNFTokenSellOffers : lsfNFTokenBuyOffers;
                (*sle)[sfNFTokenID] = nftokenID;
            });
 
        if (!offerNode)
            return tecDIR_FULL;  // LCOV_EXCL_LINE
 
        std::uint32_t sleFlags = 0;
 
        if (isSellOffer)
            sleFlags |= lsfSellNFToken;
 
        auto offer = std::make_shared<SLE>(offerID);
        (*offer)[sfOwner] = acctID;
        (*offer)[sfNFTokenID] = nftokenID;
        (*offer)[sfAmount] = amount;
        (*offer)[sfFlags] = sleFlags;
        (*offer)[sfOwnerNode] = *ownerNode;
        (*offer)[sfNFTokenOfferNode] = *offerNode;
 
        if (expiration)
            (*offer)[sfExpiration] = *expiration;
 
        if (dest)
            (*offer)[sfDestination] = *dest;
 
        view.insert(offer);
    }
 
    // Update owner count.
    adjustOwnerCount(view, view.peek(acctKeylet), 1, j);
 
    return tesSUCCESS;
}
 
TER
checkTrustlineAuthorized(
    ReadView const& view,
    AccountID const id,
    beast::Journal const j,
    Issue const& issue)
{
    // Only valid for custom currencies
    XRPL_ASSERT(!isXRP(issue.currency), "xrpl::nft::checkTrustlineAuthorized : valid to check.");
 
    if (view.rules().enabled(fixEnforceNFTokenTrustlineV2))
    {
        auto const issuerAccount = view.read(keylet::account(issue.account));
        if (!issuerAccount)
        {
            JLOG(j.debug()) << "xrpl::nft::checkTrustlineAuthorized: can't "
                               "receive IOUs from non-existent issuer: "
                            << to_string(issue.account);
 
            return tecNO_ISSUER;
        }
 
        // An account can not create a trustline to itself, so no line can
        // exist to be authorized. Additionally, an issuer can always accept
        // its own issuance.
        if (issue.account == id)
        {
            return tesSUCCESS;
        }
 
        if (issuerAccount->isFlag(lsfRequireAuth))
        {
            auto const trustLine = view.read(keylet::line(id, issue.account, issue.currency));
 
            if (!trustLine)
            {
                return tecNO_LINE;
            }
 
            // Entries have a canonical representation, determined by a
            // lexicographical "greater than" comparison employing strict
            // weak ordering. Determine which entry we need to access.
            if (!trustLine->isFlag(id > issue.account ? lsfLowAuth : lsfHighAuth))
            {
                return tecNO_AUTH;
            }
        }
    }
 
    return tesSUCCESS;
}
 
TER
checkTrustlineDeepFrozen(
    ReadView const& view,
    AccountID const id,
    beast::Journal const j,
    Issue const& issue)
{
    // Only valid for custom currencies
    XRPL_ASSERT(!isXRP(issue.currency), "xrpl::nft::checkTrustlineDeepFrozen : valid to check.");
 
    if (view.rules().enabled(featureDeepFreeze))
    {
        auto const issuerAccount = view.read(keylet::account(issue.account));
        if (!issuerAccount)
        {
            JLOG(j.debug()) << "xrpl::nft::checkTrustlineDeepFrozen: can't "
                               "receive IOUs from non-existent issuer: "
                            << to_string(issue.account);
 
            return tecNO_ISSUER;
        }
 
        // An account can not create a trustline to itself, so no line can
        // exist to be frozen. Additionally, an issuer can always accept its
        // own issuance.
        if (issue.account == id)
        {
            return tesSUCCESS;
        }
 
        auto const trustLine = view.read(keylet::line(id, issue.account, issue.currency));
 
        if (!trustLine)
        {
            return tesSUCCESS;
        }
 
        // There's no difference which side enacted deep freeze, accepting
        // tokens shouldn't be possible.
        bool const deepFrozen = (*trustLine)[sfFlags] & (lsfLowDeepFreeze | lsfHighDeepFreeze);
 
        if (deepFrozen)
        {
            return tecFROZEN;
        }
    }
 
    return tesSUCCESS;
}
 
}  // namespace nft
}  // namespace xrpl