rippled/src/test/app/NFTokenBurn_test.cpp

#include <test/jtx/Account.h>
#include <test/jtx/Env.h>
#include <test/jtx/TestHelpers.h>
#include <test/jtx/acctdelete.h>
#include <test/jtx/amount.h>
#include <test/jtx/fee.h>
#include <test/jtx/owners.h>  // IWYU pragma: keep
#include <test/jtx/ter.h>
#include <test/jtx/token.h>
#include <test/jtx/txflags.h>
#include <test/unit_test/SuiteJournal.h>

#include <xrpl/basics/base_uint.h>
#include <xrpl/beast/unit_test/suite.h>
#include <xrpl/beast/utility/Journal.h>
#include <xrpl/json/json_forwards.h>
#include <xrpl/json/json_value.h>
#include <xrpl/json/to_string.h>
#include <xrpl/ledger/ApplyView.h>
#include <xrpl/ledger/OpenView.h>
#include <xrpl/protocol/Feature.h>
#include <xrpl/protocol/Indexes.h>
#include <xrpl/protocol/Protocol.h>
#include <xrpl/protocol/SField.h>
#include <xrpl/protocol/STObject.h>
#include <xrpl/protocol/STTx.h>
#include <xrpl/protocol/TER.h>
#include <xrpl/protocol/TxFlags.h>
#include <xrpl/protocol/TxFormats.h>
#include <xrpl/protocol/jss.h>
#include <xrpl/protocol/nft.h>
#include <xrpl/tx/ApplyContext.h>

#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <ostream>
#include <random>
#include <vector>

namespace xrpl {

class NFTokenBurn_test : public beast::unit_test::suite
{
    // Helper function that returns the number of nfts owned by an account.
    static std::uint32_t
    nftCount(test::jtx::Env& env, test::jtx::Account const& acct)
    {
        Json::Value params;
        params[jss::account] = acct.human();
        params[jss::type] = "state";
        Json::Value nfts = env.rpc("json", "account_nfts", to_string(params));
        return nfts[jss::result][jss::account_nfts].size();
    };

    // Helper function that returns new nft id for an account and create
    // specified number of sell offers
    static uint256
    createNftAndOffers(
        test::jtx::Env& env,
        test::jtx::Account const& owner,
        std::vector<uint256>& offerIndexes,
        size_t const tokenCancelCount)
    {
        using namespace test::jtx;
        uint256 const nftokenID = token::getNextID(env, owner, 0, tfTransferable);
        env(token::mint(owner, 0),
            token::uri(std::string(maxTokenURILength, 'u')),
            txflags(tfTransferable));
        env.close();

        offerIndexes.reserve(tokenCancelCount);

        for (uint32_t i = 0; i < tokenCancelCount; ++i)
        {
            // Create sell offer
            offerIndexes.push_back(keylet::nftoffer(owner, env.seq(owner)).key);
            env(token::createOffer(owner, nftokenID, drops(1)), txflags(tfSellNFToken));
            env.close();
        }

        return nftokenID;
    };

    // printNFTPages is a helper function that may be used for debugging.
    //
    // It uses the ledger RPC command to show the NFT pages in the ledger.
    // This parameter controls how noisy the output is.
    enum Volume : bool {
        quiet = false,
        noisy = true,
    };

    static void
    printNFTPages(test::jtx::Env& env, Volume vol)
    {
        Json::Value jvParams;
        jvParams[jss::ledger_index] = "current";
        jvParams[jss::binary] = false;
        {
            Json::Value jrr = env.rpc("json", "ledger_data", to_string(jvParams));

            // Iterate the state and print all NFTokenPages.
            if (!jrr.isMember(jss::result) || !jrr[jss::result].isMember(jss::state))
            {
                std::cout << "No ledger state found!" << std::endl;
                return;
            }
            Json::Value& state = jrr[jss::result][jss::state];
            if (!state.isArray())
            {
                std::cout << "Ledger state is not array!" << std::endl;
                return;
            }
            for (Json::UInt i = 0; i < state.size(); ++i)
            {
                if (state[i].isMember(sfNFTokens.jsonName) &&
                    state[i][sfNFTokens.jsonName].isArray())
                {
                    std::uint32_t const tokenCount = state[i][sfNFTokens.jsonName].size();
                    std::cout << tokenCount << " NFtokens in page "
                              << state[i][jss::index].asString() << std::endl;

                    if (vol == noisy)
                    {
                        std::cout << state[i].toStyledString() << std::endl;
                    }
                    else
                    {
                        if (tokenCount > 0)
                        {
                            std::cout
                                << "first: " << state[i][sfNFTokens.jsonName][0u].toStyledString()
                                << std::endl;
                        }
                        if (tokenCount > 1)
                        {
                            std::cout
                                << "last: "
                                << state[i][sfNFTokens.jsonName][tokenCount - 1].toStyledString()
                                << std::endl;
                        }
                    }
                }
            }
        }
    }

    void
    testBurnRandom(FeatureBitset features)
    {
        // Exercise a number of conditions with NFT burning.
        testcase("Burn random");

        using namespace test::jtx;

        Env env{*this, features};

        // Keep information associated with each account together.
        struct AcctStat
        {
            test::jtx::Account const acct;
            std::vector<uint256> nfts;

            AcctStat(char const* name) : acct(name)
            {
            }

            operator test::jtx::Account() const
            {
                return acct;
            }
        };
        AcctStat alice{"alice"};
        AcctStat becky{"becky"};
        AcctStat minter{"minter"};

        env.fund(XRP(10000), alice, becky, minter);
        env.close();

        // Both alice and minter mint nfts in case that makes any difference.
        env(token::setMinter(alice, minter));
        env.close();

        // Create enough NFTs that alice, becky, and minter can all have
        // at least three pages of NFTs.  This will cause more activity in
        // the page coalescing code.  If we make 210 NFTs in total, we can
        // have alice and minter each make 105.  That will allow us to
        // distribute 70 NFTs to our three participants.
        //
        // Give each NFT a pseudo-randomly chosen fee so the NFTs are
        // distributed pseudo-randomly through the pages.  This should
        // prevent alice's and minter's NFTs from clustering together
        // in becky's directory.
        //
        // Use a default initialized mersenne_twister because we want the
        // effect of random numbers, but we want the test to run the same
        // way each time.
        std::mt19937 engine;
        std::uniform_int_distribution<std::size_t> feeDist(
            decltype(maxTransferFee){}, maxTransferFee);

        alice.nfts.reserve(105);
        while (alice.nfts.size() < 105)
        {
            std::uint16_t const xferFee = feeDist(engine);
            alice.nfts.push_back(
                token::getNextID(env, alice, 0u, tfTransferable | tfBurnable, xferFee));
            env(token::mint(alice), txflags(tfTransferable | tfBurnable), token::xferFee(xferFee));
            env.close();
        }

        minter.nfts.reserve(105);
        while (minter.nfts.size() < 105)
        {
            std::uint16_t const xferFee = feeDist(engine);
            minter.nfts.push_back(
                token::getNextID(env, alice, 0u, tfTransferable | tfBurnable, xferFee));
            env(token::mint(minter),
                txflags(tfTransferable | tfBurnable),
                token::xferFee(xferFee),
                token::issuer(alice));
            env.close();
        }

        // All of the NFTs are now minted.  Transfer 35 each over to becky so
        // we end up with 70 NFTs in each account.
        becky.nfts.reserve(70);
        {
            auto aliceIter = alice.nfts.begin();
            auto minterIter = minter.nfts.begin();
            while (becky.nfts.size() < 70)
            {
                // We do the same work on alice and minter, so make a lambda.
                auto xferNFT = [&env, &becky](AcctStat& acct, auto& iter) {
                    uint256 const offerIndex = keylet::nftoffer(acct.acct, env.seq(acct.acct)).key;
                    env(token::createOffer(acct, *iter, XRP(0)), txflags(tfSellNFToken));
                    env.close();
                    env(token::acceptSellOffer(becky, offerIndex));
                    env.close();
                    becky.nfts.push_back(*iter);
                    iter = acct.nfts.erase(iter);
                    iter += 2;
                };
                xferNFT(alice, aliceIter);
                xferNFT(minter, minterIter);
            }
            BEAST_EXPECT(aliceIter == alice.nfts.end());
            BEAST_EXPECT(minterIter == minter.nfts.end());
        }

        // Now all three participants have 70 NFTs.
        BEAST_EXPECT(nftCount(env, alice.acct) == 70);
        BEAST_EXPECT(nftCount(env, becky.acct) == 70);
        BEAST_EXPECT(nftCount(env, minter.acct) == 70);

        // Next we'll create offers for all of those NFTs.  This calls for
        // another lambda.
        auto addOffers = [&env](AcctStat& owner, AcctStat& other1, AcctStat& other2) {
            for (uint256 const nft : owner.nfts)
            {
                // Create sell offers for owner.
                env(token::createOffer(owner, nft, drops(1)),
                    txflags(tfSellNFToken),
                    token::destination(other1));
                env(token::createOffer(owner, nft, drops(1)),
                    txflags(tfSellNFToken),
                    token::destination(other2));
                env.close();

                // Create buy offers for other1 and other2.
                env(token::createOffer(other1, nft, drops(1)), token::owner(owner));
                env(token::createOffer(other2, nft, drops(1)), token::owner(owner));
                env.close();

                env(token::createOffer(other2, nft, drops(2)), token::owner(owner));
                env(token::createOffer(other1, nft, drops(2)), token::owner(owner));
                env.close();
            }
        };
        addOffers(alice, becky, minter);
        addOffers(becky, minter, alice);
        addOffers(minter, alice, becky);
        BEAST_EXPECT(ownerCount(env, alice) == 424);
        BEAST_EXPECT(ownerCount(env, becky) == 424);
        BEAST_EXPECT(ownerCount(env, minter) == 424);

        // Now each of the 270 NFTs has six offers associated with it.
        // Randomly select an NFT out of the pile and burn it.  Continue
        // the process until all NFTs are burned.
        AcctStat* const stats[3] = {&alice, &becky, &minter};
        std::uniform_int_distribution<std::size_t> acctDist(0, 2);
        std::uniform_int_distribution<std::size_t> mintDist(0, 1);

        while (!stats[0]->nfts.empty() || !stats[1]->nfts.empty() || !stats[2]->nfts.empty())
        {
            // Pick an account to burn an nft.  If there are no nfts left
            // pick again.
            AcctStat& owner = *(stats[acctDist(engine)]);
            if (owner.nfts.empty())
                continue;

            // Pick one of the nfts.
            std::uniform_int_distribution<std::size_t> nftDist(0lu, owner.nfts.size() - 1);
            auto nftIter = owner.nfts.begin() + nftDist(engine);
            uint256 const nft = *nftIter;
            owner.nfts.erase(nftIter);

            // Decide which of the accounts should burn the nft.  If the
            // owner is becky then any of the three accounts can burn.
            // Otherwise either alice or minter can burn.
            AcctStat const& burner = [&]() -> AcctStat& {
                if (owner.acct == becky.acct)
                    return *(stats[acctDist(engine)]);
                return mintDist(engine) ? alice : minter;
            }();

            if (owner.acct == burner.acct)
            {
                env(token::burn(burner, nft));
            }
            else
            {
                env(token::burn(burner, nft), token::owner(owner));
            }
            env.close();

            // Every time we burn an nft, the number of nfts they hold should
            // match the number of nfts we think they hold.
            BEAST_EXPECT(nftCount(env, alice.acct) == alice.nfts.size());
            BEAST_EXPECT(nftCount(env, becky.acct) == becky.nfts.size());
            BEAST_EXPECT(nftCount(env, minter.acct) == minter.nfts.size());
        }
        BEAST_EXPECT(nftCount(env, alice.acct) == 0);
        BEAST_EXPECT(nftCount(env, becky.acct) == 0);
        BEAST_EXPECT(nftCount(env, minter.acct) == 0);

        // When all nfts are burned none of the accounts should have
        // an ownerCount.
        BEAST_EXPECT(ownerCount(env, alice) == 0);
        BEAST_EXPECT(ownerCount(env, becky) == 0);
        BEAST_EXPECT(ownerCount(env, minter) == 0);
    }

    void
    testBurnSequential(FeatureBitset features)
    {
        // The earlier burn test randomizes which nft is burned.  There are
        // a couple of directory merging scenarios that can only be tested by
        // inserting and deleting in an ordered fashion.  We do that testing
        // now.
        testcase("Burn sequential");

        using namespace test::jtx;

        Account const alice{"alice"};

        Env env{*this, features};
        env.fund(XRP(1000), alice);

        // A lambda that generates 96 nfts packed into three pages of 32 each.
        // Returns a sorted vector of the NFTokenIDs packed into the pages.
        auto genPackedTokens = [this, &env, &alice]() {
            std::vector<uint256> nfts;
            nfts.reserve(96);

            // We want to create fully packed NFT pages.  This is a little
            // tricky since the system currently in place is inclined to
            // assign consecutive tokens to only 16 entries per page.
            //
            // By manipulating the internal form of the taxon we can force
            // creation of NFT pages that are completely full.  This lambda
            // tells us the taxon value we should pass in in order for the
            // internal representation to match the passed in value.
            auto internalTaxon = [&env](Account const& acct, std::uint32_t taxon) -> std::uint32_t {
                std::uint32_t tokenSeq = env.le(acct)->at(~sfMintedNFTokens).value_or(0);

                // We must add FirstNFTokenSequence.
                tokenSeq += env.le(acct)->at(~sfFirstNFTokenSequence).value_or(env.seq(acct));

                return toUInt32(nft::cipheredTaxon(tokenSeq, nft::toTaxon(taxon)));
            };

            for (std::uint32_t i = 0; i < 96; ++i)
            {
                // In order to fill the pages we use the taxon to break them
                // into groups of 16 entries.  By having the internal
                // representation of the taxon go...
                //   0, 3, 2, 5, 4, 7...
                // in sets of 16 NFTs we can get each page to be fully
                // populated.
                std::uint32_t const intTaxon = (i / 16) + (i & 0b10000 ? 2 : 0);
                uint32_t const extTaxon = internalTaxon(alice, intTaxon);
                nfts.push_back(token::getNextID(env, alice, extTaxon));
                env(token::mint(alice, extTaxon));
                env.close();
            }

            // Sort the NFTs so they are listed in storage order, not
            // creation order.
            std::ranges::sort(nfts);

            // Verify that the ledger does indeed contain exactly three pages
            // of NFTs with 32 entries in each page.
            Json::Value jvParams;
            jvParams[jss::ledger_index] = "current";
            jvParams[jss::binary] = false;
            {
                Json::Value jrr = env.rpc("json", "ledger_data", to_string(jvParams));

                Json::Value& state = jrr[jss::result][jss::state];

                int pageCount = 0;
                for (Json::UInt i = 0; i < state.size(); ++i)
                {
                    if (state[i].isMember(sfNFTokens.jsonName) &&
                        state[i][sfNFTokens.jsonName].isArray())
                    {
                        BEAST_EXPECT(state[i][sfNFTokens.jsonName].size() == 32);
                        ++pageCount;
                    }
                }
                // If this check fails then the internal NFT directory logic
                // has changed.
                BEAST_EXPECT(pageCount == 3);
            }
            return nfts;
        };
        {
            // Generate three packed pages.  Then burn the tokens in order from
            // first to last.  This exercises specific cases where coalescing
            // pages is not possible.
            std::vector<uint256> const nfts = genPackedTokens();
            BEAST_EXPECT(nftCount(env, alice) == 96);
            BEAST_EXPECT(ownerCount(env, alice) == 3);

            for (uint256 const& nft : nfts)
            {
                env(token::burn(alice, {nft}));
                env.close();
            }
            BEAST_EXPECT(nftCount(env, alice) == 0);
            BEAST_EXPECT(ownerCount(env, alice) == 0);
        }

        // A lambda verifies that the ledger no longer contains any NFT pages.
        auto checkNoTokenPages = [this, &env]() {
            Json::Value jvParams;
            jvParams[jss::ledger_index] = "current";
            jvParams[jss::binary] = false;
            {
                Json::Value jrr = env.rpc("json", "ledger_data", to_string(jvParams));

                Json::Value& state = jrr[jss::result][jss::state];

                for (Json::UInt i = 0; i < state.size(); ++i)
                {
                    BEAST_EXPECT(!state[i].isMember(sfNFTokens.jsonName));
                }
            }
        };
        checkNoTokenPages();
        {
            // Generate three packed pages.  Then burn the tokens in order from
            // last to first.  This exercises different specific cases where
            // coalescing pages is not possible.
            std::vector<uint256> nfts = genPackedTokens();
            BEAST_EXPECT(nftCount(env, alice) == 96);
            BEAST_EXPECT(ownerCount(env, alice) == 3);

            // Verify that that all three pages are present and remember the
            // indexes.
            auto lastNFTokenPage = env.le(keylet::nftpage_max(alice));
            if (!BEAST_EXPECT(lastNFTokenPage))
                return;

            uint256 const middleNFTokenPageIndex = lastNFTokenPage->at(sfPreviousPageMin);
            auto middleNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
            if (!BEAST_EXPECT(middleNFTokenPage))
                return;

            uint256 const firstNFTokenPageIndex = middleNFTokenPage->at(sfPreviousPageMin);
            auto firstNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
            if (!BEAST_EXPECT(firstNFTokenPage))
                return;

            // Burn almost all the tokens in the very last page.
            for (int i = 0; i < 31; ++i)
            {
                env(token::burn(alice, {nfts.back()}));
                nfts.pop_back();
                env.close();
            }

            // Verify that the last page is still present and contains just one
            // NFT.
            lastNFTokenPage = env.le(keylet::nftpage_max(alice));
            if (!BEAST_EXPECT(lastNFTokenPage))
                return;

            BEAST_EXPECT(lastNFTokenPage->getFieldArray(sfNFTokens).size() == 1);
            BEAST_EXPECT(lastNFTokenPage->isFieldPresent(sfPreviousPageMin));
            BEAST_EXPECT(!lastNFTokenPage->isFieldPresent(sfNextPageMin));

            // Delete the last token from the last page.
            env(token::burn(alice, {nfts.back()}));
            nfts.pop_back();
            env.close();

            if (features[fixNFTokenPageLinks])
            {
                // Removing the last token from the last page deletes the
                // _previous_ page because we need to preserve that last
                // page an an anchor.  The contents of the next-to-last page
                // are moved into the last page.
                lastNFTokenPage = env.le(keylet::nftpage_max(alice));
                BEAST_EXPECT(lastNFTokenPage);
                BEAST_EXPECT(lastNFTokenPage->at(~sfPreviousPageMin) == firstNFTokenPageIndex);
                BEAST_EXPECT(!lastNFTokenPage->isFieldPresent(sfNextPageMin));
                BEAST_EXPECT(lastNFTokenPage->getFieldArray(sfNFTokens).size() == 32);

                // The "middle" page should be gone.
                middleNFTokenPage =
                    env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
                BEAST_EXPECT(!middleNFTokenPage);

                // The "first" page should still be present and linked to
                // the last page.
                firstNFTokenPage =
                    env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
                BEAST_EXPECT(firstNFTokenPage);
                BEAST_EXPECT(!firstNFTokenPage->isFieldPresent(sfPreviousPageMin));
                BEAST_EXPECT(firstNFTokenPage->at(~sfNextPageMin) == lastNFTokenPage->key());
                BEAST_EXPECT(lastNFTokenPage->getFieldArray(sfNFTokens).size() == 32);
            }
            else
            {
                // Removing the last token from the last page deletes the last
                // page.  This is a bug.  The contents of the next-to-last page
                // should have been moved into the last page.
                lastNFTokenPage = env.le(keylet::nftpage_max(alice));
                BEAST_EXPECT(!lastNFTokenPage);

                // The "middle" page is still present, but has lost the
                // NextPageMin field.
                middleNFTokenPage =
                    env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
                if (!BEAST_EXPECT(middleNFTokenPage))
                    return;
                BEAST_EXPECT(middleNFTokenPage->isFieldPresent(sfPreviousPageMin));
                BEAST_EXPECT(!middleNFTokenPage->isFieldPresent(sfNextPageMin));
            }

            // Delete the rest of the NFTokens.
            while (!nfts.empty())
            {
                env(token::burn(alice, {nfts.back()}));
                nfts.pop_back();
                env.close();
            }
            BEAST_EXPECT(nftCount(env, alice) == 0);
            BEAST_EXPECT(ownerCount(env, alice) == 0);
        }
        checkNoTokenPages();
        {
            // Generate three packed pages.  Then burn all tokens in the middle
            // page.  This exercises the case where a page is removed between
            // two fully populated pages.
            std::vector<uint256> nfts = genPackedTokens();
            BEAST_EXPECT(nftCount(env, alice) == 96);
            BEAST_EXPECT(ownerCount(env, alice) == 3);

            // Verify that that all three pages are present and remember the
            // indexes.
            auto lastNFTokenPage = env.le(keylet::nftpage_max(alice));
            if (!BEAST_EXPECT(lastNFTokenPage))
                return;

            uint256 const middleNFTokenPageIndex = lastNFTokenPage->at(sfPreviousPageMin);
            auto middleNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
            if (!BEAST_EXPECT(middleNFTokenPage))
                return;

            uint256 const firstNFTokenPageIndex = middleNFTokenPage->at(sfPreviousPageMin);
            auto firstNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
            if (!BEAST_EXPECT(firstNFTokenPage))
                return;

            for (std::size_t i = 32; i < 64; ++i)
            {
                env(token::burn(alice, nfts[i]));
                env.close();
            }
            nfts.erase(nfts.begin() + 32, nfts.begin() + 64);
            BEAST_EXPECT(nftCount(env, alice) == 64);
            BEAST_EXPECT(ownerCount(env, alice) == 2);

            // Verify that middle page is gone and the links in the two
            // remaining pages are correct.
            middleNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
            BEAST_EXPECT(!middleNFTokenPage);

            lastNFTokenPage = env.le(keylet::nftpage_max(alice));
            BEAST_EXPECT(!lastNFTokenPage->isFieldPresent(sfNextPageMin));
            BEAST_EXPECT(lastNFTokenPage->getFieldH256(sfPreviousPageMin) == firstNFTokenPageIndex);

            firstNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
            BEAST_EXPECT(
                firstNFTokenPage->getFieldH256(sfNextPageMin) == keylet::nftpage_max(alice).key);
            BEAST_EXPECT(!firstNFTokenPage->isFieldPresent(sfPreviousPageMin));

            // Burn the remaining nfts.
            for (uint256 const& nft : nfts)
            {
                env(token::burn(alice, {nft}));
                env.close();
            }
            BEAST_EXPECT(nftCount(env, alice) == 0);
            BEAST_EXPECT(ownerCount(env, alice) == 0);
        }
        checkNoTokenPages();
        {
            // Generate three packed pages.  Then burn all the tokens in the
            // first page followed by all the tokens in the last page.  This
            // exercises a specific case where coalescing pages is not possible.
            std::vector<uint256> nfts = genPackedTokens();
            BEAST_EXPECT(nftCount(env, alice) == 96);
            BEAST_EXPECT(ownerCount(env, alice) == 3);

            // Verify that that all three pages are present and remember the
            // indexes.
            auto lastNFTokenPage = env.le(keylet::nftpage_max(alice));
            if (!BEAST_EXPECT(lastNFTokenPage))
                return;

            uint256 const middleNFTokenPageIndex = lastNFTokenPage->at(sfPreviousPageMin);
            auto middleNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
            if (!BEAST_EXPECT(middleNFTokenPage))
                return;

            uint256 const firstNFTokenPageIndex = middleNFTokenPage->at(sfPreviousPageMin);
            auto firstNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
            if (!BEAST_EXPECT(firstNFTokenPage))
                return;

            // Burn all the tokens in the first page.
            std::ranges::reverse(nfts);
            for (int i = 0; i < 32; ++i)
            {
                env(token::burn(alice, {nfts.back()}));
                nfts.pop_back();
                env.close();
            }

            // Verify the first page is gone.
            firstNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
            BEAST_EXPECT(!firstNFTokenPage);

            // Check the links in the other two pages.
            middleNFTokenPage =
                env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
            if (!BEAST_EXPECT(middleNFTokenPage))
                return;
            BEAST_EXPECT(!middleNFTokenPage->isFieldPresent(sfPreviousPageMin));
            BEAST_EXPECT(middleNFTokenPage->isFieldPresent(sfNextPageMin));

            lastNFTokenPage = env.le(keylet::nftpage_max(alice));
            if (!BEAST_EXPECT(lastNFTokenPage))
                return;
            BEAST_EXPECT(lastNFTokenPage->isFieldPresent(sfPreviousPageMin));
            BEAST_EXPECT(!lastNFTokenPage->isFieldPresent(sfNextPageMin));

            // Burn all the tokens in the last page.
            std::ranges::reverse(nfts);
            for (int i = 0; i < 32; ++i)
            {
                env(token::burn(alice, {nfts.back()}));
                nfts.pop_back();
                env.close();
            }

            if (features[fixNFTokenPageLinks])
            {
                // Removing the last token from the last page deletes the
                // _previous_ page because we need to preserve that last
                // page an an anchor.  The contents of the next-to-last page
                // are moved into the last page.
                lastNFTokenPage = env.le(keylet::nftpage_max(alice));
                BEAST_EXPECT(lastNFTokenPage);
                BEAST_EXPECT(!lastNFTokenPage->isFieldPresent(sfPreviousPageMin));
                BEAST_EXPECT(!lastNFTokenPage->isFieldPresent(sfNextPageMin));
                BEAST_EXPECT(lastNFTokenPage->getFieldArray(sfNFTokens).size() == 32);

                // The "middle" page should be gone.
                middleNFTokenPage =
                    env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
                BEAST_EXPECT(!middleNFTokenPage);

                // The "first" page should still be gone.
                firstNFTokenPage =
                    env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
                BEAST_EXPECT(!firstNFTokenPage);
            }
            else
            {
                // Removing the last token from the last page deletes the last
                // page.  This is a bug.  The contents of the next-to-last page
                // should have been moved into the last page.
                lastNFTokenPage = env.le(keylet::nftpage_max(alice));
                BEAST_EXPECT(!lastNFTokenPage);

                // The "middle" page is still present, but has lost the
                // NextPageMin field.
                middleNFTokenPage =
                    env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
                if (!BEAST_EXPECT(middleNFTokenPage))
                    return;
                BEAST_EXPECT(!middleNFTokenPage->isFieldPresent(sfPreviousPageMin));
                BEAST_EXPECT(!middleNFTokenPage->isFieldPresent(sfNextPageMin));
            }

            // Delete the rest of the NFTokens.
            while (!nfts.empty())
            {
                env(token::burn(alice, {nfts.back()}));
                nfts.pop_back();
                env.close();
            }
            BEAST_EXPECT(nftCount(env, alice) == 0);
            BEAST_EXPECT(ownerCount(env, alice) == 0);
        }
        checkNoTokenPages();

        if (features[fixNFTokenPageLinks])
        {
            // Exercise the invariant that the final NFTokenPage of a directory
            // may not be removed if there are NFTokens in other pages of the
            // directory.
            //
            // We're going to fire an Invariant failure that is difficult to
            // cause.  We do it here because the tools are here.
            //
            // See Invariants_test.cpp for examples of other invariant tests
            // that this one is modeled after.

            // Generate three closely packed NFTokenPages.
            std::vector<uint256> nfts = genPackedTokens();
            BEAST_EXPECT(nftCount(env, alice) == 96);
            BEAST_EXPECT(ownerCount(env, alice) == 3);

            // Burn almost all the tokens in the very last page.
            for (int i = 0; i < 31; ++i)
            {
                env(token::burn(alice, {nfts.back()}));
                nfts.pop_back();
                env.close();
            }
            {
                // Create an ApplyContext we can use to run the invariant
                // checks.  These variables must outlive the ApplyContext.
                OpenView ov{*env.current()};
                STTx const tx{ttACCOUNT_SET, [](STObject&) {}};
                test::StreamSink sink{beast::severities::kWarning};
                beast::Journal const jlog{sink};
                ApplyContext ac{
                    env.app(), ov, tx, tesSUCCESS, env.current()->fees().base, tapNONE, jlog};

                // Verify that the last page is present and contains one NFT.
                auto lastNFTokenPage = ac.view().peek(keylet::nftpage_max(alice));
                if (!BEAST_EXPECT(lastNFTokenPage))
                    return;
                BEAST_EXPECT(lastNFTokenPage->getFieldArray(sfNFTokens).size() == 1);

                // Erase that last page.
                ac.view().erase(lastNFTokenPage);

                // Exercise the invariant.
                TER terActual = tesSUCCESS;
                for (TER const& terExpect : {TER(tecINVARIANT_FAILED), TER(tefINVARIANT_FAILED)})
                {
                    terActual = ac.checkInvariants(terActual, XRPAmount{});
                    BEAST_EXPECT(terExpect == terActual);
                    BEAST_EXPECT(sink.messages().str().starts_with("Invariant failed:"));
                    // uncomment to log the invariant failure message
                    // log << "   --> " << sink.messages().str() << std::endl;
                    BEAST_EXPECT(
                        sink.messages().str().find(
                            "Last NFT page deleted with non-empty directory") != std::string::npos);
                }
            }
            {
                // Create an ApplyContext we can use to run the invariant
                // checks.  These variables must outlive the ApplyContext.
                OpenView ov{*env.current()};
                STTx const tx{ttACCOUNT_SET, [](STObject&) {}};
                test::StreamSink sink{beast::severities::kWarning};
                beast::Journal const jlog{sink};
                ApplyContext ac{
                    env.app(), ov, tx, tesSUCCESS, env.current()->fees().base, tapNONE, jlog};

                // Verify that the middle  page is present.
                auto lastNFTokenPage = ac.view().peek(keylet::nftpage_max(alice));
                auto middleNFTokenPage = ac.view().peek(
                    keylet::nftpage(
                        keylet::nftpage_min(alice),
                        lastNFTokenPage->getFieldH256(sfPreviousPageMin)));
                BEAST_EXPECT(middleNFTokenPage);

                // Remove the NextMinPage link from the middle page to fire
                // the invariant.
                middleNFTokenPage->makeFieldAbsent(sfNextPageMin);
                ac.view().update(middleNFTokenPage);

                // Exercise the invariant.
                TER terActual = tesSUCCESS;
                for (TER const& terExpect : {TER(tecINVARIANT_FAILED), TER(tefINVARIANT_FAILED)})
                {
                    terActual = ac.checkInvariants(terActual, XRPAmount{});
                    BEAST_EXPECT(terExpect == terActual);
                    BEAST_EXPECT(sink.messages().str().starts_with("Invariant failed:"));
                    // uncomment to log the invariant failure message
                    // log << "   --> " << sink.messages().str() << std::endl;
                    BEAST_EXPECT(
                        sink.messages().str().find("Lost NextMinPage link") != std::string::npos);
                }
            }
        }
    }

    void
    testBurnTooManyOffers(FeatureBitset features)
    {
        // Look at the case where too many offers prevents burning a token.
        testcase("Burn too many offers");

        using namespace test::jtx;

        // Test that up to 499 buy/sell offers will be removed when NFT is
        // burned. This is to test that we can successfully remove all offers
        // if the number of offers is less than 500.
        {
            Env env{*this, features};

            Account const alice("alice");
            Account const becky("becky");
            env.fund(XRP(100000), alice, becky);
            env.close();

            // alice creates 498 sell offers and becky creates 1 buy offers.
            // When the token is burned, 498 sell offers and 1 buy offer are
            // removed. In total, 499 offers are removed
            std::vector<uint256> offerIndexes;
            auto const nftokenID =
                createNftAndOffers(env, alice, offerIndexes, maxDeletableTokenOfferEntries - 2);

            // Verify all sell offers are present in the ledger.
            for (uint256 const& offerIndex : offerIndexes)
            {
                BEAST_EXPECT(env.le(keylet::nftoffer(offerIndex)));
            }

            // Becky creates a buy offer
            uint256 const beckyOfferIndex = keylet::nftoffer(becky, env.seq(becky)).key;
            env(token::createOffer(becky, nftokenID, drops(1)), token::owner(alice));
            env.close();

            // Burn the token
            env(token::burn(alice, nftokenID));
            env.close();

            // Burning the token should remove all 498 sell offers
            // that alice created
            for (uint256 const& offerIndex : offerIndexes)
            {
                BEAST_EXPECT(!env.le(keylet::nftoffer(offerIndex)));
            }

            // Burning the token should also remove the one buy offer
            // that becky created
            BEAST_EXPECT(!env.le(keylet::nftoffer(beckyOfferIndex)));

            // alice and becky should have ownerCounts of zero
            BEAST_EXPECT(ownerCount(env, alice) == 0);
            BEAST_EXPECT(ownerCount(env, becky) == 0);
        }

        // Test that up to 500 buy offers are removed when NFT is burned.
        {
            Env env{*this, features};

            Account const alice("alice");
            Account const becky("becky");
            env.fund(XRP(100000), alice, becky);
            env.close();

            // alice creates 501 sell offers for the token
            // After we burn the token, 500 of the sell offers should be
            // removed, and one is left over
            std::vector<uint256> offerIndexes;
            auto const nftokenID =
                createNftAndOffers(env, alice, offerIndexes, maxDeletableTokenOfferEntries + 1);

            // Verify all sell offers are present in the ledger.
            for (uint256 const& offerIndex : offerIndexes)
            {
                BEAST_EXPECT(env.le(keylet::nftoffer(offerIndex)));
            }

            // Burn the token
            env(token::burn(alice, nftokenID));
            env.close();

            uint32_t offerDeletedCount = 0;
            // Count the number of sell offers that have been deleted
            for (uint256 const& offerIndex : offerIndexes)
            {
                if (!env.le(keylet::nftoffer(offerIndex)))
                    offerDeletedCount++;
            }

            BEAST_EXPECT(offerIndexes.size() == maxTokenOfferCancelCount + 1);

            // 500 sell offers should be removed
            BEAST_EXPECT(offerDeletedCount == maxTokenOfferCancelCount);

            // alice should have ownerCounts of one for the orphaned sell offer
            BEAST_EXPECT(ownerCount(env, alice) == 1);
        }

        // Test that up to 500 buy/sell offers are removed when NFT is burned.
        {
            Env env{*this, features};

            Account const alice("alice");
            Account const becky("becky");
            env.fund(XRP(100000), alice, becky);
            env.close();

            // alice creates 499 sell offers and becky creates 2 buy offers.
            // When the token is burned, 499 sell offers and 1 buy offer
            // are removed.
            // In total, 500 offers are removed
            std::vector<uint256> offerIndexes;
            auto const nftokenID =
                createNftAndOffers(env, alice, offerIndexes, maxDeletableTokenOfferEntries - 1);

            // Verify all sell offers are present in the ledger.
            for (uint256 const& offerIndex : offerIndexes)
            {
                BEAST_EXPECT(env.le(keylet::nftoffer(offerIndex)));
            }

            // becky creates 2 buy offers
            env(token::createOffer(becky, nftokenID, drops(1)), token::owner(alice));
            env.close();
            env(token::createOffer(becky, nftokenID, drops(1)), token::owner(alice));
            env.close();

            // Burn the token
            env(token::burn(alice, nftokenID));
            env.close();

            // Burning the token should remove all 499 sell offers from the
            // ledger.
            for (uint256 const& offerIndex : offerIndexes)
            {
                BEAST_EXPECT(!env.le(keylet::nftoffer(offerIndex)));
            }

            // alice should have ownerCount of zero because all her
            // sell offers have been deleted
            BEAST_EXPECT(ownerCount(env, alice) == 0);

            // becky has ownerCount of one due to an orphaned buy offer
            BEAST_EXPECT(ownerCount(env, becky) == 1);
        }
    }

    void
    exerciseBrokenLinks(FeatureBitset features)
    {
        // Amendment fixNFTokenPageLinks prevents the breakage we want
        // to observe.
        if (features[fixNFTokenPageLinks])
            return;

        // a couple of directory merging scenarios that can only be tested by
        // inserting and deleting in an ordered fashion.  We do that testing
        // now.
        testcase("Exercise broken links");

        using namespace test::jtx;

        Account const alice{"alice"};
        Account const minter{"minter"};

        Env env{*this, features};
        env.fund(XRP(1000), alice, minter);

        // A lambda that generates 96 nfts packed into three pages of 32 each.
        // Returns a sorted vector of the NFTokenIDs packed into the pages.
        auto genPackedTokens = [this, &env, &alice, &minter]() {
            std::vector<uint256> nfts;
            nfts.reserve(96);

            // We want to create fully packed NFT pages.  This is a little
            // tricky since the system currently in place is inclined to
            // assign consecutive tokens to only 16 entries per page.
            //
            // By manipulating the internal form of the taxon we can force
            // creation of NFT pages that are completely full.  This lambda
            // tells us the taxon value we should pass in in order for the
            // internal representation to match the passed in value.
            auto internalTaxon = [&env](Account const& acct, std::uint32_t taxon) -> std::uint32_t {
                std::uint32_t tokenSeq = env.le(acct)->at(~sfMintedNFTokens).value_or(0);

                // We must add FirstNFTokenSequence.
                tokenSeq += env.le(acct)->at(~sfFirstNFTokenSequence).value_or(env.seq(acct));

                return toUInt32(nft::cipheredTaxon(tokenSeq, nft::toTaxon(taxon)));
            };

            for (std::uint32_t i = 0; i < 96; ++i)
            {
                // In order to fill the pages we use the taxon to break them
                // into groups of 16 entries.  By having the internal
                // representation of the taxon go...
                //   0, 3, 2, 5, 4, 7...
                // in sets of 16 NFTs we can get each page to be fully
                // populated.
                std::uint32_t const intTaxon = (i / 16) + (i & 0b10000 ? 2 : 0);
                uint32_t const extTaxon = internalTaxon(minter, intTaxon);
                nfts.push_back(token::getNextID(env, minter, extTaxon, tfTransferable));
                env(token::mint(minter, extTaxon), txflags(tfTransferable));
                env.close();

                // Minter creates an offer for the NFToken.
                uint256 const minterOfferIndex = keylet::nftoffer(minter, env.seq(minter)).key;
                env(token::createOffer(minter, nfts.back(), XRP(0)), txflags(tfSellNFToken));
                env.close();

                // alice accepts the offer.
                env(token::acceptSellOffer(alice, minterOfferIndex));
                env.close();
            }

            // Sort the NFTs so they are listed in storage order, not
            // creation order.
            std::ranges::sort(nfts);

            // Verify that the ledger does indeed contain exactly three pages
            // of NFTs with 32 entries in each page.
            Json::Value jvParams;
            jvParams[jss::ledger_index] = "current";
            jvParams[jss::binary] = false;
            {
                Json::Value jrr = env.rpc("json", "ledger_data", to_string(jvParams));

                Json::Value& state = jrr[jss::result][jss::state];

                int pageCount = 0;
                for (Json::UInt i = 0; i < state.size(); ++i)
                {
                    if (state[i].isMember(sfNFTokens.jsonName) &&
                        state[i][sfNFTokens.jsonName].isArray())
                    {
                        BEAST_EXPECT(state[i][sfNFTokens.jsonName].size() == 32);
                        ++pageCount;
                    }
                }
                // If this check fails then the internal NFT directory logic
                // has changed.
                BEAST_EXPECT(pageCount == 3);
            }
            return nfts;
        };

        // Generate three packed pages.
        std::vector<uint256> nfts = genPackedTokens();
        BEAST_EXPECT(nftCount(env, alice) == 96);
        BEAST_EXPECT(ownerCount(env, alice) == 3);

        // Verify that that all three pages are present and remember the
        // indexes.
        auto lastNFTokenPage = env.le(keylet::nftpage_max(alice));
        if (!BEAST_EXPECT(lastNFTokenPage))
            return;

        uint256 const middleNFTokenPageIndex = lastNFTokenPage->at(sfPreviousPageMin);
        auto middleNFTokenPage =
            env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
        if (!BEAST_EXPECT(middleNFTokenPage))
            return;

        uint256 const firstNFTokenPageIndex = middleNFTokenPage->at(sfPreviousPageMin);
        auto firstNFTokenPage =
            env.le(keylet::nftpage(keylet::nftpage_min(alice), firstNFTokenPageIndex));
        if (!BEAST_EXPECT(firstNFTokenPage))
            return;

        // Sell all the tokens in the very last page back to minter.
        std::vector<uint256> last32NFTs;
        for (int i = 0; i < 32; ++i)
        {
            last32NFTs.push_back(nfts.back());
            nfts.pop_back();

            // alice creates an offer for the NFToken.
            uint256 const aliceOfferIndex = keylet::nftoffer(alice, env.seq(alice)).key;
            env(token::createOffer(alice, last32NFTs.back(), XRP(0)), txflags(tfSellNFToken));
            env.close();

            // minter accepts the offer.
            env(token::acceptSellOffer(minter, aliceOfferIndex));
            env.close();
        }

        // Removing the last token from the last page deletes alice's last
        // page.  This is a bug.  The contents of the next-to-last page
        // should have been moved into the last page.
        lastNFTokenPage = env.le(keylet::nftpage_max(alice));
        BEAST_EXPECT(!lastNFTokenPage);
        BEAST_EXPECT(ownerCount(env, alice) == 2);

        // The "middle" page is still present, but has lost the
        // NextPageMin field.
        middleNFTokenPage =
            env.le(keylet::nftpage(keylet::nftpage_min(alice), middleNFTokenPageIndex));
        if (!BEAST_EXPECT(middleNFTokenPage))
            return;
        BEAST_EXPECT(middleNFTokenPage->isFieldPresent(sfPreviousPageMin));
        BEAST_EXPECT(!middleNFTokenPage->isFieldPresent(sfNextPageMin));

        // Attempt to delete alice's account, but fail because she owns NFTs.
        auto const acctDelFee{drops(env.current()->fees().increment)};
        env(acctdelete(alice, minter), fee(acctDelFee), ter(tecHAS_OBLIGATIONS));
        env.close();

        // minter sells the last 32 NFTs back to alice.
        for (uint256 const nftID : last32NFTs)
        {
            // minter creates an offer for the NFToken.
            uint256 const minterOfferIndex = keylet::nftoffer(minter, env.seq(minter)).key;
            env(token::createOffer(minter, nftID, XRP(0)), txflags(tfSellNFToken));
            env.close();

            // alice accepts the offer.
            env(token::acceptSellOffer(alice, minterOfferIndex));
            env.close();
        }
        BEAST_EXPECT(ownerCount(env, alice) == 3);  // Three NFTokenPages.

        // alice has an NFToken directory with a broken link in the middle.
        {
            // Try the account_objects RPC command.  Alice's account only shows
            // two NFT pages even though she owns more.
            Json::Value acctObjs = [&env, &alice]() {
                Json::Value params;
                params[jss::account] = alice.human();
                return env.rpc("json", "account_objects", to_string(params));
            }();
            BEAST_EXPECT(!acctObjs.isMember(jss::marker));
            BEAST_EXPECT(acctObjs[jss::result][jss::account_objects].size() == 2);
        }
        {
            // Try the account_nfts RPC command.  It only returns 64 NFTs
            // although alice owns 96.
            Json::Value aliceNFTs = [&env, &alice]() {
                Json::Value params;
                params[jss::account] = alice.human();
                params[jss::type] = "state";
                return env.rpc("json", "account_nfts", to_string(params));
            }();
            BEAST_EXPECT(!aliceNFTs.isMember(jss::marker));
            BEAST_EXPECT(aliceNFTs[jss::result][jss::account_nfts].size() == 64);
        }
    }

protected:
    FeatureBitset const allFeatures{test::jtx::testable_amendments()};

    void
    testWithFeats(FeatureBitset features)
    {
        testBurnRandom(features);
        testBurnSequential(features);
        testBurnTooManyOffers(features);
        exerciseBrokenLinks(features);
    }

public:
    void
    run() override
    {
        testWithFeats(allFeatures - fixNFTokenPageLinks);
        testWithFeats(allFeatures);
    }
};

BEAST_DEFINE_TESTSUITE_PRIO(NFTokenBurn, app, xrpl, 3);

}  // namespace xrpl