Allow NFT to be burned when number of offers is greater than 500 (#4346)

* Allow offers to be removable
* Delete sell offers first

Signed-off-by: Shawn Xie <[email protected]>

src/ripple/app/tx/impl/NFTokenBurn.cpp

@@ -77,9 +77,14 @@ NFTokenBurn::preclaim(PreclaimContext const& ctx)
         }
     }
 
-    // If there are too many offers, then burning the token would produce too
-    // much metadata.  Disallow burning a token with too many offers.
-    return nft::notTooManyOffers(ctx.view, ctx.tx[sfNFTokenID]);
+    if (!ctx.view.rules().enabled(fixUnburnableNFToken))
+    {
+        // If there are too many offers, then burning the token would produce
+        // too much metadata.  Disallow burning a token with too many offers.
+        return nft::notTooManyOffers(ctx.view, ctx.tx[sfNFTokenID]);
+    }
+
+    return tesSUCCESS;
 }
 
 TER
@@ -104,9 +109,38 @@ NFTokenBurn::doApply()
         view().update(issuer);
     }
 
-    // Optimized deletion of all offers.
-    nft::removeAllTokenOffers(view(), keylet::nft_sells(ctx_.tx[sfNFTokenID]));
-    nft::removeAllTokenOffers(view(), keylet::nft_buys(ctx_.tx[sfNFTokenID]));
+    if (ctx_.view().rules().enabled(fixUnburnableNFToken))
+    {
+        // Delete up to 500 offers in total.
+        // Because the number of sell offers is likely to be less than
+        // the number of buy offers, we prioritize the deletion of sell
+        // offers in order to clean up sell offer directory
+        std::size_t const deletedSellOffers = nft::removeTokenOffersWithLimit(
+            view(),
+            keylet::nft_sells(ctx_.tx[sfNFTokenID]),
+            maxDeletableTokenOfferEntries);
+
+        if (maxDeletableTokenOfferEntries > deletedSellOffers)
+        {
+            nft::removeTokenOffersWithLimit(
+                view(),
+                keylet::nft_buys(ctx_.tx[sfNFTokenID]),
+                maxDeletableTokenOfferEntries - deletedSellOffers);
+        }
+    }
+    else
+    {
+        // Deletion of all offers.
+        nft::removeTokenOffersWithLimit(
+            view(),
+            keylet::nft_sells(ctx_.tx[sfNFTokenID]),
+            std::numeric_limits<int>::max());
+
+        nft::removeTokenOffersWithLimit(
+            view(),
+            keylet::nft_buys(ctx_.tx[sfNFTokenID]),
+            std::numeric_limits<int>::max());
+    }
 
     return tesSUCCESS;
 }

src/ripple/app/tx/impl/details/NFTokenUtils.cpp

@@ -520,34 +520,55 @@ findTokenAndPage(
     }
     return std::nullopt;
 }
-void
-removeAllTokenOffers(ApplyView& view, Keylet const& directory)
-{
-    view.dirDelete(directory, [&view](uint256 const& id) {
-        auto offer = view.peek(Keylet{ltNFTOKEN_OFFER, id});
 
-        if (!offer)
-            Throw<std::runtime_error>(
-                "Offer " + to_string(id) + " not found in ledger!");
+std::size_t
+removeTokenOffersWithLimit(
+    ApplyView& view,
+    Keylet const& directory,
+    std::size_t maxDeletableOffers)
+{
+    if (maxDeletableOffers == 0)
+        return 0;
 
-        auto const owner = (*offer)[sfOwner];
+    std::optional<std::uint64_t> pageIndex{0};
+    std::size_t deletedOffersCount = 0;
 
-        if (!view.dirRemove(
-                keylet::ownerDir(owner),
-                (*offer)[sfOwnerNode],
-                offer->key(),
-                false))
-            Throw<std::runtime_error>(
-                "Offer " + to_string(id) + " not found in owner directory!");
+    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!");
+            }
 
-        adjustOwnerCount(
-            view,
-            view.peek(keylet::account(owner)),
-            -1,
-            beast::Journal{beast::Journal::getNullSink()});
+            if (maxDeletableOffers == deletedOffersCount)
+                break;
+        }
+    } while (pageIndex.value_or(0) && maxDeletableOffers != deletedOffersCount);
 
-        view.erase(offer);
-    });
+    return deletedOffersCount;
 }
 
 TER

src/ripple/app/tx/impl/details/NFTokenUtils.h

@@ -53,9 +53,13 @@ constexpr std::uint16_t const flagOnlyXRP = 0x0002;
 constexpr std::uint16_t const flagCreateTrustLines = 0x0004;
 constexpr std::uint16_t const flagTransferable = 0x0008;
 
-/** Deletes all offers from the specified token offer directory. */
-void
-removeAllTokenOffers(ApplyView& view, Keylet const& directory);
+/** Delete up to a specified number of offers from the specified token offer
+ * directory. */
+std::size_t
+removeTokenOffersWithLimit(
+    ApplyView& view,
+    Keylet const& directory,
+    std::size_t maxDeletableOffers);
 
 /** Returns tesSUCCESS if NFToken has few enough offers that it can be burned */
 TER