Refactor ApplyView::dirAdd to give access to low-level operations

- Takes a page from #5362, which may turn out to be useful!

src/xrpld/ledger/ApplyView.h

@@ -383,6 +383,45 @@ public:
     emptyDirDelete(Keylet const& directory);
 };
 
+namespace directory {
+/** Helper functions for managing low-level directory operations.
+    These are not part of the ApplyView interface.
+
+    Don't use them unless you really, really know what you're doing.
+    Instead use dirAdd, dirInsert, etc.
+ */
+
+std::uint64_t
+createRoot(
+    ApplyView& view,
+    Keylet const& directory,
+    uint256 const& key,
+    std::function<void(std::shared_ptr<SLE> const&)> const& describe);
+
+auto
+findPreviousPage(ApplyView& view, Keylet const& directory, SLE::ref start);
+
+std::uint64_t
+insertKey(
+    ApplyView& view,
+    SLE::ref node,
+    std::uint64_t page,
+    bool preserveOrder,
+    STVector256& indexes,
+    uint256 const& key);
+
+std::optional<std::uint64_t>
+insertPage(
+    ApplyView& view,
+    std::uint64_t page,
+    SLE::pointer node,
+    std::uint64_t nextPage,
+    SLE::ref next,
+    uint256 const& key,
+    Keylet const& directory,
+    std::function<void(std::shared_ptr<SLE> const&)> const& describe);
+
+}  // namespace directory
 }  // namespace ripple
 
 #endif

src/xrpld/ledger/detail/ApplyView.cpp

@@ -25,45 +25,53 @@
 
 namespace ripple {
 
-std::optional<std::uint64_t>
-ApplyView::dirAdd(
-    bool preserveOrder,
+namespace directory {
+
+std::uint64_t
+createRoot(
+    ApplyView& view,
     Keylet const& directory,
     uint256 const& key,
     std::function<void(std::shared_ptr<SLE> const&)> const& describe)
 {
-    auto root = peek(directory);
-
-    if (!root)
-    {
-        // No root, make it.
-        root = std::make_shared<SLE>(directory);
-        root->setFieldH256(sfRootIndex, directory.key);
-        describe(root);
+    auto newRoot = std::make_shared<SLE>(directory);
+    newRoot->setFieldH256(sfRootIndex, directory.key);
+    describe(newRoot);
 
     STVector256 v;
     v.push_back(key);
-        root->setFieldV256(sfIndexes, v);
+    newRoot->setFieldV256(sfIndexes, v);
 
-        insert(root);
+    view.insert(newRoot);
     return std::uint64_t{0};
 }
 
-    std::uint64_t page = root->getFieldU64(sfIndexPrevious);
+auto
+findPreviousPage(ApplyView& view, Keylet const& directory, SLE::ref start)
+{
+    std::uint64_t page = start->getFieldU64(sfIndexPrevious);
 
-    auto node = root;
+    auto node = start;
 
     if (page)
     {
-        node = peek(keylet::page(directory, page));
+        node = view.peek(keylet::page(directory, page));
         if (!node)
             LogicError("Directory chain: root back-pointer broken.");
     }
 
     auto indexes = node->getFieldV256(sfIndexes);
+    return std::make_tuple(page, node, indexes);
+}
 
-    // If there's space, we use it:
-    if (indexes.size() < dirNodeMaxEntries)
+std::uint64_t
+insertKey(
+    ApplyView& view,
+    SLE::ref node,
+    std::uint64_t page,
+    bool preserveOrder,
+    STVector256& indexes,
+    uint256 const& key)
 {
     if (preserveOrder)
     {
@@ -88,24 +96,37 @@ ApplyView::dirAdd(
     }
 
     node->setFieldV256(sfIndexes, indexes);
-        update(node);
+    view.update(node);
     return page;
 }
 
+std::optional<std::uint64_t>
+insertPage(
+    ApplyView& view,
+    std::uint64_t page,
+    SLE::pointer node,
+    std::uint64_t nextPage,
+    SLE::ref next,
+    uint256 const& key,
+    Keylet const& directory,
+    std::function<void(std::shared_ptr<SLE> const&)> const& describe)
+{
     // Check whether we're out of pages.
     if (++page >= dirNodeMaxPages)
+    {
         return std::nullopt;
+    }
 
     // We are about to create a new node; we'll link it to
     // the chain first:
     node->setFieldU64(sfIndexNext, page);
-    update(node);
+    view.update(node);
 
-    root->setFieldU64(sfIndexPrevious, page);
-    update(root);
+    next->setFieldU64(sfIndexPrevious, page);
+    view.update(next);
 
     // Insert the new key:
-    indexes.clear();
+    STVector256 indexes;
     indexes.push_back(key);
 
     node = std::make_shared<SLE>(keylet::page(directory, page));
@@ -116,12 +137,45 @@ ApplyView::dirAdd(
     // it's the default.
     if (page != 1)
         node->setFieldU64(sfIndexPrevious, page - 1);
+    if (nextPage)
+        node->setFieldU64(sfIndexNext, nextPage);
     describe(node);
-    insert(node);
+    view.insert(node);
 
     return page;
 }
 
+}  // namespace directory
+
+std::optional<std::uint64_t>
+ApplyView::dirAdd(
+    bool preserveOrder,
+    Keylet const& directory,
+    uint256 const& key,
+    std::function<void(std::shared_ptr<SLE> const&)> const& describe)
+{
+    auto root = peek(directory);
+
+    if (!root)
+    {
+        // No root, make it.
+        return directory::createRoot(*this, directory, key, describe);
+    }
+
+    auto [page, node, indexes] =
+        directory::findPreviousPage(*this, directory, root);
+
+    // If there's space, we use it:
+    if (indexes.size() < dirNodeMaxEntries)
+    {
+        return directory::insertKey(
+            *this, node, page, preserveOrder, indexes, key);
+    }
+
+    return directory::insertPage(
+        *this, page, node, 0, root, key, directory, describe);
+}
+
 bool
 ApplyView::emptyDirDelete(Keylet const& directory)
 {