From bb0a62e0255ec24d19e68806e9b14abb684e695f Mon Sep 17 00:00:00 2001
From: Bart <11445373+bthomee@users.noreply.github.com>
Date: Sat, 1 Aug 2026 21:34:05 -0400
Subject: [PATCH] refactor: Add `SHAMapNodeID::isPrefixOf`

A node at depth d names the tree path spelled by the first d nibbles of its
key, so any leaf beneath it must agree on that prefix. Three call sites
open-coded this check against `depthMask`, and a fourth rebuilt a whole node
ID with `createID` just to compare it back.

No behavior change: each converted site tests the same condition it did
before.
---
 include/xrpl/shamap/SHAMapNodeID.h                | 14 ++++++++++++++
 src/libxrpl/shamap/SHAMapNodeID.cpp               | 11 ++++++++---
 src/libxrpl/shamap/SHAMapSync.cpp                 |  7 +++----
 src/xrpld/app/ledger/detail/LedgerNodeHelpers.cpp |  5 ++---
 4 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/include/xrpl/shamap/SHAMapNodeID.h b/include/xrpl/shamap/SHAMapNodeID.h
index 9fbfca90ceb..37337b73765 100644
--- a/include/xrpl/shamap/SHAMapNodeID.h
+++ b/include/xrpl/shamap/SHAMapNodeID.h
@@ -54,6 +54,20 @@ class SHAMapNodeID : public CountedObject<SHAMapNodeID>
     [[nodiscard]] SHAMapNodeID
     getChildNodeID(unsigned int branch) const;
 
+    /**
+     * Test whether this node ID lies on the path to the given leaf key
+     *
+     * A node at depth d identifies the tree path spelled by the first d
+     * nibbles of its key, so any leaf beneath it must agree on that prefix.
+     * A node ID that fails this test names a different subtree than the one
+     * it was built for.
+     *
+     * @param key  the key of a leaf below this node
+     * @return whether this node ID is a prefix of the leaf key
+     */
+    [[nodiscard]] bool
+    isPrefixOf(uint256 const& key) const;
+
     /**
      * Create a SHAMapNodeID of a node with the depth of the node and
      * the key of a leaf
diff --git a/src/libxrpl/shamap/SHAMapNodeID.cpp b/src/libxrpl/shamap/SHAMapNodeID.cpp
index ecde22a63d5..8fd7afe8fc1 100644
--- a/src/libxrpl/shamap/SHAMapNodeID.cpp
+++ b/src/libxrpl/shamap/SHAMapNodeID.cpp
@@ -46,8 +46,7 @@ SHAMapNodeID::SHAMapNodeID(unsigned int depth, uint256 const& hash) : id_(hash),
     XRPL_ASSERT(
         depth <= SHAMap::kLeafDepth, "xrpl::SHAMapNodeID::SHAMapNodeID : maximum depth input");
     XRPL_ASSERT(
-        id_ == (id_ & depthMask(depth)),
-        "xrpl::SHAMapNodeID::SHAMapNodeID : hash and depth inputs do match");
+        isPrefixOf(id_), "xrpl::SHAMapNodeID::SHAMapNodeID : hash and depth inputs do match");
 }
 
 std::string
@@ -79,7 +78,7 @@ SHAMapNodeID::getChildNodeID(unsigned int branch) const
     if (depth_ >= SHAMap::kLeafDepth)
         Throw<std::logic_error>("Request for child node ID of " + to_string(*this));
 
-    if (id_ != (id_ & depthMask(depth_)))
+    if (!isPrefixOf(id_))
         Throw<std::logic_error>("Incorrect mask for " + to_string(*this));
 
     SHAMapNodeID node{depth_ + 1, id_};
@@ -87,6 +86,12 @@ SHAMapNodeID::getChildNodeID(unsigned int branch) const
     return node;
 }
 
+bool
+SHAMapNodeID::isPrefixOf(uint256 const& key) const
+{
+    return (key & depthMask(depth_)) == id_;
+}
+
 [[nodiscard]] std::optional<SHAMapNodeID>
 deserializeSHAMapNodeID(void const* data, std::size_t size)
 {
diff --git a/src/libxrpl/shamap/SHAMapSync.cpp b/src/libxrpl/shamap/SHAMapSync.cpp
index e6948ec3ac2..a12e524a5f4 100644
--- a/src/libxrpl/shamap/SHAMapSync.cpp
+++ b/src/libxrpl/shamap/SHAMapSync.cpp
@@ -555,10 +555,9 @@ SHAMap::addKnownNode(
 {
     XRPL_ASSERT(!nodeID.isRoot(), "xrpl::SHAMap::addKnownNode : valid node");
     XRPL_ASSERT(treeNode, "xrpl::SHAMap::addKnownNode : non-null tree node");
-    XRPL_ASSERT(
-        !treeNode->isLeaf() ||
-            SHAMapNodeID::createID(nodeID.getDepth(), leafKey(*treeNode)).getNodeID() ==
-                nodeID.getNodeID(),
+    XRPL_ASSERT_IF(
+        treeNode->isLeaf(),
+        nodeID.isPrefixOf(leafKey(*treeNode)),
         "xrpl::SHAMap::addKnownNode : leaf position consistent with node ID");
 
     if (!isSynching())
diff --git a/src/xrpld/app/ledger/detail/LedgerNodeHelpers.cpp b/src/xrpld/app/ledger/detail/LedgerNodeHelpers.cpp
index abd669d4461..230c802022e 100644
--- a/src/xrpld/app/ledger/detail/LedgerNodeHelpers.cpp
+++ b/src/xrpld/app/ledger/detail/LedgerNodeHelpers.cpp
@@ -75,11 +75,10 @@ getSHAMapNodeID(protocol::TMLedgerNode const& ledgerNode, SHAMapTreeNode const&
     if (treeNode.isLeaf())
     {
         auto const key = leafKey(treeNode);
-        auto const expectedID = SHAMapNodeID::createID(nodeID->getDepth(), key);
         SOMETIMES(
-            nodeID->getNodeID() != expectedID.getNodeID(),
+            !nodeID->isPrefixOf(key),
             "xrpl::getSHAMapNodeID : legacy leaf ID inconsistent with key");
-        if (nodeID->getNodeID() != expectedID.getNodeID())
+        if (!nodeID->isPrefixOf(key))
             return std::nullopt;
     }