From 80c5f881366e32d484b572b9948df064a6f32573 Mon Sep 17 00:00:00 2001
From: Jeremy Powell <jeremy@visionaid.com>
Date: Tue, 19 Nov 2024 15:48:54 +1300
Subject: [PATCH] Validate directory tree

---
 OpenMcdf/DirectoryTree.cs | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/OpenMcdf/DirectoryTree.cs b/OpenMcdf/DirectoryTree.cs
index cf2d605..2f8a08e 100644
--- a/OpenMcdf/DirectoryTree.cs
+++ b/OpenMcdf/DirectoryTree.cs
@@ -38,11 +38,27 @@ public bool TryGetDirectoryEntry(string name, out DirectoryEntry? entry)
             int compare = DirectoryEntryComparer.Compare(nameSpan, child.NameCharSpan);
             if (compare < 0)
             {
-                directories.TryGetDictionaryEntry(child.LeftSiblingId, out child);
+                directories.TryGetDictionaryEntry(child.LeftSiblingId, out DirectoryEntry? leftChild);
+                if (leftChild is not null)
+                {
+                    compare = DirectoryEntryComparer.Compare(leftChild.NameCharSpan, child.NameCharSpan);
+                    if (compare >= 0)
+                        throw new FormatException("Directory tree is not sorted.");
+                }
+
+                child = leftChild;
             }
             else if (compare > 0)
             {
-                directories.TryGetDictionaryEntry(child.RightSiblingId, out child);
+                directories.TryGetDictionaryEntry(child.RightSiblingId, out DirectoryEntry? rightChild);
+                if (rightChild is not null)
+                {
+                    compare = DirectoryEntryComparer.Compare(rightChild.NameCharSpan, child.NameCharSpan);
+                    if (compare <= 0)
+                        throw new FormatException("Directory tree is not sorted.");
+                }
+
+                child = rightChild;
             }
             else
             {