From f0ec068430b27ba97bc2659aa2e111e431e4312c Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Thu, 28 May 2026 15:30:08 -0400
Subject: [PATCH] galaxy: add cycle guard to HasMatchingDescendant

---
 .../Galaxy/GalaxyBrowseProjector.cs           | 14 +++-
 .../Galaxy/GalaxyBrowseProjectorTests.cs      | 71 +++++++++++++++++++
 2 files changed, 83 insertions(+), 2 deletions(-)

diff --git a/src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyBrowseProjector.cs b/src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyBrowseProjector.cs
index a9b7501..2d69391 100644
--- a/src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyBrowseProjector.cs
+++ b/src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyBrowseProjector.cs
@@ -163,10 +163,17 @@ public static class GalaxyBrowseProjector
             return false;
         }
 
+        // Defend against pathological cycles in Galaxy data (e.g. a corrupt A→B→A chain).
+        // BuildContainedPath uses the same visited-id pattern; mirror it so this walk
+        // terminates even when ChildrenByParent forms a cycle.
+        HashSet<int> visited = new() { parent.Object.GobjectId };
         Stack<GalaxyObjectView> stack = new();
         foreach (GalaxyObjectView child in children)
         {
-            stack.Push(child);
+            if (visited.Add(child.Object.GobjectId))
+            {
+                stack.Push(child);
+            }
         }
         while (stack.Count > 0)
         {
@@ -180,7 +187,10 @@ public static class GalaxyBrowseProjector
             {
                 foreach (GalaxyObjectView grandchild in grandchildren)
                 {
-                    stack.Push(grandchild);
+                    if (visited.Add(grandchild.Object.GobjectId))
+                    {
+                        stack.Push(grandchild);
+                    }
                 }
             }
         }
diff --git a/src/ZB.MOM.WW.MxGateway.Tests/Galaxy/GalaxyBrowseProjectorTests.cs b/src/ZB.MOM.WW.MxGateway.Tests/Galaxy/GalaxyBrowseProjectorTests.cs
index 98fee57..50a7d62 100644
--- a/src/ZB.MOM.WW.MxGateway.Tests/Galaxy/GalaxyBrowseProjectorTests.cs
+++ b/src/ZB.MOM.WW.MxGateway.Tests/Galaxy/GalaxyBrowseProjectorTests.cs
@@ -223,6 +223,77 @@ public sealed class GalaxyBrowseProjectorTests
         Assert.Equal("Plant.Line_A", result.Children[0].TagName);
     }
 
+    /// <summary>
+    ///     Verifies <see cref="GalaxyBrowseProjector"/> terminates when the Galaxy data
+    ///     contains a cyclic parent chain (A→B→C→A). Without the visited-id guard in
+    ///     <c>HasMatchingDescendant</c>, the depth-first walk would loop forever; the
+    ///     5-second xUnit timeout asserts termination.
+    /// </summary>
+    [Fact(Timeout = 5000)]
+    public async Task Project_CyclicDescendants_DoesNotInfiniteLoop()
+    {
+        await Task.Yield();
+        // Construct a 3-node cycle: A(10)→B(11)→C(12)→A. Each node's ParentGobjectId
+        // points to the next, so GalaxyHierarchyIndex.ChildrenByParent has
+        //   [12] = [A], [10] = [B], [11] = [C].
+        // None of them are historized, so HistorizedOnly=true forces the projector to
+        // call HasMatchingDescendant on every direct child, exercising the cycle walk.
+        GalaxyObject a = new()
+        {
+            GobjectId = 10,
+            ParentGobjectId = 12,
+            ContainedName = "A",
+            BrowseName = "A",
+            TagName = "A",
+        };
+        GalaxyObject b = new()
+        {
+            GobjectId = 11,
+            ParentGobjectId = 10,
+            ContainedName = "B",
+            BrowseName = "B",
+            TagName = "B",
+        };
+        GalaxyObject c = new()
+        {
+            GobjectId = 12,
+            ParentGobjectId = 11,
+            ContainedName = "C",
+            BrowseName = "C",
+            TagName = "C",
+        };
+
+        IReadOnlyList<GalaxyObject> objects = new[] { a, b, c };
+        GalaxyHierarchyCacheEntry entry = GalaxyHierarchyCacheEntry.Empty with
+        {
+            Status = GalaxyCacheStatus.Healthy,
+            Sequence = 1,
+            LastSuccessAt = DateTimeOffset.UtcNow,
+            Objects = objects,
+            Index = GalaxyHierarchyIndex.Build(objects),
+            DashboardSummary = DashboardGalaxySummary.Unknown with
+            {
+                Status = DashboardGalaxyStatus.Healthy,
+                ObjectCount = objects.Count,
+            },
+            ObjectCount = objects.Count,
+        };
+
+        // Browse children of A (id=10). Its direct child B fails HistorizedOnly, so the
+        // projector falls back to HasMatchingDescendant(B), which walks B→C→A→B…
+        // without the visited-id guard. With the guard, the walk terminates and returns
+        // an empty page (no historized descendants exist anywhere in the cycle).
+        GalaxyBrowseChildrenResult result = GalaxyBrowseProjector.ProjectChildren(
+            entry,
+            new BrowseChildrenRequest { ParentGobjectId = 10, HistorizedOnly = true },
+            browseSubtreeGlobs: null,
+            offset: 0,
+            pageSize: 10);
+
+        Assert.Empty(result.Children);
+        Assert.Equal(0, result.TotalChildCount);
+    }
+
     private static GalaxyHierarchyCacheEntry CreateEntry()
     {
         IReadOnlyList<GalaxyObject> objects = CreateObjects();