address code review feedback: count the arrays themselves

src/libraries/System.Formats.Nrbf/src/System/Formats/Nrbf/ArrayRecord.cs

@@ -50,7 +50,7 @@ private protected ArrayRecord(ArrayInfo arrayInfo)
 
     internal long ValuesToRead { get; private protected set; }
 
-    private protected ArrayInfo ArrayInfo { get; }
+    internal ArrayInfo ArrayInfo { get; }
 
     internal bool IsJagged
         => ArrayInfo.ArrayType == BinaryArrayType.Jagged

src/libraries/System.Formats.Nrbf/src/System/Formats/Nrbf/BinaryArrayRecord.cs

@@ -191,51 +191,42 @@ private static long GetJaggedArrayFlattenedLength(BinaryArrayRecord jaggedArrayR
 
             Debug.Assert(jaggedArrayRecord.IsJagged);
 
+            // In theory somebody could create a payload that would represent
+            // a very nested array with total elements count > long.MaxValue.
+            // That is why this method is using checked arithmetic.
+            result = checked(result + jaggedArrayRecord.Length); // count the arrays themselves
+
             foreach (object value in jaggedArrayRecord.Values)
             {
-                object item = value is MemberReferenceRecord referenceRecord
-                    ? referenceRecord.GetReferencedRecord()
-                    : value;
-
-                if (item is not SerializationRecord record)
+                if (value is not SerializationRecord record)
                 {
-                    result++;
                     continue;
                 }
 
+                if (record.RecordType == SerializationRecordType.MemberReference)
+                {
+                    record = ((MemberReferenceRecord)record).GetReferencedRecord();
+                }
+
                 switch (record.RecordType)
                 {
-                    case SerializationRecordType.BinaryArray:
                     case SerializationRecordType.ArraySinglePrimitive:
                     case SerializationRecordType.ArraySingleObject:
                     case SerializationRecordType.ArraySingleString:
+                    case SerializationRecordType.BinaryArray:
                         ArrayRecord nestedArrayRecord = (ArrayRecord)record;
                         if (nestedArrayRecord.IsJagged)
                         {
                             (jaggedArrayRecords ??= new()).Enqueue((BinaryArrayRecord)nestedArrayRecord);
                         }
                         else
                         {
-                            Debug.Assert(nestedArrayRecord is not BinaryArrayRecord, "Ensure lack of recursive call");
-                            checked
-                            {
-                                // In theory somebody could create a payload that would represent
-                                // a very nested array with total elements count > long.MaxValue.
-                                result += nestedArrayRecord.FlattenedLength;
-                            }
-                        }
-                        break;
-                    case SerializationRecordType.ObjectNull:
-                    case SerializationRecordType.ObjectNullMultiple256:
-                    case SerializationRecordType.ObjectNullMultiple:
-                        // All nulls need to be included, as it's another form of possible attack.
-                        checked
-                        {
-                            result += ((NullsRecord)item).NullCount;
+                            // Don't call nestedArrayRecord.FlattenedLength to avoid any potential recursion,
+                            // just call nestedArrayRecord.ArrayInfo.FlattenedLength that returns pre-computed value.
+                            result = checked(result + nestedArrayRecord.ArrayInfo.FlattenedLength);
                         }
                         break;
                     default:
-                        result++;
                         break;
                 }
             }

src/libraries/System.Formats.Nrbf/tests/JaggedArraysTests.cs

@@ -7,20 +7,25 @@ namespace System.Formats.Nrbf.Tests;
 
 public class JaggedArraysTests : ReadTests
 {
-    [Fact]
-    public void CanReadJaggedArraysOfPrimitiveTypes_2D()
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public void CanReadJaggedArraysOfPrimitiveTypes_2D(bool useReferences)
     {
         int[][] input = new int[7][];
+        int[] same = [1, 2, 3];
         for (int i = 0; i < input.Length; i++)
         {
-            input[i] = [i, i, i];
+            input[i] = useReferences
+                ? same // reuse the same object (represented as a single record that is referenced multiple times)
+                : [i, i, i]; // create new array
         }
 
         var arrayRecord = (ArrayRecord)NrbfDecoder.Decode(Serialize(input));
 
         Verify(input, arrayRecord);
         Assert.Equal(input, arrayRecord.GetArray(input.GetType()));
-        Assert.Equal(input.Length * 3, arrayRecord.FlattenedLength);
+        Assert.Equal(input.Length + input.Length * 3, arrayRecord.FlattenedLength);
     }
 
     [Theory]
@@ -42,13 +47,17 @@ public void FlattenedLengthIncludesNullArrays(int nullCount)
     public void ItIsPossibleToHaveBinaryArrayRecordsHaveAnElementTypeOfArrayWithoutBeingMarkedAsJagged()
     {
         int[][][] input = new int[3][][];
+        long totalElementsCount = 0;
         for (int i = 0; i < input.Length; i++)
         {
             input[i] = new int[4][];
+            totalElementsCount++; // count the arrays themselves
 
             for (int j = 0; j < input[i].Length; j++)
             {
                 input[i][j] = [i, j, 0, 1, 2];
+                totalElementsCount += input[i][j].Length;
+                totalElementsCount++; // count the arrays themselves
             }
         }
 
@@ -67,25 +76,31 @@ public void ItIsPossibleToHaveBinaryArrayRecordsHaveAnElementTypeOfArrayWithoutB
 
         Verify(input, arrayRecord);
         Assert.Equal(input, arrayRecord.GetArray(input.GetType()));
-        Assert.Equal(3 * 4 * 5, arrayRecord.FlattenedLength);
+        Assert.Equal(3 + 3 * 4 + 3 * 4 * 5, totalElementsCount);
+        Assert.Equal(totalElementsCount, arrayRecord.FlattenedLength);
     }
 
     [Fact]
     public void CanReadJaggedArraysOfPrimitiveTypes_3D()
     {
         int[][][] input = new int[7][][];
+        long totalElementsCount = 0;
         for (int i = 0; i < input.Length; i++)
         {
+            totalElementsCount++; // count the arrays themselves
             input[i] = new int[1][];
+            totalElementsCount++; // count the arrays themselves
             input[i][0] = [i, i, i];
+            totalElementsCount += input[i][0].Length;
         }
 
         var arrayRecord = (ArrayRecord)NrbfDecoder.Decode(Serialize(input));
 
         Verify(input, arrayRecord);
         Assert.Equal(input, arrayRecord.GetArray(input.GetType()));
         Assert.Equal(1, arrayRecord.Rank);
-        Assert.Equal(input.Length * 1 * 3, arrayRecord.FlattenedLength);
+        Assert.Equal(7 + 7 * 1 + 7 * 1 * 3, totalElementsCount);
+        Assert.Equal(totalElementsCount, arrayRecord.FlattenedLength);
     }
 
     [Fact]
@@ -110,7 +125,7 @@ public void CanReadJaggedArrayOfRectangularArrays()
         Verify(input, arrayRecord);
         Assert.Equal(input, arrayRecord.GetArray(input.GetType()));
         Assert.Equal(1, arrayRecord.Rank);
-        Assert.Equal(input.Length * 3 * 3, arrayRecord.FlattenedLength);
+        Assert.Equal(input.Length + input.Length * 3 * 3, arrayRecord.FlattenedLength);
     }
 
     [Fact]
@@ -126,7 +141,7 @@ public void CanReadJaggedArraysOfStrings()
 
         Verify(input, arrayRecord);
         Assert.Equal(input, arrayRecord.GetArray(input.GetType()));
-        Assert.Equal(input.Length * 3, arrayRecord.FlattenedLength);
+        Assert.Equal(input.Length + input.Length * 3, arrayRecord.FlattenedLength);
     }
 
     [Fact]
@@ -142,7 +157,7 @@ public void CanReadJaggedArraysOfObjects()
 
         Verify(input, arrayRecord);
         Assert.Equal(input, arrayRecord.GetArray(input.GetType()));
-        Assert.Equal(input.Length * 3, arrayRecord.FlattenedLength);
+        Assert.Equal(input.Length + input.Length * 3, arrayRecord.FlattenedLength);
     }
 
     [Serializable]
@@ -160,6 +175,7 @@ public void CanReadJaggedArraysOfComplexTypes()
         {
             input[i] = Enumerable.Range(0, i + 1).Select(j => new ComplexType { SomeField = j }).ToArray();
             totalElementsCount += input[i].Length;
+            totalElementsCount++; // count the arrays themselves
         }
 
         var arrayRecord = (ArrayRecord)NrbfDecoder.Decode(Serialize(input));