Fix reachable Debug.Assert in StreamPipeReader.AdvanceTo

src/libraries/System.IO.Pipelines/src/System/IO/Pipelines/StreamPipeReader.cs

@@ -106,9 +106,12 @@ private void AdvanceTo(BufferSegment? consumedSegment, int consumedIndex, Buffer
 
             long consumedBytes = BufferSegment.GetLength(returnStart, _readIndex, consumedSegment, consumedIndex);
 
-            _bufferedBytes -= consumedBytes;
+            if (consumedBytes < 0 || consumedBytes > _bufferedBytes)
+            {
+                ThrowHelper.ThrowInvalidOperationException_AdvanceToInvalidCursor();
+            }
 
-            Debug.Assert(_bufferedBytes >= 0);
+            _bufferedBytes -= consumedBytes;
 
             _examinedEverything = false;
 

src/libraries/System.IO.Pipelines/tests/StreamPipeReaderTests.cs

@@ -570,6 +570,22 @@ public async Task InvalidCursorThrows()
             reader.Complete();
         }
 
+        [Fact]
+        public async Task AdvanceWithPositionFromDifferentReaderThrows()
+        {
+            PipeReader reader1 = PipeReader.Create(new MemoryStream(new byte[10]));
+            PipeReader reader2 = PipeReader.Create(new MemoryStream(new byte[1000]));
+
+            ReadResult result1 = await reader1.ReadAsync();
+            ReadResult result2 = await reader2.ReadAsync();
+
+            SequencePosition posFrom2 = result2.Buffer.End;
+            Assert.Throws<InvalidOperationException>(() => reader1.AdvanceTo(posFrom2));
+
+            reader1.Complete();
+            reader2.Complete();
+        }
+
         [Fact]
         public void NullStreamThrows()
         {