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com.unity.ml-agents/Runtime/SideChannels/OutgoingMessage.cs

         /// <param name="data"></param>
         public void SetRawBytes(byte[] data)
         {
-            // Reset first.
+            // Reset first. Set the length to zero so that if there's more data than we're going to
+            // write, we don't have any of the original data.
-            // Then append the data
+            // Then append the data. Increase the capacity if needed (but don't shrink it).
             m_Stream.Capacity = (m_Stream.Capacity < data.Length) ? data.Length : m_Stream.Capacity;
             m_Stream.Write(data, 0, data.Length);
         }

com.unity.ml-agents/Tests/Editor/SideChannelTests.cs

         [Test]
         public void TestOutgoingMessageRawBytes()
         {
+            // Make sure that SetRawBytes resets the buffer correctly.
+            // Write 8 bytes (an int and float) then call SetRawBytes with 4 bytes
             var msg = new OutgoingMessage();
             msg.WriteInt32(42);
             msg.WriteFloat32(1.0f);