netcore/System.Private.CoreLib/shared/System/UnitySerializationHolder.cs

   1 // Licensed to the .NET Foundation under one or more agreements.
   2 // The .NET Foundation licenses this file to you under the MIT license.
   3 // See the LICENSE file in the project root for more information.
   4
   5 using System.Runtime.Serialization;
   6
   7 namespace System
   8 {
   9     /// <summary>
  10     /// Holds Null class for which we guarantee that there is only ever one instance of.
  11     /// This only exists for compatibility with .NET Framework.
  12     /// </summary>
  13     [Serializable]
  14     // Needs to be public to support binary serialization compatibility
  15     public sealed class UnitySerializationHolder : ISerializable, IObjectReference
  16     {
  17         internal const int NullUnity = 0x0002;
  18         private readonly int _unityType;
  19         private readonly string? _data;
  20
  21         /// <summary>
  22         /// A helper method that returns the SerializationInfo that a class utilizing
  23         /// UnitySerializationHelper should return from a call to GetObjectData. It contains
  24         /// the unityType (defined above) and any optional data (used only for the reflection types).
  25         /// </summary>
  26         internal static void GetUnitySerializationInfo(SerializationInfo info, int unityType)
  27         {
  28             info.SetType(typeof(UnitySerializationHolder));
  29             info.AddValue("Data", null, typeof(string));
  30             info.AddValue("UnityType", unityType);
  31             info.AddValue("AssemblyName", string.Empty);
  32         }
  33
  34 #pragma warning disable CA2229 // public for compat
  35         public UnitySerializationHolder(SerializationInfo info, StreamingContext context)
  36 #pragma warning restore CA2229
  37         {
  38             if (info == null)
  39             {
  40                 throw new ArgumentNullException(nameof(info));
  41             }
  42
  43             // We are ignoring any other serialization input as we are only concerned about DBNull.
  44             // We also store data and use it for erorr logging.
  45             _unityType = info.GetInt32("UnityType");
  46             _data = info.GetString("Data");
  47         }
  48
  49         public void GetObjectData(SerializationInfo info, StreamingContext context) =>
  50             throw new NotSupportedException(SR.NotSupported_UnitySerHolder);
  51
  52         public object GetRealObject(StreamingContext context)
  53         {
  54             // We are only support deserializing DBNull and throwing for everything else.
  55             if (_unityType != NullUnity)
  56             {
  57                 throw new ArgumentException(SR.Format(SR.Argument_InvalidUnity, _data ?? "UnityType"));
  58             }
  59
  60             // We are always returning the same DBNull instance.
  61             return DBNull.Value;
  62         }
  63     }
  64 }