Deserialize Interface-Type

Question

I have a Client-Server-Application where I want to send an encrypted object from the server to the client.

The client is sending a request to the server like:

byte[] encryptedResponse = authenticationService.SendRequest(sessionId, requestData);

Then the client gets an encrypted response-byte-array. Then he calls

byte[] clearResponse = Cryptography.DecryptSymmetric(key, iv, encryptedResponse);

In clearResponse is now the clear binary-serialized object from the server.

Client and Server are sharing an Interface-Library which contains the IUser-Interface which looks like:

public interface IUser : ISerializable
{
   Guid UserId { get; }
   string Username { get; }
} 

The Server contains an implementation of this interface which looks like:

[Serializable]
    internal class User : IUser
    {
        public User(){}

        public User(SerializationInfo info, StreamingContext context)
        {
            Id = Guid.Parse(info.GetString(XmlNodes.UserId));
            Username = info.GetString(XmlNodes.Username);
        }

        public Guid Id { get; set; }

        public string Username { get; set; }

        public void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.AddValue(XmlNodes.UserId, Id.ToString());
            info.AddValue(XmlNodes.Username, Username);            
        }
    }

The server uses the following code to serialize the user for the client:

byte[] responseData;
IUser user = new User { Id = Guid.NewGuid(), Username = "Dummy" };
using(MemoryStream memoryStream = new MemoryStream())
{
  BinaryFormatter binaryFormatter = new BinaryFormatter();
  binaryFormatter.Serialize(memoryStream, user);
  responseData = memoryStream.ToArray();
}
// encrypt the responseData and send it to the client.

Now if I try to deserialize the user with:

using(MemoryStream memoryStream = new MemoryStream(clearResponse))
{
  BinaryFormatter binaryFormatter = new BinaryFormatter();
  IUser user = (IUser)binaryFormatter.Deserialize(memoryStream)
}

I get an exception.

An unhandled exception of type 'System.Runtime.Serialization.SerializationException' occurred in mscorlib.dll

Additional information: The Assembly "Users, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" could not be found.

How can I deserialize a type where I only know the interface?

Answer 1

Using BinaryFormatter you can't as the type is part of the data.

You could use XmlSerializer and send the resulting string as (possibly encrypted) byte[] to the cliend. Then the client needs just a "compatible type" to deserialize it.

If you want to stick with BinaryFormatter you could also move the User type to a shared library (if not already) and reference this by the server and client.