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?

Christoph Fink · Accepted Answer · 2014-05-13T11:32:24.133

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.

edited May 13 '14 at 11:32

answered May 13 '14 at 11:26

Christoph Fink

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[This answer](http://stackoverflow.com/a/1154429/706456) says you can, probably OP just doesn't have a reference to the assembly where `User` type is defined. If he adds that (like you say in the last paragraph), code probably starts working fine. – oleksii May 13 '14 at 11:29
@oleksii: Not really: `This means that when the binary formatter **deserializes the object it knows its type**, builds the correct object and you can then cast that to an interface type that object implements.` and in this cast it does NOT know the type... – Christoph Fink May 13 '14 at 11:31
Yes. I don't have a reference to the assembly where User-type is defined. But my client is not allowed to know this assembly. Is there another way to send an interface-type as byte[] to a client? – Tomtom May 13 '14 at 11:32
Using the `XmlSerializer` is the only one I know. What is your problem with that approach? – Christoph Fink May 13 '14 at 11:36

Deserialize Interface-Type

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