Sending binary message with metadata from C# client to XSockets server

Client.cs

//client memeber is of type IXSocketClient that is connected to controller "foo"

//Read a dummy file from disk
var bytes = File.ReadAllBytes(@"c:\temp\HelloWorld.txt");
//Create message with the custom helper "CreateBinaryMessage" and add the metadata of choice
var binaryMessage = client.CreateBinaryMessage(bytes, new FileInfo { FileName = "HelloWorld.txt" });
//Send the binary message
client.Send(binaryMessage);

ClientHelper.cs

public static class BinaryMessageExtentions
{
    public static BinaryArgs CreateBinaryMessage(this IXSocketClient client, IList<byte> buffer, object metadata, string @event = "binary")
    {
        //Transform metadata into JSON
        var jsonMeta = client.Serializer.SerializeToString(metadata);
            
        //Add metadata to a TextArgs object
        var json = client.Serializer.SerializeToString(new TextArgs(jsonMeta, @event));
                    
        //Set the metadata as header in the binary message
        var ms = new List<byte>();
        var payload = json;
        var header = BitConverter.GetBytes((Int64)payload.Length);
        ms.AddRange(header);
        ms.AddRange(Encoding.UTF8.GetBytes(payload));
        ms.AddRange(buffer);
        return new BinaryArgs(ms);
    }
}

Controller.cs

//Serverside controller where the binary message arrives...
public class Foo : XSocketController
{
    public override void OnMessage(IBinaryArgs binaryArgs)
    {
        //Convert the binaryArgs to a combinedMessage            
        var bm = binaryArgs.AsCombinedMessage();            
        //Get the metadata included from client
        var fileInfo = bm.Extract<FileInfo>();
        //Get the filecontent
        var file = Encoding.UTF8.GetString(bm.BinaryArgs.data.ToArray());

        //Add logic for saving, sending back etc...
    }
}

FileInfo.cs

//Stupid metadata class know both by server and client
public class FileInfo
{
    public string FileName { get; set; }
}