EventStreamResponse.cs

public class EventStreamResponse : Response
{
    public EventStreamResponse(IResponseFormatter formatter, string id, dynamic body)
    {
        var serializer = formatter.Serializers.FirstOrDefault(s => s.CanSerialize("application/json"));
        ContentType = "text/event-stream";
        Contents = s =>
        {
            var idBytes = Encoding.UTF8.GetBytes(id + "\n");
            s.Write(idBytes, 0, idBytes.Length);

            serializer.Serialize("application/json", body, s);
            s.Flush();
        };
    }
}