messengerapi.Broker/code/MessengerBroker/Model/Http/Sync.cs

namespace MessengerBroker.Model.Http
{
    public class Sync
    {
        public class SyncRequest
        {
            public Guid BrokerId { get; set; }

            public DateTime SinceUtc { get; set; }
        }

        public class SyncResponse
        {
            public Message[] Messages { get; set; }

            public class Message
            {
                public Guid Id { get; set; }

                public DateTime CreatedUtc { get; set; }

                public Guid? From { get; set; }

                public Guid? To { get; set; }

                public bool IsDelivered { get; set; }

                public bool IsAcknowledged { get; set; }

                public string PayloadId { get; set; }

                public string PayloadType { get; set; }

                public string Payload { get; set; }

                public DateTime? PayloadTimestamp { get; set; }

                public int? PayloadLifespanInSeconds { get; set; }
            }
        }
    }
}