HandlerDemo.cs

using System.Threading.Tasks;
using SqsMessage = Amazon.SQS.Model.Message;

namespace JustSaying.Messaging.MessageHandling
{
    public interface IHandlerAsync<in T>
    {
        /// <summary>
        /// Handle a message of a given type
        /// </summary>
        /// <param name="message">Message to handle</param>
        /// <returns>Was handling successful?</returns>
        Task<bool> Handle(T message);
    }

    /// <summary>
    /// Async message handler
    /// </summary>
    /// <typeparam name="T">Type of message to be handled</typeparam>
    public interface IRawHandlerAsync<in T>
    {
        /// <summary>
        /// Handle a message of a given type and also access SQS metadata
        /// </summary>
        /// <param name="message">Message to handle</param>
        /// <param name="rawMessage">Raw SQS data</param>
        /// <returns>Was handling successful?</returns>
        Task<bool> Handle(T message, SqsMessage rawMessage);
    }

    public class HandlerShim<T> : IRawHandlerAsync<T>
    {
        private readonly IHandlerAsync<T> _inner;

        public HandlerShim(IHandlerAsync<T> inner)
        {
            _inner = inner;
        }

        public Task<bool> Handle(T message, SqsMessage rawMessage)
        {
            return _inner.Handle(message);
        }
    }
}