cacheimplementation.cs

public class Cache : ICache
{
    private ConcurrentDictionary<int, Response> cachedResponses = new ConcurrentDictionary<int,Response>(); //Use Redis in Production

    public Response GetOrInvalidate(NancyContext ctx)
    {   
        Response resp;
    
        if(ctx.Request.Method == "GET")
        {
            if (!cache.TryGetValue(ctx.Request.Headers.IfNoneMatch.Value, out resp)
            {
                return null;
            }
            return resp;
        }
        
        this.Invalidate(ctx.Request.Headers.IfNoneMatch.Value);
        return null;
    }
    
        
    public Invalidate(NancyContext ctx)
    {
         cachedResponse.Remove(ctx.Request.Headers.IfNoneMatch.Value);
    }
    
    public Add(int Id, Response resp)
    {
       cache.Add(id,resp);   
    }
}

etag.cs

namespace Nancy.ETag
{
    using System;
    using Nancy;

    public class MainModule : NancyModule
    {
        public MainModule(ICache cache, ISomeRepoOrServiceOrOtherLayerYouLove someRepoOrServiceOrOtherLayerYouLove)
        {
            Get["/{int:id}"] = x => {
                return someRepoOrServiceOrOtherLayerYouLove.Get(x.id);
            };

            Put["/{int:id}"] = x => {
                var model = this.BindAndValidate<MyModel>();
                someRepoOrServiceOrOtherLayerYouLove.Update(x.id,model);
                return 204;
            };
            
            Before += ctx => {
                return cache.GetOrInvalidate(ctx);
            };
            
            After += ctx => {
                if (ctx.Request.Method == "GET")
                {
                    var id = GenerateUniqueId();
                    ctx.Response.Headers.ETag = id;
                    cache.Add(id, ctx.Response); //Get response body
                }
            };
        }
    }
}