Q:

Get the time of request in ASP.NET core 2.1

I need to get the time of the request to version some database records and other records that will be created throughout the request.
I can't use DateTime now because I want the same time to be accessible throughout the request.
I can't seem to find anything in the HTTPContext class to help me.

A:

Using HttpContext.Features and your HTTP request pipeline middleware
public interface IHttpRequestTimeFeature
{
    DateTime RequestTime { get; }
}

public class HttpRequestTimeFeature : IHttpRequestTimeFeature
{
    public DateTime RequestTime { get; }    

    public HttpRequestTimeFeature()
    {
        RequestTime = DateTime.Now;
    }
}

// You don't need a separate class for this
public class RequestTimeMiddleware
{
    private readonly RequestDelegate _next;

    public RequestTimeMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public Task InvokeAsync(HttpContext context)
    {
        var httpRequestTimeFeature = new HttpRequestTimeFeature();
        context.Features.Set<IHttpRequestTimeFeature>(httpRequestTimeFeature);

        // Call the next delegate/middleware in the pipeline
        return this._next(context);
    }
}

You have to add this middleware in your Startup.Configure:
app.UseMiddleware<RequestTimeMiddleware>();
You can access request time like:
var httpRequestTimeFeature = HttpContext.Features.Get<IHttpRequestTimeFeature>();
if (httpRequestTimeFeature != null)
{
    var requestTime = httpRequestTimeFeature.RequestTime;
}

Using HttpContext.Items
HttpContext.Items["RequestTime"] = DateTime.Now;
You can also store it in your scoped service(services.AddScoped<YourService>()) if I'm not wrong, that will be valid through the entire request.
I'm not aware if there's such thing as request time built-in into ASP.NET Core though.
You can also set this in MVC filters but I think this is more valid in the lower level (HTTP request pipeline).

