TracingMiddleware.cs for @jchannon

TracingMiddleware.cs

namespace TracingMiddleware
{
    using System;
    using System.Diagnostics;
    using System.IO;
    using System.Linq;
    using System.Text;
    using MidFunc = System.Func<
           System.Func<System.Collections.Generic.IDictionary<string, object>, System.Threading.Tasks.Task>,
           System.Func<System.Collections.Generic.IDictionary<string, object>, System.Threading.Tasks.Task>
           >;

    public static class TracingMiddleware
    {
        public static MidFunc Tracing(TracingMiddlewareOptions tracingMiddlewareOptions = null)
        {
            tracingMiddlewareOptions = tracingMiddlewareOptions ?? new TracingMiddlewareOptions();
            return
                next =>
                    async environment =>
                    {
                        using (var capturingStream = new MemoryStream())
                        {
                            var capturedStream = (Stream)environment["owin.ResponseBody"];
                            environment["owin.ResponseBody"] = capturingStream;
                            var stopWatch = new Stopwatch();
                            tracingMiddlewareOptions.Interpreter.Interpret("Request Start", "");

                            var requestItems =
                                environment.Where(x => x.Key.StartsWith("owin.request", StringComparison.OrdinalIgnoreCase));

                            foreach (var item in requestItems)
                            {
                                tracingMiddlewareOptions.Interpreter.Interpret(item.Key, item.Value);
                            }

                            stopWatch.Start();

                            await next(environment);

                            stopWatch.Stop();

                            capturingStream.Seek(0, SeekOrigin.Begin);
                            var bytes = capturingStream.ToArray();
                            await capturedStream.WriteAsync(bytes, 0, bytes.Length);

                            var responseItems =
                                environment.Where(x => !x.Key.StartsWith("owin.request", StringComparison.OrdinalIgnoreCase));

                            foreach (var item in responseItems)
                            {
                                tracingMiddlewareOptions.Interpreter.Interpret(item.Key, item.Value);
                            }
                            tracingMiddlewareOptions.Interpreter.Interpret("Response", Encoding.UTF8.GetString(bytes));

                            tracingMiddlewareOptions.Interpreter.Interpret("Request Finished", "");
                            tracingMiddlewareOptions.Interpreter.Interpret("Execution Time", stopWatch.ElapsedMilliseconds);
                        }
                    };
        }
    }
}