Tracing.cs

public static MidFunc Tracing(ITracer tracer)
{
    if (tracer == null) throw new ArgumentNullException("tracer");

    tracer = new SafeTracer(tracer);

    return next => async env =>
    {
    	if (!tracer.IsEnabled)
    	{
    	    await next(env);	
    	}
        else 
        {
            tracer.Trace("Request Start");
            
            var stopWatch = Stopwatch.StartNew();
            
            await next(env);
            
            stopWatch.Stop();
    
            if (tracer.Filters.All(filter => filter.Invoke(env)))
            {
                foreach (var item in env)
                {
                    tracer.Trace(item.Key, item.Value);
                }
            }
    
            tracer.Trace(string.Format("Request completed in {0} ms", stopWatch.ElapsedMilliseconds));
        }
    };
}