[Proposal] Lazy requestId and move TraceIdentifier to HttpAbstractions

src/Microsoft.AspNet.Hosting/Internal/HostingEngine.cs

@@ -96,7 +96,6 @@ public virtual IApplication Start()
                 {
                     var httpContext = contextFactory.CreateHttpContext(features);
                     httpContext.ApplicationServices = _applicationServices;
-                    var requestIdentifier = GetRequestIdentifier(httpContext);
                     contextAccessor.HttpContext = httpContext;
 #pragma warning disable 0618
                     if (telemetrySource.IsEnabled("Microsoft.AspNet.Hosting.BeginRequest"))
@@ -107,7 +106,7 @@ public virtual IApplication Start()
                     try
                     {
                         using (logger.IsEnabled(LogLevel.Critical)
-                            ? logger.BeginScope("Request Id: {RequestId}", requestIdentifier) 
+                            ? logger.BeginScope("Request Id: {RequestId}", httpContext.TraceIdentifier) 
                             : null)
                         {
                             await application(httpContext);
@@ -276,18 +275,6 @@ private void EnsureServer()
             }
         }
 
-        private string GetRequestIdentifier(HttpContext httpContext)
-        {
-            var requestIdentifierFeature = httpContext.Features.Get<IHttpRequestIdentifierFeature>();
-            if (requestIdentifierFeature == null)
-            {
-                requestIdentifierFeature = new FastHttpRequestIdentifierFeature();
-                httpContext.Features.Set(requestIdentifierFeature);
-            }
-
-            return requestIdentifierFeature.TraceIdentifier;
-        }
-
         private class Disposable : IDisposable
         {
             private Action _dispose;

src/Microsoft.AspNet.Hosting/project.json

@@ -6,8 +6,7 @@
         "url": "git://github.com/aspnet/hosting"
     },
     "compilationOptions": {
-        "warningsAsErrors": true,
-        "allowUnsafe": true
+        "warningsAsErrors": true
     },
     "dependencies": {
         "Microsoft.AspNet.FileProviders.Physical": "1.0.0-*",

test/Microsoft.AspNet.Hosting.Tests/HostingEngineTests.cs

@@ -305,7 +305,13 @@ public void HostingEngine_CreatesDefaultRequestIdentifierFeature_IfNotPresent()
 
             // Assert
             Assert.NotNull(httpContext);
-            Assert.IsType<FastHttpRequestIdentifierFeature>(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
+            Assert.Null(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
+
+            Assert.NotNull(httpContext.TraceIdentifier);
+            Assert.NotNull(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
+            Assert.IsType<HttpRequestIdentifierFeature>(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
+
+            Assert.Same(httpContext.TraceIdentifier, httpContext.Features.Get<IHttpRequestIdentifierFeature>().TraceIdentifier);
         }
 
         [Fact]