#134 - Add HeadersSent api.

src/Microsoft.AspNet.Http/HttpResponse.cs

@@ -5,7 +5,6 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Security.Claims;
-using System.Threading.Tasks;
 using Microsoft.AspNet.Http.Security;
 
 namespace Microsoft.AspNet.Http
@@ -24,6 +23,8 @@ namespace Microsoft.AspNet.Http
 
         public abstract IResponseCookies Cookies { get; }
 
+        public abstract bool HeadersSent { get; }
+
         public abstract void OnSendingHeaders(Action<object> callback, object state);
 
         public virtual void Redirect(string location)

src/Microsoft.AspNet.HttpFeature/IHttpResponseFeature.cs

@@ -15,6 +15,7 @@ namespace Microsoft.AspNet.HttpFeature
         string ReasonPhrase { get; set; }
         IDictionary<string, string[]> Headers { get; set; }
         Stream Body { get; set; }
+        bool HeadersSent { get; }
         void OnSendingHeaders(Action<object> callback, object state);
     }
 }

src/Microsoft.AspNet.Owin/OwinFeatureCollection.cs

@@ -35,11 +35,22 @@ namespace Microsoft.AspNet.Owin
         IOwinEnvironmentFeature
     {
         public IDictionary<string, object> Environment { get; set; }
+        private bool _headersSent;
 
         public OwinFeatureCollection(IDictionary<string, object> environment)
         {
             Environment = environment;
             SupportsWebSockets = true;
+
+            var register = Prop<Action<Action<object>, object>>(OwinConstants.CommonKeys.OnSendingHeaders);
+            if (register != null)
+            {
+                register(state =>
+                {
+                    var collection = (OwinFeatureCollection)state;
+                    collection._headersSent = true;
+                }, this);
+            }
         }
 
         T Prop<T>(string key)
@@ -129,6 +140,11 @@ namespace Microsoft.AspNet.Owin
             set { Prop(OwinConstants.ResponseBody, value); }
         }
 
+        bool IHttpResponseFeature.HeadersSent
+        {
+            get { return _headersSent; }
+        }
+
         void IHttpResponseFeature.OnSendingHeaders(Action<object> callback, object state)
         {
             var register = Prop<Action<Action<object>, object>>(OwinConstants.CommonKeys.OnSendingHeaders);

src/Microsoft.AspNet.PipelineCore/DefaultHttpResponse.cs

@@ -105,6 +105,11 @@ namespace Microsoft.AspNet.PipelineCore
             get { return ResponseCookiesFeature.Cookies; }
         }
 
+        public override bool HeadersSent
+        {
+            get { return HttpResponseFeature.HeadersSent; }
+        }
+
         public override void OnSendingHeaders(Action<object> callback, object state)
         {
             HttpResponseFeature.OnSendingHeaders(callback, state);

src/Microsoft.AspNet.PipelineCore/DefaultHttpResponseFeature.cs

@@ -25,6 +25,11 @@ namespace Microsoft.AspNet.PipelineCore
 
         public Stream Body { get; set; }
 
+        public bool HeadersSent
+        {
+            get { return false; }
+        }
+
         public void OnSendingHeaders(Action<object> callback, object state)
         {
             throw new NotSupportedException();