Move IHeaderDictionary to Features to reduce wrapping.

src/Microsoft.AspNet.Http.Features/IHeaderDictionary.cs

@@ -0,0 +1,21 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using Microsoft.Extensions.Primitives;
+
+namespace Microsoft.AspNet.Http
+{
+    /// <summary>
+    /// Represents request and response headers
+    /// </summary>
+    public interface IHeaderDictionary : IDictionary<string, StringValues>
+    {
+        /// <summary>
+        /// IHeaderDictionary has a different indexer contract than IDictionary, where it will return StringValues.Empty for missing entries.
+        /// </summary>
+        /// <param name="key"></param>
+        /// <returns>The stored value, or StringValues.Empty if the key is not present.</returns>
+        new StringValues this[string key] { get; set; }
+    }
+}

src/Microsoft.AspNet.Http.Features/IHttpRequestFeature.cs

@@ -1,9 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System.Collections.Generic;
 using System.IO;
-using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNet.Http.Features
 {
@@ -15,7 +13,7 @@ public interface IHttpRequestFeature
         string PathBase { get; set; }
         string Path { get; set; }
         string QueryString { get; set; }
-        IDictionary<string, StringValues> Headers { get; set; }
+        IHeaderDictionary Headers { get; set; }
         Stream Body { get; set; }
     }
 }

src/Microsoft.AspNet.Http.Features/IHttpResponseFeature.cs

@@ -2,18 +2,16 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
-using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNet.Http.Features
 {
     public interface IHttpResponseFeature
     {
         int StatusCode { get; set; }
         string ReasonPhrase { get; set; }
-        IDictionary<string, StringValues> Headers { get; set; }
+        IHeaderDictionary Headers { get; set; }
         Stream Body { get; set; }
         bool HasStarted { get; }
         void OnStarting(Func<object, Task> callback, object state);

src/Microsoft.AspNet.Http/DefaultHttpRequest.cs

@@ -123,7 +123,7 @@ public override string Protocol
 
         public override IHeaderDictionary Headers
         {
-            get { return new HeaderDictionary(HttpRequestFeature.Headers); }
+            get { return HttpRequestFeature.Headers; }
         }
 
         public override IReadableStringCollection Cookies

src/Microsoft.AspNet.Http/DefaultHttpResponse.cs

@@ -43,7 +43,7 @@ public override int StatusCode
 
         public override IHeaderDictionary Headers
         {
-            get { return new HeaderDictionary(HttpResponseFeature.Headers); }
+            get { return HttpResponseFeature.Headers; }
         }
 
         public override Stream Body

src/Microsoft.AspNet.Http/Features/HttpRequestFeature.cs

@@ -1,18 +1,16 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System;
-using System.Collections.Generic;
 using System.IO;
-using Microsoft.Extensions.Primitives;
+using Microsoft.AspNet.Http.Internal;
 
 namespace Microsoft.AspNet.Http.Features.Internal
 {
     public class HttpRequestFeature : IHttpRequestFeature
     {
         public HttpRequestFeature()
         {
-            Headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
+            Headers = new HeaderDictionary();
             Body = Stream.Null;
             Protocol = string.Empty;
             Scheme = string.Empty;
@@ -28,7 +26,7 @@ public HttpRequestFeature()
         public string PathBase { get; set; }
         public string Path { get; set; }
         public string QueryString { get; set; }
-        public IDictionary<string, StringValues> Headers { get; set; }
+        public IHeaderDictionary Headers { get; set; }
         public Stream Body { get; set; }
     }
 }

src/Microsoft.AspNet.Http/Features/HttpResponseFeature.cs

@@ -2,10 +2,9 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
-using Microsoft.Extensions.Primitives;
+using Microsoft.AspNet.Http.Internal;
 
 namespace Microsoft.AspNet.Http.Features.Internal
 {
@@ -14,15 +13,15 @@ public class HttpResponseFeature : IHttpResponseFeature
         public HttpResponseFeature()
         {
             StatusCode = 200;
-            Headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
+            Headers = new HeaderDictionary();
             Body = Stream.Null;
         }
 
         public int StatusCode { get; set; }
 
         public string ReasonPhrase { get; set; }
 
-        public IDictionary<string, StringValues> Headers { get; set; }
+        public IHeaderDictionary Headers { get; set; }
 
         public Stream Body { get; set; }
 

src/Microsoft.AspNet.Owin/DictionaryStringArrayWrapper.cs

@@ -4,18 +4,19 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
+using Microsoft.AspNet.Http;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNet.Owin
 {
     internal class DictionaryStringArrayWrapper : IDictionary<string, string[]>
     {
-        public DictionaryStringArrayWrapper(IDictionary<string, StringValues> inner)
+        public DictionaryStringArrayWrapper(IHeaderDictionary inner)
         {
             Inner = inner;
         }
 
-        public readonly IDictionary<string, StringValues> Inner;
+        public readonly IHeaderDictionary Inner;
 
         private KeyValuePair<string, StringValues> Convert(KeyValuePair<string, string[]> item) => new KeyValuePair<string, StringValues>(item.Key, item.Value);
 
@@ -27,7 +28,7 @@ public DictionaryStringArrayWrapper(IDictionary<string, StringValues> inner)
 
         string[] IDictionary<string, string[]>.this[string key]
         {
-            get { return Inner[key]; }
+            get { return ((IDictionary<string, StringValues>)Inner)[key]; }
             set { Inner[key] = value; }
         }
 

src/Microsoft.AspNet.Owin/DictionaryStringValuesWrapper.cs

@@ -4,11 +4,12 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
+using Microsoft.AspNet.Http;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNet.Owin
 {
-    internal class DictionaryStringValuesWrapper : IDictionary<string, StringValues>
+    internal class DictionaryStringValuesWrapper : IHeaderDictionary
     {
         public DictionaryStringValuesWrapper(IDictionary<string, string[]> inner)
         {
@@ -25,6 +26,16 @@ public DictionaryStringValuesWrapper(IDictionary<string, string[]> inner)
 
         private string[] Convert(StringValues item) => item;
 
+        StringValues IHeaderDictionary.this[string key]
+        {
+            get
+            {
+                string[] values;
+                return Inner.TryGetValue(key, out values) ? values : null;
+            }
+            set { Inner[key] = value; }
+        }
+
         StringValues IDictionary<string, StringValues>.this[string key]
         {
             get { return Inner[key]; }

src/Microsoft.AspNet.Owin/OwinEnvironment.cs

@@ -56,13 +56,13 @@ public OwinEnvironment(HttpContext context)
                 { OwinConstants.RequestPath, new FeatureMap<IHttpRequestFeature>(feature => feature.Path, () => string.Empty, (feature, value) => feature.Path = Convert.ToString(value)) },
                 { OwinConstants.RequestQueryString, new FeatureMap<IHttpRequestFeature>(feature => Utilities.RemoveQuestionMark(feature.QueryString), () => string.Empty,
                     (feature, value) => feature.QueryString = Utilities.AddQuestionMark(Convert.ToString(value))) },
-                { OwinConstants.RequestHeaders, new FeatureMap<IHttpRequestFeature>(feature => Utilities.MakeDictionaryStringArray(feature.Headers), (feature, value) => feature.Headers = Utilities.MakeDictionaryStringValues((IDictionary<string, string[]>)value)) },
+                { OwinConstants.RequestHeaders, new FeatureMap<IHttpRequestFeature>(feature => Utilities.MakeDictionaryStringArray(feature.Headers), (feature, value) => feature.Headers = Utilities.MakeHeaderDictionary((IDictionary<string, string[]>)value)) },
                 { OwinConstants.RequestBody, new FeatureMap<IHttpRequestFeature>(feature => feature.Body, () => Stream.Null, (feature, value) => feature.Body = (Stream)value) },
                 { OwinConstants.RequestUser, new FeatureMap<IHttpAuthenticationFeature>(feature => feature.User, () => null, (feature, value) => feature.User = (ClaimsPrincipal)value) },
 
                 { OwinConstants.ResponseStatusCode, new FeatureMap<IHttpResponseFeature>(feature => feature.StatusCode, () => 200, (feature, value) => feature.StatusCode = Convert.ToInt32(value)) },
                 { OwinConstants.ResponseReasonPhrase, new FeatureMap<IHttpResponseFeature>(feature => feature.ReasonPhrase, (feature, value) => feature.ReasonPhrase = Convert.ToString(value)) },
-                { OwinConstants.ResponseHeaders, new FeatureMap<IHttpResponseFeature>(feature => Utilities.MakeDictionaryStringArray(feature.Headers), (feature, value) => feature.Headers = Utilities.MakeDictionaryStringValues((IDictionary<string, string[]>)value)) },
+                { OwinConstants.ResponseHeaders, new FeatureMap<IHttpResponseFeature>(feature => Utilities.MakeDictionaryStringArray(feature.Headers), (feature, value) => feature.Headers = Utilities.MakeHeaderDictionary((IDictionary<string, string[]>)value)) },
                 { OwinConstants.ResponseBody, new FeatureMap<IHttpResponseFeature>(feature => feature.Body, () => Stream.Null, (feature, value) => feature.Body = (Stream)value) },
                 { OwinConstants.CommonKeys.OnSendingHeaders, new FeatureMap<IHttpResponseFeature>(
                     feature => new Action<Action<object>, object>((cb, state) => {

src/Microsoft.AspNet.Owin/OwinFeatureCollection.cs

@@ -106,9 +106,9 @@ string IHttpRequestFeature.QueryString
             set { Prop(OwinConstants.RequestQueryString, Utilities.RemoveQuestionMark(value)); }
         }
 
-        IDictionary<string, StringValues> IHttpRequestFeature.Headers
+        IHeaderDictionary IHttpRequestFeature.Headers
         {
-            get { return Utilities.MakeDictionaryStringValues(Prop<IDictionary<string, string[]>>(OwinConstants.RequestHeaders)); }
+            get { return Utilities.MakeHeaderDictionary(Prop<IDictionary<string, string[]>>(OwinConstants.RequestHeaders)); }
             set { Prop(OwinConstants.RequestHeaders, Utilities.MakeDictionaryStringArray(value)); }
         }
 
@@ -136,9 +136,9 @@ string IHttpResponseFeature.ReasonPhrase
             set { Prop(OwinConstants.ResponseReasonPhrase, value); }
         }
 
-        IDictionary<string, StringValues> IHttpResponseFeature.Headers
+        IHeaderDictionary IHttpResponseFeature.Headers
         {
-            get { return Utilities.MakeDictionaryStringValues(Prop<IDictionary<string, string[]>>(OwinConstants.ResponseHeaders)); }
+            get { return Utilities.MakeHeaderDictionary(Prop<IDictionary<string, string[]>>(OwinConstants.ResponseHeaders)); }
             set { Prop(OwinConstants.ResponseHeaders, Utilities.MakeDictionaryStringArray(value)); }
         }
 

src/Microsoft.AspNet.Owin/Utilities.cs

@@ -46,7 +46,7 @@ internal static ClaimsPrincipal MakeClaimsPrincipal(IPrincipal principal)
             return new ClaimsPrincipal(principal);
         }
 
-        internal static IDictionary<string, StringValues> MakeDictionaryStringValues(IDictionary<string, string[]> dictionary)
+        internal static IHeaderDictionary MakeHeaderDictionary(IDictionary<string, string[]> dictionary)
         {
             var wrapper = dictionary as DictionaryStringArrayWrapper;
             if (wrapper != null)
@@ -56,7 +56,7 @@ internal static ClaimsPrincipal MakeClaimsPrincipal(IPrincipal principal)
             return new DictionaryStringValuesWrapper(dictionary);
         }
 
-        internal static IDictionary<string, string[]> MakeDictionaryStringArray(IDictionary<string, StringValues> dictionary)
+        internal static IDictionary<string, string[]> MakeDictionaryStringArray(IHeaderDictionary dictionary)
         {
             var wrapper = dictionary as DictionaryStringValuesWrapper;
             if (wrapper != null)

test/Microsoft.AspNet.Http.Extensions.Tests/ResponseExtensionTests.cs

@@ -44,7 +44,7 @@ private class StartedResponseFeature : IHttpResponseFeature
 
             public bool HasStarted { get { return true; } }
 
-            public IDictionary<string, StringValues> Headers { get; set; }
+            public IHeaderDictionary Headers { get; set; }
 
             public string ReasonPhrase { get; set; }
 

test/Microsoft.AspNet.Http.Tests/DefaultHttpRequestTests.cs

@@ -65,7 +65,7 @@ public void Host_GetsHostFromHeaders()
             // Arrange
             const string expected = "localhost:9001";
 
-            var headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase)
+            var headers = new HeaderDictionary()
             {
                 { "Host", expected },
             };
@@ -85,7 +85,7 @@ public void Host_DecodesPunyCode()
             // Arrange
             const string expected = "löcalhöst";
 
-            var headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase)
+            var headers = new HeaderDictionary()
             {
                 { "Host", "xn--lcalhst-90ae" },
             };
@@ -105,7 +105,7 @@ public void Host_EncodesPunyCode()
             // Arrange
             const string expected = "xn--lcalhst-90ae";
 
-            var headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
+            var headers = new HeaderDictionary();
 
             var request = CreateRequest(headers);
 
@@ -188,7 +188,7 @@ public void Cookies_GetAndSet()
             Assert.Equal(new[] { "name2=value2" }, cookieHeaders);
         }
 
-        private static HttpRequest CreateRequest(IDictionary<string, StringValues> headers)
+        private static HttpRequest CreateRequest(IHeaderDictionary headers)
         {
             var context = new DefaultHttpContext();
             context.Features.Get<IHttpRequestFeature>().Headers = headers;
@@ -217,7 +217,7 @@ private static HttpRequest GetRequestWithAcceptCharsetHeader(string acceptCharse
 
         private static HttpRequest GetRequestWithHeader(string headerName, string headerValue)
         {
-            var headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
+            var headers = new HeaderDictionary();
             if (headerValue != null)
             {
                 headers.Add(headerName, headerValue);