From 10336effe7ce5e685749df5f7c17b9da44d75520 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Wed, 21 Mar 2018 18:49:38 +0000
Subject: [PATCH] React to StringValues

---
 .../ModelBinding/ValueProviderResult.cs        |  4 ++--
 .../ModelBinding/Binders/HeaderModelBinder.cs  | 18 +++++++++---------
 .../ModelBinding/ValueProviderResultTest.cs    |  4 ++--
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ValueProviderResult.cs b/src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ValueProviderResult.cs
index c9bf19ad4c..ded7d9af83 100644
--- a/src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ValueProviderResult.cs
+++ b/src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ValueProviderResult.cs
@@ -32,7 +32,7 @@ public struct ValueProviderResult : IEquatable<ValueProviderResult>, IEnumerable
         /// <summary>
         /// A <see cref="ValueProviderResult"/> that represents a lack of data.
         /// </summary>
-        public static ValueProviderResult None = new ValueProviderResult(new string[0]);
+        public static ValueProviderResult None = new ValueProviderResult(default);
 
         /// <summary>
         /// Creates a new <see cref="ValueProviderResult"/> using <see cref="CultureInfo.InvariantCulture"/>.
@@ -73,7 +73,7 @@ public string FirstValue
         {
             get
             {
-                if (Values.Count == 0)
+                if (Values.IsNull)
                 {
                     return null;
                 }
diff --git a/src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Binders/HeaderModelBinder.cs b/src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Binders/HeaderModelBinder.cs
index 48c3ae2304..9cdc8e7240 100644
--- a/src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Binders/HeaderModelBinder.cs
+++ b/src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Binders/HeaderModelBinder.cs
@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Diagnostics;
 using System.Globalization;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
@@ -10,6 +9,7 @@
 using Microsoft.AspNetCore.Mvc.ModelBinding.Internal;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
 {
@@ -128,16 +128,18 @@ private HeaderValueProvider GetHeaderValueProvider(string headerName, ModelBindi
 
             // Prevent breaking existing users in scenarios where they are binding to a 'string' property
             // and expect the whole comma separated string, if any, as a single string and not as a string array.
-            var values = Array.Empty<string>();
+            var values = default(StringValues);
             if (request.Headers.ContainsKey(headerName))
             {
                 if (bindingContext.ModelMetadata.IsEnumerableType)
                 {
+                    // Convert to multiple values
                     values = request.Headers.GetCommaSeparatedValues(headerName);
                 }
                 else
                 {
-                    values = new[] { (string)request.Headers[headerName] };
+                    // Convert to single value
+                    values = (string)request.Headers[headerName];
                 }
             }
 
@@ -212,23 +214,21 @@ private static object GetCompatibleCollection(ModelBindingContext bindingContext
 
         private class HeaderValueProvider : IValueProvider
         {
-            private readonly string[] _values;
+            private readonly StringValues _values;
 
-            public HeaderValueProvider(string[] values)
+            public HeaderValueProvider(StringValues values)
             {
-                Debug.Assert(values != null);
-
                 _values = values;
             }
 
             public bool ContainsPrefix(string prefix)
             {
-                return _values.Length != 0;
+                return !_values.IsNull;
             }
 
             public ValueProviderResult GetValue(string key)
             {
-                if (_values.Length == 0)
+                if (_values.IsNull)
                 {
                     return ValueProviderResult.None;
                 }
diff --git a/test/Microsoft.AspNetCore.Mvc.Abstractions.Test/ModelBinding/ValueProviderResultTest.cs b/test/Microsoft.AspNetCore.Mvc.Abstractions.Test/ModelBinding/ValueProviderResultTest.cs
index dd639bc564..0ccc285ca2 100644
--- a/test/Microsoft.AspNetCore.Mvc.Abstractions.Test/ModelBinding/ValueProviderResultTest.cs
+++ b/test/Microsoft.AspNetCore.Mvc.Abstractions.Test/ModelBinding/ValueProviderResultTest.cs
@@ -20,7 +20,7 @@ public void Construct_With_NullString()
             Assert.Null(result.FirstValue);
             Assert.Equal(ValueProviderResult.None, result);
             Assert.Null((string)result);
-            Assert.Null((string[])result);
+            Assert.Empty((string[])result);
         }
 
         [Fact]
@@ -35,7 +35,7 @@ public void Construct_With_NullArray()
             Assert.Null(result.FirstValue);
             Assert.Equal(ValueProviderResult.None, result);
             Assert.Null((string)result);
-            Assert.Null((string[])result);
+            Assert.Empty((string[])result);
         }
 
         [Fact]