Fix for #38: Fallback to wrong language preference when the top preference is unavailable

src/Microsoft.AspNet.Localization/AcceptLanguageHeaderRequestCultureProvider.cs

@@ -57,7 +57,7 @@ namespace Microsoft.AspNet.Localization
 
                         requestCulture = ValidateRequestCulture(requestCulture);
 
-                        if (requestCulture != null)
+                        if (requestCulture.Culture == culture)
                         {
                             return Task.FromResult(requestCulture);
                         }

test/Microsoft.AspNet.Localization.Tests/AccessLanguageHeaderRequestCultureProviderTest.cs

@@ -16,7 +16,7 @@ namespace Microsoft.Framework.Localization.Tests
     public class AccessLanguageHeaderRequestCultureProviderTest
     {
         [Fact]
-        public async void GetFallbackLanguage()
+        public async void GetFallbackLanguage_ReturnsFirstNonNullCultureFromSupportedCultureList()
         {
             using (var server = TestServer.Create(app =>
             {
@@ -44,5 +44,67 @@ namespace Microsoft.Framework.Localization.Tests
                 var response = await client.GetAsync(string.Empty);
             }
         }
+
+        [Fact]
+        public async void GetFallbackLanguage_ReturnsFromSupportedCulture_AcceptLanguageListContainsSupportedCultures()
+        {
+            using (var server = TestServer.Create(app =>
+            {
+                var options = new RequestLocalizationOptions
+                {
+                    DefaultRequestCulture = new RequestCulture(new CultureInfo("fr-FR")),
+                    SupportedCultures = new List<CultureInfo>
+                    {
+                        new CultureInfo("ar-SA"),
+                        new CultureInfo("en-US")
+                    }
+                };
+                app.UseRequestLocalization(options);
+                app.Run(context =>
+                {
+                    var requestCultureFeature = context.Features.Get<IRequestCultureFeature>();
+                    var requestCulture = requestCultureFeature.RequestCulture;
+                    Assert.Equal("ar-SA", requestCulture.Culture.Name);
+                    return Task.FromResult(0);
+                });
+            }))
+            {
+                var client = server.CreateClient();
+                client.DefaultRequestHeaders.AcceptLanguage.ParseAdd("en-GB,ar-SA,en-US");
+                var count = client.DefaultRequestHeaders.AcceptLanguage.Count;
+                var response = await client.GetAsync(string.Empty);
+            }
+        }
+
+        [Fact]
+        public async void GetFallbackLanguage_ReturnsDefault_AcceptLanguageListDoesnotContainSupportedCultures()
+        {
+            using (var server = TestServer.Create(app =>
+            {
+                var options = new RequestLocalizationOptions
+                {
+                    DefaultRequestCulture = new RequestCulture(new CultureInfo("fr-FR")),
+                    SupportedCultures = new List<CultureInfo>
+                    {
+                        new CultureInfo("ar-SA"),
+                        new CultureInfo("af-ZA")
+                    }
+                };
+                app.UseRequestLocalization(options);
+                app.Run(context =>
+                {
+                    var requestCultureFeature = context.Features.Get<IRequestCultureFeature>();
+                    var requestCulture = requestCultureFeature.RequestCulture;
+                    Assert.Equal("fr-FR", requestCulture.Culture.Name);
+                    return Task.FromResult(0);
+                });
+            }))
+            {
+                var client = server.CreateClient();
+                client.DefaultRequestHeaders.AcceptLanguage.ParseAdd("en-GB,ar-MA,en-US");
+                var count = client.DefaultRequestHeaders.AcceptLanguage.Count;
+                var response = await client.GetAsync(string.Empty);
+            }
+        }
     }
 }