Made IRequestCultureStrategy async to support things like user profile lookup

samples/LocalizationSample/Startup.cs

@@ -35,6 +35,14 @@ namespace LocalizationSample
                 //    new CultureInfo("en-AU")
                 //}
             };
+
+            // Optionally create an app-specific strategy with just a delegate, e.g. look up user preference from DB.
+            // Inserting it as position 0 ensures it has priority over any of the default strategies.
+            //options.RequestCultureStrategies.Insert(0, new CustomRequestCultureStrategy(async context =>
+            //{
+                
+            //}));
+
             app.UseRequestLocalization(options);
 
             app.Use(async (context, next) =>

src/Microsoft.AspNet.Localization/AcceptLanguageHeaderRequestCultureStrategy.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
 using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Localization.Internal;
 using Microsoft.Framework.Internal;
@@ -22,13 +23,13 @@ namespace Microsoft.AspNet.Localization
         public int MaximumAcceptLanguageHeaderValuesToTry { get; set; } = 3;
 
         /// <inheritdoc />
-        public override RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
         {
             var acceptLanguageHeader = httpContext.Request.GetTypedHeaders().AcceptLanguage;
 
             if (acceptLanguageHeader == null || acceptLanguageHeader.Count == 0)
             {
-                return null;
+                return Task.FromResult((RequestCulture)null);
             }
 
             var languages = acceptLanguageHeader.AsEnumerable();
@@ -58,13 +59,13 @@ namespace Microsoft.AspNet.Localization
 
                         if (requestCulture != null)
                         {
-                            return requestCulture;
+                            return Task.FromResult(requestCulture);
                         }
                     }
                 }
             }
 
-            return null;
+            return Task.FromResult((RequestCulture)null);
         }
     }
 }

src/Microsoft.AspNet.Localization/CookieRequestCultureStrategy.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
 using System;
+using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Localization.Internal;
 using Microsoft.Framework.Internal;
@@ -24,20 +25,20 @@ namespace Microsoft.AspNet.Localization
         public string CookieName { get; set; } = DefaultCookieName;
 
         /// <inheritdoc />
-        public override RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
         {
             var cookie = httpContext.Request.Cookies[CookieName];
 
             if (cookie == null)
             {
-                return null;
+                return Task.FromResult((RequestCulture)null);
             }
 
             var requestCulture = ParseCookieValue(cookie);
 
             requestCulture = ValidateRequestCulture(requestCulture);
 
-            return requestCulture;
+            return Task.FromResult(requestCulture);
         }
 
         /// <summary>

src/Microsoft.AspNet.Localization/CustomRequestCultureStrategy.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
 using System;
+using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.Framework.Internal;
 
@@ -12,19 +13,19 @@ namespace Microsoft.AspNet.Localization
     /// </summary>
     public class CustomRequestCultureStrategy : RequestCultureStrategy
     {
-        private readonly Func<HttpContext, RequestCulture> _strategy;
+        private readonly Func<HttpContext, Task<RequestCulture>> _strategy;
 
         /// <summary>
         /// Creates a new <see cref="CustomRequestCultureStrategy"/> using the specified delegate.
         /// </summary>
         /// <param name="strategy">The strategy delegate.</param>
-        public CustomRequestCultureStrategy([NotNull] Func<HttpContext, RequestCulture> strategy)
+        public CustomRequestCultureStrategy([NotNull] Func<HttpContext, Task<RequestCulture>> strategy)
         {
             _strategy = strategy;
         }
 
         /// <inheritdoc />
-        public override RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
         {
             return _strategy(httpContext);
         }

src/Microsoft.AspNet.Localization/IRequestCultureStrategy.cs

@@ -1,6 +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.Threading.Tasks;
 using Microsoft.AspNet.Http;
 
 namespace Microsoft.AspNet.Localization
@@ -18,6 +19,6 @@ namespace Microsoft.AspNet.Localization
         ///     The determined <see cref="RequestCulture"/>.
         ///     Returns <c>null</c> if the strategy couldn't determine a <see cref="RequestCulture"/>.
         /// </returns>
-        RequestCulture DetermineRequestCulture(HttpContext httpContext);
+        Task<RequestCulture> DetermineRequestCulture(HttpContext httpContext);
     }
 }

src/Microsoft.AspNet.Localization/QueryStringRequestCultureStrategy.cs

@@ -1,6 +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.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Localization.Internal;
 using Microsoft.Framework.Internal;
@@ -26,12 +27,12 @@ namespace Microsoft.AspNet.Localization
         public string UIQueryStringKey { get; set; } = "ui-culture";
 
         /// <inheritdoc />
-        public override RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
         {
             var request = httpContext.Request;
             if (!request.QueryString.HasValue)
             {
-                return null;
+                return Task.FromResult((RequestCulture)null);
             }
 
             string queryCulture = null;
@@ -50,7 +51,7 @@ namespace Microsoft.AspNet.Localization
             if (queryCulture == null && queryUICulture == null)
             {
                 // No values specified for either so no match
-                return null;
+                return Task.FromResult((RequestCulture)null);
             }
 
             if (queryCulture != null && queryUICulture == null)
@@ -64,14 +65,14 @@ namespace Microsoft.AspNet.Localization
 
             if (culture == null || uiCulture == null)
             {
-                return null;
+                return Task.FromResult((RequestCulture)null);
             }
 
             var requestCulture = new RequestCulture(culture, uiCulture);
 
             requestCulture = ValidateRequestCulture(requestCulture);
 
-            return requestCulture;
+            return Task.FromResult(requestCulture);
         }
     }
 }

src/Microsoft.AspNet.Localization/RequestCultureStrategy.cs

@@ -1,6 +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.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.Framework.Internal;
 
@@ -17,7 +18,7 @@ namespace Microsoft.AspNet.Localization
         public RequestLocalizationOptions Options { get; set; }
 
         /// <inheritdoc />
-        public abstract RequestCulture DetermineRequestCulture(HttpContext httpContext);
+        public abstract Task<RequestCulture> DetermineRequestCulture(HttpContext httpContext);
 
         /// <summary>
         /// Determines if the given <see cref="RequestCulture"/> is valid according to the currently configured.

src/Microsoft.AspNet.Localization/RequestLocalizationMiddleware.cs

@@ -46,7 +46,7 @@ namespace Microsoft.AspNet.Localization
             {
                 foreach (var strategy in _options.RequestCultureStrategies)
                 {
-                    var result = strategy.DetermineRequestCulture(context);
+                    var result = await strategy.DetermineRequestCulture(context);
                     if (result != null)
                     {
                         requestCulture = result;