Bunch of changes:

- Implemented pluggable strategies for determining request culture
- Added NotNull on public APIs
- Added support for a default request culture
- Added options class for configuring the middleware
- Improved the query string logic to support separate formatting & language cultures
- Implemented the logic for accept-language header
- Added more doc comments

src/Microsoft.AspNet.Localization/AcceptLanguageHeaderRequestCultureStrategy.cs

@@ -0,0 +1,67 @@
+// 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.Globalization;
+using System.Linq;
+using Microsoft.AspNet.Http;
+using Microsoft.AspNet.Localization.Internal;
+using Microsoft.Framework.Internal;
+using Microsoft.Net.Http.Headers;
+
+namespace Microsoft.AspNet.Localization
+{
+    /// <summary>
+    /// Determines the culture information for a request via the value of the Accept-Language header.
+    /// </summary>
+    /// <remarks>
+    /// 
+    /// </remarks>
+    public class AcceptLanguageHeaderRequestCultureStrategy : IRequestCultureStrategy
+    {
+        /// <summary>
+        /// The maximum number of values in the Accept-Language header to attempt to create a <see cref="CultureInfo"/>
+        /// from for the current request.
+        /// Defaults to <c>3</c>.
+        /// </summary>
+        public int MaximumAcceptLanguageHeaderValuesToTry { get; set; } = 3;
+
+        /// <inheritdoc />
+        public RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        {
+            var acceptLanguageHeader = httpContext.Request.GetTypedHeaders().AcceptLanguage;
+
+            if (acceptLanguageHeader == null || acceptLanguageHeader.Count == 0)
+            {
+                return null;
+            }
+
+            var languages = acceptLanguageHeader.AsEnumerable();
+
+            if (MaximumAcceptLanguageHeaderValuesToTry > 0)
+            {
+                // We take only the first configured number of languages from the header and then order those that we
+                // attempt to parse as a CultureInfo to mitigate potentially spinning CPU on lots of parse attempts.
+                languages = languages.Take(MaximumAcceptLanguageHeaderValuesToTry);
+            }
+            
+            var orderedLanguages = languages.OrderByDescending(h => h, StringWithQualityHeaderValueComparer.QualityComparer)
+                .ToList();
+
+            foreach (var language in orderedLanguages)
+            {
+                // Allow empty string values as they map to InvariantCulture, whereas null culture values will throw in
+                // the CultureInfo ctor
+                if (language.Value != null)
+                {
+                    try
+                    {
+                        return new RequestCulture(CultureUtilities.GetCultureFromName(language.Value));
+                    }
+                    catch (CultureNotFoundException) { }
+                }
+            }
+
+            return null;
+        }
+    }
+}

src/Microsoft.AspNet.Localization/CookieRequestCultureStrategy.cs

@@ -0,0 +1,18 @@
+// 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 Microsoft.AspNet.Http;
+using Microsoft.Framework.Internal;
+
+namespace Microsoft.AspNet.Localization
+{
+    public class CookieRequestCultureStrategy : IRequestCultureStrategy
+    {
+        public RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        {
+            // TODO
+            return null;
+        }
+    }
+}

src/Microsoft.AspNet.Localization/CustomRequestCultureStrategy.cs

@@ -0,0 +1,24 @@
+// 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 Microsoft.AspNet.Http;
+using Microsoft.Framework.Internal;
+
+namespace Microsoft.AspNet.Localization
+{
+    public class CustomRequestCultureStrategy : IRequestCultureStrategy
+    {
+        private readonly Func<HttpContext, RequestCulture> _strategy;
+
+        public CustomRequestCultureStrategy([NotNull] Func<HttpContext, RequestCulture> strategy)
+        {
+            _strategy = strategy;
+        }
+
+        public RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        {
+            return _strategy(httpContext);
+        }
+    }
+}

src/Microsoft.AspNet.Localization/IApplicationBuilderExtensions.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
 using Microsoft.AspNet.Localization;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Builder
 {
@@ -12,13 +13,29 @@ namespace Microsoft.AspNet.Builder
     {
         /// <summary>
         /// Adds the <see cref="RequestLocalizationMiddleware"/> to automatically set culture information for
-        /// requests based on information provided by the client.
+        /// requests based on information provided by the client using the default options.
         /// </summary>
         /// <param name="builder">The <see cref="IApplicationBuilder"/>.</param>
         /// <returns>The <see cref="IApplicationBuilder"/>.</returns>
-        public static IApplicationBuilder UseRequestLocalization(this IApplicationBuilder builder)
+        public static IApplicationBuilder UseRequestLocalization([NotNull] this IApplicationBuilder builder)
         {
-            return builder.UseMiddleware<RequestLocalizationMiddleware>();
+            var options = new RequestLocalizationMiddlewareOptions();
+
+            return UseRequestLocalization(builder, options);
+        }
+
+        /// <summary>
+        /// Adds the <see cref="RequestLocalizationMiddleware"/> to automatically set culture information for
+        /// requests based on information provided by the client.
+        /// </summary>
+        /// <param name="builder">The <see cref="IApplicationBuilder"/>.</param>
+        /// <param name="options">The options to configure the middleware with.</param>
+        /// <returns>The <see cref="IApplicationBuilder"/>.</returns>
+        public static IApplicationBuilder UseRequestLocalization(
+            [NotNull] this IApplicationBuilder builder,
+            [NotNull] RequestLocalizationMiddlewareOptions options)
+        {
+            return builder.UseMiddleware<RequestLocalizationMiddleware>(options);
         }
     }
 }

src/Microsoft.AspNet.Localization/IRequestCultureFeature.cs

@@ -12,5 +12,12 @@ namespace Microsoft.AspNet.Localization
         /// The <see cref="Localization.RequestCulture"/> of the request.
         /// </summary>
         RequestCulture RequestCulture { get; }
+
+        /// <summary>
+        /// The <see cref="IRequestCultureStrategy"/> that determined the request's culture information.
+        /// If the value is <c>null</c> then no strategy was used and the request's culture was set to the value of
+        /// <see cref="RequestLocalizationMiddlewareOptions.DefaultRequestCulture"/>.
+        /// </summary>
+        IRequestCultureStrategy Strategy { get; }
     }
 }

src/Microsoft.AspNet.Localization/IRequestCultureStrategy.cs

@@ -0,0 +1,12 @@
+// 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 Microsoft.AspNet.Http;
+
+namespace Microsoft.AspNet.Localization
+{
+    public interface IRequestCultureStrategy
+    {
+        RequestCulture DetermineRequestCulture(HttpContext httpContext);
+    }
+}

src/Microsoft.AspNet.Localization/Internal/CultureUtilities.cs

@@ -0,0 +1,29 @@
+// 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.Globalization;
+
+namespace Microsoft.AspNet.Localization.Internal
+{
+    public static class CultureUtilities
+    {
+        public static CultureInfo GetCultureFromName(string cultureName)
+        {
+            // Allow empty string values as they map to InvariantCulture, whereas null culture values will throw in
+            // the CultureInfo ctor
+            if (cultureName == null)
+            {
+                return null;
+            }
+
+            try
+            {
+                return new CultureInfo(cultureName);
+            }
+            catch (CultureNotFoundException)
+            {
+                return null;
+            }
+        }
+    }
+}

src/Microsoft.AspNet.Localization/QueryStringRequestCultureStrategy.cs

@@ -0,0 +1,67 @@
+// 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 Microsoft.AspNet.Http;
+using Microsoft.AspNet.Localization.Internal;
+using Microsoft.Framework.Internal;
+
+namespace Microsoft.AspNet.Localization
+{
+    /// <summary>
+    /// Determines the culture information for a request via values in the query string.
+    /// </summary>
+    public class QueryStringRequestCultureStrategy : IRequestCultureStrategy
+    {
+        /// <summary>
+        /// The key that contains the culture name.
+        /// Defaults to "culture".
+        /// </summary>
+        public string QueryStringKey { get; set; } = "culture";
+
+        /// <summary>
+        /// The key that contains the UI culture name. If not specified or no value is found,
+        /// <see cref="QueryStringKey"/> will be used.
+        /// Defaults to "ui-culture".
+        /// </summary>
+        public string UIQueryStringKey { get; set; } = "ui-culture";
+
+        /// <inheritdoc />
+        public RequestCulture DetermineRequestCulture([NotNull] HttpContext httpContext)
+        {
+            var request = httpContext.Request;
+            if (!request.QueryString.HasValue)
+            {
+                return null;
+            }
+
+            string queryCulture = null;
+            string queryUICulture = null;
+
+            if (!string.IsNullOrWhiteSpace(QueryStringKey))
+            {
+                queryCulture = request.Query[QueryStringKey];
+            }
+
+            if (!string.IsNullOrWhiteSpace(UIQueryStringKey))
+            {
+                queryUICulture = request.Query[UIQueryStringKey];
+            }
+
+            if (queryCulture == null && queryUICulture == null)
+            {
+                // No values specified for either so no match
+                return null;
+            }
+
+            if (queryCulture != null && queryUICulture == null)
+            {
+                // Value for culture but not for UI culture so default to culture value for both
+                queryUICulture = queryCulture;
+            }
+
+            return new RequestCulture(
+                CultureUtilities.GetCultureFromName(queryCulture),
+                CultureUtilities.GetCultureFromName(queryUICulture));
+        }
+    }
+}

src/Microsoft.AspNet.Localization/RequestCulture.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.Globalization;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -15,7 +16,7 @@ namespace Microsoft.AspNet.Localization
         /// properties set to the same <see cref="CultureInfo"/> value.
         /// </summary>
         /// <param name="culture">The <see cref="CultureInfo"/> for the request.</param>
-        public RequestCulture(CultureInfo culture)
+        public RequestCulture([NotNull] CultureInfo culture)
             : this (culture, culture)
         {
 
@@ -27,7 +28,7 @@ namespace Microsoft.AspNet.Localization
         /// </summary>
         /// <param name="culture">The <see cref="CultureInfo"/> for the request to be used for formatting.</param>
         /// <param name="uiCulture">The <see cref="CultureInfo"/> for the request to be used for text, i.e. language.</param>
-        public RequestCulture(CultureInfo culture, CultureInfo uiCulture)
+        public RequestCulture([NotNull] CultureInfo culture, [NotNull] CultureInfo uiCulture)
         {
             Culture = culture;
             UICulture = uiCulture;

src/Microsoft.AspNet.Localization/RequestCultureFeature.cs

@@ -1,6 +1,8 @@
 // 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 Microsoft.Framework.Internal;
+
 namespace Microsoft.AspNet.Localization
 {
     /// <summary>
@@ -12,12 +14,16 @@ namespace Microsoft.AspNet.Localization
         /// Creates a new <see cref="RequestCultureFeature"/> with the specified <see cref="Localization.RequestCulture"/>.
         /// </summary>
         /// <param name="requestCulture">The <see cref="Localization.RequestCulture"/>.</param>
-        public RequestCultureFeature(RequestCulture requestCulture)
+        public RequestCultureFeature([NotNull] RequestCulture requestCulture, IRequestCultureStrategy strategy)
         {
             RequestCulture = requestCulture;
+            Strategy = strategy;
         }
 
         /// <inheritdoc />
         public RequestCulture RequestCulture { get; }
+
+        /// <inheritdoc />
+        public IRequestCultureStrategy Strategy { get; }
     }
 }

src/Microsoft.AspNet.Localization/RequestLocalizationMiddleware.cs

@@ -6,6 +6,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Builder;
 using Microsoft.AspNet.Http;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -16,14 +17,17 @@ namespace Microsoft.AspNet.Localization
     public class RequestLocalizationMiddleware
     {
         private readonly RequestDelegate _next;
+        private readonly RequestLocalizationMiddlewareOptions _options;
         
         /// <summary>
         /// Creates a new <see cref="RequestLocalizationMiddleware"/>.
         /// </summary>
         /// <param name="next">The <see cref="RequestDelegate"/> representing the next middleware in the pipeline.</param>
-        public RequestLocalizationMiddleware(RequestDelegate next)
+        /// <param name="options"></param>
+        public RequestLocalizationMiddleware([NotNull] RequestDelegate next, [NotNull] RequestLocalizationMiddlewareOptions options)
         {
             _next = next;
+            _options = options;
         }
 
         /// <summary>
@@ -31,42 +35,35 @@ namespace Microsoft.AspNet.Localization
         /// </summary>
         /// <param name="context">The <see cref="HttpContext"/>.</param>
         /// <returns>A <see cref="Task"/> that completes when the middleware has completed processing.</returns>
-        public async Task Invoke(HttpContext context)
+        public async Task Invoke([NotNull] HttpContext context)
         {
-            // TODO: Make this read from Accept-Language header, cookie, app-provided delegate, etc.
+            var requestCulture = _options.DefaultRequestCulture ??
-            if (context.Request.QueryString.HasValue)
+                new RequestCulture(CultureInfo.DefaultThreadCurrentCulture, CultureInfo.DefaultThreadCurrentUICulture);
+
+            IRequestCultureStrategy winningStrategy = null;
+
+            if (_options.RequestCultureStrategies != null)
             {
-                var queryCulture = context.Request.Query["culture"];
+                foreach (var strategy in _options.RequestCultureStrategies)
-                if (!string.IsNullOrEmpty(queryCulture))
                 {
-                    var requestCulture = new RequestCulture(new CultureInfo(queryCulture));
+                    var result = strategy.DetermineRequestCulture(context);
-
+                    if (result != null)
-                    context.SetFeature<IRequestCultureFeature>(new RequestCultureFeature(requestCulture));
+                    {
-
+                        requestCulture = result;
-                    var originalCulture = CultureInfo.CurrentCulture;
+                        winningStrategy = strategy;
-                    var originalUICulture = CultureInfo.CurrentUICulture;
+                        break;
-
+                    }
-                    SetCurrentCulture(requestCulture);
-
-                    await _next(context);
-
-                    return;
                 }
             }
-            else
+
-            {
+            context.SetFeature<IRequestCultureFeature>(new RequestCultureFeature(requestCulture, winningStrategy));
-                // NOTE: The below doesn't seem to be needed anymore now that DNX is correctly managing culture across
+
-                //       async calls but we'll need to verify properly.
+            SetCurrentThreadCulture(requestCulture);
-                // Forcibly set thread to en-US as sometimes previous threads have wrong culture across async calls, 
-                // see note above.
-                //var defaultRequestCulture = new RequestCulture(new CultureInfo("en-US"));
-                //SetCurrentCulture(defaultRequestCulture);
-            }
 
             await _next(context);
         }
 
-        private void SetCurrentCulture(RequestCulture requestCulture)
+        private static void SetCurrentThreadCulture(RequestCulture requestCulture)
         {
 #if DNX451
             Thread.CurrentThread.CurrentCulture = requestCulture.Culture;

src/Microsoft.AspNet.Localization/RequestLocalizationMiddlewareOptions.cs

@@ -0,0 +1,76 @@
+// 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.Diagnostics.CodeAnalysis;
+using System.Globalization;
+
+namespace Microsoft.AspNet.Localization
+{
+    /// <summary>
+    /// Specifies options for the <see cref="RequestLocalizationMiddleware"/>.
+    /// </summary>
+    public class RequestLocalizationMiddlewareOptions
+    {
+        /// <summary>
+        /// Creates a new <see cref="RequestLocalizationMiddlewareOptions"/> with default values.
+        /// </summary>
+        public RequestLocalizationMiddlewareOptions()
+        {
+            DefaultRequestCulture = new RequestCulture(CultureInfo.DefaultThreadCurrentCulture, CultureInfo.DefaultThreadCurrentUICulture);
+
+            RequestCultureStrategies = new List<IRequestCultureStrategy>
+            {
+                new QueryStringRequestCultureStrategy(),
+                new CookieRequestCultureStrategy(),
+                new AcceptLanguageHeaderRequestCultureStrategy { MaximumAcceptLanguageHeaderValuesToTry = MaximumAcceptLanguageHeaderValuesToTry }
+            };
+        }
+
+        /// <summary>
+        /// The maximum number of values in the Accept-Language header to attempt to create a <see cref="CultureInfo"/>
+        /// from for the current request.
+        /// Defaults to <c>3</c>.
+        /// </summary>
+        public int MaximumAcceptLanguageHeaderValuesToTry { get; set; } = 3;
+
+        /// <summary>
+        /// The default <see cref="RequestCulture"/> to use. This value will be used if none of the configured
+        /// <see cref="IRequestCultureStrategy"/> options result in a non-<c>null</c> result.
+        /// Defaults to <see cref="RequestCulture.Culture"/> set to <see cref="CultureInfo.DefaultThreadCurrentCulture"/>
+        /// and <see cref="RequestCulture.UICulture"/> set to <see cref="CultureInfo.DefaultThreadCurrentUICulture"/>.
+        /// </summary>
+        public RequestCulture DefaultRequestCulture { get; set; }
+
+        /// <summary>
+        /// The cultures supported by the application. If this value is non-<c>null</c>, the
+        /// <see cref="RequestLocalizationMiddleware"/> will only set the current request culture to an entry in this
+        /// list. A value of <c>null</c> means all cultures are supported.
+        /// Defaults to <c>null</c>.
+        /// </summary>
+        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly", Justification = "Improves usability")]
+        public IList<CultureInfo> SupportedCultures { get; set; }
+
+        /// <summary>
+        /// The UI cultures supported by the application. If this value is non-<c>null</c>, the
+        /// <see cref="RequestLocalizationMiddleware"/> will only set the current request culture to an entry in this
+        /// list. A value of <c>null</c> means all cultures are supported.
+        /// Defaults to <c>null</c>.
+        /// </summary>
+        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly", Justification = "Improves usability")]
+        public IList<CultureInfo> SupportedUICultures { get; set; }
+
+        /// <summary>
+        /// An ordered list of strategies used to determine a request's culture information. The first strategy that
+        /// returns a non-<c>null</c> result for a given request will be used.
+        /// Defaults to the following:
+        /// <list type="number">
+        ///     <item><description><see cref="QueryStringRequestCultureStrategy"/></description></item>
+        ///     <item><description><see cref="CookieRequestCultureStrategy"/></description></item>
+        ///     <item><description><see cref="AcceptLanguageHeaderRequestCultureStrategy"/></description></item>
+        /// </list>
+        /// </summary>
+        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly", Justification = "Improves usability")]
+        public IList<IRequestCultureStrategy> RequestCultureStrategies { get; set; }
+    }
+}

src/Microsoft.AspNet.Localization/project.json

@@ -4,6 +4,7 @@
 
   "dependencies": {
     "Microsoft.Framework.Localization.Abstractions": "1.0.0-*",
+    "Microsoft.Framework.NotNullAttribute.Internal": { "type": "build", "version": "1.0.0-*" },
     "Microsoft.AspNet.Http.Extensions": "1.0.0-*"
   },
 
@@ -13,6 +14,7 @@
       "dependencies": {
         "System.Collections": "4.0.10-*",
         "System.Linq": "4.0.0-*",
+        "System.Globalization": "4.0.10-*",
         "System.Threading": "4.0.10-*",
         "Microsoft.CSharp": "4.0.0-*"
       }

src/Microsoft.Framework.Localization.Abstractions/LocalizedString.cs

@@ -1,6 +1,8 @@
 // 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 Microsoft.Framework.Internal;
+
 namespace Microsoft.Framework.Localization
 {
     /// <summary>
@@ -13,7 +15,7 @@ namespace Microsoft.Framework.Localization
         /// </summary>
         /// <param name="name">The name of the string in the resource it was loaded from.</param>
         /// <param name="value">The actual string.</param>
-        public LocalizedString(string name, string value)
+        public LocalizedString([NotNull] string name, [NotNull] string value)
             : this(name, value, resourceNotFound: false)
         {
 
@@ -25,7 +27,7 @@ namespace Microsoft.Framework.Localization
         /// <param name="name">The name of the string in the resource it was loaded from.</param>
         /// <param name="value">The actual string.</param>
         /// <param name="resourceNotFound">Whether the string was found in a resource. Set this to <c>false</c> to indicate an alternate string value was used.</param>
-        public LocalizedString(string name, string value, bool resourceNotFound)
+        public LocalizedString([NotNull] string name, [NotNull] string value, bool resourceNotFound)
         {
             Name = name;
             Value = value;

src/Microsoft.Framework.Localization.Abstractions/StringLocalizerOfT.cs

@@ -4,6 +4,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Globalization;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.Framework.Localization
 {
@@ -19,7 +20,7 @@ namespace Microsoft.Framework.Localization
         /// Creates a new <see cref="StringLocalizer{TResourceSource}"/>.
         /// </summary>
         /// <param name="factory">The <see cref="IStringLocalizerFactory"/> to use.</param>
-        public StringLocalizer(IStringLocalizerFactory factory)
+        public StringLocalizer([NotNull] IStringLocalizerFactory factory)
         {
             _localizer = factory.Create(typeof(TResourceSource));
         }
@@ -28,16 +29,17 @@ namespace Microsoft.Framework.Localization
         public virtual IStringLocalizer WithCulture(CultureInfo culture) => _localizer.WithCulture(culture);
 
         /// <inheritdoc />
-        public virtual LocalizedString this[string key] => _localizer[key];
+        public virtual LocalizedString this[[NotNull] string key] => _localizer[key];
 
         /// <inheritdoc />
-        public virtual LocalizedString this[string key, params object[] arguments] => _localizer[key, arguments];
+        public virtual LocalizedString this[[NotNull] string key, params object[] arguments] =>
+            _localizer[key, arguments];
 
         /// <inheritdoc />
-        public virtual LocalizedString GetString(string key) => _localizer.GetString(key);
+        public virtual LocalizedString GetString([NotNull] string key) => _localizer.GetString(key);
 
         /// <inheritdoc />
-        public virtual LocalizedString GetString(string key, params object[] arguments) =>
+        public virtual LocalizedString GetString([NotNull] string key, params object[] arguments) =>
             _localizer.GetString(key, arguments);
 
         /// <inheritdoc />

src/Microsoft.Framework.Localization.Abstractions/project.json

@@ -3,7 +3,7 @@
   "description": "Abstractions of application localization services.",
 
   "dependencies": {
-    
+    "Microsoft.Framework.NotNullAttribute.Internal": { "type": "build", "version": "1.0.0-*" }
   },
 
   "frameworks": {

src/Microsoft.Framework.Localization/LocalizationServiceCollectionExtensions.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 Microsoft.Framework.Internal;
 using Microsoft.Framework.Localization;
 
 namespace Microsoft.Framework.DependencyInjection
@@ -15,7 +16,7 @@ namespace Microsoft.Framework.DependencyInjection
         /// </summary>
         /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
         /// <returns>The <see cref="IServiceCollection"/>.</returns>
-        public static IServiceCollection AddLocalization(this IServiceCollection services)
+        public static IServiceCollection AddLocalization([NotNull] this IServiceCollection services)
         {
             services.TryAdd(new ServiceDescriptor(
                 typeof(IStringLocalizerFactory),

src/Microsoft.Framework.Localization/ResourceManagerStringLocalizer.cs

@@ -8,6 +8,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Reflection;
 using System.Resources;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.Framework.Localization
 {
@@ -27,9 +28,9 @@ namespace Microsoft.Framework.Localization
         /// <param name="resourceAssembly">The <see cref="Assembly"/> that contains the strings as embedded resources.</param>
         /// <param name="baseName">The base name of the embedded resource in the <see cref="Assembly"/> that contains the strings.</param>
         public ResourceManagerStringLocalizer(
-                    ResourceManager resourceManager,
+            [NotNull] ResourceManager resourceManager,
-                    Assembly resourceAssembly,
+            [NotNull] Assembly resourceAssembly,
-                    string baseName)
+            [NotNull] string baseName)
         {
             ResourceManager = resourceManager;
             ResourceAssembly = resourceAssembly;
@@ -52,20 +53,20 @@ namespace Microsoft.Framework.Localization
         protected string ResourceBaseName { get; }
         
         /// <inheritdoc />
-        public virtual LocalizedString this[string name] => GetString(name);
+        public virtual LocalizedString this[[NotNull] string name] => GetString(name);
 
         /// <inheritdoc />
-        public virtual LocalizedString this[string name, params object[] arguments] => GetString(name, arguments);
+        public virtual LocalizedString this[[NotNull] string name, params object[] arguments] => GetString(name, arguments);
 
         /// <inheritdoc />
-        public virtual LocalizedString GetString(string name)
+        public virtual LocalizedString GetString([NotNull] string name)
         {
             var value = GetStringSafely(name, null);
             return new LocalizedString(name, value ?? name, resourceNotFound: value == null);
         }
 
         /// <inheritdoc />
-        public virtual LocalizedString GetString(string name, params object[] arguments)
+        public virtual LocalizedString GetString([NotNull] string name, params object[] arguments)
         {
             var format = GetStringSafely(name, null);
             var value = string.Format(format ?? name, arguments);
@@ -95,7 +96,7 @@ namespace Microsoft.Framework.Localization
         /// <param name="name">The name of the string resource.</param>
         /// <param name="culture">The <see cref="CultureInfo"/> to get the string for.</param>
         /// <returns>The resource string, or <c>null</c> if none was found.</returns>
-        protected string GetStringSafely(string name, CultureInfo culture)
+        protected string GetStringSafely([NotNull] string name, [NotNull] CultureInfo culture)
         {
             var cacheKey = new MissingManifestCacheKey(name, culture);
             if (_missingManifestCache.ContainsKey(cacheKey))
@@ -133,7 +134,7 @@ namespace Microsoft.Framework.Localization
         /// </summary>
         /// <param name="culture">The <see cref="CultureInfo"/> to get strings for.</param>
         /// <returns>The <see cref="IEnumerator{LocalizedString}"/>.</returns>
-        protected IEnumerator<LocalizedString> GetEnumerator(CultureInfo culture)
+        protected IEnumerator<LocalizedString> GetEnumerator([NotNull] CultureInfo culture)
         {
             // TODO: I'm sure something here should be cached, probably the whole result
             var resourceNames = GetResourceNamesFromCultureHierarchy(culture);

src/Microsoft.Framework.Localization/ResourceManagerStringLocalizerFactory.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Reflection;
 using System.Resources;
+using Microsoft.Framework.Internal;
 using Microsoft.Framework.Runtime;
 
 namespace Microsoft.Framework.Localization
@@ -19,7 +20,7 @@ namespace Microsoft.Framework.Localization
         /// Creates a new <see cref="ResourceManagerStringLocalizer"/>.
         /// </summary>
         /// <param name="applicationEnvironment"></param>
-        public ResourceManagerStringLocalizerFactory(IApplicationEnvironment applicationEnvironment)
+        public ResourceManagerStringLocalizerFactory([NotNull] IApplicationEnvironment applicationEnvironment)
         {
             _applicationEnvironment = applicationEnvironment;
         }
@@ -30,7 +31,7 @@ namespace Microsoft.Framework.Localization
         /// </summary>
         /// <param name="resourceSource">The <see cref="Type"/>.</param>
         /// <returns>The <see cref="ResourceManagerStringLocalizer"/>.</returns>
-        public IStringLocalizer Create(Type resourceSource)
+        public IStringLocalizer Create([NotNull] Type resourceSource)
         {
             var typeInfo = resourceSource.GetTypeInfo();
             var assembly = typeInfo.Assembly;
@@ -44,7 +45,7 @@ namespace Microsoft.Framework.Localization
         /// <param name="baseName">The base name of the resource to load strings from.</param>
         /// <param name="location">The location to load resources from.</param>
         /// <returns>The <see cref="ResourceManagerStringLocalizer"/>.</returns>
-        public IStringLocalizer Create(string baseName, string location)
+        public IStringLocalizer Create([NotNull] string baseName, [NotNull] string location)
         {
             var assembly = Assembly.Load(new AssemblyName(location ?? _applicationEnvironment.ApplicationName));
 

src/Microsoft.Framework.Localization/ResourceManagerWithCultureStringLocalizer.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Reflection;
 using System.Resources;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.Framework.Localization
 {
@@ -25,30 +26,30 @@ namespace Microsoft.Framework.Localization
         /// <param name="baseName">The base name of the embedded resource in the <see cref="Assembly"/> that contains the strings.</param>
         /// <param name="culture">The specific <see cref="CultureInfo"/> to use.</param>
         public ResourceManagerWithCultureStringLocalizer(
-            ResourceManager resourceManager,
+            [NotNull] ResourceManager resourceManager,
-            Assembly assembly,
+            [NotNull] Assembly assembly,
-            string baseName,
+            [NotNull] string baseName,
-            CultureInfo culture)
+            [NotNull] CultureInfo culture)
             : base(resourceManager, assembly, baseName)
         {
             _culture = culture;
         }
 
         /// <inheritdoc />
-        public override LocalizedString this[string name] => GetString(name);
+        public override LocalizedString this[[NotNull] string name] => GetString(name);
 
         /// <inheritdoc />
-        public override LocalizedString this[string name, params object[] arguments] => GetString(name, arguments);
+        public override LocalizedString this[[NotNull] string name, params object[] arguments] => GetString(name, arguments);
 
         /// <inheritdoc />
-        public override LocalizedString GetString(string name)
+        public override LocalizedString GetString([NotNull] string name)
         {
             var value = GetStringSafely(name, _culture);
             return new LocalizedString(name, value ?? name);
         }
 
         /// <inheritdoc />
-        public override LocalizedString GetString(string name, params object[] arguments)
+        public override LocalizedString GetString([NotNull] string name, params object[] arguments)
         {
             var format = GetStringSafely(name, _culture);
             var value = string.Format(_culture, format ?? name, arguments);

src/Microsoft.Framework.Localization/project.json

@@ -5,6 +5,7 @@
   "dependencies": {
     "Microsoft.Framework.DependencyInjection.Abstractions": "1.0.0-*",
     "Microsoft.Framework.Localization.Abstractions": "1.0.0-*",
+    "Microsoft.Framework.NotNullAttribute.Internal": { "type": "build", "version": "1.0.0-*" },
     "Microsoft.Framework.Runtime.Abstractions": "1.0.0-*",
     "System.Resources.ReaderWriter": "4.0.0-*"
   },