Add request culture provider for request localization

Author: tomasherceg

src/Framework/Framework/Hosting/Middlewares/DotvvmRoutingMiddleware.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net.Http;
 using System.Reflection;
 using System.Threading.Tasks;
 using DotVVM.Framework.Runtime.Tracing;
@@ -40,9 +41,14 @@ private static bool TryParseGooglebotHashbangEscapedFragment(string queryString,
 
         public static string GetRouteMatchUrl(IDotvvmRequestContext context)
         {
-            if (!TryParseGooglebotHashbangEscapedFragment(context.HttpContext.Request.Url.Query, out var url))
+            return GetRouteMatchUrl(context.HttpContext.Request.Path.Value!, context.HttpContext.Request.Url.Query);
+        }
+
+        public static string GetRouteMatchUrl(string requestPath, string queryString)
+        {
+            if (!TryParseGooglebotHashbangEscapedFragment(queryString, out var url))
             {
-                url = context.HttpContext.Request.Path.Value;
+                url = requestPath;
             }
             url = url?.Trim('/') ?? "";
 

src/Framework/Hosting.AspNetCore/Localization/DotvvmRoutingRequestCultureProvider.cs

@@ -0,0 +1,60 @@
+#nullable enable
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using DotVVM.Framework.Configuration;
+using DotVVM.Framework.Hosting.Middlewares;
+using DotVVM.Framework.Routing;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Localization;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DotVVM.Framework.Hosting.AspNetCore.Localization;
+
+public class DotvvmRoutingRequestCultureProvider : IRequestCultureProvider
+{
+    private static readonly object locker = new();
+    private static IReadOnlyList<LocalizedDotvvmRoute>? cachedRoutes;
+
+    public Task<ProviderCultureResult?> DetermineProviderCultureResult(HttpContext httpContext)
+    {
+        EnsureCachedRoutes(httpContext);
+
+        // find matching localizable route and extract culture from it
+        var url = DotvvmRoutingMiddleware.GetRouteMatchUrl(httpContext.Request.Path.Value!, httpContext.Request.QueryString.Value!);
+        foreach (var route in cachedRoutes!)
+        {
+            if (route.IsPartialMatch(url, out _, out var values, out var matchedCulture))
+            {
+                return Task.FromResult<ProviderCultureResult?>(new ProviderCultureResult(matchedCulture));
+            }
+        }
+
+        return Task.FromResult<ProviderCultureResult?>(null);
+    }
+
+    private void EnsureCachedRoutes(HttpContext httpContext)
+    {
+        if (cachedRoutes == null)
+        {
+            lock (locker)
+            {
+                if (cachedRoutes == null)
+                {
+                    // try to obtain DotVVM configuration
+                    if (httpContext.RequestServices.GetService<DotvvmConfiguration>() is not { } config)
+                    {
+                        throw new InvalidOperationException("DotVVM configuration not found in the service provider.");
+                    }
+
+                    // try to obtain DotVVM routes
+                    cachedRoutes = config.RouteTable
+                        .OfType<LocalizedDotvvmRoute>()
+                        .ToArray();
+                }
+            }
+        }
+    }
+}