#485 Pick up locale requested by the client

GenHTTP.sln

@@ -87,23 +87,25 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Testing", "Testing\
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Modules.Pages", "Modules\Pages\GenHTTP.Modules.Pages.csproj", "{4CDA31EB-A6C2-4634-9379-9306D3996B21}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Modules.OpenApi", "Modules\OpenApi\GenHTTP.Modules.OpenApi.csproj", "{A5149821-D510-4854-9DC9-D489323BC545}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Modules.OpenApi", "Modules\OpenApi\GenHTTP.Modules.OpenApi.csproj", "{A5149821-D510-4854-9DC9-D489323BC545}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Modules.Websockets", "Modules\Websockets\GenHTTP.Modules.Websockets.csproj", "{9D3D3B40-691D-4EE1-B948-82525F28FBB2}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Modules.Websockets", "Modules\Websockets\GenHTTP.Modules.Websockets.csproj", "{9D3D3B40-691D-4EE1-B948-82525F28FBB2}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Modules.ServerSentEvents", "Modules\ServerSentEvents\GenHTTP.Modules.ServerSentEvents.csproj", "{69F3862A-0027-4312-A890-45549AF5D2B1}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Modules.ServerSentEvents", "Modules\ServerSentEvents\GenHTTP.Modules.ServerSentEvents.csproj", "{69F3862A-0027-4312-A890-45549AF5D2B1}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Modules.Inspection", "Modules\Inspection\GenHTTP.Modules.Inspection.csproj", "{2FE9B758-187F-41B3-96BF-1C2BB006F809}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Modules.Inspection", "Modules\Inspection\GenHTTP.Modules.Inspection.csproj", "{2FE9B758-187F-41B3-96BF-1C2BB006F809}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Engine.Internal", "Engine\Internal\GenHTTP.Engine.Internal.csproj", "{4A492C9D-4338-4CCD-A227-F7829D032221}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Engine.Internal", "Engine\Internal\GenHTTP.Engine.Internal.csproj", "{4A492C9D-4338-4CCD-A227-F7829D032221}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Engine.Kestrel", "Engine\Kestrel\GenHTTP.Engine.Kestrel.csproj", "{4137673D-9218-4D42-924C-A36A6F412F5E}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Engine.Kestrel", "Engine\Kestrel\GenHTTP.Engine.Kestrel.csproj", "{4137673D-9218-4D42-924C-A36A6F412F5E}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Engine.Shared", "Engine\Shared\GenHTTP.Engine.Shared.csproj", "{7CEE048E-FA6A-4D8C-B6A6-EEEA0B048C54}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Engine.Shared", "Engine\Shared\GenHTTP.Engine.Shared.csproj", "{7CEE048E-FA6A-4D8C-B6A6-EEEA0B048C54}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Adapters", "Adapters", "{C3265C1A-E9A9-45FD-BD24-66DE9C7062F1}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Adapters.AspNetCore", "Adapters\AspNetCore\GenHTTP.Adapters.AspNetCore.csproj", "{AD7904BC-27BE-4EB5-84BC-62FF32DCBB78}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "GenHTTP.Adapters.AspNetCore", "Adapters\AspNetCore\GenHTTP.Adapters.AspNetCore.csproj", "{AD7904BC-27BE-4EB5-84BC-62FF32DCBB78}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenHTTP.Modules.I18n", "Modules\GenHTTP.Modules.I18n\GenHTTP.Modules.I18n.csproj", "{E17F6CF0-295D-408C-9664-FE18C6E83433}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -255,6 +257,10 @@ Global
 		{AD7904BC-27BE-4EB5-84BC-62FF32DCBB78}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{AD7904BC-27BE-4EB5-84BC-62FF32DCBB78}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{AD7904BC-27BE-4EB5-84BC-62FF32DCBB78}.Release|Any CPU.Build.0 = Release|Any CPU
+		{E17F6CF0-295D-408C-9664-FE18C6E83433}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E17F6CF0-295D-408C-9664-FE18C6E83433}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E17F6CF0-295D-408C-9664-FE18C6E83433}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E17F6CF0-295D-408C-9664-FE18C6E83433}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -298,9 +304,10 @@ Global
 		{4137673D-9218-4D42-924C-A36A6F412F5E} = {AFBFE61E-0C33-42F6-9370-9F5088EB8633}
 		{7CEE048E-FA6A-4D8C-B6A6-EEEA0B048C54} = {AFBFE61E-0C33-42F6-9370-9F5088EB8633}
 		{AD7904BC-27BE-4EB5-84BC-62FF32DCBB78} = {C3265C1A-E9A9-45FD-BD24-66DE9C7062F1}
+		{E17F6CF0-295D-408C-9664-FE18C6E83433} = {23B23225-275E-4F52-8B29-6F44C85B6ACE}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
-		LessCompiler = 2603124e-1287-4d61-9540-6ac3efad4eb9
 		SolutionGuid = {9C67B3AF-0BF6-4E21-8C39-3F74CFCF9632}
+		LessCompiler = 2603124e-1287-4d61-9540-6ac3efad4eb9
 	EndGlobalSection
 EndGlobal

Modules/GenHTTP.Modules.I18n/GenHTTP.Modules.I18n.csproj

@@ -0,0 +1,47 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+	<PropertyGroup>
+
+		<TargetFrameworks>net8.0;net9.0</TargetFrameworks>
+
+		<LangVersion>13.0</LangVersion>
+		<Nullable>enable</Nullable>
+		<TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+		<ImplicitUsings>enable</ImplicitUsings>
+
+		<AssemblyVersion>9.3.0.0</AssemblyVersion>
+		<FileVersion>9.3.0.0</FileVersion>
+		<Version>9.3.0</Version>
+
+		<Authors>Andreas Nägeli, Martin Maťátko</Authors>
+		<Company />
+
+		<PackageLicenseFile>LICENSE</PackageLicenseFile>
+		<PackageProjectUrl>https://genhttp.org/</PackageProjectUrl>
+
+		<Description>Allows to handle requests in a culture specific manner.</Description>
+		<PackageTags>HTTP Webserver C# Module i18n</PackageTags>
+
+		<PublishRepositoryUrl>true</PublishRepositoryUrl>
+		<IncludeSymbols>true</IncludeSymbols>
+		<SymbolPackageFormat>snupkg</SymbolPackageFormat>
+
+		<GenerateDocumentationFile>true</GenerateDocumentationFile>
+		<NoWarn>CS1591,CS1587,CS1572,CS1573</NoWarn>
+
+		<PackageIcon>icon.png</PackageIcon>
+
+	</PropertyGroup>
+
+	<ItemGroup>
+
+		<None Include="..\..\LICENSE" Pack="true" PackagePath="\" />
+		<None Include="..\..\Resources\icon.png" Pack="true" PackagePath="\" />
+
+	</ItemGroup>
+
+	<ItemGroup>
+	  <ProjectReference Include="..\..\API\GenHTTP.Api.csproj" />
+	</ItemGroup>
+
+</Project>

Modules/GenHTTP.Modules.I18n/Localization.cs

@@ -0,0 +1,19 @@
+using System.Globalization;
+using GenHTTP.Modules.I18n.Provider;
+
+namespace GenHTTP.Modules.I18n;
+
+public static class Localization
+{
+    #region Builder
+
+    /// <summary>
+    /// Creates a localization handler that parses and sets 
+    /// <see cref="CultureInfo"/> based on defined rules.
+    /// </summary>
+    /// <returns>By default culture is read from request header 
+    /// and is set to <see cref=" CultureInfo.CurrentUICulture"/>.</returns>
+    public static LocalizationConcernBuilder Create() => new();
+
+    #endregion
+}

Modules/GenHTTP.Modules.I18n/Parsers/CultureInfoParser.cs

@@ -0,0 +1,139 @@
+using System.Buffers;
+using System.Globalization;
+
+namespace GenHTTP.Modules.I18n.Parsers;
+
+public static class CultureInfoParser
+{
+    private static readonly Comparer<(string Language, double Quality)> QualityComparer =
+        Comparer<(string Language, double Quality)>.Create((a, b) => b.Quality.CompareTo(a.Quality));
+
+    /// <summary>
+    /// Parses the given language header (e.g. from Accept-Language) into an array of CultureInfo,
+    /// sorted by their quality values in descending order. If no valid languages are found,
+    /// returns an empty array.
+    /// 
+    /// Specification: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language
+    /// 
+    /// This implementation uses ArrayPool to minimize allocations.
+    /// </summary>
+    /// <param name="language">The language header string to parse.</param>
+    /// <returns>An array of <see cref="CultureInfo"/> objects parsed from the input string.</returns>
+    public static CultureInfo[] ParseFromLanguage(string? language)
+    {
+        if (string.IsNullOrWhiteSpace(language))
+        {
+            return [];
+        }
+
+        var span = language.AsSpan().Trim();
+        if (span.IsEmpty)
+        {
+            return [];
+        }
+
+        // Count how many segments (comma-delimited)
+        var count = 1;
+        for (int i = 0; i < span.Length; i++)
+        {
+            if (span[i] == ',') count++;
+        }
+
+        var pool = ArrayPool<(string Language, double Quality)>.Shared;
+        (string Language, double Quality)[] rentedArray = pool.Rent(count);
+
+        try
+        {
+            var actualCount = 0;
+            var start = 0;
+            int commaIndex;
+            do
+            {
+                commaIndex = span[start..].IndexOf(',');
+                ReadOnlySpan<char> segment;
+                if (commaIndex >= 0)
+                {
+                    segment = span.Slice(start, commaIndex).Trim();
+                    start += commaIndex + 1;
+                }
+                else
+                {
+                    segment = span[start..].Trim();
+                }
+
+                if (!segment.IsEmpty)
+                {
+                    // segment format: "lang[-region][;q=...]" or just "lang[-region]"
+                    var semicolonIndex = segment.IndexOf(';');
+                    var qValue = 1d;
+                    ReadOnlySpan<char> languagePart;
+
+                    if (semicolonIndex >= 0)
+                    {
+                        languagePart = segment[..semicolonIndex].Trim();
+                        var afterSemicolon = segment[(semicolonIndex + 1)..].Trim();
+
+                        // afterSemicolon should look like "q=0.5"
+                        if (afterSemicolon.StartsWith("q=", StringComparison.OrdinalIgnoreCase))
+                        {
+                            var qSpan = afterSemicolon[2..].Trim(); // skip 'q='
+                            if (!double.TryParse(qSpan, NumberStyles.Number, CultureInfo.InvariantCulture, out qValue))
+                            {
+                                qValue = 1;
+                            }
+                        }
+                    }
+                    else
+                    {
+                        languagePart = segment;
+                    }
+
+                    if (!languagePart.IsEmpty && actualCount < rentedArray.Length)
+                    {
+                        // Convert languagePart to string only once here
+                        rentedArray[actualCount++] = (languagePart.ToString(), qValue);
+                    }
+                }
+            } while (commaIndex >= 0);
+
+            if (actualCount == 0)
+            {
+                return [];
+            }
+
+            // Sort by quality descending
+            Array.Sort(rentedArray, 0, actualCount, QualityComparer);
+
+            // Convert to CultureInfo array and return rented array
+            List<CultureInfo> results = new(actualCount);
+
+            for (int i = 0; i < actualCount; i++)
+            {
+                var (lang, _) = rentedArray[i];
+                if (string.IsNullOrWhiteSpace(lang))
+                {
+                    continue;
+                }
+
+                try
+                { 
+                    var parsed = CultureInfo.CreateSpecificCulture(lang);
+                    if (parsed.LCID != CultureInfo.InvariantCulture.LCID)
+                    {
+                        results.Add(parsed);
+                    }
+                }
+                catch (CultureNotFoundException)
+                {
+                    // skip invalid cultures
+                }
+            }
+
+            return results.Count > 0 ? [.. results] : [];
+        }
+        finally
+        {
+            pool.Return(rentedArray);
+        }
+    }
+}

Modules/GenHTTP.Modules.I18n/Provider/LocalizationConcern.cs

@@ -0,0 +1,76 @@
+using GenHTTP.Api.Content;
+using GenHTTP.Api.Protocol;
+using System.Globalization;
+
+namespace GenHTTP.Modules.I18n.Provider;
+
+public sealed class LocalizationConcern : IConcern
+{
+    #region Get-/Setters
+
+    public IHandler Content { get; }
+
+    private readonly CultureInfo _defaultCulture;
+    private readonly CultureSelectorCombinedAsyncDelegate _cultureSelector;
+    private readonly CultureFilterAsyncDelegate _cultureFilter;
+    private readonly AsyncOrSyncSetter[] _cultureSetters;
+
+    #endregion
+
+    #region Initialization
+
+    public LocalizationConcern(
+        IHandler content,
+        CultureInfo defaultCulture,
+        CultureSelectorCombinedAsyncDelegate cultureSelector,
+        CultureFilterAsyncDelegate cultureFilter,
+        AsyncOrSyncSetter[] cultureSetters
+        )
+    {
+        Content = content;
+
+        _defaultCulture = defaultCulture;
+        _cultureSelector = cultureSelector;
+        _cultureFilter = cultureFilter;
+
+        _cultureSetters = cultureSetters;
+    }
+
+    #endregion
+
+    #region Functionality
+
+    public ValueTask PrepareAsync() => Content.PrepareAsync();
+
+    public async ValueTask<IResponse?> HandleAsync(IRequest request)
+    {
+        var culture = await ResolveCultureInfoAsync(request) ?? _defaultCulture;
+
+        foreach(var _cultureSetter in _cultureSetters)
+        {
+            _cultureSetter.SyncSetter?.Invoke(request, culture);
+
+            if (_cultureSetter.AsyncSetter != null)
+            {
+                await _cultureSetter.AsyncSetter(request, culture);
+            }
+        }
+
+        return await Content.HandleAsync(request);
+    }
+
+    private async ValueTask<CultureInfo?> ResolveCultureInfoAsync(IRequest request)
+    {
+        await foreach (var candidate in _cultureSelector(request))
+        {
+            if (await _cultureFilter(request, candidate))
+            {
+                return candidate;
+            }
+        }
+        return null;
+    }
+
+    #endregion
+
+}