#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 functional manner.</Description>
+		<PackageTags>HTTP Webserver C# Module Functional Inline Request Response</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 +1,18 @@
+using System.Globalization;
+
+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/LocalizationConcern.cs

@@ -0,0 +1,57 @@
+using GenHTTP.Api.Content;
+using GenHTTP.Api.Protocol;
+using System.Globalization;
+
+namespace GenHTTP.Modules.I18n;
+
+public sealed class LocalizationConcern : IConcern
+{
+    #region Get-/Setters
+
+    public IHandler Content { get; }
+
+    private readonly CultureInfo _defaultCulture;
+    private readonly CultureSelector_Delegate _cultureSelector;
+    private readonly CultureFilter_Delegate _cultureFilter;
+    private readonly CultureSetter_Delegate _cultureSetter;
+
+    #endregion
+
+    #region Initialization
+
+    public LocalizationConcern(
+        IHandler content,
+        CultureInfo defaultCulture,
+        CultureSelector_Delegate cultureSelector,
+        CultureFilter_Delegate cultureFilter,
+        CultureSetter_Delegate cultureSetter
+        )
+    {
+        Content = content;
+
+        _defaultCulture = defaultCulture;
+        _cultureSelector = cultureSelector;        
+        _cultureFilter = cultureFilter;
+
+        _cultureSetter = cultureSetter;
+    }
+
+    #endregion
+
+    #region Functionality
+
+    public async ValueTask<IResponse?> HandleAsync(IRequest request)
+    {
+        var culture = (_cultureSelector(request) ?? [])
+            .FirstOrDefault(c => _cultureFilter(request, c))
+            ?? _defaultCulture;
+
+        _cultureSetter(request, culture);
+
+        return await Content.HandleAsync(request);
+    }
+
+    public ValueTask PrepareAsync() => Content.PrepareAsync();
+
+    #endregion
+}

Modules/GenHTTP.Modules.I18n/LocalizationConcernBuilder.cs

@@ -0,0 +1,162 @@
+using GenHTTP.Api.Content;
+using GenHTTP.Api.Protocol;
+using GenHTTP.Modules.I18n.Parsers;
+using System.Globalization;
+
+namespace GenHTTP.Modules.I18n;
+
+/// <summary>
+/// Builder class to configure and create an instance of <see cref="LocalizationConcern"/>.
+/// </summary>
+public sealed class LocalizationConcernBuilder : IConcernBuilder
+{
+    #region Fields
+
+    private CultureInfo _defaultCulture = CultureInfo.CurrentCulture;
+
+    private readonly List<CultureSelector_Delegate> _cultureSelectors = [];
+    private CultureFilter_Delegate _cultureFilter = (_, _) => true;
+    private readonly List<CultureSetter_Delegate> _cultureSetters = [];
+
+    #endregion
+
+    #region Functionality
+
+    #region Selectors
+
+    public LocalizationConcernBuilder AddFromCookie(string cookieName = "lang")
+        => AddFromLanguage(request =>
+        {
+            if (request.Cookies.TryGetValue(cookieName, out var languageCookie))
+            {
+                return languageCookie.Value;
+            }
+            return null;
+        });
+
+    public LocalizationConcernBuilder AddFromQuery(string queryName = "lang")
+        => AddFromLanguage(request =>
+        {
+            if (request.Query.TryGetValue(queryName, out var language))
+            {
+                return language;
+            }
+            return null;
+        });
+
+    public LocalizationConcernBuilder AddFromHeader(string headerName = "Accept-Language")
+        => AddFromLanguage(request =>
+        {
+            request.Headers.TryGetValue(headerName, out var language);
+            return language;
+        });
+
+    public LocalizationConcernBuilder AddFromLanguage(Func<IRequest, string?> languageSelector)
+        => AddFromRequest(request =>
+        {
+            var language = languageSelector(request);
+            return CultureInfoParser.ParseFromLanguage(language);
+        });
+
+    public LocalizationConcernBuilder AddFromRequest(CultureSelector_Delegate cultureSelector)
+    {
+        _cultureSelectors.Add(cultureSelector);
+        return this;
+    }
+
+    #endregion
+
+    #region Filters
+
+    public LocalizationConcernBuilder Supports(params CultureInfo[] supportedCultures)
+    {
+        var closure = supportedCultures.ToHashSet();
+        return Supports(closure.Contains);
+    }
+
+    public LocalizationConcernBuilder Supports(Predicate<CultureInfo> culturePredicate)
+        => Supports((_, culture) => culturePredicate(culture));
+
+    public LocalizationConcernBuilder Supports(CultureFilter_Delegate cultureFilter)
+    {
+        _cultureFilter = cultureFilter;
+        return this;
+    }
+
+    #endregion
+
+    #region Setters
+
+    public LocalizationConcernBuilder AddSet(bool currentCulture = false, bool currentUICulture = true)
+    {
+        //Note: this is a minor optimization so that the flags are not evaluated for each request
+        if (currentCulture)
+        {
+            AddSet(culture => CultureInfo.CurrentCulture = culture);
+        }
+        if (currentUICulture)
+        {
+            AddSet(culture => CultureInfo.CurrentUICulture = culture);
+        }
+        return this;
+    }
+
+    public LocalizationConcernBuilder AddSet(Action<CultureInfo> cultureSetter)
+        => AddSet((_, culture) => cultureSetter(culture));
+
+    public LocalizationConcernBuilder AddSet(CultureSetter_Delegate cultureSetter)
+    {
+        _cultureSetters.Add(cultureSetter);
+        return this;
+    }
+
+    #endregion
+
+    #region Default
+
+    public LocalizationConcernBuilder Default(CultureInfo culture)
+    {
+        _defaultCulture = culture;
+        return this;
+    }
+
+    #endregion
+
+    public IConcern Build(IHandler content)
+    {
+        if (_cultureSelectors.Count == 0)
+        {
+            AddFromHeader();
+        }
+
+        if (_cultureSetters.Count == 0)
+        {
+            AddSet();
+        }
+
+        return new LocalizationConcern(
+            content, 
+            _defaultCulture,
+            CultureSelector,
+            _cultureFilter, 
+            CultureSetter
+            );
+    }
+
+    #endregion
+
+    #region Composite functions
+
+    private IEnumerable<CultureInfo> CultureSelector(IRequest request)
+        => _cultureSelectors.SelectMany(selector => selector(request));   
+
+    private void CultureSetter(IRequest request, CultureInfo cultureInfo)
+    {
+        foreach (var setter in _cultureSetters)
+        {
+            setter(request, cultureInfo);
+        }
+    }
+
+    #endregion
+}

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

@@ -0,0 +1,28 @@
+using System.Globalization;
+
+namespace GenHTTP.Modules.I18n.Parsers;
+
+public static class CultureInfoParser
+{
+    public static CultureInfo[] ParseFromLanguage(string? language)
+        => Parse(LanguageParser.ParseAcceptLanguageHeader(language));
+
+    public static CultureInfo[] Parse(IEnumerable<string> languages)
+        => languages
+            .Select(Parse)
+            .Where(culture => culture != null)
+            .Select(culture => culture!)
+            .ToArray();
+
+    private static CultureInfo? Parse(string name)
+    {
+        try
+        {
+            return CultureInfo.CreateSpecificCulture(name);
+        }
+        catch (CultureNotFoundException)
+        {
+            return null;
+        }
+    }
+}