feat: Add CSharp SDK

[FLI-783 - C# Server Side SDK](flipt-io#86)
- Add Authentication
- Add Evaluation (Boolean, Variant, and Batch)

Signed-off-by: vgwizardx <[email protected]>

.gitignore

@@ -19,3 +19,32 @@ Cargo.lock
 /flipt-python/.mypy_cache/
 /flipt-python/.pytest_cache/
 /flipt-python/.ruff_cache/
+
+# User-specific files
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+# Build results
+[Dd]ebug/
+[Dd]ebugPublic/
+[Rr]elease/
+x64/
+x86/
+bld/
+[Bb]in/
+[Oo]bj/
+[Ll]og/
+
+# Visual Studio 2015 cache/options directory
+.vs/
+
+# .NET Core
+project.lock.json
+project.fragment.lock.json
+artifacts/
+**/Properties/launchSettings.json
+
+# VS Code
+.vscode/

flipt-csharp/.editorconfig

@@ -0,0 +1,84 @@
+[*.cs]
+
+# IDE0290: Use primary constructor
+dotnet_diagnostic.IDE0290.severity = none
+csharp_indent_labels = one_less_than_current
+csharp_using_directive_placement = outside_namespace:silent
+csharp_prefer_simple_using_statement = true:suggestion
+csharp_prefer_braces = true:silent
+csharp_style_namespace_declarations = block_scoped:silent
+csharp_style_prefer_method_group_conversion = true:silent
+csharp_style_prefer_top_level_statements = true:silent
+csharp_style_prefer_primary_constructors = false:suggestion
+csharp_style_expression_bodied_methods = false:silent
+csharp_style_expression_bodied_constructors = false:silent
+csharp_style_expression_bodied_operators = false:silent
+csharp_style_expression_bodied_properties = true:silent
+csharp_style_expression_bodied_indexers = true:silent
+csharp_style_expression_bodied_accessors = true:silent
+csharp_style_expression_bodied_lambdas = true:silent
+csharp_style_expression_bodied_local_functions = false:silent
+csharp_space_around_binary_operators = before_and_after
+csharp_style_deconstructed_variable_declaration = true:suggestion
+csharp_style_allow_blank_lines_between_consecutive_braces_experimental = true:silent
+csharp_style_allow_blank_line_after_colon_in_constructor_initializer_experimental = true:silent
+csharp_style_allow_blank_line_after_token_in_conditional_expression_experimental = true:silent
+csharp_style_conditional_delegate_call = true:suggestion
+
+[*.{cs,vb}]
+#### Naming styles ####
+
+# Naming rules
+
+dotnet_naming_rule.interface_should_be_begins_with_i.severity = suggestion
+dotnet_naming_rule.interface_should_be_begins_with_i.symbols = interface
+dotnet_naming_rule.interface_should_be_begins_with_i.style = begins_with_i
+
+dotnet_naming_rule.types_should_be_pascal_case.severity = suggestion
+dotnet_naming_rule.types_should_be_pascal_case.symbols = types
+dotnet_naming_rule.types_should_be_pascal_case.style = pascal_case
+
+dotnet_naming_rule.non_field_members_should_be_pascal_case.severity = suggestion
+dotnet_naming_rule.non_field_members_should_be_pascal_case.symbols = non_field_members
+dotnet_naming_rule.non_field_members_should_be_pascal_case.style = pascal_case
+
+# Symbol specifications
+
+dotnet_naming_symbols.interface.applicable_kinds = interface
+dotnet_naming_symbols.interface.applicable_accessibilities = public, internal, private, protected, protected_internal, private_protected
+dotnet_naming_symbols.interface.required_modifiers = 
+
+dotnet_naming_symbols.types.applicable_kinds = class, struct, interface, enum
+dotnet_naming_symbols.types.applicable_accessibilities = public, internal, private, protected, protected_internal, private_protected
+dotnet_naming_symbols.types.required_modifiers = 
+
+dotnet_naming_symbols.non_field_members.applicable_kinds = property, event, method
+dotnet_naming_symbols.non_field_members.applicable_accessibilities = public, internal, private, protected, protected_internal, private_protected
+dotnet_naming_symbols.non_field_members.required_modifiers = 
+
+# Naming styles
+
+dotnet_naming_style.begins_with_i.required_prefix = I
+dotnet_naming_style.begins_with_i.required_suffix = 
+dotnet_naming_style.begins_with_i.word_separator = 
+dotnet_naming_style.begins_with_i.capitalization = pascal_case
+
+dotnet_naming_style.pascal_case.required_prefix = 
+dotnet_naming_style.pascal_case.required_suffix = 
+dotnet_naming_style.pascal_case.word_separator = 
+dotnet_naming_style.pascal_case.capitalization = pascal_case
+
+dotnet_naming_style.pascal_case.required_prefix = 
+dotnet_naming_style.pascal_case.required_suffix = 
+dotnet_naming_style.pascal_case.word_separator = 
+dotnet_naming_style.pascal_case.capitalization = pascal_case
+dotnet_style_operator_placement_when_wrapping = beginning_of_line
+tab_width = 4
+indent_size = 4
+end_of_line = crlf
+dotnet_style_coalesce_expression = true:suggestion
+dotnet_style_prefer_collection_expression = true:suggestion
+dotnet_style_collection_initializer = true:suggestion
+dotnet_style_prefer_conditional_expression_over_assignment = true:silent
+dotnet_style_prefer_conditional_expression_over_return = true:silent
+dotnet_style_prefer_compound_assignment = true:suggestion

flipt-csharp/flipt-csharp.sln

@@ -0,0 +1,27 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.8.34316.72
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "FliptCSharp", "src\FliptCSharp.csproj", "{5BAA5E95-A58B-4346-9C78-8076C81ED2D2}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{13F95778-A052-43D1-88B2-4AF06F7E1AC2}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{5BAA5E95-A58B-4346-9C78-8076C81ED2D2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{5BAA5E95-A58B-4346-9C78-8076C81ED2D2}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{5BAA5E95-A58B-4346-9C78-8076C81ED2D2}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{5BAA5E95-A58B-4346-9C78-8076C81ED2D2}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {35FFF068-2AD7-470B-88B0-A8254F952CD7}
+	EndGlobalSection
+EndGlobal

flipt-csharp/src/Authentication/ClientTokenAuthenticationStrategy.cs

@@ -0,0 +1,18 @@
+namespace FliptCSharp.Authentication;
+
+/// <summary>
+/// This class is responsible for providing the client token authentication strategy.
+/// </summary>
+public class ClientTokenAuthenticationStrategy : IAuthenticationStrategy
+{
+    private readonly string _clientToken;
+
+    public ClientTokenAuthenticationStrategy(string clientToken)
+    {
+        _clientToken = clientToken;
+    }
+    public string GetAuthorizationHeader()
+    {
+        return $"Bearer {_clientToken}";
+    }
+}

flipt-csharp/src/Authentication/IAuthenticationStrategy.cs

@@ -0,0 +1,9 @@
+namespace FliptCSharp.Authentication;
+
+/// <summary>
+/// This interface is responsible for providing the authentication strategy.
+/// </summary>
+public interface IAuthenticationStrategy
+{
+    string GetAuthorizationHeader();
+}

flipt-csharp/src/Authentication/JWTAuthenticationStrategy.cs

@@ -0,0 +1,19 @@
+namespace FliptCSharp.Authentication;
+
+/// <summary>
+/// This class is responsible for providing the JWT authentication strategy.
+/// </summary>
+public class JWTAuthenticationStrategy : IAuthenticationStrategy
+{
+    private readonly string _jwtToken;
+
+    public JWTAuthenticationStrategy(string jwtToken)
+    {
+        _jwtToken = jwtToken;
+    }
+
+    public string GetAuthorizationHeader()
+    {
+        return $"JWT {_jwtToken}";
+    }
+}

flipt-csharp/src/Clients/Evaluation.cs

@@ -0,0 +1,155 @@
+using System.Net.Http.Headers;
+using System.Text;
+using System.Text.Json;
+using FliptCSharp.Authentication;
+using FliptCSharp.DTOs;
+
+namespace FliptCSharp.Clients;
+/// <summary>
+/// This class is responsible for making requests to the Flipt server to evaluate flags.
+/// </summary>
+public class Evaluation 
+{
+        private readonly HttpClient _httpClient;
+        private readonly string _baseUrl;
+        private readonly IAuthenticationStrategy? _authenticationStrategy;
+        private readonly IDictionary<string, string>? _headers;
+
+        /// <summary>
+        /// This method creates a new instance of the Evaluation class.
+        /// </summary>
+        /// <param name="builder"></param>
+        private Evaluation(EvaluationBuilder builder)
+        {
+            _httpClient = builder.HttpClient;
+            _baseUrl = builder.BaseUrl;
+            _authenticationStrategy = builder.AuthenticationStrategy;
+            _headers = builder.Headers;
+        }
+
+        /// <summary>
+        /// This method returns a new instance of the EvaluationBuilder class.
+        /// </summary>
+        /// <returns></returns>
+        public static EvaluationBuilder Builder()
+        {
+            return new EvaluationBuilder();
+        }
+
+        /// <summary>
+        /// This class is a builder for the Evaluation class.
+        /// </summary>
+        public class EvaluationBuilder
+        {
+            public HttpClient HttpClient { get; private set; } = null!;
+            public string BaseUrl { get; private set; } = null!;
+            public IAuthenticationStrategy? AuthenticationStrategy { get; private set; }
+            public IDictionary<string, string>? Headers { get; private set; }
+
+            public EvaluationBuilder WithHttpClient(HttpClient httpClient)
+            {
+                HttpClient = httpClient;
+                return this;
+            }
+
+            public EvaluationBuilder WithBaseUrl(string baseUrl)
+            {
+                BaseUrl = baseUrl;
+                return this;
+            }
+
+            public EvaluationBuilder WithAuthenticationStrategy(IAuthenticationStrategy? authenticationStrategy)
+            {
+                AuthenticationStrategy = authenticationStrategy;
+                return this;
+            }
+
+            public EvaluationBuilder WithHeaders(IDictionary<string, string>? headers)
+            {
+                Headers = headers;
+                return this;
+            }
+
+            public Evaluation Build()
+            {
+                if (HttpClient == null)
+                {
+                    throw new InvalidOperationException("HttpClient must be provided.");
+                }
+
+                if (string.IsNullOrEmpty(BaseUrl))
+                {
+                    throw new InvalidOperationException("BaseURL must be provided.");
+                }
+
+                return new Evaluation(this);
+            }
+        }
+
+        /// <summary>
+        /// This method evaluates a variant for a given flag key and entity id.
+        /// </summary>
+        /// <param name="request"></param>
+        /// <returns></returns>
+        public async Task<VariantEvaluationResponse?> EvaluateVariantAsync(EvaluationRequest request)
+        {
+            return await EvaluateAsync<VariantEvaluationResponse>("/evaluate/v1/variant", request);
+        }
+
+        /// <summary>
+        /// This method evaluates a boolean flag for a given flag key and entity id.
+        /// </summary>
+        /// <param name="request"></param>
+        /// <returns></returns>
+        public async Task<BooleanEvaluationResponse?> EvaluateBooleanAsync(EvaluationRequest request)
+        {
+            return await EvaluateAsync<BooleanEvaluationResponse>("/evaluate/v1/boolean", request);
+        }
+
+        /// <summary>
+        /// This method evaluates a batch of flags for a given flag key and entity id.
+        /// </summary>
+        /// <param name="request"></param>
+        /// <returns></returns>
+        public async Task<BatchEvaluationResponse?> EvaluateBatchAsync(BatchEvaluationRequest request)
+        {
+            return await EvaluateAsync<BatchEvaluationResponse>("/evaluate/v1/batch", request);
+        }
+
+        /// <summary>
+        /// This method evaluates a flag for a given flag key and entity id.
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="path"></param>
+        /// <param name="request"></param>
+        /// <returns></returns>
+        private async Task<T?> EvaluateAsync<T>(string path, object request)
+        {
+            var url = new Uri(new Uri(_baseUrl), path);
+
+            var jsonContent = JsonSerializer.Serialize(request);
+            var content = new StringContent(jsonContent, Encoding.UTF8, "application/json");
+
+            var httpRequest = new HttpRequestMessage(HttpMethod.Post, url)
+            {
+                Content = content
+            };
+
+            if (_headers != null)
+                foreach (var header in _headers)
+                {
+                    httpRequest.Headers.Add(header.Key, header.Value);
+                }
+
+            if (_authenticationStrategy != null)
+                httpRequest.Headers.Authorization =
+                    new AuthenticationHeaderValue("Bearer", _authenticationStrategy.GetAuthorizationHeader());
+
+            var response = await _httpClient.SendAsync(httpRequest);
+            response.EnsureSuccessStatusCode();
+
+            var responseContent = await response.Content.ReadAsStringAsync();
+            return string.IsNullOrEmpty(responseContent) ? default : JsonSerializer.Deserialize<T>(responseContent);
+        }
+
+}

flipt-csharp/src/DTOs/BatchEvaluationRequest.cs

@@ -0,0 +1,19 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace FliptCSharp.DTOs;
+
+/// <summary>
+/// Represents a batch evaluation request.
+/// </summary>
+public class BatchEvaluationRequest
+{
+    public BatchEvaluationRequest(List<EvaluationRequest> evaluationRequests)
+    {
+        EvaluationRequests = evaluationRequests;
+    }
+    public string? RequestId { get; set; }
+
+    [Required]
+    public List<EvaluationRequest> EvaluationRequests { get; set; }
+    public string? Reference { get; set; }
+}