Add MicCheck.Client library with FeatureClient.IsEnabledAsync

Client-side SDK for checking feature flag state against the flags API,
with unit tests mocking HttpMessageHandler.

MicCheck.slnx

@@ -12,10 +12,12 @@
     </Project>
     <Project Path="src/api/MicCheck.Api/MicCheck.Api.csproj" />
     <Project Path="src/MicCheck.AppHost/MicCheck.AppHost.csproj" />
+    <Project Path="src/MicCheck.Client/MicCheck.Client.csproj" />
     <Project Path="src/MicCheck.ServiceDefaults/MicCheck.ServiceDefaults.csproj" />
   </Folder>
   <Folder Name="/tests/">
     <Project Path="tests/api/MicCheck.Api.Tests.Unit/MicCheck.Api.Tests.Unit.csproj" />
     <Project Path="tests/api/MicCheck.Api.Tests.Integration/MicCheck.Api.Tests.Integration.csproj" />
+    <Project Path="tests/client/MicCheck.Client.Tests.Unit/MicCheck.Client.Tests.Unit.csproj" />
   </Folder>
 </Solution>

src/MicCheck.Client/Common/Guard.cs

@@ -0,0 +1,40 @@
+namespace MicCheck.Common;
+
+internal static class Guard
+{
+    public static void Null<T>(T t, string parameterName) where T : class
+    {
+        if (t is null)
+            throw new ArgumentNullException(parameterName, $"{nameof(parameterName)} can not be null");
+    }
+
+    public static void Empty(string value, string parameterName)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+            throw new ArgumentException($"{parameterName} can not be empty", parameterName);
+    }
+
+    public static void Empty<T>(IEnumerable<T> collection, string parameterName)
+    {
+        if (collection == null || !collection.Any())
+            throw new ArgumentException($"{parameterName} can not be empty", parameterName);
+    }
+
+    public static void Negative(int value, string parameterName)
+    {
+        if (value < 0)
+            throw new ArgumentOutOfRangeException(parameterName, $"{parameterName} must be a positive number or zero");
+    }
+
+    public static void NegativeOrZero(int value, string parameterName)
+    {
+        if (value <= 0)
+            throw new ArgumentOutOfRangeException(parameterName, $"{nameof(parameterName)} must be a positive number greater then zero");
+    }
+
+    public static void Default<T>(T value, string parameterName)
+    {
+        if (EqualityComparer<T>.Default.Equals(value, default))
+            throw new ArgumentException($"{parameterName} can not be a default value", parameterName);
+    }
+}

src/MicCheck.Client/FeatureClient.cs

@@ -0,0 +1,22 @@
+using System.Net.Http.Json;
+using MicCheck.Common;
+
+namespace MicCheck;
+
+public class FeatureClient(HttpClient httpClient) : IFeatureClient
+{
+    public async Task<bool> IsEnabledAsync(string featureName, bool defaultValue = false, CancellationToken cancellationToken = default)
+    {
+        Guard.Empty(featureName, nameof(featureName));
+
+        var flags = await httpClient.GetFromJsonAsync<List<FlagResult>>("api/v1/flags", cancellationToken);
+        var match = flags?.FirstOrDefault(flag => string.Equals(flag.Feature.Name, featureName, StringComparison.OrdinalIgnoreCase));
+
+        return match?.Enabled ?? defaultValue;
+    }
+}
+
+public interface IFeatureClient
+{
+    Task<bool> IsEnabledAsync(string featureName, bool defaultValue = false, CancellationToken cancellationToken = default);
+}

src/MicCheck.Client/FlagResult.cs

@@ -0,0 +1,5 @@
+namespace MicCheck;
+
+public record FlagResult(int Id, FeatureSummary Feature, bool Enabled, string? FeatureStateValue);
+
+public record FeatureSummary(int Id, string Name, string Type);

src/MicCheck.Client/MicCheck.Client.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <LangVersion>latest</LangVersion>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <RootNamespace>MicCheck</RootNamespace>
+  </PropertyGroup>
+
+</Project>

tests/client/MicCheck.Client.Tests.Unit/FeatureClientTests.cs

@@ -0,0 +1,79 @@
+using System.Net;
+using System.Text;
+using Moq;
+using Moq.Protected;
+using NUnit.Framework;
+
+namespace MicCheck.Client.Tests.Unit;
+
+[TestFixture]
+public class FeatureClientTests
+{
+    [Test]
+    public async Task WhenFeatureIsEnabled_ThenIsEnabledAsyncReturnsTrue()
+    {
+        var client = CreateClient(HttpStatusCode.OK, """
+            [{"id":1,"feature":{"id":1,"name":"my-feature","type":"STANDARD"},"enabled":true,"featureStateValue":null}]
+            """);
+
+        var result = await client.IsEnabledAsync("my-feature");
+
+        Assert.That(result, Is.True);
+    }
+
+    [Test]
+    public async Task WhenFeatureIsDisabled_ThenIsEnabledAsyncReturnsFalse()
+    {
+        var client = CreateClient(HttpStatusCode.OK, """
+            [{"id":1,"feature":{"id":1,"name":"my-feature","type":"STANDARD"},"enabled":false,"featureStateValue":null}]
+            """);
+
+        var result = await client.IsEnabledAsync("my-feature");
+
+        Assert.That(result, Is.False);
+    }
+
+    [Test]
+    public async Task WhenFeatureNameDiffersOnlyByCase_ThenIsEnabledAsyncStillMatches()
+    {
+        var client = CreateClient(HttpStatusCode.OK, """
+            [{"id":1,"feature":{"id":1,"name":"My-Feature","type":"STANDARD"},"enabled":true,"featureStateValue":null}]
+            """);
+
+        var result = await client.IsEnabledAsync("my-feature");
+
+        Assert.That(result, Is.True);
+    }
+
+    [Test]
+    public async Task WhenFeatureIsNotFound_ThenIsEnabledAsyncReturnsProvidedDefaultValue()
+    {
+        var client = CreateClient(HttpStatusCode.OK, "[]");
+
+        var result = await client.IsEnabledAsync("missing-feature", defaultValue: true);
+
+        Assert.That(result, Is.True);
+    }
+
+    [Test]
+    public void WhenFeatureNameIsEmpty_ThenIsEnabledAsyncThrowsArgumentException()
+    {
+        var client = CreateClient(HttpStatusCode.OK, "[]");
+
+        Assert.That(async () => await client.IsEnabledAsync(" "), Throws.ArgumentException);
+    }
+
+    private static FeatureClient CreateClient(HttpStatusCode responseStatus, string responseBody)
+    {
+        var handler = new Mock<HttpMessageHandler>();
+        handler.Protected()
+            .Setup<Task<HttpResponseMessage>>("SendAsync", ItExpr.IsAny<HttpRequestMessage>(), ItExpr.IsAny<CancellationToken>())
+            .ReturnsAsync(new HttpResponseMessage(responseStatus)
+            {
+                Content = new StringContent(responseBody, Encoding.UTF8, "application/json")
+            });
+
+        var httpClient = new HttpClient(handler.Object) { BaseAddress = new Uri("https://example.com") };
+        return new FeatureClient(httpClient);
+    }
+}

tests/client/MicCheck.Client.Tests.Unit/MicCheck.Client.Tests.Unit.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <LangVersion>latest</LangVersion>
+    <IsPackable>false</IsPackable>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="NUnit" Version="4.5.1" />
+    <PackageReference Include="NUnit3TestAdapter" Version="6.2.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../../../src/MicCheck.Client/MicCheck.Client.csproj" />
+  </ItemGroup>
+
+</Project>