feat: implement in-memory provider (#232)

Implements in-memory provider as per spec, updates gherkin to use spec
version, removes flagd deps.

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>
Co-authored-by: Joris Goovaerts <1333336+CommCody@users.noreply.github.com>
Co-authored-by: André Silva <2493377+askpt@users.noreply.github.com>

.github/workflows/e2e.yml

@@ -13,11 +13,6 @@ on:
 jobs:
   e2e-tests:
     runs-on: ubuntu-latest
-    services:
-      flagd:
-        image: ghcr.io/open-feature/flagd-testbed:latest
-        ports:
-          - 8013:8013
     steps:
     - uses: actions/checkout@v4
       with:
@@ -36,7 +31,7 @@ jobs:
     - name: Initialize Tests
       run: |
         git submodule update --init --recursive
-        cp test-harness/features/evaluation.feature test/OpenFeature.E2ETests/Features/
+        cp spec/specification/assets/gherkin/evaluation.feature test/OpenFeature.E2ETests/Features/
 
     - name: Run Tests
       run: dotnet test test/OpenFeature.E2ETests/ --configuration Release --logger GitHubActions

.gitmodules

@@ -1,3 +1,3 @@
-[submodule "test-harness"]
-	path = test-harness
-	url = https://github.com/open-feature/test-harness.git
+[submodule "spec"]
+	path = spec
+	url = https://github.com/open-feature/spec.git

CONTRIBUTING.md

@@ -67,12 +67,6 @@ To be able to run the e2e tests, first we need to initialize the submodule and c
 git submodule update --init --recursive && cp test-harness/features/evaluation.feature test/OpenFeature.E2ETests/Features/
 ```
 
-Afterwards, you need to start flagd locally:
-
-```bash
-docker run -p 8013:8013 ghcr.io/open-feature/flagd-testbed:latest
-```
-
 Now you can run the tests using:
 
 ```bash

Directory.Packages.props

@@ -20,7 +20,6 @@
     <PackageVersion Include="GitHubActionsTestLogger" Version="2.3.3" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
     <PackageVersion Include="NSubstitute" Version="5.1.0" />
-    <PackageVersion Include="OpenFeature.Contrib.Providers.Flagd" Version="0.1.8" />
     <PackageVersion Include="SpecFlow" Version="3.9.74" />
     <PackageVersion Include="SpecFlow.Tools.MsBuild.Generation" Version="3.9.74" />
     <PackageVersion Include="SpecFlow.xUnit" Version="3.9.74" />

src/OpenFeature/Providers/Memory/Flag.cs

@@ -0,0 +1,78 @@
+using System;
+using System.Collections.Generic;
+using OpenFeature.Constant;
+using OpenFeature.Error;
+using OpenFeature.Model;
+
+#nullable enable
+namespace OpenFeature.Providers.Memory
+{
+    /// <summary>
+    /// Flag representation for the in-memory provider.
+    /// </summary>
+    public interface Flag
+    {
+
+    }
+
+    /// <summary>
+    /// Flag representation for the in-memory provider.
+    /// </summary>
+    public sealed class Flag<T> : Flag
+    {
+        private Dictionary<string, T> Variants;
+        private string DefaultVariant;
+        private Func<EvaluationContext, string>? ContextEvaluator;
+
+        /// <summary>
+        /// Flag representation for the in-memory provider.
+        /// </summary>
+        /// <param name="variants">dictionary of variants and their corresponding values</param>
+        /// <param name="defaultVariant">default variant (should match 1 key in variants dictionary)</param>
+        /// <param name="contextEvaluator">optional context-sensitive evaluation function</param>
+        public Flag(Dictionary<string, T> variants, string defaultVariant, Func<EvaluationContext, string>? contextEvaluator = null)
+        {
+            this.Variants = variants;
+            this.DefaultVariant = defaultVariant;
+            this.ContextEvaluator = contextEvaluator;
+        }
+
+        internal ResolutionDetails<T> Evaluate(string flagKey, T _, EvaluationContext? evaluationContext)
+        {
+            T? value = default;
+            if (this.ContextEvaluator == null)
+            {
+                if (this.Variants.TryGetValue(this.DefaultVariant, out value))
+                {
+                    return new ResolutionDetails<T>(
+                        flagKey,
+                        value,
+                        variant: this.DefaultVariant,
+                        reason: Reason.Static
+                    );
+                }
+                else
+                {
+                    throw new GeneralException($"variant {this.DefaultVariant} not found");
+                }
+            }
+            else
+            {
+                var variant = this.ContextEvaluator.Invoke(evaluationContext ?? EvaluationContext.Empty);
+                if (!this.Variants.TryGetValue(variant, out value))
+                {
+                    throw new GeneralException($"variant {variant} not found");
+                }
+                else
+                {
+                    return new ResolutionDetails<T>(
+                        flagKey,
+                        value,
+                        variant: variant,
+                        reason: Reason.TargetingMatch
+                    );
+                }
+            }
+        }
+    }
+}

src/OpenFeature/Providers/Memory/InMemoryProvider.cs

@@ -0,0 +1,139 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+using System.Threading.Tasks;
+using OpenFeature.Constant;
+using OpenFeature.Error;
+using OpenFeature.Model;
+
+#nullable enable
+namespace OpenFeature.Providers.Memory
+{
+    /// <summary>
+    /// The in memory provider.
+    /// Useful for testing and demonstration purposes.
+    /// </summary>
+    /// <seealso href="https://openfeature.dev/specification/appendix-a#in-memory-provider">In Memory Provider specification</seealso>
+    public class InMemoryProvider : FeatureProvider
+    {
+
+        private readonly Metadata _metadata = new Metadata("InMemory");
+
+        private Dictionary<string, Flag> _flags;
+
+        /// <inheritdoc/>
+        public override Metadata GetMetadata()
+        {
+            return this._metadata;
+        }
+
+        /// <summary>
+        /// Construct a new InMemoryProvider.
+        /// </summary>
+        /// <param name="flags">dictionary of Flags</param>
+        public InMemoryProvider(IDictionary<string, Flag>? flags = null)
+        {
+            if (flags == null)
+            {
+                this._flags = new Dictionary<string, Flag>();
+            }
+            else
+            {
+                this._flags = new Dictionary<string, Flag>(flags); // shallow copy
+            }
+        }
+
+        /// <summary>
+        /// Updating provider flags configuration, replacing all flags.
+        /// </summary>
+        /// <param name="flags">the flags to use instead of the previous flags.</param>
+        public async ValueTask UpdateFlags(IDictionary<string, Flag>? flags = null)
+        {
+            var changed = this._flags.Keys.ToList();
+            if (flags == null)
+            {
+                this._flags = new Dictionary<string, Flag>();
+            }
+            else
+            {
+                this._flags = new Dictionary<string, Flag>(flags); // shallow copy
+            }
+            changed.AddRange(this._flags.Keys.ToList());
+            var @event = new ProviderEventPayload
+            {
+                Type = ProviderEventTypes.ProviderConfigurationChanged,
+                ProviderName = _metadata.Name,
+                FlagsChanged = changed, // emit all
+                Message = "flags changed",
+            };
+            await this.EventChannel.Writer.WriteAsync(@event).ConfigureAwait(false);
+        }
+
+        /// <inheritdoc/>
+        public override Task<ResolutionDetails<bool>> ResolveBooleanValue(
+            string flagKey,
+            bool defaultValue,
+            EvaluationContext? context = null)
+        {
+            return Task.FromResult(Resolve(flagKey, defaultValue, context));
+        }
+
+        /// <inheritdoc/>
+        public override Task<ResolutionDetails<string>> ResolveStringValue(
+            string flagKey,
+            string defaultValue,
+            EvaluationContext? context = null)
+        {
+            return Task.FromResult(Resolve(flagKey, defaultValue, context));
+        }
+
+        /// <inheritdoc/>
+        public override Task<ResolutionDetails<int>> ResolveIntegerValue(
+            string flagKey,
+            int defaultValue,
+            EvaluationContext? context = null)
+        {
+            return Task.FromResult(Resolve(flagKey, defaultValue, context));
+        }
+
+        /// <inheritdoc/>
+        public override Task<ResolutionDetails<double>> ResolveDoubleValue(
+            string flagKey,
+            double defaultValue,
+            EvaluationContext? context = null)
+        {
+            return Task.FromResult(Resolve(flagKey, defaultValue, context));
+        }
+
+        /// <inheritdoc/>
+        public override Task<ResolutionDetails<Value>> ResolveStructureValue(
+            string flagKey,
+            Value defaultValue,
+            EvaluationContext? context = null)
+        {
+            return Task.FromResult(Resolve(flagKey, defaultValue, context));
+        }
+
+        private ResolutionDetails<T> Resolve<T>(string flagKey, T defaultValue, EvaluationContext? context)
+        {
+            if (!this._flags.TryGetValue(flagKey, out var flag))
+            {
+                throw new FlagNotFoundException($"flag {flagKey} not found");
+            }
+            else
+            {
+                // This check returns False if a floating point flag is evaluated as an integer flag, and vice-versa.
+                // In a production provider, such behavior is probably not desirable; consider supporting conversion.
+                if (typeof(Flag<T>).Equals(flag.GetType()))
+                {
+                    return ((Flag<T>)flag).Evaluate(flagKey, defaultValue, context);
+                }
+                else
+                {
+                    throw new TypeMismatchException($"flag {flagKey} is not of type ${typeof(T)}");
+                }
+            }
+        }
+    }
+}

test/OpenFeature.E2ETests/OpenFeature.E2ETests.csproj

@@ -16,7 +16,6 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="OpenFeature.Contrib.Providers.Flagd" />
     <PackageReference Include="SpecFlow" />
     <PackageReference Include="SpecFlow.Tools.MsBuild.Generation" />
     <PackageReference Include="SpecFlow.xUnit" />