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feat(dotnet): add .NET WASM evaluator package (#107)
## Summary - Adds a .NET 8.0 package (`dotnet/`) wrapping the Rust WASM evaluator using **Wasmtime for .NET v34.0.2** - Implements the same optimized architecture as Java/Go packages: WASM instance pool, lock-free pre-evaluated cache, context key filtering, index-based evaluation, and generation guard - Includes 17 xunit tests (all passing), BenchmarkDotNet suite with evaluation + comparison benchmarks, Makefile, and README ## Architecture - **WASM Instance Pool**: `BlockingCollection<WasmInstance>` sized to `ProcessorCount` for parallel evaluation - **Pre-evaluated Cache**: Static/disabled flags served lock-free via `volatile` reference swap (13 ns, zero alloc) - **Context Key Filtering**: Only serialize context keys referenced in targeting rules - **Index-based Evaluation**: `evaluate_by_index(u32)` avoids flag key string serialization - **Generation Guard**: Detects stale cache snapshots during concurrent UpdateState/EvaluateFlag - **Prefix-based Host Function Matching**: Survives wasm-bindgen hash suffix changes across WASM rebuilds ## Comparison: WASM vs Old JsonLogic Provider (json-everything v5.4.0) | Scenario | Old (JsonLogic) | New (WASM) | Speedup | Memory | |----------|-----------------|------------|---------|--------| | Simple flag (pre-eval) | 38 ns / 72 B | **13 ns / 0 B** | **2.9x** | **100% less** | | Targeting (small ctx) | 6,993 ns / 7,120 B | **5,082 ns / 592 B** | **1.4x** | **12x less** | | Targeting (empty ctx) | 3,440 ns / 3,768 B | **2,669 ns / 288 B** | **1.3x** | **13x less** | | Targeting (large ctx, 100+ attrs) | 32,881 ns / 33,448 B | **5,328 ns / 592 B** | **6.2x** | **56x less** | | 8-thread large ctx | 229,529 ns / 268 KB | **105,425 ns / 5.6 KB** | **2.2x** | **48x less** | Context key filtering gives the biggest win: with 100+ attributes, the old provider serializes everything (33 KB allocations), while the WASM evaluator only serializes the 2 keys referenced in targeting rules (592 B). ## Standalone Evaluation Benchmarks | Benchmark | Mean | Allocated | |-----------|------|-----------| | PreEvaluated (static flag) | 12.5 ns | 0 B | | SimpleTargeting SmallCtx | 4.67 µs | 568 B | | SimpleTargeting LargeCtx | 4.30 µs | 568 B | | ComplexTargeting SmallCtx | 5.65 µs | 584 B | | ComplexTargeting LargeCtx | 5.87 µs | 584 B | ## Test plan - [x] 17 xunit tests passing (bool/string/numeric flags, targeting, concurrency, generation guard, pool size 1) - [x] BenchmarkDotNet evaluation + comparison suites run successfully - [ ] Verify `make wasm && make build && make test` from clean checkout Closes #105 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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‎dotnet/.gitignore‎

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bin/
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obj/
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*.wasm
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BenchmarkDotNet.Artifacts/

‎dotnet/Makefile‎

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WASM_SRC := ../target/wasm32-unknown-unknown/release/flagd_evaluator.wasm
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WASM_DST := src/FlagdEvaluator/flagd_evaluator.wasm
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.PHONY: wasm build test bench clean
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wasm:
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cargo build --manifest-path ../Cargo.toml --target wasm32-unknown-unknown --no-default-features --release --lib
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cp $(WASM_SRC) $(WASM_DST)
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build:
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dotnet build dotnet.sln -c Release
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test:
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dotnet test dotnet.sln -c Release --logger "console;verbosity=detailed"
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bench:
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dotnet run --project benchmarks/FlagdEvaluator.Benchmarks/FlagdEvaluator.Benchmarks.csproj -c Release
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clean:
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dotnet clean dotnet.sln
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rm -rf src/FlagdEvaluator/bin src/FlagdEvaluator/obj
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rm -rf tests/FlagdEvaluator.Tests/bin tests/FlagdEvaluator.Tests/obj
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rm -rf benchmarks/FlagdEvaluator.Benchmarks/bin benchmarks/FlagdEvaluator.Benchmarks/obj

‎dotnet/README.md‎

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# flagd-evaluator .NET
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.NET wrapper for the flagd-evaluator WASM module. Provides high-performance feature flag evaluation using a pool of Wasmtime WASM instances with lock-free pre-evaluated caching and context key filtering.
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## Requirements
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- .NET 8.0 SDK
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- Rust toolchain with `wasm32-unknown-unknown` target (for building WASM from source)
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## Quick Start
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```csharp
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using FlagdEvaluator;
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// Create evaluator (pool size defaults to Environment.ProcessorCount)
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using var evaluator = new FlagEvaluator();
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// Load flag configuration
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var result = evaluator.UpdateState("""
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{
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"flags": {
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"my-flag": {
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"state": "ENABLED",
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"defaultVariant": "on",
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"variants": { "on": true, "off": false },
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"targeting": {
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"if": [
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{ "==": [{ "var": "email" }, "admin@example.com"] },
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"on", "off"
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]
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}
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}
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}
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}
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""");
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// Evaluate with context
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var context = new Dictionary<string, object?> { ["email"] = "admin@example.com" };
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var eval = evaluator.EvaluateFlag("my-flag", context);
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// eval.Value = true, eval.Variant = "on", eval.Reason = "TARGETING_MATCH"
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// Typed convenience methods (return default on error)
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bool value = evaluator.EvaluateBool("my-flag", context, defaultValue: false);
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```
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## API Reference
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### `FlagEvaluator`
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| Method | Description |
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|--------|-------------|
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| `FlagEvaluator(FlagEvaluatorOptions?)` | Create evaluator with optional configuration |
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| `UpdateState(string configJson)` | Update flag configuration across all instances |
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| `EvaluateFlag(string flagKey, Dictionary<string, object?>?)` | Evaluate a flag, returns full `EvaluationResult` |
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| `EvaluateBool(flagKey, context, defaultValue)` | Evaluate boolean flag with default fallback |
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| `EvaluateString(flagKey, context, defaultValue)` | Evaluate string flag with default fallback |
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| `EvaluateInt(flagKey, context, defaultValue)` | Evaluate integer flag with default fallback |
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| `EvaluateDouble(flagKey, context, defaultValue)` | Evaluate double flag with default fallback |
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| `PoolSize` | Number of WASM instances |
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| `Dispose()` | Release all resources |
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### `FlagEvaluatorOptions`
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| Property | Default | Description |
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|----------|---------|-------------|
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| `PoolSize` | `Environment.ProcessorCount` | Number of WASM instances for parallel evaluation |
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| `PermissiveValidation` | `false` | Accept invalid configs with warnings instead of rejecting |
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### `EvaluationResult`
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| Property | Type | Description |
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|----------|------|-------------|
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| `Value` | `JsonElement?` | The resolved flag value |
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| `Variant` | `string` | The variant name |
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| `Reason` | `string` | `STATIC`, `DEFAULT`, `TARGETING_MATCH`, `DISABLED`, `ERROR`, `FLAG_NOT_FOUND` |
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| `ErrorCode` | `string?` | Error code if evaluation failed |
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| `ErrorMessage` | `string?` | Error description |
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| `FlagMetadata` | `Dictionary<string, JsonElement>?` | Flag metadata |
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| `IsError` | `bool` | True if evaluation resulted in an error |
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## Build & Test
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```bash
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cd dotnet
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# Build WASM from Rust source
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make wasm
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# Build .NET solution
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make build
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# Run tests
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make test
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# Run benchmarks
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make bench
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```
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## Architecture
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- **WASM Instance Pool**: `BlockingCollection<WasmInstance>` sized to `ProcessorCount` for parallel evaluation
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- **Pre-evaluated Cache**: Static/disabled flags served lock-free via `volatile` reference swap
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- **Context Key Filtering**: Only serialize context keys referenced in targeting rules (32-34x speedup for large contexts)
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- **Index-based Evaluation**: `evaluate_by_index(u32)` avoids flag key string serialization
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- **Generation Guard**: Detects stale cache snapshots when `UpdateState` races with `EvaluateFlag`
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- **Pre-allocated Buffers**: Each instance pre-allocates 256B (flag key) + 1MB (context) buffers in WASM memory
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## Thread Safety
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`FlagEvaluator` is fully thread-safe:
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- `UpdateState()` serialized via lock; drains all pool instances, updates in parallel, swaps cache atomically
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- `EvaluateFlag()` acquires a pool instance, evaluates, returns it — concurrent up to pool size
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- Pre-evaluated flags bypass the pool entirely (lock-free volatile read)

‎dotnet/benchmarks/FlagdEvaluator.Benchmarks/ComparisonBenchmarks.cs‎

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using BenchmarkDotNet.Attributes;
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using BenchmarkDotNet.Jobs;
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using Eval = FlagdEvaluator;
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namespace FlagdEvaluator.Benchmarks;
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/// <summary>
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/// Comparison benchmarks: old JsonLogic provider (json-everything) vs new WASM evaluator.
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///
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/// Mirrors the Java ComparisonBenchmark and Go comparison_test.go patterns:
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/// - X1: Simple flag (old vs new, single-threaded)
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/// - X2: Targeting evaluation (old vs new, single-threaded)
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/// - X3: Context size sweep (empty, small, large — old vs new)
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/// - X4: Concurrent targeting (4 threads)
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/// - X5: Concurrent large context (8 threads)
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/// </summary>
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[MemoryDiagnoser]
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public class ComparisonBenchmarks
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{
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private Eval.FlagEvaluator _newEvaluator = null!;
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private MinimalInProcessResolver _oldResolver = null!;
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private Dictionary<string, object?> _emptyCtx = null!;
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private Dictionary<string, object?> _smallCtx = null!;
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private Dictionary<string, object?> _largeCtx = null!;
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private const string FlagConfig = """
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{
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"flags": {
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"simple-bool": {
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"state": "ENABLED",
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"defaultVariant": "on",
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"variants": { "on": true, "off": false }
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},
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"targeted-access": {
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"state": "ENABLED",
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"defaultVariant": "denied",
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"variants": { "denied": false, "granted": true },
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"targeting": {
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"if": [
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{ "and": [
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{ "==": [{ "var": "role" }, "admin"] },
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{ "in": [{ "var": "tier" }, ["premium", "enterprise"]] }
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]},
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"granted", null
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]
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}
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}
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}
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}
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""";
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[GlobalSetup]
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public void Setup()
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{
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// New WASM evaluator
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_newEvaluator = new Eval.FlagEvaluator(new Eval.FlagEvaluatorOptions
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{
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PermissiveValidation = true,
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});
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_newEvaluator.UpdateState(FlagConfig);
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// Old JsonLogic resolver
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_oldResolver = new MinimalInProcessResolver();
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_oldResolver.LoadFlags(FlagConfig);
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// Contexts
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_emptyCtx = new Dictionary<string, object?>();
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_smallCtx = new Dictionary<string, object?>
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{
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["targetingKey"] = "user-123",
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["role"] = "admin",
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["tier"] = "premium",
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["region"] = "us-east",
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["score"] = 85,
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};
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_largeCtx = new Dictionary<string, object?> { ["targetingKey"] = "user-123" };
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_largeCtx["role"] = "admin";
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_largeCtx["tier"] = "premium";
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_largeCtx["region"] = "us-east";
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_largeCtx["score"] = 85;
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for (int i = 0; i < 100; i++)
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{
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object val = (i % 4) switch
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{
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0 => $"value_{i}",
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1 => (object)(i * 7),
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2 => (object)(i % 2 == 0),
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_ => (object)(i * 1.5),
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};
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_largeCtx[$"attr_{i}"] = val;
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}
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}
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[GlobalCleanup]
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public void Cleanup() => _newEvaluator.Dispose();
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// ========================================================================
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// X1: Old vs New — Simple flag evaluation (single-threaded)
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// ========================================================================
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[Benchmark(Description = "X1: Old simple flag")]
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public OldEvaluationResult X1_Old_Simple() => _oldResolver.Evaluate("simple-bool", _emptyCtx);
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[Benchmark(Description = "X1: New simple flag (pre-eval)")]
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public Eval.EvaluationResult X1_New_Simple() => _newEvaluator.EvaluateFlag("simple-bool", _emptyCtx);
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// ========================================================================
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// X2: Old vs New — Targeting evaluation (single-threaded, small context)
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// ========================================================================
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[Benchmark(Description = "X2: Old targeting")]
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public OldEvaluationResult X2_Old_Targeting() => _oldResolver.Evaluate("targeted-access", _smallCtx);
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[Benchmark(Description = "X2: New targeting")]
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public Eval.EvaluationResult X2_New_Targeting() => _newEvaluator.EvaluateFlag("targeted-access", _smallCtx);
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// ========================================================================
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// X3: Context size sweep — Old resolver
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// ========================================================================
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[Benchmark(Description = "X3: Old empty ctx")]
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public OldEvaluationResult X3_Old_EmptyCtx() => _oldResolver.Evaluate("targeted-access", _emptyCtx);
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[Benchmark(Description = "X3: Old small ctx")]
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public OldEvaluationResult X3_Old_SmallCtx() => _oldResolver.Evaluate("targeted-access", _smallCtx);
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[Benchmark(Description = "X3: Old large ctx")]
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public OldEvaluationResult X3_Old_LargeCtx() => _oldResolver.Evaluate("targeted-access", _largeCtx);
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// ========================================================================
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// X3: Context size sweep — New evaluator
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// ========================================================================
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[Benchmark(Description = "X3: New empty ctx")]
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public Eval.EvaluationResult X3_New_EmptyCtx() => _newEvaluator.EvaluateFlag("targeted-access", _emptyCtx);
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[Benchmark(Description = "X3: New small ctx")]
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public Eval.EvaluationResult X3_New_SmallCtx() => _newEvaluator.EvaluateFlag("targeted-access", _smallCtx);
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[Benchmark(Description = "X3: New large ctx")]
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public Eval.EvaluationResult X3_New_LargeCtx() => _newEvaluator.EvaluateFlag("targeted-access", _largeCtx);
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// ========================================================================
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// X4: Concurrent targeting — 4 threads
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// ========================================================================
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[Benchmark(Description = "X4: Old 4-thread targeting")]
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public void X4_Old_Concurrent() => RunConcurrent(4, () => _oldResolver.Evaluate("targeted-access", _smallCtx));
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[Benchmark(Description = "X4: New 4-thread targeting")]
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public void X4_New_Concurrent() => RunConcurrent(4, () => _newEvaluator.EvaluateFlag("targeted-access", _smallCtx));
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// ========================================================================
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// X5: Concurrent large context — 8 threads
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// ========================================================================
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[Benchmark(Description = "X5: Old 8-thread large ctx")]
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public void X5_Old_ConcurrentLarge() => RunConcurrent(8, () => _oldResolver.Evaluate("targeted-access", _largeCtx));
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[Benchmark(Description = "X5: New 8-thread large ctx")]
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public void X5_New_ConcurrentLarge() => RunConcurrent(8, () => _newEvaluator.EvaluateFlag("targeted-access", _largeCtx));
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private static void RunConcurrent(int threads, Action action)
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{
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var tasks = new Task[threads];
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for (int i = 0; i < threads; i++)
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{
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tasks[i] = Task.Run(action);
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}
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Task.WaitAll(tasks);
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}
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}

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