ZeroAlloc.Rest.Generator 1.1.2

ZeroAlloc.Rest

ZeroAlloc.Rest is a source-generated, Native AOT-compatible REST client for .NET 10+. Define your HTTP API as a C# interface — the Roslyn generator emits a fully type-safe, zero-reflection implementation at compile time. No runtime code generation, no IL emit, no allocations beyond the HTTP layer itself.

Install

The source generator is bundled into the main package — a single PackageReference is all you need:

dotnet add package ZeroAlloc.Rest
dotnet add package ZeroAlloc.Rest.SystemTextJson

Or via <PackageReference>:

<PackageReference Include="ZeroAlloc.Rest" Version="x.y.z" />
<PackageReference Include="ZeroAlloc.Rest.SystemTextJson" Version="x.y.z" />

The standalone ZeroAlloc.Rest.Generator package is still published for backwards compatibility with existing direct PackageReferences, but new consumers should reference only ZeroAlloc.Rest.

Optional: resilience policies

To add retry, timeout, and circuit-breaker behaviour to a client, install the bridge package alongside ZeroAlloc.Resilience:

dotnet add package ZeroAlloc.Rest.Resilience
dotnet add package ZeroAlloc.Resilience

Quick Start

1. Define your API interface:

using ZeroAlloc.Rest.Attributes;

[ZeroAllocRestClient]
public interface IUserApi
{
    [Get("/users/{id}")]
    Task<UserDto> GetUserAsync(int id, CancellationToken ct = default);

    [Get("/users")]
    Task<List<UserDto>> ListUsersAsync([Query] string? name = null, CancellationToken ct = default);

    [Post("/users")]
    Task<UserDto> CreateUserAsync([Body] CreateUserRequest request, CancellationToken ct = default);

    [Delete("/users/{id}")]
    Task DeleteUserAsync(int id, CancellationToken ct = default);
}

2. Register in DI:

builder.Services.AddIUserApi(options =>
{
    options.BaseAddress = new Uri("https://api.example.com");
    options.UseSerializer<SystemTextJsonSerializer>();
});

3. Inject and use:

public class UserService(IUserApi api)
{
    public Task<UserDto> GetAsync(int id) => api.GetUserAsync(id);
}

The generator produces UserApiClient — a sealed class implementing IUserApi — at compile time. No reflection, no proxies, no DynamicMethod.

Performance

Measured on .NET 10.0.4, Windows 11, X64. In-memory handler; no real network I/O. See docs/benchmarks.md for methodology and full results.

Features

• Source-generated — zero runtime reflection; compile-time type safety
• Native AOT compatible — no DynamicMethod, no IL emit, no Type.GetType
• Per-method serializer override — [Serializer(typeof(MySerializer))] for mixed protocols
• Path, query, body, and header parameters — {id}, [Query], [Body], [Header("X-Api-Key")]
• Result<T, HttpError> — typed success/error returns via ZeroAlloc.Results; no exception-throwing on 4xx/5xx
• OpenAPI code generation — OpenApiInterfaceGenerator API + MSBuild <ZeroAllocApiSpec> task
• Pluggable serializers — System.Text.Json, MemoryPack, MessagePack, or bring your own
• IHttpClientFactory integration — AddI{Interface} generated extension method
• Resilience bridge — ZeroAlloc.Rest.Resilience wraps any client with [Retry], [Timeout], [CircuitBreaker], and [RateLimit] via AddRestResilience<,,>()

Telemetry

Every generated client emits OpenTelemetry-compatible signals out of the box, with no extra dependency beyond the BCL System.Diagnostics primitives.

Tracing. An ActivitySource("ZeroAlloc.Rest") produces one span per call, named Interface.Method. Tags: http.method, http.status_code, server.address, rest.method. Exceptions set ActivityStatusCode.Error with the message.

Metrics. The generator emits rest.requests_total (counter) and rest.request_duration_ms (histogram) under the ZeroAlloc.Rest Meter. Tags: http.method, http.status_code, server.address, rest.method (the generated Interface.Method identifier).

The counter is incremented only on the success path. On exception, the histogram records the elapsed duration but the counter is left untouched — this lets operators distinguish failed attempts via histogram count vs. counter delta. The exception-path histogram carries only http.method and rest.method, since http.status_code and server.address may not be known.

Subscription:

services.AddOpenTelemetry()
        .WithTracing(t => t.AddSource("ZeroAlloc.Rest"))
        .WithMetrics(m => m.AddMeter("ZeroAlloc.Rest"));

Documentation

License

MIT