ResourceMachine

HTTP decision machine for API gateways and microservices — Node.js port of Webmachine

---

HTTP is not just if (req.method === 'GET'). A production API has to get dozens of things right: content negotiation, conditional requests, ETags, caching headers, authorization, correct 4xx/5xx codes for every edge case. Most frameworks leave all of that to you, and most implementations get it quietly wrong.

ResourceMachine implements the full Webmachine v3 HTTP decision diagram — roughly 40 decision points that correctly model HTTP semantics. You describe your resource; the machine handles the protocol.

Who it's for

ResourceMachine is designed for engineers building API gateways and microservices — backends where HTTP correctness matters and separation of concerns reduces bugs. It is not a web application framework and does not try to be.

If your service needs to:

• Return different representations based on Accept headers
• Respect If-None-Match / If-Modified-Since for cache validation
• Handle PUT / DELETE / PATCH with correct precondition checking
• Enforce authorization and permission rules per endpoint
• Do all of the above correctly, every time, without repeating yourself

…ResourceMachine handles the HTTP layer so you handle the business logic.

How it works

You define a Resource class per endpoint. Override only the methods relevant to that endpoint — everything else falls back to safe HTTP defaults. The decision machine instantiates your class per request and walks the diagram, calling your methods at the right moment.

import { createServer, Resource } from "resource-machine";

class ArticleResource extends Resource {
  private article: Article | null = null;

  // Which HTTP methods are allowed?
  override async allowedMethods() {
    return ["GET", "HEAD", "PUT", "DELETE"];
  }

  // Does this resource exist? Fetch it once, cache on `this`.
  override async resourceExists() {
    this.article = await db.find(this.req.params.id);
    return this.article !== null;
  }

  // Serve it — article already fetched above, no second DB call.
  override async contentTypesProvided() {
    return {
      "application/json": () => JSON.stringify(this.article),
    };
  }

  // Accept a PUT body.
  override async contentTypesAccepted() {
    return {
      "application/json": async () => {
        const body = JSON.parse((await this.req.getBody()).toString());
        this.article = await db.update(this.req.params.id, body);
        return true;
      },
    };
  }
}

const server = createServer({ name: "articles-api" });
server.addRoute("/articles/:id", ArticleResource);
await server.listen(3000);

The machine takes care of: 404 when resourceExists() is false, 405 for disallowed methods, 406 when no content type matches, 412 on failed preconditions, 304 for unmodified resources — all without you touching a status code.

Requirements

• Node.js 22.0.0 or later
• TypeScript (optional but strongly recommended)

Installation

npm install resource-machine

Documentation

Full documentation at jongretar.github.io/ResourceMachine.

Examples are in examples/.

License

MIT — Copyright © 2026 Jón Grétar Borgþórsson