Adapters

Adapters expose values derived from the Fastify instance. They can read instance information and access decorators added by external plugins, but they receive a restricted, read-only view of Fastify.

They are resolved once for each module that uses them, ensuring the correct encapsulation context and state.

Restricted Fastify access

Configuration and control APIs—such as plugin or route registration, hooks, error handlers, and server lifecycle methods—are unavailable in TypeScript and throw a TypeError at runtime. Use an installer whenever you need unrestricted Fastify access.

Examples

Fastify version Adapter

import { adapter, controller } from "@stratify/core";

// Adapter that exposes the running Fastify version
export const VersionAdapter = adapter({
  expose: ({ fastify }) => fastify.version,
});

export const VersionController = controller({
  adaps: { version: VersionAdapter },
  build: ({ builder, adaps }) => {
    builder.addRoute({
      method: "GET",
      url: "/version",
      handler: async () => ({ version: adaps.version }),
    });
  },
});

@fastify/redis Adapter

First, register the @fastify/redis plugin via an installer:

// src/installers/redis.installer.ts
import { installer } from "@stratify/core";
import fastifyRedis from "@fastify/redis";

export const RedisInstaller = installer({
  name: "redis",
  install: async ({ fastify }) => {
    await fastify.register(fastifyRedis, {
      url: process.env.REDIS_URL,
    });
  },
});

Must be registered at a higher level module with encapsulate: false

Registering the plugin has made the Redis client available via fastify.redis, so we can create the adapter:

// src/adapters/redis.adapter.ts
import { adapter } from "@stratify/core";

export const RedisAdapter = adapter({
  expose: ({ fastify }) => fastify.redis,
});

Limitations

Adapters cannot be injected into providers because they are scoped to Fastify. If you are interested in creating official Stratify provider packages to replace certain Fastify plugins, you can open an issue.