Fetch.functions.makeMiddlewareLayer

fx-fetch

---

fx-fetch / Fetch / makeMiddlewareLayer

Function: makeMiddlewareLayer()

makeMiddlewareLayer<R1, R2>(options): Layer<Fetch, never, R1 | R2>

Defined in: packages/fx-fetch/src/Fetch/makeMiddlewareLayer.ts:73

Creates a middleware Layer that allows customizing request and response handling.

The middleware can transform requests before they are sent and responses after they are received. Both mapRequest and mapResponse are optional - if not provided, they pass through unchanged.

Type Parameters

R1

R1 = never

R2

R2 = never

Parameters

options

MiddlewareOptions<R1, R2>

Returns

Layer<Fetch, never, R1 | R2>

Examples

import { Effect } from 'effect';
import { Fetch, Request } from 'fx-fetch';

// Middleware that adds authorization header to all requests
const authMiddlewareLayer = Fetch.makeMiddlewareLayer({
  mapRequest: (request) =>
    Effect.succeed(
      Request.appendHeaders(request, { Authorization: 'Bearer token' })
    ),
});

Effect.gen(function* () {
  const request = Request.unsafeMake({ url: 'https://api.example.com/data' });
  const response = yield* Fetch.fetch(request);
}).pipe(
  Effect.provide(authMiddlewareLayer), // ◀︎── Provide middleware layer
  Effect.runPromise
);

import { Context, Effect, Layer } from 'effect';
import { Fetch, Request } from 'fx-fetch';

// Service for configuration
class Config extends Context.Tag('Config')<Config, { apiKey: string }>() {}

// Middleware with requirements - the Layer properly tracks Config requirement
const authMiddlewareLayer = Fetch.makeMiddlewareLayer({
  mapRequest: (request) =>
    Effect.gen(function* () {
      const config = yield* Config;
      return Request.appendHeaders(request, { 'X-API-Key': config.apiKey });
    }),
});
// Type: Layer<Fetch, never, Config>

Effect.gen(function* () {
  const request = Request.unsafeMake({ url: 'https://api.example.com/data' });
  const response = yield* Fetch.fetch(request);
}).pipe(
  Effect.provide(authMiddlewareLayer),
  Effect.provide(Layer.succeed(Config, { apiKey: 'secret' })),
  Effect.runPromise
);

Since

1.2.0