feat: duck type undici option (#321)

lib/request.js

@@ -22,10 +22,17 @@ function shouldUseUndici (opts) {
   return true
 }
 
+function isRequestable (obj) {
+  return obj !== null &&
+    typeof obj === 'object' &&
+    typeof obj.request === 'function'
+}
+
 function isUndiciInstance (obj) {
   return obj instanceof undici.Pool ||
     obj instanceof undici.Client ||
-    obj instanceof undici.Dispatcher
+    obj instanceof undici.Dispatcher ||
+    isRequestable(obj)
 }
 
 function buildRequest (opts) {

test/undici-custom-dispatcher.test.js

@@ -0,0 +1,73 @@
+'use strict'
+
+const { test } = require('tap')
+const undici = require('undici')
+const Fastify = require('fastify')
+const From = require('..')
+
+class CustomDispatcher {
+  constructor (...args) {
+    this._dispatcher = new undici.Pool(...args)
+  }
+
+  request (...args) {
+    return this._dispatcher.request(...args)
+  }
+
+  close (...args) {
+    return this._dispatcher.close(...args)
+  }
+
+  destroy (...args) {
+    return this._dispatcher.destroy(...args)
+  }
+}
+
+test('use a custom instance of \'undici\'', async t => {
+  const target = Fastify({
+    keepAliveTimeout: 1
+  })
+
+  target.get('/', (req, reply) => {
+    t.pass('request proxied')
+
+    reply.headers({
+      'Content-Type': 'text/plain',
+      'x-my-header': 'hello!'
+    })
+
+    reply.statusCode = 205
+    reply.send('hello world')
+  })
+
+  await target.listen({ port: 3001 })
+  t.teardown(async () => {
+    await target.close()
+  })
+
+  const instance = Fastify({
+    keepAliveTimeout: 1
+  })
+
+  instance.register(From, {
+    undici: new CustomDispatcher('http://localhost:3001')
+  })
+
+  instance.get('/', (request, reply) => {
+    reply.from('http://myserver.local')
+  })
+
+  await instance.listen({ port: 0 })
+  t.teardown(async () => {
+    await instance.close()
+  })
+
+  const res = await undici.request(`http://localhost:${instance.server.address().port}`)
+
+  t.equal(res.headers['content-type'], 'text/plain')
+  t.equal(res.headers['x-my-header'], 'hello!')
+  t.equal(res.statusCode, 205)
+
+  const data = await res.body.text()
+  t.equal(data, 'hello world')
+})