feat: Allow fetch custom dispatcher

README.md

@@ -194,6 +194,21 @@ Basic usage example:
     }
 ```
 
+You can pass an optional dispatcher to `fetch` as:
+
+```js
+import { fetch, Agent } from 'undici'
+
+const res = await fetch('https://example.com', {
+  // Mocks are also supported
+  dispatcher: new Agent({
+    keepAliveTimeout: 10,
+    keepAliveMaxTimeout: 10
+  })
+})
+const json = await res.json()
+console.log(json)
+```
 
 #### `request.body`
 

index-fetch.js

@@ -4,7 +4,8 @@ const { getGlobalDispatcher } = require('./lib/global')
 const fetchImpl = require('./lib/fetch')
 
 module.exports.fetch = async function fetch (resource) {
-  return fetchImpl.apply(getGlobalDispatcher(), arguments)
+  const dispatcher = arguments[1]?.dispatcher || getGlobalDispatcher()
+  return fetchImpl.apply(dispatcher, arguments)
 }
 module.exports.FormData = require('./lib/fetch/formdata').FormData
 module.exports.Headers = require('./lib/fetch/headers').Headers

index.js

@@ -86,7 +86,7 @@ if (nodeMajor > 16 || (nodeMajor === 16 && nodeMinor >= 5)) {
     if (!fetchImpl) {
       fetchImpl = require('./lib/fetch')
     }
-    const dispatcher = getGlobalDispatcher()
+    const dispatcher = arguments[1]?.dispatcher || getGlobalDispatcher()
     return fetchImpl.apply(dispatcher, arguments)
   }
   module.exports.Headers = require('./lib/fetch/headers').Headers

test/fetch/client-fetch.js

@@ -7,6 +7,13 @@ const { createServer } = require('http')
 const { ReadableStream } = require('stream/web')
 const { Blob } = require('buffer')
 const { fetch, Response, Request, FormData, File } = require('../..')
+const { Client, setGlobalDispatcher, Agent } = require('../..')
+const nodeFetch = require('../../index-fetch')
+
+setGlobalDispatcher(new Agent({
+  keepAliveTimeout: 1,
+  keepAliveMaxTimeout: 1
+}))
 
 test('function signature', (t) => {
   t.plan(2)
@@ -342,3 +349,57 @@ test('invalid url', async (t) => {
     t.match(e.cause.message, 'invalid')
   }
 })
+
+test('custom agent', (t) => {
+  t.plan(2)
+
+  const obj = { asd: true }
+  const server = createServer((req, res) => {
+    res.end(JSON.stringify(obj))
+  })
+  t.teardown(server.close.bind(server))
+
+  server.listen(0, async () => {
+    const dispatcher = new Client('http://localhost:' + server.address().port, {
+      keepAliveTimeout: 1,
+      keepAliveMaxTimeout: 1
+    })
+    const oldDispatch = dispatcher.dispatch
+    dispatcher.dispatch = function (options, handler) {
+      t.pass('custom dispatcher')
+      return oldDispatch.call(this, options, handler)
+    }
+    t.teardown(server.close.bind(server))
+    const body = await fetch(`http://localhost:${server.address().port}`, {
+      dispatcher
+    })
+    t.strictSame(obj, await body.json())
+  })
+})
+
+test('custom agent node fetch', (t) => {
+  t.plan(2)
+
+  const obj = { asd: true }
+  const server = createServer((req, res) => {
+    res.end(JSON.stringify(obj))
+  })
+  t.teardown(server.close.bind(server))
+
+  server.listen(0, async () => {
+    const dispatcher = new Client('http://localhost:' + server.address().port, {
+      keepAliveTimeout: 1,
+      keepAliveMaxTimeout: 1
+    })
+    const oldDispatch = dispatcher.dispatch
+    dispatcher.dispatch = function (options, handler) {
+      t.pass('custom dispatcher')
+      return oldDispatch.call(this, options, handler)
+    }
+    t.teardown(server.close.bind(server))
+    const body = await nodeFetch.fetch(`http://localhost:${server.address().port}`, {
+      dispatcher
+    })
+    t.strictSame(obj, await body.json())
+  })
+})

test/types/fetch.test-d.ts

@@ -3,6 +3,7 @@ import { Blob } from 'buffer'
 import { ReadableStream } from 'stream/web'
 import { expectType, expectError } from 'tsd'
 import {
+  Agent,
   BodyInit,
   fetch,
   FormData,
@@ -23,6 +24,9 @@ import {
 
 const requestInit: RequestInit = {}
 const responseInit: ResponseInit = { status: 200, statusText: 'OK' }
+const requestInit2: RequestInit = {
+  dispatcher: new Agent()
+}
 
 declare const request: Request
 declare const headers: Headers

types/fetch.d.ts

@@ -7,6 +7,8 @@ import { URL, URLSearchParams } from 'url'
 import { ReadableStream } from 'stream/web'
 import { FormData } from './formdata'
 
+import Dispatcher = require('./dispatcher')
+
 export type RequestInfo = string | URL | Request
 
 export declare function fetch (
@@ -99,6 +101,7 @@ export interface RequestInit {
   readonly referrer?: string
   readonly referrerPolicy?: ReferrerPolicy
   readonly window?: null
+  readonly dispatcher?: Dispatcher
 }
 
 export type ReferrerPolicy =