A HTTP/1.1 client, written from scratch for Node.js.

Undici means eleven in Italian. 1.1 -> 11 -> Eleven -> Undici. It is also a Stranger Things reference.

Have a question about using Undici? Open a Q&A Discussion or join our official OpenJS Slack channel.

npm i undici

The benchmark is a simple hello world example using a number of unix sockets (connections) with a pipelining depth of 10 running on Node 16. The benchmarks below have the simd feature enabled.

import { request } from 'undici'

const {
  statusCode,
  headers,
  trailers,
  body
} = await request('http://localhost:3000/foo')

console.log('response received', statusCode)
console.log('headers', headers)

for await (const data of body) {
  console.log('data', data)
}

console.log('trailers', trailers)

Using the body mixin from the Fetch Standard.

import { request } from 'undici'

const {
  statusCode,
  headers,
  trailers,
  body
} = await request('http://localhost:3000/foo')

console.log('response received', statusCode)
console.log('headers', headers)
console.log('data', await body.json())
console.log('trailers', trailers)

This section documents our most commonly used API methods. Additional APIs are documented in their own files within the docs folder and are accessible via the navigation list on the left side of the docs site.

Arguments:

• url string | URL | UrlObject
• options RequestOptions
  • dispatcher Dispatcher - Default: getGlobalDispatcher
  • method String - Default: PUT if options.body, otherwise GET
  • maxRedirections Integer - Default: 0

Returns a promise with the result of the Dispatcher.request method.

Calls options.dispatcher.request(options).

See Dispatcher.request for more details.

Arguments:

• url string | URL | UrlObject
• options StreamOptions
  • dispatcher Dispatcher - Default: getGlobalDispatcher
  • method String - Default: PUT if options.body, otherwise GET
  • maxRedirections Integer - Default: 0
• factory Dispatcher.stream.factory

Returns a promise with the result of the Dispatcher.stream method.

Calls options.dispatcher.stream(options, factory).

See Dispatcher.stream for more details.

Arguments:

• url string | URL | UrlObject
• options PipelineOptions
  • dispatcher Dispatcher - Default: getGlobalDispatcher
  • method String - Default: PUT if options.body, otherwise GET
  • maxRedirections Integer - Default: 0
• handler Dispatcher.pipeline.handler

Returns: stream.Duplex

Calls options.dispatch.pipeline(options, handler).

See Dispatcher.pipeline for more details.

Starts two-way communications with the requested resource using HTTP CONNECT.

Arguments:

• url string | URL | UrlObject
• options ConnectOptions
  • dispatcher Dispatcher - Default: getGlobalDispatcher
  • maxRedirections Integer - Default: 0
• callback (err: Error | null, data: ConnectData | null) => void (optional)

Returns a promise with the result of the Dispatcher.connect method.

Calls options.dispatch.connect(options).

See Dispatcher.connect for more details.

Implements fetch.

• https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
• https://fetch.spec.whatwg.org/#fetch-method

Only supported on Node 16+.

This is experimental and is not yet fully compliant with the Fetch Standard. We plan to ship breaking changes to this feature until it is out of experimental.

Basic usage example:

    import {fetch} from 'undici';
    
    async function fetchJson() {
        const res = await fetch('https://example.com')
        const json = await res.json()
        console.log(json);
    }

Nodejs has two kinds of streams: web streams which follow the API of the WHATWG web standard found in browsers, and an older Node-specific streams API. response.body returns a readable web stream. If you would prefer to work with a Node stream you can convert a web stream using .fromWeb().

    import {fetch} from 'undici';
    import {Readable} from 'node:stream';

    async function fetchStream() {
        const response = await fetch('https://example.com')
        const readableWebStream = response.body;
        const readableNodeStream = Readable.fromWeb(readableWebStream);
    }

This section documents parts of the Fetch Standard which Undici does not support or does not fully implement.

• https://fetch.spec.whatwg.org/#garbage-collection

The Fetch Standard allows users to skip consuming the response body by relying on garbage collection to release connection resources. Undici does the same. However, garbage collection in Node is less aggressive and deterministic (due to the lack of clear idle periods that browser have through the rendering refresh rate) which means that leaving the release of connection resources to the garbage collector can lead to excessive connection usage, reduced performance (due to less connection re-use), and even stalls or deadlocks when running out of connections. Therefore, it is highly recommended to always either consume or cancel the response body.

// Do
const headers = await fetch(url)
  .then(async res => {
    for await (const chunk of res) {
      // force consumption of body
    }
    return res.headers
  })

// Do not
const headers = await fetch(url)
  .then(res => res.headers)

Upgrade to a different protocol. See MDN - HTTP - Protocol upgrade mechanism for more details.

Arguments:

• url string | URL | UrlObject
• options UpgradeOptions
  • dispatcher Dispatcher - Default: getGlobalDispatcher
  • maxRedirections Integer - Default: 0
• callback (error: Error | null, data: UpgradeData) => void (optional)

Returns a promise with the result of the Dispatcher.upgrade method.

Calls options.dispatcher.upgrade(options).

See Dispatcher.upgrade for more details.

• dispatcher Dispatcher

Sets the global dispatcher used by Common API Methods.

Gets the global dispatcher used by Common API Methods.

Returns: Dispatcher

• port string | number (optional)
• path string (optional)
• pathname string (optional)
• hostname string (optional)
• origin string (optional)
• protocol string (optional)
• search string (optional)

This section documents parts of the HTTP/1.1 specification which Undici does not support or does not fully implement.

Undici does not support the Expect request header field. The request body is always immediately sent and the 100 Continue response will be ignored.

Refs: https://tools.ietf.org/html/rfc7231#section-5.1.1

Undici will only use pipelining if configured with a pipelining factor greater than 1.

Undici always assumes that connections are persistent and will immediately pipeline requests, without checking whether the connection is persistent. Hence, automatic fallback to HTTP/1.0 or HTTP/1.1 without pipelining is not supported.

Undici will immediately pipeline when retrying requests afters a failed connection. However, Undici will not retry the first remaining requests in the prior pipeline and instead error the corresponding callback/promise/stream.

Undici will abort all running requests in the pipeline when any of them are aborted.

• Refs: https://tools.ietf.org/html/rfc2616#section-8.1.2.2
• Refs: https://tools.ietf.org/html/rfc7230#section-6.3.2

• Daniele Belardi, https://www.npmjs.com/~dnlup
• Ethan Arrowood, https://www.npmjs.com/~ethan_arrowood
• Matteo Collina, https://www.npmjs.com/~matteo.collina
• Robert Nagy, https://www.npmjs.com/~ronag
• Szymon Marczak, https://www.npmjs.com/~szmarczak
• Tomas Della Vedova, https://www.npmjs.com/~delvedor

• Ethan Arrowood, https://www.npmjs.com/~ethan_arrowood
• Matteo Collina, https://www.npmjs.com/~matteo.collina
• Robert Nagy, https://www.npmjs.com/~ronag

MIT