An 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.

npm i undici

Machine: 2.7 GHz Quad-Core Intel Core i7
Configuration: Node v14.2, HTTP/1.1 without TLS, 100 connections

http - keepalive - pipe x 6,545 ops/sec ±12.47% (64 runs sampled)
undici - pipeline - pipe x 9,560 ops/sec ±3.68% (77 runs sampled)
undici - request - pipe x 9,797 ops/sec ±6.80% (77 runs sampled)
undici - stream - pipe x 11,599 ops/sec ±0.89% (78 runs sampled)

The benchmark is a simple hello world example.

A basic HTTP/1.1 client, mapped on top a single TCP/TLS connection. Keepalive is enabled by default, and it cannot be turned off.

url can be a string or a URL object. It should only include the protocol, hostname, and the port. Options:

• socketTimeout, the timeout after which a socket will time out, in milliseconds. Monitors time between activity on a connected socket. Use 0 to disable it entirely. Default: 30e3 milliseconds (30s).

• requestTimeout, the timeout after which a request will time out, in milliseconds. Monitors time between request being enqueued and receiving a response. Use 0 to disable it entirely. Default: 30e3 milliseconds (30s).

• maxAbortedPayload, the maximum number of bytes read after which an aborted response will close the connection. Closing the connection will error other inflight requests in the pipeline. Default: 1e6 bytes (1MiB).

• pipelining, the amount of concurrent requests to be sent over the single TCP/TLS connection according to RFC7230. Default: 1.

• tls, an options object which in the case of https will be passed to tls.connect.

Performs an HTTP request.

Options:

• path
• method
• body, it can be a String, a Buffer, Uint8Array or a stream.Readable.
• headers, an object with header-value pairs.
• signal, either an AbortController or an EventEmitter.
• requestTimeout, the timeout after which a request will time out, in milliseconds. Monitors time between request being enqueued and receiving a response. Use 0 to disable it entirely. Default: 30e3 milliseconds (30s).
• idempotent, whether the requests can be safely retried or not. If false the request won't be sent until all preceeding requests in the pipeline has completed. Default: true if method is HEAD or GET.

Headers are represented by an object like this:

{
  'content-length': '123',
  'content-type': 'text/plain',
  connection: 'keep-alive',
  host: 'mysite.com',
  accept: '*/*'
}

Keys are lowercased. Values are not modified. If you don't specify a host header, it will be derived from the url of the client instance.

The data parameter in callback is defined as follow:

• statusCode
• headers
• body, a stream.Readable with the body to read. A user must either fully consume or destroy the body unless there is an error, or no further requests will be processed.

headers is an object where all keys have been lowercased.

Returns a promise if no callback is provided.

Example:

const { Client } = require('undici')
const client = new Client(`https://localhost:3000`)

client.request({
  path: '/',
  method: 'GET'
}, function (err, data) {
  if (err) {
    // handle this in some way!
    return
  }

  const {
    statusCode,
    headers,
    body
  } = data

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

  body.setEncoding('utf8')
  body.on('data', console.log)

  client.close()
})

Non-idempotent requests will not be pipelined in order to avoid indirect failures.

Idempotent requests will be automatically retried if they fail due to indirect failure from the request at the head of the pipeline. This does not apply to idempotent requests with a stream request body.

A request can may be aborted using either an AbortController or an EventEmitter. To use AbortController, you will need to npm i abort-controller.

const { AbortController } = require('abort-controller')
const { Client } = require('undici')

const client = new Client'https://localhost:3000')
const abortController = new AbortController()

client.request({
  path: '/',
  method: 'GET',
  signal: abortController.signal
}, function (err, data) {
  console.log(err) // RequestAbortedError
  client.close()
})

abortController.abort()

Alternatively, any EventEmitter that emits an 'abort' event may be used as an abort controller:

const EventEmitter = require('events')
const { Client } = require('undici')

const client = new Client'https://localhost:3000')
const ee = new EventEmitter()

client.request({
  path: '/',
  method: 'GET',
  signal: ee
}, function (err, data) {
  console.log(err) // RequestAbortedError
  client.close()
})

ee.emit('abort')

Destroying the request or response body will have the same effect.

A faster version of request.

Unlike request this method expects factory to return a Writable which the response will be written to. This improves performance by avoiding creating an intermediate Readable when the user expects to directly pipe the response body to a Writable.

Options:

• ... same as client.request(opts, callback).
• opaque, passed as opaque to factory. Used to avoid creating a closure.

The data parameter in factory is defined as follow:

• statusCode
• headers
• opaque

headers is an object where all keys have been lowercased.

Returns a promise if no callback is provided.

const { Client } = require('undici')
const client = new Client(`https://localhost:3000`)
const fs = require('fs')

client.stream({
  path: '/',
  method: 'GET',
  opaque: filename
}, ({ statusCode, headers, opaque: filename }) => {
  console.log('response received', statusCode)
  console.log('headers', headers)
  return fs.createWriteStream(filename)
}, (err) => {
  if (err) {
    console.error('failure', err)
  } else {
    console.log('success')
  }
})

opaque makes it possible to avoid creating a closure for the factory method:

function (req, res) {
   return client.stream({ ...opts, opaque: res }, proxy)
}

Instead of:

function (req, res) {
   return client.stream(opts, (data) => {
     // Creates closure to capture `res`.
     proxy({ ...data, opaque: res })
   }
}

For easy use with stream.pipeline.

Options:

• ... same as client.request(opts, callback).
• objectMode, true if the handler will return an object stream.
• opaque, passed as opaque to handler. Used to avoid creating a closure.

The data parameter in handler is defined as follow:

• statusCode
• headers
• opaque
• body, a stream.Readable with the body to read. A user must either fully consume or destroy the body unless there is an error, or no further requests will be processed.

handler should return a Readable from which the result will be read. Usually it should just return the body argument unless some kind of transformation needs to be performed based on e.g. headers or statusCode.

headers is an object where all keys have been lowercased.

The handler should validate the response and save any required state. If there is an error it should be thrown.

Returns a Duplex which writes to the request and reads from the response.

const { Client } = require('undici')
const client = new Client(`https://localhost:3000`)
const fs = require('fs')
const stream = require('stream')

stream.pipeline(
  fs.createReadStream('source.raw'),
  client.pipeline({
    path: '/',
    method: 'PUT',
  }, ({ statusCode, headers, body }) => {
    if (statusCode !== 201) {
      throw new Error('invalid response')
    }

    if (isZipped(headers)) {
      return pipeline(body, unzip(), () => {})
    }

    return body
  }),
  fs.createWriteStream('response.raw'),
  (err) => {
    if (err) {
      console.error('failed')
    } else {
      console.log('succeeded')
    }
  }
)

Closes the client and gracefully waits fo enqueued requests to complete before invoking the callback.

Returns a promise if no callback is provided.

Destroy the client abruptly with the given err. All the pending and running requests will be aborted and error. Waits until socket is closed before invoking the callback.

Returns a promise if no callback is provided.

Property to get and set the pipelining factor.

Number of queued requests.

Number of inflight requests.

Number of pending and running requests.

True if the client has an active connection. The client will lazily create a connection when it receives a request and will destroy it if there is no activity for the duration of the timeout value.

True if client.size is greater than the client.pipelining factor. Keeping a client full ensures that once a inflight requests finishes the the pipeline will schedule new one and keep the pipeline saturated.

True after client.close() has been called.

True after client.destroyed() has been called or client.close() has been called and the client shutdown has completed.

• 'connect', emitted when a socket has been created and connected. The client will connect once client.size > 0.

• 'disconnect', emitted when socket has disconnected. The first argument of the event is the error which caused the socket to disconnect. The client will reconnect if or once client.size > 0.

A pool of Client connected to the same upstream target.

Options:

• ... same as Client.
• connections, the number of clients to create. Default 100.

Calls client.request(opts, callback) on one of the clients.

Calls client.stream(opts, factory, callback) on one of the clients.

Calls client.pipeline(opts, handler) on one of the clients.

Calls client.close(callback) on all the clients.

Calls client.destroy(err, callback) on all the clients.

Undici exposes a variety of error objects that you can use to enhance your error handling. You can find all the error objects inside the errors key.

const { errors } = require('undici')

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

Undici does not support 1xx informational responses and will either ignore or error them.

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 does not support the the Upgrade request header field. A 101 Switching Protocols response will cause an UND_ERR_NOT_SUPPORTED error.

Refs: https://tools.ietf.org/html/rfc7230#section-6.7

Undici does not support early hints. A 103 Early Hint response will be ignored.

Refs: https://tools.ietf.org/html/rfc8297

Undici does not support the the Trailer response header field. Any response trailer headers will be ignored.

Refs: https://tools.ietf.org/html/rfc7230#section-4.4

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

Undici always assumes that connections are persistent and will immediatly 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.

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

• Robert Nagy, https://www.npmjs.com/~ronag

MIT