undici/lib/fetch/index.js

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

// https://github.com/Ethan-Arrowood/undici-fetch

'use strict'

const {
  Response,
  makeNetworkError,
  makeAppropriateNetworkError,
  filterResponse,
  makeResponse
} = require('./response')
const { Headers } = require('./headers')
const { Request, makeRequest } = require('./request')
const zlib = require('zlib')
const {
  bytesMatch,
  makePolicyContainer,
  clonePolicyContainer,
  requestBadPort,
  TAOCheck,
  appendRequestOriginHeader,
  responseLocationURL,
  requestCurrentURL,
  setRequestReferrerPolicyOnRedirect,
  tryUpgradeRequestToAPotentiallyTrustworthyURL,
  createOpaqueTimingInfo,
  appendFetchMetadata,
  corsCheck,
  crossOriginResourcePolicyCheck,
  determineRequestsReferrer,
  coarsenedSharedCurrentTime,
  createDeferredPromise,
  isBlobLike,
  sameOrigin,
  isCancelled,
  isAborted,
  isErrorLike,
  fullyReadBody,
  readableStreamClose,
  isomorphicEncode,
  urlIsLocal,
  urlIsHttpHttpsScheme,
  urlHasHttpsScheme
} = require('./util')
const { kState, kHeaders, kGuard, kRealm } = require('./symbols')
const assert = require('assert')
const { safelyExtractBody } = require('./body')
const {
  redirectStatusSet,
  nullBodyStatus,
  safeMethodsSet,
  requestBodyHeader,
  subresourceSet,
  DOMException
} = require('./constants')
const { kHeadersList } = require('../core/symbols')
const EE = require('events')
const { Readable, pipeline } = require('stream')
const { addAbortListener, isErrored, isReadable, nodeMajor, nodeMinor } = require('../core/util')
const { dataURLProcessor, serializeAMimeType } = require('./dataURL')
const { TransformStream } = require('stream/web')
const { getGlobalDispatcher } = require('../global')
const { webidl } = require('./webidl')
const { STATUS_CODES } = require('http')
const GET_OR_HEAD = ['GET', 'HEAD']

/** @type {import('buffer').resolveObjectURL} */
let resolveObjectURL
let ReadableStream = globalThis.ReadableStream

class Fetch extends EE {
  constructor (dispatcher) {
    super()

    this.dispatcher = dispatcher
    this.connection = null
    this.dump = false
    this.state = 'ongoing'
    // 2 terminated listeners get added per request,
    // but only 1 gets removed. If there are 20 redirects,
    // 21 listeners will be added.
    // See https://github.com/nodejs/undici/issues/1711
    // TODO (fix): Find and fix root cause for leaked listener.
    this.setMaxListeners(21)
  }

  terminate (reason) {
    if (this.state !== 'ongoing') {
      return
    }

    this.state = 'terminated'
    this.connection?.destroy(reason)
    this.emit('terminated', reason)
  }

  // https://fetch.spec.whatwg.org/#fetch-controller-abort
  abort (error) {
    if (this.state !== 'ongoing') {
      return
    }

    // 1. Set controller’s state to "aborted".
    this.state = 'aborted'

    // 2. Let fallbackError be an "AbortError" DOMException.
    // 3. Set error to fallbackError if it is not given.
    if (!error) {
      error = new DOMException('The operation was aborted.', 'AbortError')
    }

    // 4. Let serializedError be StructuredSerialize(error).
    //    If that threw an exception, catch it, and let
    //    serializedError be StructuredSerialize(fallbackError).

    // 5. Set controller’s serialized abort reason to serializedError.
    this.serializedAbortReason = error

    this.connection?.destroy(error)
    this.emit('terminated', error)
  }
}

// https://fetch.spec.whatwg.org/#fetch-method
function fetch (input, init = {}) {
  webidl.argumentLengthCheck(arguments, 1, { header: 'globalThis.fetch' })

  // 1. Let p be a new promise.
  const p = createDeferredPromise()

  // 2. Let requestObject be the result of invoking the initial value of
  // Request as constructor with input and init as arguments. If this throws
  // an exception, reject p with it and return p.
  let requestObject

  try {
    requestObject = new Request(input, init)
  } catch (e) {
    p.reject(e)
    return p.promise
  }

  // 3. Let request be requestObject’s request.
  const request = requestObject[kState]

  // 4. If requestObject’s signal’s aborted flag is set, then:
  if (requestObject.signal.aborted) {
    // 1. Abort the fetch() call with p, request, null, and
    //    requestObject’s signal’s abort reason.
    abortFetch(p, request, null, requestObject.signal.reason)

    // 2. Return p.
    return p.promise
  }

  // 5. Let globalObject be request’s client’s global object.
  const globalObject = request.client.globalObject

  // 6. If globalObject is a ServiceWorkerGlobalScope object, then set
  // request’s service-workers mode to "none".
  if (globalObject?.constructor?.name === 'ServiceWorkerGlobalScope') {
    request.serviceWorkers = 'none'
  }

  // 7. Let responseObject be null.
  let responseObject = null

  // 8. Let relevantRealm be this’s relevant Realm.
  const relevantRealm = null

  // 9. Let locallyAborted be false.
  let locallyAborted = false

  // 10. Let controller be null.
  let controller = null

  // 11. Add the following abort steps to requestObject’s signal:
  addAbortListener(
    requestObject.signal,
    () => {
      // 1. Set locallyAborted to true.
      locallyAborted = true

      // 2. Assert: controller is non-null.
      assert(controller != null)

      // 3. Abort controller with requestObject’s signal’s abort reason.
      controller.abort(requestObject.signal.reason)

      // 4. Abort the fetch() call with p, request, responseObject,
      //    and requestObject’s signal’s abort reason.
      abortFetch(p, request, responseObject, requestObject.signal.reason)
    }
  )

  // 12. Let handleFetchDone given response response be to finalize and
  // report timing with response, globalObject, and "fetch".
  const handleFetchDone = (response) =>
    finalizeAndReportTiming(response, 'fetch')

  // 13. Set controller to the result of calling fetch given request,
  // with processResponseEndOfBody set to handleFetchDone, and processResponse
  // given response being these substeps:

  const processResponse = (response) => {
    // 1. If locallyAborted is true, terminate these substeps.
    if (locallyAborted) {
      return Promise.resolve()
    }

    // 2. If response’s aborted flag is set, then:
    if (response.aborted) {
      // 1. Let deserializedError be the result of deserialize a serialized
      //    abort reason given controller’s serialized abort reason and
      //    relevantRealm.

      // 2. Abort the fetch() call with p, request, responseObject, and
      //    deserializedError.

      abortFetch(p, request, responseObject, controller.serializedAbortReason)
      return Promise.resolve()
    }

    // 3. If response is a network error, then reject p with a TypeError
    // and terminate these substeps.
    if (response.type === 'error') {
      p.reject(
        Object.assign(new TypeError('fetch failed'), { cause: response.error })
      )
      return Promise.resolve()
    }

    // 4. Set responseObject to the result of creating a Response object,
    // given response, "immutable", and relevantRealm.
    responseObject = new Response()
    responseObject[kState] = response
    responseObject[kRealm] = relevantRealm
    responseObject[kHeaders][kHeadersList] = response.headersList
    responseObject[kHeaders][kGuard] = 'immutable'
    responseObject[kHeaders][kRealm] = relevantRealm

    // 5. Resolve p with responseObject.
    p.resolve(responseObject)
  }

  controller = fetching({
    request,
    processResponseEndOfBody: handleFetchDone,
    processResponse,
    dispatcher: init.dispatcher ?? getGlobalDispatcher() // undici
  })

  // 14. Return p.
  return p.promise
}

// https://fetch.spec.whatwg.org/#finalize-and-report-timing
function finalizeAndReportTiming (response, initiatorType = 'other') {
  // 1. If response is an aborted network error, then return.
  if (response.type === 'error' && response.aborted) {
    return
  }

  // 2. If response’s URL list is null or empty, then return.
  if (!response.urlList?.length) {
    return
  }

  // 3. Let originalURL be response’s URL list[0].
  const originalURL = response.urlList[0]

  // 4. Let timingInfo be response’s timing info.
  let timingInfo = response.timingInfo

  // 5. Let cacheState be response’s cache state.
  let cacheState = response.cacheState

  // 6. If originalURL’s scheme is not an HTTP(S) scheme, then return.
  if (!urlIsHttpHttpsScheme(originalURL)) {
    return
  }

  // 7. If timingInfo is null, then return.
  if (timingInfo === null) {
    return
  }

  // 8. If response’s timing allow passed flag is not set, then:
  if (!timingInfo.timingAllowPassed) {
    //  1. Set timingInfo to a the result of creating an opaque timing info for timingInfo.
    timingInfo = createOpaqueTimingInfo({
      startTime: timingInfo.startTime
    })

    //  2. Set cacheState to the empty string.
    cacheState = ''
  }

  // 9. Set timingInfo’s end time to the coarsened shared current time
  // given global’s relevant settings object’s cross-origin isolated
  // capability.
  // TODO: given global’s relevant settings object’s cross-origin isolated
  // capability?
  timingInfo.endTime = coarsenedSharedCurrentTime()

  // 10. Set response’s timing info to timingInfo.
  response.timingInfo = timingInfo

  // 11. Mark resource timing for timingInfo, originalURL, initiatorType,
  // global, and cacheState.
  markResourceTiming(
    timingInfo,
    originalURL,
    initiatorType,
    globalThis,
    cacheState
  )
}

// https://w3c.github.io/resource-timing/#dfn-mark-resource-timing
function markResourceTiming (timingInfo, originalURL, initiatorType, globalThis, cacheState) {
  if (nodeMajor > 18 || (nodeMajor === 18 && nodeMinor >= 2)) {
    performance.markResourceTiming(timingInfo, originalURL.href, initiatorType, globalThis, cacheState)
  }
}

// https://fetch.spec.whatwg.org/#abort-fetch
function abortFetch (p, request, responseObject, error) {
  // Note: AbortSignal.reason was added in node v17.2.0
  // which would give us an undefined error to reject with.
  // Remove this once node v16 is no longer supported.
  if (!error) {
    error = new DOMException('The operation was aborted.', 'AbortError')
  }

  // 1. Reject promise with error.
  p.reject(error)

  // 2. If request’s body is not null and is readable, then cancel request’s
  // body with error.
  if (request.body != null && isReadable(request.body?.stream)) {
    request.body.stream.cancel(error).catch((err) => {
      if (err.code === 'ERR_INVALID_STATE') {
        // Node bug?
        return
      }
      throw err
    })
  }

  // 3. If responseObject is null, then return.
  if (responseObject == null) {
    return
  }

  // 4. Let response be responseObject’s response.
  const response = responseObject[kState]

  // 5. If response’s body is not null and is readable, then error response’s
  // body with error.
  if (response.body != null && isReadable(response.body?.stream)) {
    response.body.stream.cancel(error).catch((err) => {
      if (err.code === 'ERR_INVALID_STATE') {
        // Node bug?
        return
      }
      throw err
    })
  }
}

// https://fetch.spec.whatwg.org/#fetching
function fetching ({
  request,
  processRequestBodyChunkLength,
  processRequestEndOfBody,
  processResponse,
  processResponseEndOfBody,
  processResponseConsumeBody,
  useParallelQueue = false,
  dispatcher // undici
}) {
  // 1. Let taskDestination be null.
  let taskDestination = null

  // 2. Let crossOriginIsolatedCapability be false.
  let crossOriginIsolatedCapability = false

  // 3. If request’s client is non-null, then:
  if (request.client != null) {
    // 1. Set taskDestination to request’s client’s global object.
    taskDestination = request.client.globalObject

    // 2. Set crossOriginIsolatedCapability to request’s client’s cross-origin
    // isolated capability.
    crossOriginIsolatedCapability =
      request.client.crossOriginIsolatedCapability
  }

  // 4. If useParallelQueue is true, then set taskDestination to the result of
  // starting a new parallel queue.
  // TODO

  // 5. Let timingInfo be a new fetch timing info whose start time and
  // post-redirect start time are the coarsened shared current time given
  // crossOriginIsolatedCapability.
  const currenTime = coarsenedSharedCurrentTime(crossOriginIsolatedCapability)
  const timingInfo = createOpaqueTimingInfo({
    startTime: currenTime
  })

  // 6. Let fetchParams be a new fetch params whose
  // request is request,
  // timing info is timingInfo,
  // process request body chunk length is processRequestBodyChunkLength,
  // process request end-of-body is processRequestEndOfBody,
  // process response is processResponse,
  // process response consume body is processResponseConsumeBody,
  // process response end-of-body is processResponseEndOfBody,
  // task destination is taskDestination,
  // and cross-origin isolated capability is crossOriginIsolatedCapability.
  const fetchParams = {
    controller: new Fetch(dispatcher),
    request,
    timingInfo,
    processRequestBodyChunkLength,
    processRequestEndOfBody,
    processResponse,
    processResponseConsumeBody,
    processResponseEndOfBody,
    taskDestination,
    crossOriginIsolatedCapability
  }

  // 7. If request’s body is a byte sequence, then set request’s body to
  //    request’s body as a body.
  // NOTE: Since fetching is only called from fetch, body should already be
  // extracted.
  assert(!request.body || request.body.stream)

  // 8. If request’s window is "client", then set request’s window to request’s
  // client, if request’s client’s global object is a Window object; otherwise
  // "no-window".
  if (request.window === 'client') {
    // TODO: What if request.client is null?
    request.window =
      request.client?.globalObject?.constructor?.name === 'Window'
        ? request.client
        : 'no-window'
  }

  // 9. If request’s origin is "client", then set request’s origin to request’s
  // client’s origin.
  if (request.origin === 'client') {
    // TODO: What if request.client is null?
    request.origin = request.client?.origin
  }

  // 10. If all of the following conditions are true:
  // TODO

  // 11. If request’s policy container is "client", then:
  if (request.policyContainer === 'client') {
    // 1. If request’s client is non-null, then set request’s policy
    // container to a clone of request’s client’s policy container. [HTML]
    if (request.client != null) {
      request.policyContainer = clonePolicyContainer(
        request.client.policyContainer
      )
    } else {
      // 2. Otherwise, set request’s policy container to a new policy
      // container.
      request.policyContainer = makePolicyContainer()
    }
  }

  // 12. If request’s header list does not contain `Accept`, then:
  if (!request.headersList.contains('accept')) {
    // 1. Let value be `*/*`.
    const value = '*/*'

    // 2. A user agent should set value to the first matching statement, if
    // any, switching on request’s destination:
    // "document"
    // "frame"
    // "iframe"
    // `text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8`
    // "image"
    // `image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5`
    // "style"
    // `text/css,*/*;q=0.1`
    // TODO

    // 3. Append `Accept`/value to request’s header list.
    request.headersList.append('accept', value)
  }

  // 13. If request’s header list does not contain `Accept-Language`, then
  // user agents should append `Accept-Language`/an appropriate value to
  // request’s header list.
  if (!request.headersList.contains('accept-language')) {
    request.headersList.append('accept-language', '*')
  }

  // 14. If request’s priority is null, then use request’s initiator and
  // destination appropriately in setting request’s priority to a
  // user-agent-defined object.
  if (request.priority === null) {
    // TODO
  }

  // 15. If request is a subresource request, then:
  if (subresourceSet.has(request.destination)) {
    // TODO
  }

  // 16. Run main fetch given fetchParams.
  mainFetch(fetchParams)
    .catch(err => {
      fetchParams.controller.terminate(err)
    })

  // 17. Return fetchParam's controller
  return fetchParams.controller
}

// https://fetch.spec.whatwg.org/#concept-main-fetch
async function mainFetch (fetchParams, recursive = false) {
  // 1. Let request be fetchParams’s request.
  const request = fetchParams.request

  // 2. Let response be null.
  let response = null

  // 3. If request’s local-URLs-only flag is set and request’s current URL is
  // not local, then set response to a network error.
  if (request.localURLsOnly && !urlIsLocal(requestCurrentURL(request))) {
    response = makeNetworkError('local URLs only')
  }

  // 4. Run report Content Security Policy violations for request.
  // TODO

  // 5. Upgrade request to a potentially trustworthy URL, if appropriate.
  tryUpgradeRequestToAPotentiallyTrustworthyURL(request)

  // 6. If should request be blocked due to a bad port, should fetching request
  // be blocked as mixed content, or should request be blocked by Content
  // Security Policy returns blocked, then set response to a network error.
  if (requestBadPort(request) === 'blocked') {
    response = makeNetworkError('bad port')
  }
  // TODO: should fetching request be blocked as mixed content?
  // TODO: should request be blocked by Content Security Policy?

  // 7. If request’s referrer policy is the empty string, then set request’s
  // referrer policy to request’s policy container’s referrer policy.
  if (request.referrerPolicy === '') {
    request.referrerPolicy = request.policyContainer.referrerPolicy
  }

  // 8. If request’s referrer is not "no-referrer", then set request’s
  // referrer to the result of invoking determine request’s referrer.
  if (request.referrer !== 'no-referrer') {
    request.referrer = determineRequestsReferrer(request)
  }

  // 9. Set request’s current URL’s scheme to "https" if all of the following
  // conditions are true:
  // - request’s current URL’s scheme is "http"
  // - request’s current URL’s host is a domain
  // - Matching request’s current URL’s host per Known HSTS Host Domain Name
  //   Matching results in either a superdomain match with an asserted
  //   includeSubDomains directive or a congruent match (with or without an
  //   asserted includeSubDomains directive). [HSTS]
  // TODO

  // 10. If recursive is false, then run the remaining steps in parallel.
  // TODO

  // 11. If response is null, then set response to the result of running
  // the steps corresponding to the first matching statement:
  if (response === null) {
    response = await (async () => {
      const currentURL = requestCurrentURL(request)

      if (
        // - request’s current URL’s origin is same origin with request’s origin,
        //   and request’s response tainting is "basic"
        (sameOrigin(currentURL, request.url) && request.responseTainting === 'basic') ||
        // request’s current URL’s scheme is "data"
        (currentURL.protocol === 'data:') ||
        // - request’s mode is "navigate" or "websocket"
        (request.mode === 'navigate' || request.mode === 'websocket')
      ) {
        // 1. Set request’s response tainting to "basic".
        request.responseTainting = 'basic'

        // 2. Return the result of running scheme fetch given fetchParams.
        return await schemeFetch(fetchParams)
      }

      // request’s mode is "same-origin"
      if (request.mode === 'same-origin') {
        // 1. Return a network error.
        return makeNetworkError('request mode cannot be "same-origin"')
      }

      // request’s mode is "no-cors"
      if (request.mode === 'no-cors') {
        // 1. If request’s redirect mode is not "follow", then return a network
        // error.
        if (request.redirect !== 'follow') {
          return makeNetworkError(
            'redirect mode cannot be "follow" for "no-cors" request'
          )
        }

        // 2. Set request’s response tainting to "opaque".
        request.responseTainting = 'opaque'

        // 3. Return the result of running scheme fetch given fetchParams.
        return await schemeFetch(fetchParams)
      }

      // request’s current URL’s scheme is not an HTTP(S) scheme
      if (!urlIsHttpHttpsScheme(requestCurrentURL(request))) {
        // Return a network error.
        return makeNetworkError('URL scheme must be a HTTP(S) scheme')
      }

      // - request’s use-CORS-preflight flag is set
      // - request’s unsafe-request flag is set and either request’s method is
      //   not a CORS-safelisted method or CORS-unsafe request-header names with
      //   request’s header list is not empty
      //    1. Set request’s response tainting to "cors".
      //    2. Let corsWithPreflightResponse be the result of running HTTP fetch
      //    given fetchParams and true.
      //    3. If corsWithPreflightResponse is a network error, then clear cache
      //    entries using request.
      //    4. Return corsWithPreflightResponse.
      // TODO

      // Otherwise
      //    1. Set request’s response tainting to "cors".
      request.responseTainting = 'cors'

      //    2. Return the result of running HTTP fetch given fetchParams.
      return await httpFetch(fetchParams)
    })()
  }

  // 12. If recursive is true, then return response.
  if (recursive) {
    return response
  }

  // 13. If response is not a network error and response is not a filtered
  // response, then:
  if (response.status !== 0 && !response.internalResponse) {
    // If request’s response tainting is "cors", then:
    if (request.responseTainting === 'cors') {
      // 1. Let headerNames be the result of extracting header list values
      // given `Access-Control-Expose-Headers` and response’s header list.
      // TODO
      // 2. If request’s credentials mode is not "include" and headerNames
      // contains `*`, then set response’s CORS-exposed header-name list to
      // all unique header names in response’s header list.
      // TODO
      // 3. Otherwise, if headerNames is not null or failure, then set
      // response’s CORS-exposed header-name list to headerNames.
      // TODO
    }

    // Set response to the following filtered response with response as its
    // internal response, depending on request’s response tainting:
    if (request.responseTainting === 'basic') {
      response = filterResponse(response, 'basic')
    } else if (request.responseTainting === 'cors') {
      response = filterResponse(response, 'cors')
    } else if (request.responseTainting === 'opaque') {
      response = filterResponse(response, 'opaque')
    } else {
      assert(false)
    }
  }

  // 14. Let internalResponse be response, if response is a network error,
  // and response’s internal response otherwise.
  let internalResponse =
    response.status === 0 ? response : response.internalResponse

  // 15. If internalResponse’s URL list is empty, then set it to a clone of
  // request’s URL list.
  if (internalResponse.urlList.length === 0) {
    internalResponse.urlList.push(...request.urlList)
  }

  // 16. If request’s timing allow failed flag is unset, then set
  // internalResponse’s timing allow passed flag.
  if (!request.timingAllowFailed) {
    response.timingAllowPassed = true
  }

  // 17. If response is not a network error and any of the following returns
  // blocked
  // - should internalResponse to request be blocked as mixed content
  // - should internalResponse to request be blocked by Content Security Policy
  // - should internalResponse to request be blocked due to its MIME type
  // - should internalResponse to request be blocked due to nosniff
  // TODO

  // 18. If response’s type is "opaque", internalResponse’s status is 206,
  // internalResponse’s range-requested flag is set, and request’s header
  // list does not contain `Range`, then set response and internalResponse
  // to a network error.
  if (
    response.type === 'opaque' &&
    internalResponse.status === 206 &&
    internalResponse.rangeRequested &&
    !request.headers.contains('range')
  ) {
    response = internalResponse = makeNetworkError()
  }

  // 19. If response is not a network error and either request’s method is
  // `HEAD` or `CONNECT`, or internalResponse’s status is a null body status,
  // set internalResponse’s body to null and disregard any enqueuing toward
  // it (if any).
  if (
    response.status !== 0 &&
    (request.method === 'HEAD' ||
      request.method === 'CONNECT' ||
      nullBodyStatus.includes(internalResponse.status))
  ) {
    internalResponse.body = null
    fetchParams.controller.dump = true
  }

  // 20. If request’s integrity metadata is not the empty string, then:
  if (request.integrity) {
    // 1. Let processBodyError be this step: run fetch finale given fetchParams
    // and a network error.
    const processBodyError = (reason) =>
      fetchFinale(fetchParams, makeNetworkError(reason))

    // 2. If request’s response tainting is "opaque", or response’s body is null,
    // then run processBodyError and abort these steps.
    if (request.responseTainting === 'opaque' || response.body == null) {
      processBodyError(response.error)
      return
    }

    // 3. Let processBody given bytes be these steps:
    const processBody = (bytes) => {
      // 1. If bytes do not match request’s integrity metadata,
      // then run processBodyError and abort these steps. [SRI]
      if (!bytesMatch(bytes, request.integrity)) {
        processBodyError('integrity mismatch')
        return
      }

      // 2. Set response’s body to bytes as a body.
      response.body = safelyExtractBody(bytes)[0]

      // 3. Run fetch finale given fetchParams and response.
      fetchFinale(fetchParams, response)
    }

    // 4. Fully read response’s body given processBody and processBodyError.
    await fullyReadBody(response.body, processBody, processBodyError)
  } else {
    // 21. Otherwise, run fetch finale given fetchParams and response.
    fetchFinale(fetchParams, response)
  }
}

// https://fetch.spec.whatwg.org/#concept-scheme-fetch
// given a fetch params fetchParams
function schemeFetch (fetchParams) {
  // Note: since the connection is destroyed on redirect, which sets fetchParams to a
  // cancelled state, we do not want this condition to trigger *unless* there have been
  // no redirects. See https://github.com/nodejs/undici/issues/1776
  // 1. If fetchParams is canceled, then return the appropriate network error for fetchParams.
  if (isCancelled(fetchParams) && fetchParams.request.redirectCount === 0) {
    return Promise.resolve(makeAppropriateNetworkError(fetchParams))
  }

  // 2. Let request be fetchParams’s request.
  const { request } = fetchParams

  const { protocol: scheme } = requestCurrentURL(request)

  // 3. Switch on request’s current URL’s scheme and run the associated steps:
  switch (scheme) {
    case 'about:': {
      // If request’s current URL’s path is the string "blank", then return a new response
      // whose status message is `OK`, header list is « (`Content-Type`, `text/html;charset=utf-8`) »,
      // and body is the empty byte sequence as a body.

      // Otherwise, return a network error.
      return Promise.resolve(makeNetworkError('about scheme is not supported'))
    }
    case 'blob:': {
      if (!resolveObjectURL) {
        resolveObjectURL = require('buffer').resolveObjectURL
      }

      // 1. Let blobURLEntry be request’s current URL’s blob URL entry.
      const blobURLEntry = requestCurrentURL(request)

      // https://github.com/web-platform-tests/wpt/blob/7b0ebaccc62b566a1965396e5be7bb2bc06f841f/FileAPI/url/resources/fetch-tests.js#L52-L56
      // Buffer.resolveObjectURL does not ignore URL queries.
      if (blobURLEntry.search.length !== 0) {
        return Promise.resolve(makeNetworkError('NetworkError when attempting to fetch resource.'))
      }

      const blobURLEntryObject = resolveObjectURL(blobURLEntry.toString())

      // 2. If request’s method is not `GET`, blobURLEntry is null, or blobURLEntry’s
      //    object is not a Blob object, then return a network error.
      if (request.method !== 'GET' || !isBlobLike(blobURLEntryObject)) {
        return Promise.resolve(makeNetworkError('invalid method'))
      }

      // 3. Let bodyWithType be the result of safely extracting blobURLEntry’s object.
      const bodyWithType = safelyExtractBody(blobURLEntryObject)

      // 4. Let body be bodyWithType’s body.
      const body = bodyWithType[0]

      // 5. Let length be body’s length, serialized and isomorphic encoded.
      const length = isomorphicEncode(`${body.length}`)

      // 6. Let type be bodyWithType’s type if it is non-null; otherwise the empty byte sequence.
      const type = bodyWithType[1] ?? ''

      // 7. Return a new response whose status message is `OK`, header list is
      //    « (`Content-Length`, length), (`Content-Type`, type) », and body is body.
      const response = makeResponse({
        statusText: 'OK',
        headersList: [
          ['content-length', { name: 'Content-Length', value: length }],
          ['content-type', { name: 'Content-Type', value: type }]
        ]
      })

      response.body = body

      return Promise.resolve(response)
    }
    case 'data:': {
      // 1. Let dataURLStruct be the result of running the
      //    data: URL processor on request’s current URL.
      const currentURL = requestCurrentURL(request)
      const dataURLStruct = dataURLProcessor(currentURL)

      // 2. If dataURLStruct is failure, then return a
      //    network error.
      if (dataURLStruct === 'failure') {
        return Promise.resolve(makeNetworkError('failed to fetch the data URL'))
      }

      // 3. Let mimeType be dataURLStruct’s MIME type, serialized.
      const mimeType = serializeAMimeType(dataURLStruct.mimeType)

      // 4. Return a response whose status message is `OK`,
      //    header list is « (`Content-Type`, mimeType) »,
      //    and body is dataURLStruct’s body as a body.
      return Promise.resolve(makeResponse({
        statusText: 'OK',
        headersList: [
          ['content-type', { name: 'Content-Type', value: mimeType }]
        ],
        body: safelyExtractBody(dataURLStruct.body)[0]
      }))
    }
    case 'file:': {
      // For now, unfortunate as it is, file URLs are left as an exercise for the reader.
      // When in doubt, return a network error.
      return Promise.resolve(makeNetworkError('not implemented... yet...'))
    }
    case 'http:':
    case 'https:': {
      // Return the result of running HTTP fetch given fetchParams.

      return httpFetch(fetchParams)
        .catch((err) => makeNetworkError(err))
    }
    default: {
      return Promise.resolve(makeNetworkError('unknown scheme'))
    }
  }
}

// https://fetch.spec.whatwg.org/#finalize-response
function finalizeResponse (fetchParams, response) {
  // 1. Set fetchParams’s request’s done flag.
  fetchParams.request.done = true

  // 2, If fetchParams’s process response done is not null, then queue a fetch
  // task to run fetchParams’s process response done given response, with
  // fetchParams’s task destination.
  if (fetchParams.processResponseDone != null) {
    queueMicrotask(() => fetchParams.processResponseDone(response))
  }
}

// https://fetch.spec.whatwg.org/#fetch-finale
function fetchFinale (fetchParams, response) {
  // 1. If response is a network error, then:
  if (response.type === 'error') {
    // 1. Set response’s URL list to « fetchParams’s request’s URL list[0] ».
    response.urlList = [fetchParams.request.urlList[0]]

    // 2. Set response’s timing info to the result of creating an opaque timing
    // info for fetchParams’s timing info.
    response.timingInfo = createOpaqueTimingInfo({
      startTime: fetchParams.timingInfo.startTime
    })
  }

  // 2. Let processResponseEndOfBody be the following steps:
  const processResponseEndOfBody = () => {
    // 1. Set fetchParams’s request’s done flag.
    fetchParams.request.done = true

    // If fetchParams’s process response end-of-body is not null,
    // then queue a fetch task to run fetchParams’s process response
    // end-of-body given response with fetchParams’s task destination.
    if (fetchParams.processResponseEndOfBody != null) {
      queueMicrotask(() => fetchParams.processResponseEndOfBody(response))
    }
  }

  // 3. If fetchParams’s process response is non-null, then queue a fetch task
  // to run fetchParams’s process response given response, with fetchParams’s
  // task destination.
  if (fetchParams.processResponse != null) {
    queueMicrotask(() => fetchParams.processResponse(response))
  }

  // 4. If response’s body is null, then run processResponseEndOfBody.
  if (response.body == null) {
    processResponseEndOfBody()
  } else {
  // 5. Otherwise:

    // 1. Let transformStream be a new a TransformStream.

    // 2. Let identityTransformAlgorithm be an algorithm which, given chunk,
    // enqueues chunk in transformStream.
    const identityTransformAlgorithm = (chunk, controller) => {
      controller.enqueue(chunk)
    }

    // 3. Set up transformStream with transformAlgorithm set to identityTransformAlgorithm
    // and flushAlgorithm set to processResponseEndOfBody.
    const transformStream = new TransformStream({
      start () {},
      transform: identityTransformAlgorithm,
      flush: processResponseEndOfBody
    }, {
      size () {
        return 1
      }
    }, {
      size () {
        return 1
      }
    })

    // 4. Set response’s body to the result of piping response’s body through transformStream.
    response.body = { stream: response.body.stream.pipeThrough(transformStream) }
  }

  // 6. If fetchParams’s process response consume body is non-null, then:
  if (fetchParams.processResponseConsumeBody != null) {
    // 1. Let processBody given nullOrBytes be this step: run fetchParams’s
    // process response consume body given response and nullOrBytes.
    const processBody = (nullOrBytes) => fetchParams.processResponseConsumeBody(response, nullOrBytes)

    // 2. Let processBodyError be this step: run fetchParams’s process
    // response consume body given response and failure.
    const processBodyError = (failure) => fetchParams.processResponseConsumeBody(response, failure)

    // 3. If response’s body is null, then queue a fetch task to run processBody
    // given null, with fetchParams’s task destination.
    if (response.body == null) {
      queueMicrotask(() => processBody(null))
    } else {
      // 4. Otherwise, fully read response’s body given processBody, processBodyError,
      // and fetchParams’s task destination.
      return fullyReadBody(response.body, processBody, processBodyError)
    }
    return Promise.resolve()
  }
}

// https://fetch.spec.whatwg.org/#http-fetch
async function httpFetch (fetchParams) {
  // 1. Let request be fetchParams’s request.
  const request = fetchParams.request

  // 2. Let response be null.
  let response = null

  // 3. Let actualResponse be null.
  let actualResponse = null

  // 4. Let timingInfo be fetchParams’s timing info.
  const timingInfo = fetchParams.timingInfo

  // 5. If request’s service-workers mode is "all", then:
  if (request.serviceWorkers === 'all') {
    // TODO
  }

  // 6. If response is null, then:
  if (response === null) {
    // 1. If makeCORSPreflight is true and one of these conditions is true:
    // TODO

    // 2. If request’s redirect mode is "follow", then set request’s
    // service-workers mode to "none".
    if (request.redirect === 'follow') {
      request.serviceWorkers = 'none'
    }

    // 3. Set response and actualResponse to the result of running
    // HTTP-network-or-cache fetch given fetchParams.
    actualResponse = response = await httpNetworkOrCacheFetch(fetchParams)

    // 4. If request’s response tainting is "cors" and a CORS check
    // for request and response returns failure, then return a network error.
    if (
      request.responseTainting === 'cors' &&
      corsCheck(request, response) === 'failure'
    ) {
      return makeNetworkError('cors failure')
    }

    // 5. If the TAO check for request and response returns failure, then set
    // request’s timing allow failed flag.
    if (TAOCheck(request, response) === 'failure') {
      request.timingAllowFailed = true
    }
  }

  // 7. If either request’s response tainting or response’s type
  // is "opaque", and the cross-origin resource policy check with
  // request’s origin, request’s client, request’s destination,
  // and actualResponse returns blocked, then return a network error.
  if (
    (request.responseTainting === 'opaque' || response.type === 'opaque') &&
    crossOriginResourcePolicyCheck(
      request.origin,
      request.client,
      request.destination,
      actualResponse
    ) === 'blocked'
  ) {
    return makeNetworkError('blocked')
  }

  // 8. If actualResponse’s status is a redirect status, then:
  if (redirectStatusSet.has(actualResponse.status)) {
    // 1. If actualResponse’s status is not 303, request’s body is not null,
    // and the connection uses HTTP/2, then user agents may, and are even
    // encouraged to, transmit an RST_STREAM frame.
    // See, https://github.com/whatwg/fetch/issues/1288
    if (request.redirect !== 'manual') {
      fetchParams.controller.connection.destroy()
    }

    // 2. Switch on request’s redirect mode:
    if (request.redirect === 'error') {
      // Set response to a network error.
      response = makeNetworkError('unexpected redirect')
    } else if (request.redirect === 'manual') {
      // Set response to an opaque-redirect filtered response whose internal
      // response is actualResponse.
      // NOTE(spec): On the web this would return an `opaqueredirect` response,
      // but that doesn't make sense server side.
      // See https://github.com/nodejs/undici/issues/1193.
      response = actualResponse
    } else if (request.redirect === 'follow') {
      // Set response to the result of running HTTP-redirect fetch given
      // fetchParams and response.
      response = await httpRedirectFetch(fetchParams, response)
    } else {
      assert(false)
    }
  }

  // 9. Set response’s timing info to timingInfo.
  response.timingInfo = timingInfo

  // 10. Return response.
  return response
}

// https://fetch.spec.whatwg.org/#http-redirect-fetch
function httpRedirectFetch (fetchParams, response) {
  // 1. Let request be fetchParams’s request.
  const request = fetchParams.request

  // 2. Let actualResponse be response, if response is not a filtered response,
  // and response’s internal response otherwise.
  const actualResponse = response.internalResponse
    ? response.internalResponse
    : response

  // 3. Let locationURL be actualResponse’s location URL given request’s current
  // URL’s fragment.
  let locationURL

  try {
    locationURL = responseLocationURL(
      actualResponse,
      requestCurrentURL(request).hash
    )

    // 4. If locationURL is null, then return response.
    if (locationURL == null) {
      return response
    }
  } catch (err) {
    // 5. If locationURL is failure, then return a network error.
    return Promise.resolve(makeNetworkError(err))
  }

  // 6. If locationURL’s scheme is not an HTTP(S) scheme, then return a network
  // error.
  if (!urlIsHttpHttpsScheme(locationURL)) {
    return Promise.resolve(makeNetworkError('URL scheme must be a HTTP(S) scheme'))
  }

  // 7. If request’s redirect count is 20, then return a network error.
  if (request.redirectCount === 20) {
    return Promise.resolve(makeNetworkError('redirect count exceeded'))
  }

  // 8. Increase request’s redirect count by 1.
  request.redirectCount += 1

  // 9. If request’s mode is "cors", locationURL includes credentials, and
  // request’s origin is not same origin with locationURL’s origin, then return
  //  a network error.
  if (
    request.mode === 'cors' &&
    (locationURL.username || locationURL.password) &&
    !sameOrigin(request, locationURL)
  ) {
    return Promise.resolve(makeNetworkError('cross origin not allowed for request mode "cors"'))
  }

  // 10. If request’s response tainting is "cors" and locationURL includes
  // credentials, then return a network error.
  if (
    request.responseTainting === 'cors' &&
    (locationURL.username || locationURL.password)
  ) {
    return Promise.resolve(makeNetworkError(
      'URL cannot contain credentials for request mode "cors"'
    ))
  }

  // 11. If actualResponse’s status is not 303, request’s body is non-null,
  // and request’s body’s source is null, then return a network error.
  if (
    actualResponse.status !== 303 &&
    request.body != null &&
    request.body.source == null
  ) {
    return Promise.resolve(makeNetworkError())
  }

  // 12. If one of the following is true
  // - actualResponse’s status is 301 or 302 and request’s method is `POST`
  // - actualResponse’s status is 303 and request’s method is not `GET` or `HEAD`
  if (
    ([301, 302].includes(actualResponse.status) && request.method === 'POST') ||
    (actualResponse.status === 303 &&
      !GET_OR_HEAD.includes(request.method))
  ) {
    // then:
    // 1. Set request’s method to `GET` and request’s body to null.
    request.method = 'GET'
    request.body = null

    // 2. For each headerName of request-body-header name, delete headerName from
    // request’s header list.
    for (const headerName of requestBodyHeader) {
      request.headersList.delete(headerName)
    }
  }

  // 13. If request’s current URL’s origin is not same origin with locationURL’s
  //     origin, then for each headerName of CORS non-wildcard request-header name,
  //     delete headerName from request’s header list.
  if (!sameOrigin(requestCurrentURL(request), locationURL)) {
    // https://fetch.spec.whatwg.org/#cors-non-wildcard-request-header-name
    request.headersList.delete('authorization')

    // "Cookie" and "Host" are forbidden request-headers, which undici doesn't implement.
    request.headersList.delete('cookie')
    request.headersList.delete('host')
  }

  // 14. If request’s body is non-null, then set request’s body to the first return
  // value of safely extracting request’s body’s source.
  if (request.body != null) {
    assert(request.body.source != null)
    request.body = safelyExtractBody(request.body.source)[0]
  }

  // 15. Let timingInfo be fetchParams’s timing info.
  const timingInfo = fetchParams.timingInfo

  // 16. Set timingInfo’s redirect end time and post-redirect start time to the
  // coarsened shared current time given fetchParams’s cross-origin isolated
  // capability.
  timingInfo.redirectEndTime = timingInfo.postRedirectStartTime =
    coarsenedSharedCurrentTime(fetchParams.crossOriginIsolatedCapability)

  // 17. If timingInfo’s redirect start time is 0, then set timingInfo’s
  //  redirect start time to timingInfo’s start time.
  if (timingInfo.redirectStartTime === 0) {
    timingInfo.redirectStartTime = timingInfo.startTime
  }

  // 18. Append locationURL to request’s URL list.
  request.urlList.push(locationURL)

  // 19. Invoke set request’s referrer policy on redirect on request and
  // actualResponse.
  setRequestReferrerPolicyOnRedirect(request, actualResponse)

  // 20. Return the result of running main fetch given fetchParams and true.
  return mainFetch(fetchParams, true)
}

// https://fetch.spec.whatwg.org/#http-network-or-cache-fetch
async function httpNetworkOrCacheFetch (
  fetchParams,
  isAuthenticationFetch = false,
  isNewConnectionFetch = false
) {
  // 1. Let request be fetchParams’s request.
  const request = fetchParams.request

  // 2. Let httpFetchParams be null.
  let httpFetchParams = null

  // 3. Let httpRequest be null.
  let httpRequest = null

  // 4. Let response be null.
  let response = null

  // 5. Let storedResponse be null.
  // TODO: cache

  // 6. Let httpCache be null.
  const httpCache = null

  // 7. Let the revalidatingFlag be unset.
  const revalidatingFlag = false

  // 8. Run these steps, but abort when the ongoing fetch is terminated:

  //    1. If request’s window is "no-window" and request’s redirect mode is
  //    "error", then set httpFetchParams to fetchParams and httpRequest to
  //    request.
  if (request.window === 'no-window' && request.redirect === 'error') {
    httpFetchParams = fetchParams
    httpRequest = request
  } else {
    // Otherwise:

    // 1. Set httpRequest to a clone of request.
    httpRequest = makeRequest(request)

    // 2. Set httpFetchParams to a copy of fetchParams.
    httpFetchParams = { ...fetchParams }

    // 3. Set httpFetchParams’s request to httpRequest.
    httpFetchParams.request = httpRequest
  }

  //    3. Let includeCredentials be true if one of
  const includeCredentials =
    request.credentials === 'include' ||
    (request.credentials === 'same-origin' &&
      request.responseTainting === 'basic')

  //    4. Let contentLength be httpRequest’s body’s length, if httpRequest’s
  //    body is non-null; otherwise null.
  const contentLength = httpRequest.body ? httpRequest.body.length : null

  //    5. Let contentLengthHeaderValue be null.
  let contentLengthHeaderValue = null

  //    6. If httpRequest’s body is null and httpRequest’s method is `POST` or
  //    `PUT`, then set contentLengthHeaderValue to `0`.
  if (
    httpRequest.body == null &&
    ['POST', 'PUT'].includes(httpRequest.method)
  ) {
    contentLengthHeaderValue = '0'
  }

  //    7. If contentLength is non-null, then set contentLengthHeaderValue to
  //    contentLength, serialized and isomorphic encoded.
  if (contentLength != null) {
    contentLengthHeaderValue = isomorphicEncode(`${contentLength}`)
  }

  //    8. If contentLengthHeaderValue is non-null, then append
  //    `Content-Length`/contentLengthHeaderValue to httpRequest’s header
  //    list.
  if (contentLengthHeaderValue != null) {
    httpRequest.headersList.append('content-length', contentLengthHeaderValue)
  }

  //    9. If contentLengthHeaderValue is non-null, then append (`Content-Length`,
  //    contentLengthHeaderValue) to httpRequest’s header list.

  //    10. If contentLength is non-null and httpRequest’s keepalive is true,
  //    then:
  if (contentLength != null && httpRequest.keepalive) {
    // NOTE: keepalive is a noop outside of browser context.
  }

  //    11. If httpRequest’s referrer is a URL, then append
  //    `Referer`/httpRequest’s referrer, serialized and isomorphic encoded,
  //     to httpRequest’s header list.
  if (httpRequest.referrer instanceof URL) {
    httpRequest.headersList.append('referer', isomorphicEncode(httpRequest.referrer.href))
  }

  //    12. Append a request `Origin` header for httpRequest.
  appendRequestOriginHeader(httpRequest)

  //    13. Append the Fetch metadata headers for httpRequest. [FETCH-METADATA]
  appendFetchMetadata(httpRequest)

  //    14. If httpRequest’s header list does not contain `User-Agent`, then
  //    user agents should append `User-Agent`/default `User-Agent` value to
  //    httpRequest’s header list.
  if (!httpRequest.headersList.contains('user-agent')) {
    httpRequest.headersList.append('user-agent', typeof esbuildDetection === 'undefined' ? 'undici' : 'node')
  }

  //    15. If httpRequest’s cache mode is "default" and httpRequest’s header
  //    list contains `If-Modified-Since`, `If-None-Match`,
  //    `If-Unmodified-Since`, `If-Match`, or `If-Range`, then set
  //    httpRequest’s cache mode to "no-store".
  if (
    httpRequest.cache === 'default' &&
    (httpRequest.headersList.contains('if-modified-since') ||
      httpRequest.headersList.contains('if-none-match') ||
      httpRequest.headersList.contains('if-unmodified-since') ||
      httpRequest.headersList.contains('if-match') ||
      httpRequest.headersList.contains('if-range'))
  ) {
    httpRequest.cache = 'no-store'
  }

  //    16. If httpRequest’s cache mode is "no-cache", httpRequest’s prevent
  //    no-cache cache-control header modification flag is unset, and
  //    httpRequest’s header list does not contain `Cache-Control`, then append
  //    `Cache-Control`/`max-age=0` to httpRequest’s header list.
  if (
    httpRequest.cache === 'no-cache' &&
    !httpRequest.preventNoCacheCacheControlHeaderModification &&
    !httpRequest.headersList.contains('cache-control')
  ) {
    httpRequest.headersList.append('cache-control', 'max-age=0')
  }

  //    17. If httpRequest’s cache mode is "no-store" or "reload", then:
  if (httpRequest.cache === 'no-store' || httpRequest.cache === 'reload') {
    // 1. If httpRequest’s header list does not contain `Pragma`, then append
    // `Pragma`/`no-cache` to httpRequest’s header list.
    if (!httpRequest.headersList.contains('pragma')) {
      httpRequest.headersList.append('pragma', 'no-cache')
    }

    // 2. If httpRequest’s header list does not contain `Cache-Control`,
    // then append `Cache-Control`/`no-cache` to httpRequest’s header list.
    if (!httpRequest.headersList.contains('cache-control')) {
      httpRequest.headersList.append('cache-control', 'no-cache')
    }
  }

  //    18. If httpRequest’s header list contains `Range`, then append
  //    `Accept-Encoding`/`identity` to httpRequest’s header list.
  if (httpRequest.headersList.contains('range')) {
    httpRequest.headersList.append('accept-encoding', 'identity')
  }

  //    19. Modify httpRequest’s header list per HTTP. Do not append a given
  //    header if httpRequest’s header list contains that header’s name.
  //    TODO: https://github.com/whatwg/fetch/issues/1285#issuecomment-896560129
  if (!httpRequest.headersList.contains('accept-encoding')) {
    if (urlHasHttpsScheme(requestCurrentURL(httpRequest))) {
      httpRequest.headersList.append('accept-encoding', 'br, gzip, deflate')
    } else {
      httpRequest.headersList.append('accept-encodin