fetcher.ts

/* global $SolidTestEnvironment */
/**
 *
 * Project: rdflib.js
 *
 * @file: fetcher.js
 *
 * Description: contains functions for requesting/fetching/retracting
 *  This implements quite a lot of the web architecture.
 * A fetcher is bound to a specific quad store, into which
 * it loads stuff and into which it writes its metadata
 * @@ The metadata could be optionally a separate graph
 *
 * - implements semantics of HTTP headers, Internet Content Types
 * - selects parsers for rdf/xml, n3, rdfa, grddl
 *
 * TO do:
 * - Implement a runtime registry for parsers and serializers
 * -
 */

/**
 * Things to test: callbacks on request, refresh, retract
 *   loading from HTTP, HTTPS, FTP, FILE, others?
 * To do:
 * Firing up a mail client for mid:  (message:) URLs
 */
import IndexedFormula from './store'
import log from './log'
import N3Parser from './n3parser'
import RDFlibNamedNode from './named-node'
import Namespace from './namespace'
import rdfParse from './parse'
import { parseRDFaDOM } from './rdfaparser'
import RDFParser from './rdfxmlparser'
import * as Uri from './uri'
import { isCollection, isNamedNode} from './utils/terms'
import * as Util from './utils-js'
import serialize from './serialize'
import crossFetch, { Headers } from 'cross-fetch'

import {
  ContentType, TurtleContentType, RDFXMLContentType, XHTMLContentType
} from './types'
import { termValue } from './utils/termValue'
import {
  BlankNode,
  RdfJsDataFactory,
  Quad_Graph,
  NamedNode,
  Quad_Predicate,
  Quad_Subject
} from './tf-types'
import jsonldParser from './jsonldparser'

const Parsable = {
  'text/n3': true,
  'text/turtle': true,
  'application/rdf+xml': true,
  'application/xhtml+xml': true,
  'text/html': true,
  'application/ld+json': true
}

// This is a minimal set to allow the use of damaged servers if necessary
const CONTENT_TYPE_BY_EXT = {
  'rdf': RDFXMLContentType,
  'owl': RDFXMLContentType,
  'n3': 'text/n3',
  'ttl': 'text/turtle',
  'nt': 'text/n3',
  'acl': 'text/n3',
  'html': 'text/html',
  'xml': 'text/xml'
}

// Convenience namespaces needed in this module.
// These are deliberately not exported as the user application should
// make its own list and not rely on the prefixes used here,
// and not be tempted to add to them, and them clash with those of another
// application.
const getNS = (factory?: RdfJsDataFactory) => {
  return {
    link: Namespace('http://www.w3.org/2007/ont/link#', factory),
    http: Namespace('http://www.w3.org/2007/ont/http#', factory),
    httph: Namespace('http://www.w3.org/2007/ont/httph#', factory),  // headers
    rdf: Namespace('http://www.w3.org/1999/02/22-rdf-syntax-ns#', factory),
    rdfs: Namespace('http://www.w3.org/2000/01/rdf-schema#', factory),
    dc: Namespace('http://purl.org/dc/elements/1.1/', factory),
    ldp: Namespace('http://www.w3.org/ns/ldp#', factory)
  }
}
const ns = getNS()

export interface FetchError extends Error {
  statusText?: string
  status?: StatusValues
  response?: ExtendedResponse
}

/** An extended interface of Response, since RDFlib.js adds some properties. */
export interface ExtendedResponse extends Response {
  /** String representation of the Body */
  responseText?: string
  /** Identifier of the reqest */
  req?: Quad_Subject
  size?: number
  timeout?: number
  /** Used in UpdateManager.updateDav */
  error?: string
}

/** tell typescript that a 'panes' child may exist on Window */
declare global {
  interface Window {
    panes?: any
    solidFetcher?: any
    solidFetch?: any
  }
  var solidFetcher: Function
  var solidFetch: Function
}
declare var $SolidTestEnvironment: {
  localSiteMap?: any
}

type UserCallback = (
  ok: boolean,
  message: string,
  response?: any
) => void

type HTTPMethods = 'GET' | 'PUT' | 'POST' | 'PATCH' | 'HEAD' | 'DELETE' | 'CONNECT' | 'TRACE' | 'OPTIONS'

/** All valid inputs for initFetchOptions */
type Options = Partial<AutoInitOptions>

/** Initiated by initFetchOptions, which runs on load */
export interface AutoInitOptions extends RequestInit{
  /** The used Fetch function */
  fetch?: Fetch
  /**
   * Referring term, the resource which
   * referred to this (for tracking bad links).
   * The document in which this link was found.
   */
  referringTerm?: NamedNode
  /** Provided content type (for writes) */
  contentType?: string
  /**
   * Override the incoming header to
   * force the data to be treated as this content-type (for reads)
   */
  forceContentType?: ContentType
  /**
   * Load the data even if loaded before.
   * Also sets the `Cache-Control:` header to `no-cache`
   */
  force?: boolean
  /**
   * Original uri to preserve
   * through proxying etc (`xhr.original`).
   */
  baseURI: string
  /**
   * Whether this request is a retry via
   * a proxy (generally done from an error handler)
   */
  proxyUsed?: boolean
  actualProxyURI?: string
  /** flag for XHR/CORS etc */
  withCredentials?: boolean
  /** Before we parse new data, clear old, but only on status 200 responses */
  clearPreviousData?: boolean
  /** Prevents the addition of various metadata triples (about the fetch request) to the store*/
  noMeta?: boolean
  noRDFa?: boolean
  handlers?: Handler[]
  timeout?: number
  method?: HTTPMethods
  retriedWithNoCredentials?: boolean
  requestedURI?: string
  // Seems to be required in some functions, such as XHTML parse and RedirectToProxy
  resource: Quad_Subject
  /** The serialized resource in the body*/
  // Used for storing metadata of requests
  original: NamedNode
  // Like requeststatus? Can contain text with error.
  data?: string
  // Probably an identifier for request?s
  req: BlankNode
  // Might be the same as Options.data
  body?: string
  headers: HeadersInit
  credentials?: 'include' | 'omit'
}

class Handler {
  // TODO: Document, type
  response: ExtendedResponse
  // TODO: Document, type
  dom: Document
  static pattern: RegExp

  constructor (response: ExtendedResponse, dom?: Document) {
    this.response = response
    // The type assertion operator here might need to be removed.
    this.dom = dom!
  }
}

class RDFXMLHandler extends Handler {
  static toString () {
    return 'RDFXMLHandler'
  }

  static register (fetcher: Fetcher) {
    fetcher.mediatypes[RDFXMLContentType] = {
      'q': 0.9
    }
  }

  parse (
    fetcher: Fetcher,
    /** An XML String */
    responseText: String,
    /** Requires .original */
    options: {
      original: Quad_Subject
      req: Quad_Subject
    } & Options,
  ) {
    let kb = fetcher.store
    if (!this.dom) {
      this.dom = Util.parseXML(responseText)
    }
    let root = this.dom.documentElement
    if (root.nodeName === 'parsererror') { // Mozilla only See issue/issue110
      // have to fail the request
      return fetcher.failFetch(options, 'Badly formed XML in ' +
        options.resource!.value, 'parse_error')
    }
    let parser = new RDFParser(kb)
    try {
      parser.parse(this.dom, options.original.value, options.original)
    } catch (err) {
      return fetcher.failFetch(options, 'Syntax error parsing RDF/XML! ' + err,
        'parse_error')
    }
    if (!options.noMeta) {
      kb.add(options.original, ns.rdf('type'), ns.link('RDFDocument'), fetcher.appNode)
    }

    return fetcher.doneFetch(options, this.response)
  }
}
RDFXMLHandler.pattern = new RegExp('application/rdf\\+xml')

class XHTMLHandler extends Handler {
  static toString () {
    return 'XHTMLHandler'
  }

  static register (fetcher: Fetcher) {
    fetcher.mediatypes[XHTMLContentType] = {}
  }

  parse (
    fetcher: Fetcher,
    responseText: string,
    options: {
      resource: Quad_Subject
      original: Quad_Subject
    } & Options,
  ): Promise<FetchError> | ExtendedResponse {
    let relation, reverse: boolean
    if (!this.dom) {
      this.dom = Util.parseXML(responseText)
    }
    let kb = fetcher.store

    // dc:title
    let title = this.dom.getElementsByTagName('title')
    if (title.length > 0) {
      kb.add(options.resource, ns.dc('title'), kb.rdfFactory.literal(title[0].textContent as string),
        options.resource)
      // log.info("Inferring title of " + xhr.resource)
    }

    // link rel
    let links = this.dom.getElementsByTagName('link')
    for (let x = links.length - 1; x >= 0; x--) { // @@ rev
      relation = links[x].getAttribute('rel')
      reverse = false
      if (!relation) {
        relation = links[x].getAttribute('rev')
        reverse = true
      }
      if (relation) {
        fetcher.linkData(options.original, relation,
          links[x].getAttribute('href') as string, options.resource, reverse)
      }
    }

    // Data Islands
    let scripts = this.dom.getElementsByTagName('script')
    for (let i = 0; i < scripts.length; i++) {
      let contentType = scripts[i].getAttribute('type')
      if (Parsable[contentType!]) {
        // @ts-ignore incompatibility between Store.add and Formula.add
        rdfParse(scripts[i].textContent as string, kb, options.original.value, contentType)
        // @ts-ignore incompatibility between Store.add and Formula.add
        rdfParse(scripts[i].textContent as string, kb, options.original.value, contentType)
      }
    }

    if (!options.noMeta) {
      kb.add(options.resource, ns.rdf('type'), ns.link('WebPage'), fetcher.appNode)
    }

    if (!options.noRDFa && parseRDFaDOM) { // enable by default
      try {
        parseRDFaDOM(this.dom, kb, options.original.value)
      } catch (err) {
        // @ts-ignore
        let msg = 'Error trying to parse ' + options.resource + ' as RDFa:\n' + err + ':\n' + err.stack
        return fetcher.failFetch(options as AutoInitOptions, msg, 'parse_error')
      }
    }

    return fetcher.doneFetch(options as AutoInitOptions, this.response)
  }
}
XHTMLHandler.pattern = new RegExp('application/xhtml')

class XMLHandler extends Handler {
  static toString () {
    return 'XMLHandler'
  }

  static register (fetcher: Fetcher) {
    fetcher.mediatypes['text/xml'] = { 'q': 0.5 }
    fetcher.mediatypes['application/xml'] = { 'q': 0.5 }
  }

  static isElement(node: Node): node is Element {
    return node.nodeType === Node.ELEMENT_NODE;
  }


  parse (
    fetcher: Fetcher,
    responseText: string,
    options: {
      original: Quad_Subject
      req: BlankNode
      resource: Quad_Subject
    } & Options,
  ): ExtendedResponse | Promise<FetchError> {
    let dom = Util.parseXML(responseText)

    // XML Semantics defined by root element namespace
    // figure out the root element
    for (let c = 0; c < dom.childNodes.length; c++) {
      const node = dom.childNodes[c]
      // is this node an element?
      if (XMLHandler.isElement(node)) {

        // We've found the first element, it's the root
        let ns = node.namespaceURI

        // Is it RDF/XML?
        if (ns && ns === ns['rdf']) {
          fetcher.addStatus(options.req,
            'Has XML root element in the RDF namespace, so assume RDF/XML.')

          let rdfHandler = new RDFXMLHandler(this.response, dom)
          return rdfHandler.parse(fetcher, responseText, options)
        }

        break
      }
    }

    // Or it could be XHTML?
    // Maybe it has an XHTML DOCTYPE?
    if (dom.doctype) {
      // log.info("We found a DOCTYPE in " + xhr.resource)
      if (dom.doctype.name === 'html' &&
          dom.doctype.publicId.match(/^-\/\/W3C\/\/DTD XHTML/) &&
          dom.doctype.systemId.match(/http:\/\/www.w3.org\/TR\/xhtml/)) {
        fetcher.addStatus(options.req,
          'Has XHTML DOCTYPE. Switching to XHTML Handler.\n')

        let xhtmlHandler = new XHTMLHandler(this.response, dom)
        return xhtmlHandler.parse(fetcher, responseText, options)
      }
    }

    // Or what about an XHTML namespace?
    let html = dom.getElementsByTagName('html')[0]
    if (html) {
      let xmlns = html.getAttribute('xmlns')
      if (xmlns && xmlns.match(/^http:\/\/www.w3.org\/1999\/xhtml/)) {
        fetcher.addStatus(options.req,
          'Has a default namespace for ' + 'XHTML. Switching to XHTMLHandler.\n')

        let xhtmlHandler = new XHTMLHandler(this.response, dom)
        return xhtmlHandler.parse(fetcher, responseText, options)
      }
    }

    // At this point we should check the namespace document (cache it!) and
    // look for a GRDDL transform
    // @@  Get namespace document <n>, parse it, look for  <n> grddl:namespaceTransform ?y
    // Apply ?y to   dom
    // We give up. What dialect is this?
    return fetcher.failFetch(options,
      'Unsupported dialect of XML: not RDF or XHTML namespace, etc.\n' +
      responseText.slice(0, 80), 901)
  }
}
XMLHandler.pattern = new RegExp('(text|application)/(.*)xml')

class HTMLHandler extends Handler {
  static toString () {
    return 'HTMLHandler'
  }

  static register (fetcher: Fetcher) {
    fetcher.mediatypes['text/html'] = {
      'q': 0.9
    }
  }

  parse (
    fetcher: Fetcher,
    responseText: string,
    options: {
      req: BlankNode,
      resource: Quad_Subject,
      original: Quad_Subject,
    } & Options
  ): Promise<FetchError> | ExtendedResponse {
    let kb = fetcher.store

    // We only handle XHTML so we have to figure out if this is XML
    // log.info("Sniffing HTML " + xhr.resource + " for XHTML.")
    if (isXML(responseText)) {
      fetcher.addStatus(options.req, "Has an XML declaration. We'll assume " +
        "it's XHTML as the content-type was text/html.\n")

      let xhtmlHandler = new XHTMLHandler(this.response)
      return xhtmlHandler.parse(fetcher, responseText, options)
    }

    // DOCTYPE html
    if (isXHTML(responseText)) {
      fetcher.addStatus(options.req,
        'Has XHTML DOCTYPE. Switching to XHTMLHandler.\n')

      let xhtmlHandler = new XHTMLHandler(this.response)
      return xhtmlHandler.parse(fetcher, responseText, options)
    }

    // xmlns
    if (isXMLNS(responseText)) {
      fetcher.addStatus(options.req,
        'Has default namespace for XHTML, so switching to XHTMLHandler.\n')

      let xhtmlHandler = new XHTMLHandler(this.response)
      return xhtmlHandler.parse(fetcher, responseText, options)
    }

    // dc:title
    // no need to escape '/' here
    let titleMatch = (new RegExp('<title>([\\s\\S]+?)</title>', 'im')).exec(responseText)
    if (titleMatch) {
      kb.add(options.resource, ns.dc('title'), kb.rdfFactory.literal(titleMatch[1]),
        options.resource) // think about xml:lang later
    }
    kb.add(options.resource, ns.rdf('type'), ns.link('WebPage'), fetcher.appNode)
    fetcher.addStatus(options.req, 'non-XML HTML document, not parsed for data.')

    return fetcher.doneFetch(options, this.response)
  }
}
HTMLHandler.pattern = new RegExp('text/html')

class JsonLdHandler extends Handler {
  static toString () {
    return 'JsonLdHandler'
  }
  static register (fetcher: Fetcher) {
    fetcher.mediatypes['application/ld+json'] = {
      'q': 0.9
    }
  }
  parse (
    fetcher: Fetcher,
    responseText: string,
    options: {
      req: Quad_Subject
      original: Quad_Subject
      resource: Quad_Subject
    } & Options,
    response: ExtendedResponse
  ): Promise<ExtendedResponse | FetchError> {
    const kb = fetcher.store
    return new Promise((resolve, reject) => {
      try {
        jsonldParser (responseText, kb, options.original.value, () => {
          resolve(fetcher.doneFetch(options, response))
        })
      } catch (err) {
        const msg = 'Error trying to parse ' + options.resource +
          ' as JSON-LD:\n' + err  // not err.stack -- irrelevant
        resolve(fetcher.failFetch(options, msg, 'parse_error', response))
      }
    })
  }
}
JsonLdHandler.pattern = /application\/ld\+json/

class TextHandler extends Handler {
  static toString () {
    return 'TextHandler'
  }

  static register (fetcher: Fetcher) {
    fetcher.mediatypes['text/plain'] = {
      'q': 0.5
    }
  }

  parse (
    fetcher: Fetcher,
    responseText: string,
    options: {
      req: Quad_Subject
      original: Quad_Subject
      resource: Quad_Subject
    } & Options
  ): ExtendedResponse | Promise<FetchError> {
    // We only speak dialects of XML right now. Is this XML?

    // Look for an XML declaration
    if (isXML(responseText)) {
      fetcher.addStatus(options.req, 'Warning: ' + options.resource +
        " has an XML declaration. We'll assume " +
        "it's XML but its content-type wasn't XML.\n")

      let xmlHandler = new XMLHandler(this.response)
      return xmlHandler.parse(fetcher, responseText, options)
    }

    // Look for an XML declaration
    if (responseText.slice(0, 500).match(/xmlns:/)) {
      fetcher.addStatus(options.req, "May have an XML namespace. We'll assume " +
        "it's XML but its content-type wasn't XML.\n")

      let xmlHandler = new XMLHandler(this.response)
      return xmlHandler.parse(fetcher, responseText, options)
    }

    // We give up finding semantics - this is not an error, just no data
    fetcher.addStatus(options.req, 'Plain text document, no known RDF semantics.')

    return fetcher.doneFetch(options, this.response)
  }
}
TextHandler.pattern = new RegExp('text/plain')

class N3Handler extends Handler {
  static toString () {
    return 'N3Handler'
  }

  static register (fetcher: Fetcher) {
    fetcher.mediatypes['text/n3'] = {
      'q': '1.0'
    } // as per 2008 spec
    /*
     fetcher.mediatypes['application/x-turtle'] = {
     'q': 1.0
     } // pre 2008
     */
    fetcher.mediatypes['text/turtle'] = {
      'q': 1.0
    } // post 2008
  }

  parse (
    fetcher: Fetcher,
    responseText: string,
    options: {
      original: NamedNode
      req: Quad_Subject
    } & Options,
    response: ExtendedResponse
  ): ExtendedResponse | Promise<FetchError> {
    // Parse the text of this N3 file
    let kb = fetcher.store
    let p = N3Parser(kb, kb, options.original.value, options.original.value,
      null, null, '', null)
    //                p.loadBuf(xhr.responseText)
    try {
      p.loadBuf(responseText)
    } catch (err) {
      let msg = 'Error trying to parse ' + options.resource +
        ' as Notation3:\n' + err  // not err.stack -- irrelevant
      return fetcher.failFetch(options, msg, 'parse_error', response)
    }

    fetcher.addStatus(options.req, 'N3 parsed: ' + p.statementCount + ' triples in ' + p.lines + ' lines.')
    fetcher.store.add(options.original, ns.rdf('type'), ns.link('RDFDocument'), fetcher.appNode)

    return fetcher.doneFetch(options, this.response)
  }
}
N3Handler.pattern = new RegExp('(application|text)/(x-)?(rdf\\+)?(n3|turtle)')

const defaultHandlers = {
  RDFXMLHandler, XHTMLHandler, XMLHandler, HTMLHandler, TextHandler, N3Handler, JsonLdHandler
}

function isXHTML (responseText) {
  const docTypeStart = responseText.indexOf('<!DOCTYPE html')
  const docTypeEnd = responseText.indexOf('>')
  if (docTypeStart === -1 || docTypeEnd === -1 || docTypeStart > docTypeEnd) {
    return false
  }
  return responseText.substr(docTypeStart, docTypeEnd - docTypeStart).indexOf('XHTML') !== -1
}

function isXML (responseText: string): boolean {
  const match = responseText.match(/\s*<\?xml\s+version\s*=[^<>]+\?>/)
  return !!match
}

function isXMLNS (responseText: string): boolean {
  const match = responseText.match(/[^(<html)]*<html\s+[^<]*xmlns=['"]http:\/\/www.w3.org\/1999\/xhtml["'][^<]*>/)
  return !!match
}

type StatusValues =
  /** No record of web access or record reset */
  undefined |
  /** Has been requested, fetch in progress */
  true |
  /** Received, OK */
  'done' |
  /** Not logged in */
  401 |
  /** HTTP status unauthorized */
  403 |
  /** Not found, resource does not exist */
  404 |
  /** In attempt to counter CORS problems retried */
  'redirected' |
  /** If it did fail */
  'failed' |
  'parse_error' |
  /**
   * URI is not a protocol Fetcher can deal with
   * other strings mean various other errors.
   */
  'unsupported_protocol' |
  'timeout' |
  /** Any other HTTP status code */
  number

interface MediatypesMap {
  [id: string]: {
    // Either string '1.0' or number 1.0 is allowed
    'q'?: number | string
  };
}

interface RequestedMap {
  [uri: string]: StatusValues
}

interface TimeOutsMap {
  [uri: string]: number[]
}

interface FetchQueue {
  [uri: string]: Promise<ExtendedResponse>
}

interface FetchCallbacks {
  [uri: string]: UserCallback[]
}

interface BooleanMap {
  [uri: string]: boolean
}

// Not sure about the shapes of this. Response? FetchError?
type Result = Response

/** Differs from normal Fetch, has an extended Response type */
type Fetch = (input: RequestInfo, init?: RequestInit) => Promise<ExtendedResponse>;

interface CallbackifyInterface {
  fireCallbacks: Function
}

/** Fetcher
 *
 * The Fetcher object is a helper object for a quadstore
 * which turns it from an offline store to an online store.
 * The fetcher deals with loading data files rom the web,
  * figuring how to parse them.  It will also refresh, remove, the data
  * and put back the data to the web.
 */
export default class Fetcher implements CallbackifyInterface {
  store: IndexedFormula
  timeout: number
  _fetch: Fetch
  mediatypes: MediatypesMap
  /** Denoting this session */
  appNode: BlankNode
  /**
   * this.requested[uri] states:
   * undefined     no record of web access or records reset
   * true          has been requested, fetch in progress
   * 'done'        received, Ok
   * 401           Not logged in
   * 403           HTTP status unauthorized
   * 404           Resource does not exist. Can be created etc.
   * 'redirected'  In attempt to counter CORS problems retried.
   * 'parse_error' Parse error
   * 'unsupported_protocol'  URI is not a protocol Fetcher can deal with
   * other strings mean various other errors.
   */
  requested: RequestedMap
  /** List of timeouts associated with a requested URL */
  timeouts: TimeOutsMap
  /** Redirected from *key uri* to *value uri* */
  redirectedTo: Record<string, string>
  fetchQueue: FetchQueue
  /** fetchCallbacks[uri].push(callback) */
  fetchCallbacks: FetchCallbacks
  /** Keep track of explicit 404s -> we can overwrite etc */
  nonexistent: BooleanMap
  lookedUp: BooleanMap
  handlers: Array<typeof Handler>
  ns: { [k: string]: (ln: string) => Quad_Predicate }
  static HANDLERS: {
    [handlerName: number]: Handler
  }
  static CONTENT_TYPE_BY_EXT: Record<string, string>
  // TODO: Document this
  static crossSiteProxyTemplate: any

  /** Methods added by calling Util.callbackify in the constructor*/
  fireCallbacks!: Function

  constructor (store: IndexedFormula, options: Options = {}) {
    this.store = store || new IndexedFormula()
    this.ns = getNS(this.store.rdfFactory)
    this.timeout = options.timeout || 30000

    // solidFetcher is deprecated
    this._fetch = options.fetch
               || (typeof global !== 'undefined' && (global.solidFetcher || global.solidFetch))
               || (typeof window !== 'undefined' && (window.solidFetcher || window.solidFetch))
               || crossFetch
    if (!this._fetch) {
      throw new Error('No _fetch function available for Fetcher')
    }

    this.appNode = this.store.rdfFactory.blankNode()
    this.store.fetcher = this // Bi-linked
    this.requested = {}
    this.timeouts = {}
    this.redirectedTo = {}
    this.fetchQueue = {}
    this.fetchCallbacks = {}
    this.nonexistent = {}
    this.lookedUp = {}
    this.handlers = []
    this.mediatypes = {
      'image/*': { 'q': 0.9 },
      '*/*': { 'q': 0.1 }  // Must allow access to random content
    }

    // Util.callbackify(this, ['request', 'recv', 'headers', 'load', 'fail',
    //   'refresh', 'retract', 'done'])
    // In switching to fetch(), 'recv', 'headers' and 'load' do not make sense
    Util.callbackify(this, ['request', 'fail', 'refresh', 'retract', 'done'])

    Object.keys(options.handlers || defaultHandlers).map(key => this.addHandler(defaultHandlers[key]))
  }

  static crossSiteProxy (uri: string): undefined | any {
    if (Fetcher.crossSiteProxyTemplate) {
      return Fetcher.crossSiteProxyTemplate
        .replace('{uri}', encodeURIComponent(uri))
    } else {
      return undefined
    }
  }

  static offlineOverride (uri: string): string {
    // Map the URI to a localhost proxy if we are running on localhost
    // This is used for working offline, e.g. on planes.
    // Is the script itself is running in localhost, then access all
    //   data in a localhost mirror.
    // Do not remove without checking with TimBL
    let requestedURI = uri

    var UI
    if (typeof window !== 'undefined' && window.panes && (UI = window.panes.UI) &&
      UI.preferences && UI.preferences.get('offlineModeUsingLocalhost')) {
      if (requestedURI.slice(0, 7) === 'http://' && requestedURI.slice(7, 17) !== 'localhost/') {
        requestedURI = 'http://localhost/' + requestedURI.slice(7)
        log.warn('Localhost kludge for offline use: actually getting <' +
          requestedURI + '>')
      } else {
        // log.warn("Localhost kludge NOT USED <" + requestedURI + ">")
      }
    } else {
      // log.warn("Localhost kludge OFF offline use: actually getting <" +
      //   requestedURI + ">")
    }

    return requestedURI
  }

  static proxyIfNecessary (uri: string) {
    var UI
    if (
      typeof window !== 'undefined' &&
      (window as any).panes &&
      (UI = (window as any).panes.UI) &&
      UI.isExtension
    ) {
      return uri
    } // Extension does not need proxy

    if (typeof $SolidTestEnvironment !== 'undefined' &&
      $SolidTestEnvironment.localSiteMap) {
      // nested dictionaries of URI parts from origin down
      let hostpath = uri.split('/').slice(2) // the bit after the //

      const lookup = (parts, index) => {
        let z = index[parts.shift()]

        if (!z) { return null }

        if (typeof z === 'string') {
          return z + parts.join('/')
        }

        if (!parts) { return null }

        return lookup(parts, z)
      }

      const y = lookup(hostpath, $SolidTestEnvironment.localSiteMap)

      if (y) {
        return y
      }
    }

    // browser does 2014 on as https browser script not trusted
    // If the web app origin is https: then the mixed content rules
    // prevent it loading insecure http: stuff so we need proxy.
    if (Fetcher.crossSiteProxyTemplate &&
        typeof document !== 'undefined' && document.location &&
        ('' + document.location).slice(0, 6) === 'https:' && // origin is secure
        uri.slice(0, 5) === 'http:') { // requested data is not
      return Fetcher.crossSiteProxyTemplate
        .replace('{uri}', encodeURIComponent(uri))
    }

    return uri
  }

  /**
   * Tests whether the uri's protocol is supported by the Fetcher.
   * @param uri
   */
  static unsupportedProtocol (uri: string): boolean {
    let pcol = Uri.protocol(uri)

    return (pcol === 'tel' || pcol === 'mailto' || pcol === 'urn')
  }

  /** Decide on credentials using old XXHR api or new fetch()  one
   * @param requestedURI
   * @param options
   */
  static setCredentials (requestedURI: string, options: Options = {}) {
    // 2014 CORS problem:
    // XMLHttpRequest cannot load http://www.w3.org/People/Berners-Lee/card.
    // A wildcard '*' cannot be used in the 'Access-Control-Allow-Origin'
    //   header when the credentials flag is true.
    // @ Many ontology files under http: and need CORS wildcard ->
    //   can't have credentials
    if (options.credentials === undefined) { // Caller using new fetch convention
      if (options.withCredentials !== undefined) { // XHR style is what Fetcher specified before
        options.credentials = options.withCredentials ? 'include' : 'omit'
      } else {
        options.credentials = 'include' // default is to be logged on
      }
    }
  }

  /**
   * Promise-based load function
   *
   * Loads a web resource or resources into the store.
   *
   * A resource may be given as NamedNode object, or as a plain URI.
   * an array of resources will be given, in which they will be fetched in parallel.
   * By default, the HTTP headers are recorded also, in the same store, in a separate graph.
   * This allows code like editable() for example to test things about the resource.
   *
   * @param uri {Array<RDFlibNamedNode>|Array<string>|RDFlibNamedNode|string}
   *
   * @param [options={}] {Object}
   *
   * @param [options.fetch] {Function}
   *
   * @param [options.referringTerm] {RDFlibNamedNode} Referring term, the resource which
   *   referred to this (for tracking bad links)
   *
   * @param [options.contentType] {string} Provided content type (for writes)
   *
   * @param [options.forceContentType] {string} Override the incoming header to
   *   force the data to be treated as this content-type (for reads)
   *
   * @param [options.force] {boolean} Load the data even if loaded before.
   *   Also sets the `Cache-Control:` header to `no-cache`
   *
   * @param [options.baseURI=docuri] {Node|string} Original uri to preserve
   *   through proxying etc (`xhr.original`).
   *
   * @param [options.proxyUsed] {boolean} Whether this request is a retry via
   *   a proxy (generally done from an error handler)
   *
   * @param [options.withCredentials] {boolean} flag for XHR/CORS etc
   *
   * @param [options.clearPreviousData] {boolean} Before we parse new data,
   *   clear old, but only on status 200 responses
   *
   * @param [options.noMeta] {boolean} Prevents the addition of various metadata
   *   triples (about the fetch request) to the store
   *
   * @param [options.noRDFa] {boolean}
   *
   * @returns {Promise<Result>}
   */
  load <T extends NamedNode | string | Array<string | NamedNode>>(
    uri: T,
    options: Options = {}
  ): T extends Array<string | NamedNode> ? Promise<Result[]> : Promise<Result> {
    options = Object.assign({}, options) // Take a copy as we add stuff to the options!!
    if (uri instanceof Array) {
      return Promise.all(uri.map((x) => {
        return this.load(x, Object.assign({}, options)) as unknown as Promise<Result>
      })) as T extends Array<string | NamedNode> ? Promise<Result[]> : Promise<Result>
    }

    const uriIn: NamedNode | string = uri as NamedNode

    let docuri = termValue(uriIn)
    docuri = docuri.split('#')[0]

    options = this.initFetchOptions(docuri, options)

    const initialisedOptions = this.initFetchOptions(docuri, options)

    return this.pendingFetchPromise(docuri, initialisedOptions.baseURI, initialisedOptions) as any
  }

  pendingFetchPromise (
    uri: string,
    originalUri: string,
    options: AutoInitOptions
  ): Promise<Result> {
    let pendingPromise

    // Check to see if some request is already dealing with this uri
    if (!options.force && this.fetchQueue[originalUri]) {
      pendingPromise = this.fetchQueue[originalUri]
    } else {
      pendingPromise = Promise
        .race([
          this.setRequestTimeout(uri, options),
          this.fetchUri(uri, options)
        ])
      this.fetchQueue[originalUri] = pendingPromise

      // Clean up the queued promise after a time, if it's resolved
      this.cleanupFetchRequest(originalUri, undefined, this.timeout)
    }

    return pendingPromise.then(x => {
      if (uri in this.timeouts) {
        this.timeouts[uri].forEach(clearTimeout)
        delete this.timeouts[uri]
      }
      return x
    })
  }

  /**
   * @param _options - DEPRECATED
   */
  cleanupFetchRequest (
    originalUri: string,
    _options,
    timeout: number
  ) {
    if (_options !== undefined) {
      console.warn("_options is deprecated")
    }
    this.timeouts[originalUri] = (this.timeouts[originalUri] || []).concat(setTimeout(() => {
      if (!this.isPending(originalUri)) {
        delete this.fetchQueue[originalUri]
      }
    }, timeout) as unknown as number)
  }

  initFetchOptions (
    uri: string,
    options: Options
  ): AutoInitOptions {
    let kb = this.store

    let isGet = !options.method || options.method.toUpperCase() === 'GET'
    if (!isGet) {
      options.force = true
    }

    options.resource = kb.rdfFactory.namedNode(uri) // This might be proxified
    options.baseURI = options.baseURI || uri // Preserve though proxying etc
    options.original = kb.rdfFactory.namedNode(options.baseURI)
    options.req = kb.bnode()
    options.headers = options.headers || new Headers()

    if (options.contentType) {
      // @ts-ignore
      options.headers['content-type'] = options.contentType
    }

    if (options.force) {
      options.cache = 'no-cache'
    }

    let acceptString = this.acceptString()
    // @ts-ignore
    options.headers['accept'] = acceptString

    let requestedURI = Fetcher.offlineOverride(uri)
    options.requestedURI = requestedURI

    Fetcher.setCredentials(requestedURI, options)

    let actualProxyURI = Fetcher.proxyIfNecessary(requestedURI)
    if (requestedURI !== actualProxyURI) {
      options.proxyUsed = true
    }
    options.actualProxyURI = actualProxyURI

    return options as AutoInitOptions
  }

  /**
   * (The promise chain ends in either a `failFetch()` or a `doneFetch()`)
   *
   * @param docuri {string}
   * @param options {Object}
   *
   * @returns {Promise<Object>} fetch() result or an { error, status } object
   */
  fetchUri (docuri: string, options: AutoInitOptions): Promise<ExtendedResponse | FetchError> {
    if (!docuri) {
      return Promise.reject(new Error('Cannot fetch an empty uri'))
    }

    if (Fetcher.unsupportedProtocol(docuri)) {
      return this.failFetch(options, 'fetcher: Unsupported protocol', 'unsupported_protocol')
    }

    let state = this.getState(docuri)

    if (!options.force) {
      if (state === 'fetched') {  // URI already fetched and added to store
        return Promise.resolve(
          // @ts-ignore This is not a valid response object
          this.doneFetch(options, {
            status: 200,
            ok: true,
            statusText: 'Already loaded into quadstore.'
          })
        )
      }
      if (state === 'failed' && this.requested[docuri] === 404) { // Remember nonexistence
        let message = 'Previously failed: ' + this.requested[docuri]
        // @ts-ignore This is not a valid response object
        let dummyResponse: ExtendedResponse = {
          url: docuri,
          // This does not comply to Fetch spec, it can be a string value in rdflib
          status: this.requested[docuri] as number,
          statusText: message,
          responseText: message,
          headers: new Headers,  // Headers() ???
          ok: false,
          body: null,
          bodyUsed: false,
          size: 0,
          timeout: 0
        }
        return this.failFetch(options, message,
          this.requested[docuri], dummyResponse)
      }
    } else {
      // options.force == true
      delete this.nonexistent[docuri]
    }

    this.fireCallbacks('request', [docuri])

    this.requested[docuri] = true  // mark this uri as 'requested'

    if (!options.noMeta) {
      this.saveRequestMetadata(docuri, options)
    }

    let { actualProxyURI } = options

    // Map might get mistakenly added into headers
    // error TS2339: Property 'map' does not exist on type 'Headers'.
    /* let map
    if (options.headers && map in options.headers) {
      delete options.headers.map
    } */

    return this._fetch((actualProxyURI as string), options)
      .then(response => this.handleResponse(response, docuri, options),
      error => { // @@ handleError?
        // @ts-ignore Invalid response object
        let dummyResponse: ExtendedResponse = {
          url: actualProxyURI as string,
          status: 999, // @@ what number/string should fetch failures report?
          statusText: (error.name || 'network failure') + ': ' +
            (error.errno || error.code || error.type),
          responseText: error.message,
          headers: new Headers(),  // Headers() ???
          ok: false,
          body: null,
          bodyUsed: false,
          size: 0,
          timeout: 0
        }
        console.log('Fetcher: <' + actualProxyURI + '> Non-HTTP fetch exception: ' + error)
        return this.handleError(dummyResponse, docuri, options) // possible credentials retry
        // return this.failFetch(options, 'fetch failed: ' + error, 999, dummyResponse) // Fake status code: fetch exception

        // handleError expects a response so we fake some important bits.
        /*
        this.handleError(, docuri, options)
        */
      }
    )
  }

  /**
   * Asks for a doc to be loaded if necessary then calls back
   *
   * Calling methods:
   *   nowOrWhenFetched (uri, userCallback)
   *   nowOrWhenFetched (uri, options, userCallback)
   *   nowOrWhenFetched (uri, referringTerm, userCallback, options)  <-- old
   *   nowOrWhenFetched (uri, referringTerm, userCallback) <-- old
   *
   *  Options include:
   *   referringTerm    The document in which this link was found.
   *                    this is valuable when finding the source of bad URIs
   *   force            boolean.  Never mind whether you have tried before,
   *                    load this from scratch.
   *   forceContentType Override the incoming header to force the data to be
   *                    treated as this content-type.
   *
   *  Callback function takes:
   *
   *    ok               True if the fetch worked, and got a 200 response.
   *                     False if any error happened
   *
   *    errmessage       Text error message if not OK.
   *
   *    response         The fetch Response object (was: XHR) if there was was one
   *                     includes response.status as the HTTP status if any.
   */
  nowOrWhenFetched (
    uriIn: string | NamedNode,
    p2?: UserCallback | Options,
    userCallback?: UserCallback,
    options: Options = {}
  ): void {
    const uri = termValue(uriIn)

    if (typeof p2 === 'function') {
      // nowOrWhenFetched (uri, userCallback)
      userCallback = p2
    } else if (typeof p2 === 'undefined') { // original calling signature
      // referringTerm = undefined
    } else if (isNamedNode(p2)) {
      // referringTerm = p2
      options.referringTerm = p2
    } else {
      // nowOrWhenFetched (uri, options, userCallback)
      options = p2
    }

    (this.load(uri, options) as Promise<Response>)
      .then((fetchResponse: ExtendedResponse) => {
        if (userCallback) {
          if (fetchResponse) {
            if ((fetchResponse as Response).ok) {
              userCallback(true, 'OK', fetchResponse)
            } else {
              // console.log('@@@ fetcher.js Should not take this path !!!!!!!!!!!!')
              let oops = 'HTTP error: Status ' + fetchResponse.status + ' (' + fetchResponse.statusText + ')'
              if (fetchResponse.responseText) {
                oops += ' ' + fetchResponse.responseText // not in 404, dns error, nock failure
              }
              console.log(oops + ' fetching ' + uri)
              userCallback(false, oops, fetchResponse)
            }
          } else {
            let oops = ('@@ nowOrWhenFetched:  no response object!')
            console.log(oops)
            userCallback(false, oops)
          }
        }
      }, function (err: FetchError) {
        var message = err.message || err.statusText
        message = 'Failed to load  <' + uri + '> ' + message
        console.log(message)
        if (err.response && err.response.status) {
          message += ' status: ' + err.response.status
        }
        (userCallback as any)(false, message, err.response)
      })
  }

  /**
   * Records a status message (as a literal node) by appending it to the
   * request's metadata status collection.
   *
   */
  addStatus (req: BlankNode, statusMessage: string) {
    // <Debug about="parsePerformance">
    let now = new Date()
    statusMessage = '[' + now.getHours() + ':' + now.getMinutes() + ':' +
      now.getSeconds() + '.' + now.getMilliseconds() + '] ' + statusMessage
    // </Debug>
    let kb = this.store

    const statusNode = kb.the(req, this.ns.link('status'))
    if (isCollection(statusNode)) {
      statusNode.append(kb.rdfFactory.literal(statusMessage))
    } else {
      log.warn('web.js: No list to add to: ' + statusNode + ',' + statusMessage)
    }
  }

  /**
   * Records errors in the system on failure:
   *
   *  - Adds an entry to the request status collection
   *  - Adds an error triple with the fail message to the metadata
   *  - Fires the 'fail' callback
   *  - Rejects with an error result object, which has a response object if any
   */
  failFetch (
    options: {
      req: BlankNode
      original: Quad_Subject
    } & Options,
    errorMessage: string,
    statusCode: StatusValues,
    response?: ExtendedResponse
  ): Promise<FetchError> {
    this.addStatus(options.req, errorMessage)

    if (!options.noMeta) {
      this.store.add(
        options.original,
        this.ns.link('error'),
        this.store.rdfFactory.literal(errorMessage)
      )
    }

    let meth = (options.method || 'GET').toUpperCase()
    let isGet = meth === 'GET' || meth === 'HEAD'

    if (isGet) {  // only cache the status code on GET or HEAD
      if (!(options as any).resource.equals(options.original)) {
        // console.log('@@ Recording failure  ' + meth + '  original ' + options.original +option '( as ' + options.resource + ') : ' + statusCode)
      } else {
        // console.log('@@ Recording ' + meth + ' failure for ' + options.original + ': ' + statusCode)
      }
      this.requested[Uri.docpart(options.original.value)] = statusCode
      this.fireCallbacks('fail', [options.original.value, errorMessage])
    }

    var err: FetchError = new Error('Fetcher: ' + errorMessage)

    // err.ok = false // Is taken as a response, will work too @@ phase out?
    err.status = statusCode
    err.statusText = errorMessage
    err.response = response

    return Promise.reject(err)
  }

  // in the why part of the quad distinguish between HTML and HTTP header
  // Reverse is set iif the link was rev= as opposed to rel=
  linkData (
    originalUri: NamedNode,
    rel: string,
    uri: string,
    why: Quad_Graph,
    reverse?: boolean
  ) {
    if (!uri) return
    let kb = this.store
    let predicate
    // See http://www.w3.org/TR/powder-dr/#httplink for describedby 2008-12-10
    let obj = kb.rdfFactory.namedNode(Uri.join(uri, originalUri.value))

    if (rel === 'alternate' || rel === 'seeAlso' || rel === 'meta' ||
        rel === 'describedby') {
      if (obj.value === originalUri.value) { return }
      predicate = this.ns.rdfs('seeAlso')
    } else if (rel === 'type') {
      predicate = kb.rdfFactory.namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type')
    } else {
      // See https://www.iana.org/assignments/link-relations/link-relations.xml
      // Alas not yet in RDF yet for each predicate
      // encode space in e.g. rel="shortcut icon"
      predicate = kb.rdfFactory.namedNode(
        Uri.join(encodeURIComponent(rel),
          'http://www.iana.org/assignments/link-relations/')
      )
    }
    if (reverse) {
      kb.add(obj, predicate, originalUri, why)
    } else {
      kb.add(originalUri, predicate, obj, why)
    }
  }

  parseLinkHeader (
    linkHeader: string,
    originalUri: NamedNode,
    reqNode: Quad_Graph
  ): void {
    if (!linkHeader) { return }

    // const linkexp = /<[^>]*>\s*(\s*;\s*[^()<>@,;:"/[\]?={} \t]+=(([^()<>@,;:"/[]?={} \t]+)|("[^"]*")))*(,|$)/g
    // const paramexp = /[^()<>@,;:"/[]?={} \t]+=(([^()<>@,;:"/[]?={} \t]+)|("[^"]*"))/g

    // From https://www.dcode.fr/regular-expression-simplificator:
    // const linkexp = /<[^>]*>\s*(\s*;\s*[^()<>@,;:"/[\]?={} t]+=["]))*[,$]/g
    // const paramexp = /[^\\<>@,;:"\/\[\]?={} \t]+=["])/g
    // Original:
    const linkexp = /<[^>]*>\s*(\s*;\s*[^()<>@,;:"/[\]?={} \t]+=(([^\(\)<>@,;:"\/\[\]\?={} \t]+)|("[^"]*")))*(,|$)/g
    const paramexp = /[^\(\)<>@,;:"\/\[\]\?={} \t]+=(([^\(\)<>@,;:"\/\[\]\?={} \t]+)|("[^"]*"))/g

    const matches = linkHeader.match(linkexp)

    if (matches == null) return;

    for (let i = 0; i < matches.length; i++) {
      let split = matches[i].split('>')
      let href = split[0].substring(1)
      let ps = split[1]
      let s = ps.match(paramexp)
      if (s == null) return
      for (let j = 0; j < s.length; j++) {
        let p = s[j]
        let paramsplit = p.split('=')
        // var name = paramsplit[0]
        let rel = paramsplit[1].replace(/["']/g, '') // '"
        this.linkData(originalUri, rel, href, reqNode)
      }
    }
  }

  doneFetch (
    options: {
      req: Quad_Subject,
      original: Quad_Subject
    } & Options,
    response: ExtendedResponse
  ): Response {
    this.addStatus(options.req, 'Done.')
    this.requested[options.original.value] = 'done'

    this.fireCallbacks('done', [options.original.value])

    response.req = options.req  // Set the request meta blank node

    return response
  }

  /**
   * Note two nodes are now smushed
   * If only one was flagged as looked up, then the new node is looked up again,
   * which will make sure all the URIs are dereferenced
   */
  nowKnownAs (was: Quad_Subject, now: Quad_Subject): void {
    if (this.lookedUp[was.value]) {
      // Transfer userCallback
      if (!this.lookedUp[now.value]) {
        this.lookUpThing(now, was)
      }
    } else if (this.lookedUp[now.value]) {
      if (!this.lookedUp[was.value]) {
        this.lookUpThing(was, now)
      }
    }
  }

  /**
   * Writes back to the web what we have in the store for this uri
   */
  putBack (
    uri: NamedNode | string,
    options: Options = {}
  ): Promise<Response> {
    const uriSting = termValue(uri)
    let doc = new RDFlibNamedNode(uriSting).doc() // strip off #
    options.contentType = options["content-type"] || options["Content-Type"] || options.contentType || TurtleContentType
    if (options.contentType === 'application/ld+json') {
      return new Promise((resolve, reject) => {
        serialize(doc, this.store, doc.uri, options.contentType, (err, jsonString) => {
          if (err) {
            reject(err)
          } else {
            // @ts-ignore
            options.data = jsonString
            this.webOperation('PUT', uri, options)
              .then((res) => resolve(res))
              .catch((error) => reject(error))
          }
        })
      })
    }
    options.data = serialize(doc, this.store, doc.value, options.contentType) as string
    return this.webOperation('PUT', uriSting, options)
  }

  webCopy (here: string, there: string, contentType): Promise<ExtendedResponse> {
    return this.webOperation('GET', here)
      .then((result) => {
        return this.webOperation(
          'PUT', // change to binary from text
          there, { data: result.responseText, contentType })
      })
  }

  delete (uri: string, options?: Options): Promise<ExtendedResponse> {
    return this.webOperation('DELETE', uri, options)
      .then(response => {
        this.requested[uri] = 404
        this.nonexistent[uri] = true
        this.unload(this.store.rdfFactory.namedNode(uri))

        return response
      })
  }

  /** Create an empty resource if it really does not exist
   *  Be absolutely sure something does not exist before creating a new empty file
   * as otherwise existing could  be deleted.
   * @param doc - The resource
  */
  async createIfNotExists (
    doc: RDFlibNamedNode,
    contentType = TurtleContentType,
    data = ''
  ): Promise<ExtendedResponse> {
    const fetcher = this
    try {
      var response = await fetcher.load(doc as NamedNode)
    } catch (err) {
      // @ts-ignore
      if (err.response.status === 404) {
        console.log('createIfNotExists: doc does NOT exist, will create... ' + doc)
        try {
          response = await fetcher.webOperation('PUT', doc.value, {data, contentType})
        } catch (err) {
          console.log('createIfNotExists doc FAILED: ' + doc + ': ' + err)
          throw err
        }
        delete fetcher.requested[doc.value] // delete cached 404 error
        // console.log('createIfNotExists doc created ok ' + doc)
        return response
      } else {
        console.log('createIfNotExists doc load error NOT 404:  ' + doc + ': ' + err)
        throw err
      }
    }
    // console.log('createIfNotExists: doc exists, all good: ' + doc)
    return response as Response
  }

  /**
   * @param parentURI URI of parent container
   * @param folderName - Optional folder name (slug)
   * @param data - Optional folder metadata
   */
  createContainer (
    parentURI: string,
    folderName: string,
    data: string
  ): Promise<Response> {
    let headers = {
      // Force the right mime type for containers
      'content-type': TurtleContentType,
      'link': this.ns.ldp('BasicContainer') + '; rel="type"'
    }

    if (folderName) {
      headers['slug'] = folderName
    }

    // @ts-ignore These headers lack some of the required operators.
    let options: Options = { headers }

    if (data) {
      options.body = data
    }

    return this.webOperation('POST', parentURI, options)
  }

  invalidateCache (iri: string | NamedNode): void {
    const uri = termValue(iri)
    const fetcher = this
    // @ts-ignore
    if (fetcher.fetchQueue && fetcher.fetchQueue[uri]) {
      console.log('Internal error - fetchQueue exists ' + uri)
      var promise = fetcher.fetchQueue[uri]
      if (promise['PromiseStatus'] === 'resolved') {
        delete fetcher.fetchQueue[uri]
      } else { // pending
        delete fetcher.fetchQueue[uri]
        console.log('*** Fetcher: pending fetchQueue deleted ' + uri)
      }
    } if (fetcher.requested[uri] && fetcher.requested[uri] !== 'done' &&
     fetcher.requested[uri] !== 'failed' && fetcher.requested[uri] !== 404) {
       let msg = `Rdflib: fetcher: Destructive operation on <${fetcher.requested[uri]}> file being fetched! ` + uri
      console.error(msg)
      // alert(msg)
    } else {
      delete fetcher.requested[uri] // invalidate read cache -- @@ messes up logic if request in progress ??
      delete fetcher.nonexistent[uri]
    }
  }

  /**
   * A generic web opeation, at the fetch() level.
   * does not invole the quadstore.
   *
   *  Returns promise of Response
   *  If data is returned, copies it to response.responseText before returning
   */
  webOperation (
    method: HTTPMethods,
    uriIn: string | NamedNode,
    // Not sure about this type. Maybe this Options is different?
    options: Options = {}
  ): Promise<ExtendedResponse> {
    const uri = termValue(uriIn)
    options.method = method
    options.body = options.data || options.body
    options.force = true
    const fetcher = this

    if (options.body && !options.contentType) {
      throw new Error('Web operation sending data must have a defined contentType.')
    }
    if (options.contentType) {
      (options as any).headers = options.headers || {};
      (options as any).headers['content-type'] = options.contentType
    }
    Fetcher.setCredentials(uri, options)

    return new Promise(function (resolve, reject) {
      fetcher._fetch(uri, options).then(response => {
        if (response.ok) {
          if (method === 'PUT' || method === 'PATCH' || method === 'POST' || method === 'DELETE') {
            fetcher.invalidateCache (uri)
          } // response.body with Chrome can't be relied on
          if (response.text) { // Was: response.body https://github.com/linkeddata/rdflib.js/issues/506
            response.text().then(data => {
              response.responseText = data
              resolve(response)
            })
          } else {
            resolve(response)
          }
        } else {
          let msg = 'Web error: ' + response.status
          if (response.statusText) msg += ' (' + response.statusText + ')'
          msg += ' on ' + method + ' of <' + uri + '>'
          if (response.responseText) msg += ': ' + response.responseText
          let e2: FetchError = new Error(msg)
          e2.response = response
          reject(e2)
        }
      }, (err: Error) => {
        let msg = 'Fetch error for ' + method + ' of <' + uri + '>:' + err
        reject(new Error(msg))
      })
    })
  }

  /**
   * Looks up something.
   * Looks up all the URIs a things has.
   *
   * @param term - canonical term for the thing whose URI is
   *   to be dereferenced
   * @param rterm - the resource which referred to this
   *   (for tracking bad links)
   */
  lookUpThing (
    term: Quad_Subject,
    rterm: Quad_Subject
  ): Promise<Response> | Promise<Response>[] {
    let uris = this.store.uris(term)  // Get all URIs
    uris = uris.map(u => Uri.docpart(u))  // Drop hash fragments

    uris.forEach(u => {
      this.lookedUp[u] = true
    })

    // @ts-ignore Recursive type
    return this.load(uris, { referringTerm: rterm })
  }

  /**
   * Looks up response header.
   *
   * @returns {Array|undefined} a list of header values found in a stored HTTP
   *   response, or [] if response was found but no header found,
   *   or undefined if no response is available.
   * Looks for { [] link:requestedURI ?uri; link:response [ httph:header-name  ?value ] }
   */
  getHeader (
    doc: NamedNode,
    header: string
  ): undefined | string[] {
    const kb = this.store // look for the URI (AS A STRING NOT A NODE) for a stored request
    const docuri: string = doc.value
    const requests = kb.each(undefined, this.ns.link('requestedURI'), kb.rdfFactory.literal(docuri)) as Quad_Subject[]

    for (let r = 0; r < requests.length; r++) {
      let request = requests[r]
      if (request !== undefined) {
        let response = kb.any(request, this.ns.link('response')) as Quad_Subject
        if (response !== undefined && kb.anyValue(response, this.ns.http('status')) && (kb.anyValue(response, this.ns.http('status')) as string).startsWith('2')) {
          // Only look at success returns - not 401 error messagess etc
          let results = kb.each(response, this.ns.httph(header.toLowerCase()))

          if (results.length) {
            return results.map(v => { return v.value })
          }

          return []
        }
      }
    }
    return undefined
  }

  saveRequestMetadata (
    docuri: string,
    options: AutoInitOptions
  ) {
    let req = options.req
    let kb = this.store
    let rterm = options.referringTerm

    this.addStatus(options.req, 'Accept: ' + options.headers['accept'])

    if (isNamedNode(rterm)) {
      kb.add(kb.rdfFactory.namedNode(docuri), this.ns.link('requestedBy'), rterm, this.appNode)
    }

    if (options.original && options.original.value !== docuri) {
      kb.add(req, this.ns.link('orginalURI'), kb.rdfFactory.literal(options.original.value),
        this.appNode)
    }

    const now = new Date()
    const timeNow = '[' + now.getHours() + ':' + now.getMinutes() + ':' +
      now.getSeconds() + '] '

    kb.add(req, this.ns.rdfs('label'),
      kb.rdfFactory.literal(timeNow + ' Request for ' + docuri), this.appNode)
    // We store the docuri as a string, not as a node,
    // see https://github.com/linkeddata/rdflib.js/pull/427#pullrequestreview-447910061
    kb.add(req, this.ns.link('requestedURI'), kb.rdfFactory.literal(docuri), this.appNode)
    kb.add(req, this.ns.link('status'), kb.collection(), this.appNode)
  }

  saveResponseMetadata (
    response: Response,
    options: {
      req: BlankNode,
      resource: Quad_Subject
    } & Options
  ): BlankNode {
    const kb = this.store

    let responseNode = kb.bnode()

    kb.add(options.req, this.ns.link('response'), responseNode, responseNode)
    kb.add(responseNode, this.ns.http('status'),
    kb.rdfFactory.literal(response.status as any), responseNode)
    kb.add(responseNode, this.ns.http('statusText'),
    kb.rdfFactory.literal(response.statusText), responseNode)

    // Save the response headers
    response.headers.forEach((value, header) => {
      kb.add(responseNode, this.ns.httph(header), this.store.rdfFactory.literal(value), responseNode)

      if (header === 'content-type') {
        kb.add(
          options.resource,
          this.ns.rdf('type'),
          kb.rdfFactory.namedNode(Util.mediaTypeClass(value).value),
          responseNode
        )
      }
    })

    return responseNode
  }

  objectRefresh (term: NamedNode): void {
    let uris = this.store.uris(term) // Get all URIs
    if (typeof uris !== 'undefined') {
      for (let i = 0; i < uris.length; i++) {
        this.refresh(this.store.rdfFactory.namedNode(Uri.docpart(uris[i])))
        // what about rterm?
      }
    }
  }

  /* refresh  Reload data from a given document
  **
  ** @param term - An RDF Named Node for the eodcument in question
  ** @param userCallback - A function userCallback(ok, message, response)
  */
  refresh (
    term: NamedNode,
    userCallback?: UserCallback
  ): void { // sources_refresh
    this.fireCallbacks('refresh', arguments)

    this.nowOrWhenFetched(term, { force: true, clearPreviousData: true },
      userCallback)
  }

 /* refreshIfExpired   Conditional refresh if Expired
 **
 ** @param term - An RDF Named Node for the eodcument in question
 ** @param userCallback - A function userCallback(ok, message, response)
 */
  refreshIfExpired (
    term: NamedNode,
    userCallback: UserCallback
  ): void {
    let exp = this.getHeader(term, 'Expires')
    if (!exp || (new Date(exp[0]).getTime()) <= (new Date().getTime())) {
      this.refresh(term, userCallback)
    } else {
      userCallback(true, 'Not expired', {})
    }
  }

  retract (term: Quad_Graph) { // sources_retract
    this.store.removeMany(undefined, undefined, undefined, term)
    if (term.value) {
      delete this.requested[Uri.docpart(term.value)]
    }
    this.fireCallbacks('retract', arguments)
  }

  getState (docuri: string) {
    if (typeof this.requested[docuri] === 'undefined') {
      return 'unrequested'
    } else if (this.requested[docuri] === true) {
      return 'requested'
    } else if (this.requested[docuri] === 'done') {
      return 'fetched'
    } else if (this.requested[docuri] === 'redirected') {
      return this.getState(this.redirectedTo[docuri])
    } else { // An non-200 HTTP error status
      return 'failed'
    }
  }

  isPending (docuri: string) { // sources_pending
    // doing anyStatementMatching is wasting time
    // if it's not pending: false -> flailed
    //   'done' -> done 'redirected' -> redirected
    return this.requested[docuri] === true
  }

  unload (term: NamedNode) {
    this.store.removeDocument(term)
    delete this.requested[term.value] // So it can be load2ed again
  }

  addHandler (handler: typeof Handler) {
    this.handlers.push(handler);
    (handler as any).register(this)
  }

  retryNoCredentials (
    docuri: string,
    options
  ): Promise<Result> {
    console.log('Fetcher: CORS: RETRYING with NO CREDENTIALS for ' + options.resource)

    options.retriedWithNoCredentials = true // protect against being called twice

    delete this.requested[docuri] // forget the original request happened
    delete this.fetchQueue[docuri]
    // Note: XHR property was withCredentials, but fetch property is just credentials
    let newOptions = Object.assign({}, options, { credentials: 'omit' })

    this.addStatus(options.req,
      'Abort: Will retry with credentials SUPPRESSED to see if that helps')

    return this.load(docuri, newOptions) as Promise<Result>
  }

  /**
   * Tests whether a request is being made to a cross-site URI (for purposes
   * of retrying with a proxy)
   */
  isCrossSite (uri: string): boolean {
    // Mashup situation, not node etc
    if (typeof document === 'undefined' || !document.location) {
      return false
    }

    const hostpart = Uri.hostpart
    const here = '' + document.location
    return (hostpart(here) && hostpart(uri) && hostpart(here)) !== hostpart(uri)
  }

  /**
   * Called when there's a network error in fetch(), or a response
   * with status of 0.
   */
  handleError (
    response: ExtendedResponse | Error,
    docuri: string,
    options: AutoInitOptions
  ): Promise<ExtendedResponse | FetchError> {
    if (this.isCrossSite(docuri)) {
      // Make sure we haven't retried already
      if (options.credentials && options.credentials === 'include' && !options.retriedWithNoCredentials) {
        return this.retryNoCredentials(docuri, options)
      }

      // Now attempt retry via proxy
      let proxyUri = Fetcher.crossSiteProxy(docuri)

      if (proxyUri && !options.proxyUsed) {
        console.log('web: Direct failed so trying proxy ' + proxyUri)

        return this.redirectToProxy(proxyUri, options)
      }
    }

    var message
    if (response instanceof Error) {
      message = 'Fetch error: ' + response.message
    } else {
      message = response.statusText
      if (response.responseText) {
        message += ` ${response.responseText}`
      }
    }

    // This is either not a CORS error, or retries have been made
    return this.failFetch(options, message, (response as Response).status || 998, (response as Response))
  }

  // deduce some things from the HTTP transaction
  addType (
    rdfType: NamedNode,
    req: Quad_Subject,
    kb: IndexedFormula,
    locURI: string
  ): void { // add type to all redirected resources too
    let prev = req
    if (locURI) {
      var reqURI = kb.any(prev, this.ns.link('requestedURI'))
      if (reqURI && reqURI.value !== locURI) {
        kb.add(kb.rdfFactory.namedNode(locURI), this.ns.rdf('type'), rdfType, this.appNode)
      }
    }
    for (;;) {
      const doc = kb.any(prev, this.ns.link('requestedURI'))
      if (doc && doc.value) {
        kb.add(kb.rdfFactory.namedNode(doc.value), this.ns.rdf('type'), rdfType, this.appNode)
      } // convert Literal
      prev = kb.any(undefined, kb.rdfFactory.namedNode('http://www.w3.org/2007/ont/link#redirectedRequest'), prev) as Quad_Subject
      if (!prev) { break }
      var response = kb.any(prev, kb.rdfFactory.namedNode('http://www.w3.org/2007/ont/link#response'))
      if (!response) { break }
      var redirection = kb.any((response as NamedNode), kb.rdfFactory.namedNode('http://www.w3.org/2007/ont/http#status'))
      if (!redirection) { break }
      // @ts-ignore always true?
      if ((redirection !== '301') && (redirection !== '302')) { break }
    }
  }

  /**
   * Handle fetch() response
   */
  handleResponse (
    response: ExtendedResponse,
    docuri: string,
    options: AutoInitOptions
  ): Promise<FetchError | ExtendedResponse> | ExtendedResponse {

    const kb = this.store
    const headers = (response as Response).headers

    const reqNode = options.req

    const responseNode = this.saveResponseMetadata(response, options)

    const contentType = this.normalizedContentType(options, headers) || ''
    let contentLocation = headers.get('content-location')

    // this.fireCallbacks('recv', xhr.args)
    // this.fireCallbacks('headers', [{uri: docuri, headers: xhr.headers}])

    // Check for masked errors (CORS, etc)
    if (response.status === 0) {
      console.log('Masked error - status 0 for ' + docuri)
      return this.handleError(response, docuri, options)
    }

    if (response.status >= 400) {
      if (response.status === 404) {
        this.nonexistent[options.original.value] = true
        this.nonexistent[docuri] = true
      }

      return this.saveErrorResponse(response, responseNode)
        .then(() => {
          let errorMessage = options.resource + ' ' + response.statusText

          return this.failFetch(options, errorMessage, response.status, response)
        })
    }

    var diffLocation: null | string = null
    var absContentLocation: null | string = null
    if (contentLocation) {
      absContentLocation = Uri.join(contentLocation, docuri)
      if (absContentLocation !== docuri) {
        diffLocation = absContentLocation
      }
    }
    if (response.status === 200) {
      this.addType(this.ns.link('Document') as NamedNode, reqNode, kb, docuri)
      if (diffLocation) {
        this.addType(this.ns.link('Document') as NamedNode, reqNode, kb,
          diffLocation)
      }

      // Before we parse new data clear old but only on 200
      if (options.clearPreviousData) {
        kb.removeDocument(options.resource)
      }

      let isImage = contentType.includes('image/') ||
        contentType.includes('application/pdf')

      if (contentType && isImage) {
        this.addType(kb.rdfFactory.namedNode('http://purl.org/dc/terms/Image'), reqNode, kb,
          docuri)
        if (diffLocation) {
          this.addType(kb.rdfFactory.namedNode('http://purl.org/dc/terms/Image'), reqNode, kb,
            diffLocation)
        }
      }
    }

    // If we have already got the thing at this location, abort
    if (contentLocation) {
      if (!options.force && diffLocation && this.requested[absContentLocation as string] === 'done') {
        // we have already fetched this
        // should we smush too?
        // log.info("HTTP headers indicate we have already" + " retrieved " +
        // xhr.resource + " as " + absContentLocation + ". Aborting.")
        return this.doneFetch(options, response)
      }

      this.requested[absContentLocation as string] = true
    }

    this.parseLinkHeader(headers.get('link') as string, options.original, reqNode)

    let handler = this.handlerForContentType(contentType, response) as Handler

    if (!handler) {
      //  Not a problem, we just don't extract data
      this.addStatus(reqNode, 'Fetch over. No data handled.')
      return this.doneFetch(options, response)
    }

    return response
      .text()
      // @ts-ignore Types seem right
      .then(responseText => {
        response.responseText = responseText
        return (handler as N3Handler).parse(this, responseText, options, response)
      })
  }

  saveErrorResponse (
    response: ExtendedResponse,
    responseNode: Quad_Subject
  ): Promise<void> {
    let kb = this.store

    return response.text()
      .then(content => {
        if (content.length > 10) {
          kb.add(responseNode, this.ns.http('content'), kb.rdfFactory.literal(content), responseNode)
        }
      })
  }

  handlerForContentType (contentType: string, response: ExtendedResponse): Handler | null {
    if (!contentType) {
      return null
    }

    let Handler = this.handlers.find(handler => {
      return contentType.match(handler.pattern)
    })

    // @ts-ignore in practice all Handlers have constructors.
    return Handler ? new Handler(response) : null
  }

  guessContentType (uri: string): ContentType | undefined {
    return CONTENT_TYPE_BY_EXT[uri.split('.').pop() as string]
  }

  normalizedContentType (
    options: AutoInitOptions,
    headers: Headers
  ): ContentType | string | null {
    if (options.forceContentType) {
      return options.forceContentType
    }

    let contentType = headers.get('content-type')
    if (!contentType || contentType.includes('application/octet-stream')) {
      let guess = this.guessContentType(options.resource.value)

      if (guess) {
        return guess
      }
    }

    let protocol = Uri.protocol(options.resource.value) as string

    if (!contentType && ['file', 'chrome'].includes(protocol)) {
      return 'text/xml'
    }

    return contentType
  }

  /**
   * Sends a new request to the specified uri. (Extracted from `onerrorFactory()`)
   */
  redirectToProxy (
    newURI: string,
    options: AutoInitOptions
  ): Promise<ExtendedResponse | FetchError> {
    this.addStatus(options.req, 'BLOCKED -> Cross-site Proxy to <' + newURI + '>')

    options.proxyUsed = true

    const kb = this.store
    const oldReq = options.req  // request metadata blank node

    if (!options.noMeta) {
      kb.add(oldReq, this.ns.link('redirectedTo'), kb.rdfFactory.namedNode(newURI), oldReq)
      this.addStatus(oldReq, 'redirected to new request') // why
    }

    this.requested[options.resource.value] = 'redirected'
    this.redirectedTo[options.resource.value] = newURI

    let newOptions = Object.assign({}, options)
    newOptions.baseURI = options.resource.value

    return this.fetchUri(newURI, newOptions)
      .then(response => {
        if (!newOptions.noMeta) {
          kb.add(oldReq, this.ns.link('redirectedRequest'), newOptions.req, this.appNode)
        }

        return response
      })
  }

  setRequestTimeout (
    uri: string,
    options: {
      req: Quad_Subject
      original: Quad_Subject
    } & Options
  ): Promise<number | FetchError> {
    return new Promise((resolve) => {
      this.timeouts[uri] = (this.timeouts[uri] || []).concat(setTimeout(() => {
        if (this.isPending(uri) &&
            !options.retriedWithNoCredentials &&
            !options.proxyUsed) {
          resolve(this.failFetch(options, `Request to ${uri} timed out`, 'timeout'))
        }
      }, this.timeout) as unknown as number)
    })
  }

  addFetchCallback (
    uri: string,
    callback: UserCallback
  ): void {
    if (!this.fetchCallbacks[uri]) {
      this.fetchCallbacks[uri] = [callback]
    } else {
      this.fetchCallbacks[uri].push(callback)
    }
  }

  acceptString () {
    let acceptstring = ''

    for (let mediaType in this.mediatypes) {
      if (acceptstring !== '') {
        acceptstring += ', '
      }

      acceptstring += mediaType

      for (let property in this.mediatypes[mediaType]) {
        acceptstring += ';' + property + '=' + this.mediatypes[mediaType][property]
      }
    }

    return acceptstring
  }
  // var updatesVia = new $rdf.UpdatesVia(this) // Subscribe to headers
// @@@@@@@@ This is turned off because it causes a websocket to be set up for ANY fetch
// whether we want to track it ot not. including ontologies loaed though the XSSproxy
}

Fetcher.HANDLERS = defaultHandlers
Fetcher.CONTENT_TYPE_BY_EXT = CONTENT_TYPE_BY_EXT