Function fetchLocalOrRemote

lib/acl-checker.mjs:292–337

* Returns a fetch document handler used by the ACLChecker to fetch .acl * resources up the inheritance chain. * The `fetch(uri, callback)` results in the callback, with either: * - `callback(err, graph)` if any error is encountered, or * - `callback(null, graph)` with the parsed RDF graph of

(mapper, serverUri)

 * @return {Function} Returns a `fetch(uri, callback)` handler
 */
function fetchLocalOrRemote (mapper, serverUri) {
  async function doFetch (url) {
    // Convert the URL into a filename
    let body, path, contentType

    if (Url.parse(url).host.includes(Url.parse(serverUri).host)) {
      // Fetch the acl from local
      try {
        ({ path, contentType } = await mapper.mapUrlToFile({ url }))
      } catch (err) {
        // delete from cache
        delete temporaryCache[url]
        throw new HTTPError(404, err)
      }
      // Read the file from disk
      body = await promisify(fs.readFile)(path, { encoding: 'utf8' })
    } else {
      // Fetch the acl from the internet
      const response = await fetch(url)
      body = await response.text()
      contentType = response.headers.get('content-type')
    }
    return { body, contentType }
  }
  return async function fetch (url, graph = rdf.graph()) {
    graph.initPropertyActions(['sameAs']) // activate sameAs
    if (!temporaryCache[url]) {
      // debugCache('Populating cache', url)
      temporaryCache[url] = {
        timer: setTimeout(() => {
          // debugCache('Expunging from cache', url)
          delete temporaryCache[url]
          if (Object.keys(temporaryCache).length === 0) {
            // debugCache('Cache is empty again')
          }
        }, EXPIRY_MS),
        promise: doFetch(url)
      }
    }
    // debugCache('Cache hit', url)
    const { body, contentType } = await temporaryCache[url].promise
    // Parse the file as Turtle
    rdf.parse(body, graph, url, contentType)
    return graph
  }
}

// Returns the index of the last slash before the given position
function lastSlash (string, pos = string.length) {