compress.ts

import * as zlib from 'zlib'
import { InterfaceRequest, InterfaceResponseData } from '../../types'

/*
The following COMPRESSIBLE list generated with:
curl -s https://raw.githubusercontent.com/jshttp/mime-db/master/db.json | jq '. | to_entries | map(select(.value.compressible == true)) | map(.key)'
*/

const COMPRESSIBLE: ReadonlyArray<string> = [
  'application/activity+json',
  'application/alto-costmap+json',
  'application/alto-costmapfilter+json',
  'application/alto-directory+json',
  'application/alto-endpointcost+json',
  'application/alto-endpointcostparams+json',
  'application/alto-endpointprop+json',
  'application/alto-endpointpropparams+json',
  'application/alto-error+json',
  'application/alto-networkmap+json',
  'application/alto-networkmapfilter+json',
  'application/atom+xml',
  'application/calendar+json',
  'application/coap-group+json',
  'application/csvm+json',
  'application/dart',
  'application/dicom+json',
  'application/ecmascript',
  'application/fhir+json',
  'application/fido.trusted-apps+json',
  'application/geo+json',
  'application/javascript',
  'application/jf2feed+json',
  'application/jose+json',
  'application/jrd+json',
  'application/json',
  'application/json-patch+json',
  'application/jsonml+json',
  'application/jwk+json',
  'application/jwk-set+json',
  'application/ld+json',
  'application/manifest+json',
  'application/merge-patch+json',
  'application/mud+json',
  'application/postscript',
  'application/ppsp-tracker+json',
  'application/problem+json',
  'application/raml+yaml',
  'application/rdap+json',
  'application/rdf+xml',
  'application/reputon+json',
  'application/rss+xml',
  'application/rtf',
  'application/scim+json',
  'application/soap+xml',
  'application/tar',
  'application/vcard+json',
  'application/vnd.amadeus+json',
  'application/vnd.api+json',
  'application/vnd.apothekende.reservation+json',
  'application/vnd.avalon+json',
  'application/vnd.bbf.usp.msg+json',
  'application/vnd.bekitzur-stech+json',
  'application/vnd.capasystems-pg+json',
  'application/vnd.collection+json',
  'application/vnd.collection.doc+json',
  'application/vnd.collection.next+json',
  'application/vnd.coreos.ignition+json',
  'application/vnd.dart',
  'application/vnd.datapackage+json',
  'application/vnd.dataresource+json',
  'application/vnd.document+json',
  'application/vnd.drive+json',
  'application/vnd.geo+json',
  'application/vnd.google-earth.kml+xml',
  'application/vnd.hal+json',
  'application/vnd.hc+json',
  'application/vnd.heroku+json',
  'application/vnd.hyper+json',
  'application/vnd.hyper-item+json',
  'application/vnd.hyperdrive+json',
  'application/vnd.ims.lis.v2.result+json',
  'application/vnd.ims.lti.v2.toolconsumerprofile+json',
  'application/vnd.ims.lti.v2.toolproxy+json',
  'application/vnd.ims.lti.v2.toolproxy.id+json',
  'application/vnd.ims.lti.v2.toolsettings+json',
  'application/vnd.ims.lti.v2.toolsettings.simple+json',
  'application/vnd.las.las+json',
  'application/vnd.mason+json',
  'application/vnd.micro+json',
  'application/vnd.miele+json',
  'application/vnd.mozilla.xul+xml',
  'application/vnd.ms-fontobject',
  'application/vnd.ms-opentype',
  'application/vnd.nearst.inv+json',
  'application/vnd.oftn.l10n+json',
  'application/vnd.oma.lwm2m+json',
  'application/vnd.oracle.resource+json',
  'application/vnd.pagerduty+json',
  'application/vnd.restful+json',
  'application/vnd.siren+json',
  'application/vnd.sun.wadl+xml',
  'application/vnd.tableschema+json',
  'application/vnd.vel+json',
  'application/vnd.xacml+json',
  'application/voucher-cms+json',
  'application/wasm',
  'application/webpush-options+json',
  'application/x-httpd-php',
  'application/x-javascript',
  'application/x-ns-proxy-autoconfig',
  'application/x-sh',
  'application/x-tar',
  'application/x-virtualbox-hdd',
  'application/x-virtualbox-ova',
  'application/x-virtualbox-ovf',
  'application/x-virtualbox-vbox',
  'application/x-virtualbox-vdi',
  'application/x-virtualbox-vhd',
  'application/x-virtualbox-vmdk',
  'application/x-web-app-manifest+json',
  'application/x-www-form-urlencoded',
  'application/xhtml+xml',
  'application/xml',
  'application/xml-dtd',
  'application/xop+xml',
  'application/yang-data+json',
  'application/yang-patch+json',
  'font/otf',
  'image/bmp',
  'image/svg+xml',
  'image/vnd.adobe.photoshop',
  'image/x-icon',
  'image/x-ms-bmp',
  'message/imdn+xml',
  'message/rfc822',
  'model/gltf+json',
  'model/gltf-binary',
  'model/x3d+xml',
  'text/cache-manifest',
  'text/calender',
  'text/cmd',
  'text/css',
  'text/csv',
  'text/html',
  'text/javascript',
  'text/jsx',
  'text/markdown',
  'text/n3',
  'text/plain',
  'text/richtext',
  'text/rtf',
  'text/tab-separated-values',
  'text/uri-list',
  'text/vcard',
  'text/vtt',
  'text/x-gwt-rpc',
  'text/x-jquery-tmpl',
  'text/x-markdown',
  'text/x-org',
  'text/x-processing',
  'text/x-suse-ymp',
  'text/xml',
  'x-shader/x-fragment',
  'x-shader/x-vertex',
]

const ZLIB_DEFAULT_OPTIONS = {
  level: 5,
}

function acceptEncoding(
  accepts: ReadonlyArray<string>,
  encodings: ReadonlyArray<string>,
): string | undefined {
  return accepts.find(
    accept => !!encodings.find(encoding => accept === encoding),
  )
}

function getBestAcceptEncoding(request: InterfaceRequest): string | undefined {
  const { headers } = request
  const acceptEncodings = (headers['accept-encoding'] || '').split(/, */)

  const encoding = acceptEncoding(acceptEncodings, [
    'gzip',
    'deflate',
    'identity',
  ])

  // prefer gzip over deflate
  return encoding === 'deflate' && acceptEncoding(acceptEncodings, ['gzip'])
    ? acceptEncoding(acceptEncodings, ['gzip', 'identity'])
    : encoding
}

function compressResponse(
  response: InterfaceResponseData,
  encoding: string,
): InterfaceResponseData {
  const { body, headers, ...rest } = response

  const compressed =
    encoding === 'gzip'
      ? zlib.gzipSync(body, ZLIB_DEFAULT_OPTIONS)
      : zlib.deflateSync(body, ZLIB_DEFAULT_OPTIONS)

  return {
    ...rest,
    body: compressed.toString('base64'),
    headers: {
      ...headers,
      'content-encoding': encoding,
      'content-length': compressed.byteLength,
    },
    isBase64Encoded: true,
  }
}

// Gzip/deflate response body when appropriate
export default function compress(
  response: InterfaceResponseData,
  request: InterfaceRequest,
): InterfaceResponseData {
  const { body, headers } = response
  const encoding = getBestAcceptEncoding(request)

  const weShouldCompress =
    COMPRESSIBLE.includes(headers['content-type']) &&
    typeof encoding !== 'undefined' &&
    encoding !== 'identity' &&
    body &&
    body.length > 256

  return weShouldCompress && encoding
    ? compressResponse(response, encoding)
    : response
}