mimeScore.js

// 'mime-score' back-ported to CommonJS

// Score RFC facets (see https://tools.ietf.org/html/rfc6838#section-3)
var FACET_SCORES = {
  'prs.': 100,
  'x-': 200,
  'x.': 300,
  'vnd.': 400,
  default: 900
}

// Score mime source (Logic originally from `jshttp/mime-types` module)
var SOURCE_SCORES = {
  nginx: 10,
  apache: 20,
  iana: 40,
  default: 30 // definitions added by `jshttp/mime-db` project?
}

var TYPE_SCORES = {
  // prefer application/xml over text/xml
  // prefer application/rtf over text/rtf
  application: 1,

  // prefer font/woff over application/font-woff
  font: 2,

  default: 0
}

/**
 * Get each component of the score for a mime type.  The sum of these is the
 * total score.  The higher the score, the more "official" the type.
 */
module.exports = function mimeScore (mimeType, source = 'default') {
  if (mimeType === 'application/octet-stream') {
    return 0
  }

  const [type, subtype] = mimeType.split('/')

  const facet = subtype.replace(/(\.|x-).*/, '$1')

  const facetScore = FACET_SCORES[facet] || FACET_SCORES.default
  const sourceScore = SOURCE_SCORES[source] || SOURCE_SCORES.default
  const typeScore = TYPE_SCORES[type] || TYPE_SCORES.default

  // All else being equal prefer shorter types
  const lengthScore = 1 - mimeType.length / 100

  return facetScore + sourceScore + typeScore + lengthScore
}