Function extractMimeType

deps/undici/src/lib/web/fetch/util.js:1288–1346

* @see https://fetch.spec.whatwg.org/#concept-header-extract-mime-type * @param {import('./headers').HeadersList} headers

(headers)

 * @param {import('./headers').HeadersList} headers
 */
function extractMimeType (headers) {
  // 1. Let charset be null.
  let charset = null

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

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

  // 4. Let values be the result of getting, decoding, and splitting `Content-Type` from headers.
  const values = getDecodeSplit('content-type', headers)

  // 5. If values is null, then return failure.
  if (values === null) {
    return 'failure'
  }

  // 6. For each value of values:
  for (const value of values) {
    // 6.1. Let temporaryMimeType be the result of parsing value.
    const temporaryMimeType = parseMIMEType(value)

    // 6.2. If temporaryMimeType is failure or its essence is "*/*", then continue.
    if (temporaryMimeType === 'failure' || temporaryMimeType.essence === '*/*') {
      continue
    }

    // 6.3. Set mimeType to temporaryMimeType.
    mimeType = temporaryMimeType

    // 6.4. If mimeType’s essence is not essence, then:
    if (mimeType.essence !== essence) {
      // 6.4.1. Set charset to null.
      charset = null

      // 6.4.2. If mimeType’s parameters["charset"] exists, then set charset to
      //        mimeType’s parameters["charset"].
      if (mimeType.parameters.has('charset')) {
        charset = mimeType.parameters.get('charset')
      }

      // 6.4.3. Set essence to mimeType’s essence.
      essence = mimeType.essence
    } else if (!mimeType.parameters.has('charset') && charset !== null) {
      // 6.5. Otherwise, if mimeType’s parameters["charset"] does not exist, and
      //      charset is non-null, set mimeType’s parameters["charset"] to charset.
      mimeType.parameters.set('charset', charset)
    }
  }

  // 7. If mimeType is null, then return failure.
  if (mimeType == null) {
    return 'failure'
  }

  // 8. Return mimeType.
  return mimeType