index.js

const libheif = require('@freiraum/libheif-js')

const uint8ArrayUtf8ByteString = (array, start, end) => {
  return String.fromCharCode(...array.slice(start, end))
}

// brands explained: https://github.com/strukturag/libheif/issues/83
// code adapted from: https://github.com/sindresorhus/file-type/blob/6f901bd82b849a85ca4ddba9c9a4baacece63d31/core.js#L428-L438
const isHeic = (buffer) => {
  const brandMajor = uint8ArrayUtf8ByteString(buffer, 8, 12)
    .replace('\0', ' ')
    .trim()

  switch (brandMajor) {
    case 'mif1':
      return true // {ext: 'heic', mime: 'image/heif'};
    case 'msf1':
      return true // {ext: 'heic', mime: 'image/heif-sequence'};
    case 'heic':
    case 'heix':
      return true // {ext: 'heic', mime: 'image/heic'};
    case 'hevc':
    case 'hevx':
      return true // {ext: 'heic', mime: 'image/heic-sequence'};
  }

  return false
}

const decodeImage = async (image) => {
  const width = image.get_width()
  const height = image.get_height()

  const arrayBuffer = await new Promise((resolve, reject) => {
    image.display(
      { data: new Uint8ClampedArray(width * height * 4), width, height },
      (displayData) => {
        if (!displayData) {
          return reject(new Error('HEIF processing error'))
        }

        // get the ArrayBuffer from the Uint8Array
        resolve(displayData.data.buffer)
      },
    )
  })

  return { width, height, data: arrayBuffer }
}

const decodeBuffer = async ({ buffer, all }) => {
  if (!isHeic(buffer)) {
    throw new TypeError('input buffer is not a HEIC image')
  }

  const decoder = new libheif.HeifDecoder()
  const data = decoder.decode(buffer)

  if (!data.length) {
    throw new Error('HEIF image not found')
  }

  if (!all) {
    return await decodeImage(data[0])
  }

  return data.map((image) => {
    return {
      decode: async () => await decodeImage(image),
    }
  })
}

module.exports = async ({ buffer }) =>
  await decodeBuffer({ buffer, all: false })
module.exports.all = async ({ buffer }) =>
  await decodeBuffer({ buffer, all: true })