egg-kit/lib/image.js

'use strict'

/**
 * 根据文件头识别图片类型（png, jpg, gif, bmp, ico, tiff）
 * @param {Buffer} buf 图片的 buffer
 * @returns {string | undefined}
 * @since 0.0.4
 */
function recognizeImageType(buf) {
  const PNG_BUFFER = Buffer.from('89504e470d0a1a0a', 'hex')
  const JPG_BUFFER = Buffer.from('ffd8', 'hex')
  const GIF_BUFFER = Buffer.from('47494638', 'hex')
  const BMP_BUFFER = Buffer.from('424d', 'hex')
  const ICO_BUFFER = Buffer.from('000001000100', 'hex')
  const TIFF_BUFFER_1 = Buffer.from('4d4d', 'hex')
  const TIFF_BUFFER_2 = Buffer.from('4949', 'hex')

  if (!Buffer.isBuffer(buf)) {
    throw new Error('错误：输入的参数不是一个Buffer对象')
  }

  const BUFFER_START_INDEX = 0
  if (buf.indexOf(PNG_BUFFER) === BUFFER_START_INDEX) {
    return 'png'
  } else if (buf.indexOf(JPG_BUFFER) === BUFFER_START_INDEX) {
    return 'jpg'
  } else if (buf.indexOf(GIF_BUFFER) === BUFFER_START_INDEX) {
    return 'gif'
  } else if (buf.indexOf(BMP_BUFFER) === BUFFER_START_INDEX) {
    return 'bmp'
  } else if (buf.indexOf(ICO_BUFFER) === BUFFER_START_INDEX) {
    return 'ico'
  } else if (buf.indexOf(TIFF_BUFFER_1) === BUFFER_START_INDEX) {
    return 'tiff'
  } else if (buf.indexOf(TIFF_BUFFER_2) === BUFFER_START_INDEX) {
    return 'tiff'
  } else {
    // empty
  }
}

module.exports = {
  recognizeImageType,
}