function createDecompressionStream (encoding, debug) {
  switch (encoding) {
    case 'deflate':
      debug('inflate body')
      return zlib.createInflate()
    case 'gzip':
      debug('gunzip body')
      return zlib.createGunzip()
    case 'br':
      debug('brotli decompress body')
      return zlib.createBrotliDecompress()
    default:
      throw createError(415, 'unsupported content encoding "' + encoding + '"', {
        encoding: encoding,
        type: 'encoding.unsupported'
      })
  }
}
Create a decompression stream for the given encoding.
@param {string} encoding
@param {function} debug
@return {object}
@api private