function getcontenttype(obj) {
  if (typeof obj.getHeader === 'function') {
    // res-like
    return obj.getHeader('content-type')
  }

  if (typeof obj.headers === 'object') {
    // req-like
    return obj.headers && obj.headers['content-type']
  }
}
Get content-type from req/res objects.

@param {object}
@return {Object}
@api private