If you’re getting this error with the Twitter gem’s update_with_media method. And googling around for the solution. I’m here to help you.

Twitter::Error::UnacceptableIO
The IO object for media must respond to to_io

Why this happens

When you call open in Ruby with a URL. It uses Open::URI to open the file. If the file is under 10kb then it will return a StringIO object. If the file is > 10kb, it will return a File object.

Under normal circumstances, this is what we want. It’s more efficient.

The problem is, the Twitter gem, does not handle the case where it is a StringIO object. So you get the error Twitter::Error::UnacceptableIO.

Solution

There are a bunch of ways to hack this so it works. Here is what I landed on as the least hacky way to fix this issue.

Add this module to your lib folder. This will handle both the normal and StringIO cases for you by converting StringIO’s to a File.

# lib/twitter/image.rb
module Twitter::Image
  # The Twitter gem is particular about the type of IO object it
  #   recieves when tweeting an image. If an image is < 10kb, Ruby opens it as a
  #   StringIO object. Which is not supported by the Twitter gem/api.
  #
  #   This method ensures we always have a valid IO object for Twitter.
  def self.open_from_url(image_url)
    image_file = open(image_url)
    return image_file unless image_file.is_a?(StringIO)

    file_name = File.basename(image_url)

    temp_file = Tempfile.new(file_name)
    temp_file.binmode
    temp_file.write(image_file.read)
    temp_file.close

    open(temp_file.path)
  end
end

Now, when you’re tweeting an image. You can do this.

image = Twitter::Image.open_from_url(image_url)
twitter_client.update_with_media("Tweet tweet", image)

I hope this helps. If you come across an even better solution, let me know!