Ruby File IO: Can't open url as File object

I have a function in my code that takes a string representing the url of an image and creates a File object from that string, to be attached to a Tweet. This seems to work about 90% of the time, but occasionally fails.

require 'open-uri'
attachment_url = "https://s3.amazonaws.com/FirmPlay/photos/images/000/002/443/medium/applying_too_many_jobs_-_daniel.jpg?1448392757"
image = File.new(open(attachment_url))

If I run the above code it returns TypeError: no implicit conversion of StringIO into String. If I change open(attachment_url) to open(attachment_url).read I get ArgumentError: string contains null byte. I also tried stripping out the null bytes from the file like so, but that also made no difference.

image = File.new(open(attachment_url).read.gsub("\u0000", ''))

Now if I try the original code with a different image, such as the one below, it works fine. It returns a File object as expected:

attachment_url = "https://s3.amazonaws.com/FirmPlay/photos/images/000/002/157/medium/mike_4.jpg"

I thought maybe it had something to do with the params in the original url, so I stripped those out, but it made no difference. If I open the images in Chrome they appear to be fine.

I'm not sure what I'm missing here. How can I resolve this issue?

Thanks!

Update

Here is the working code I have in my app:

filename = self.attachment_url.split(/[\/]/)[-1].split('?')[0]
stream = open(self.attachment_url)
image = File.open(filename, 'w+b') do |file|
    stream.respond_to?(:read) ? IO.copy_stream(stream, file) : file.write(stream)
    open(file)
end

Jordan's answer works except that calling File.new returns an empty File object, whereas File.open returns a File object containing the image data from stream.

Solution

The reason you're getting TypeError: no implicit conversion of StringIO into String is that open sometimes returns a String object and sometimes returns a StringIO object, which is unfortunate and confusing. Which it does depends on the size of the file. See this answer for more information: open-uri returning ASCII-8BIT from webpage encoded in iso-8859 (Although I don't recommend using the ensure-encoding gem mentioned therein, since it hasn't been updated since 2010 and Ruby has had significant encoding-related changes since then.)

The reason you're getting ArgumentError: string contains null byte is that you're trying to pass the image data as the first argument to File.new:

image = File.new(open(attachment_url))

The first argument of File.new should be a filename, and null bytes aren't allowed in filenames on most systems. Try this instead:

image_data = open(attachment_url)

filename = 'some-filename.jpg'

File.new(filename, 'wb') do |file|
  if image_data.respond_to?(:read)
    IO.copy_stream(image_data, file)
  else
    file.write(image_data)
  end
end

The above opens the file (creating it if it doesn't exist; the b in 'wb' tells Ruby that you're going to write binary data), then writes the data from image_data to it using IO.copy_stream if it's a StreamIO object or File#write otherwise, then closes the file again.