Why Does Openuri Treat Files Under 10Kb in Size as Stringio

Why does OpenURI treat files under 10kb in size as StringIO?

When one does network programming, you allocate a buffer of a reasonably large size and send and read units of data which will fit in the buffer. However, when dealing with files (or sometimes things called BLOBs) you cannot assume that the data will fit into your buffer. So, you need special handling for these large streams of data.

(Sometimes the units of data which fit into the buffer are called packets. However, packets are really a layer 4 thing, like frames are at layer 2. Since this is happening a layer 7, they might better be called messages.)

For replies larger than 10K, the open-uri library is setting up the extra overhead to write to a stream objects. When under the StringMax size, it just includes the string in the message, since it knows it can fit in the buffer.

Why does Ruby open-uri's open return a StringIO in my unit test, but a FileIO in my controller?

The code responsible for this is in the Buffer class in open-uri. It starts by creating a StringIO object and only creates an actual temp file in the local filesystem when the data exceeds a certain size (10 KB).

I assume that whatever data your test is loading is small enough to be held in a StringIO and the images you are using in the actual application are large enough to warrant a TempFile. The solution is to use methods which are common to both classes, in particular the read method, with MiniMagick::Image#from_blob:

temp_image = MiniMagick::Image.from_blob(open(self.public_filename, &:read))

Sinatra, Twitter, and StringIO

I faced with same issue but using Rails.

Problem is in size of image: if size of image is less than 10kb then open(photo_url) will give you StringIO object, if size is more then 10kb then - File object which is saved in tmp/ folder. File object respond's to to_io method and StringIO object doesn't.

What you can do - create file in tmp folder from your file, and then use this this file for posting to TW.
For example:

  img = open(url)
  if img.is_a?(StringIO)
    ext = File.extname(url)
    name = File.basename(url, ext)
    Tempfile.new([name, ext])
  else
    img
  end

Write StringIO to Tempfile

You're super close:

file.binmode
file.write stringIo.read

open(url) is just opening the stream for reading. It doesn't actually read the data until you call .read on it (which you can then pass in to file.write).

Add image from URL to Excel with Axlsx

Try using read to pull the contents into a tempfile and use that location:

t = Tempfile.new('my_image')
t.binmode
t.write image.read
t.close
ws.add_image(:image_src => t.path, ...

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