ChunkyPNG: Is it possible to read an image directly from a URL?

Question

I tried (with some success)

require 'open-uri'
require 'chunky_png'

image_url = "http://res.cloudinary.com/houlihan-lokey/image/upload/c_limit,h_75,w_120/ixl7z4c1czlvrqnbt0mm.png"
# image_url = "http://res.cloudinary.com/houlihan-lokey/image/upload/c_limit,h_75,w_120/zqw2pgczdzbtyj3aib2o.png" # this works

image_file = open(image_url)
image = ChunkyPNG::Image.from_file(image_file)
puts image.width

Some images work, others don't. The error:

TypeError: no implicit conversion of StringIO into String
from /Users/theuser/.rvm/gems/ruby-2.0.0-p247/gems/chunky_png-1.3.3/lib/chunky_png/datastream.rb:66:in `initialize'
from /Users/theuser/.rvm/gems/ruby-2.0.0-p247/gems/chunky_png-1.3.3/lib/chunky_png/datastream.rb:66:in `open'
from /Users/theuser/.rvm/gems/ruby-2.0.0-p247/gems/chunky_png-1.3.3/lib/chunky_png/datastream.rb:66:in `from_file'
from /Users/theuser/.rvm/gems/ruby-2.0.0-p247/gems/chunky_png-1.3.3/lib/chunky_png/canvas/png_decoding.rb:53:in `from_file'
from (irb):5
from /Users/theuser/.rvm/rubies/ruby-2.0.0-p247/bin/irb:16:in `<main>'

I will be running this on Heroku and am wondering -- is there a reliable way to achieve this without creating temporary files?

Answer 1

The issue was with files which were too small for open to create a temp file for.

The solution is to not rely on temp files but to read the image into memory and use ChunkyPNG's Image.from_blob:

require 'open-uri'
require 'chunky_png'

image_url = "http://res.cloudinary.com/houlihan-lokey/image/upload/c_limit,h_75,w_120/ixl7z4c1czlvrqnbt0mm.png"

image_file = open(image_url).read
image = ChunkyPNG::Image.from_blob(image_file)
puts image.width

This may not work with large images, but is OK for my application.