How to get a bitmap image in ruby? - ruby-on-rails

Question

The google vision API requires a bitmap sent as an argument. I am trying to convert a png from a URL to a bitmap to pass to the google api:
require "google/cloud/vision"
PROJECT_ID = Rails.application.secrets["project_id"]
KEY_FILE = "#{Rails.root}/#{Rails.application.secrets["key_file"]}"
google_vision = Google::Cloud::Vision.new project: PROJECT_ID, keyfile: KEY_FILE
img = open("https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_272x92dp.png").read
image = google_vision.image img
ArgumentError: string contains null byte
This is the source code processing of the gem:
def self.from_source source, vision = nil
if source.respond_to?(:read) && source.respond_to?(:rewind)
return from_io(source, vision)
end
# Convert Storage::File objects to the URL
source = source.to_gs_url if source.respond_to? :to_gs_url
# Everything should be a string from now on
source = String source
# Create an Image from a HTTP/HTTPS URL or Google Storage URL.
return from_url(source, vision) if url? source
# Create an image from a file on the filesystem
if File.file? source
unless File.readable? source
fail ArgumentError, "Cannot read #{source}"
end
return from_io(File.open(source, "rb"), vision)
end
fail ArgumentError, "Unable to convert #{source} to an Image"
end
https://github.com/GoogleCloudPlatform/google-cloud-ruby
Why is it telling me string contains null byte? How can I get a bitmap in ruby?

Answer 1

According to the documentation (which, to be fair, is not exactly easy to find without digging into the source code), Google::Cloud::Vision#image doesn't want the raw image bytes, it wants a path or URL of some sort:
Use Vision::Project#image to create images for the Cloud Vision service.
You can provide a file path:
[...]
Or any publicly-accessible image HTTP/HTTPS URL:
[...]
Or, you can initialize the image with a Google Cloud Storage URI:
So you'd want to say something like:
image = google_vision.image "https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_272x92dp.png"
instead of reading the image data yourself.

Answer 2

Instead of using write you want to use IO.copy_stream as it streams the download straight to the file system instead of reading the whole file into memory and then writing it:
require 'open-uri'
require 'tempfile'
uri = URI("https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_272x92dp.png")
tmp_img = Tempfile.new(uri.path.split('/').last)
IO.copy_stream(open(uri), tmp_img)
Note that you don't need to set the 'r:BINARY' flag as the bytes are just streamed without actually reading the file.
You can then use the file by:
require "google/cloud/vision"
# Use fetch as it raises an error if the key is not present
PROJECT_ID = Rails.application.secrets.fetch("project_id")
# Rails.root is a Pathname object so use `.join` to construct paths
KEY_FILE = Rails.root.join(Rails.application.secrets.fetch("key_file"))
google_vision = Google::Cloud::Vision.new(
project: PROJECT_ID,
keyfile: KEY_FILE
)
image = google_vision.image(File.absolute_path(tmp_img))
When you are done you clean up by calling tmp_img.unlink.

Answer 3

Remember to read things in binary format:
open("https://www.google.com/..._272x92dp.png",'r:BINARY').read
If you forget this it might try and open it as UTF-8 textual data which would cause lots of problems.