Allow URLs as images

Using Prawn in an environment where assets are served
dynamically can be painful. This aims to solve it.

For instance, it is convenient to use Rails' ActionController
helper asset_path to retrieve a specific image. Trying to come
up with rules to assess the asset relative path looks brittle.
Precisely, frameworks like the Asset Pipeline solves this.
However, Prawn lacks support for these scenarios.

lib/prawn/images.rb

@@ -10,6 +10,7 @@
 
 require 'digest/sha1'
 require 'pathname'
+require 'open-uri'
 
 module Prawn
   module Images
@@ -146,6 +147,15 @@ def verify_and_read_image(io_or_path)
         io.binmode if io.respond_to?(:binmode)
         return io.read
       end
+
+      if io_or_path.to_s =~ URI::DEFAULT_PARSER.make_regexp
+        # Handle URL case
+        url_io = URI.parse(io_or_path.to_s).open
+        url_io.binmode if url_io.respond_to?(:binmode)
+
+        return url_io.read
+      end
+
       # String or Pathname
       io_or_path = Pathname.new(io_or_path)
       raise ArgumentError, "#{io_or_path} not found" unless io_or_path.file?

spec/prawn/images_spec.rb

@@ -37,6 +37,19 @@
     expect(info.height).to eq(453)
   end
 
+  it 'accepts an image URL address' do
+    current_directory = File.dirname(__FILE__)
+    fixture_path = File.join(current_directory, '..', 'fixtures')
+    image_bin_data = File.open(File.join(fixture_path, 'image_in_bytes'), 'rb').read
+    tempfile_mock = double('Tempfile', binmode: nil, read: image_bin_data, rewind: nil)
+
+    allow(URI).to receive(:open).and_return(tempfile_mock)
+
+    info = pdf.image('https://github.com/prawnpdf/prawn/blob/master/data/images/ruport.png?raw=true')
+
+    expect(info.height).to eq(105)
+  end
+
   it 'rewinds IO objects to be able to embed them multiply' do
     info =
       File.open(filename, 'rb') do |file|