VRFS-2481 : Better implementation of external script. Getting proper stdout and stderr, as well as a clean implicit shutdown.

ruby/lib/jam_ruby/jam_tracks_manager.rb

@@ -1,5 +1,6 @@
 require 'json'
 require 'tempfile'
+require 'open3'
 
 module JamRuby
 
@@ -19,10 +20,15 @@ module JamRuby
         output_jkz=""
         title=""
         
-        output = `python #{py_root}/jkcreate.py -D -k #{sku} -c art.png -p #{public_key} -s #{private_key} -I #{tracks_filename} -o #{output_jkz} -t '#{title}'`
-        puts "#{output} :: #{!!output.index(/Error/i)}"
-        raise ArgumentError, "Error calling python script: #{output}" if !!output.index(/Error.*:/i) 
-
+        # From http://stackoverflow.com/questions/690151/getting-output-of-system-calls-in-ruby/5970819#5970819:
+        #Open3.popen3("ls") do |stdin, stdout, stderr, wait_thr|
+        Open3.popen3("python", "#{py_root}/jkcreate.py -D -k #{sku} -c art.png -p #{public_key} -s #{private_key} -I #{tracks_filename} -o #{output_jkz} -t '#{title}'") do |stdin, stdout, stderr, wait_thr|
+          pid = wait_thr.pid
+          exit_status = wait_thr.value
+          err = stderr.read(1000)
+          raise ArgumentError, "Error calling python script: #{err}" if err.present?
+        end
+        
         tmp_dir
       end
     end