allow choosing rails 5.1 via consul

also add a hook so plugins can preset $canvas_cluster

Change-Id: I508ffc6e5c73e87f9f086dd9a3877833286bb83b
Reviewed-on: https://gerrit.instructure.com/129327


Tested-by: Jenkins
Reviewed-by: James Williams <jamesw@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

Gemfile

@@ -12,8 +12,13 @@
 # these gems to prevent regression, and the indentation serves to alert us to the relationship between the gem and canvas-lms
 source 'https://rubygems.org/'
 
+
+Dir[File.join(File.dirname(__FILE__), 'gems/plugins/*/Gemfile.d/_before.rb')].each do |file|
+  eval(File.read(file), nil, file)
+end
+
 require File.expand_path("../config/canvas_rails5", __FILE__)
 
 Dir.glob(File.join(File.dirname(__FILE__), 'Gemfile.d', '*.rb')).sort.each do |file|
   eval(File.read(file), nil, file)
-end
\ No newline at end of file
+end

Gemfile.d/~after.rb

@@ -18,5 +18,6 @@
 # Non-standard Canvas extension to Bundler behavior -- load the Gemfiles from
 # plugins.
 Dir[File.join(File.dirname(__FILE__), '../gems/plugins/*/Gemfile.d/*')].each do |g|
+  next if g.end_with?('/_before.rb')
   eval(File.read(g), nil, g)
 end

config/canvas_rails5.rb

@@ -16,11 +16,39 @@
 # with this program. If not, see <http://www.gnu.org/licenses/>.
 
 # You can enable the Rails 5.1 support by either defining a
-# CANVAS_RAILS5_1=1 env var, or create an empty RAILS5_1 file in the canvas config dir
+# CANVAS_RAILS5_1=1 env var, creating an empty RAILS5_1 file in the canvas config dir,
+# or setting `private/canvas/rails5.1` to `true` in a locally accessible consul
 if !defined?(CANVAS_RAILS5_0)
   if ENV['CANVAS_RAILS5_1']
     CANVAS_RAILS5_0 = ENV['CANVAS_RAILS5_1'] != '1'
+  elsif File.exist?(File.expand_path("../RAILS5_1", __FILE__))
+    CANVAS_RAILS5_0 = false
   else
-    CANVAS_RAILS5_0 = !File.exist?(File.expand_path("../RAILS5_1", __FILE__))
+    begin
+      # have to do the consul communication without any gems, because
+      # we're in the context of loading the gemfile
+      require 'base64'
+      require 'json'
+      require 'net/http'
+      require 'yaml'
+
+      environment = YAML.load(File.read(File.expand_path("../consul.yml", __FILE__))).dig(ENV['RAILS_ENV'] || 'development', 'environment')
+
+      keys = [
+        ["private/canvas", environment, $canvas_cluster, "rails5.1"].compact.join("/"),
+        ["private/canvas", environment, "rails5.1"].compact.join("/"),
+        ["global/private/canvas", environment, "rails5.1"].compact.join("/")
+      ].uniq
+
+      result = nil
+      keys.each do |key|
+        result = Net::HTTP.get_response(URI("http://localhost:8500/v1/kv/#{key}"))
+        result = nil unless result.is_a?(Net::HTTPSuccess)
+        break if result
+      end
+      CANVAS_RAILS5_0 = !(result && Base64.decode64(JSON.load(result.body).first['Value']) == 'true')
+    rescue
+      CANVAS_RAILS5_0 = true
+    end
   end
 end