Add support for ingesting etag data from API endpoints

Most of the YouTube API endpoints that return resources expose an etag
property. It is highly desireable for consumers to be able to have
access to this property in order to perform conditional requests (using
If-Match / If-None-Match) or to verify that resources have changed.

Author: eddorre

lib/yt/actions/list.rb

@@ -63,7 +63,7 @@ def resource_class
       #   Can be overwritten by subclasses that initialize instance with
       #   a different set of parameters.
       def new_item(data)
-        resource_class.new attributes_for_new_item(data)
+        resource_class.new attributes_for_new_item(data).merge(etag: data['etag'])
       end
 
       # @private

lib/yt/collections/assets.rb

@@ -17,7 +17,7 @@ def insert(attributes = {})
 
       def new_item(data)
         klass = (data["kind"] == "youtubePartner#assetSnippet") ? Yt::AssetSnippet : Yt::Asset
-        klass.new attributes_for_new_item(data)
+        klass.new attributes_for_new_item(data).merge(etag: data['etag'])
       end
 
       # @return [Hash] the parameters to submit to YouTube to list assets

lib/yt/collections/resources.rb

@@ -19,7 +19,7 @@ def insert(attributes = {}, options = {}) #
     private
 
       def attributes_for_new_item(data)
-        {id: data['id'], snippet: data['snippet'], status: data['status'], auth: @auth}
+        {id: data['id'], snippet: data['snippet'], status: data['status'], auth: @auth, etag: data['etag']}
       end
 
       def resources_params

lib/yt/models/resource.rb

@@ -6,7 +6,7 @@ module Yt
   module Models
     class Resource < Base
       # @private
-      attr_reader :auth
+      attr_reader :auth, :etag
 
     ### ID ###
 
@@ -56,6 +56,7 @@ def initialize(options = {})
           @id = options[:id]
         end
         @auth = options[:auth]
+        @etag = options[:etag]
         @snippet = Snippet.new(data: options[:snippet]) if options[:snippet]
         @status = Status.new(data: options[:status]) if options[:status]
       end

spec/models/channel_spec.rb

@@ -4,6 +4,13 @@
 describe Yt::Channel do
   subject(:channel) { Yt::Channel.new attrs }
 
+  describe '#etag' do
+    context 'given the API response includes an etag' do
+      let(:attrs) { { etag: '12345' } }
+      it { expect(channel.etag).to eq '12345' }
+    end
+  end
+
   describe '#title' do
     context 'given a snippet with a title' do
       let(:attrs) { {snippet: {"title"=>"Fullscreen"}} }

spec/models/playlist_spec.rb

@@ -4,6 +4,12 @@
 describe Yt::Playlist do
   subject(:playlist) { Yt::Playlist.new attrs }
 
+  describe '#etag' do
+    context 'given the API response includes an etag' do
+      let(:attrs) { { etag: '12345' } }
+      it { expect(playlist.etag).to eq '12345' }
+    end
+  end
 
   describe '#title' do
     context 'given a snippet with a title' do

spec/models/video_spec.rb

@@ -4,6 +4,13 @@
 describe Yt::Video do
   subject(:video) { Yt::Video.new attrs }
 
+  describe '#etag' do
+    context 'given the API response includes an etag' do
+      let(:attrs) { { etag: '12345' } }
+      it { expect(video.etag).to eq '12345' }
+    end
+  end
+
   describe '#snippet' do
     context 'given fetching a video returns a snippet' do
       let(:attrs) { {snippet: {"title"=>"Fullscreen Creator Platform"}} }