add validations to MediaTrack

test plan: passing incorrectly formatted data in the
`kind` and `locale` parameters to POST
/media_objects/:media_object_id/media_tracks
should result in an error

refs LA-172
flag=none

Change-Id: Ibe9e13022dc858b15c0341a058a1cf9c9d528d39
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/219869
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Tested-by: Jenkins
QA-Review: Anju Reddy <areddy@instructure.com>
Reviewed-by: Mysti Lilla <mysti@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>

app/models/media_track.rb

@@ -20,6 +20,8 @@ class MediaTrack < ActiveRecord::Base
   belongs_to :media_object, :touch => true
   before_save :convert_srt_to_wvtt
   validates :media_object_id, presence: true
+  validates :kind, inclusion: { in: %w(subtitles captions descriptions chapters metadata) }
+  validates :locale, format: { with: /\A[A-Za-z\-]+\z/ }
   validates :content, presence: true
 
   RE_LOOKS_LIKE_TTML = /<tt\s+xml/i

spec/controllers/media_tracks_controller_spec.rb

@@ -53,6 +53,16 @@ describe MediaTracksController do
       post 'create', params: {:media_object_id => @mo.media_id, :kind => 'subtitles', :locale => 'en', :content => example_ttml_susceptible_to_xss}
       expect(response).to have_http_status(:unprocessable_entity)
     end
+
+    it "should validate :kind" do
+      post 'create', params: {:media_object_id => @mo.media_id, :kind => 'unkind', :locale => 'en', :content => '1'}
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it "should validate :locale" do
+      post 'create', params: {:media_object_id => @mo.media_id, :kind => 'subtitles', :locale => '<img src="lolcats.gif">', :content => '1'}
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
   end
 
   describe "#show" do