old_contents: Meteor.methods({
      updateAvatar: function(base64) {
          var id = this.userId;
          if (!id) {
              throw new Meteor.Error(403, "You must be logged in");
          }
          try {
              validateImgBase64(base64);
              return Meteor.users.update({_id: id},
                  {$set: {'profile.cover_image': base64, 'profile.upgraded': new Date()}}
              );
          }
          catch(e){
              throw new Meteor.Error(403, e.message);
          }
          return true;
      }
  });
  
new_contents: Meteor.methods({
      updateCover: function(base64) {
          var id = this.userId;
          if (!id) {
              throw new Meteor.Error(403, "You must be logged in");
          }
          try {
              validateImgBase64(base64);
              return Meteor.users.update({_id: id},
                  {$set: {'profile.cover_image': base64, 'profile.upgraded': new Date()}}
              );
          }
          catch(e){
              throw new Meteor.Error(403, e.message);
          }
          return true;
      }
  });
  
subject: validate and save cover image