Support downloading asciicast JSON file as "attachment"

app/controllers/asciicasts_controller.rb

@@ -28,11 +28,13 @@ class AsciicastsController < ApplicationController
       end
 
       format.json do
-        if url = asciicast.file_url
-          redirect_to url
-        else
-          render nothing: true, status: 404
-        end
+        opts = if params[:dl]
+          { query: { "response-content-disposition" => "attachment; filename=#{asciicast.download_filename}" } }
+               else
+                 {}
+               end
+
+        redirect_to asciicast.data_url(opts)
       end
 
       format.png do

app/models/asciicast.rb

@@ -85,8 +85,12 @@ class Asciicast < ActiveRecord::Base
     end
   end
 
-  def data_url
-    file_url || stdout_frames_url
+  def data_url(options = {})
+    file_url(options) || stdout_frames_url(options)
+  end
+
+  def download_filename
+    "asciicast-#{id}.json"
   end
 
   def stdout

app/serializers/asciicast_serializer.rb

@@ -13,7 +13,7 @@ class AsciicastSerializer < ActiveModel::Serializer
     if v0_url?
       object.stdout_frames_url
     else
-      object.data_url
+      asciicast_path(object, format: :json)
     end
   end
 

spec/serializers/asciicast_serializer_spec.rb

@@ -13,7 +13,7 @@ describe AsciicastSerializer do
     end
 
     it 'includes url' do
-      expect(subject['url']).to eq(asciicast.file_url)
+      expect(subject['url']).to eq("/a/#{asciicast.to_param}.json")
     end
 
     it 'includes snapshot' do