Add support for running CodeOcean under a subpath

* Also refactor (JavaScript) routes

config/application.rb

@@ -40,7 +40,9 @@ module CodeOcean
     config.autoload_paths += extra_paths
     config.eager_load_paths += extra_paths
 
-    config.action_cable.mount_path = '/cable'
+    config.relative_url_root = ENV.fetch('RAILS_RELATIVE_URL_ROOT', '/').to_s
+
+    config.action_cable.mount_path = "#{ENV.fetch('RAILS_RELATIVE_URL_ROOT', '')}/cable"
 
     config.telegraf.tags = {application: 'codeocean'}
 

config/environments/staging.rb

@@ -100,7 +100,4 @@ Rails.application.configure do
 
   # Do not dump schema after migrations.
   config.active_record.dump_schema_after_migration = false
-
-  # Run on subfolder in production environment.
-  # config.relative_url_root = '/co-staging'
 end

config/initializers/session_store.rb

@@ -2,4 +2,7 @@
 
 # Be sure to restart your server when you modify this file.
 
-Rails.application.config.session_store :cookie_store, key: '_code_ocean_session', expire_after: 1.month
+Rails.application.config.session_store :cookie_store,
+  key: '_code_ocean_session',
+  expire_after: 1.month,
+  path: Rails.application.config.relative_url_root

config/webpack/environment.js

@@ -4,8 +4,8 @@ Info for this file can be found
 github.com/rails/webpacker/blob/master/docs/webpack.md
 */
 
-const { environment } = require('@rails/webpacker')
-const { merge } = require('webpack-merge')
+const {environment} = require('@rails/webpacker')
+const {merge} = require('webpack-merge')
 const webpack = require('webpack')
 const erb = require('./loaders/erb')
 
@@ -25,6 +25,14 @@ environment.plugins.prepend('Provide', new webpack.ProvidePlugin({
     })
 )
 
+// This setting will change the absolute path used to refer
+// external files (images, fonts, ...) in the generated assets
+const relative_url_root = process.env.RAILS_RELATIVE_URL_ROOT || '';
+const public_output_path = environment.config.output.publicPath;
+environment.loaders.get('file')
+    .use.find(item => item.loader === 'file-loader')
+    .options.publicPath = relative_url_root + public_output_path;
+
 environment.loaders.append('erb', erb)
 
 const envConfig = module.exports = environment