Add ShopHost concern for fetching and saving host

app/controllers/concerns/shopify_app/ensure_authenticated_links.rb

@@ -11,7 +11,7 @@ module EnsureAuthenticatedLinks
     private
 
     def splash_page
-      splash_page_with_params(shop: current_shopify_domain, host: params[:host])
+      splash_page_with_params(shop: current_shopify_domain, host: @host)
     end
 
     def base_splash_page

app/controllers/concerns/shopify_app/shop_host.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module ShopifyApp
+  module ShopHost
+    extend ActiveSupport::Concern
+
+    SHOP_HOST_COOKIE = :shop_host
+
+    included do
+      before_action :set_shop_host
+    end
+
+    def set_shop_host
+      @host = fetch_host_from_params
+      @host ||= fetch_host_from_cookies
+      save_shop_host(@host) if @host
+      @host
+    end
+
+    private
+
+    def fetch_host_from_params
+      params[:host]
+    end
+
+    def fetch_host_from_cookies
+      cookies[SHOP_HOST_COOKIE]
+    end
+
+    def save_shop_host(host)
+      cookies[SHOP_HOST_COOKIE] = {
+        value: host,
+        expires: 1.day.from_now,
+      }
+    end
+  end
+end

app/controllers/shopify_app/callback_controller.rb

@@ -3,6 +3,7 @@
 module ShopifyApp
   # Performs login after OAuth completes
   class CallbackController < ActionController::Base
+    include ShopifyApp::ShopHost
     include ShopifyApp::LoginProtection
 
     def callback

app/controllers/shopify_app/sessions_controller.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 module ShopifyApp
   class SessionsController < ActionController::Base
+    include ShopifyApp::ShopHost
     include ShopifyApp::LoginProtection
 
     layout false, only: :new

lib/generators/shopify_app/home_controller/templates/home_controller.rb

@@ -1,18 +1,11 @@
 # frozen_string_literal: true
 
 class HomeController < AuthenticatedController
+  include ShopifyApp::ShopHost
   include ShopifyApp::ShopAccessScopesVerification
 
-  before_action :set_host
-
   def index
     @products = ShopifyAPI::Product.find(:all, params: { limit: 10 })
     @webhooks = ShopifyAPI::Webhook.find(:all)
   end
-
-  private
-
-  def set_host
-    @host = params[:host]
-  end
 end

lib/generators/shopify_app/home_controller/templates/unauthenticated_home_controller.rb

@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 
 class HomeController < ApplicationController
+  include ShopifyApp::ShopHost
   include ShopifyApp::EmbeddedApp
   include ShopifyApp::RequireKnownShop
   include ShopifyApp::ShopAccessScopesVerification
 
   def index
     @shop_origin = current_shopify_domain
-    @host = params[:host]
   end
 end

lib/shopify_app/controller_concerns/login_protection.rb

@@ -112,7 +112,7 @@ def jwt_shopify_user_id
     end
 
     def host
-      return params[:host] if params[:host].present?
+      return @host if @host.present?
 
       raise ShopifyHostNotFound
     end

test/controllers/concerns/ensure_authenticated_links_test.rb

@@ -4,6 +4,7 @@
 
 class EnsureAuthenticatedLinksTest < ActionController::TestCase
   class TurbolinksTestController < ActionController::Base
+    include ShopifyApp::ShopHost
     include ShopifyApp::EnsureAuthenticatedLinks
 
     def root