Add RSS feed to posts

This displays an rss feed for posts at blog.edwardloveall.com/rss. I
used this for the specification:
https://cyber.law.harvard.edu/rss/rss.html

Of note, the post content is converted from markdown to html, including
syntax highlighting, which seems to work in my limited testing of RSS
readers.

app/controllers/posts_controller.rb

@@ -4,6 +4,11 @@ class PostsController < ApplicationController
   def index
     page = params[:page] || 1
     @posts = Post.newest_first.page(page).per(10)
+
+    respond_to do |format|
+      format.html
+      format.rss { render :index, layout: nil }
+    end
   end
 
   def show

app/views/posts/index.rss.builder

@@ -0,0 +1,20 @@
+xml.instruct! :xml, version: '1.0'
+
+xml.rss version: '2.0' do
+  xml.channel do
+    xml.title title
+    xml.link root_url(subdomain: 'blog') + 'rss'
+    xml.lastBuildDate @posts.first.created_at
+    xml.language 'en-US'
+
+    @posts.each do |post|
+      xml.item do
+        xml.title post.title
+        xml.link post_url(post.slug, subdomain: 'blog')
+        xml.description convert_markdown(post.body)
+        xml.pubDate post.created_at
+        xml.guid post.guid, isPermalink: false
+      end
+    end
+  end
+end

config/routes.rb

@@ -1,6 +1,7 @@
 Rails.application.routes.draw do
   constraints(subdomain: /blog.*/) do
     get '/', to: 'posts#index'
+    get '/rss', to: 'posts#index', defaults: { format: :rss }
     get '/:slug', to: 'posts#show', as: :post
     resources :posts, only: [:index]
   end

spec/controllers/posts_controller_spec.rb

@@ -8,32 +8,42 @@
   end
 
   describe 'GET #index' do
-    it 'assigns all posts as @posts' do
-      post = create(:post)
+    context 'in html format' do
+      it 'assigns all posts as @posts' do
+        post = create(:post)
 
-      get :index
+        get :index
 
-      expect(assigns(:posts)).to eq([post])
-    end
+        expect(assigns(:posts)).to eq([post])
+      end
 
-    context 'pagination' do
-      it 'returns maximum 10 posts' do
-        create(:post)
-        posts = create_list(:post, 10)
-        posts.reverse!
+      context 'pagination' do
+        it 'returns maximum 10 posts' do
+          create(:post)
+          posts = create_list(:post, 10)
+          posts.reverse!
 
-        get :index
+          get :index
 
-        expect(assigns(:posts)).to eq(posts)
-      end
+          expect(assigns(:posts)).to eq(posts)
+        end
 
-      it 'returns posts from a page offset' do
-        post = create(:post)
-        create_list(:post, 10)
+        it 'returns posts from a page offset' do
+          post = create(:post)
+          create_list(:post, 10)
 
-        get :index, page: 2
+          get :index, page: 2
 
-        expect(assigns(:posts)).to eq([post])
+          expect(assigns(:posts)).to eq([post])
+        end
+      end
+    end
+
+    context 'in xml format' do
+      it 'uses no base layout' do
+        get :index, format: :rss
+
+        expect(response).not_to render_template(:blog)
       end
     end
   end

spec/factories/posts.rb

@@ -2,6 +2,6 @@
   factory :post do
     title 'A Scary Story'
     body 'It was a dark and stormy night...'
-    slug { |n| "a-scary-story-#{n}" }
+    sequence(:slug) { |n| "a-scary-story-#{n}" }
   end
 end

spec/requests/post_requests_spec.rb

@@ -0,0 +1,84 @@
+require 'rails_helper'
+
+RSpec.describe 'Posts requests' do
+  it 'returns an rss response' do
+    create(:post)
+
+    get feed_url
+
+    expect(response.content_type).to eq(Mime::Type.lookup_by_extension(:rss))
+  end
+
+  it 'has channel and meta attributes' do
+    post = create(:post)
+
+    get feed_url
+
+    rss = xml[:rss]
+    channel = rss[:channel]
+
+    expect(rss[:version]).to eq('2.0')
+    expect(channel[:title]).to eq('Edward Loveall')
+    expect(channel[:link]).to eq(feed_url)
+    expect(channel[:lastBuildDate]).to eq(post.created_at.to_s)
+    expect(channel[:language]).to eq('en-US')
+  end
+
+  it 'has entry attributes' do
+    create(:post)
+    post = create(:post)
+    post_body = MarkdownRenderer.to_html(post.body).html_safe
+
+    get feed_url
+
+    entry = xml[:rss][:channel][:item].first
+
+    expect(entry[:title]).to eq(post.title)
+    expect(entry[:link]).to eq(post_url(post.slug, subdomain: 'blog'))
+    expect(entry[:description]).to eq(post_body)
+    expect(entry[:pubDate]).to eq(post.created_at.to_s)
+    expect(entry[:guid]).to eq(post.guid)
+  end
+
+  it 'reports the guid as a non-permalink' do
+    create(:post)
+
+    get feed_url
+
+    xml = Nokogiri::XML(response.body)
+    guid = xml.at('guid')
+
+    expect(guid.attribute('isPermalink').value).to eq('false')
+  end
+
+  it 'returns a 304 when there are no new posts' do
+    create(:post)
+    get feed_url
+    headers = { 'HTTP_IF_NONE_MATCH' => response.etag }
+
+    get feed_url, {}, headers
+
+    expect(response).to have_http_status(:not_modified)
+  end
+
+  it 'returns a 200 when there are new posts' do
+    Timecop.travel(Date.yesterday)
+    create(:post)
+    get feed_url
+    headers = { 'HTTP_IF_NONE_MATCH' => response.etag }
+    Timecop.return
+    create(:post)
+
+    get feed_url, {}, headers
+
+    expect(response).to have_http_status(:ok)
+  end
+
+  def xml
+    Hash.from_xml(response.body).deep_symbolize_keys
+  end
+
+  def feed_url
+    "#{root_url(subdomain: 'blog')}rss"
+  end
+end