Use Redis for CacheMarkDownField on non AR models

This allows using `CacheMarkdownField` for models that are not backed
by ActiveRecord.

When the including class inherits `ActiveRecord::Base` we include
`Gitlab::MarkdownCache::ActiveRecord::Extension`. This will cause the
markdown fields to be rendered and the generated HTML stored in a
`<field>_html` attribute on the record. We also store the version
used for generating the markdown.

All other classes that include this model will include the
`Gitlab::MarkdownCache::Redis::Extension`. This add the `<field>_html`
attributes to that model and will generate the html in them. The
generated HTML will be cached in redis under the key
`markdown_cache:<class>:<id>`. The class this included in must
therefore respond to `id`.

2 files changed, 144 insertions, 0 deletions

diff --git a/spec/lib/gitlab/markdown_cache/redis/extension_spec.rb b/spec/lib/gitlab/markdown_cache/redis/extension_spec.rb
new file mode 100644
index 00000000000..d3d3cd6f03c
--- /dev/null
+++ b/spec/lib/gitlab/markdown_cache/redis/extension_spec.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+require 'spec_helper'
+
+describe Gitlab::MarkdownCache::Redis::Extension, :clean_gitlab_redis_cache do
+  class ThingWithMarkdownFields
+    include CacheMarkdownField
+
+    def initialize(title: nil, description: nil)
+      @title, @description = title, description
+    end
+
+    attr_reader :title, :description
+
+    cache_markdown_field :title, pipeline: :single_line
+    cache_markdown_field :description
+
+    def id
+      "test-markdown-cache"
+    end
+  end
+
+  let(:cache_version) { Gitlab::MarkdownCache::CACHE_COMMONMARK_VERSION << 16 }
+  let(:thing) { ThingWithMarkdownFields.new(title: "`Hello`", description: "`World`") }
+  let(:expected_cache_key) { "markdown_cache:ThingWithMarkdownFields:test-markdown-cache" }
+
+  it 'defines the html attributes' do
+    thing = ThingWithMarkdownFields.new
+
+    expect(thing).to respond_to(:title_html, :description_html, :cached_markdown_version)
+  end
+
+  it 'loads the markdown from the cache only once' do
+    expect(thing).to receive(:load_cached_markdown).once.and_call_original
+
+    thing.title_html
+    thing.description_html
+  end
+
+  it 'correctly loads the markdown if it was stored in redis' do
+    Gitlab::Redis::Cache.with do |r|
+      r.mapped_hmset(expected_cache_key,
+                     title_html: 'hello',
+                     description_html: 'world',
+                     cached_markdown_version: cache_version)
+    end
+
+    expect(thing.title_html).to eq('hello')
+    expect(thing.description_html).to eq('world')
+    expect(thing.cached_markdown_version).to eq(cache_version)
+  end
+
+  describe "#refresh_markdown_cache!" do
+    it "stores the value in redis" do
+      expected_results = { "title_html" => "`Hello`",
+                           "description_html" => "<p data-sourcepos=\"1:1-1:7\" dir=\"auto\"><code>World</code></p>",
+                           "cached_markdown_version" => cache_version.to_s }
+
+      thing.refresh_markdown_cache!
+
+      results = Gitlab::Redis::Cache.with do |r|
+        r.mapped_hmget(expected_cache_key,
+                       "title_html", "description_html", "cached_markdown_version")
+      end
+
+      expect(results).to eq(expected_results)
+    end
+
+    it "assigns the values" do
+      thing.refresh_markdown_cache!
+
+      expect(thing.title_html).to eq('`Hello`')
+      expect(thing.description_html).to eq("<p data-sourcepos=\"1:1-1:7\" dir=\"auto\"><code>World</code></p>")
+      expect(thing.cached_markdown_version).to eq(cache_version)
+    end
+  end
+end
diff --git a/spec/lib/gitlab/markdown_cache/redis/store_spec.rb b/spec/lib/gitlab/markdown_cache/redis/store_spec.rb
new file mode 100644
index 00000000000..59c038cfb2f
--- /dev/null
+++ b/spec/lib/gitlab/markdown_cache/redis/store_spec.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+require 'spec_helper'
+
+describe Gitlab::MarkdownCache::Redis::Store, :clean_gitlab_redis_cache do
+  let(:storable_class) do
+    Class.new do
+      cattr_reader :cached_markdown_fields do
+        Gitlab::MarkdownCache::FieldData.new.tap do |field_data|
+          field_data[:field_1] = {}
+          field_data[:field_2] = {}
+        end
+      end
+
+      attr_accessor :field_1, :field_2, :field_1_html, :field_2_html, :cached_markdown_version
+
+      def id
+        'test-redisbacked-store'
+      end
+    end
+  end
+  let(:storable) { storable_class.new }
+  let(:cache_key) { "markdown_cache:#{storable_class}:#{storable.id}" }
+
+  subject(:store) { described_class.new(storable) }
+
+  def read_values
+    Gitlab::Redis::Cache.with do |r|
+      r.mapped_hmget(cache_key,
+                     :field_1_html, :field_2_html, :cached_markdown_version)
+    end
+  end
+
+  def store_values(values)
+    Gitlab::Redis::Cache.with do |r|
+      r.mapped_hmset(cache_key,
+                     values)
+    end
+  end
+
+  describe '#save' do
+    it 'stores updates to html fields and version' do
+      values_to_store = { field_1_html: "hello", field_2_html: "world", cached_markdown_version: 1 }
+
+      store.save(values_to_store)
+
+      expect(read_values)
+        .to eq({ field_1_html: "hello", field_2_html: "world", cached_markdown_version: "1" })
+    end
+  end
+
+  describe '#read' do
+    it 'reads the html fields and version from redis if they were stored' do
+      stored_values = { field_1_html: "hello", field_2_html: "world", cached_markdown_version: 1 }
+
+      store_values(stored_values)
+
+      expect(store.read.symbolize_keys).to eq(stored_values)
+    end
+
+    it 'is mared loaded after reading' do
+      expect(store).not_to be_loaded
+
+      store.read
+
+      expect(store).to be_loaded
+    end
+  end
+end