Caching improvements

Gemfile

@@ -3,6 +3,7 @@ source "https://rubygems.org"
 gemspec
 
 gem "rake"
+gem "rails", require: false # Version is used by the Rakefile to decide which tests to run
 gem "mocha", require: false
 gem "appraisal"
 gem "pry"

Rakefile

@@ -2,22 +2,22 @@ require "bundler/setup"
 require "bundler/gem_tasks"
 require "rake/testtask"
 
+Rake::TestTask.new do |test|
+  require "rails/version"
+
+  test.libs << "test"
+
+  if Rails::VERSION::MAJOR == 3
+    test.test_files = %w[test/jbuilder_template_test.rb test/jbuilder_test.rb]
+  else
+    test.test_files = FileList["test/*_test.rb"]
+  end
+end
+
 if !ENV["APPRAISAL_INITIALIZED"] && !ENV["TRAVIS"]
   require "appraisal/task"
   Appraisal::Task.new
   task default: :appraisal
 else
-  Rake::TestTask.new do |test|
-    require "rails/version"
-
-    test.libs << "test"
-
-    if Rails::VERSION::MAJOR == 3
-      test.test_files = %w[test/jbuilder_template_test.rb test/jbuilder_test.rb]
-    else
-      test.test_files = FileList["test/*_test.rb"]
-    end
-  end
-
   task default: :test
 end

jbuilder.gemspec

@@ -9,6 +9,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '>= 1.9.3'
 
+  s.add_dependency 'actionpack',    '>= 3.0.0', '< 5.1'
   s.add_dependency 'activesupport', '>= 3.0.0', '< 5.1'
   s.add_dependency 'multi_json',    '~> 1.2'
 

lib/jbuilder/jbuilder_template.rb

@@ -7,10 +7,18 @@ class << self
     attr_accessor :template_lookup_options
   end
 
+  CACHE_REVISION = 3
+
+  # Passed to `ActiveSupport::Cache.expand_cache_key` so that we can expire
+  # old entries if our on-disk format changes
+  CACHE_TAG = "jbuilder-revision-#{CACHE_REVISION}".to_sym
+
   self.template_lookup_options = { handlers: [:jbuilder] }
 
   def initialize(context, *args)
     @context = context
+    @deferred_caches = {}
+
     super(*args)
   end
 
@@ -30,13 +38,21 @@ def partial!(*args)
   #   json.cache! ['v1', @person], expires_in: 10.minutes do
   #     json.extract! @person, :name, :age
   #   end
-  def cache!(key=nil, options={})
+  def cache!(key=nil, options={}, &block)
     if @context.controller.perform_caching
-      value = _cache_fragment_for(key, options) do
-        _scope { yield self }
+      token = "jbuilder-#{::SecureRandom.hex(8)}"
+
+      fetcher = -> do
+        _cache_fragment_for(key, options) do
+          value = _scope { block.call self }
+
+          ::MultiJson.dump value
+        end
       end
 
-      merge! value
+      @deferred_caches[token] = fetcher
+
+      merge! token => nil
     else
       yield
     end
@@ -75,6 +91,44 @@ def set!(name, object = BLANK, *args)
     end
   end
 
+  def target!
+    # Call the superclass implementation to get the output JSON as a string.
+    output = super
+
+    @deferred_caches.each do |token, fetch_block|
+      value  = fetch_block.call
+      search = "\"#{token}\":null"
+
+      if value == "{}".freeze
+        # Special case to handle empty objects: we remove the search key
+        # entirely from the output.
+        search = ::Regexp.new ',?' + ::Regexp.escape(search)
+        value  = "".freeze
+      end
+
+      if value.start_with? "[".freeze
+        # Special case to handle arrays: we actually have to replace the
+        # object with the array.
+        search = "{#{search}}"
+      end
+
+      if value.start_with? "{".freeze
+        # Remove leading and trailing braces so it'll merge seamlessly into
+        # the surrounding object.
+        value = value.slice 1...-1
+      end
+
+      # NOTE: Doing `String#sub` or similar with a `Regexp` will make it try
+      # to do backreferencing with any backslashes found in the replacement
+      # string, this will interfere with any potential backslashes in the
+      # JSON replacement. Therefore we're using `String#[]=` which doesn't
+      # have that behavior.
+      output[search] = value
+    end
+
+    output
+  end
+
   private
 
   def _render_partial_with_options(options)
@@ -131,7 +185,7 @@ def _cache_key(key, options)
       key = url_for(key).split('://', 2).last if ::Hash === key
     end
 
-    ::ActiveSupport::Cache.expand_cache_key(key, :jbuilder)
+    ::ActiveSupport::Cache.expand_cache_key(key, CACHE_TAG)
   end
 
   def _fragment_name_with_digest(key, options)

test/jbuilder_template_test.rb

@@ -4,7 +4,7 @@
 require "action_view"
 require "action_view/testing/resolvers"
 require "active_support/cache"
-require "jbuilder/jbuilder_template"
+require "jbuilder"
 
 BLOG_POST_PARTIAL = <<-JBUILDER
   json.extract! blog_post, :id, :body
@@ -246,6 +246,42 @@ def assert_collection_rendered(result, context = nil)
     assert_equal "bar", result["foo"]
   end
 
+  test "cache a JSON string" do
+    undef_context_methods :fragment_name_with_digest, :cache_fragment_name
+
+    jbuild <<-JBUILDER
+      json.cache! "cachekey" do
+        complex = ::MultiJson.dump 'message' => 'The measurement is 1" too long.'
+
+        json.complex complex
+      end
+    JBUILDER
+
+    result = jbuild(<<-JBUILDER)
+      json.cache! "cachekey" do
+        json.complex "Miss"
+      end
+    JBUILDER
+
+    expected_json = ::MultiJson.dump 'message' => 'The measurement is 1" too long.'
+
+    assert_equal expected_json, result["complex"]
+  end
+
+  test "cache a string containing UTF-8" do
+    undef_context_methods :fragment_name_with_digest, :cache_fragment_name
+
+    # The "-" in this template and the literal in the comparison below are
+    # both in UTF-8
+    result = jbuild <<-JBUILDER
+      json.cache! "cachekey" do
+        json.encoded "a – b"
+      end
+    JBUILDER
+
+    assert_equal "a – b", result["encoded"]
+  end
+
   test "fragment caching a JSON object" do
     undef_context_methods :fragment_name_with_digest, :cache_fragment_name
 
@@ -322,8 +358,7 @@ def assert_collection_rendered(result, context = nil)
   test "fragment caching works with current cache digests" do
     undef_context_methods :fragment_name_with_digest
 
-    @context.expects :cache_fragment_name
-    ActiveSupport::Cache.expects :expand_cache_key
+    @context.expects(:cache_fragment_name).returns("cachekey/digest")
 
     jbuild <<-JBUILDER
       json.cache! "cachekey" do
@@ -357,15 +392,16 @@ def assert_collection_rendered(result, context = nil)
       end
     JBUILDER
 
-    assert_equal "jbuilder/cachekey", payloads[:read_fragment][:key]
-    assert_equal "jbuilder/cachekey", payloads[:write_fragment][:key]
+    tag = JbuilderTemplate::CACHE_TAG
+
+    assert_equal "#{tag}/cachekey", payloads[:read_fragment][:key]
+    assert_equal "#{tag}/cachekey", payloads[:write_fragment][:key]
   end
 
   test "current cache digest option accepts options" do
     undef_context_methods :fragment_name_with_digest
 
-    @context.expects(:cache_fragment_name).with("cachekey", skip_digest: true)
-    ActiveSupport::Cache.expects :expand_cache_key
+    @context.expects(:cache_fragment_name).with("cachekey", skip_digest: true).returns("cachekey")
 
     jbuild <<-JBUILDER
       json.cache! "cachekey", skip_digest: true do