Merge pull request #377 from envato/yaml-template-userdata

Introduce `user_data_file` helper method for YAML ERB templates

Author: orien

CHANGELOG.md

@@ -10,20 +10,32 @@ The format is based on [Keep a Changelog], and this project adheres to
 
 ## [Unreleased]
 
+[Unreleased]: https://github.com/envato/stack_master/compare/v2.13.4...HEAD
+
+## [2.14.0] - 2024-02-05
+
 ### Added
 
+- Allow the use of [commander](https://github.com/commander-rb/commander)
+  major version 5 ([#375]).
+
 - Test on Ruby 3.3 in the CI build ([#376]).
 
-[Unreleased]: https://github.com/envato/stack_master/compare/v2.13.4...HEAD
+- Introduce `user_data_file`, `user_data_file_as_lines`, and `include_file`
+  convenience methods to the YAML ERB template compiler ([#377]).
+
+[2.13.4]: https://github.com/envato/stack_master/compare/v2.13.4...v2.14.0
+[#375]: https://github.com/envato/stack_master/pull/375
 [#376]: https://github.com/envato/stack_master/pull/376
+[#377]: https://github.com/envato/stack_master/pull/377
 
 ## [2.13.4] - 2023-08-02
 
 ### Fixed
 
 - Resolve SparkleFormation template error caused by `SortedSet` class being removed from the `set` library in Ruby 3 ([#374]).
 
-[2.13.3]: https://github.com/envato/stack_master/compare/v2.13.3...v2.13.4
+[2.13.4]: https://github.com/envato/stack_master/compare/v2.13.3...v2.13.4
 [#374]: https://github.com/envato/stack_master/pull/374
 
 ## [2.13.3] - 2023-02-01

lib/stack_master.rb

@@ -45,6 +45,8 @@ module StackMaster
   autoload :StackDefinition, 'stack_master/stack_definition'
   autoload :TemplateCompiler, 'stack_master/template_compiler'
   autoload :Identity, 'stack_master/identity'
+  autoload :CloudFormationInterpolatingEruby, 'stack_master/cloudformation_interpolating_eruby'
+  autoload :CloudFormationTemplateEruby, 'stack_master/cloudformation_template_eruby'
 
   autoload :StackDiffer, 'stack_master/stack_differ'
   autoload :Validator, 'stack_master/validator'

lib/stack_master/cloudformation_interpolating_eruby.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'erubis'
+
+module StackMaster
+  #  This class is a modified version of `Erubis::Eruby`. It allows using
+  # `<%= %>` ERB expressions to interpolate values into a source string. We use
+  # this capability to enrich user data scripts with data and parameters pulled
+  # from the AWS CloudFormation service. The evaluation produces an array of
+  # objects ready for use in a CloudFormation `Fn::Join` intrinsic function.
+  class CloudFormationInterpolatingEruby < Erubis::Eruby
+    include Erubis::ArrayEnhancer
+
+    # Load a template from a file at the specified path and evaluate it.
+    def self.evaluate_file(source_path, context = Erubis::Context.new)
+      template_contents = File.read(source_path)
+      eruby = new(template_contents)
+      eruby.filename = source_path
+      eruby.evaluate(context)
+    end
+
+    # @return [Array] The result of evaluating the source: an array of strings
+    #         from the source intermindled with Hash objects from the ERB
+    #         expressions. To be included in a CloudFormation template, this
+    #         value needs to be used in a CloudFormation `Fn::Join` intrinsic
+    #         function.
+    # @see Erubis::Eruby#evaluate
+    # @example
+    #   CloudFormationInterpolatingEruby.new("my_variable=<%= { 'Ref' => 'Param1' } %>;").evaluate
+    #     #=> ['my_variable=', { 'Ref' => 'Param1' }, ';']
+    def evaluate(_context = Erubis::Context.new)
+      format_lines_for_cloudformation(super)
+    end
+
+    # @see Erubis::Eruby#add_expr
+    def add_expr(src, code, indicator)
+      if indicator == '='
+        src << " #{@bufvar} << (" << code << ');'
+      else
+        super
+      end
+    end
+
+    private
+
+    # Split up long strings containing multiple lines. One string per line in the
+    # CloudFormation array makes the compiled template and diffs more readable.
+    def format_lines_for_cloudformation(source)
+      source.flat_map do |lines|
+        lines = lines.to_s if lines.is_a?(Symbol)
+        next(lines) unless lines.is_a?(String)
+
+        newlines = Array.new(lines.count("\n"), "\n")
+        newlines = lines.split("\n").map { |line| "#{line}#{newlines.pop}" }
+        newlines.insert(0, "\n") if lines.start_with?("\n")
+        newlines
+      end
+    end
+  end
+end

lib/stack_master/cloudformation_template_eruby.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require 'erubis'
+require 'json'
+
+module StackMaster
+  # This class is a modified version of `Erubis::Eruby`. It provides extra
+  # helper methods to ease the dynamic creation of CloudFormation templates
+  # with ERB. These helper methods are available within `<%= %>` expressions.
+  class CloudFormationTemplateEruby < Erubis::Eruby
+    # Adds the contents of an EC2 userdata script to the CloudFormation
+    # template. Allows using the ERB `<%= %>` expressions within the user data
+    # script to interpolate CloudFormation values.
+    def user_data_file(filepath)
+      JSON.pretty_generate({ 'Fn::Base64' => { 'Fn::Join' => ['', user_data_file_as_lines(filepath)] } })
+    end
+
+    # Evaluate the ERB template at the specified filepath and return the result
+    # as an array of lines. Allows using ERB `<%= %>` expressions to interpolate
+    # CloudFormation objects into the result.
+    def user_data_file_as_lines(filepath)
+      StackMaster::CloudFormationInterpolatingEruby.evaluate_file(filepath, self)
+    end
+
+    # Add the contents of another file into the CloudFormation template as a
+    # string. ERB `<%= %>` expressions within the referenced file are not
+    # evaluated.
+    def include_file(filepath)
+      JSON.pretty_generate(File.read(filepath))
+    end
+  end
+end

lib/stack_master/sparkle_formation/template_file.rb

@@ -5,19 +5,6 @@ module StackMaster
   module SparkleFormation
     TemplateFileNotFound = ::Class.new(StandardError)
 
-    class SfEruby < Erubis::Eruby
-      include Erubis::ArrayEnhancer
-
-      def add_expr(src, code, indicator)
-        case indicator
-          when '='
-            src << " #{@bufvar} << (" << code << ');'
-          else
-            super
-        end
-      end
-    end
-
     class TemplateContext < AttributeStruct
       include ::SparkleFormation::SparkleAttribute
       include ::SparkleFormation::SparkleAttribute::Aws
@@ -49,47 +36,12 @@ def render(file_name, vars = {})
       end
     end
 
-    # Splits up long strings with multiple lines in them to multiple strings
-    # in the CF array. Makes the compiled template and diffs more readable.
-    class CloudFormationLineFormatter
-      def self.format(template)
-        new(template).format
-      end
-
-      def initialize(template)
-        @template = template
-      end
-
-      def format
-        @template.flat_map do |lines|
-          lines = lines.to_s if Symbol === lines
-          if String === lines
-            newlines = []
-            lines.count("\n").times do
-              newlines << "\n"
-            end
-            newlines = lines.split("\n").map do |line|
-              "#{line}#{newlines.pop}"
-            end
-            if lines.start_with?("\n")
-              newlines.insert(0, "\n")
-            end
-            newlines
-          else
-            lines
-          end
-        end
-      end
-    end
-
     module Template
       def self.render(prefix, file_name, vars)
         file_path = File.join(::SparkleFormation.sparkle_path, prefix, file_name)
-        template = File.read(file_path)
         template_context = TemplateContext.build(vars, prefix)
-        compiled_template = SfEruby.new(template).evaluate(template_context)
-        CloudFormationLineFormatter.format(compiled_template)
-      rescue Errno::ENOENT => e
+        CloudFormationInterpolatingEruby.evaluate_file(file_path, template_context)
+      rescue Errno::ENOENT
         Kernel.raise TemplateFileNotFound, "Could not find template file at path: #{file_path}"
       end
     end

lib/stack_master/template_compilers/yaml_erb.rb

@@ -3,13 +3,12 @@
 module StackMaster::TemplateCompilers
   class YamlErb
     def self.require_dependencies
-      require 'erubis'
       require 'yaml'
     end
 
     def self.compile(template_dir, template, compile_time_parameters, _compiler_options = {})
       template_file_path = File.join(template_dir, template)
-      template = Erubis::Eruby.new(File.read(template_file_path))
+      template = StackMaster::CloudFormationTemplateEruby.new(File.read(template_file_path))
       template.filename = template_file_path
 
       template.result(params: compile_time_parameters)

lib/stack_master/version.rb

@@ -1,3 +1,3 @@
 module StackMaster
-  VERSION = "2.13.4"
+  VERSION = "2.14.0"
 end

spec/fixtures/templates/erb/user_data.sh.erb

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+echo 'Hello, World!'
+REGION=<%= { 'Ref' => 'AWS::Region' } %>
+echo $REGION

spec/fixtures/templates/erb/user_data.yml.erb

@@ -0,0 +1,7 @@
+Description: A test case for storing the userdata script in a dedicated file
+
+Resources:
+  LaunchConfig:
+    Type: 'AWS::AutoScaling::LaunchConfiguration'
+    Properties:
+      UserData: <%= user_data_file(File.join(__dir__, 'user_data.sh.erb')) %>

spec/stack_master/cloudformation_interpolating_eruby_spec.rb

@@ -0,0 +1,62 @@
+RSpec.describe(StackMaster::CloudFormationInterpolatingEruby) do
+  describe('#evaluate') do
+    subject(:evaluate) { described_class.new(user_data).evaluate }
+
+    context('given a simple user data script') do
+      let(:user_data) { <<~SHELL }
+        #!/bin/bash
+
+        REGION=ap-southeast-2
+        echo $REGION
+      SHELL
+
+      it 'returns an array of lines' do
+        expect(evaluate).to eq([
+          "#!/bin/bash\n",
+          "\n",
+          "REGION=ap-southeast-2\n",
+          "echo $REGION\n",
+        ])
+      end
+    end
+
+    context('given a user data script referring parameters') do
+      let(:user_data) { <<~SHELL }
+        #!/bin/bash
+        <%= { 'Ref' => 'Param1' } %> <%= { 'Ref' => 'Param2' } %>
+      SHELL
+
+      it 'includes CloudFormation objects in the array' do
+        expect(evaluate).to eq([
+          "#!/bin/bash\n",
+          { 'Ref' => 'Param1' },
+          ' ',
+          { 'Ref' => 'Param2' },
+          "\n",
+        ])
+      end
+    end
+  end
+
+  describe('.evaluate_file') do
+    subject(:evaluate_file) { described_class.evaluate_file('my/userdata.sh') }
+
+    context('given a simple user data script file') do
+      before { allow(File).to receive(:read).with('my/userdata.sh').and_return(<<~SHELL) }
+        #!/bin/bash
+
+        REGION=ap-southeast-2
+        echo $REGION
+      SHELL
+
+      it 'returns an array of lines' do
+        expect(evaluate_file).to eq([
+          "#!/bin/bash\n",
+          "\n",
+          "REGION=ap-southeast-2\n",
+          "echo $REGION\n",
+        ])
+      end
+    end
+  end
+end