Refactor environment variable handling into new Sources::EnvSource (#299)

* Extract env var handling to new EnvSource class

* Allow overriding settings for parsing env sources

By default, EnvSource will use "global" settings specified like
`Config.env_prefix`, `Config.env_separator`, `Config.env_separator`, and
`Config.env_parse_values`. Those configurations will be used when
parsing the ENV hash.

But when using EnvSource to load settings from some unrelated flat
string-keyed Hash source, we want to allow folks to override the settings.

* Update CHANGELOG

* Add AWS Secrets Manager usage to README

Author: cjlarose

CHANGELOG.md

@@ -5,11 +5,16 @@
 ### BREAKING CHANGES
 
 After upgrade behaviour of `to_h` would change and match behaviour of `to_hash`. Check [#217](https://github.com/rubyconfig/config/issues/217#issuecomment-741953382) for more details.
+`Config::Options#load_env!` and `Config::Options#reload_env!` have been removed. If you need to reload settings after modifying the `ENV` hash, use `Config.reload!` or `Config::Options#reload!` instead.
 
 ### Bug fixes
 
 * Added alias `to_h` for `to_hash` ([#277](https://github.com/railsconfig/config/issues/277))
 
+### Changes
+
+* Add `Config::Sources::EnvSource` for loading settings from flat `Hash`es with `String` keys and `String` values ([#299](https://github.com/railsconfig/config/pull/299))
+
 ## 2.2.3
 
 ### Bug fixes

README.md

@@ -480,6 +480,50 @@ Settings.section.server # => 'google.com'
 Settings.section.ssl_enabled # => false
 ```
 
+### Working with AWS Secrets Manager
+
+It is possible to parse variables stored in an AWS Secrets Manager Secret as if they were environment variables by using `Config::Sources::EnvSource`.
+
+For example, the plaintext secret might look like this:
+
+```json
+{
+  "Settings.foo": "hello",
+  "Settings.bar": "world",
+}
+```
+
+In order to load those settings, fetch the settings from AWS Secrets Manager, parse the plaintext as JSON, pass the resulting `Hash` into a new `EnvSource`, load the new source, and reload.
+
+```ruby
+# fetch secrets from AWS
+client = Aws::SecretsManager::Client.new
+response = client.get_secret_value(secret_id: "#{ENV['ENVIRONMENT']}/my_application")
+secrets = JSON.parse(response.secret_string)
+
+# load secrets into config
+secret_source = Config::Sources::EnvSource.new(secrets)
+Settings.add_source!(secret_source)
+Settings.reload!
+```
+
+In this case, the following settings will be available:
+
+```ruby
+Settings.foo # => "hello"
+Settings.bar # => "world"
+```
+
+By default, `EnvSource` will use configuration for `env_prefix`, `env_separator`, `env_converter`, and `env_parse_values`, but any of these can be overridden in the constructor.
+
+```ruby
+secret_source = Config::Sources::EnvSource.new(secrets,
+                                               prefix: 'MyConfig',
+                                               separator: '__',
+                                               converter: nil,
+                                               parse_values: false)
+```
+
 ## Contributing
 
 You are very warmly welcome to help. Please follow our [contribution guidelines](CONTRIBUTING.md)

lib/config.rb

@@ -4,6 +4,7 @@
 require 'config/version'
 require 'config/sources/yaml_source'
 require 'config/sources/hash_source'
+require 'config/sources/env_source'
 require 'config/validation/schema'
 require 'deep_merge'
 
@@ -41,6 +42,8 @@ def self.load_files(*files)
       config.add_source!(file.to_s)
     end
 
+    config.add_source!(Sources::EnvSource.new(ENV)) if Config.use_env
+
     config.load!
     config
   end

lib/config/options.rb

@@ -31,47 +31,6 @@ def prepend_source!(source)
       @config_sources.unshift(source)
     end
 
-    def reload_env!
-      return self if ENV.nil? || ENV.empty?
-
-      hash = Hash.new
-
-      ENV.each do |variable, value|
-        separator = Config.env_separator
-        prefix = (Config.env_prefix || Config.const_name).to_s.split(separator)
-
-        keys = variable.to_s.split(separator)
-
-        next if keys.shift(prefix.size) != prefix
-
-        keys.map! { |key|
-          case Config.env_converter
-            when :downcase then
-              key.downcase.to_sym
-            when nil then
-              key.to_sym
-            else
-              raise "Invalid ENV variables name converter: #{Config.env_converter}"
-          end
-        }
-
-        leaf = keys[0...-1].inject(hash) { |h, key|
-          h[key] ||= {}
-        }
-
-        unless leaf.is_a?(Hash)
-          conflicting_key = (prefix + keys[0...-1]).join(separator)
-          raise "Environment variable #{variable} conflicts with variable #{conflicting_key}"
-        end
-
-        leaf[keys.last] = Config.env_parse_values ? __value(value) : value
-      end
-
-      merge!(hash)
-    end
-
-    alias :load_env! :reload_env!
-
     # look through all our sources and rebuild the configuration
     def reload!
       conf = {}
@@ -96,7 +55,6 @@ def reload!
       # swap out the contents of the OStruct with a hash (need to recursively convert)
       marshal_load(__convert(conf).marshal_dump)
 
-      reload_env! if Config.use_env
       validate!
 
       self
@@ -223,17 +181,5 @@ def __convert(h) #:nodoc:
       end
       s
     end
-
-    # Try to convert string to a correct type
-    def __value(v)
-      case v
-      when 'false'
-        false
-      when 'true'
-        true
-      else
-        Integer(v) rescue Float(v) rescue v
-      end
-    end
   end
 end

lib/config/sources/env_source.rb

@@ -0,0 +1,73 @@
+module Config
+  module Sources
+    # Allows settings to be loaded from a "flat" hash with string keys, like ENV.
+    class EnvSource
+      attr_reader :prefix
+      attr_reader :separator
+      attr_reader :converter
+      attr_reader :parse_values
+
+      def initialize(env,
+                     prefix: Config.env_prefix || Config.const_name,
+                     separator: Config.env_separator,
+                     converter: Config.env_converter,
+                     parse_values: Config.env_parse_values)
+        @env = env
+        @prefix = prefix.to_s.split(separator)
+        @separator = separator
+        @converter = converter
+        @parse_values = parse_values
+      end
+
+      def load
+        return {} if @env.nil? || @env.empty?
+
+        hash = Hash.new
+
+        @env.each do |variable, value|
+          keys = variable.to_s.split(separator)
+
+          next if keys.shift(prefix.size) != prefix
+
+          keys.map! { |key|
+            case converter
+              when :downcase then
+                key.downcase
+              when nil then
+                key
+              else
+                raise "Invalid ENV variables name converter: #{converter}"
+            end
+          }
+
+          leaf = keys[0...-1].inject(hash) { |h, key|
+            h[key] ||= {}
+          }
+
+          unless leaf.is_a?(Hash)
+            conflicting_key = (prefix + keys[0...-1]).join(separator)
+            raise "Environment variable #{variable} conflicts with variable #{conflicting_key}"
+          end
+
+          leaf[keys.last] = parse_values ? __value(value) : value
+        end
+
+        hash
+      end
+
+      private
+
+      # Try to convert string to a correct type
+      def __value(v)
+        case v
+        when 'false'
+          false
+        when 'true'
+          true
+        else
+          Integer(v) rescue Float(v) rescue v
+        end
+      end
+    end
+  end
+end

spec/sources/env_source_spec.rb

@@ -0,0 +1,79 @@
+require 'spec_helper'
+
+module Config::Sources
+  describe EnvSource do
+    context 'configuration options' do
+      before :each do
+        Config.reset
+        Config.env_prefix           = nil
+        Config.env_separator        = '.'
+        Config.env_converter        = :downcase
+        Config.env_parse_values     = true
+      end
+
+      context 'default configuration' do
+        it 'should use global prefix configuration by default' do
+          Config.env_prefix = 'MY_CONFIG'
+
+          source = EnvSource.new({ 'MY_CONFIG.ACTION_MAILER' => 'enabled' })
+          results = source.load
+          expect(results['action_mailer']).to eq('enabled')
+        end
+
+        it 'should use global separator configuration by default' do
+          Config.env_separator = '__'
+
+          source = EnvSource.new({ 'Settings__ACTION_MAILER__ENABLED' => 'yes' })
+          results = source.load
+          expect(results['action_mailer']['enabled']).to eq('yes')
+        end
+
+        it 'should use global converter configuration by default' do
+          Config.env_converter = nil
+
+          source = EnvSource.new({ 'Settings.ActionMailer.Enabled' => 'yes' })
+          results = source.load
+          expect(results['ActionMailer']['Enabled']).to eq('yes')
+        end
+
+        it 'should use global parse_values configuration by default' do
+          Config.env_parse_values = false
+
+          source = EnvSource.new({ 'Settings.ACTION_MAILER.ENABLED' => 'true' })
+          results = source.load
+          expect(results['action_mailer']['enabled']).to eq('true')
+        end
+      end
+
+      context 'configuration overrides' do
+        it 'should allow overriding prefix configuration' do
+          source = EnvSource.new({ 'MY_CONFIG.ACTION_MAILER' => 'enabled' },
+                                 prefix: 'MY_CONFIG')
+          results = source.load
+          expect(results['action_mailer']).to eq('enabled')
+        end
+
+        it 'should allow overriding separator configuration' do
+          source = EnvSource.new({ 'Settings__ACTION_MAILER__ENABLED' => 'yes' },
+                                 separator: '__')
+          results = source.load
+          expect(results['action_mailer']['enabled']).to eq('yes')
+        end
+
+        it 'should allow overriding converter configuration' do
+          source = EnvSource.new({ 'Settings.ActionMailer.Enabled' => 'yes' },
+                                 converter: nil)
+          results = source.load
+          expect(results['ActionMailer']['Enabled']).to eq('yes')
+        end
+
+        it 'should allow overriding parse_values configuration' do
+          source = EnvSource.new({ 'Settings.ACTION_MAILER.ENABLED' => 'true' },
+                                 parse_values: false)
+          results = source.load
+          expect(results['action_mailer']['enabled']).to eq('true')
+        end
+      end
+    end
+  end
+end