A Ruby library for the human-friendly data format NestedText.

Provided is support for decoding a NestedText file or string to Ruby data structures, as well as encoding Ruby objects to a NestedText file or string. Furthermore, there is support for serialization and deserialization of custom classes. The supported language version of the data format can be seen in the badge above. This implementation passes all the official tests.

This library is inspired by Ruby's stdlib modules JSON and YAML as well as the Python reference implementation of NestedText. Parsing is done with an LL(1) recursive descent parser, and dumping is with a recursive DFS traversal of the object references.

Citing from the official introduction page:

NestedText is a file format for holding structured data to be entered, edited, or viewed by people. It organizes the data into a nested collection of dictionaries, lists, and strings without the need for quoting or escaping. A unique feature of this file format is that it only supports one scalar type: strings. While the decision to eschew integer, real, date, etc. types may seem counterintuitive, it leads to simpler data files and applications that are more robust.

NestedText is convenient for configuration files, address books, account information, and the like. Because there is no need for quoting or escaping, it is particularly nice for holding code fragments.

"Why do we need another data format?" is the right question to ask. The answer is that the current popular formats (JSON, YAML, TOML, INI, etc.) all have shortcomings which NestedText addresses.

Here's a full-fledged example of an address book (from the official docs):

# Contact information for our officers

president:
    name: Katheryn McDaniel
    address:
        > 138 Almond Street
        > Topeka, Kansas 20697
    phone:
        cell: 1-210-555-5297
        home: 1-210-555-8470
            # Katheryn prefers that we always call her on her cell phone.
    email: KateMcD@aol.com
    additional roles:
        - board member

vice president:
    name: Margaret Hodge
    ...

See the language introduction for more details.

The full API documentation can be found at rubydocs.info. A minimal & fully working example of a project using this library can be found at erikw/nestedtext-ruby-test.

This is how you can decode NestedText from a string or directly from a file (*.nt) to Ruby object instances:

require 'nestedtext'

ntstr = "- objitem1\n- list item 2"
obj1 = NestedText::load(ntstr)

obj2 = NestedText::load_file("path/to/data.nt")

The type of the returned object depends on the top-level type in the NestedText data and will be of the corresponding native Ruby type. In the example above, obj1 will be an Array and obj2 will be a Hash if data.nt looks like e.g.

key1: value1
key2: value2

Thus, you must know what you're parsing, or test what you decoded after.

If you already know what you expect to have, you can guarantee that this is what you will get by telling either function what the expected top type is. If not, an error will be raised.

require 'nestedtext'

ntstr = "- objitem1\n- list item 2"
array = NestedText::load(ntstr, top_class: Array)

hash = NestedText::load_file("path/to/data.nt", top_class: Hash)

# will raise NestedText::Error as we specify top-level String, but it will be an Array.
NestedText::load(ntstr, top_class: String)

This is how you can decode Ruby objects to a NestedText string or file:

require 'nestedtext'

data = ["i1", "i2"]

ntstr = NestedText::dump(data)

NestedText::dump_file(data, "path/to/data.nt")

To make it more convenient, the Ruby Core is extended with a #to_nt method on the supported types that will dump a String of the data structure. Here's an IRB session showing how it works:

irb> require 'nestedtext'
irb> puts "a\nstring".to_nt
> a
> string
irb> puts ["i1", "i2", "i3"].to_nt
- i1
- i2
- i3
irb> hash = {"k1" => "v1",
            "multiline\nkey" => "v2",
            "k3" => ["a", "list"]}
irb> puts hash.to_nt
k1: v1
: multiline
: key
    > v2
k3:
    - a
    - list

Ruby classes map like this to NestedText types:

The strict mode determines how classes other than the basic types String, Array, and Hash are handled during encoding and decoding. By default strict mode is false.

With strict: true

With strict: false

• (1.) How empty strings and nil are handled depends on where it is used. This library follows how the official implementation does it.

This library has support for serialization/deserialization of custom classes as well. This is done by letting the objects tell NestedText what data should be used to represent the object instance with the #encode_nt_with method (inspired by YAML's #encode_with method). All objects being recursively referenced from a root object being serialized must either implement this method or be one of the core supported NestedText data types from the table above.

A class implementing #encode_nt_with is referred to as a Custom Class in this document.

class Apple
  def initialize(type, weight)
    @type = type
    @weight = weight
  end

  def encode_nt_with
    [@type, @weight]
  end
end

When an Apple instance will be serialized, e.g., by apple.to_nt, NestedText will call Apple.encode_nt_with if it exists and let the returned data be encoded to represent the instance.

To be able to get this instance back when deserializing the NestedText, there must be a class method Class.nt_create(data). When deserializing NestedText and the class Apple is detected, and the method #nt_create exists on the class, it will be called with the decoded data belonging to it. This method should create and return a new instance of the class. In the simplest case, it's just translating this to a call to #new.

In full, the Apple class should look like:

class Apple
  def self.nt_create(data)
    new(*data)
  end

  def initialize(type, weight)
    @type = type
    @weight = weight
  end

  def encode_nt_with
    [@type, @weight]
  end
end

An instance of this class would be encoded like this:

irb> puts NestedText::dump(Apple.new("granny smith", 12))
__nestedtext_class__: Apple
data:
    - granny smith
    - 12

If you want to add some more superpowers to your custom class, you can add the #to_nt shortcut by including the ToNTMixin:

class Apple
  include NestedText::ToNTMixin
  ...
end

Apple.new("granny smith", 12).to_nt

Important notes:

• The special key to denote the class name is subject to change in future versions, and you must not rely on it.
• Custom Classes can not be a key in a Hash. Trying to do this will raise an Error.
• When deserializing a custom class, this custom class must be available when calling the #dump* method,s e.g.

  require 'nestedtext'
  require_relative 'apple'  # This is needed if Apple is defined in apple.rb and not in this scope already.
  
  NestedText::load_file('path/to/apple_dump.nt')

The point of NestedText is not to get into to business of supporting ambiguous types. That's why all values are simple strings. Having only simple strings is not useful in practice, though. This is why NestedText is intended to be paired with a Schema Validator!

A schema validator can:

• assert that the parsed values are of the expected types
• automatically convert them to Ruby class instances like Integer, Float, etc.

The reference implementation in Python lists provides a few examples of Python validators. Below is an example of how this Ruby implementation of NestedText can be paired with RSchema.

The full and working example can be found at erikw/nestedtext-ruby-test.

Let's say that you have a program that should connect to a few servers. The list of servers should be stored in a configuration file. With NestedText, a conf.nt file could look like:

-
  name: global-service
  ip: 192.167.1.1
  port: 8080
-
  name: aux-service
  ip: 17.245.14.2
  port: 67
  # Unstable server, don't use this
  stable: false

After parsing this file with the NestedText library, the values for all keys will be strings. But to make practical use of this, we would of course like the values for the port keys to be Integer, and stable should have a value of either true or false. RSchema can do this conversion for us!

# Define schema for our list of servers
schema = RSchema.define do
  array(
    hash(
      'name' => _String,
      'ip' => _String,
      'port' => _Integer,
      optional('stable') => boolean
    )
  )
end

# The coercer will automatically convert types
coercer = RSchema::CoercionWrapper::RACK_PARAMS.wrap(schema)

# Parse config file with NestedText
data = NestedText.load_file('conf.nt')

# Validate
result = coercer.validate(data)
raise result.error.to_s unless result.valid?

# Now we have validated data of the right type specified in the schema!
servers = result.value

# Let's use the values for something in our app
stable_servers = servers.select { |server| server['stable'] }
# Not a meaningful sum - just demonstrating that 'port' values are integers and not strings anymore!
port_sum = servers.map { |server| server['port'] }.sum

1. Add this gem to your Ruby project's Gemfile
   • Simply with $ bundle add nestedtext when standing inside your project
   • Or manually by adding to Gemfile

     gem 'nestedtext'

   and then running $ bundle install.
2. Require the library and start using it!

     require 'nestedtext'
   
     NestedText::load(...)
     NestedText::dump(...)
     obj.to_nt

1. Clone the repo

   git clone https://github.com/erikw/nestedtext-ruby.git && cd $(basename "$_" .git)

2. Install a supported Ruby version (see .gemspec) with a Ruby version manager e.g., rbenv, asdf or RVM
3. run $ scripts/setup or $ bundle install to install dependencies
4. run $ scripts/test or bundle exec rake test to run the tests
5. You can also run $ scripts/console for an interactive prompt that will allow you to experiment.
6. For local testing, install the gem on the local machine with: $ bundle exec rake install.
   • or manually with $ gem build *.gemscpec && gem install *.gem
7. Watch changes on the file system and execute tests with $ bundle exec guard.

Extra:

• Make sure that only intended constants and methods are exposed publicly from the module NestedText. Check with

  irb> require 'nestedtext'
  irb> NestedText.constants
  irb> NestedText.methods(false)
  

• To see undocumented methods with YARD: $ yard stats --list-undoc

Instructions for releasing on rubygems.org are below. Optionally make a GitHub release after this for the pushed git tag.

Following instructions from bundler.io:

vi -p lib/nestedtext/version.rb CHANGELOG.md
bundle exec rake build
ver=$(ruby -r ./lib/nestedtext/version.rb -e 'puts NestedText::VERSION')
bundle exec rake release

Using gem-release:

vi CHANGELOG.md && git commit -am "Update CHANGELOG.md" && git push
gem signin
gem bump --version minor --tag --sign --push --release

For --version, use major|minor|patch as needed.

Just push a new semver tag and the workflow cd.yml will publish a new release at rubygems.org.

vi -p lib/nestedtext/version.rb CHANGELOG.md
git commit -am "Prepare vX.Y.Z" && git push
git tag vX.Y.Z && git push --tags

or preferred combined with gem-release:

vi CHANGELOG.md
git commit -am "Update CHANGELOG.md" && git push
gem signin
gem bump --version minor --tag --push --sign

then watch progress with gh.

For --version, use major|minor|patch as needed.

gh run watch

Bug reports and pull requests are welcome on GitHub at erikw/nestedtext-ruby.

The gem is available as open source with the License.

• Thanks to the data format authors for making it easier to make new implementations by providing an official test suite.
• Thanks to pixteller & mp4.to for offering the tools needed for creating an animated logo.