Udon

High-performance UDON (Universal Document & Object Notation) parser for Ruby.

Uses a native Rust extension for maximum performance:

• ~1.3 GiB/s raw Rust parsing throughput
• Zero-copy event emission
• Streaming event model (no DOM overhead)

Installation

Add to your Gemfile:

gem 'udon'

Then run:

bundle install

This requires Rust to be installed (for compilation). Install via rustup.

Usage

require 'udon'

# Parse a UDON document
events = Udon.parse(<<~UDON)
  |article[my-post].featured
    :title "Hello, World!"
    :published true

    |section
      This is the first paragraph.

      |ul
        |li First item
        |li Second item
UDON

# Process events
events.each do |event|
  case event[:type]
  when :element_start
    puts "Element started"
  when :name
    puts "Name: #{event[:content]}"
  when :attr
    puts "Attr: #{event[:content]}"
  when :string_value, :bare_value
    puts "Value: #{event[:content]}"
  when :text
    puts "Text: #{event[:content].strip}"
  when :element_end
    puts "Element ended"
  end
end

Event Types

Each event is a Hash with :type and :span keys. Content events also have :content.

Bracket events (start/end pairs):

• :element_start, :element_end
• :embedded_start, :embedded_end
• :directive_start, :directive_end
• :array_start, :array_end
• :freeform_start, :freeform_end
• :comment_start, :comment_end

Content events (have :content):

• :name - element/directive name
• :text - text content
• :attr - attribute name
• :string_value - quoted string value
• :bare_value - unquoted value
• :bool_true, :bool_false - boolean values
• :nil - nil/null value
• :integer, :float, :rational, :complex - numeric values
• :interpolation - interpolation expression
• :reference - reference content
• :raw_content, :raw - raw content

Error events:

• :error - has :code instead of :content

Performance

Benchmarks comparing UDON against other Ruby parsers (parse + full traversal):

Parser	Elements/sec	vs Psych
UDON	150-175K	2x faster
Psych (YAML)	80-90K	baseline
REXML (XML)	50-60K	0.6x
Nokogiri (XML)	350-380K	4x faster

UDON's streaming model emits ~12 events per element (Name, Attr, Value, Text, etc.), while DOM parsers like Nokogiri build the tree in C++ and create fewer Ruby objects. This makes UDON competitive with Psych while providing streaming benefits (no DOM memory overhead, early termination, etc.).

Run benchmarks yourself:

bundle exec rake bench

Development

# Install dependencies
bundle install

# Compile native extension
bundle exec rake compile

# Run tests
bundle exec rake test

# Run benchmarks
bundle exec rake bench

License

MIT