VT 100 Parser Gem

This gem is a parser for VT100 terminal escape sequences. It is based on the C code from https://github.com/haberman/vtparse/ and implements the statemachine from https://www.vt100.net/emu/dec_ansi_parser.

The purpose of this Gem is to have a relatively easy way to filter/modify the output of child/sub-processes (for instance launched via PTY::spawn) which use animation or colors.

Uses keyboard mapping logic from https://github.com/vidarh/keyboard_map/

Background on VT100 Escape Sequences

See https://gist.github.com/fnky/458719343aabd01cfb17a3a4f7296797

Installation

Install the gem and add to the application's Gemfile by executing:

bundle add vtparser

If bundler is not being used to manage dependencies, install the gem by executing:

gem install vtparser

Basic Usage

See the minimal example below:

require_relative '../lib/vtparser'

# Instantiate the parser with a block to handle actions
parser = VTParser.new do |action|

  # For this minimal example, we'll just turn everything back strings to print
  print action.to_ansi

end

# Sample input containing ANSI escape sequences (red text, bold text)
input = "\e[31mHello, \e[1mWorld!\e[0m\n"

# Parse the input
parser.parse(input)

Further samples in the examples directory:

• echo_keys.rb: Echoes the keys pressed by the user
• indent_cli.rb: Indents the output of simple command line tools
• colorswap.rb: Swaps the colors red / green in the input program
• analyze.rb: Output all VT100 escape sequences written by the subprocess.
• roundtrip.rb: Runs the given command and compares characters written by the command to the output of running the characters through the parser and serializing the actions back to_ansi. If the parser works correctly the output should be the same.

Limitations

• The parser is based on the implementation https://github.com/haberman/vtparse/ and based on a state machine which precedes Unicode. As such it does not have state transitions for Unicode characters. Rather, it will output them as :ignore actions. In case unicode characters are used inside escape sequences, the parser will likely not be able to handle them correctly.

• The state machine does not expose all input characters to the implementation in relationship to the DSC (Device Control String) sequences. In particular the "Final Character" is swallowed by the statemachine from https://www.vt100.net/emu/dec_ansi_parser. To circumvent this limitation, I have modified the parser to expose the final character as intermediate_chars to the :hook action.

• The parser only outputs full actions. So triggering an event for the ESC key doesn't work (as expected).

• The parser does not emit actions for commands which are 'interrupted' by another command."

• The parser does not explain any of the actions.

Development

After checking out the repo, run bin/setup to install dependencies. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/coezbek/vtparser.