DNSMessage

DNSMessage is a Ruby library for building and parsing DNS messages.

Features

A full featured DNS parser. The library supports DNS name compression and gives access to parse, build, and manipulate all aspects of the DNS queries and replies.

Installation

Add this line to your application's Gemfile:

gem 'dnsmessage'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install dnsmessage

Usage

require 'dnsmessage'

# Parse some byte string from a server or somewhere else
msg = DNSMessage::Message.parse(byte_string)

# Look at the questions and resource records in that byte string
puts msg.questions.inspect
puts msg.answers.inspect
puts msg.additionals.inspect
puts msg.authority.inspect

# Create a reply based on the message (even if it's a reply itself)
reply = DNSMessage::Message.reply_to(msg)

# Add an answer to the reply
answer = DNSMessage::RR.new(name: "some.domain.tld",
                            type: DNSMessage::Type::A,
                            klass: DNSMessage::Class::IN,
                            ttl: 7200,
                            rdata: IPAddr.new("4.3.2.1"))
reply.answers << answer

# (optional) Add EDNS with a 512 maximum size
reply.additionals << DNSMessage::RR.default_opt(512)

# Build reply into a byte string
reply_bytes = reply.build

An example of an IP discovery server can be found in the examples directory.

Supported Resource Record types

Currently implemented types are:

• A
• AAAA
• CNAME
• OPT
• TXT

Other records should be easy to add on a per-need basis as they can be based on the building blocks of already existing parsers and builders. Look at contributing for details on adding RR types.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. 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 tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/cmol/dnsmessage. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

Adding Resource Record Types

To add a Resource Record you need to find documentation for the structure of that record, or create a dump using something like wireshark. After that is done, you can use an existing builder or parser from lib/dnsmessage/resource_record.rb. If you are creating a pull request, please add tests for the given type.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the dnsmessage project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.