It's a simple Ruby gem to get a random TCP port.

First, install it:

$ gem install random-port

Then, use it like this, to reserve a random TCP port:

require 'random-port'
port = RandomPort::Pool.new.acquire

The Pool guarantees that the port won't be used again. You can put the port back to the pool after usage:

RandomPort::Pool.new.acquire do |port|
  # Use the TCP port. It will be returned back
  # to the pool afterwards.
end

You can do it without the block:

pool = RandomPort::Pool.new
port = pool.acquire
pool.release(port)

You can also use a pre-defined Pool::SINGLETON singleton:

RandomPort::Pool::SINGLETON.acquire do |port|
  # Use it here...
end

The pool is thread-safe by default. You can configure it to be not-thread-safe, using optional sync argument of the constructor.

Read these guidelines. Make sure you build is green before you contribute your pull request. You will need to have Ruby 2.3+ and Bundler installed. Then:

$ bundle update
$ bundle exec rake

If it's clean and you don't see any error messages, submit your pull request.