a useful wrapper of the Open3.popen3 interface to run commands on a shell

command_runner.rb

require 'open3'
require 'logger'

class CommandRunner
  class CommandFailedError < StandardError
    def initialize(command, status)
      super("Exit status (#{status}) is non-zero for command: #{command}")
    end
  end
  EXIT_STATUS_INTERRUPT = 130

  attr_reader :logger, :dry_run

  def initialize(logger:, dry_run: false)
    @logger = logger
    @dry_run = dry_run
  end

  def run(command, stdin: STDIN, stdout: STDOUT, stderr: STDERR)
    if dry_run
      logger.warn("dry-running: `#{command}`")
    else
      logger.info("running: `#{command}`")
      status = Open3.popen3(command) do |i, o, e, cmd_status|
        redirect(stdin => i, o => stdout, e => stderr)
        logger.debug cmd_status.value
        cmd_status.value.exitstatus
      end
      raise CommandFailedError.new(command, status) if status != 0
    end
  end

  private

  def redirect(mapping)
    inputs = mapping.keys

    logger.debug mapping.inspect

    until inputs.empty? || (inputs.size == 1 && inputs.first == STDIN) do
      logger.debug 'starting `select`'

      readable_inputs, = IO.select(inputs, [], [])

      ios_ready_for_eof_check = readable_inputs

      logger.debug 'finished `select`'

      logger.debug 'starting eof check'
      ios_ready_for_eof_check.select(&:eof).each do |src|
        logger.debug "Stopping redirection from an IO in EOF: " + src.inspect
        inputs.delete src

        mapping[src].close if src == STDIN
      end

      break if inputs.empty? || (inputs.size == 1 && inputs.first == STDIN)

      readable_inputs.each do |input|
        begin
          data = input.read_nonblock(1024)
          output = mapping[input]
          output.write(data)
          output.flush
        rescue EOFError => e
          logger.debug "Reached EOF: #{e}"
          inputs.delete input
        rescue => e
          logger.debug "Handled error: #{e}: io: #{input.inspect}"
          inputs.delete input
        end
      end
    end
  end

  def all_eof?(files)
    begin
      files.all?(&:eof)
    rescue Interrupt => e
      logger.warn "You've interrupted while running a command."
      EXIT_STATUS_INTERRUPT
    end
  end
end