Module: Kernel

Defined in:
lib/donce.rb

Overview

Execute Docker container and clean up afterwards.

This function helps building temporary Docker images, run Docker containers, and clean up afterwards — may be convenient for automated tests (for example, with Minitest):

class MyTest < Minitest::Test
  def test_prints_hello_world
    stdout = donce(
      dockerfile: '
        FROM ubuntu
        CMD echo "Hello, world!"
      '
    )
    assert_equal("Hello, world!\n", stdout)
  end
end

It’s possible to pass a block to it too, which will lead to background execution of the container (in daemon mode):

def test_runs_daemon
  donce(dockerfile: "FROM ubuntu\nCMD sleep 9999") do |id|
    refute_empty(id)  # the ID of the container
  end
end

If you need to run docker via sudo, simply set DONCE_SUDO environment variable to any value.

Author

Yegor Bugayenko ([email protected])

Copyright

Copyright © 2024-2025 Yegor Bugayenko

License

MIT

Instance Method Summary collapse

Instance Method Details

#donce(dockerfile: nil, image: nil, home: nil, log: $stdout, args: '', env: {}, root: false, command: '', timeout: 60, volumes: {}, ports: {}, build_args: {}) ⇒ String

Build Docker image (or use existing one), run Docker container, and then clean up.

Parameters:

  • dockerfile (String) (defaults to: nil) —

    The content of the Dockerfile (if array is provided, it will be concatenated)

  • home (String) (defaults to: nil) —

    The directory with Dockerfile and all other necessary files

  • image (String) (defaults to: nil) —

    The name of Docker image, e.g. “ubuntu:22.04”

  • log (Logger) (defaults to: $stdout) —

    The logging destination, can be $stdout

  • args (String|Array<String>) (defaults to: '') —

    List of extra arguments for the docker command

  • env (Hash<String,String>) (defaults to: {}) —

    Environment variables going into the container

  • volumes (Hash<String,String>) (defaults to: {}) —

    Local to container volumes mapping

  • ports (Hash<String,String>) (defaults to: {}) —

    Local to container port mapping

  • build_args (Hash<String,String>) (defaults to: {}) —

    Arguments for docker build as --build-arg may need

  • root (Boolean) (defaults to: false) —

    Let user inside the container be “root”?

  • command (String|Array<String>) (defaults to: '') —

    The command for the script inside the container

  • timeout (Integer) (defaults to: 60) —

    Maximum seconds to spend on each docker call

Returns:

  • (String) —

    The stdout of the container



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# File 'lib/donce.rb', line 69

def donce(dockerfile: nil, image: nil, home: nil, log: $stdout, args: '', env: {}, root: false, command: '',
          timeout: 60, volumes: {}, ports: {}, build_args: {})
  raise 'Either use "dockerfile" or "home"' if dockerfile && home
  raise 'Either use "dockerfile" or "image"' if dockerfile && image
  raise 'Either use "image" or "home"' if home && image
  raise 'Either "dockerfile", or "home", or "image" must be provided' if !dockerfile && !home && !image
  raise 'The "timeout" must be an integer or nil' unless timeout.nil? || timeout.is_a?(Integer)
  raise 'The "volumes" is nil' if volumes.nil?
  raise 'The "volumes" must be a Hash' unless volumes.is_a?(Hash)
  raise 'The "log" is nil' if log.nil?
  raise 'The "args" is nil' if args.nil?
  raise 'The "args" must be a String' unless args.is_a?(String)
  raise 'The "env" is nil' if env.nil?
  raise 'The "env" must be a Hash' unless env.is_a?(Hash)
  raise 'The "command" is nil' if command.nil?
  raise 'The "command" must be a String or an Array' unless command.is_a?(String) || command.is_a?(Array)
  raise 'The "timeout" is nil' if timeout.nil?
  raise 'The "timeout" must be a number' unless timeout.is_a?(Integer) || timeout.is_a?(Float)
  raise 'The "ports" is nil' if ports.nil?
  raise 'The "ports" must be a Hash' unless ports.is_a?(Hash)
  raise 'The "build_args" is nil' if build_args.nil?
  raise 'The "build_args" must be a Hash' unless build_args.is_a?(Hash)
  docker = ENV['DONCE_SUDO'] ? 'sudo docker' : 'docker'
  command = command.join(' ') if command.is_a?(Array)
  img =
    if image
      image
    else
      i = "donce-#{SecureRandom.hex(6)}"
      a = [
        "--tag #{i}",
        build_args.map { |k, v| "--build-arg #{Shellwords.escape("#{k}=#{v}")}" }.join(' ')
      ].compact.join(' ')
      if dockerfile
        Dir.mktmpdir do |tmp|
          dockerfile = dockerfile.join("\n") if dockerfile.is_a?(Array)
          File.write(File.join(tmp, 'Dockerfile'), dockerfile)
          qbash("#{docker} build #{a} #{Shellwords.escape(tmp)}", log:)
        end
      elsif home
        qbash("#{docker} build #{a} #{Shellwords.escape(home)}", log:)
      else
        raise 'Either "dockerfile" or "home" must be provided'
      end
      i
    end
  container = "donce-#{SecureRandom.hex(6)}"
  stdout = nil
  code = 0
  cmd = [
    docker, 'run',
    ('--detach' if block_given?),
    '--name', Shellwords.escape(container),
    ("--add-host #{donce_host}:host-gateway" unless OS.linux?),
    args,
    env.map { |k, v| "--env #{Shellwords.escape("#{k}=#{v}")}" }.join(' '),
    ports.map { |k, v| "--publish #{Shellwords.escape("#{k}:#{v}")}" }.join(' '),
    volumes.map { |k, v| "--volume #{Shellwords.escape("#{k}:#{v}")}" }.join(' '),
    ("--user=#{Shellwords.escape("#{Process.uid}:#{Process.gid}")}" unless root),
    Shellwords.escape(img),
    command
  ].compact.join(' ')
  begin
    begin
      stdout, code =
        Timeout.timeout(timeout) do
          qbash(
            cmd,
            log:,
            accept: nil,
            both: true,
            env:
          )
        end
      unless code.zero?
        log.error(stdout)
        raise \
          "Failed to run #{cmd} " \
          "(exit code is ##{code}, stdout has #{stdout.split("\n").count} lines)"
      end
      yield container if block_given?
    ensure
      logs = qbash(
        "#{docker} logs #{Shellwords.escape(container)}",
        level: code.zero? ? Logger::DEBUG : Logger::ERROR,
        log:
      )
      stdout = logs if block_given?
      qbash("#{docker} rm --force #{Shellwords.escape(container)}", log:)
    end
    stdout
  ensure
    Timeout.timeout(10) do
      qbash("#{docker} rmi #{img}", log:) unless image
    end
  end
end

#donce_host ⇒ String

The name of the localhost inside Docker container.

Returns:

  • (String) —

    The hostname



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# File 'lib/donce.rb', line 50

def donce_host
  OS.linux? ? '172.17.0.1' : 'host.docker.internal'
end