Generic Retry Helper

retry.gemspec

Gem::Specification.new do |s|
  s.name        = 'retry'
  s.version     = '0.0.1'
  s.platform    = Gem::Platform::RUBY
  s.author      = 'Peter Schröder'
  s.email       = 'phoetmail@googlemail.com'
  s.license     = 'MIT'
  s.homepage    = 'https://gist.github.com/phoet/92767354f7d78a9f8e2985bc29df88c4'
  s.description = s.summary = 'retry helper as a gist'

  s.files         = ['retry.rb']
  s.require_path  = '.'
end

retry.rb

module Retry
  def with_retry(max_retry_count: 3, retry_timeout: 0.5, backoff: false)
    Thread.current[:retry_count] ||= 0
    yield(Thread.current[:retry_count])
  rescue
    raise if Thread.current[:retry_count] >= max_retry_count - 1
    sleep backoff ? exponential_timeout(retry_timeout) : retry_timeout
    Thread.current[:retry_count] += 1
    retry
  ensure
    Thread.current[:retry_count] = nil
  end

  private

  def exponential_timeout(retry_timeout, iteration = Thread.current[:retry_count].to_i)
    retry_timeout = 2 if retry_timeout < 2
    retry_timeout ** (iteration + 1)
  end
end

retry_test.rb

require_relative 'retry'
require 'minitest/autorun'

class RetryTest < Minitest::Test
  def setup
    @mock = MiniTest::Mock.new
    @retryer = Retryer.new(@mock)
    Thread.current[:retry_count] = nil
  end

  def test_exponential_has_minimum_of_two_seconds
    assert_equal 2, @retryer.send(:exponential_timeout, 0.5)
    assert_equal 2, @retryer.send(:exponential_timeout, 1)
    assert_equal 2, @retryer.send(:exponential_timeout, 2)
  end

  def test_exponential_uses_passed_timeout
    assert_equal 3, @retryer.send(:exponential_timeout, 3)
  end

  def test_exponential_increases_exponentially
    Thread.current[:retry_count] = 1
    assert_equal 4, @retryer.send(:exponential_timeout, 2)

    Thread.current[:retry_count] = 2
    assert_equal 8, @retryer.send(:exponential_timeout, 2)

    Thread.current[:retry_count] = 3
    assert_equal 16, @retryer.send(:exponential_timeout, 2)
  end

  def test_retrying_doesnt_do_anything_on_success
    @mock.expect(:doit, true, [0])

    assert @retryer.retry
    assert_nil Thread.current[:retry_count]
  end

  def test_retrying_works_up_to_max_retry_count
    def @mock.doit(iteration)
      raise "error that should be retried, #{iteration}"
    end
    begin
      @retryer.retry
      fail 'expected an error to be raised'
    rescue
      assert_equal "error that should be retried, 2", $!.message
    end
  end

  def test_retrying_works_up_to_custom_max_retry_count
    def @mock.doit(iteration)
      raise "error that should be retried, #{iteration}"
    end
    begin
      @retryer.retry(max_retry_count: 2)
      fail 'expected an error to be raised'
    rescue
      assert_equal "error that should be retried, 1", $!.message
    end
  end

  class Retryer
    include Retry

    def initialize(mock)
      @mock = mock
    end

    def retry(**args)
      with_retry(**args) do |iteration|
        @mock.doit(iteration)
      end
    end
  end
end