redis/redis-rb#924

.ruby-version

2.7.1

Gemfile

source 'https://rubygems.org'

gem 'goliath', github: 'postrank-labs/goliath'
gem 'redis'
gem 'hiredis'

# Goliath declares rack (>= 1.2.2), which is too lax now that rack 2 exists.
gem 'rack', '~> 1'

Gemfile.lock

GIT
  remote: https://github.com/postrank-labs/goliath.git
  revision: bdbf254eca6ff59e5a83d9969db7c5462e06ed61
  specs:
    goliath (1.0.6)
      async-rack
      einhorn
      em-synchrony (>= 1.0.0)
      em-websocket (= 0.3.8)
      eventmachine (>= 1.0.0.beta.4)
      http_parser.rb (>= 0.6.0)
      log4r
      multi_json
      rack (>= 1.2.2)
      rack-contrib
      rack-respond_to

GEM
  remote: https://rubygems.org/
  specs:
    addressable (2.7.0)
      public_suffix (>= 2.0.2, < 5.0)
    async-rack (0.5.1)
      rack (~> 1.1)
    einhorn (0.7.4)
    em-synchrony (1.0.6)
      eventmachine (>= 1.0.0.beta.1)
    em-websocket (0.3.8)
      addressable (>= 2.1.1)
      eventmachine (>= 0.12.9)
    eventmachine (1.2.7)
    hiredis (0.6.3)
    http_parser.rb (0.6.0)
    log4r (1.1.10)
    multi_json (1.14.1)
    public_suffix (4.0.5)
    rack (1.6.13)
    rack-accept-media-types (0.9)
    rack-contrib (1.8.0)
      rack (~> 1.4)
    rack-respond_to (0.9.8)
      rack-accept-media-types (>= 0.6)
    redis (4.2.1)

PLATFORMS
  ruby

DEPENDENCIES
  goliath!
  hiredis
  rack (~> 1)
  redis

BUNDLED WITH
   2.1.4

repro.rb

require 'goliath'
require 'redis'

class Repro < Goliath::API
  use Goliath::Rack::Params

  def response(env)
    head? ? head : tail
  rescue Redis::BaseError => e
    [500, {}, e.message]
  end

  def self.redis
    @redis ||= Redis.new(url: ENV['REDIS_URL'], driver: :synchrony)
  end

  def redis
    self.class.redis
  end

  def id
    params['id']
  end

  def lock
    @lock ||= SecureRandom.urlsafe_base64
  end

  def entries
    "#{id}:entries"
  end

  def head?
    redis.set(id, lock, nx: true, ex: 300)
  end

  def head
    redis.pipelined do
      redis.rpush(entries, %w[b c d e])
      redis.expire(entries, 300)
    end

    [200, {}, 'a']
  end

  def tail
    response = redis.blpop(entries, timeout: 1)
    response ? [200, {}, response.last] : [500, {}, 'timeout']
  end
end