S3 strong consistency

gistfile1.rb

def write_with_strong_consistency(*args, &block)
  result = write(*args, &block)
  redis.set("s3:key:#{key}", result.etag, ex: 24*60*60)
  result
end

def delete_with_strong_consistency(options = {})
  result = delete(options)
  redis.set("s3:key:#{key}", 'deleted', ex: 24*60*60) unless options[:version_id]
  result
end

def read_with_strong_consistency(options = {}, &read_block)
  read(options, &read_block) if options[:version_id] #  short-circuit the whole thing for versions
  
  redis_etag = redis.get("s3:key:#{key}")
  options[:if_match] ||= redis_etag

  raise NoSuchKey, "The specified key does not exist" if redis_etag == 'deleted'

  if redis_etag && redis_etag == options[:if_match]
    begin
      read(options, &read_block)
    rescue AWS::S3::Errors::NoSuchKey => e
      # if the key has actually been deleted, the next time you check you will get
      # a real NoSuchKey exception
      raise AWS::S3::Errors::PreconditionFailed, "The specified key does not exist yet"
    end
  else
    read(options, &read_block)
  end
end