Simple redis cache helper, always evaluates value if Redis is down

gistfile1.rb

module RedisHelper
  def redis
    @redis ||= Redis.new.tap do
      @redis_available = true
    end
  end

  def ns_key(k)
    "enfo_sm:#{k}"
  end

  def maybe_get(k)
    redis.get(k)
  rescue Redis::CannotConnectError
    warn "Cannot connect to redis instance"
    @redis_available = false
    nil
  end

  # call value stored under key, optionally setting expire time in seconds (default 10). 
  # If not found, block is called and value is cached.
  # Object must be serializable with Marshal. Expire is set only when calling the block.
  def cache_get(key, opts={}, &block)
    k = ns_key(k)

    if v = maybe_get(k) # either key is not found, or cannot connect to redis
      Marshal::load(v)
    else
      block.call.tap do |v| 
        if @redis_available
          redis.set(k, Marshal::dump(v)) 
          redis.expire(k, opts.fetch(:expire, 10))
        end
      end
    end
  end
end