scala - Redis 中的 "Null reply"到底是什么？

Question

我将 Redis 与 Scala(rediscala 库)结合使用。我需要创建这样的交易:

redisTransaction.watch(key)
redisTransaction.zremrangebyscore(key, limit, limit) *>
redisTransaction.zadd(key, (someValue, entry)) *>
redisTransaction.set[ByteString](s"$lastSeqNumKey", sequenceNum) *>
redisTransaction.exec().void

最后一个表达式应该返回一个 Future[Unit]，我希望它在事务失败的情况下失败。但是，Redis 文档指出:

When using WATCH, EXEC can return a Null reply if the execution was aborted.

“空回复”到底是什么？我的 Future[Unit] 是否有可能以 null 值或空字符串或类似的值成功？我想编写一个测试，我需要一些有关它的提示。

Answer 1

一个更正，redisTransaction.exec() 上没有void 方法。

简答:

exec() 如果事务失败或执行中止，调用将返回 Future(MultiBulk(None))。

长答案:

正如文档所说，

When using WATCH, EXEC can return a Null reply if the execution was aborted.

并链接到 NULL reply的解释

RESP Bulk Strings can also be used in order to signal non-existence of a value using a special format that is used to represent a Null value. In this special format the length is -1, and there is no data, so a Null is represented as:

"$-1\r\n" This is called a Null Bulk String.

The client library API should not return an empty string, but a nil object, when the server replies with a Null Bulk String. For example a Ruby library should return 'nil' while a C library should return NULL (or set a special flag in the reply object), and so forth

这表明服务器将回复 NULL 响应，客户端必须处理它。它不能是空字符串，在这个库中，它处理解码并将来自服务器的响应映射为 MultiBulk(None)

有一个test case用于解码来自 Redis 的 NULL 响应。