Using the TYPE command inside a Redis / Lua Script

Question

I am attempting to use the Redis TYPE command inside a Lua script (executed via EVAL) ``` local key_type = redis.call("TYPE", key) ``` According to the Redis documentation, this should return a string of `"none"`, `"zset"` etc. However the type of the returned value is a lua `table`. Comparing the value to a string always returns false. I've managed to get around the problem by changing the call to ``` local key_type = redis.call("TYPE", key)["ok"] ``` This value is indeed a string and does work in string comparison commands. I am worried that this is a bug in my particular version of Redis and it will break in future versions when I upgrade. Does anyone know if this is expected behaviour, or a bug?

Accepted Answer

The `TYPE` command returns a status reply (a.k.a simple string), e.g `"+list
"`.

On Redis scripting side, `call` is implemented by `luaRedisCallCommand` which performs the real Redis command behind the scenes.

Once successfully executed, this function converts the command result with `redisProtocolToLuaType`.

When a status reply is encountered, this function creates a Lua table with `"ok"` as key, and the status reply as value (see `redisProtocolToLuaType_Status`). So:

- there is no bug,

- this is why `redis.call("TYPE", key)` is a table (and thus you need to get the value for the `"ok"` key as you did, to get `key`'s type as a string).

Note: when you directly return the table, Redis takes care to get the value associated to the `"ok"` key, and returns it as a status reply, e.g:

```
> EVAL 'return redis.call("TYPE", "foo")' 
set
```

See this code section for more details.

Using the TYPE command inside a Redis / Lua Script

Solution

Problem