Empty lua table returns EmptyMap since 5.0.1

[ngavrailov]

Hello,
What is the point of this change? Currently we are having issues with existing lua scripts, because of difference when the lua table is populated as list and when it is returned empty. Maybe we are not using the output correct expecting lists? Can you suggest how to handle table responses?
Best regards,
Nikolay

[thachlp]

Hi @ngavrailov, I checked, and I see that AGGRESSIVE_ENCODED_OBJECT was added since jedis5, there are no previous implementing before.
So could you give more information about the issue, such as the input, output ...

[ngavrailov]

I am asking what is the point of this part of the implementation. When 'data' is instance of List to return Collection.emptyMap(). Doesn't make sense for me and also caused issues in our code with existing lua scripts when I upgraded to Jedis 5.

Here is one lua script example which starts to break:
local bingoTickets = {} ... return bingoTickets

List<Object> scriptResult = (List<Object>) runScript(progressOnTicketsScript

In case there are no 'bingoTickets' and the table doesn't change we hit an issue casting the result to list. The issue is because the empty lua table is returned as Collection.emptyMap() (as I mentioned earlier and show from the jedis code where it comes from). The worst part is that when the table bingoTickets has anything added it is returned as List, so this code works fine. Doesn't make sense for me why jedis has inconsistency with the data types when one table is filled with data as list and when empty. Looks like it is done for other specific case ignoring you can want to return list sometimes.

Can you explain why this change is done in Jedis 5?

[ngavrailov]

Just spotted there is a bug opened already:
#3876

[willianmrs]

Hi guys I'm having a similar problem so that I will join this thread.

I am encountering a significant issue after migrating from Jedis version 4.3 to 5.1. My code, which worked fine in 4.3, is now encountering inconsistent and unexpected behavior.

Code Overview

Here is a simplified version of my Scala code:

val result = redisCluster.eval(script, keys, arguments)

import java.util
val asList = result.asInstanceOf[util.ArrayList[_]]
val state = asList.get(0).asInstanceOf[String]
val latestEvents = asList.get(1).asInstanceOf[util.ArrayList[_]].asInstanceOf[util.ArrayList[String]]

Lua Script

The Lua script being executed is as follows:

local nrt_feature = redis.call('HMGET', nrt_key, "value1", "value2")
local nrt_feature_value = nrt_feature[2]

local events_to_aggregate = redis.call("ZRANGEBYSCORE", key, min, max)

return { nrt_feature_value, events_to_aggregate }

Behavior in Jedis 4.3

In Jedis 4.3, the returned data structures were consistent and the Scala code processed them correctly. For example:

• nrt_feature_value was a string containing the expected value.
• events_to_aggregate was a list of strings.

Issues in Jedis 5.1

After upgrading to Jedis 5.1, I am encountering the following problems:

1. Inconsistent nrt_feature_value:

   • When events_to_aggregate contains elements, nrt_feature_value is empty.
   • Conversely, when events_to_aggregate is empty, nrt_feature_value is populated correctly.

2. Empty events_to_aggregate:

   • When events_to_aggregate is supposed to be empty, it is returned as an empty map (java.util.Collections$EmptyMap) instead of an empty list. This is causing ClassCastException when attempting to cast to ArrayList.

Example Scenarios

• Scenario 1:

  nrt_feature_value = "f_value1"
  events_to_aggregate = ["event1", "event2"]

  • Observed Behavior: In Scala, events_to_aggregate can be parsed as a list, but nrt_feature_value is empty.

• Scenario 2:

  nrt_feature_value = "f_value1"
  events_to_aggregate = []

  • Observed Behavior: nrt_feature_value is correctly populated, but events_to_aggregate is an empty map, causing type-casting issues.

Additional Information

It appears that the return type handling of the eval command has changed between versions, causing these inconsistencies. This behavior is making it challenging to migrate to the newer version of Jedis.

Could you please advise on whether this is an intended change, or if there might be a bug or configuration issue that I need to address?

Thank you for your assistance!

---

Details

• Jedis Version: 5.1.3
• Redis Version: 6.2 (But we have the same behavior on 7.2)
• Scala Version: 2.12
• Java Version: 8
• Sark Version: 3.4.1 (that happens outside spark, but since it adds a lot of dependency with it, I'm adding the version we are using here)