[#2341] Initialize slots with empty BitSet in RedisClusterNode's constructors

[zeze1004]

Issue: #2341
This PR supersedes the previously closed PR #2798

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[zeze1004]

@mp911de

I kindly request your review of this pull request. Your feedback would be greatly appreciated. 🙇🏻

[zeze1004]

I tested everything locally and it passed, but it failed on GitHub Actions. I'll make the necessary fixes and commit again soon.

[tishun]

I tested everything locally and it passed, but it failed on GitHub Actions. I'll make the necessary fixes and commit again soon.

Please ignore the failure of the SslIntegrationTests.pubSubSsl:396 - it is unstable and if you pull the latest sources you will see it is disabled

[tishun]

Thanks for working on this!

Please check my comments and let me know if you need any clarifications or have some concerns.

[tishun]

I think part of the idea behind the existing code is to clone the content of the slots, instead of directly assigning the provided value.

This has the added benefit of isolation, because the code that called the constructor could no longer modify the contents of the slot (as a side effect).

However you are correct that a good design should consider this method receiving a null for the slots argument. Perhaps something in the line of:

this.slots = new BitSet(SlotHash.SLOT_COUNT);
this.slots.or(slots);

This way:

• if the slots argument are null then the or() method handles it correctly
• the this.slots is always initialized with an empty list of slots

IMHO the consistency of always having BitSet initialized with the SlotHash.SLOT_COUNT pays off for the "waste" of memory.

[zeze1004]

@tishun Thank you for your feedback. I have made the suggested changes.

[tishun]

I think the same logic can be followed here. See my previous comment.

[tishun]

I think the most important test is the one described in #2341 and it is missing:

• create one RedisClusterNode instance from the constructor on line 102-103 (parsed nodes use this constructor)
• create one RedisClusterNode instance from the constructor on line 112-125 (cloned nodes use this constructor)
• check if RedisClusterNode::hasSameSlotsAs() returns that they are the same

If you see the last mention of an issue in the original issue you'll see that there is also a 3rd constructor (the one on line 78-79) that calls the setSlotBits() method and it would also result in an null slots field if the array is empty. If we had a test for that we would have caught that this condition is not handled right now.

I think a good design would address this and make sure there is no way we set null to the slots field. What do you think?

[zeze1004]

Thank you. I forgot to add the necessary test. I've added it. Could you please review again?

[tishun]

Hey thanks for addressing the last comments.

There are still two things that I am worried about:

1. We are still missing the same logic on line 90 (the first of the three constructors)
2. The test is not really verifying the issue from RedisClusterNode.hasSameSlotsAs() is unreliable  #2341

[tishun]

This test is OK, but it tests something different than what is explained in #2341

In #2341 the problems is that one part of the logic uses RedisClusterNode(RedisURI uri, String nodeId, boolean connected, String slaveOf, long pingSentTimestamp, long pongReceivedTimestamp, long configEpoch, BitSet slots, Set<NodeFlag> flags) to create a RedisClusterNode, while another uses the public RedisClusterNode(RedisClusterNode redisClusterNode) constructor. Both are provided an empty BitSet.

When later on both resulting objects are compared with .hasSameSlotsAs() it would return false, when it should return true, because the first object would have an empty slots BitSet, while the second would have a null slots BitSet.

I think the proper test scenario is :

public void testHasDifferentSlotsAs() {
        BitSet emptySlots = new BitSet(SlotHash.SLOT_COUNT);

        RedisClusterNode node1 = new RedisClusterNode(RedisURI.create("localhost", 6379), "nodeId1", true, "slaveOf", 0L, 0L,
                0L, emptySlots, new HashSet<>());
        RedisClusterNode node2 = new RedisClusterNode(node1);

        assertThat(node1.hasSameSlotsAs(node2)).isTrue();

You can test if this case fails when you remove your changes to RedisClusterNode.java