[Iris] Crash for SubObject with only COND_InitialOnly properties

Development Programming & Scripting Multiplayer & Networking
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1

Hello,

we’ve run into an issue with SubObjects which only contain “InitialOnly” properties.

When creating a SubObject which only contains replicating properties with the condition COND_InitialOnly, we get a crash in FNetBitStreamWriter::InitBytes and when starting PIE the below check triggers.

UE_NETBITSTREAMWRITER_CHECKF((ByteCount >= 4) && (ByteCount & 3) == 0, TEXT("Buffer capacity needs to be a multiple of 4 and at least 4."));We can make a change in FReplicationInstanceOperationsInternal::QuantizeObjectStateData to also check “Object.Protocol->ChangeMaskBitCount > 0”, and this seems to fix the crash. But we’re not sure if this is the correct way to fix the issue?

Additionally, objects which only contain COND_InitialOnly properties should ideally not be considered for poll (in UObjectReplicationBridge::BuildPollList they still get marked for poll when the owner is marked for poll).

Thanks for your time,

Kind regards,

Céleste

2

Steps to Reproduce
Create a replicating SubObject with only COND_InitialOnly properties. Then mark a property dirty on one of the properties after object creation.

3

Hi,

Thank you for the report and the potential fix!

This is a known issue with Iris, although with other bug fixes taking priority, I can’t provide an estimate as to when this may be fixed. In the meanwhile, I’ve included the information you’ve provided here on our internal tracker for the issue.

Thanks,

Alex

4

Hello Alex,

Thanks for that! But what about the issue where objects which only have COND_InitialOnly properties are still being polled? Is that intentional, or is that also a bug?

Kind regards,

Céleste

5

Hi,

Apologies for not addressing this in my first reply. I have been able to confirm that FObjectPoller::PushModelPollObject will be called for the subobject, which does seem unexpected.

In cases where a replication condition should apply to the whole object, I believe it is recommended to set this condition when adding it to the registered subobjects list:

AddReplicatedSubObject(MyTestSubobject, COND_InitialOnly);I tested this out, and I was still able to observe the initial-only object being polled on each update. Despite this polling, I also found that a subobject with this condition doesn’t appear to be replicated to the client at all.

Given that a COND_InitialOnly subobject will replicate as expected in the existing replication system, I’ve opened a new issue for this, UE-289553, which should be visible in the public tracker in a day or so. On that issue, I’ve also brought up how the subobject will be constantly polled.

Thanks,

Alex