Possible Int overflow in AggregateEventTag

Lagom Version

1.4.5, 1.5.0, Master

API (Scala / Java / Neither / Both)

Both Scala and Java API.

Expected Behavior

AggregateEventTag.selectShard should always return positive value.

Actual Behavior

AggregateEventTag.selectShard can return a negative value, if entityId.hashCode == Int.MinValue. Then, if numShards is e.g. 6, the the result will be -2.

AggregateEventTag.scala:78

def selectShard(numShards: Int, entityId: String): Int = {
    Math.abs(entityId.hashCode) % numShards
}

Here Math.abs(entityId.hashCode) % numShards will reduce to Int.MinValue % numShards, if entityId.hashCode equals Int.MinValue.

As there is no guarantee that String.hashCode will not return Int.MinValue, it is possible, albeit very unlikely, that the tag shard tag name generation will return an invalid tag name.

[octonato]

I think you mean:

if (shard < 0) 0 else shard

Could also be: Math.abs(shard)

[ignasi35]

I think the solution is:

def selectShard(numShards: Int, entityId: String): Int = {
    val shard = Math.abs(entityId.hashCode) % numShards
    if (shard == Int.MinValue) 0 else shard
}

Which hardcodes the mapping of Int.MinValue to 0 and maintains all other mappings.