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https://issues.apache.org/jira/browse/CASSANDRA-15790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17102806#comment-17102806
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David Capwell commented on CASSANDRA-15790:
-------------------------------------------
reading closer I think readValue should return empty buffer and not null, that
way it works with org.apache.cassandra.serializers.EmptySerializer#validate and
org.apache.cassandra.serializers.EmptySerializer#deserialize; null would break
those call sites.
> EmptyType doesn't override writeValue so could attempt to write bytes when
> expected not to
> ------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-15790
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15790
> Project: Cassandra
> Issue Type: Bug
> Components: CQL/Semantics
> Reporter: David Capwell
> Assignee: David Capwell
> Priority: Normal
> Fix For: 3.0.x, 3.11.x, 4.0-alpha
>
>
> EmptyType.writeValues is defined here
> https://github.com/apache/cassandra/blob/e394dc0bb32f612a476269010930c617dd1ed3cb/src/java/org/apache/cassandra/db/marshal/AbstractType.java#L407-L414
> {code}
> public void writeValue(ByteBuffer value, DataOutputPlus out) throws
> IOException
> {
> assert value.hasRemaining();
> if (valueLengthIfFixed() >= 0)
> out.write(value);
> else
> ByteBufferUtil.writeWithVIntLength(value, out);
> }
> {code}
> This is fine when the value is empty as the write of empty no-ops (the
> readValue also noops since the length is 0), but if the value is not empty
> (possible during upgrades or random bugs) then this could silently cause
> corruption; ideally this should throw a exception if the ByteBuffer has data.
> This was called from
> org.apache.cassandra.db.rows.BufferCell.Serializer#serialize, here we check
> to see if data is present or not and update the flags. If data is present
> then and only then do we call type.writeValue (which requires bytes is not
> empty). The problem is that EmptyType never expects writes to happen, but it
> still writes them; and does not read them (since it says it is fixed length
> of 0, so does read(buffer, 0)).
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