[jira] [Commented] (XERCESJ-1421) Temporary inconsistent data inside Xerces2-J when removing a first child of a node.

["Thiwanka Somasiri (JIRA)" <xe...@xml.apache.org>]

    [ https://issues.apache.org/jira/browse/XERCESJ-1421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13018115#comment-13018115 ] 

Thiwanka Somasiri commented on XERCESJ-1421:
--------------------------------------------

What is actual operation by "checkNormalizationAfterRemove(ChileNode previousSibling)" in org.apache.xerces.dom.ParentNode.java ?

> Temporary inconsistent data inside Xerces2-J when removing a first child of a node.
> -----------------------------------------------------------------------------------
>
>                 Key: XERCESJ-1421
>                 URL: https://issues.apache.org/jira/browse/XERCESJ-1421
>             Project: Xerces2-J
>          Issue Type: Improvement
>          Components: DOM (Level 3 Core)
>    Affects Versions: 2.9.1
>            Reporter: Ludger Bünger
>            Priority: Minor
>         Attachments: PreviousSiblingInconsistentDataPatch.txt
>
>
> When removing a first child, currently there is a local field inside ParentNode.internalRemoveChild that contains inconsistent data.
> Since in this specific case the following code still performs correct, there is currently no harm done.
> However I think it should be fixed nonetheless since future changes to the code might cause problems.
> And here the description of the issue:
> Xerces2-J uses an internal optimization by overloading the ChildNode.previousSibling field.
> 1) If a node has a previous sibling, this field contains the previous sibling.
> 2) if a node is the first child of it's parent (and thus has no previous sibling), this field is re-used for a different purpose and contains the last sibling thus allowing quick access to the end of a node list
> Now ChildNode.internalRemoveNode stores a reference to the previousSibling of the removed node for normalization checking purposes in the local field oldPreviousSibling.
> However this is done after removal of the node is already done but before null'ing of the tree structure fields of the node.
> Since this node has already been removed, the isFirstChild() check fails and instead of 'null' the last sibling is stored in the oldPreviousSibling field.
> By chance the normalization checking code still works correct if the previous sibling field contains the last sibling instead of the correct value 'null' but this still should be fixed.
> See attached patch.

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