BasisLibrary.nodeList2Iterator broken
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Key: XALANJ-2493
URL: https://issues.apache.org/jira/browse/XALANJ-2493
Project: XalanJ2
Issue Type: Bug
Security Level: No security risk; visible to anyone (Ordinary problems in
Xalan projects. Anybody can view the issue.)
Components: XSLTC
Affects Versions: The Latest Development Code
Reporter: Martin von Gagern
The current implementation of nodeList2Iterator is broken, because it can not
deal with attribute nodes. It relies on copyNodes which in turn tries to add
attribute nodes as children of some top level node. Attributes don't live on
the children axis, though, so this is against DOM and causes a DOM exception in
the Xerces DOM implementation and probably most other implementations. The
resulting HIERARCHY_REQUEST_ERR was noted e.g. in XALANJ-2424.
Furthermore, the implementation is inefficient, because it manually copies each
and every node from the source document to a new DTM to some new DTM. The time
overhead for the copying as well as the memory overhead for the additional DOM
can be avoided in cases where the nodes come from some input document, as
opposed to a document completely loaded within some extension function.
A comment in the related XALANJ-2425 suggests returning DTMIterator from
extension functions and avoiding the re-import for those. I don't like this
idea because it exposes a lot of Xalans internals to extension functions, and
because the returned node list might be newly created, while at least some of
thenodes might still be from the same document. So instead of special cases for
the list type, I implemented special cases for every node of the list. If it is
a proxy node of the same (Multi)DOM, we simply use its handle.
If not, we add it to some w3c DOM and turn that into a DTM, pretty much like
the current implementation does. However, I dropped copyNodes in favor of
Document.importNode, to avoid code duplication and rely on supposedly more
heavily tested code. I also added another level of elements, so that there is
one such dummy node for every item of the source list, with always a single
child or element. A few assertions help ensure this single child policy. This
is especially important in the new implementation, because otherwise it would
become difficult to get the proxied nodes and the newly DTMified nodes into
correct order.
Right now, the import of DOM nodes is only implemented for those nodes I expect
to turn up in the DTM in pretty much the same form as they do in the w3c DOM.
For all other nodes, an internal error is thrown. This especially concerns
document fragment nodes. At least in w3c DOM, a document fragment can never be
a child, so if DTM behaves the same, we would need to import document fragments
seperately, or expand them to the list of their children instead. I'm not sure
what correct behaviour would be here, so I'd rather throw an exception than
implement wrong behaviour.
I also noticed that
org.apache.xml.dtm.ref.DTMManagerDefault.getDTMHandleFromNode would in theory
provide an implementation for turning w3c nodes into DTM handles - exactly what
we need here. That method seems to start importing from the topmost ancestor of
a node, giving as much context as possible, in contrast to both current and my
suggested XSLTC approach, which destroys ancestor references. That method also
seems to employ caches in order to avoid importing a document repeatedly.
Sadly, actually using that method throws a ClassCastException as it expects a
DTM generate from a DOM source to be a DOM2DTM, which SAXImpl is not. A comment
inside that method also indicates that future implementations might drop
auto-importing and instead leave it to the caller to import a DOM if it hasn't
been imported before.
I left my own attempt at an nodeList2Iterator implementation using
getDTMHandleFromNode in place, renamed to nodeList2IteratorUsingHandleFromNode
and made private. So it's there, it even gets compiled, but it won't get used.
If that method gets fixed in XSLTCDTMManager or its ancestor, then this method
might be used instead, giving a much simpler and cleaner implementation. If
some of my code would be useful for such an implementation as well, like the
check for "is same DOM", feel free to copy or move my code to those classes as
well.
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