A node got with expand becomes invalid after the Reader is advanced about libxml-ruby HOT 6 CLOSED

Right, not valid. As the docs say:

/*

• call-seq:
• reader.expand -> node

• Returns the current node and its full subtree. Note the returned node
• is valid ONLY until the next read call. */

So once you call next, the element is freed by libxml. It was just luck in worked in earlier versions - libxml does in fact free the underlying node object on the #next call. So now the bindings try to protect you from a potential segmentation fault.

Thanks - Charlie

from libxml-ruby.

Okay, thank you for the explanation.

However, retaining the old behavior was not straightforward. To recursively copy the element appears insufficient to have a fully-functional node after the reader is advanced. To overcome this, I added a spurious document, because XPath lookup wouldn't work on the node (reporting the error A node must belong to a document before a xpath context can be created (TypeError)).

Here's how the working, fixed sample program now looks like:

#!/usr/bin/ruby
require 'rubygems'
require 'xml'
doc = XML::Reader.string "<one/>"
doc.next
# Copy the element and make a phony document
element = doc.expand.copy(true)
new_doc = XML::Document.new
new_doc.root = element
# This works well
puts element

doc.next

# This now works well
puts element
# And this too
puts element.find_first('/one')

Are there any more quirks?

from libxml-ruby.

Looks ok, but I think you are fighting the library. Can you change your code to avoid the problem entirely?

Charlie

from libxml-ruby.

Well, my second comment shows how I changed my code. I like the mixed DOM+Stream parsing and the ability to stash nodes for later processing very much, and I am ready to "fight" for it. Especially if I can get it that cheap.

from libxml-ruby.

Yes, the reader + xpath + expand is nice.

Good luck on your project!

Thanks - Charlie

from libxml-ruby.

@pshved Thanks for your workaround, and indeed your article at http://coldattic.info/shvedsky/s/blogs/a-foo-walks-into-a-bar/posts/56

Helped me out.

from libxml-ruby.