Re: [xml] greetings & a question

[Ignacio Vazquez-Abrams <ignacio openservices net>]

On Sat, 18 Aug 2001 tlewis mindspring com wrote:

> Greetings.  I am using libxml2 for a new, free network intrusion detection
> system called hank.  I hope to announce it publically next month.
> So far, I have been very pleased by my experiences using it.
>
> My rule file is xml, and reports are specified like this:
>
>   [snip]
>
> This approach was very simple and easy to code; copy the text and replace
> the <field> nodes with my field data structure in C.
>
> Now, I would like to allow people to have their reports as more than
> plain text documents; I would like to generate xml for such purposes
> as supporting idmef or other NIDS xml report formats.  Under such a scheme,
> users would instead state rules like this:
>
>   [snip]
>
> The naive way to code this is: make a copy and walk the tree, looking
> for all "field" nodes and replacing them.  This, however, seems rather a
> lot of work, and repetitive at that.  I also thought about caching their
> location, but the representation of nodes as linked lists makes this
> cumbersome to do for a humble C journeyman as myself, and potentially
> even more work than walking the entire tree, since large portions of the
> tree could be traversed repeatedly unless I get even more adventurous
> with my coding, etc.
>
> My question is, is there a way to identify these nodes before-hand, copy
> the tree and replace the corresponding nodes in the new tree?  I don't
> know if I could xlink them or use some other xml magic to make this easy
> or if there's a more obvious approach that I'm just too dumb to realize.
> I had ruled out replacing them in the original before copying because of
> memory leak fears, but maybe there's a way to adopt this approach.
>
> Any and all advice is welcome and appreciated.
>
> --
> Todd Lewis
> tlewis mindspring com

Have you looked at XSLT? You're basically translating one type of XML document
into another, even if it's as simple as replacing elements with text. XSLT
excels at manipulating XML.

You could even change your original C code to output an XSLT stylesheet
instead of doing search-and-replace on an xmlDoc, then use libxslt to apply
the stylesheet to any report you choose, copying any elements it doesn't know
about, and replacing ones it does know about with the appropriate value.

-- 
Ignacio Vazquez-Abrams  <ignacio openservices net>