From jw at raven.inka.de  Mon Jan 10 07:34:28 2022
From: jw at raven.inka.de (Josef Wolf)
Date: Mon, 10 Jan 2022 08:34:28 +0100
Subject: Need help with filtering elements and/or attributes
Message-ID: <20220110073428.GC6604@raven.inka.de>

Hello,

I am new to cxml and need some assistance to get started.

Thanks to https://common-lisp.net/project/cxml/quickstart.html, it is fairly
easy to read existing xml and write them back (almost) identical:

  (defun parse-dom (file)
    (cxml:parse file (cxml-dom:make-dom-builder)))

  (defun serialize-dom (file dom new-extension)
    (with-open-file (out (make-pathname :defaults file :type new-extension)
                         :direction :output
                         :if-exists :supersede
                         :element-type '(unsigned-byte 8))

      (write-sequence #(#xef #xbb #xbf) out)     ;; byte order mask

      (dom:map-document (cxml:make-octet-stream-sink out :encoding "utf-8")
                        dom)))

  (let ((file #p"some-file.xml"))
    (serialize-dom file
                   (parse-dom file)
                   "new-xml"))

with this, I can read a file and write it back. With

  diff -uw some-file.xml some-file.new-xml

I can confirm that those files are (semantically) identical.

But how do I go further? As a start, I would like to remove elements and/or
attributes while writing. From the docs, I seem to understand that this can be
done using sinks. But I just can't figure how to create my custom sink to do
the filtering. And three das googling did not reveal any
examples/howtos/tutorials.

Can somebody provide an example how to create a custom sink and which methods
can be specialized to do such filtering?

Thanx!

-- 
Josef Wolf
jw at raven.inka.de