[feature] XPath queries should support multiple handlers by using namespaces

[sdalu]

XPathContext#evalute use the xmlXPathRegisterFuncLookup function to register a lookup function, unfortunately namespace is not used during the lookup phase.

To fix it:

• Node#extract_params should allow a hash as handler (as for XSLT#parse)
• lookup should use the ns_uri parameter

[flavorjones]

Apologies for not responding to this issue for so many years.

Without a specific use case, I am guessing a bit, but I think what you're asking for is an interface something like:

#! /usr/bin/env ruby

require "nokogiri"

xml = <<~EOF
  <root>
    <message>a</message>
    <message>b</message>
  </root>
EOF

handler_uri = "http://example.com/handler"
handler = Class.new do
  def contents(x)
    x.map(&:content).join(",")
  end
end.new

upcase_uri = "http://example.com/upcase"
upcase_handler = Class.new do
  def contents(x)
    x.map(&:content).map(&:upcase).join(",")
  end
end.new

handlers = {handler_uri => handler, upcase_uri => upcase_handler}
namespaces = {handler: handler_uri, upcase: upcase_uri}

doc = Nokogiri::XML::Document.parse(xml)

doc.xpath("handler:contents(//message)", namespaces, handlers) == "a,b" or raise("no")
doc.xpath("upcase:contents(//message)", namespaces, handlers) == "A,B" or raise("no")

That is: the hash-of-handlers would have URI keys that could be used to scope the xpath function lookup.

Is that about right?

If so, the way we'd have to do this is introduce keyword arguments to eliminate ambiguity between the namespaces hash and the handlers hash.

I'm not overly opposed to doing this, but it does feel like the easy workaround is to create a custom handler class with all your custom functions defined on it.

Can you help me understand your use case more deeply?