How do I get Nokogiri to understand my namespaces?
Question
I have the following XML document:
<samlp:LogoutRequest ID="123456789" Version="2.0" IssueInstant="200904051217">
<saml:NameID>@NOT_USED@</saml:NameID>
<samlp:SessionIndex>abcdefg</samlp:SessionIndex>
</samlp:LogoutRequest>
I'd like to get the content of the SessionIndex
(that is, 'abcdefg') out of it. I've tried this:
XPATH_QUERY = "LogoutRequest[@ID][@Version='2.0'][IssueInstant]/SessionIndex"
SAML_XMLNS = 'urn:oasis:names:tc:SAML:2.0:assertion'
SAMLP_XMLNS = 'urn:oasis:names:tc:SAML:2.0:protocol'
require 'nokogiri'
doc = Nokogiri::XML(xml)
doc.xpath(XPATH_QUERY, 'saml' => SAML_XMLNS, 'samlp' => SAMLP_XMLNS)
but I get the following errors:
Nokogiri::XML::SyntaxError: Namespace prefix samlp on LogoutRequest is not defined
Nokogiri::XML::SyntaxError: Namespace prefix saml on NameID is not defined
Nokogiri::XML::SyntaxError: Namespace prefix samlp on SessionIndex is not defined
I've tried adding the namespaces to the XPath query, but that doesn't change anything.
Why can't I convince Nokogiri that the namespaces are valid?
Solution
It doesn't look like the namespaces in this document are correctly declared - there should be xmlns:samlp
and xmlns:saml
attributes on the root node. In cases like this, Nokogiri essentially ignores the namespaces (as it can't map them to URIs or URNs), so your XPath works if you remove them, i.e.
doc.xpath(XPATH_QUERY)
OTHER TIPS
I see a two different options for you:
Remove all the namespaces
Brute force way of doing it. Could lead to problems where there are namespace collisions.
Use collect_namespaces
A much better solution. You could use this once to identify the namespaces (say in irb) and hard-code them.
OR
Use it at runtime, and supply it as the second argument to https://www.rubydoc.info/github/sparklemotion/nokogiri/Nokogiri/XML/Searchable#xpath-instance_method