I am trying to gather some information about an environment once it has been created and save it in a small Django app. This is about my adventures trying to discover the Weblogic version from the it’s registry which is an XML file.

The XML registry is in the Oracle inventory, and starts like this:

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<?xml version = '1.0' encoding = 'UTF-8' standalone = 'yes'?>
<registry home="/opt/oracle/psft/pt/bea" platform="226" sessions="7" xmlns:ns2="http://xmlns.oracle.com/cie/gdr/dei" xmlns:ns3="http://xmlns.oracle.com/cie/gdr/nfo" xmlns="http://xmlns.oracle.com/cie/gdr/rgy">
   <distributions>
      <distribution status="installed" name="WebLogic Server" version="12.2.1.4.0">

I’d like to extract the WebLogic Server version which is on line 4. As I don’t know XML it’s tempting to use grep and sed to find the information I want, but I notice there is an XML module in Ansible. It is community maintained, and it’s not stable, so it’s behaviour might change. This is valid from versions between 2.4 and 4, maybe later.

What I had to do was:

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  - name: Find weblogic version
    xml:
      path: "/weblogic/home/inventory/registry.xml"
      xpath: "/x:registry/x:distributions/x:distribution[@name='WebLogic Server']"
      content: attribute
      namespaces:
        x: "http://xmlns.oracle.com/cie/gdr/rgy"
    register: webinfo
    
  - debug: var=webinfo

Namespaces

One thing I find confusing about XML is the namespaces. This document lists three namespaces, but we are only interested in one, the default. This is the one without an alias:

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xmlns="http://xmlns.oracle.com/cie/gdr/rgy"

The annoying thing is that while this is the default namespace in the document, the tools used to parse the document don’t default to this namespace, they default to no namespace, which means we won’t get any data returned. So we have to tell Ansible about the namespace. This is a dictionary, so I just created x as an alias. If I needed more than one namespace I could add more elements to the dictionary. I define it in Ansible as follows:

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      namespaces:
        x: "http://xmlns.oracle.com/cie/gdr/rgy"

Another thing that isn’t obvious is that the attributes within the elements don’t obey the default namespace. Attributes don’t have a namespace unless it is explicitly stated.

Xpath

Now I have set up the namespace, I need to add it to the elements in the xpath, but as I said above, not to the attributes. So I am left with the following as an xpath:

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      xpath: "/x:registry/x:distributions/x:distribution[@name='WebLogic Server']"

I think of the XML document like a filesystem. I am selecting the element /registry/distributions/distribution. There are a number elements that match this criterion. I only want the one where the name is set to WebLogic Server, which is what the [@name='WebLogic Server'] part does.

I’d like to be able to specify I only want the version attribute. I believe I should be able to do by adding @version on the end of the xpath, but that didn’t seem to work. The documentation says to limit xpath selectors to simple expressions, maybe that is why. Or maybe I just don’t understand XML.

Using the output

Ansible gives me the following output from the debug statement:

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ok: [webserver] => {
    "webinfo": {
        "actions": {
            "namespaces": {
                "x": "http://xmlns.oracle.com/cie/gdr/rgy"
            },
            "state": "present",
            "xpath": "/x:registry/x:distributions/x:distribution[@name='WebLogic Server']"
        },
        "changed": false,
        "count": 1,
        "failed": false,
        "failed_when_result": false,
        "matches": [
            {
                "{http://xmlns.oracle.com/cie/gdr/rgy}distribution": {
                    "name": "WebLogic Server",
                    "status": "installed",
                    "version": "12.2.1.4.0"
                }
            }
        ],
        "msg": 1
    }
}

I want to access the version. It took me ages to work out how to do this because of the braces in the key. The way to do it in Ansible is (I do this in the defaults, or vars):

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  weblogic_ver: "{{ webinfo.matches[0]['{http://xmlns.oracle.com/cie/gdr/rgy}distribution'].version }}"