Due to the complete failure of my previous name host provider (freeparking.co.uk - not only did they fail to renew my domain for the second year in a row but also didn't respond to any of my support tickets leaving my domain unavailable for 3 days. The situation was only resolved when I contacted their upstream registrar..<sigh>) I moved my name hosting to Zen Internet. Zen's support is excellent - highly recommended.

The only downside is that I can no longer set the @ record to a CNAME (seems to work fine for the subdomains however). Previously I'd been pointing sodnpoo.com to sodnpoo.ath.cx, this is in turn updated from the dyndns client on my router.

I thought the easy way to solve this would be to just use curl to form post to Zen's customer portal. Login was easy but when I tried to post to the DNS management form it failed with an error, upon closer examination I noticed a huge (several K) parameter being passed called VIEWSTATE.

After doing some research I discovered that VIEWSTATE is an opaque data blob produced by ASP.NET forms to hold the persistent state of the page. I pulled the page with curl and used some simple sed to extract the VIEWSTATE value and posted it back. It still didn't work so I started to add more parameters and soon hit the "html isn't regular so you can't parse it with a regex" problem, so I looked for another solution.

I decided I should parse the html properly and thought that XSLT was really the best solution - I just needed to generate post data as expected by curl (i.e. uri encoded name=values pairs). I tried to run it through xlstproc but the html was too dirty, so I ran it through tidy which cleaned it up enough to not trip up xsltproc. The following XSLT was matched against all input tags to build the post data.

  <xsl:template match="xhtml:input">
    <xsl:value-of select="@name"/>=<xsl:value-of select="str:encode-uri(@value ,true())"/>&#38;
  </xsl:template>
  

Extracting the form data and posting it back still failed though. I looked again at what the browser was doing and saw that some of the parameters were being modified, some dropped and some added by the javascript in the page. I also notice one parameter didn't exist at all in the form when using curl's default user agent - setting it to Firefox's made the parameter appear.

I fixed up XLST to modify what was needed to match what the browser was sending and posted the results again - this time there were no errors and a html page was returned. I modified the XSLT to change the IP it was sending and ran through it again - I refreshed the page in my browser and the IP had been changed - success!

The code is implemented as a shell script, a template for the login part and a couple of XSLT's. It requires that the zen friendly name is set to the domains name e.g. 'sodnpoo.com'.

Autozen.sh is the main script - don't forget to set the USERNAME/PASSWORD/DOMAINS and probably the method of getting the latest IP (IPADDR). (You might need to change the DOMLISTURL - this is the page in the Zen portal where you select the domain to modify).

Zen.login.post is a quick and dirty static template - we just poke the USERNAME/PASSWORD values in there with sed.

Getdomains.xml is an XSLT to extract the POST URLs of all domains with their friendly name set.

Zenasp.xsl is another XSLT that takes the four octets of the desired IP and pokes them into the form data to be sent to the POST URLs.

Code can be found on github.