Problems

dudders and reliable DNS zone updates

I’ve released a new version of dudders, 1.04, and finally submitted it as a package to OpenWRT. The focus of this release was on making the update more robust to network failure as the result of an email correspondence with Peter Holik. I am of the opinion that DNS UPDATE is a strong candidate for being TCP by default (along with zone-transfers).

In RFC 1123 it is stipulated that:

a DNS resolver or server that is sending a non-zone-transfer query MUST send a UDP query first.

However, if you are doing a DNS UPDATE you really want the reliability that TCP offers, even if you don’t expect truncation to be an issue. The update is sent to the relevant authority server, so the arguments about load on root servers in the RFC aren’t applicable.

I’ve made the UDP implementation retry by default, but I think if you need more than 2 retries, you should be considering using TCP with its (much more advanced) retransmission algorithms.

Peter also found a bug in glibc’s res_send (actually in their send_dg function) whereby the resolver interprets the lack of the DNS “recursion available” flag in the header as an error. However, that flag isn’t even meaningful for DNS UPDATE responses; according to RFC 2136, those bits:

Should be zero (0) in all requests and responses. A non-zero Z field should be ignored by implementations of this specification.

As a result, glibc was setting errno to ECONNREFUSED or ETIMEDOUT even when the update was successful. I’ve hacked dudders to double-check after res_send, but it’s making me question the wisdom of using res_send at all, given that I’m constantly working around it.

Update: submitted glibc bug report #11950

To get dudders-1.04 on OpenWRT, simply update the official package feed and select dudders from the Net > DNS > dudders menu in the buildroot config. For systems other than OpenWRT, you can grab the source from sourceforge, or even github.

XHTML fixes for the WordPress reCAPTCHA plugin

The wp-recaptcha plugin for WordPress breaks when you’re serving pages as application/xhtml+xml. I inadvertently broke comments when I installed it (silly me for not testing!). I’ve written a patch that fixes it.

The default javascript API uses document.write, which isn’t a DOM method and hence is not a method of true XML documents. It’s not a new issue either, wp-recaptcha has had a history of breaking XHTML. The thing is, the WordPress plugin (which uses the PHP library by the recaptcha people) has an option to “Be XHTML 1.0 Strict compliant”; but this only fixes the use of iframes and noscript!

Updated: pushed fork to github
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Duplicating ggplot axis labels

Update: the lemon package’s facet_rep_wrap gives the user control over repeated facet labels (thanks to Flore for pointing it out).

I’ve been trying for a while to find an elegant solution for duplicating axis ticks and labels in a ggplot chart. Hadley replied on the ggplot2 mailing list, but a working solution within ggplot2 seems a way off.

The situation is this: imagine you have a faceted plot that is tall enough that the x-axis ticks and labels become obscured (e.g. when using a clipped viewport such as a browser window). This is particularly destructive when you’re using an x-scale with manual breaks or a transformation.

library(ggplot2)
g <- ggplot(diamonds, aes(carat, ..density..)) + 
   geom_histogram(aes(fill = clarity), binwidth = 0.2) + 
   facet_grid(cut ~ .)
print(g)

Faceted Plot where the x-axis labels have been clipped out

There simply isn’t a way to repeat the x-axis labels in ggplot2 at the moment without discarding faceting and rendering each facet as a separate ggplot call. I’ve seen some examples of selective plotting used to good effect in combining multiple plots with common elements, but I can’t find anything applicable to keep consistent scales and binning without duplicating a lot of the (internal) facet and bin logic.

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