Caius Theory

Now with even more cowbell…

SmartOS Recovery mount /usbkey

Recently I managed to hose a box in a perfectly self-inflicted storm of idiocy. Imagine a SmartOS server with the following issues:

Needless to say, this caused a tiny issue in the server doing what it's supposed to. Luckily I had access to a KVM remote console for the box and the following worked.

I brought the machine up, choosing the second option for recovery at the grub menu. Waited for a login prompt, then logged in with root/root.

Realised quite quickly that /usbkey must be persisted on the zones zfs pool otherwise the configuration would be lost after shutdown, so imported the correct pool, created a directory to mount into and then mounted the zfs share.

zpool import zones
mkdir /usbkey
mount -F zfs zones/usbkey /usbkey

Add to iCloud Reading List programmatically

One piece of a larger puzzle I'm trying to solve currently, was how to add a given URL to my Apple "Reading List" that is stored in iCloud and synced across all my OS X and iOS devices. More specifically, I wanted to add URLs to the list from my mac running Mavericks (10.9). I had a quick look at the Cocoa APIs and couldn't see anything in OS X to do this. (iOS has an API to do it from Cocoa-land it seems though.)

I figured was the key to getting this done on OS X, given it has the ability itself to add the current page to the reading list, either via a keyboard command, a menu item, or a button in the address bar. One quick mental leap later, and I was wondering if the engineers at Apple had been nice enough to expose that via Applescript for me to take advantage of.

One quick stop in "Script" later, and I had the Applescript dictionary open for Lo and behold, there is rather handily an Applescript command called "add reading list item", which does exactly what I want. It has a few different options you can call it with, depending on whether you want Safari to go populate the title & preview text, or if you want to specify it yourself at save-time.

As I want to be able to call this from multiple runtimes, I've chosen to save it as an executable, which leans on osascript to run the actual Applescript. And here it is:

#!/usr/bin/env osascript

on run argv
    if (count of argv) > 0
        tell app "Safari" to add reading list item (item 1 of argv as text)
    end if
end run

Save it as whatever you want (eg. add_to_reading_list), make it executable (chmod +x add_to_reading_list), and then run it with the URL you want saving as the first argument.

$ add_to_reading_list ""
$ add_to_reading_list ""
# … etc …

(Adding support for specifying preview text and title is left as an exercise for the reader!)

Have fun reading later!

Pair new device with Nexxus Drive Transmit Pro

The device is a bluetooth to FM transmitter with Model number NEX-FMTX-BTCK. (Hereafter DTP.)

The set of instructions I use to pair it to a new device, having lost the user manual/instruction booklet, is as follows:

  1. Remove all previously paired devices from range (turn them off/move them away from the DTP.)
  2. Turn the power on to the DTP without touching any buttons.
  3. Let it flash the blue call button a couple of times as it searches for known devices.
  4. Hold the call button down until the call/hangup buttons flash blue/red respectively.
  5. Find the "Drive Transmit Pro" on your device you want paired to it and pair with DTP.
  6. Test out the pairing by calling your girlfriend and talking to her in a funny accent.
  7. Celebrate with a beer!

Mounting Harman Kardon Soundsticks on the wall

Having recently moved my Soundstick III's into the front room, I've been thinking of a way to wall mount them safely to free up table room. Googling eventually turned up just one person who has previously documented mounting his soundsticks on the wall, using 22mm plumbing clips (intended for 22mm central heating pipes).

A quick scrounge round the local Homebase this afternoon yielded a pack of similar clips, 5x 22mm push clips for £1.99. Having just fitted the speakers to the wall, they're nice and secure (providing no-one hangs on them, which they shouldn't do), fairly neat and simple to fit.

I've left the subwoofer on the floor under the table, and only mounted the "sticks" (tweeters) on the wall, one each side of the mirror over our dining table. I can then conveniently run the cables to the "sticks" behind the mirror and keep it looking neater.

I affixed the clips to the wall, one either side of the mirror with enough space for the speaker to sit without overlapping the mirror. Mostly just held the stick up and guessed at where to put the clip, but it looks ok.

Speaker clip without speaker in it

Then I bent the speaker stand backwards behind the stick (don't worry, it's on a hinge!) and threaded the cable through the middle of the ring to make it sit flusher against the wall.

Speaker ring bent behind the unit

And then it was just a case of easing the speaker ring into the clip, with the clip at the top of the ring (picture below if you can't visualise that easily). I think the rings are more like 24-25mm so it takes a bit of easing to get them in there. Once it's in there's no play in the clip for it to wiggle out though, even though it's plastic. I tried not to fatigue the clip arms too much wiggling it in there as well, so as to minimise the chance of it failing over time. (Something to check periodically!)

Close up of speaker unit in clip

Lastly, I just zip tied the cables together behind the mirror, and ran them down vertically from the middle to the floor and plugged them in. Sounds fantastic, and due to being plugged into an Airport Express, anything compatible can stream audio through them wirelessly. Fabulous darling!

(Click any image for a larger version)

Install capybara-webkit gem on Ubuntu

Dear future Caius searching for this issue,

The apt package you need to install to use the capybara-webkit rubygem on ubuntu (tested on 10.04 and 11.10) is libqt4-dev. That is, to gem install capybara-webkit, you need to run aptitude install libqt4-dev.

Yours helpfully,
Past Caius

Use Readline With Default Ruby on OS X

OS X Lion comes with ruby 1.8.7-p249 installed, although it's compiled against libedit rather than libreadline. Whilst libedit is a mostly-compatible replacement for libreadline, I find there's a couple of settings I'm used to that don't work in libedit. (Like history-beginning-search-backward.)

Luckily you can grab the source of ruby and compile just the readline extension, and move it into the right place for it to just work. Here's what's been working for me:

# Install readline using homebrew
brew install readline

# Download the ruby source and check out 1.8.7-p249
mkdir ~/tmp && cd ~/tmp
git clone git://
cd ruby
git checkout v1_8_7_249
cd ext/readline
ruby extconf.rb --with-readline-dir=$(brew --prefix readline) --disable-libedit

Now you should have readline.bundle in the current directory, and it should be compiled against your homebrew-installed readline library, rather than libedit that comes with the system. We can quickly double-check that by using otool to check what the binary is linked against.

$ otool -L readline.bundle
    /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/libruby.1.dylib (compatibility version 1.8.0, current version 1.8.7)
    /usr/local/Cellar/readline/6.2.2/lib/libreadline.6.2.dylib (compatibility version 6.0.0, current version 6.2.0)
    /usr/lib/libncurses.5.4.dylib (compatibility version 5.4.0, current version 5.4.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 159.1.0)

And in the output you should see a line listing "libreadline", and no lines listing "libedit". Which that shows, we've compiled it properly then. Now the bundle is built we need to move it into the right place so it's loaded when ruby is invoked.

# Back up the original bundle, just in cases
sudo mv "$RL_PATH/readline.bundle" "$RL_PATH/readline.bundle.libedit"
sudo mv readline.bundle "$RL_PATH/readline.bundle"

And that's it. You've got a proper compiled-against-readline installed ruby 1.8.7-p249 on 10.7 now.

One gotcha I ran into was needing to pass the same arguments to rvm when installing any other version of 1.8.7 on the same machine. Simple enough, just need to remember to do it though.

CC=gcc-4.2 rvm install 1.8.7-p357 -C --with-readline-dir=$(brew --prefix readline) --disable-libedit

Install GCC-4.2.1 (Apple build 5666.3) with Xcode 4.2

As of Xcode 4.2 Apple have stopped bundling GCC with it, shipping only the (mostly) compatible llvm-gcc binary instead. The suggested fix is to install GCC using the osx-gcc-installer project. However, I wanted to build and install it from source, which apple provides at

You should already have installed Xcode 4.2 from the app store, then basically the following steps are to grab the tarball from the 4.1 developer tools source, unpack & compile it, then install it into the right places.

Update 2016-07-03: I'd suggest just using homebrew to install this these days:

brew install homebrew/dupes/apple-gcc42


# Grab and unpack the tarball
mkdir ~/tmp && cd ~/tmp
curl -O
tar zxf gcc-5666.3.tar.gz
cd gcc-5666.3

# Setup some stuff it requires
mkdir -p build/obj build/dst build/sym
# And then build it. You should go make a cup of tea or five whilst this runs.
gnumake install RC_OS=macos RC_ARCHS='i386 x86_64' TARGETS='i386 x86_64' \
  SRCROOT=`pwd` OBJROOT=`pwd`/build/obj DSTROOT=`pwd`/build/dst \

# And finally install it
sudo ditto build/dst /

And now you should have gcc-4.2 in your $PATH, available to build all the things that llvm-gcc fails to compile.


I've had a dream for a while. A simple webapp that takes the last tweet in a conversation and outputs that conversation in chronological order on a page you can link to forevermore. Occasionally I'll google to see if anything new's turned up, but they all seem to do far more, require the start and end tweets or are covered in ads.

So one friday evening I just built it. It's called TweetSavr. It's very simple—to the point the error page is just a standard 500 server error page currently. It fetches, caches and displays a conversation, given just the last tweet in said conversation.

KISS extends to the interface as well, I'm quite a fan of URL hacking to use webapps, so TweetSavr works on that basis as well. The homepage sort of has some help telling you how to use it, but you basically take the (old-twitter) URL of the last tweet and paste it after in the address bar. Eg, It'll then redirect you through to the actual page for that conversation. You can also put just the status id on the end of the URL, and hey presto, it loads.

The caching layer is moderately rudimentary, after fetching a tweet that isn't in the cache it writes out a hash of data for that tweet into a yaml file. And when looking up a tweet it checks to see if that file exists, reading it in from disk if it is. Bonus side-effect is it builds up a corpus of tweets as yaml files on disk.

It lives on the internet at and the source is on github at

Side note: isn't it wonderful what we can create given just a few hours, a server somewhere in the cloud, and an idea? Never ceases to amaze me what can be built in just a short amount of time, even the dead simple things.

#to_param and keyword slugs

Imagine you've got a blogging app and it's currently generating URL paths like posts/10 for individual posts. You decide the path should contain the post title (in some form) to make your URLs friendlier when someone reads them. I know I certainly prefer to read vs (That's a fun blog post if you're into (ab)using ruby occasionally!)

Now you know all about how to change the URL path that rails generates—just define to_param in your app. Something simple that generates a slug consisting of hyphens and lowercase alphanumerical characters. For example:

# 70-abusing-ruby-1-9-json-for-fun
def to_param
  "#{id}-#{title.gsub(/\W/, "-").squeeze("-")}".downcase

NB: You might want to go the route of storing the slug against the post record in the database and thus generating it before saving the record. In which case the rest of this post is sort of moot and you just need to search on that column. If not, then read on!

Now we're generating a nice human-readable URL we need to change the way we find the post in the controller's show action. Up until now it's been a simple @post = Post.find(params[:id]) to grab the record out the database. Problem now is params[:id] is "70-abusing-ruby-1-9-json-for-fun", rather than just "70". A quick check in the String#to_i docs reveals it "Returns the result of interpreting leading characters in str as an integer base base (between 2 and 36)." Basically it extracts the first number it comes across and returns it.

Knowing that we can just lean on it to extract the id before using find to look for the post: @post = Post.find(params[:id].to_i). Fantastic! We've got nice human readable paths on our blog posts and they can be found in the database. All finished… or are we?

There's still a rather embarassing bug in our code where we're not explicitly checking the slug in the URL against the slug of the Post we've extracted from the database. If we visited /posts/70-ruby-19-sucks-and-python-rules-4eva it would load the blog post and render it without batting an eyelid. This has caused rather a few embarrassing situations for some high profile media outlets who don't (or didn't) check their URLs and just output the content. Luckily there's a simple way for us to check this.

All we want to do is render the content if the id param matches the slug of the post exactly, and return a 404 page if it doesn't. We already know the id param (params[:id]) and have pulled the Post object out of the database and stored it in an instance variable (@post). The @post knows how to generate it's own slug, using #to_param.

So we end up with something like the following in our posts controller, which does all the above and correctly returns a 404 if someone enters an invalid slug (even if it starts with a valid post id):

def show
  @post = Post.find(params[:id].to_i)
  render_404 && return unless params[:id] == @post.to_param

def render_404
  render :file => Rails.root + "public/404.html", :status => :not_found

And going to an invalid path like /posts/70-ruby-19-sucks-and-python-rules-4eva just renders the default rails 404 page with a 404 HTTP status. (If you want the id to appear at the end of the path, alter to_param accordingly and do something like params[:id].match(/\d+$/) to extract the Post's id to search on.)

Hey presto, we've implemented human readable slugs that are tamper-proof (without storing them in the database.)

(And bonus points if in fact you spotted I used my blog as an example, but that it isn't a rails app. (Nor contains the blog post ID in the pretty URL.) It's actually powered by Habari at the time of posting!

App Store Hidden Preferences

See the Update at the end before you get excited :(

Having just installed 10.6.6 to use the Mac App Store, I was slightly annoyed that it fills my dock with apps as I install them. I'm a bit strange, in that I use a hidden preference to make the dock uneditable (it stops me accidentally dragging an app off.) But that means I can't drag off the Mac App Store installed apps either.

Had a quick look through /Applications/App Store with strings (love that tool) and noted a few strings that looked interesting. (There's a full list in this gist.) There wasn't anything that explicitly stated it stopped it putting anything in the dock, but I did notice an option that stopped it showing install progress in the dock.

Yank up a terminal window, bash out the following…

defaults write FRDebugShowInstallProgress -bool NO

…head back to the MAS and install another (free) app, and hey presto, it's leaving my dock alone! Hopefully that's all I needed to continue using my Dock as I like. (Hidden, and left alone.)

Update 2011-01-06:

Seems my joy was short-lived. I'd re-downloaded an app I'd already purchased and it just showed download progress in the MAS app, not in the dock. Installing new applications still shows up in the dock (annoyingly.)

I've been having a poke through how it all hangs together, and if it's possible to actually block downloads from the Dock or not. It doesn't look like there's a hidden preference to hide new apps from downloading in the dock, you can just disable the progress bars in the dock with prefs. The seems to be codenamed "Firenze", with the "hidden" prefs being prefixed with "FRDebug".

As I understand it, the App\ invokes a binary inside /System/Library/PrivateFrameworks/CommerceKit.framework called "storeagent" to do the actual downloading/talking to the dock. From looking at the class-dump of storeagent it communicates with the dock to place a new type of DockTile. Interesting sounding methods to (potentially?) swizzle are -[DownloadQueue sendDownloadListToDock] and -[DownloadQueue tellDockToAddDownload:].

I've given up for now, but I reckon it should be possible to create a bundle that swizzles the right methods in storeagent to stop it placing the downloads on the Dock.