Entries from 2008

Streaming your iTunes library, improved

The recent post on TUAW about streaming your iTunes library over the internet inspired me to stop using SimplifyMedia and to roll my own solution. The downside was that I found that the software TUAW linked to did not consistantly work. Worse was that the Mac specific version of the application did not work on Leopard.

I compiled a fresh version of the application that works on Leopard. Its much nicer than the generic Java version. When you run it you’ll notice a new icon in your menu bar.

Click on it and you will be able to set up the hosts as they describe in the directions at TUAW.

Download RendezvousProxy for Mac.

Better “max-width” workaround for IE 6

IE 6 famously lacks support for CSS 2.1′s max-width and max-height properties. Most solutions involve an IE 6-exclusive expression(…) with an inline conditional:

max-width: 100px;
width: expression(this.clientWidth > 102 ? "100px" : "auto");

Despite the apparent success of this technique, I’ve still found the inline conditional to be intermittently problematic. A slightly different take on the same solution has worked better for me:

max-width: 100px;
width: expression(Math.min(this.clientWidth, 100) + "px");

Shorter, and IMO, marginally more elegant… if any IE hack could bear that label.

Using mdfind to preview all tracks by an artist

Two among OS X’s more underutilised CLI tools are mdls and mdfind.

These both query the detailed metadata in Spotlight’s database (hence the md prefix).  The first command will return all the attributes of a file or directory.  The second will find all files that match a given attribute query string.  O’Reilly’s MacDevCenter has an article detailing advanced use of these commands.

The first example uses Apple’s afplay, but since the AudioFile API seems to be incapable of understanding its own DRM (*.m4p), the second example uses qtplay from MacPorts.

  • Listen to the first 5 seconds of all tracks by Mute Math:
    mdfind "kMDItemAuthors == 'Mute Math'" | while read f; do afplay -s 0 5 "$f"; done
  • Listen to a random track of 148 – 152bpm:
    mdfind "kMDItemTempo >= 148 && kMDItemTempo <= 152" | qtplay -1 -- -

Given the pervasive nature of Spotlight’s metadata, the possibilities are vast.  Hint: SSH and “&”.

Dealing with TextMate slowness when multitasking

TextMate makes sure that the project you are working on has an up to date file list. One of the ways that it does this is by scanning the directory tree of your project every time TextMate regains focus. This is usually good. However, when working with large projects or a project based on file server via NFS or CIFS, TextMate can take seemingly forever to actually regain focus when switching back to it from another application.

Luckily there is ReMate, which gives the ability to disable the project refresh feature. This option is added under the Window menu and also if you right click on any file inside a project there is a new menu item in there called Refresh All Projects.

Transcoding video for Blackberry on Mac OS X using ffmpegX

The newer Blackberry models all have media players installed on them out of the box. I recently started using a Blackberry Curve and wanted to transcode some of my podcast videos I download to watch on the bus.

ffmpegX handles this conversion well. You’ll need to use the following settings for the transcoded video to work on a Blackberry.

These are the important settings for the video to work.

  • Video Codec: MPEG4 (MP4) (ffmpeg)
  • Video Bitrate: 600–800 kbit/s (higher bitrates will lead to stuttering)
  • Video Size: 320×240
  • Autosize: 4:3
  • Audio Codec: AAC (MOV/MP4/3GP)
  • Audio bitrate: 96kbit/s
  • Sampling: 44100Hz

To save everyone time, I saved these settings to a ffmpegX preset file.

Tab completion and syntax coloring in irb using Wirble

I generally code in python and am used to the default features of the ipython interactive python shell. One of the features that I use a lot is tab completion. It helps me locate method names and also just do exploration inside modules that are new to me.

Wirble is a gem for ruby that enhances the irb interactive ruby shell to have tab completion, syntax coloring, and a few other irb tweaks that I haven’t looked in to yet.

Its pretty easy to install wirble on most unix systems with ruby gem support installed:

gem install wirble

Then, add the following lines to your ~/.irbrc

require 'rubygems'
require 'wirble'
require 'irb/completion'
Wirble.init
Wirble.colorize

Next time you start up irb save typing using tab completion and relax your eyes using the syntax coloring.

SSH Tricks #2: SSH as a proxy

We talked about port forwarding recently. This helps you get access to single resources but it requires a lot of planning and configuration. It would be pretty awesome if SSH had a proxy feature.

Lucky for us all there is the -D option for the ssh command. This option turns the ssh connection in to a SOCKS proxy on the remote server. The potential uses for this are huge. I often use this feature to gain quick access to my whole network.

Setting it up

superbox$ ssh -D 31337 someserver

Using it

Firefox SOCKS Proxy is set to localhost port 31337

To use this you will need to configure your applications to connect through the SOCKS proxy. Firefox is pretty easy to configure. The settings for the proxy live in the Preferences under the Advanced section in the Network tab. Click the Settings… button to bring up a dialog similar to the one on the right. Set the SOCKS host to localhost and the port to the one you chose when connecting.

Now that the proxy is setup you can test out that you’re proxy is working by visiting http://whatismyipaddress.com/ to check to see if it looks like you are accessing the site from a new IP address.

In the next installment of SSH Tricks we’ll talk about using ssh config files to save time and energy.

Dealing with long tracks in iTunes

This is apparently really old news however it was news to me a few days ago.

iTunes 7+ has an option for tracks to “remember playback position”. This feature is pretty handy for those 30 minute long progressive rock tracks and also for things like MIT’s OpenCourseWare.

It can be set in the Info for any item in iTunes. Right click on any item in iTunes and click Get Info or ⌘+i on a Mac. Under the Options tab in the Info box that shows you’ll find the Remember playback position option.

Mimic Positive Lookbehind in Javascript

JavaScript’s regular expression engine, while useful, lacks a few less frequently-used constructs.

I recently needed to remove all single whitespace characters (\s) immediately following semicolons (;) in a given block of text.  A simple way to accomplish this uses the positive lookbehind construct – that is, to match certain characters (;), but not to consume them, only to assert whether a match occurred or not.

This would normally be written as:

text.replace(/(?<=;)\s/g, '');

Though JavaScript doesn’t support lookbehinds, we can use a lambda expression to mimic its zero-width assertion behaviour:

text.replace(/(\;|:)?\s/g, function(str, p1) {
	return p1 ? p1 : str;
});

I haven’t tested this workaround exhaustively, but it solved the problem that needed to be overcome.

Update

It seems I’m not the first to have tackled this.  Steve Levithan’s regex skills far exceed my own, and his blog entry on the subject offers a more comprehensive solution to the problem.

SSH Tricks #1: SSH Port Forwards

SSH is the ultimate tool for shifting bits around networks in a secure manner. This is the first of a series of articles on SSH tips. This article is all about the basics; as the tips progress, we will get trickier.

Overview

Port forwards are a way of mapping a TCP from one side of the ssh connection to the other. They are established using the -L and -R parameters to the ssh command. These stand for local and remote port forwards. A local forward takes a port on the local machine and connects it to an IP address and port from the remote machine. As you suspect, a remote forward takes a port on the remote machine and connects is to an IP address and port from machine you are connecting from.

Examples

You could forward port 80 from an  internal web server to port 8188 on the machine you are connecting from. This is a sort of poorman’s VPN. You can gain access to resources inside your network via SSH local port forwards. After connecting to your gateway machine you would be able to access the web server at http://localhost:8188.  To actually do this the command would look like this:

superbox$ ssh -L 8188:internalweb:80 homerouter

Another common use for this is securing VNC access. Many VNC servers offer the option to only accept connections from localhost. By combining this option with a ssh local forward  you can create an encrypted VNC session. This would be done by doing:

superbox$ ssh -L 5900:localhost:5900 vncserver

Remote port forwards are much less common. Lets say you have a local web server running on your workstation and you’d like your friend to take a look at an error on a hot new web app. you’re developing. The catch is you don’t want to let them login to your machine to do a local forward to gain access to your server. In this case you could use a remote port forward like this:

superbox$ ssh -R 8188:localhost:80 untrusted-friend

Your somewhat trustworthy friend could then access your web server at http://localhost:8188.

In the next installment of this series we will reveal a way to make your SSH connection behave even more like a VPN.