Tech

This one stumped me for a while today. I had an application to deploy which worked fine in development. Deploying to production led to this error:

/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.5/lib/active_support/dependencies.rb:249:in `load_missing_constant': Expected /myapp/releases/20090617160914/app/models/widget.rb to define Widget (LoadError)

Googling that error turned up lots of pages for Rails 1.2.x and issues with underscores in names. None of it applied. Widget was definitely being defined in widget.rb. Following the stack trace it appeared that the error was thrown in the Ultrasphinx plugin. After trying a lot of other things, I decided to comment out the Ultrasphinx code in the model and retry. The error changed to this, which was helpful:

Errno::EACCES: Permission denied - /myapp/releases/20090617160914/public/widget/myfile

This model was also using the file_column plugin, and the underlying error was just a permissions problem in the file attachment target directory. I fixed the permissions and put the Ultrasphinx code back in the model, and all was happy. If only that permissions error had shown up first!

After much frustration, I found a way to get the Ruby mysql Gem installed and talking to my MySQL server on MAMP. Credit goes largely to "Hootbah" who followed a similar path to get MAMP talking to Perl's MySQL library. Here's the steps I followed for MAMP 1.7.2:
Success!

I recently needed to run through one data file, pull a number, and look that number up in several other data files. So in Ruby, I first opened the initial file, pulled the number, and then opened the other files, iterating through every line until I found a match, then call break to move on. This worked, but it was sort of slow.

It occurred to me that I could use grep to see if the number was in the other files. So I had to figure out how to call it from Ruby. Here's what I came up with:

The speed improvement depends on how many searches you're doing and the size of the files you're searching, but in a quick test the grep calls were 5x faster.

Shoulda is a handy plugin for Rails (now a Gem), which makes writing tests easier. It's worth checking out. Shoulda has been very helpful with a big Rails project I've been working on all summer, and I submitted a couple small contributions and bug fixes. I was surprised to see my name mentioned in the newest release, but I appreciate it, and it was fun helping out!

Here's a gotcha that I came across today: don't define a constant as something in one Rails rake task file, and then define the same constant as something different in another file, because the last constant will supercede them all:


I guess this happens because Rake is loading all of the task files before running the requested task. There's probably a way to namespace the constant, but I need to do more research on that. In the meantime I'll use different constant names!

I was initially disappointed when it was announced that Ruby on Rails was moving its version control system from Subversion to Git. There's enough to keep up with in Rails that I didn't relish having to keep up with this as well. It wasn't so much that Rails was moving, but related code began to move too, so we're currently in this limbo where many plugins have both git and soon-to-be-deprecated SVN repositories, and it's just another detail to keep track of. Hopefully there will be tools to sort all this out soon.

I like my SVN GUI tools, but it turns out that git works pretty well on Windows under Cygwin, if you can live with the command line. It's certainly sufficient for cloning plugin repositories.

I could take or leave git by itself, but I love GitHub. They make it so easy to fork an existing project, make your own changes to it, and share it back with the world. Your changes can easily be pulled back into the original projects, too. I've been able to make a couple of small contributions to shoulda and acts_as_xapian.

So git is fun after all, and I'm looking forward to using it more; especially when the GUI tools show up.

I've had a Canon Pixma MX700 multifunction printer since the beginning of the year. I've been pretty happy with it. It's worked well for scanning, copying, faxing and printing. Until today. Today I needed to scan something, and was greeted with the following message when I turned it on:

U150 The following ink tank cannot be recognized.

The yellow cartridge was indicated. I though that it was an odd problem, but I didn't care for the moment, because I didn't want to print, just scan. But no button on the printer would bypass this error and let me scan.

I ended up calling Canon, and happily received a domestic phone rep. He had me try a couple things, but eventually decided that the yellow ink would need to be replaced. They would send me one free. I asked if there was any way to bypass the error so I could just scan, and he said there was not. If I wanted to use it today I would have to go out and buy a yellow ink cartridge. So after driving all the way across town and spending $16, I have my printer back...for now.

It seems like questionable design to cripple all the functions of the printer just because one color cartridge is faulty. A better failure mode would be to only prevent color printing. Black and white printing, and the other printer functions should still be usable. Hey Canon, how about updated firmware for this? Please?

Today I came across a PNG file that had been uploaded from a browser with a .JPG extension and image/jpeg MIME type. It's too bad that MIME types are apparently unreliable when it comes to file uploads. I went looking for a way to determine the file type by actually reading the file. This is probably a solved problem, but I was unsuccessful Googling for the answer. I came up with the following Ruby method which decides the image file type using up to the first 10 bytes:


This works well on a small set of test files (400+ from a browser temp files directory). Let me know if there's a case where this code doesn't work, or if there's a better solution in general.

I've made a code contribution to Ruby on Rails. It was minor, but I'm glad I could help. See ticket 10435 and changeset 8386.

Supposed to get some rain today...keeping my fingers crossed.

Update 2007-12-17: Looks like my patch made it into Rails 2.0.2. And we did get that rain, but more would be good.

Update 2008-03-17: I managed to get another small patch committed. Go open source!

I don't like to code in JavaScript, but that's the Ajax-y wave of the future. So I write it when I have to. This week I needed to format a Javascript date as a MySQL-style date like 2007-12-08.

JavaScript apparently doesn't have a nice date formatting function or even a generalized sprintf. Another Javascript quirk is that the Date.getMonth() function returns 0-11, while the getDate() function returns 1-31. I'm not sure what the designer was thinking on that one.

I came up with this function...feel free to use it in your code with or without credit: