Archive for the ‘Web Development’ Category

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Treetop: Grammar’s Cool

Released February 12th, 2008

Treetop was one of the more exciting projects I saw at last year’s RubyConf. Nathan Sobo’s Treetop talk is available online and I urge you to watch it. Nathan did a great job of explaining the basics of syntactic analysis, and then got into the specifics of using Treetop’s implementation of parsing expression grammars to put the concepts to work.

Treetop appeared to gather all the concepts together into an understandable domain specific language. All of the tokenization and node structure can go into a single file, and the interactive nature of Ruby makes for the perfect sand box. I felt like I could get somewhere if I invested just an hour into this. I was happy to find that my impressions were correct.

After a short time I had caught on enough to start writing my own code. Once over the hump the rest was easy. I was able to write and test a Treetop grammar for parsing CSV files within a few hours. I chose CSV parsing because I was already familiar with the format, and I could compare my implementation to not just one but two existing Ruby libraries.
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Handling Session Timeouts (and other errors) using Ajax

Released January 11th, 2008

Ajax can bring a much more responsive and intuitive feel to web applications. However, many times developers overlook error cases when using Ajax. What if the request fails? In one particular case a user’s session may have timed out before they made an Ajax call. This post describes one such way of handling this in a somewhat friendly way.
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Latest on Rails Performance

Released April 1st, 2007

Updated Rails 1.2 performance numbers have been released. While these number look pretty good it is hard to get a good idea of exactly what the performance of Rails is. A couple of other benchmarks that include Rails such as performance tests for 6 frameworks and Grails vs Rails benchmarks show a different picture. Both of these come up with much worse performance than the first. Maybe the issue is that the second two benchmarks are using Apache ab but the first uses a new version of rails bench. Of course most people probably aren’t that worried about the benchmarks that much because you can find ways to make anything fast as shown with Rails doing 4000 requests a second.

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Tomcat + UTF8 + HTTP Get

Released March 19th, 2007

By default tomcat doesn’t UTF-8 encode get parameters like it does post parameters. This doesn’t seem to be the case with other application servers. So before you get yourself into trouble with your internationalized web application, make sure you make this change.

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Building a better world with Google Spreadsheets

Released December 6th, 2006

I was tickled when I ran across the GoogleLookup and GoogleFinance functions in Google Spreadsheets. I was very tickled when I found there was a REST API for interacting with the spreadsheets.

So not only can you lookup the current volume of Google stock in a spreadsheet (=GoogleFinance(”GOOG”, “volume”)) or find out Roger Clemens’s ERA (=GoogleLookup(”Roger Clemens”,”earned run average”)) you can access those values real time using an open API. I cobbled together a quick ruby program that can retrieve values from a private or public (published) Google spreadsheet.

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IE7 adds native XMLHTTPRequest object

Released October 26th, 2006

The recently released IE7 supports a native XMLHTTPRequest object. On the surface this can be considered a good thing and should be commended. However, to the people that erroneously (in hindsight) assumed that…

window.XMLHttpRequest == ! (not) IE

…they are in for some strange behavior (here, here, here, and here for example).

The problem occurs when the code is optimized for non-IE browsers and does not recreate the XMLHTTPRequest object on each event. Back when “window.XMLHttpRequest == !IE” was true, this code worked as expected: IE browsers created a new XMLHttpRequest object on each event and non-IE browsers reused the same XMLHttpRequest object. Now IE7 will correctly process the first event but then fails on the second (and subsequent) requests because you still can’t reuse XMLHttpRequest objects.

We chose to just remove the optimization all together and recreate the object on each event for all browsers. Others may wish to come up with some other check that will allow them to keep it.

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Cleaning Up Rails Sessions, Revisited

Released September 16th, 2006

In an earlier post, we detailed a method for removing stale Rails session files. In more recent version of Rails, there is a Rake task built in for this administration task.

rake tmp:sessions:clear # Clears all files in tmp/sessions

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Cleaning up stale rails sessions (removing ruby_sess files)

Released June 8th, 2006

I’m not sure if something isn’t set up correctly of if this is just a fact of life with rails but the sessions it creates never seem to go away. I think before rails 1.1 the sessions where stored in /tmp and now they are stored in the apps directory along with everything else so they is probably no internal mechanism to delete them. I only noticed because after about a month of an certain app running the disk on the machine started to fill up. After digging a little I found 50K ruby_sess.* files hanging out in the rails session directory.

Anyway it was easy enough to clean up the stale ruby_sess files by going into the rails webapp/session directory and then running the following command:

find -type f -name "ruby_sess*" -exec rm -f {} \;

I’m not sure why the app is creating sessions but it isn’t something that stores state so I didn’t have to worry about killing active sessions here. If you do need to worry about that you will probably want to toss a time on the find command.

After looking a little more I found a post about this that has a ruby way of cleaning up the sessions.

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Ruby’s DBI or ActiveRecord

Released April 9th, 2006

While creating a small CGI web application in Ruby the question came up about how much slower ActiveRecord is than DBI. Considering that ActiveRecord is initialized each time the CGI runs the performance hit could be significant.

So why not use Rails instead? The server that I am running the application on has limited resources. Rails is reported to need about 20 MB of memory and the node I have is already paging out memory to disk.

To emulate the webserver getting hit repeatedly with connections I created a connect_dbi.rb and and connect_ar.rb that insert the same row into a Tests database table. The ActiveRecord test also has the model file test.rb

The test was run using a PostGreSQL database on Ubuntu 5.10 with Ruby 1.8.4. The table was truncated between tests. I just wanted to get an idea of the performance difference between ActiveRecord and DBI. So this isn’t the strictest performance test but does provide an idea of the magnitude of difference.

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AJAX file upload progress for Java using commons fileupload and prototype

Released April 2nd, 2006

This has been done before with PHP (AJAX upload progress meter for PHP) etc but I needed something a little different because I wanted to upload a file and then have it loaded into a database. I looked around and found that someone had already made something that used the commons file upload package to do the upload part (AJAX Upload progress monitor for Commons-FileUpload Example). It wasn’t exactly what I was looking for but it a good start.

To understand the way this works I think it is easiest to break it down into parts:

  1. A file upload extention that counts bytes as they are uploaded
  2. An interface that monitors the progress of something running on the server
  3. AJAX to pull the monitoring into the current screen

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