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hacker lee carmichael software engineer consulting programmer Perl Perl5 Javascript JavaScript PHP C web application developer cakephp

Blog

My blog is where I keep my notes. Most of the time updates will happen in bursts of activity. All links go offsite to blog.leecarmichael.com at Blogger since Google has a very good service.

Please don't create tests like this in Perl

09:44:00 13-May-2014

I just came across a test like:

And of course, it was silently doing something/nothing/everything. I'd guess most experience Perl coders will notice that the eval will only run the test if the request doesn't throw an exception. Which might be kind of ok but there is no catch or check of the $@ later.

If a check is added for $@ later, it will make the test pattern pretty messy

Please don't write this type of test. Please.

Instead use Test::Exception and drop into a sub. Something along the lines of:

This is better for a couple of reasons:
  • test will show some output in case of exception
  • test will stop instead of just pushing on with a bunch of mostly false error (unless the test wants to this to check bad input :)
  • test is simpler to understand (no response, give up)
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Dancer Sessions using PSGI

15:17:00 23-Mar-2014

A few weeks on #dancer channel, a user was having issues using Dancer::Session::PSGI. I've never worked directly with Plack besides reading the handbook and few play apps. (well a few weeks ago, I dug into Dancer::Debug.). Using both together was an intriguing problem stuck in my mind.

The person on the channel was reporting unreliable reading of session data and other odd behavior. As I started to dig into the problem, I realized that i need to create two apps, one pure Plack and one Dancer with middleware wrapper. I created a public repo on github with my test apps: Dancer and Plack session.

Since, I didn't want to deal with html and wanted a bit of structure with return data, I made both test apps return JSON and have pretty simple routes

I started off using the documentation from Plack::Middleware::Session to create this test app:

Next I created a Test Dancer PSGI app, which basically had a way to show value and update it. Here is the non-exciting Dancer app:

I updated bin/app.pl to use Plack::Builder directly instead of creating a wrapper (which I'd like to try as well probably in a branch):

With those all setup, I started both apps using plackup but each with slightly different command lines:


magic-bus> plackup pure_plack/bin/app.psgi &
magic-bus> plackup -p 3000 dancer_plack_session/bin/app.pl &

I created a curl_cookie script to use and store cookies and verbose dump out request/response information. I needed to see what cookies where getting sent in and back.

After i fired up each app server, the first set of requests dumped the following:

Well that is odd. A couple quick bullets:

  • plack app did what was expected (the app increments counter in session after return response therefore on 2nd request being set to 1 is ok).
  • dancer app didn't return '2' (since other app has write to the counter twice) plus it appears to be using both 'dancer.session' and 'plack_session'. This is wrong.
After I dug around a bit (since that session name seems wrong), I found two things.
  • A bug with Dancer::Session::Abstract: #1004
  • And in this case, Dancer::Session is only creating the session not retrieving (since it doesn't think there is one yet) which makes sense. (why retrieve when you are first generating the session.)

The initial session being created to the first request to Dancer not finding the existing plack session information. After that initial request, then it would pick up plack session data. The current behavior would lead to this confusing response the 2nd time from Dancer app:


{
"visits" : 2
}

I fixed up Dancer::Session::Abstract to use 'plack_session' cookie and that resolved the session not getting read on initial request.

A bit unexpectedly, I see that Dancer is setting cookie with different session id than PSGI. PSGI includes its own session cookie. This is expected since the Plack middleware runs after Dancer (think of the onion from handbook: ).

Here is example of response made to Dancer app:

In the end its working now. Dancer is able to pull in session information from Plack session but its still a bit messy. I'm not sure if multiple session cookies is considered a bug or not. I think it might be best to have Dancer not do any cookie stuff and only use the session data if its available in the environment but looking over the Dancer session code, this doesn't look straightforward w/out major changes to core Dancer code.

Any ideas out there?

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Template Toolkit Debugging inside of Perl Dancer

08:44:00 12-Mar-2014

The other day someone was asking how to enable Template Toolkit debugging inside of Perl Dancer in the #dancer IRC channel, it seemed like a good time for a write up.

The template engine configuration directive supports passing through various options like start_tag and stop_tag as explained in Dancer::Template::TemplateToolkit POD. And alludes to being able to pass other options.

How

To pass TT options like those found in Template::Constants, there must be a DEBUG section in engines -> template_toolkit, usually found in config.yml.

Example Snippet

Here is an example:

A few notes

  • Remove leading DEBUG_ from TT constants. The option DEBUG_PLUGINS becomes plugins.
  • Multiple options can be separated with a comma. Example:DEBUG: "provider,plugins".
  • Be warned, some of these options can lead to tons of information :)
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What's installed on my ec2

12:57:00 04-Nov-2013

What's installed on my ec2?

I swear between debian/ubuntu/mac os x/irix (well not anymore), I can never remember how to list installed packages on my ec2. 

Here is is:

   sudo yum list installed

Plus or minus sudo depending on who you are. For once, the command is what i'd expect.

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