Gavin Terrill's Blog

Changing github origin repo to use SSH

Quick tip about accessing git repositories.

If you initially cloned a repository using the default https: url then you will be prompted for your username and password everytime you want to pull or push.

The fix is to access the remote repository using SSH instead (so it uses your keys for authentication).

To do this follow the instructions documented on github here: Changing a Remote's URL.

 

Vent: RubyMine/Gems/Bundler/Backward Compatibility

My preferred framework of choice for a lot of the web apps I'm playing with these days is Rails. But I've got to tell you there is some stuff that really ticks me off....

First is backward compatibility. 2 years is like a whole new eon in Ruby land. Going from Rails 2 to 3 breaks all sorts of things outright, and other stuff in subtle ways. The community's answer to this is to ensure you've got tests up the wazoo (which is a good thing, but not everything can be automated especially the edge cases). Ruby itself from 1.8 to 1.9 breaks things. Net result for me is locking in gems at specific versions and deferring updates so ultimately this is driving up Tech debt.

As an example, I'm trying to upgrade one of my Shopify Apps to use OAuth because the "old" way is going to be turned off. Of course, the OAuth Gem is not compatible with Rails 2 so upgrade here we come. 2 weeks later and I'm still working through it. Partly because of...

Next pain point is the whole ruby gem nightmare. Maybe it's because of my preferred IDE (RubyMine - which on the whole is awesome by the way) in conjunction with rbenv, but yesterday was blown because after doing a reboot it couldn't find Rails in the SDK. I haven't rebooted for a while so it is likely something I did weeks ago. I tried all sorts of stuff to get it working again - reinstalling rbenv, gems, setting environment variables etc. In the end I closed all projects, rebooted again and restarted the IDE and guess what it starting working again (sort of, now it says I've got the wrong version of rack installed, sheesh!).

It all just feels kind of random and fragile. I don't know what the answer is, but I think this really turns a lot of people off Ruby. In my day job we are planning on moving to a Micro-Service style architecture and it would be great to see some of those implemented in Ruby but the folks who have tried it at some point got turned away after not being able to get their heads around the environmental stuff.

I do see some positive signs. So far ruby 2 seems to play nicely with my existing stuff.

People talk about the drag maintaining backward compatibility would involve (looking at you Java) and how it stiffles innovation. In this case I think the pendulum may have swung a little too far. It may be better to cut down the surface area - E.g. the Asset Pipeline stuff introduced in Rails 3 probably should have been an optional extra, particularly now that our thinking about the performance benefits of it are changing.

Ok, vent over. Thanks for listening!

Update 3 days later: Ok, so to get Rubymine to understand the gems, go to Rubymine > Preferences and delete your SDK. After that a little reset button will appear in the top right. Click that and it sorts itself out.

 

 

 

Phusion Passenger RewindableInput Error Parsing with REXML

Ran into this funny little bug and didn't find too much about it on the interwebs, so for prosperities' sake here are the gory details...

The error is "RuntimeError: PhusionPassenger::Utils::RewindableInput is not a valid input stream. It must walk like either a String, an IO, or a Source."

The offending line of code occures when using REXML to parse an XML document as part of a webhook controller:

doc = REXML::Document.new request.body()

Under the covers, it is this line of code that generates the error:

/opt/ruby-enterprise-1.8.7-2011.03/lib/ruby/1.8/rexml/source.rb:21:in `create_from'

This is a rails 3 app, running under Phusion Passenger 3.0.10 and REE 1.8.7.

The solution, courtesy of jsierles, is to fixup Passenger with an ImprovedRewindableInput: https://gist.github.com/281126 Basically, create a /config/initializers/phusion-rexml-phixup.rb file and paste the code from that gist.

 

 

Target non-mobile Devices using JS

Some regex to use when you don't want something to happen on a mobile device:

if (!/android|iphone|ipod|series60|symbian|windows ce|blackberry/i.test(navigator.userAgent)) {
 // regular browser stuff here...
}

jQuery Cycle Plugin - Adding Image Links

The jQuery cycle plugin is pretty freakin' awesome, but I couldn't figure out how to put a link behind each image. Sure there is a tutorial, but the images refused to show up no matter how much CSS tweaking I applied.

So I came up with a quick and dirty solution that uses jQuery to handle the click event for each image in the slideshow.

First the markup for the slideshow images:

<div id="slideshow">
  <img src="'banner1.jpg" alt="" rel="/" />
  <img src="'banner2.jpg" alt="" rel="/collections/skincare" />
  <img src="'banner3.jpg" alt="" rel="/collections/men" />
  <img src="'banner4.jpg" alt="" rel="/collections/men" />
  <img src="'banner5.jpg" alt="" rel="/products/the-ultimate-guide-to-beauty-by-anjana-gosai" />
</div>

It is basically the same as what you normally use, but each image has an additional "rel" attribute with the location to link to.

Now the javascript:

<script type="text/javascript">
  jQuery.noConflict();
  jQuery(document).ready(function() {
    jQuery('#slideshow').cycle({fx: 'fade', timeout:5000, speed:1000});
    jQuery('#slideshow img').click(function (){
      document.location.href = jQuery(this).attr('rel');
    }).css('cursor', 'pointer');
  });
</script>


I am adding a click handler to each <img> element in the slideshow div, and using whatever is specified in the rel attribute as the location to go to. Finally, I make the cursor a pointer for each image so the user knows it is click-able.

You can see it in action here.

Handling Errors Using jQuery.load

Following on from my last post on integrating HTML content from another  system into an existing site, I realized I wasn't handling failures very gracefully. To recap, I was using the load method of jQuery:

$(document).ready(function() {
 $('#races a').click(function () {
  $('#results').load('Racing/' + $(this).attr('href') + ' #wrap');
  return false;
 });
});

I was surprised to find there wasn't much information about how to go about capturing an error if it occurs. It turns out you can get it by passing a callback function to the load function. This function accepts 3 parameters: responseText, textStatus and an XMLHttpRequest. I'm not exactly sure why they decided to give you responseText and textStatus when you have an XMLHttpRequest (an object that already encapsulates both of these values so passing them as parameters is a violation of the DRY principle).

Anyways, here is how to do it using the callback function:

$(document).ready(function() {
 $('#races a').click(function () {
  $('#results').load('Racing/' + $(this).attr('href') + ' #wrap', "", function(responseText, textStatus, XMLHttpRequest) {
   switch (XMLHttpRequest.status) {
    case 200: break;
    case 404:
     $('#results').html('<p>Looks like the results have not been uploaded to the server yet. Please check back later.</p>');
     break;
    default:
     $('#results').html('<p>' + XMLHttpRequest.status + ': ' + XMLHttpRequest.statusText + '. Please contact the club and let them know.</p>');
     break;
   }
  });
  return false;
 });
});

Now you can get specific about how you report your error based on the response code. For example, if you see something in the 400 range you know there has been a client problem (e.g. 404 not found), versus a 500 series status for server side problems. In this case, I explicitly handle 404 errors and have a generic catch-all for anything else.

HTTP Response Codes

HTTP has a pretty well thought out set of response codes.

• Server borked? 503.
• Access denied? 403.
• Not found? 404. 
• All good? 200.

Up until now there hasn't really been a concise, easy to follow, way of figuring out what response code is the most appropriate. Allan Dean fixes that with his handy dandy activity guide for determining the appropriate HTTP response. Nice to see it also covers ETags.

It's kind of fun - now you can play the "find the 201" game.

Should be very useful for RESTful developers.

Scala Compiler Plugins

Did you know you can write plugins for the Scala Compiler? I can imagine using this to implement DBC analysis at compile time. How cool would that be?!

Wide Finder, Two.Oh!

Tim Bray started a project last year that attempted to find the fastest way to do string wrangling on log files using Erlang. The idea is to see how languages (like Erlang) that work  well on multi-core machines  compare with more traditional languages; in terms of designing a solution and performance. Pretty soon, Really Smart People were contributing solutions, including those written in languages that are not concurrent savvy per se (e.g. Perl). As it turns out, a Perl implementation kicked Erlang's butt, but the project was somewhat flawed as Tim points out in "Wide Finder 2":

There were a few problems last time. First, the disk wasn’t big enough and the sample data was too small (much smaller than the computer’s memory). Second, I could never get big Java programs to run properly on that system, something locked up and went weird. Finally, when I had trouble compiling other people’s code, I eventually ran out of patience and gave up. One consequence is that no C or C++ candidates ever ran successfully.

This time, we have sample data that’s larger than main memory and we have our own computer, and I’ll be willing to give anyone who’s seriously interested their own account to get on and fine-tune their own code.

What I loved about this the first time around was the discussion around how people approached the problem and their refinement of strategies based on some serious analysis of the bottlenecks. This is kind of geeky, but this is the type of stuff I find fascinating. Tim must have spent a fair bit of time lobbying for the corporate resources needed to get round 2 off the ground, so hat's off to you Tim, and well done Sun for having the foresight to back this project.

Simple Spring 2.5 App with 2.5

Wanted to send some link love to Cagatay Civici who has created a really nice, minimal, concise sample application that showcases a bunch of latest and greatest Java webapp technologies:

• JSF (MyFaces 1.2.2 with Facelets)
• Spring 2.5
• JPA with Hibernate
• HSQLDB for persistence
• Jetty for deployment
• Maven2 for build

I like the Generic DAO idea. Get it here: Annotation Driven JSF-Spring-JPA.