A variety of disinformation

This Ruby regular expression checker/tester is a hidden gem that’s far too low in the serps: http://rubular.com/.

I needed a crc16 in order to feed some data to a dinosaur.
Google couldn’t help me this time so I rolled my own. The pre-calc table was borrowed from a python implementation.

Hope this saves someone else the hassle…


CCITT_16 = [
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,
0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
]

• Installing was easy as pie. I was missing the Apache development headers and the installer told me which ‘yum’ command I should use to install them. Nice.
• When you don’t have heaps of memory, remember setting RailsMaxPoolSize to a lower value to avoid swapping. I’d experiment with RailsMaxPoolSize and saturating the number of concurrent requests using ApacheBench in any case. More concurrent threads is only better until a certain point.
• Apache/HAProxy/Mongrel was a bit slower than Apache/mod_rails, which was a bit slower than HAProxy/mongrel (without Apache). The difference was nothing to loose sleep over. RailsMaxPoolSize was set the same as the nr of mongrels.
• While ApacheBench testing, touching tmp/restart.txt to force a restart could cause a hang. Only restart of Apache helped.
• I would get an occasional time-out and ab stopped (heavy testing, large nr of concurrent requests). BUT this also happened with Apache/HAProxy/mongrel (NOT when using HAProxy/mongrel ‘direct’) so I’d guess this is rather an Apache issue.

Mod_rails seems to be a surprising stable and finished product, and this for a first public release! I’m anxious to check out their Ruby Enterprise Edition.

The occasional hang when touching tmp/restart.txt makes me a bit weary, but this only seems to happen under heavy ApacheBench testing with a high number of concurrent threads. The hangs of Apache under heavy load on my test system, even when no mod_rails is involved might indicate this isn’t even a mod_rails problem. I don’t see this being an immediate issue under normal circumstances.

Thank you Phusion! (I don’t like the logo though)

I’ve been planning on checking out nginx for a while. Mainly as an alternative for apache in my currently preferred apache/haproxy/mongrel Rails install.

I guess I’ll have to hold on to apache a little while longer and check this one first: http://www.modrails.com/

From where I’m standing this is the most interesting thing to happen to Ruby on Rails deployment since mongrel.

I used to use the regexp tool in Komodo. But since they stopped offering the $25 ‘personal’ version I lost my enthusiasm a bit.

The online alternative I keep returning to: http://www.mochikit.com/examples/mochiregexp/index.html

Only ‘javascript’ regular expressions, but so far this worked out just fine every time I needed it.

It’s often not possible or wanted to take down your rails application for updates. Even if it is, I still regard downtime as something that should be avoided if possible.

When using the absolutely fantastic HAProxy to load-balance between your mongrels, you can take down a mongrel process without any adverse effects. When a mongrel process is not answering anymore, HAProxy just forwards the request to the next available mongrel and no harm is done.

So all you need is a way to stop and restart each mongrel, one after the other. I cooked up a bash script to do this. It’s not perfect, but I’ve been using it on several projects. The script stops each mongrel, waits until it’s really stopped, then restarts and checks if it’s really running.

Why a bash script ? I wanted to sharpen my (limited) bash scripting skills (so if you have any tips: feel free to comment).

Customize where needed. (properly indented version here)

If you are running monit, remember to ‘unmonitor’ before and ‘monitor’ after.


#!/usr/bin/env bash

done


This should work with other load-balancers too, but since HAProxy had all features I expected to find and is very resource friendly and has a tiny footprint (and irons a shirt in 2 mins), I didn’t look any further (after looking at Pound, which only advantage is that it’s easy to install/configure and cisco css switches which are just a tiny bit expensive for my needs)

Ok, 2007 was a bit quiet on the blogging side. Been squeezing the max out of every minute of spare time and been working/learning as hell. Maybe more about what I’ve been upto later.

The layout started looking a bit stale so I modded a layout I like (credits: see bottom of page) to something I like even more (gustibus and stuff) and gave WP the much needed update. So there, giving a reason to unsubscribe to the 3 people that had forgotten that they were following my feed!

This tool has been around for quite some time, but it often surprises me how few people (also ‘professional’ ones) seem to have heard about it. Since it’s the only FREE live CSS IE editing tool I know, and since (added bonus!) it actually offers split-view Firefox/Internet Explorer editing, there’s no harm in spreading the word a bit.

Get it at: http://litmusapp.com/labs. DL link is sent to email address provided. However, I’m pretty sure they honour their no-spam policy.

Oh yes… it only runs on windows. But since there’s no escape having to consider IE users browsing your site, it’s almost worth keeping a windows installation for (that, and homebanking).

Tip: If your site requires a login and you have problems logging in using CSSVista: save the page you want to edit using Firefox and open it in CSSVista for editing.

And just in case you’ve been hiding under a rock, for day-to-day live CSS editing use (running fine under Linux!) there’s the webdev swiss army knife: Chris Pederick Web Developer Extension.

I recently read ‘Getting Real‘, a book (only available as pdf) by 37 signals. 37 signals are the people behind the much hyped Ruby on Rails and a bunch of webapps based on this RoR (=Ruby on Rails) framework.

Why I wanted to read this book
I use RoR with success for an ongoing project at my daytime job and also used it for an ‘after-hours’ sideproject of which at least the development was a success thanks to Rails. I’ve also used Ruby (it works without Rails too) for more little projects and ‘glue’ than I can count.
Seeing that Getting Real is almost as hyped as RoR itself I figured I’d shell out the $19 and check what Getting Real is all about. After all, Rails has turned out to be a very productive and really quite fun web development framework. (but then, after years of doing VC++/MFC development even a lobotomy would seem ‘fun’… or even cobol… nah… just kidding about the cobol)
Continue Reading »

El Problemo
When issuing a ‘rake db:schema:dump’ (or a simple ‘rake test’ since it uses db:schema:dump) on the legacy oracle db mentioned in the previous post the schema.rb contained some weird entries like:

t.column "timestamp", :datetime, :default => #<date : 4903089/2,0,2299161>, :null => false

The culprits were basically field defaults (like the above, using ’sysdate’ as default) that aren’t handled properly (not even sure if they should). Since this is a legacy db accessed by tons of mainly C/C++ code on which I’m tacking a web ui, changing this to something that suits Rails is usually not possible.

Any other rake tasks using the schema.rb stumbled over these entries so I was basically unable to do a simple ‘rake test’.

Unfortunately I only found the occasional mention of this issue but not a real solution (yet).

El (hack’n’slash) Solution
Basically all I needed db:schema:dump to work correctly for was being able to run tests. For a variety of accidental reasons I choose to run these tests on a mysql db on a w2k box. (at work I’m using xwin under cygwin on a wxp installation to connect to a CentOS server for my rails development… so this might not seem a logical decision… but explaining the reason behind choosing mysql to run the tests is really totally out of scope of this post)

Easiest solution was to filter the badies (renegades and outlaws) out of schema.rb before it was used for something else.

I made an extra db:schema:clean task to read/filter/write schema.rb, called it from db:schema:dump and put these in a file called ‘databases.rake’ in my Rails lib/tasks folder.

databases.rake:

namespace :db do
namespace :schema do
desc "Create a db/schema.rb file that can be portably used against any DB supported by AR"
task :dump => :environment do
require 'active_record/schema_dumper'
File.open(ENV['SCHEMA'] || "db/schema.rb", "w") do |file|
ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
end
Rake::Task["db:schema:clean"].invoke
end
desc "Fix the sysdate timestamps from an oracle schema.rb"
task :clean => :environment do
File.open(ENV['SCHEMA'] || "db/schema.rb", 'r+') do |f|
lines = f.readlines
lines.each do |it|
it.gsub!(/:default => #<date : 4903089\/2,0,2299161>,/, '')
it.gsub!(/:default => "EMPTY_BLOB\(\)",/, '')
end
f.pos = 0
f.print lines
f.truncate(f.pos)
end
end
end
end


(blame WordPress for losing indentation… at least I do!)

Ok… probably really basic stuff for the harcore Railsers out there, but I hope this will help some ‘nuby’ Railsers save some time hunting for where/what/how with this great framework.

(2nd post today, I’ve got another one up my sleeve but will stop now before someone asks me to take a ‘doping test’)