rapid habits ❧

Web Based Truth Table Generator

Mon, 23 Jan 2012 02:38:00 -0500

Web Based Truth Table Generator:

I wrote this a while ago, recently ported it to run on GitHub Pages: http://mustpax.github.com/Truth-Table-Generator/

From Malchesine, Italy.

Sat, 19 Nov 2011 18:10:31 -0500

From Malchesine, Italy.

Netflix, Qwikster and the impending introduction premium pricing

Mon, 19 Sep 2011 11:07:00 -0400

Netflix just announced that they are spinning off their DVD-rental-by-mail service under a new brand Qwikster while the streaming service retains the Netflix name. Many commentators have duly noted Netflix’s boldness in leaving its cash cow behind and looking to the future, a true example of a company facing up to the Innovator’s Dilemma.

However, this latest change serves a purpose beyond merely signaling Netflix’s future direction to customers and investors. Namely, Netflix is setting itself up to offer premium pricing options for its streaming product. The company has already been burnt by customer confusion stemming from its most recent pricing changes. Netflix knows it needs to clearly delineate the two product offerings to be able to say “pay another $10 a month to watch all Fox shows” without customers wondering they will still be able to rent Family Guy Season 3 DVDs by mail.

At $10 a month unlimited streaming is a great deal. The cable plans that that Netflix’s service replaces run around $40-50 which means there’s a lot of consumer surplus Netflix can absorb to widens its product offering. As evidenced by the latest Starz loss, Netflix needs to make more compelling bids for streaming rights and offering premium streaming packages is the key to that. I for one can’t wait.

"Leadership is about taking risks, while management is about mitigating them. They are thus often in..."

Wed, 07 Sep 2011 01:41:11 -0400

“Leadership is about taking risks, while management is about mitigating them. They are thus often in direct tension. Yahoo had a lot of management and not much leadership.”

- Joshua Schachter on Hacker News

Simple staging on Heroku

Wed, 31 Aug 2011 15:06:00 -0400

Not everything runs the same on production as it does on localhost so you need a staging environment to vet changes before making them public.

When developing Piazza (on GitHub) we put together a simple workflow to manage production and staging deployments. Our app is built on the Heroku Cedar stack with Java and the Play framework but this workflow should be applicable to all other apps on Heroku.

Git branches

We need Git branches to track what we have on Heroku. We will be pushing these back to our central repository origin (GitHub in our case) to facilitate easier collaboration.

git checkout -b prod
git checkout -b staging
git push origin prod
git push origin staging

Heroku setup

You will need two different Heroku applications, one for staging and one for production. If you’re starting from scratch you can create these applications and attach them to the right Git remote repository.

heroku create --stack cedar --remote prod
heroku create --stack cedar --remote staging

If you already have a Heroku app under the Git remote heroku you can rename it and create a new app for staging.

git remote rename heroku prod
heroku create --stack cedar --remote staging

`make` me a sandwich

Create a file in your project root named makefile (with the lowercase m). We will create two make targets in this file which are basically project specific shortcuts. There’s a lot more you can do with make but we’re sticking to basics. Our two make targets look like this:

make stage will now deploy the contents of the staging branch to the appropriate Heroku app followed by GitHub. make deploy will do the same with the prod branch. You will have to merge changes from master into these branches yourself like so:

git checkout staging
git merge master
make stage

Bonus: Keeping branches clean

Since you have to update the staging and prod branches manually it is good to put in some safety measures to prevent bad deployments. For our part, we require the Git branch to be clean. A simple Bash script can check Git to see if there are any uncommitted changes and abort the make target

The new make targets should look like

Now if you try to make stage with a dirty repo the deployment will be aborted.

$ git checkout prod
Switched to branch 'prod'
$ touch newfile
$ make deploy
There are uncommitted changes.
make: *** [deploy] Error 1

Appendix

"Go the F*** to Sleep not funny"

Fri, 01 Jul 2011 18:42:00 -0400

From “Go the F*** to Sleep not funny”

“She has good reason to be concerned about the message behind such a parody. Demarest was the prosecuting attorney in one of Oregon’s most high-profile child murder cases. […] Nobody is suggesting that there’s a connection between Adam Mansbach’s book and child abuse or child neglect.”

Dear CNN op-ed author, I believe you’ve made that very suggestion.

Lazy loading click handlers with onmousedown

Wed, 22 Jun 2011 00:51:17 -0400

Just today I was thinking about how annoying it is that Facebook redirects all outgoing links to an internal page. They do this to mitigate the spread of clickjacking worms and whatnot but I like to think I’m smart enough to not click a post titled “I can’t believe she isnt werring a bra LOL WORM!!” So I figured I’d write a quick greasmonkey script to switch the links back to their pristine form. Well, I didn’t exactly get around to writing the script but I discovered something nifty instead.

Take the following innocuous link to a humorous imgur image a friend posted on my wall:


        http://i.imgur.com/7XSdO.jpg

The link target (href) is not rewritten on the server so the click must be getting intercepted via JavaScript. But you can’t preventDefault for a click via onmousedown, you have to catch the onclick event instead. Here’s what UntrustedLink looks like once beautified:

function UntrustedLink(a, d, b, c) {
    this.dom = a;
    this.url = a.href;
    this.hash = d;
    this.func_get_params = c ||
    function () {
        return {};
    };
    Event.listen(this.dom, 'click', this.onclick.bind(this));
    Event.listen(this.dom, 'mousedown', this.onmousedown.bind(this));
    Event.listen(this.dom, 'mouseup', this.onmouseup.bind(this));
    Event.listen(this.dom, 'mouseout', this.onmouseout.bind(this));
    this.onmousedown($E(b));
}

Facebook is adding onclick handlers to links right before the click happens. No wasting time with pesky onload initializations, links are self-initializing! Pretty neat.

Well, not that interactive

Thu, 16 Jun 2011 11:23:00 -0400

I always alias rm to rm -i to prevent fat-fingered mishaps. This is usually too chatty if you try to recursively delete even a moderately big directory, so you have to go all out with rm -rf.

I get chills every time I type that little f in there and it turns out the new version of rm from GNU coreutils allows an alternate interactive mode -I that will prompt you once for all arguments. It also skips prompting altogether if you specify less than 4 files for deletion.

From the man page for rm:

If the -I or --interactive=once option is given, and there are more than three files or the -r, -R, or --recursive are given, then rm prompts the user for whether to proceed with the entire operation. If the response is not affirmative, the entire command is aborted.

One Instruction Set Computer VM and Assembler on GitHub

Mon, 13 Jun 2011 23:22:10 -0400

One Instruction Set Computer VM and Assembler on GitHub:

I wrote this with a friend for a Computer Architecture course final project back in 2005. It is one of the first significant chunks of Java I’ve written, which shows. The concept is still interesting though.

HELO EHLO

Sat, 11 Jun 2011 23:50:00 -0400

Why is it that ubiquitous internet protocols can’t spell? HTTP’s got “referer”. SMTP has not one but two misspellings of hello.

My ideal reader is a second version of me. The whole series is...

Fri, 04 Mar 2011 14:59:44 -0500

My ideal reader is a second version of me.

The whole series is wonderful and candid snapshot of Merlin and John’s talk.

"When you’re young, you look at television and think, There’s a conspiracy. The networks..."

Wed, 02 Feb 2011 15:03:35 -0500

“When you’re young, you look at television and think, There’s a conspiracy. The networks have conspired to dumb us down. But when you get a little older, you realize that’s not true. The networks are in business to give people exactly what they want. That’s a far more depressing thought. Conspiracy is optimistic! You can shoot the bastards! We can have a revolution! But the networks are really in business to give people what they want. It’s the truth.”

- Steve Jobs in WIRED magazine, February 1996

The origin of Unix file delete permissions

Wed, 26 Jan 2011 12:24:00 -0500

Unix file permissions fall into three basic categories, read, write and execute. Which one do you think controls file deletion? It’s probably write, right? Well, let’s test it:

$ touch foo; chmod -w foo
$ ls -l foo
-r-------- 1 user group 0 2011-01-24 12:16 foo
$ rm foo
$ ls foo
ls: cannot access foo: No such file or directory

That’s weird, it looks like I successfully deleted that file. Maybe it’s governed by user/group ownership.

$ touch foo; sudo chown root:root foo
$ ls -l foo
-rw------- 1 root root 0 2011-01-24 12:18 foo
$ rm foo
$ ls foo
ls: cannot access foo: No such file or directory

I just deleted a file owned by root. WTF?

It turns out, Unix file deletion (and creation) is controlled by write access to the parent directory. Let’s demonstrate quickly:

$ mkdir test; touch test/foo
$ chmod -w test
$ rm test/foo
rm: test/foo: Permission denied

You see, each Unix file has a dedicated datastructure that stores metadata called an inode. While inodes store permissions, access/modification timestamps and other useful info, they do not track file location or name. Instead, directories map file names to inodes. The name of an inode is derived from its location. When we delete a file with the rm command, we are merely removing a directory entry. Hence, we only need write permissions to the directory in question.

You can even link to an inode from multiple directory locations with the ln command. These references are called hard links and are counted by the inode. The inode is reclaimed and the disk storage freed only when the reference count reaches zero. So not all rm operations will result in the underlying file being destroyed, which is yet another reason for file deletion being controlled by the parent directory.

Apparently the iPhone also has a universal orientation lock like...

Wed, 05 Jan 2011 06:44:22 -0500

Apparently the iPhone also has a universal orientation lock like the iPad. Here’s how to use it:

Doube-tap the home button to view the recent apps selector.
Swipe right on the selector to reveal the iPod controls and, lo and behold, the orientation lock.
Lie in bed all morning browsing the web.

(Step 3 is optional.)

Keep trying till you succeed with Bash

Wed, 10 Nov 2010 16:18:00 -0500

The following Bash snippet will repeat a command with the given delay until it succeeds.

while [ "$?" -gt "0" ] ; do
    sleep 120 # delay in seconds between retries
    # insert command to retry here
done

Unix processes return integers when they exit. These values can be read via $? in Bash. As a matter of convention, a process that completes without errors will return 0, so by checking for exit codes greater than zero we can detect errors and retry.

Click on album art. ⌘-W main window. Pretend iTunes is a...

Sun, 24 Oct 2010 21:56:00 -0400

Click on album art.
⌘-W main window.
Pretend iTunes is a minimalist music player.

Secure delete with rm on OS X

Sat, 23 Oct 2010 21:02:00 -0400

I discovered this gem in the rm man page on OS X the other day:

-P  Overwrite regular files before deleting them.  Files are
    overwritten three times, first with the byte pattern 0xff,
    then 0x00, and then 0xff again, before they are deleted.

So there you go rm -P will securely delete a file from your disk with minimum hassle (i.e. without having to through the Thrash folder). This might be one of those goodies OS X inherited from BSD. On Linux you have to use something like shred to achieve the same thing.

Addendum: santry on the HN Thread points out the same thing can done via the srm command. Several people also noted that secure delete interacts unpredictably with modern file systems. jrockway points out that full disk encryption should be used in place of secure delete for this reason.

"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong..."

Sat, 14 Aug 2010 12:40:15 -0400

“The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair.”

- Douglas Adams, presumably talking about how distributed systems are more reliable since fault tolerance is baked into the architecture

I keep coming back to this one.

Sat, 07 Aug 2010 21:50:00 -0400

I keep coming back to this one.

"My ability to decide how I feel about Wikileaks’ activities is totally annihilated by my ongoing..."

Mon, 02 Aug 2010 11:45:00 -0400

“My ability to decide how I feel about Wikileaks’ activities is totally annihilated by my ongoing realization that it cannot possibly be real. It’s a plot device in a near-future thriller novel. I mean, seriously, semi-stateless man with an unusual appearance uses an army of anonymous allies to expose governments’ secrets, and posts an insurance file in public with some kind of deadman switch in case he’s taken out by his enemies? That shit does not happen in real life. Julian Assange is a Neal Stephenson character who’s escaped in to the real world.”

- Tomorrowful on MetaFilter (via Simon Willison)

rapid habits ❧

Web Based Truth Table Generator

From Malchesine, Italy.

Netflix, Qwikster and the impending introduction premium pricing

"Leadership is about taking risks, while management is about mitigating them. They are thus often in..."

Simple staging on Heroku

Git branches

Heroku setup

make me a sandwich

Bonus: Keeping branches clean

Appendix

"Go the F*** to Sleep not funny"

Lazy loading click handlers with onmousedown

Well, not *that* interactive

One Instruction Set Computer VM and Assembler on GitHub

HELO EHLO

My ideal reader is a second version of me. The whole series is...

"When you’re young, you look at television and think, There’s a conspiracy. The networks..."

The origin of Unix file delete permissions

Apparently the iPhone also has a universal orientation lock like...

Keep trying till you succeed with Bash

Click on album art. ⌘-W main window. Pretend iTunes is a...

Secure delete with rm on OS X

"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong..."

I keep coming back to this one.

"My ability to decide how I feel about Wikileaks’ activities is totally annihilated by my ongoing..."

`make` me a sandwich

Well, not that interactive