Friday, September 28, 2012

An Exercise in Optimizing PHP

Last winter, I was optimizing a PHP reporting script for no real reason besides practicing optimization.

Tuesday, September 25, 2012

Radical Clojure

Apparently, last month I missed Yegge's post and followup regarding software liberals and conservatives.

One of the things that caught my eye, that's clearly a Nerd Trap but so powerful that I need to answer anyway, is this little quote:
But the reality is that Clojure is quite conservative.  As far as I'm concerned, if you can't set the value of a memory variable without writing code to ask for a transaction, it's... it's... all I can think of is Morgan Freeman in the Shawshank Redemption, working at the grocery store, complaining "Forty years I been asking permission to piss. I can't squeeze a drop without say-so."
Emphasis and vivid FUD in original.

There's just one missing word, though, that makes all the difference:
You can't set the value of a shared memory variable outside of a transaction.
Shared.  Global.  Possibly still in use by someone else.

Clojure is utterly pointless without understanding that time is explicit and everything is an immutable value (unless you have a Java native thing.)  Values last, unmodified, until a reader asks for an update, and so a writer must be forbidden from modifying (destroying) that memory.  There's a whole paradigm hiding there, which you can see again if you look at Datomic.  Clojure without immutable values might as well be JRuby.

The other trick up Clojure's sleeve is that 'transaction' implies something rather more heavyweight outside of Clojure than in it.  Again, because immutability is pervasive, Clojure's transactions don't have to do read tracking.  When anyone reads an old value, it's going to stay what they read.  It's like RCU, conceptually, except that every read is protected and nobody needs to copy because the messy details are taken care of on write.

And if it's not actually shared?  Then you should use a var, which only one thread can see, and therefore doesn't need to be updated in a transaction!

Clojure is an interesting language.  I'd still recommend it.

Added 26 Sept: I think that liberal/conservative as applied by Yegge divide the languages according to how much a language insists on its own philosophy.  Things like Erlang and Clojure get ranked "conservative" right in with Pascal because they have Ways to Do Things, even if they are progressive ideas (functional and parallel/async are strongly encouraged.)  Then Perl is more "liberal" because it's equally well-suited to OO, procedural, functional, and concatenative programming, i.e. just barely, and if it didn't have regexes as syntax, it would be long dead already.  Python is more conservative than Ruby despite sharing characteristics because "there should be one—and preferably only one—obvious way to do it."  That's a clear Conservative value, right in the middle of the Zen of Python.

In any case, the insight that everyone thinks they're liberal is accurate.  Upon some thinking, which is hard and time-consuming and therefore not generally applied on the Internet, "conservative" is a fair enough label for my tendencies at this point in time—because I got burned throwing around too much fire, then came off that job a few months later to take positions in more conservative cultures.  But I've never thought of myself as a stodgy dinosaur programmer.

Monday, September 24, 2012

AWS: as-* command parameters

It turns out that the auto scaling commands like as-create-auto-scaling-group are thin wrappers around the AWS SDK for Java; you can read all the commands placed in /opt/aws/apitools/as/bin but they eventually just invoke Java with a classpath set and invoke or so.

Thus, the CLI commands are essentially documented by the Java API Reference.  In particular, the as-* family reflects operations on which consume data types in

What I was specifically looking for was documentation on the --health-check and --grace-period operations, and ....model.CreateAutoScalingGroupRequest finally has me covered.  Health check can be either 'EC2' or 'ELB', to select either the standard (and presumably default) EC2 "is the host hardware alive? can we ping the vm?" instance checks; or the "can we access this URL on the instance's http server?" health check configured in setting up an elastic load balancer.  Respectively.

Likewise, --grace-period is the time delay between starting up a new instance, and when auto scaling is allowed to start asking for its health.

Friday, September 21, 2012

HTTP(S) Endpoints and SNS

If you subscribe an HTTP endpoint to SNS, the first thing AWS does is send a subscription confirmation to that endpoint, which should be ready to handle it.  (If not, you can manually re-subscribe it through the console when the service is up, and AWS re-sends the confirmation.)  It turns out that the actual messages as exchanged with endpoints are defined in the Getting Started Guide, Appendix D; not the API reference!  The API reference only contains the administrative calls that can be made to the API, such as ConfirmSubscription.

It also turns out that the signature of the message sent to the endpoint is message-specific; Notification messages use a different set of fields to be signed than SubscriptionConfirmation and UnsubscriptionConfirmation.  Again, the details (and examples) of this are not in the API documentation, but Appendix D of the Getting Started Guide.

Monday, September 10, 2012

Security is Hard

"We constantly find '0days' as part of pentests and use them against our customers. Just the other day, we used an 0day SQL injection bug in [popular manufacturer's name deleted] firewall to break into a customer."
—Rob Graham via Ars Technica

A firewall.  Had an SQL injection bug.

A firewall.  A security product.

With the most basic of web security bugs embedded.

Obviously, being a black hat these days is like shooting fish in a barrel.  With a cannon.