October 20, 2013 · 4 min read

Hermes: contextual help in 48 hours (Rails Rumble 2013)

• rails
• ruby
• open-source
• hackathon
• ifad

The Rails Rumble is — was — a 48-hour hackathon where teams of up to four people build a complete web app from scratch using Ruby. No prep work, no pre-written code. Just caffeine, git, and a deadline.

This year our team — @amedeo, @liquid1982, @maisongb, and me — built Hermes: the epic messenger service, entry #385.

(My previous Rumble entry was Guess The Friend in 2012, with a different team.)

July 2, 2013 · 3 min read

data-confirm-modal: When a User Did Too Much Damage

• ruby
• rails
• javascript
• open-source
• ifad

A user at IFAD did too much damage last week.

Not maliciously — they just clicked through a chain of destructive actions, happily dismissing the browser’s confirm() dialogs without reading them. Because nobody reads those. They’re ugly grey system dialogs that blend into the background of your workflow. Click OK, click OK, click OK — and suddenly half the data is gone.

So I fixed it. And then I extracted the fix into a gem, because this problem isn’t specific to our application. Today I’m releasing data-confirm-modal — 116 lines of JavaScript that replace Rails’ built-in confirm() with a Bootstrap modal.

October 14, 2012 · 2 min read

"Guess The Friend" — 48 hours of Rails Rumble madness

• rails
• ruby
• hackathon
• facebook

Last weekend we competed in Rails Rumble 2012 — 48 hours to build a web app from scratch using Ruby on Rails, no preparation allowed. Our team was part of the Italian 48rails community, and we built Guess The Friend: a Facebook game that implements the classic Guess Who? board game, but using your real Facebook friends as characters.

(I’d be back at the Rumble the following year with a different team, building Hermes.)

May 7, 2012 · 8 min read

ChronoModel: Time Travel for PostgreSQL

• ruby
• postgresql
• rails
• open-source
• ifad

Update, April 2019: ChronoModel reached 1.0 — seven years, 506 commits, and 31 releases later.

We’re building a CRM at IFAD — a UN specialized agency in Rome — and one of the hard requirements is temporal data. We need to know what a record looked like at any point in the past. What was this project’s budget on March 15th? When did this beneficiary’s address change? Who approved what, and what did the record look like at the time?

I’d been prototyping a PostgreSQL schema approach for this — views, rules, table inheritance — and it worked. Then Amedeo, my boss, looked at it and said: “This shouldn’t live inside the CRM. Make it a reusable framework.”

He was right. The temporal pattern has nothing to do with CRM logic. It belongs in a gem.

So I had five days of uninterrupted focus, and today I’m releasing ChronoModel — an ActiveRecord extension that gives your models full temporal capabilities on PostgreSQL. What Oracle sells as Flashback Queries and charges enterprise money for, we can do with standard SQL on Postgres 9.0+.

Abstract: add SID APT source, configure APT Pinning to give squeeze packages priority over SID ones, rebuild the nodejs package under squeeze.

• Add SID APT source by creating /etc/apt/sources.list.d/sid.list (use your nearest mirror):

deb http://ftp.us.debian.org/debian/ sid main
deb-src http://ftp.us.debian.org/debian/ sid main

• Configure APT pinning by creating /etc/apt/preferences.d/sid:

Package: *
Pin: release a=unstable
Pin-Priority: 50

• Install the latest version of libv8 manually, libv8-3.8.9.20 at the time of writing this:

apt-get install libv8-3.8.9.20

• Download the nodejs package sources, dependencies and build them:

cd
apt-get source nodejs
apt-get build-dep nodejs
cd nodejs-*
debuild -nc -uc

• If you encounter build-dependency errors, you should try first to lower the dependency in debian/control, both in Build-Depends and in Depends and re-run debuild. If the build fails (e.g. with undefined reference to 'ev_run') the previous version is missing required functions. So, you must install the updated versions of the required dependencies (e.g. libev4) from sid, using apt-get install name=version e.g. libev4=1:4.11-1. I suggest this because you’ll have to manually update packages installed from sid, so the lesser, the best.

• Install the generated package

dpkg -i nodejs_*.deb nodejs-dev*.deb

• Profit :-)

So you have a Linux VM you use for development, because you want to mirror the production environment as closely as possible. You have many applications to deal with, they have to be running at the same time because they are nifty REST JSON web services.

You are very tired of remembering which one you put on port 8081, and your configuration files slowly become a real mess. So you set up IP address aliases in for the network interface and decide to assign even host names – /etc/hosts is just fine – for each app.

Then, in such a setup, why would you still need to run them on ports higher than 1024? Wouldn’t it be just great to type the application name in the browser address bar? Indeed it is, but it’s better to not run them as root, anyway.

The solution is Linux capabilities (see also here). The one that interests us is cap_net_bind_service: it gives a process the right to bind well-known ports (< 1024). If you use an interpreted language, of course you’ll have to add the capability to the interpreter itself. That’s why there’s development in the title of this article – you should not set this up on a production server, if you don’t know what you are doing.

“If it is good, they stop making it”, the payoff printed on the conference necklaces, distributed to every participant, along with an über-l33t badge customized with our nickname and the key hash.

Being my first experience at an international security conf (I’ve only been to the ccc2k+7 camp), and being a ph outsider ‘cause I never participated to previous editions, the boot keynote held by FX, staffer and frontman, has been enlightening: “you ought to be here!”, he yelled while pointing at the stage, wearing a white shirt with the Phenoelit logo printed on both arms.

“This conference has never started on time”, he continued, “so there was no reason to do that for this last one”. the schedule is straightforward: party, the next day's talks from 12.00PM to 7.30PM, then party, and the last day's talks from 12.00PM to 5.30PM. definitely a setup well-playing with the available alcohol :-D.

Afterwards, another speaker informed us that the wi-fi access keys we received at the registration allows us to use a 6 APs/3 repeaters beast driven by an OpenBSD box – they want the audience to hack it because, well, “you are the Worst Case Scenario.” :-)

Thanks to @jodosha efforts and praising the former Javaday event, now renamed into codemotion that brought in Rome many Ruby developers from Milan, Padua and other parts of Italy – the first official Ruby Social Club in Rome has been a great success. Of course, officialty is measured only in the amount of twitter spam posted about it! :-): earlier RSCs in Rome go back in time to 2006 organized by current mikamai members and more meetups promoted by @jeko in 2007.

What matters is that there’s a community, there’s a passion, and there’s love to share knowledge - no matter who holds the meetings, the important thing is that they’re being held :-).

The event was simple and direct - some beers first, then my keynote on RVM and Ruby interpreters, then Luca’s one announcing his minege.ms project and after real social networking :-). I met @gravityblast after much time we didn’t meet, knew the PIP group and met @svarione, @punkmanit, @leonardoperna, @riggasconi, @ogeidix and other smart people. Moreover, we spent quite some nice time together, making up a really lousy and funny week-end. Of course, huge kudos to @nhaima’s car - that tirelessly carried us around Rome for two days :-)

Now, looking forward to the next meetup, thanks everyone who participated, who offered me beers and, last but not least, thanks to @etapeta for bringing me in time at the meeting - you’re the real hero :-).

I spent the last two days trying to set up the Aluminium Mac Mini (rev. 4,1) as a home NAS server with encrypted storage, and I wanted a BSD system on it. There’s already an embedded OpenBSD onto the soekris gateway, and another companion would have been nice. :-)

Guess what, there’s no way out:

• FreeBSD 8.1 doesn’t complete the boot process, due to a bug in the SATA chipset, NV MCP89;
• FreeBSD 8.2-RC1 boots but, due to the same bug, doesn’t recognize any SATA drive nor any USB umass device;
• NetBSD 5.1 boots fine, handles SATA disks via the generic pciide driver (no DMA, thus quite slow) but, unluckily, doesn’t handle the BCM57762 ethernet controller. I tried with quick and dirty patches to bring the bge driver up to date with -current, but still no luck: the MII link detection works, the card transmits but doesn’t receive. The sdmmc controller as well works with -current but not with 5.1-RELEASE. ACPI works correctly;
• OpenBSD 4.8 boots, can access the SATA drives without DMA, and recognizes the bge network card, but exposes the very same behaviour as NetBSD 5.1 with the -current driver fitted in;
• DragonFlyBSD 2.8.2 doesn’t even enter kernel mode, I suspect due to ACPI bugs;
• PureDarwin didn’t inspire me too much, due to the many blocking issues.

All of them support encrypted storage, I built up a NetBSD CGD disk flawlessly onto dk wedges; FreeBSD has got the interesting gbde(8) and geli(8) GEOM-based tools that I wasn’t able to test, while OpenBSD supports crypto via a softraid personality. Unluckily, support for the, nowadays, exotic Apple hardware is a no-brainer.

October 18, 2010 · 7 min read

From microphone to MP3: the Myousica audio pipeline

• myousica
• music
• ruby
• rails
• audio
• open-source

This is the third and final post in the Myousica series. The first covered the Rails platform, the second the Flash multitrack editor. This one covers how audio actually gets from the user’s microphone to a playable MP3 — the pipeline that connects all the services together.

The uploader is a separate Rails 2.2 application — headless, no database, no ActiveRecord. Just controllers, background workers, and audio processing tools. Andrea Franz built the initial version in April 2008, I took over from May 2008 onwards. 120 commits, originally called multitrack_server before being renamed to mewsic-uploader in March 2009.

The full pipeline¶

Here’s the complete flow from microphone to playable track:

Two entry points: the user can upload an MP3 file directly, or record via microphone (which produces an FLV stream through Red5). Both end up as an MP3 with a waveform PNG.