Entries tagged 'Rust'

A project I have been playing around with the last couple of weekends has been making a Python version of this site. The code, which is very rough because I barely know what I’m doing and I’m in the hacking-it-together phase as opposed to trying to make it pretty, is in this GitHub repository.

I am using the Flask framework with SQLAlchemy and Jinja.

I was interested to see if I could just use the same templates as my PHP version, which uses Twig, but there have been a few sticking points:

1. The Twig escape filter takes an argument to more finely control the context it is being used in so it knows how to escape within HTML, or a URI, or an HTML attribute. Jinja’s escape doesn’t take an argument. I was able to override it take an extra argument, but mostly ignore it for now.
2. Jinja doesn’t have Twig’s ternary ?: operator. Not surprising, Python doesn’t either. I rewrote those bits of templates to use slightly more verbose if blocks.
3. Jinja doesn’t have Twig’s string comparators like matches and starts with. Looks like I can get rid of the need for them, but I just punted on those for now.
4. Jinja doesn’t have a block() function. I think I can also avoid needing it.
5. Jinja’s url_for() method expects a more Python-ic argument list, like url_for('route', var = 'value') but Twig uses a dictionary like url_for('route', { 'var' : 'value' }). I was able to override Jinja’s version to handle this, too.
6. I’ll need to implement versions of Twig’s date() function and filter.

I had cobbled together a way on the Twig side to let me store some templates (side navigation, the “Hire me!” message on the front page) in the database, so my next trick is going to implement template loaders for both the PHP and Python versions so that is more cleanly abstracted. I have the Python side of that done already.

I hope to eventually create a Rust version of this, too, and it will be interesting to see what new complications using Tera will bring.

A long time ago, I implemented a quick-and-dirty daemon in C that used the vendor’s support library to display messages on an LCD pole display at the store. The state of California requires that electronic point-of-sale systems have a customer-facing display, and this fulfilled that.

It was very simple, it just listened for TCP connections and displayed the text it was sent. Every 15 seconds it would reset the display to a hardcoded default message. When an item was added to an invoice in Scat POS, it would push the name and price to the daemon. It also pushed the total when payment was initiated.

Like I said, it was quick and dirty, and we used it for a decade and I never really got around to doing any of the basic improvements that I wanted to do, like being smarter about when to go back to the default display.

The LCD display was one of the things we didn’t manage to sell off when we closed down the store, so I took it home and now it’s on my desk, hooked up to the Raspberry Pi 4 that used to be our print server. I decided to use it as an excuse to start learning Rust.

I pulled out one of the examples from the code for a crate that wraps libusb to provide access to USB devices, hit it with a hammer until I got it to push text to the display, and now I have the basis to re-implement what I had before and then give it the polish that I never did. Maybe implement a more user-friendly way of sending the various control codes from the user manual for doing things like clearing the screen.

That’s the theory, at least. The reality is that first I had to migrate all of my photos from Flickr to my own service, implement a way to add new photos to the collection, and then upload the photo I took of the display showing a simple message so I could blog about it.

And I am not sure if doing more with this is actually the next thing I’ll tackle, but writing about what I had done so far is at least something to check off the to-do list that I don’t have.

The code lives in the lcdpoled repository on GitHub. (The old C code is now off on a different branch.)