Want to try it out? We have an instance running at http://littleprinter.nordprojects.co which all are welcome to use!
How to use
Want to get your Little Printer online?
Hack the Berg Cloud bridge. Follow our step-by-step guide here.
- If you've already got a hacked bridge using the alpha.littleprinter.com backend, use the guide above but start at step 6.
Using the device key API
Use Device Keys to print through an API. Create a device key from the web interface, and go to that URL to view API documentation.
Running on Heroku
We run an instance of this server on Heroku, at littleprinter.nordprojects.co. You are welcome to use our instance!
If you want to run it yourself, this app will run on Heroku, but you need a static IP address due to the way the Berg Bridge connects. We have a droplet at Digital Ocean running nginx to forward the HTTPS connection on to Heroku.
It should also be possible to run in Docker, dokku, or directly with gunicorn, but we don't use it that way :).
The server can be configured with the following variables:
TWITTER_CONSUMER_KEY=... TWITTER_CONSUMER_SECRET=... FLASK_CONFIG=... DATABASE_URL=...
These can be set in the
.env file in your checkout.
Creating fake printers and friends
Resetting the actual hardware all the time gets a bit tiresome so there's a fake command that creates unclaimed fake little printers:
$ ./manage.py fake printer [...] Created printer address: 602d48d344b746f5 DB id: 8 secret: 66a596840f claim code: 5oop-e9dp-hh7v-fjqo
Functionally there is no difference between resetting and creating a new printer so we don't distinguish between the two.
To create a fake friend from twitter who signed up do this:
$ ./manage.py fake user stephenfry
You can also claim a printer in somebody else's name:
$ ./manage.py fake claim b7235a2b432585eb quentinsf 342f-eyh0-korc-msej testprinter
The design is somewhat stratified: each layer only talks to the one below and above. The ugliest bits are how database and protocol loop interact.
UI / database ---------------------------- protocol_loop / send_message ---------------------------- encoders / decoders ---------------------------- websockets ----------------------------
Information flow (websockets)
The entry point for the bridge is in
sirius.web.webapp. Each new
websocket connection spawns a gevent thread (specified by running the
flask_sockets gunicorn worker) which runs
the websocket/bridge_address mapping in a global dictionary; it then
loops forever, decoding messages as they come in.
Devices are associated with an account when a user enters a "claim code". This claim code contains a "hardware-xor" which is derived via a lossy 3-byte hash from the device address. The XOR-code for a device is always the same even though the address changes!
The claim codes are meant to be used "timely", i.e. within a short window of the printer reset. If there are multiple, conflicting claim codes we always pick the most recently created code.
We are also deriving this hardware xor when a device calls home with an "encryption_key_required". In that case we connect the device to the claim code via the hardware-xor and send back the correct encryption key.