Author: C. Ivan Cooper ivan@4levity.net
Crossoff was developed to provide a free system to validate print-at-home, mobile and regular pre-printed barcode tickets at an event, without needing internet access. It consists of a server and an Android app that uses a phone or tablet camera to scan barcodes.
Upon scanning a ticket, the user of the app is informed whether the scan was accepted, or if the ticket was already scanned or voided etc. Also, "door notes" can be associated with a particular ticket and those will be displayed upon successful scan of that ticket.
It's also possible to use Crossoff to check names/numbers off a central list by hand, without using the Android app at all, using just the basic HTML5 user interface provided by the server. But it's not really optimized for this use yet.
The UI includes support for easily importing ticket data and barcodes from Secret Party or Brown Paper Tickets, or you can generate your own ticket list and use that instead. NOTE: Brown Paper Tickets may change their data format at any time and that feature would stop working.
There are two subprojects:
- crossoff-server (Java ticket validation server and UI)
- Crossoff (Android barcode scanning app)
crossoff-server is a self-contained LAN web app to manage the ticket list for an event. Crossoff app works with crossoff-server to scan barcodes using an Android device camera. See below and also see README.md files in each subproject directory for further instructions.
Alice (a programmer) built her own system to collect donations and email tickets to her event. Space is limited and demand is high, so she needs to make sure that every ticket presented at the door is valid. But checking everyone off a list is too slow. She knows how to generate random barcodes and email them to her ticketholders, and she needs a free system that lets her have multiple barcode scanners running at once.
Bob (not a programmer) is selling tickets to his event using Secret Party. He wants to allow electronic ticketing so that users can print their ticket at home and send tickets to other people electronically. Or, maybe he is using Brown Paper Tickets but cannot use the free Brown Paper Tickets app, because there is no reliable Internet service available at the location where tickets will be scanned.
In both of these cases, Crossoff might be a usable solution, and they could set up their hardware the same way (see Setup section below).
Before the event starts, Alice would need to generate a JSON file using the Crossoff format. To see an example, start the server and browse to http://localhost:8080/tickets/example. It just needs to have a few fields - the barcode for each attendee, their name (optional) and a ticket description and type. Then she'd start up crossoff-server and use curl or Postman to load the tickets via the simple API.
Since Bob is using Secret Party to sell his tickets and generate barcodes, he doesn't have to deal with JSON and APIs. He just logs into the Secret Party website right before the event, and downloads the ticket list for the event. The UI on crossoff-server allows him to quickly import this file and he is ready to start scanning.
If Alice wants to allow last minute ticket sales, she could use the crossoff-server API to add more tickets as they are sold. Bob could theoretically do that too, but to keep things simple, he might want to stop new sales on Secret Party, then download his final list of attendees and load them into the database.
You can test the system end-to-end on a laptop. Using a physical Android device is optional. First, get the server running from the instructions in crossoff-server/README.md . Next, follow the instructions in Crossoff/README.md to get the Android app running on a real or virtual Android device.
Note that if you are using Android Virtual Device, the easiest way to make everything work is to run the virtual device on the same computer that crossoff-server is running on.
A basic setup at an event would look like the following. Once it is set up it should "just work" due to the magic of hard-coded IP addresses and a complete lack of built-in security - the only security is provided by WPA2, and by not connecting anything else to your ticket validation network.
- One WiFi router configured as follows:
- Router IP address 10.0.2.1
- LAN address 10.0.2.0/24 (i.e. netmask 255.255.255.0)
- DHCP range 10.0.2.100 - 10.0.2.200 (or whatever, but not including 10.0.2.2)
- WPA2-PSK (WPA2 Personal) encryption for the WiFi, using a secure+secret password
- One laptop or PC or Raspberry Pi or similar (also maybe a spare) configured as follows:
- Any operating system, Java 17 installed
- Connected to the router and set up with static ip address 10.0.2.2 (default in the Android app)
- crossoff-server installed and running (optionally you could set it to start automatically on boot up)
- tickets loaded into crossoff-server database
Minimally, a Pi Zero W or similar with hostapd to act as a WiFi access point could host the service.
For clients, at least one phone/tablet:
- Android 5 (Lollipop) or later
- Camera to read bar codes
- Connected to WiFi
- Running the Crossoff app
This project has no warranty, express or implied, yadda yadda. Use it entirely at your own risk! And I'm pretty sure I just said there's no security of any kind except for the secure network you're expected to use it on.
Assuming you tested everything out in advance, probably the biggest disaster that you could feasibly experience while using Crossoff is the loss of your ticket server or database during the event. If you cannot immediately recover the data and/or get the server working again, you will lose information on what tickets have been scanned in, and maybe lose your ticket list. You might want to have a printout and maybe a second laptop with a second copy of the database.