How to Build a One-Time QR Code with URL Redirect
Requirement
https://t.me/blacktechsharing/183161
Approach
A QR code is essentially a string of characters embedded in an image. This string can be a URL.
Since the QR code image has already been sent to others, and you can't go to their computer or phone to delete the image, how is a "one-time QR code" implemented?
If the QR code image stays the same, then the URL A corresponding to the QR code stays the same.
When you visit URL A, you're accessing a server. This server can make everyone who visits URL A redirect to a new URL B.
We define URL B as the URL that actually carries the real meaning. We let the server allow only the first visitor to URL A to be redirected to URL B; subsequent visits to URL A will have the redirection disabled.
This is how a "one-time QR code" is implemented.
For example,
The URL with actual meaning is https://google.com
We set up a server, https://1way.eu.org
We make https://1way.eu.org/HcAx62 redirect to https://google.com and only redirect once.
We generate a QR code using https://1way.eu.org/HcAx62.
When someone scans this QR code, they will visit https://1way.eu.org/HcAx62, the system redirects them to https://google.com, and then the system records that this https://1way.eu.org/HcAx62 is now invalid.
If someone else scans this QR code, they will also visit https://1way.eu.org/HcAx62, but the system will tell them that this resource is no longer valid.
Implementation
worker.js
Add a configuration option snapchat_mode, disabled by default.
Before redirecting to the original link, delete this record. Then the next time someone looks it up, the record won't be found.
Full workflow of generating a one-time QR code using a QR code encoding/decoding tool
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