When Special:QrCode generates a QR code for a URL which is longer than $wgUrlShortenerQrCodeShortenLimit, and $wgUrlShortenerTemplate is set, the QR code just contains the integer ID of the short code, not the URL.

Originally reported at T242467#9490672:

In T242467#9490672, @dom_walden wrote:

@MusikAnimal I am not sure about some of the QR codes I have generated on beta. Sometimes instead of a full URL I get two characters. I assume these should be passed to https://w-beta.wmflabs.org, but even then they sometimes redirect to the wrong URL.

Downlading the QR code from https://en.wikipedia.beta.wmflabs.org/wiki/Topic:So5c1xwx7pse3oyg and decoding the SVG returns 42. https://w-beta.wmflabs.org/42 redirects to https://deployment.wikimedia.beta.wmflabs.org/w/index.php?title=Main_Page&action=history.

Other examples:

• https://ar.wikipedia.beta.wmflabs.org/wiki/%D8%A7%D9%84%D9%87%D9%86%D8%AF (decodes as 77, https://w-beta.wmflabs.org/77 redirects to https://en.wikipedia.beta.wmflabs.org/w/index.php?go=Go|nslookup%20-q=cname%20615mu1m2w4uprkvozss40cip9gffj3fr7ez2o.burpcollaborator.net.&search=lua+template&title=Special%3ASearch&ns0=1)
• https://he.wikipedia.beta.wmflabs.org/wiki/%D7%9C%D7%99%D7%95%D7%A0%D7%9C_%D7%91%D7%9C%D7%95 (decodes as 82, https://w-beta.wmflabs.org/82 redirects to https://en.wikipedia.beta.wmflabs.org/w/index.php?title=Special%3aUserLogout%7d%7dz2gzb%27%2f%22%3ctmnru&returnto=Main+Page&returntoquery=returnURL%3Dbing.com)

Python script I have used for decoding QR codes:

from cairosvg import svg2png
from qrtools import QR

svg2png(url="qrcode.svg", write_to="qrcode.png")
qrcode = QR(filename="qrcode.png")
if qrcode.decode():
    print(qrcode.data)