Phase two of the lab asset ledger: 43 devices, one QR code each; admins scan with their phones to open the detail page and record an audit. It sounds like half a day's work. It took a week. Here is what bit us.
1. The QR Code Encoded the Auto-Increment id
The first script embedded the device's auto-increment id straight into the URL, like /asset/17. The labels were printed and stuck on; someone on the client's side scanned one, casually changed 17 to 18, and up came another device's information. Device info isn't sensitive, but 'guessable' is unacceptable in itself.
We switched to random tokens, 16 characters, with a separate asset_token mapping table; the QR code contains only the token. The generator also became a one-shot batch: 43 labels, filenames carrying the device name, sequence numbers never exposed.
2. WeChat's Scanner Ate a Parameter
The QR URL carried two parameters: token and source. Scanning with the system camera worked fine; opening via WeChat's 'Scan,' the second parameter occasionally vanished. After much digging: the & in the URL was being treated as a terminator in some contexts. We reduced it to a single token parameter and resolved the source server-side by token. Two parameters became one.
3. Old Labels Weren't Revoked, So We Double-Printed
Halfway through sticking the first batch we found one device mislabeled, printed a replacement, and didn't fully peel off the old one. Result: the same device appeared twice in the audit sheet. We added a status field to the tokens — revoked labels now respond 'label invalidated' when scanned — and put a unique index on asset_id per audit day, one record per day.
4. The Basement Has No Signal
One lab is downstairs where phones get essentially nothing. Admins scanned, the page wouldn't open, and back upstairs they forgot about it. The fix: after scanning, the record is first stored in the browser's localStorage; when the page detects connectivity it auto-uploads with a client-generated uuid, and the server deduplicates on the uuid. That round recovered seven records, all from the same day.
5. The Export Still Needs to Be Printable
After the audit the client wanted a paper sheet to sign and file. We built an export: A4 portrait, one column each for device name, code, audit status, and remarks — 43 rows, exactly two pages. The font size was deliberately set to 10; any smaller and the signatures can't be read back.
Wrap-Up
All 43 devices were scanned in the end. The system showed one more than the ledger — a centrifuge written off long ago but never removed from the books. The equipment manager took the paper sheet to process the write-off. That part had nothing to do with the system.
We kept a stack of the revoked labels. They're still sitting in a drawer at our Optics Valley office.
