Project · Local network
FlashDrop: what it solved and how
Private phone-to-Mac file transfer over the same Wi-Fi: the Mac hosts a local receiver, the phone scans a QR code and sends files from its browser.
The thinking
One decision worth defending
- 01
Problem
Moving a file from a phone to a Mac usually means a cloud service, a cable or an app to install on the phone.
- 02
Decision
Skip the app on the phone: the Mac hosts a local receiver, the phone scans a QR code and sends from its browser, and every chunk is encrypted with the session key from that QR.
- 03
Why it holds
No install and no cloud in the middle. Plain HTTP on a local network has no certificate, so the content is protected by per-chunk encryption instead, and the receiver rejects public addresses.
What it includes
Built
- 8 MiB chunks with 2 to 4 adaptive upload lanes
- ChaCha20-Poly1305 encryption per chunk, with WebAssembly workers off the main thread
- Automatic retry with exponential backoff and resume after a dropped connection
- Collision-safe filenames and partial-file staging before a transfer completes
- LAN-only by design
Removing a step is often the biggest usability win. State the limits too: local HTTP cannot prove the page itself is genuine against an active attacker on the network.
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