QR Git Sync

Transfer git repo changes between air-gapped machines using QR codes and a webcam.

Sender displays git bundle data as cycling QR codes on screen. Receiver reads them via webcam, reconstructs the bundle, and applies it.

Prerequisites

• Python 3.6+
• Git on PATH (git --version should work from terminal/command prompt)
• Webcam (for the receiving machine)

Windows notes

• Install Git for Windows — make sure "Git from the command line" is selected during install
• Use py or python (not python3) in commands below
• If camera doesn't open, try --camera 1 or close other apps using the camera

Setup (both machines)

cd qr-git-sync
pip install -r requirements.txt

Usage

Check sync state

python qr_git_sync.py status

Send changes (machine with new commits)

python qr_git_sync.py send --repo /path/to/repo

• Displays a carousel of QR codes. Point the other machine's camera at the screen.
• Uses qr-sync-* tags for incremental transfer (only new commits since last sync).
• --full to ignore tags and send the entire repo.
• --chunk-size 400 for unreliable cameras (smaller QR = easier to read).

Receive changes (other machine)

python qr_git_sync.py receive --repo /path/to/repo

• Opens webcam and watches for QR codes.
• Shows progress bar overlay on the camera feed.
• Automatically applies the bundle when all chunks are received.

How it works

1. git bundle create packages commits into a single binary
2. Bundle is compressed (zlib) and base64-encoded
3. Payload is split into ~600-byte chunks, each becomes a QR code
4. Sender cycles through QR codes in a loop
5. Receiver collects chunks via webcam (order doesn't matter, duplicates ignored)
6. On completion: verify SHA256, decompress, apply bundle
7. Both machines get a qr-sync-<timestamp> tag for incremental sync next time

Controls

Key	Send mode	Receive mode
SPACE	Pause/resume	—
+ / =	Faster cycling	—
-	Slower cycling	—
n / →	Next QR	—
p / ←	Previous QR	—
q / ESC	Quit	Quit

Bidirectional sync

Sync is one-direction per session. For two-way:

1. Machine A sends → Machine B receives
2. B resolves any merge conflicts
3. Machine B sends → Machine A receives

The machine that receives first acts as the merge authority.

Limits

• ~600 bytes per QR code at default settings
• A 100KB bundle = ~170 QR codes ≈ 85 seconds per pass
• A 1MB bundle = ~1,700 QR codes ≈ 15 minutes per pass
• For large transfers, consider sneakernet (USB drive)