SnapSync

Fast, reliable LAN file transfers over TCP — with discovery, resume, and end-to-end integrity.

---

SnapSync is a LAN file transfer CLI for reliable single-file transfers over TCP with peer discovery, resume support, and end-to-end integrity checks.

Requirements

• Go 1.22+

Build

make build

Quick Start

Machine A — Receiver:

./bin/snapsync recv --out ./downloads --accept

Machine B — Sender:

./bin/snapsync list --timeout 2s
./bin/snapsync send ./20GB.iso --to <peer-id>

Commands

Command	Description
snapsync recv	Start receiver and listen for incoming transfers
snapsync send <path> --to <peer-id|host:port>	Send a file to a discovered peer
snapsync list	List active receivers on the LAN
snapsync version	Print version information

recv flags: --listen :45999 --out <dir> --accept --overwrite --no-discovery --no-resume --keep-partial --force-restart --break-lock

send flags: --to <peer-id|host:port> --timeout 2s --name <override> --no-resume

list flags: --timeout 2s --json

Features

🔍 Peer Discovery

Receivers advertise on _snapsync._tcp.local while running. snapsync list shows discovered peers with ID, name, addresses, port, and age.

✅ Integrity Verification

SnapSync verifies transfer integrity before finalizing output. Corrupted transfers fail and incomplete outputs are removed automatically.

⏸ Resume Transfers

If a transfer is interrupted, SnapSync resumes automatically. Partial transfers are stored as *.partial with a metadata sidecar *.partial.snapsync. Integrity is re-verified on completion before finalizing.

Troubleshooting

Problem	Solution
Discovery not working	Verify both hosts are on the same subnet and multicast DNS is allowed by the firewall
Connection failures	Ensure the receiver port is open and reachable
Lock busy errors	Another transfer is using the same target; retry or use --break-lock if the lock is stale
Integrity failures	Transfer was corrupted in transit or on disk; rerun send

Known Limitations

• No folder transfer yet (files only)
• No encryption / authentication yet
• Discovery is intended for same-subnet LAN environments

License

SnapSync is released under the NC-OSL v1.0 — Non-Commercial Open-Source License.

• ✅ Free to use, modify, and distribute
• ✅ Derivatives must remain open-source under the same license
• ❌ Commercial use requires a separate written license

© 2026 Pomai / Pomaieco