Direct channels (P2P)

Without a server there is no way for Google Drive to tell a device “something changed”: Drive’s push notifications need a public web server. So devices poll, every 30 seconds by default, and a write takes 15–30 s to show up elsewhere. That is fine for most data, but not when someone sends a mission from a phone to a robot and waits for it to move.

Direct channels fix that for devices that are online at the same time.

What happens

1. A device with P2P on writes a small “online” file to the remote.
2. Another device sees it at its next poll and writes a connection offer; the first one answers. The files carry WebRTC session descriptions and are encrypted in encrypted databases.
3. The two open a direct, encrypted WebRTC data channel. That takes 10–60 s, once.
4. From then on, right after a device uploads a segment it sends the same bytes over the channel, and the peer applies them at once.

Measured from a write until the other device sees it, over Drive:

	p50
Polling only	about 30 s
Direct channel, Mac → Android	1.1–1.9 s
Direct channel, Android → Mac	1.9 s

Most of the remaining time is the Drive upload itself, which must finish before the bytes are sent.

Turning it on

let config = Config::new("notes.db", "com.example.notes").p2p(P2pConfig::new());

db = bothy.Database.open(..., p2p=True)

final db = await Bothy.open(..., p2p: true);

bothy sync --watch --p2p

P2P runs while background sync runs. p2p_status() / p2pStatus() reports whether it is looking for devices and the state of each peer.

When there is no channel

Nothing is lost: sync goes on through Drive as before.

• Durability: the remote is always the durable record. Nothing travels over the channel before it is uploaded.
• Channel loss: a lost channel is noticed within about 20 s and retried (15 s after a failure, doubling up to 10 minutes). In tests, a phone back from a network outage reconnected within about a minute and a half.
• What blocks a channel: both devices must be online with background sync running; a phone app in the background has no channel. Strict corporate or carrier networks can block direct connections, and there is no relay server (TURN), so such devices keep polling.

STUN

To connect across networks, each device asks a STUN server for its public address. The default is Google’s public server (stun.l.google.com:19302). It learns only the device’s address, never any data. Pass an empty list (stun=[], stunServers: const [], --no-stun) to stay on the local network.

On iOS, add NSLocalNetworkUsageDescription to Info.plist; a sandboxed macOS app needs the com.apple.security.network.server entitlement.