Two cans and a string. tincan: serverless peer-to-peer voice chat for your terminal

DIRECT18ms

Open a room, hand out two words.

The first person to run tincan opens the room. It prints a room name and a passphrase, and that is all anyone else needs: two things short enough to read down the phone.

$ tincan host lobby --name alice
room:        lobby
passphrase:  chestnut-ferry-lens-moss

$ tincan join lobby --name bob
passphrase: ••••••••••••••••••••••••

Leave the room name out and you get a 63-character invite code instead: the host's public key, already on your clipboard. No accounts, no port forwarding, no VPN.

DIRECT18ms

Voice goes straight between you.

Whoever opens the room keeps the roster, the channels and the chat, which comes to a few hundred bytes a second. Voice never goes through them. Everyone in a channel sends Opus packets directly to everyone else as QUIC datagrams, so the host's connection is never the bottleneck.

        alice (host)
        /    |    \
     bob   carol   dave
        \____|____/

A six-person room needs about 160 kbps of upload each.

DIRECT18ms

The passphrase never goes over the wire.

Both sides stretch it with Argon2id into an admission key. The host sends a fresh nonce; the guest answers with a keyed BLAKE2b MAC of it. An answer caught in transit is useless on the next connection, and nobody can make the host burn Argon2 work by knocking.

The passphrase decides who gets in. Keeping what is said private is QUIC's job: every connection is encrypted end to end, and each side is checked against its public key.

RELAY84ms

When the direct path fails, the string sags.

Two machines behind routers usually punch through to each other. When they can't, the traffic goes through a relay. The relay forwards packets it has no key for. It can see which two keys are talking, when and how much, but never what is said.

In tincan, the line between the channel list and the chat behaves like the one on this page. It runs taut │ when everyone is reached directly, sags ╎ through a relay, and frays ┆ when audio starts dropping. While someone talks, a pulse runs down it at the speed of the round trip, so you see a slow link before you read about it.

CHOPPY84ms

What it can't do without.

Serverless means there is no tincan server: no account, no room registry, and no copy of your conversation anywhere but on the machines having it. It doesn't mean no infrastructure. Peers find each other through the DNS and relays run by Number Zero, the company behind iroh. If those went away, new connections would stop working. Pointing tincan at your own relay is issue #136.

Being reachable also means being found. Everyone in a room learns everyone else's IP address. With a real tin-can phone, the other end knows where you are too.

DIRECT18ms

Recorded, not rendered.

The terminal at the top of this page is an imitation written for it. This is tincan itself, recorded in a real terminal.

DIRECT18ms

When Discord is blocked.

When Discord is blocked in your country, down for everyone, or filtered on a school or office network, tincan has nothing of its own to take down with it. There is no tincan domain or server address for a provider to blacklist: peers find each other through iroh's discovery service and talk directly over encrypted QUIC. A network that blocks those services, or all UDP, stops it too.