Simple Rust TURN (RFC 5766) client for UDP - traverse even strict NAT; async only currently

<bonus> A general-purpose TURN client/proxy, allowing to use TURN for custom things (you provide the scripts for signaling). There is a pre-built executable at Github releases.</bonus>.

Cleaned-up example snippet:

rust let udp : tokio::net::udp::UdpSocket; let c = turnclient::TurnClientBuilder::new(turn_server, username, password); let (turnsink, turnstream) = c.build_and_send_request(udp).split(); turnstream.map(move |event| { match event { MessageFromTurnServer::AllocationGranted{ relay_address, ..} => { MessageToTurnServer::AddPermission(peer_addr, ChannelUsage::WithChannel) }, MessageFromTurnServer::RecvFrom(sa,data) => { MessageToTurnServer::SendTo(sa, data) }, _ => MessageToTurnServer::Noop, } }).forward(turnsink); // run this with Tokio

See crate-level docs for further instructions.

Not implemented / TODO / cons:

• Removing permissions. They keep on getting refreshed until you close the entire allocation.
• Quadratical complexity, linear number of UDP datagrams in case of N actibe permissions.
• TCP or TLS transport.
• Using short-term credentials instead of long-term.
• "Don't fragment" specifier on sent datagrams
• Even/odd port allocation
• Error handling is ad-hoc Box<dyn std::error::Error>, with just a text strings.
• Message-integrity is not checked for server replies.
• Allocation-heavy, uses Vec<u8> for byte buffers.

Examples:

• echo.rs - Connect to specified TURN server, authorize specified peer and act as an echo server for it (snippet depicted above)
• proxy.rs - Exchange packets between a local UDP peer and TURN-mediated peer. Executes a script when allocation becomes available.