kitetorrent-session/io.github.yuroyami.kitetorrent.session.net/UtpSocketManager

UtpSocketManager

class UtpSocketManager(socket: UdpSocket, scope: CoroutineScope)

Demultiplexes one UDP socket across many UtpStreams: the port of libtorrent's utp_socket_manager (src/utp_socket_manager.cpp) plus the session-level routing that shares the listen socket between uTP and the DHT.

libtorrent runs uTP, the DHT and UDP trackers over the same listen socket; session_impl::on_udp_packet sniffs each datagram and hands uTP-shaped ones (incoming_packet) to the manager, which routes by connection id, turning ST_SYNs with no matching stream into new incoming connections. This class does the same:

start pumps socket; a datagram is uTP iff its first byte decodes as version == 1 with a known packet type. A bencoded DHT message starts with 'd' = 0x64, which fails that test. libtorrent discriminates the same way.
uTP datagrams are routed to the UtpStream registered under (host, port, connection-id); an unmatched ST_SYN becomes a passive open: a new stream is created, fed the SYN, and handed to onIncomingConnection.
everything else lands in the inbox behind dhtTransport, a virtual DatagramTransport the io.github.yuroyami.kitetorrent.session.dht.DhtNode consumes unchanged.

Connection-id arithmetic (see UtpStream): an active open with id I sends on I and receives on I-1; its SYN advertises I-1. The passive side derives send C/receive C+1 from the SYN's id C. Inbound routing therefore keys on the receiver's id: I-1 for streams we opened, C+1 for accepted ones.

Constructors

UtpSocketManager

constructor(socket: UdpSocket, scope: CoroutineScope)

Types

Companion

object Companion

Properties

localPort

val localPort: Int

The local UDP port (== the engine's listen port when bound there).

onIncomingConnection

var onIncomingConnection: suspend (UtpStream) -> Unit?

The manager calls this (in a fresh coroutine) for each accepted inbound uTP connection, once its SYN is processed. The engine then reads the BitTorrent handshake off the stream and routes by info-hash, exactly like a TCP accept.