multinetspeeder/transparent_edge.py

from __future__ import annotations

from pathlib import Path

import asyncio
import contextlib
import itertools
import os
import socket
import struct
from dataclasses import dataclass, field
from typing import Awaitable, Callable

from .config import Config
from .protocol import STATUS_OK, TCP_CLOSE, TCP_DATA, TCP_OPEN, TCP_STATUS, UDP_RECV, UDP_SEND, Frame, encode_json
from .relay_client import RelayConnection, RelayManager

SO_ORIGINAL_DST = 80
IP6T_SO_ORIGINAL_DST = 80
IP_RECVORIGDSTADDR = 20
IPV6_RECVORIGDSTADDR = 74


@dataclass(frozen=True)
class TargetAddress:
    host: str
    port: int
    family: int


@dataclass(frozen=True)
class PeerAddress:
    host: str
    port: int
    family: int


def parse_sockaddr(raw: bytes) -> TargetAddress:
    if len(raw) < 8:
        raise ValueError("invalid transparent destination payload")
    family = struct.unpack_from("=H", raw, 0)[0]
    port = struct.unpack_from("!H", raw, 2)[0]
    if family == socket.AF_INET:
        host = socket.inet_ntoa(raw[4:8])
        return TargetAddress(host=host, port=port, family=family)
    if family == socket.AF_INET6:
        if len(raw) < 28:
            raise ValueError("invalid IPv6 transparent destination payload")
        host = socket.inet_ntop(socket.AF_INET6, raw[8:24])
        return TargetAddress(host=host, port=port, family=family)
    raise ValueError(f"unsupported family={family}")


class BasePath:
    def __init__(self, name: str, on_frame: Callable[["BasePath", str, bytes | None], Awaitable[None]]) -> None:
        self.name = name
        self.on_frame = on_frame
        self.opened = False
        self.closed = False

    async def open(self, target: TargetAddress) -> None:
        raise NotImplementedError

    async def send(self, data: bytes) -> None:
        raise NotImplementedError

    async def close(self) -> None:
        raise NotImplementedError


class DirectTcpPath(BasePath):
    def __init__(self, name: str, on_frame: Callable[[BasePath, str, bytes | None], Awaitable[None]], open_timeout: float, happy_eyeballs_delay: float | None, tcp_nodelay: bool = True) -> None:
        super().__init__(name, on_frame)
        self.reader: asyncio.StreamReader | None = None
        self.writer: asyncio.StreamWriter | None = None
        self.pump_task: asyncio.Task | None = None
        self.open_timeout = open_timeout
        self.happy_eyeballs_delay = happy_eyeballs_delay
        self.tcp_nodelay = tcp_nodelay

    async def open(self, target: TargetAddress) -> None:
        try:
            family = socket.AF_INET6 if target.family == socket.AF_INET6 else socket.AF_INET
            kwargs = {"host": target.host, "port": target.port, "family": family}
            if self.happy_eyeballs_delay is not None:
                kwargs["happy_eyeballs_delay"] = self.happy_eyeballs_delay
            self.reader, self.writer = await asyncio.wait_for(asyncio.open_connection(**kwargs), timeout=self.open_timeout)
            sock = self.writer.get_extra_info("socket")
            if sock is not None and self.tcp_nodelay:
                with contextlib.suppress(OSError):
                    sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
            self.opened = True
            self.pump_task = asyncio.create_task(self._pump())
            await self.on_frame(self, "status", b"ok")
        except Exception as exc:
            await self.on_frame(self, "status", str(exc).encode())

    async def _pump(self) -> None:
        assert self.reader is not None
        try:
            while True:
                chunk = await self.reader.read(65536)
                if not chunk:
                    break
                await self.on_frame(self, "data", chunk)
        except Exception:
            pass
        finally:
            await self.on_frame(self, "close", None)

    async def send(self, data: bytes) -> None:
        if self.closed or self.writer is None:
            return
        self.writer.write(data)
        await self.writer.drain()

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        if self.pump_task and self.pump_task is not asyncio.current_task():
            self.pump_task.cancel()
            with contextlib.suppress(Exception):
                await self.pump_task
        if self.writer:
            self.writer.close()
            with contextlib.suppress(Exception):
                await self.writer.wait_closed()


class RelayTcpPath(BasePath):
    def __init__(self, name: str, on_frame: Callable[[BasePath, str, bytes | None], Awaitable[None]], connection: RelayConnection, session_id: int, stream_id: int) -> None:
        super().__init__(name, on_frame)
        self.connection = connection
        self.session_id = session_id
        self.stream_id = stream_id

    async def open(self, target: TargetAddress) -> None:
        if self.connection.closed:
            await self.on_frame(self, "status", b"relay unavailable")
            return
        self.connection.bind(self.session_id, self.stream_id, self._handle_frame)
        try:
            await self.connection.send(Frame(TCP_OPEN, self.session_id, self.stream_id, 0, 0, encode_json({"host": target.host, "port": target.port, "family": target.family})))
        except Exception as exc:
            await self.on_frame(self, "status", str(exc).encode())

    async def _handle_frame(self, _conn: RelayConnection, frame: Frame) -> None:
        if frame.kind == TCP_STATUS:
            if frame.packet_id == STATUS_OK:
                self.opened = True
                await self.on_frame(self, "status", b"ok")
            else:
                await self.on_frame(self, "status", frame.payload)
            return
        if frame.kind == TCP_DATA:
            await self.on_frame(self, "data", frame.payload)
            return
        if frame.kind == TCP_CLOSE:
            await self.on_frame(self, "close", None)

    async def send(self, data: bytes) -> None:
        if self.closed or self.connection.closed:
            return
        await self.connection.send(Frame(TCP_DATA, self.session_id, self.stream_id, 0, 0, data))

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        self.connection.unbind(self.session_id, self.stream_id)
        if not self.connection.closed:
            with contextlib.suppress(Exception):
                await self.connection.send(Frame(TCP_CLOSE, self.session_id, self.stream_id, 0, 0, b""))


@dataclass
class TransparentSession:
    session_id: int
    target: TargetAddress
    reader: asyncio.StreamReader
    writer: asyncio.StreamWriter
    paths: list[BasePath]
    warmup_bytes: int
    loser_grace_ms: int
    stats: dict[str, int]
    target_stats: dict[tuple[str, int], dict[str, int]]
    opened_count: int = 0
    status_count: int = 0
    errors: list[str] = field(default_factory=list)
    winner: BasePath | None = None
    uplink_bytes: int = 0
    open_event: asyncio.Event = field(default_factory=asyncio.Event)
    winner_event: asyncio.Event = field(default_factory=asyncio.Event)
    closed: bool = False
    pump_task: asyncio.Task | None = None
    loser_close_task: asyncio.Task | None = None

    def _record_win(self, winner: BasePath) -> None:
        self.stats[winner.name] = self.stats.get(winner.name, 0) + 1
        key = (self.target.host, self.target.port)
        target_stats = self.target_stats.setdefault(key, {})
        target_stats[winner.name] = target_stats.get(winner.name, 0) + 1
        direct_wins = self.stats.get("direct", 0)
        relay_wins = sum(count for name, count in self.stats.items() if name != "direct")
        target_direct = target_stats.get("direct", 0)
        target_relay = sum(count for name, count in target_stats.items() if name != "direct")
        relay_detail = ", ".join(f"{name}={count}" for name, count in sorted(self.stats.items()) if name != "direct") or "none"
        target_detail = ", ".join(f"{name}={count}" for name, count in sorted(target_stats.items()) if name != "direct") or "none"
        target_pref = "relay" if target_relay > target_direct else "direct"
        print(f"[edge] tcp win session={self.session_id} target={self.target.host}:{self.target.port} winner={winner.name} direct={direct_wins} relay={relay_wins} relay_breakdown={relay_detail} target_pref={target_pref} target_direct={target_direct} target_relay={target_relay} target_breakdown={target_detail}")

    async def start(self) -> None:
        await asyncio.gather(*(path.open(self.target) for path in self.paths), return_exceptions=True)
        await asyncio.wait_for(self.open_event.wait(), timeout=15)
        if self.opened_count == 0:
            raise ConnectionError(self.errors[0] if self.errors else "all paths failed")
        self.pump_task = asyncio.create_task(self._pump_local())

    async def _pump_local(self) -> None:
        try:
            while True:
                chunk = await self.reader.read(65536)
                if not chunk:
                    break
                self.uplink_bytes += len(chunk)
                active = [path for path in self.paths if path.opened and not path.closed]
                if not active:
                    break
                if self.uplink_bytes <= self.warmup_bytes:
                    await asyncio.gather(*(path.send(chunk) for path in active), return_exceptions=True)
                else:
                    if self.winner is None:
                        await self.winner_event.wait()
                    if self.winner:
                        await self.winner.send(chunk)
        except Exception:
            pass
        finally:
            await self.close()

    async def handle_path(self, path: BasePath, event: str, payload: bytes | None) -> None:
        if self.closed:
            return
        if event == "status":
            self.status_count += 1
            if payload == b"ok":
                self.opened_count += 1
            elif payload is not None:
                self.errors.append(payload.decode("utf-8", errors="replace"))
            if self.opened_count > 0 or self.status_count == len(self.paths):
                self.open_event.set()
            return
        if event == "data":
            if self.winner is None:
                self.winner = path
                self._record_win(path)
                self.winner_event.set()
                if self.loser_grace_ms > 0:
                    self.loser_close_task = asyncio.create_task(self._close_losers_after_grace(path))
                else:
                    await self._close_losers(path)
            if path is self.winner and payload is not None:
                self.writer.write(payload)
                await self.writer.drain()
            return
        if event == "close":
            path.closed = True
            if self.winner is None:
                remaining = [candidate for candidate in self.paths if candidate.opened and not candidate.closed]
                if not remaining:
                    await self.close()
            elif path is self.winner:
                await self.close()

    async def _close_losers(self, winner: BasePath) -> None:
        await asyncio.gather(*(path.close() for path in self.paths if path is not winner), return_exceptions=True)

    async def _close_losers_after_grace(self, winner: BasePath) -> None:
        await asyncio.sleep(self.loser_grace_ms / 1000)
        if not self.closed:
            await self._close_losers(winner)

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        print(f"[edge] session={self.session_id} closed target={self.target.host}:{self.target.port}")
        if self.pump_task and self.pump_task is not asyncio.current_task():
            self.pump_task.cancel()
            with contextlib.suppress(Exception):
                await self.pump_task
        if self.loser_close_task and self.loser_close_task is not asyncio.current_task():
            self.loser_close_task.cancel()
            with contextlib.suppress(Exception):
                await self.loser_close_task
        await asyncio.gather(*(path.close() for path in self.paths), return_exceptions=True)
        self.writer.close()
        with contextlib.suppress(Exception):
            await self.writer.wait_closed()


class DirectUdpPath(BasePath):
    def __init__(self, name: str, on_frame: Callable[[BasePath, str, bytes | None], Awaitable[None]], target: TargetAddress) -> None:
        super().__init__(name, on_frame)
        self.target = target
        self.socket: socket.socket | None = None
        self.read_task: asyncio.Task | None = None

    async def open(self, _target: TargetAddress) -> None:
        try:
            family = socket.AF_INET6 if self.target.family == socket.AF_INET6 else socket.AF_INET
            self.socket = socket.socket(family, socket.SOCK_DGRAM)
            self.socket.setblocking(False)
            await asyncio.get_running_loop().sock_connect(self.socket, (self.target.host, self.target.port))
            self.opened = True
            self.read_task = asyncio.create_task(self._pump())
            await self.on_frame(self, "status", b"ok")
        except Exception as exc:
            await self.on_frame(self, "status", str(exc).encode())

    async def _pump(self) -> None:
        assert self.socket is not None
        loop = asyncio.get_running_loop()
        try:
            while True:
                data = await loop.sock_recv(self.socket, 65535)
                if not data:
                    break
                await self.on_frame(self, "data", data)
        except Exception:
            pass
        finally:
            await self.on_frame(self, "close", None)

    async def send(self, data: bytes) -> None:
        if self.closed or self.socket is None:
            return
        await asyncio.get_running_loop().sock_sendall(self.socket, data)

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        if self.read_task and self.read_task is not asyncio.current_task():
            self.read_task.cancel()
            with contextlib.suppress(Exception):
                await self.read_task
        if self.socket:
            self.socket.close()


class RelayUdpPath(BasePath):
    def __init__(self, name: str, on_frame: Callable[[BasePath, str, bytes | None], Awaitable[None]], connection: RelayConnection, session_id: int, stream_id: int, target: TargetAddress) -> None:
        super().__init__(name, on_frame)
        self.connection = connection
        self.session_id = session_id
        self.stream_id = stream_id
        self.target = target

    async def open(self, _target: TargetAddress) -> None:
        if self.connection.closed:
            await self.on_frame(self, "status", b"relay unavailable")
            return
        self.connection.bind(self.session_id, self.stream_id, self._handle_frame)
        self.opened = True
        await self.on_frame(self, "status", b"ok")

    async def _handle_frame(self, _conn: RelayConnection, frame: Frame) -> None:
        if frame.kind == UDP_RECV:
            await self.on_frame(self, "data", frame.payload)

    async def send(self, data: bytes) -> None:
        if self.closed or self.connection.closed:
            return
        meta = encode_json({"host": self.target.host, "port": self.target.port, "family": self.target.family})
        payload = meta + data
        await self.connection.send(Frame(UDP_SEND, self.session_id, self.stream_id, 0, len(meta), payload))

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        self.connection.unbind(self.session_id, self.stream_id)


@dataclass
class UdpFlow:
    flow_id: int
    source: PeerAddress
    target: TargetAddress
    send_response: Callable[[PeerAddress, bytes], Awaitable[None]]
    paths: list[BasePath]
    winner: BasePath | None = None
    closed: bool = False
    last_activity: float = 0.0

    async def start(self) -> None:
        await asyncio.gather(*(path.open(self.target) for path in self.paths), return_exceptions=True)

    async def send(self, payload: bytes) -> None:
        self.last_activity = asyncio.get_running_loop().time()
        active = [path for path in self.paths if path.opened and not path.closed]
        if self.winner is None:
            await asyncio.gather(*(path.send(payload) for path in active), return_exceptions=True)
        elif not self.winner.closed:
            await self.winner.send(payload)

    async def handle_path(self, path: BasePath, event: str, payload: bytes | None) -> None:
        self.last_activity = asyncio.get_running_loop().time()
        if event == "data" and payload is not None:
            if self.winner is None:
                self.winner = path
                print(f"[edge] udp flow={self.flow_id} winner={path.name} target={self.target.host}:{self.target.port}")
            if path is self.winner:
                await self.send_response(self.source, payload)
        if event == "close":
            path.closed = True

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        await asyncio.gather(*(path.close() for path in self.paths), return_exceptions=True)


class TransparentUdpListener:
    def __init__(self, edge: "TransparentEdge", family: int, bind_host: str, port: int) -> None:
        self.edge = edge
        self.family = family
        self.bind_host = bind_host
        self.port = port
        self.socket: socket.socket | None = None

    def start(self) -> None:
        sock = socket.socket(self.family, socket.SOCK_DGRAM)
        sock.setblocking(False)
        if self.family == socket.AF_INET:
            sock.setsockopt(socket.SOL_IP, IP_RECVORIGDSTADDR, 1)
            sock.bind((self.bind_host, self.port))
        else:
            sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 1)
            sock.setsockopt(socket.IPPROTO_IPV6, IPV6_RECVORIGDSTADDR, 1)
            sock.bind((self.bind_host, self.port, 0, 0))
        self.socket = sock
        asyncio.get_running_loop().add_reader(sock.fileno(), self._on_readable)
        print(f"[edge] transparent udp listening on {sock.getsockname()}")

    def _on_readable(self) -> None:
        assert self.socket is not None
        try:
            data, ancdata, _flags, src = self.socket.recvmsg(65535, 512)
        except BlockingIOError:
            return
        except Exception:
            return
        original = None
        for level, ctype, cdata in ancdata:
            if self.family == socket.AF_INET and level == socket.SOL_IP and ctype == IP_RECVORIGDSTADDR:
                original = parse_sockaddr(cdata)
                break
            if self.family == socket.AF_INET6 and level == socket.IPPROTO_IPV6 and ctype == IPV6_RECVORIGDSTADDR:
                original = parse_sockaddr(cdata)
                break
        if original is None:
            return
        if self.family == socket.AF_INET:
            source = PeerAddress(host=src[0], port=src[1], family=socket.AF_INET)
        else:
            source = PeerAddress(host=src[0], port=src[1], family=socket.AF_INET6)
        if original.port == self.port and (original.host in ("127.0.0.1", "::1") or original.host == self.bind_host):
            return
        asyncio.create_task(self.edge.handle_udp_datagram(source, original, data, self))

    async def send_response(self, source: PeerAddress, payload: bytes) -> None:
        assert self.socket is not None
        if source.family == socket.AF_INET:
            self.socket.sendto(payload, (source.host, source.port))
        else:
            self.socket.sendto(payload, (source.host, source.port, 0, 0))

    async def close(self) -> None:
        if self.socket is None:
            return
        asyncio.get_running_loop().remove_reader(self.socket.fileno())
        self.socket.close()
        self.socket = None


class TransparentEdge:
    def __init__(self, listen_host: str, listen_port: int, config: Config, enable_udp: bool = False, kernel_mode: str = "auto") -> None:
        self.listen_host = listen_host
        self.listen_port = listen_port
        self.config = config
        self.enable_udp = enable_udp
        self.kernel_mode = self._resolve_kernel_mode(kernel_mode, config.kernel_mode)
        self.manager = RelayManager(config)
        self.session_ids = itertools.count(1)
        self.stream_ids = itertools.count(1)
        self.udp_listeners: list[TransparentUdpListener] = []
        self.udp_flows: dict[tuple[PeerAddress, TargetAddress], UdpFlow] = {}
        self.udp_flow_ids = itertools.count(1)
        self.udp_gc_task: asyncio.Task | None = None
        self.tcp_win_counts: dict[str, int] = {}
        self.tcp_target_wins: dict[tuple[str, int], dict[str, int]] = {}

    def _resolve_kernel_mode(self, cli_kernel_mode: str, config_kernel_mode: str) -> str:
        mode = cli_kernel_mode if cli_kernel_mode != "auto" else config_kernel_mode
        if mode != "auto":
            return mode
        try:
            if Path("/etc/os-release").exists() and 'VERSION_ID="24' in Path("/etc/os-release").read_text(errors="ignore"):
                return "24"
        except Exception:
            pass
        try:
            release = os.uname().release
            if release.startswith("6."):
                return "24"
        except Exception:
            pass
        return "20"

    async def start(self) -> None:
        if self.kernel_mode == "24":
            if self.config.direct_open_timeout == 10.0:
                self.config.direct_open_timeout = 6.0
            if self.config.relay_open_timeout == 10.0:
                self.config.relay_open_timeout = 6.0
            if self.config.tcp_connect_happy_eyeballs_delay is None:
                self.config.tcp_connect_happy_eyeballs_delay = 0.25
        await self.manager.start()
        print(f"[edge] kernel_mode={self.kernel_mode} relay snapshot: {self.manager.snapshot()}")
        server4 = await asyncio.start_server(self._accept, self.listen_host, self.listen_port, family=socket.AF_INET)
        sockets = [str(sock.getsockname()) for sock in server4.sockets or []]
        server6 = None
        if self.listen_host in ("::", "::1", "0.0.0.0", "127.0.0.1"):
            host6 = "::1" if self.listen_host == "127.0.0.1" else "::"
            try:
                server6 = await asyncio.start_server(self._accept, host6, self.listen_port, family=socket.AF_INET6)
                sockets.extend(str(sock.getsockname()) for sock in server6.sockets or [])
            except Exception as exc:
                print(f"[edge] ipv6 tcp listener skipped: {exc!r}")
        if self.enable_udp:
            self._start_udp_listeners()
        self.udp_gc_task = asyncio.create_task(self._gc_udp_flows())
        print(f"[edge] transparent tcp listening on {', '.join(sockets)}")
        if server6 is None:
            async with server4:
                await server4.serve_forever()
        else:
            async with server4, server6:
                await asyncio.gather(server4.serve_forever(), server6.serve_forever())

    def _start_udp_listeners(self) -> None:
        binds = []
        if self.listen_host == "127.0.0.1":
            binds = [(socket.AF_INET, "127.0.0.1"), (socket.AF_INET6, "::1")]
        elif self.listen_host == "0.0.0.0":
            binds = [(socket.AF_INET, "0.0.0.0"), (socket.AF_INET6, "::")]
        else:
            family = socket.AF_INET6 if ":" in self.listen_host else socket.AF_INET
            binds = [(family, self.listen_host)]
        for family, host in binds:
            try:
                listener = TransparentUdpListener(self, family, host, self.listen_port)
                listener.start()
                self.udp_listeners.append(listener)
            except Exception as exc:
                print(f"[edge] udp listener skipped family={family} host={host} error={exc!r}")

    async def _accept(self, reader: asyncio.StreamReader, writer: asyncio.StreamWriter) -> None:
        peer = writer.get_extra_info("peername")
        try:
            target = self._get_original_dst(writer)
            session_id = next(self.session_ids)
            session = TransparentSession(session_id=session_id, target=target, reader=reader, writer=writer, paths=[], warmup_bytes=self.config.tcp_warmup_bytes, loser_grace_ms=self.config.tcp_loser_grace_ms, stats=self.tcp_win_counts, target_stats=self.tcp_target_wins)
            paths: list[BasePath] = [DirectTcpPath(name="direct", on_frame=lambda path, event, payload, s=session: self._handle_tcp_session(s, path, event, payload), open_timeout=self.config.direct_open_timeout, happy_eyeballs_delay=self.config.tcp_connect_happy_eyeballs_delay, tcp_nodelay=self.config.relay_tcp_nodelay)]
            for connection in self.manager.available():
                stream_id = next(self.stream_ids)
                paths.append(RelayTcpPath(name=connection.node.name, on_frame=lambda path, event, payload, s=session: self._handle_tcp_session(s, path, event, payload), connection=connection, session_id=session_id, stream_id=stream_id))
            session.paths = paths
            print(f"[edge] accept peer={peer} session={session_id} target={target.host}:{target.port} candidates={[path.name for path in paths]}")
            await session.start()
        except Exception as exc:
            print(f"[edge] accept failed peer={peer} error={exc!r}")
            writer.close()
            with contextlib.suppress(Exception):
                await writer.wait_closed()

    async def _handle_tcp_session(self, session: TransparentSession, path: BasePath, event: str, payload: bytes | None) -> None:
        await session.handle_path(path, event, payload)

    def _get_original_dst(self, writer: asyncio.StreamWriter) -> TargetAddress:
        sock = writer.get_extra_info("socket")
        if sock is None:
            raise RuntimeError("socket unavailable")
        family = sock.family
        if family == socket.AF_INET:
            raw = sock.getsockopt(socket.SOL_IP, SO_ORIGINAL_DST, 16)
            return parse_sockaddr(raw)
        if family == socket.AF_INET6:
            raw = sock.getsockopt(socket.IPPROTO_IPV6, IP6T_SO_ORIGINAL_DST, 128)
            return parse_sockaddr(raw)
        raise RuntimeError(f"unsupported socket family={family}")

    async def handle_udp_datagram(self, source: PeerAddress, target: TargetAddress, payload: bytes, listener: TransparentUdpListener) -> None:
        if not self.enable_udp:
            return
        if target.port == self.listen_port and target.host in ("127.0.0.1", "::1", self.listen_host):
            return
        key = (source, target)
        flow = self.udp_flows.get(key)
        if flow is None:
            flow_id = next(self.udp_flow_ids)
            paths: list[BasePath] = [DirectUdpPath(name="direct", on_frame=lambda path, event, data, fid=flow_id: self._handle_udp_path(fid, path, event, data), target=target)]
            for connection in self.manager.available():
                stream_id = next(self.stream_ids)
                paths.append(RelayUdpPath(name=connection.node.name, on_frame=lambda path, event, data, fid=flow_id: self._handle_udp_path(fid, path, event, data), connection=connection, session_id=flow_id, stream_id=stream_id, target=target))
            flow = UdpFlow(flow_id=flow_id, source=source, target=target, send_response=listener.send_response, paths=paths)
            self.udp_flows[key] = flow
            print(f"[edge] udp flow={flow_id} target={target.host}:{target.port} candidates={[path.name for path in paths]}")
            await flow.start()
        await flow.send(payload)

    async def _handle_udp_path(self, flow_id: int, path: BasePath, event: str, payload: bytes | None) -> None:
        for flow in list(self.udp_flows.values()):
            if flow.flow_id == flow_id:
                await flow.handle_path(path, event, payload)
                break

    async def _gc_udp_flows(self) -> None:
        loop = asyncio.get_running_loop()
        while True:
            await asyncio.sleep(30)
            now = loop.time()
            stale = [key for key, flow in self.udp_flows.items() if flow.last_activity and now - flow.last_activity > 120]
            for key in stale:
                flow = self.udp_flows.pop(key, None)
                if flow:
                    await flow.close()