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Share the darwin route-based monitor and auto-route range building logic with FreeBSD, which uses the same AF_ROUTE and FetchRIB primitives.
Add /dev/tun based NativeTun for FreeBSD: - Clone device setup via TUNSIFHEAD/TUNSIFMODE/TUNSIFPID ioctls - Set TUNSTRANSIENT (FreeBSD 15+) for lifecycle cleanup on close - IPv4/IPv6 address assignment with NODAD and link-local scope handling - Auto route via AF_ROUTE route messages in the default FIB - Loop prevention: a dedicated FIB (iproute2_table_index) holds a copy of the real default gateway, so outbound sockets bound to that FIB never match the capture routes - gVisor link endpoint with self-address reflection
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Summary
This PR adds native FreeBSD TUN device and routing support to
sing-tun.Key Design & Implementation Details:
Device Management (
tun_freebsd.go):/dev/tunclone device, discovers the assigned interface name viaTUNGIFNAME, and sets flags withTUNSIFHEAD(4-byte packet information header),TUNSIFMODE(IFF_BROADCAST|IFF_MULTICAST), andTUNSIFPID.TUNSTRANSIENTso the device is automatically destroyed upon closing the descriptor, surviving evenSIGKILL. On FreeBSD 12–14, best-effortSIOCIFDESTROYcleanup is performed onClose().SIOCSIFNAME), safely skipping rename if the clone device already matches the requested name (avoidingEEXIST).SIOCAIFADDRandSIOCAIFADDR_IN6withIN6_IFF_NODADflag and sets ND6 flags to suppress automatic link-local generation. Link-local IPv6 default gateways are embedded with interface scope.Loop Prevention via FIB Isolation (
FIB 2022):SO_BINDTODEVICE/fwmarkand macOS's scoped routing (IP_BOUND_IF). Instead, FreeBSD natively provides per-socket routing table selection viaSO_SETFIB.auto_route) are installed into default FIB 0 via AF_ROUTE routing sockets.route.FetchRIBand replicated into a dedicated FIB (iproute2_table_index, default 2022). Outbound dialer sockets in sing-box are marked withSO_SETFIB=2022, ensuring outbound traffic never loops back into the tun capture routes.gVisor Link Endpoint (
tun_freebsd_gvisor.go):LinkEndpointfor FreeBSD with self-address reflection (packets directed to the tun interface's own IP are reflected back).Network Monitoring (
monitor_route_bsd.go):AF_ROUTEandFetchRIBroute change monitor with FreeBSD under build tagdarwin || freebsd.Test Plan
go build ./...across:GOOS=freebsd GOARCH=amd64GOOS=freebsd GOARCH=arm64GOOS=linux GOARCH=amd64GOOS=darwin GOARCH=arm64go vet ./...passes without warnings.net.fibs > 1,net.add_addr_allfibs=1): verified zero loopback, CPU idle, successful traffic capture and outbound dialing.