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tailscale/net/interfaces/defaultroute_ios.go

109 lines
3.6 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
//go:build ios
package interfaces
import (
"log"
"tailscale.com/syncs"
)
var (
lastKnownDefaultRouteIfName syncs.AtomicValue[string]
)
// UpdateLastKnownDefaultRouteInterface is called by ipn-go-bridge in the iOS app when
// our NWPathMonitor instance detects a network path transition.
func UpdateLastKnownDefaultRouteInterface(ifName string) {
if ifName == "" {
return
}
if old := lastKnownDefaultRouteIfName.Swap(ifName); old != ifName {
log.Printf("defaultroute_ios: update from Swift, ifName = %s (was %s)", ifName, old)
}
}
func defaultRoute() (d DefaultRouteDetails, err error) {
// We cannot rely on the delegated interface data on iOS. The NetworkExtension framework
// seems to set the delegate interface only once, upon the *creation* of the VPN tunnel.
// If a network transition (e.g. from Wi-Fi to Cellular) happens while the tunnel is
// connected, it will be ignored and we will still try to set Wi-Fi as the default route
// because the delegated interface is not updated by the NetworkExtension framework.
//
// We work around this on the Swift side with a NWPathMonitor instance that observes
// the interface name of the first currently satisfied network path. Our Swift code will
// call into `UpdateLastKnownDefaultRouteInterface`, so we can rely on that when it is set.
//
// If for any reason the Swift machinery didn't work and we don't get any updates, here
// we also have some fallback logic: we try finding a hardcoded Wi-Fi interface called en0.
// If en0 is down, we fall back to cellular (pdp_ip0) as a last resort. This doesn't handle
// all edge cases like USB-Ethernet adapters or multiple Ethernet interfaces, but is good
// enough to ensure connectivity isn't broken.
// Start by getting all available interfaces.
interfaces, err := netInterfaces()
if err != nil {
log.Printf("defaultroute_ios: could not get interfaces: %v", err)
return d, ErrNoGatewayIndexFound
}
getInterfaceByName := func(name string) *Interface {
for _, ifc := range interfaces {
if ifc.Name != name {
continue
}
if !ifc.IsUp() {
log.Printf("defaultroute_ios: %s is down", name)
return nil
}
addrs, _ := ifc.Addrs()
if len(addrs) == 0 {
log.Printf("defaultroute_ios: %s has no addresses", name)
return nil
}
return &ifc
}
return nil
}
// Did Swift set lastKnownDefaultRouteInterface? If so, we should use it and don't bother
// with anything else. However, for sanity, do check whether Swift gave us with an interface
// that exists, is up, and has an address.
if swiftIfName := lastKnownDefaultRouteIfName.Load(); swiftIfName != "" {
ifc := getInterfaceByName(swiftIfName)
if ifc != nil {
d.InterfaceName = ifc.Name
d.InterfaceIndex = ifc.Index
return d, nil
}
}
// Start of our fallback logic if Swift didn't give us an interface name, or gave us an invalid
// one.
// We start by attempting to use the Wi-Fi interface, which on iPhone is always called en0.
enZeroIf := getInterfaceByName("en0")
if enZeroIf != nil {
log.Println("defaultroute_ios: using en0 (fallback)")
d.InterfaceName = enZeroIf.Name
d.InterfaceIndex = enZeroIf.Index
return d, nil
}
// Did it not work? Let's try with Cellular (pdp_ip0).
cellIf := getInterfaceByName("pdp_ip0")
if cellIf != nil {
log.Println("defaultroute_ios: using pdp_ip0 (fallback)")
d.InterfaceName = cellIf.Name
d.InterfaceIndex = cellIf.Index
return d, nil
}
log.Println("defaultroute_ios: no running interfaces available")
return d, ErrNoGatewayIndexFound
}