Update

vendor/tailscale.com/net/netmon/interfaces.go

@@ -0,0 +1,103 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package netmon
+
+import (
+	"errors"
+	"net"
+
+	"tailscale.com/syncs"
+)
+
+type ifProps struct {
+	mu    syncs.Mutex
+	name  string // interface name, if known/set
+	index int    // interface index, if known/set
+}
+
+// tsIfProps tracks the properties (name and index) of the tailscale interface.
+// There is only one tailscale interface per tailscaled instance.
+var tsIfProps ifProps
+
+func (p *ifProps) tsIfName() string {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.name
+}
+
+func (p *ifProps) tsIfIndex() int {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.index
+}
+
+func (p *ifProps) set(ifName string, ifIndex int) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.name = ifName
+	p.index = ifIndex
+}
+
+// TODO (barnstar): This doesn't need the Monitor receiver anymore but we're
+// keeping it for API compatibility to avoid a breaking change.  This can be
+// removed when the various clients have switched to SetTailscaleInterfaceProps
+func (m *Monitor) SetTailscaleInterfaceName(ifName string) {
+	SetTailscaleInterfaceProps(ifName, 0)
+}
+
+// SetTailscaleInterfaceProps sets the name of the Tailscale interface and
+// its index for use by various listeners/dialers.  If the index is zero,
+// an attempt will be made to look it up by name.  This makes no attempt
+// to validate that the interface exists at the time of calling.
+//
+// If this method is called, it is the responsibility of the caller to
+// update the interface name and index if they change.
+//
+// This should be called as early as possible during tailscaled startup.
+func SetTailscaleInterfaceProps(ifName string, ifIndex int) {
+	if ifIndex != 0 {
+		tsIfProps.set(ifName, ifIndex)
+		return
+	}
+
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return
+	}
+
+	for _, iface := range ifaces {
+		if iface.Name == ifName {
+			ifIndex = iface.Index
+			break
+		}
+	}
+
+	tsIfProps.set(ifName, ifIndex)
+}
+
+// TailscaleInterfaceName returns the name of the Tailscale interface.
+// For example, "tailscale0", "tun0", "utun3", etc or an error if unset.
+//
+// Callers must handle errors, as the Tailscale interface
+// name may not be set in some environments.
+func TailscaleInterfaceName() (string, error) {
+	name := tsIfProps.tsIfName()
+	if name == "" {
+		return "", errors.New("Tailscale interface name not set")
+	}
+	return name, nil
+}
+
+// TailscaleInterfaceIndex returns the index of the Tailscale interface or
+// an error if unset.
+//
+// Callers must handle errors, as the Tailscale interface
+// index may not be set in some environments.
+func TailscaleInterfaceIndex() (int, error) {
+	index := tsIfProps.tsIfIndex()
+	if index == 0 {
+		return 0, errors.New("Tailscale interface index not set")
+	}
+	return index, nil
+}