refactor: consolidate network interface detection logic

Move platform-specific network interface detection from cmd/cli/ to root package
as ValidInterfaces function. This eliminates code duplication and provides a
consistent interface for determining valid physical network interfaces across
all platforms.

- Remove duplicate validInterfacesMap functions from platform-specific files
- Add context parameter to virtualInterfaces for proper logging
- Update all callers to use ctrld.ValidInterfaces instead of local functions
- Improve error handling in virtual interface detection on Linux

cmd/cli/dns_proxy.go

@@ -1435,7 +1435,7 @@ func (p *prog) monitorNetworkChanges(ctx context.Context) error {
 
 	mon.RegisterChangeCallback(func(delta *netmon.ChangeDelta) {
 		// Get map of valid interfaces
-		validIfaces := validInterfacesMap(ctrld.LoggerCtx(ctx, p.logger.Load()))
+		validIfaces := ctrld.ValidInterfaces(ctrld.LoggerCtx(ctx, p.logger.Load()))
 
 		isMajorChange := mon.IsMajorChangeFrom(delta.Old, delta.New)
 

cmd/cli/net_darwin.go

@@ -3,7 +3,6 @@ package cli
 import (
 	"bufio"
 	"bytes"
-	"context"
 	"io"
 	"net"
 	"os/exec"
@@ -50,28 +49,3 @@ func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bo
 	_, ok := validIfacesMap[iface.Name]
 	return ok
 }
-
-// validInterfacesMap returns a set of all valid hardware ports.
-func validInterfacesMap(ctx context.Context) map[string]struct{} {
-	b, err := exec.Command("networksetup", "-listallhardwareports").Output()
-	if err != nil {
-		return nil
-	}
-	return parseListAllHardwarePorts(bytes.NewReader(b))
-}
-
-// parseListAllHardwarePorts parses output of "networksetup -listallhardwareports"
-// and returns map presents all hardware ports.
-func parseListAllHardwarePorts(r io.Reader) map[string]struct{} {
-	m := make(map[string]struct{})
-	scanner := bufio.NewScanner(r)
-	for scanner.Scan() {
-		line := scanner.Text()
-		after, ok := strings.CutPrefix(line, "Device: ")
-		if !ok {
-			continue
-		}
-		m[after] = struct{}{}
-	}
-	return m
-}

cmd/cli/net_linux.go

@@ -1,15 +1,7 @@
 package cli
 
 import (
-	"context"
 	"net"
-	"net/netip"
-	"os"
-	"strings"
-
-	"tailscale.com/net/netmon"
-
-	"github.com/Control-D-Inc/ctrld"
 )
 
 // patchNetIfaceName patches network interface names on Linux
@@ -23,45 +15,3 @@ func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bo
 	_, ok := validIfacesMap[iface.Name]
 	return ok
 }
-
-// validInterfacesMap returns a set containing non virtual interfaces.
-// This filters out virtual interfaces to ensure DNS is only configured on physical interfaces
-func validInterfacesMap(ctx context.Context) map[string]struct{} {
-	m := make(map[string]struct{})
-	vis := virtualInterfaces(ctx)
-	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
-		if _, existed := vis[i.Name]; existed {
-			return
-		}
-		m[i.Name] = struct{}{}
-	})
-	// Fallback to the default route interface if found nothing.
-	// This ensures we always have at least one interface to configure
-	if len(m) == 0 {
-		defaultRoute, err := netmon.DefaultRoute()
-		if err != nil {
-			return m
-		}
-		m[defaultRoute.InterfaceName] = struct{}{}
-	}
-	return m
-}
-
-// virtualInterfaces returns a map of virtual interfaces on the current machine.
-// This reads from /sys/devices/virtual/net to identify virtual network interfaces
-// Virtual interfaces should not have DNS configured as they don't represent physical network connections
-func virtualInterfaces(ctx context.Context) map[string]struct{} {
-	logger := ctrld.LoggerFromCtx(ctx)
-	s := make(map[string]struct{})
-	entries, err := os.ReadDir("/sys/devices/virtual/net")
-	if err != nil {
-		logger.Error().Err(err).Msg("Failed to read /sys/devices/virtual/net")
-		return nil
-	}
-	for _, entry := range entries {
-		if entry.IsDir() {
-			s[strings.TrimSpace(entry.Name())] = struct{}{}
-		}
-	}
-	return s
-}

cmd/cli/net_others.go

@@ -3,10 +3,7 @@
 package cli
 
 import (
-	"context"
 	"net"
-
-	"tailscale.com/net/netmon"
 )
 
 // patchNetIfaceName patches network interface names on non-Linux/Darwin platforms
@@ -14,12 +11,3 @@ func patchNetIfaceName(iface *net.Interface) (bool, error) { return true, nil }
 
 // validInterface checks if an interface is valid on non-Linux/Darwin platforms
 func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bool { return true }
-
-// validInterfacesMap returns a set containing only default route interfaces.
-func validInterfacesMap(ctx context.Context) map[string]struct{} {
-	defaultRoute, err := netmon.DefaultRoute()
-	if err != nil {
-		return nil
-	}
-	return map[string]struct{}{defaultRoute.InterfaceName: {}}
-}

cmd/cli/net_windows.go

@@ -1,10 +1,7 @@
 package cli
 
 import (
-	"context"
 	"net"
-
-	"github.com/Control-D-Inc/ctrld"
 )
 
 func patchNetIfaceName(iface *net.Interface) (bool, error) {
@@ -17,12 +14,3 @@ func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bo
 	_, ok := validIfacesMap[iface.Name]
 	return ok
 }
-
-// validInterfacesMap returns a set of all physical interfaces.
-func validInterfacesMap(ctx context.Context) map[string]struct{} {
-	m := make(map[string]struct{})
-	for ifaceName := range ctrld.ValidInterfaces(ctx) {
-		m[ifaceName] = struct{}{}
-	}
-	return m
-}

cmd/cli/prog.go

@@ -1291,7 +1291,7 @@ func canBeLocalUpstream(addr string) bool {
 // the interface that matches excludeIfaceName. The context is used to clarify the
 // log message when error happens.
 func withEachPhysicalInterfaces(excludeIfaceName, contextStr string, f func(i *net.Interface) error) {
-	validIfacesMap := validInterfacesMap(ctrld.LoggerCtx(context.Background(), mainLog.Load()))
+	validIfacesMap := ctrld.ValidInterfaces(ctrld.LoggerCtx(context.Background(), mainLog.Load()))
 	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		// Skip loopback/virtual/down interface.
 		if i.IsLoopback() || len(i.HardwareAddr) == 0 {

nameservers_linux.go

@@ -24,7 +24,7 @@ func dnsFns() []dnsFn {
 	return []dnsFn{dnsFromResolvConf, dns4, dns6, dnsFromSystemdResolver}
 }
 
-func dns4(_ context.Context) []string {
+func dns4(ctx context.Context) []string {
 	f, err := os.Open(v4RouteFile)
 	if err != nil {
 		return nil
@@ -33,7 +33,7 @@ func dns4(_ context.Context) []string {
 
 	var dns []string
 	seen := make(map[string]bool)
-	vis := virtualInterfaces()
+	vis := virtualInterfaces(ctx)
 	s := bufio.NewScanner(f)
 	first := true
 	for s.Scan() {
@@ -46,7 +46,7 @@ func dns4(_ context.Context) []string {
 			continue
 		}
 		// Skip virtual interfaces.
-		if vis.contains(string(bytes.TrimSpace(fields[0]))) {
+		if _, ok := vis[string(bytes.TrimSpace(fields[0]))]; ok {
 			continue
 		}
 		gw := make([]byte, net.IPv4len)
@@ -64,7 +64,7 @@ func dns4(_ context.Context) []string {
 	return dns
 }
 
-func dns6(_ context.Context) []string {
+func dns6(ctx context.Context) []string {
 	f, err := os.Open(v6RouteFile)
 	if err != nil {
 		return nil
@@ -72,7 +72,7 @@ func dns6(_ context.Context) []string {
 	defer f.Close()
 
 	var dns []string
-	vis := virtualInterfaces()
+	vis := virtualInterfaces(ctx)
 	s := bufio.NewScanner(f)
 	for s.Scan() {
 		fields := bytes.Fields(s.Bytes())
@@ -80,7 +80,7 @@ func dns6(_ context.Context) []string {
 			continue
 		}
 		// Skip virtual interfaces.
-		if vis.contains(string(bytes.TrimSpace(fields[len(fields)-1]))) {
+		if _, ok := vis[string(bytes.TrimSpace(fields[len(fields)-1]))]; ok {
 			continue
 		}
 
@@ -110,34 +110,29 @@ func dnsFromSystemdResolver(_ context.Context) []string {
 	return ns
 }
 
-type set map[string]struct{}
-
-func (s *set) add(e string) {
-	(*s)[e] = struct{}{}
-}
-
-func (s *set) contains(e string) bool {
-	_, ok := (*s)[e]
-	return ok
-}
-
-// virtualInterfaces returns a set of virtual interfaces on current machine.
-func virtualInterfaces() set {
-	s := make(set)
-	entries, _ := os.ReadDir("/sys/devices/virtual/net")
+// virtualInterfaces returns a map of virtual interfaces on the current machine.
+// This reads from /sys/devices/virtual/net to identify virtual network interfaces
+// Virtual interfaces should not have DNS configured as they don't represent physical network connections
+func virtualInterfaces(ctx context.Context) map[string]struct{} {
+	logger := LoggerFromCtx(ctx)
+	s := make(map[string]struct{})
+	entries, err := os.ReadDir("/sys/devices/virtual/net")
+	if err != nil {
+		logger.Error().Err(err).Msg("Failed to read /sys/devices/virtual/net")
+		return nil
+	}
 	for _, entry := range entries {
 		if entry.IsDir() {
-			s.add(strings.TrimSpace(entry.Name()))
+			s[strings.TrimSpace(entry.Name())] = struct{}{}
 		}
 	}
 	return s
 }
 
-// validInterfacesMap returns a set containing non virtual interfaces.
-// TODO: deduplicated with cmd/cli/net_linux.go in v2.
-func validInterfaces() set {
+// ValidInterfaces returns a set containing non virtual interfaces.
+func ValidInterfaces(ctx context.Context) map[string]struct{} {
 	m := make(map[string]struct{})
-	vis := virtualInterfaces()
+	vis := virtualInterfaces(ctx)
 	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		if _, existed := vis[i.Name]; existed {
 			return

nameservers_linux_test.go

@@ -1,10 +1,11 @@
 package ctrld
 
 import (
+	"context"
 	"testing"
 )
 
 func Test_virtualInterfaces(t *testing.T) {
-	vis := virtualInterfaces()
+	vis := virtualInterfaces(context.Background())
 	t.Log(vis)
 }

nameservers_windows.go

@@ -444,7 +444,3 @@ func ValidInterfaces(ctx context.Context) map[string]struct{} {
 	}
 	return m
 }
-
-func validInterfaces() map[string]struct{} {
-	return ValidInterfaces(context.Background())
-}

net_darwin.go

@@ -3,14 +3,14 @@ package ctrld
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"io"
 	"os/exec"
 	"strings"
 )
 
-// validInterfaces returns a set of all valid hardware ports.
-// TODO: deduplicated with cmd/cli/net_darwin.go in v2.
-func validInterfaces() map[string]struct{} {
+// ValidInterfaces returns a set of all valid hardware ports.
+func ValidInterfaces(_ context.Context) map[string]struct{} {
 	b, err := exec.Command("networksetup", "-listallhardwareports").Output()
 	if err != nil {
 		return nil

net_others.go

@@ -2,11 +2,14 @@
 
 package ctrld
 
-import "tailscale.com/net/netmon"
+import (
+	"context"
 
-// validInterfaces returns a set containing only default route interfaces.
-// TODO: deuplicated with cmd/cli/net_others.go in v2.
-func validInterfaces() map[string]struct{} {
+	"tailscale.com/net/netmon"
+)
+
+// ValidInterfaces returns a set containing only default route interfaces.
+func ValidInterfaces(_ context.Context) map[string]struct{} {
 	defaultRoute, err := netmon.DefaultRoute()
 	if err != nil {
 		return nil

resolver.go

@@ -711,7 +711,7 @@ func newResolverWithNameserver(nameservers []string) *osResolver {
 
 // Rfc1918Addresses returns the list of local physical interfaces private IP addresses
 func Rfc1918Addresses() []string {
-	vis := validInterfaces()
+	vis := ValidInterfaces(context.Background())
 	var res []string
 	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		// Skip virtual interfaces.