Basic platform?

Former-commit-id: 423e18edc3

dns/platform/systemd.go

@@ -0,0 +1,186 @@
+//go:build linux && !android
+
+package dns
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/netip"
+	"time"
+
+	dbus "github.com/godbus/dbus/v5"
+	"golang.org/x/sys/unix"
+)
+
+const (
+	systemdResolvedDest      = "org.freedesktop.resolve1"
+	systemdDbusObjectNode    = "/org/freedesktop/resolve1"
+	systemdDbusManagerIface  = "org.freedesktop.resolve1.Manager"
+	systemdDbusGetLinkMethod = systemdDbusManagerIface + ".GetLink"
+	systemdDbusLinkInterface = "org.freedesktop.resolve1.Link"
+	systemdDbusSetDNSMethod  = systemdDbusLinkInterface + ".SetDNS"
+	systemdDbusRevertMethod  = systemdDbusLinkInterface + ".Revert"
+)
+
+// systemdDbusDNSInput maps to (iay) dbus input for SetDNS method
+type systemdDbusDNSInput struct {
+	Family  int32
+	Address []byte
+}
+
+// SystemdResolvedDNSConfigurator manages DNS settings using systemd-resolved D-Bus API
+type SystemdResolvedDNSConfigurator struct {
+	ifaceName      string
+	dbusLinkObject dbus.ObjectPath
+	originalState  *DNSState
+}
+
+// NewSystemdResolvedDNSConfigurator creates a new systemd-resolved DNS configurator
+func NewSystemdResolvedDNSConfigurator(ifaceName string) (*SystemdResolvedDNSConfigurator, error) {
+	// Get network interface
+	iface, err := net.InterfaceByName(ifaceName)
+	if err != nil {
+		return nil, fmt.Errorf("get interface: %w", err)
+	}
+
+	// Connect to D-Bus
+	conn, err := dbus.SystemBus()
+	if err != nil {
+		return nil, fmt.Errorf("connect to system bus: %w", err)
+	}
+	defer conn.Close()
+
+	obj := conn.Object(systemdResolvedDest, systemdDbusObjectNode)
+
+	// Get the link object for this interface
+	var linkPath string
+	if err := obj.Call(systemdDbusGetLinkMethod, 0, iface.Index).Store(&linkPath); err != nil {
+		return nil, fmt.Errorf("get link: %w", err)
+	}
+
+	return &SystemdResolvedDNSConfigurator{
+		ifaceName:      ifaceName,
+		dbusLinkObject: dbus.ObjectPath(linkPath),
+	}, nil
+}
+
+// Name returns the configurator name
+func (s *SystemdResolvedDNSConfigurator) Name() string {
+	return "systemd-resolved"
+}
+
+// SetDNS sets the DNS servers and returns the original servers
+func (s *SystemdResolvedDNSConfigurator) SetDNS(servers []netip.Addr) ([]netip.Addr, error) {
+	// Get current DNS settings before overriding
+	originalServers, err := s.GetCurrentDNS()
+	if err != nil {
+		// If we can't get current DNS, proceed anyway
+		originalServers = []netip.Addr{}
+	}
+
+	// Store original state
+	s.originalState = &DNSState{
+		OriginalServers:  originalServers,
+		ConfiguratorName: s.Name(),
+	}
+
+	// Apply new DNS servers
+	if err := s.applyDNSServers(servers); err != nil {
+		return nil, fmt.Errorf("apply DNS servers: %w", err)
+	}
+
+	return originalServers, nil
+}
+
+// RestoreDNS restores the original DNS configuration
+func (s *SystemdResolvedDNSConfigurator) RestoreDNS() error {
+	// Call Revert method to restore systemd-resolved defaults
+	conn, err := dbus.SystemBus()
+	if err != nil {
+		return fmt.Errorf("connect to system bus: %w", err)
+	}
+	defer conn.Close()
+
+	obj := conn.Object(systemdResolvedDest, s.dbusLinkObject)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := obj.CallWithContext(ctx, systemdDbusRevertMethod, 0).Store(); err != nil {
+		return fmt.Errorf("revert DNS settings: %w", err)
+	}
+
+	return nil
+}
+
+// GetCurrentDNS returns the currently configured DNS servers
+// Note: systemd-resolved doesn't easily expose current per-link DNS servers via D-Bus
+// This is a placeholder that returns an empty list
+func (s *SystemdResolvedDNSConfigurator) GetCurrentDNS() ([]netip.Addr, error) {
+	// systemd-resolved's D-Bus API doesn't have a simple way to query current DNS servers
+	// We would need to parse resolvectl status output or read from /run/systemd/resolve/
+	// For now, return empty list
+	return []netip.Addr{}, nil
+}
+
+// applyDNSServers applies DNS server configuration via systemd-resolved
+func (s *SystemdResolvedDNSConfigurator) applyDNSServers(servers []netip.Addr) error {
+	if len(servers) == 0 {
+		return fmt.Errorf("no DNS servers provided")
+	}
+
+	// Convert servers to systemd-resolved format
+	var dnsInputs []systemdDbusDNSInput
+	for _, server := range servers {
+		family := unix.AF_INET
+		if server.Is6() {
+			family = unix.AF_INET6
+		}
+
+		dnsInputs = append(dnsInputs, systemdDbusDNSInput{
+			Family:  int32(family),
+			Address: server.AsSlice(),
+		})
+	}
+
+	// Connect to D-Bus
+	conn, err := dbus.SystemBus()
+	if err != nil {
+		return fmt.Errorf("connect to system bus: %w", err)
+	}
+	defer conn.Close()
+
+	obj := conn.Object(systemdResolvedDest, s.dbusLinkObject)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	// Call SetDNS method
+	if err := obj.CallWithContext(ctx, systemdDbusSetDNSMethod, 0, dnsInputs).Store(); err != nil {
+		return fmt.Errorf("set DNS servers: %w", err)
+	}
+
+	return nil
+}
+
+// IsSystemdResolvedAvailable checks if systemd-resolved is available and responsive
+func IsSystemdResolvedAvailable() bool {
+	conn, err := dbus.SystemBus()
+	if err != nil {
+		return false
+	}
+	defer conn.Close()
+
+	obj := conn.Object(systemdResolvedDest, systemdDbusObjectNode)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	// Try to ping systemd-resolved
+	if err := obj.CallWithContext(ctx, "org.freedesktop.DBus.Peer.Ping", 0).Store(); err != nil {
+		return false
+	}
+
+	return true
+}