Failover: Support v6 gateway

Useful for v6 only VPNs

5 files changed, 65 insertions, 15 deletions

diff --git a/internal/failover/monitor.go b/internal/failover/monitor.go
index 0d319d6..2c14980 100644
--- a/internal/failover/monitor.go
+++ b/internal/failover/monitor.go
@@ -51,10 +51,6 @@ func (m *DroppedConMon) dropped(startBytes int64) (bool, error) {
 // This does not check Rx bytes every tick, but rather when pAlive or pDropped is reached
 // It returns an error if there was an invalid input or a ping was failed to be sent
 func (m *DroppedConMon) Start(ctx context.Context, gateway string, mtuSize int) (bool, error) {
-	if mtuSize < mtuOverhead {
-		return false, fmt.Errorf("invalid MTU size given, MTU has to be at least: %v bytes", mtuOverhead)
-	}
-
 	// Create a ping struct with our mtu size
 	p, err := m.newPinger(gateway, mtuSize)
 	if err != nil {
diff --git a/internal/failover/monitor_test.go b/internal/failover/monitor_test.go
index 33a93a7..1b41931 100644
--- a/internal/failover/monitor_test.go
+++ b/internal/failover/monitor_test.go
@@ -108,7 +108,9 @@ func TestMonitor(t *testing.T) {
 			}
 		}
 		dcm := NewDroppedMonitor(c.interval, c.pDropped, c.readRxBytes)
-		dcm.newPinger = c.mockedPinger
+		if c.mockedPinger != nil {
+			dcm.newPinger = c.mockedPinger
+		}
 		dropped, err := dcm.Start(context.Background(), c.gateway, c.mtuSize)
 		if dropped != c.wantDropped {
 			t.Fatalf("dropped is not equal to want dropped, got: %v, want: %v", dropped, c.wantDropped)
diff --git a/internal/failover/ping.go b/internal/failover/ping.go
index 59dbcc9..b37685c 100644
--- a/internal/failover/ping.go
+++ b/internal/failover/ping.go
@@ -8,16 +8,22 @@ import (
 
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
 )
 
-// mtuOverhead defines the total MTU overhead for an ICMP ECHO message: 20 bytes IP header + 8 bytes ICMP header
-var mtuOverhead = 28
+var (
+	// mtuV4Overhead defines the total MTU overhead for an ICMP ECHO message: 20 bytes IP header + 8 bytes ICMP header
+	mtuV4Overhead = 28
+	// mtuV6Overhead defines the total MTU v6 overhead for an ICMP ECHO message: 40 bytes IP header + 8 bytes ICMP header
+	mtuV6Overhead = 48
+)
 
 // Pinger sends pings
 type Pinger struct {
 	listener net.PacketConn
 	buffer   []byte
 	gateway  net.Addr
+	v4       bool
 }
 
 // Read reads from the ping listener with deadline `deadline`
@@ -33,12 +39,18 @@ func (p Pinger) Read(deadline time.Time) error {
 	if err != nil {
 		return err
 	}
-	got, err := icmp.ParseMessage(ipv4.ICMPTypeEchoReply.Protocol(), r[:n])
+	var t icmp.Type
+	if p.v4 {
+		t = ipv4.ICMPTypeEchoReply
+	} else {
+		t = ipv6.ICMPTypeEchoReply
+	}
+	got, err := icmp.ParseMessage(t.Protocol(), r[:n])
 	if err != nil {
 		return err
 	}
 	switch got.Type {
-	case ipv4.ICMPTypeEchoReply:
+	case t:
 		return nil
 	default:
 		return fmt.Errorf("not a ping echo reply, got: %+v", got)
@@ -49,10 +61,18 @@ func (p Pinger) Read(deadline time.Time) error {
 func (p Pinger) Send(seq int) error {
 	errorMessage := fmt.Sprintf("failed sending ping, seq %d", seq)
 	// Make a new ICMP message
+	var t icmp.Type
+	if p.v4 {
+		t = ipv4.ICMPTypeEcho
+	} else {
+		t = ipv6.ICMPTypeEchoRequest
+	}
 	m := icmp.Message{
-		Type: ipv4.ICMPTypeEcho, Code: 0,
+		Type: t,
+		Code: 0,
 		Body: &icmp.Echo{
-			ID: os.Getpid() & 0xffff, Seq: seq,
+			ID:   os.Getpid() & 0xffff,
+			Seq:  seq,
 			Data: p.buffer,
 		},
 	}
diff --git a/internal/failover/ping_default.go b/internal/failover/ping_default.go
index 11401bb..181f3fc 100644
--- a/internal/failover/ping_default.go
+++ b/internal/failover/ping_default.go
@@ -11,13 +11,29 @@ import (
 
 // NewPinger creates a new pinger with gateway `gateway` and size `size`
 func NewPinger(gateway string, size int) (*Pinger, error) {
-	l, err := icmp.ListenPacket("udp4", "0.0.0.0")
+	gip := net.ParseIP(gateway)
+	isV4 := gip.To4() != nil
+	mtuOverhead := mtuV6Overhead
+	if isV4 {
+		mtuOverhead = mtuV4Overhead
+	}
+	if size < mtuOverhead {
+		return nil, fmt.Errorf("invalid MTU size given, MTU has to be at least: %v bytes", mtuOverhead)
+	}
+	var l *icmp.PacketConn
+	var err error
+	if isV4 {
+		l, err = icmp.ListenPacket("udp4", "0.0.0.0")
+	} else {
+		l, err = icmp.ListenPacket("udp6", "::")
+	}
 	if err != nil {
 		return nil, fmt.Errorf("failed creating ping with error: %w", err)
 	}
 	return &Pinger{
 		listener: l,
 		buffer:   make([]byte, size-mtuOverhead),
-		gateway:  &net.UDPAddr{IP: net.ParseIP(gateway)},
+		gateway:  &net.UDPAddr{IP: gip},
+		v4:       isV4,
 	}, nil
 }
diff --git a/internal/failover/ping_windows.go b/internal/failover/ping_windows.go
index 3f181f5..eb801d8 100644
--- a/internal/failover/ping_windows.go
+++ b/internal/failover/ping_windows.go
@@ -8,13 +8,29 @@ import (
 )
 
 func NewPinger(gateway string, size int) (*Pinger, error) {
-	l, err := icmp.ListenPacket("ip4:icmp", "0.0.0.0")
+	gip := net.ParseIP(gateway)
+	isV4 := gip.To4() != nil
+	mtuOverhead := mtuV6Overhead
+	if isV4 {
+		mtuOverhead = mtuV4Overhead
+	}
+	if size < mtuOverhead {
+		return nil, fmt.Errorf("invalid MTU size given, MTU has to be at least: %v bytes", mtuOverhead)
+	}
+	var l *icmp.PacketConn
+	var err error
+	if isV4 {
+		l, err = icmp.ListenPacket("ip4:icmp", "0.0.0.0")
+	} else {
+		l, err = icmp.ListenPacket("ip6:icmp", "::")
+	}
 	if err != nil {
 		return nil, fmt.Errorf("failed creating ping with error: %w", err)
 	}
 	return &Pinger{
 		listener: l,
 		buffer:   make([]byte, size-mtuOverhead),
-		gateway:  &net.IPAddr{IP: net.ParseIP(gateway)},
+		gateway:  &net.IPAddr{IP: gip},
+		v4:       isV4,
 	}, nil
 }