Failover: Support v6 gateway

Useful for v6 only VPNs

1 files changed, 26 insertions, 6 deletions

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,
 		},
 	}