TUN-6695: Implement ICMP proxy for linux

ingress/origin_icmp_proxy.go

@@ -2,21 +2,43 @@ package ingress
 
 import (
 	"context"
-	"net"
+	"fmt"
+	"net/netip"
+	"time"
 
 	"github.com/rs/zerolog"
+	"golang.org/x/net/icmp"
 
 	"github.com/cloudflare/cloudflared/packet"
 )
 
+const (
+	defaultCloseAfterIdle = time.Second * 15
+	mtu                   = 1500
+)
+
+var (
+	errFlowInactive = fmt.Errorf("flow is inactive")
+	errPacketNil    = fmt.Errorf("packet is nil")
+)
+
 // ICMPProxy sends ICMP messages and listens for their responses
 type ICMPProxy interface {
+	// Serve starts listening for responses to the requests until context is done
+	Serve(ctx context.Context) error
 	// Request sends an ICMP message
 	Request(pk *packet.ICMP, responder packet.FlowResponder) error
-	// ListenResponse listens for responses to the requests until context is done
-	ListenResponse(ctx context.Context) error
 }
 
-func NewICMPProxy(listenIP net.IP, logger *zerolog.Logger) (ICMPProxy, error) {
+func NewICMPProxy(listenIP netip.Addr, logger *zerolog.Logger) (ICMPProxy, error) {
 	return newICMPProxy(listenIP, logger)
 }
+
+// Opens a non-privileged ICMP socket on Linux and Darwin
+func newICMPConn(listenIP netip.Addr) (*icmp.PacketConn, error) {
+	network := "udp6"
+	if listenIP.Is4() {
+		network = "udp4"
+	}
+	return icmp.ListenPacket(network, listenIP.String())
+}