fix(icmp): ICMP tunnel not working on Windows due to wildcard bind (#98)

On Windows, icmp.ListenPacket("ip4:icmp", "0.0.0.0") does not reliably
deliver ICMP packets (golang/go#38427). Add a platform-specific
ListenPacket helper that binds to a discovered interface address and
enables SIO_RCVALL via WSAIoctl for promiscuous receive.

Fixes go-gost/x#36

internal/util/icmp/listen_other.go

@@ -0,0 +1,14 @@
+//go:build !windows
+
+package icmp
+
+import (
+	"net"
+
+	"golang.org/x/net/icmp"
+)
+
+// ListenPacket listens for ICMP packets on the given network and address.
+func ListenPacket(network, address string) (net.PacketConn, error) {
+	return icmp.ListenPacket(network, address)
+}

internal/util/icmp/listen_windows.go

@@ -0,0 +1,85 @@
+//go:build windows
+
+package icmp
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"os"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/net/icmp"
+)
+
+// Windows-specific constants for WSAIoctl.
+const (
+	SIO_RCVALL = syscall.IOC_IN | syscall.IOC_VENDOR | 1
+
+	RCVALL_OFF             = 0
+	RCVALL_ON              = 1
+	RCVALL_SOCKETLEVELONLY = 2
+	RCVALL_IPLEVEL         = 3
+)
+
+// ListenPacket listens for ICMP packets on the given network and address.
+// On Windows, when the address is unspecified ("" or "0.0.0.0"/"::"), it uses
+// SIO_RCVALL to work around https://github.com/golang/go/issues/38427.
+func ListenPacket(network, address string) (net.PacketConn, error) {
+	if ip := net.ParseIP(address); ip != nil && !ip.IsUnspecified() {
+		return icmp.ListenPacket(network, address)
+	}
+
+	dialAddr, dialNetwork := probeAddr(network)
+	if dialAddr == "" {
+		return icmp.ListenPacket(network, address)
+	}
+
+	// Dial an external address to discover the correct local interface.
+	dialedConn, err := net.Dial(dialNetwork, dialAddr)
+	if err != nil {
+		return nil, fmt.Errorf("icmp: dial %s: %w", dialAddr, err)
+	}
+	localAddr := dialedConn.LocalAddr()
+	dialedConn.Close()
+
+	var socketHandle syscall.Handle
+	cfg := net.ListenConfig{
+		Control: func(network, address string, c syscall.RawConn) error {
+			return c.Control(func(s uintptr) {
+				socketHandle = syscall.Handle(s)
+			})
+		},
+	}
+
+	conn, err := cfg.ListenPacket(context.Background(), network, localAddr.String())
+	if err != nil {
+		return nil, err
+	}
+
+	// Enable promiscuous mode so the socket receives all ICMP packets,
+	// including error messages, regardless of the original destination address.
+	unused := uint32(0)
+	flag := uint32(RCVALL_IPLEVEL)
+	size := uint32(unsafe.Sizeof(flag))
+	if err := syscall.WSAIoctl(socketHandle, SIO_RCVALL, (*byte)(unsafe.Pointer(&flag)), size, nil, 0, &unused, nil, 0); err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("icmp: WSAIoctl(SIO_RCVALL): %w", os.NewSyscallError("WSAIoctl", err))
+	}
+
+	return conn, nil
+}
+
+// probeAddr returns the dial network and address to use for discovering
+// the local interface. Returns empty strings if the network is not a
+// supported ICMP type.
+func probeAddr(network string) (dialAddr, dialNetwork string) {
+	switch network {
+	case "ip4:icmp":
+		return "1.1.1.1", "ip4:icmp"
+	case "ip6:ipv6-icmp":
+		return "2001:4860:4860::8888", "ip6:ipv6-icmp"
+	}
+	return "", ""
+}