refactor: DNS

dns/transport/local/resolv_windows.go

@@ -0,0 +1,100 @@
+package local
+
+import (
+	"net"
+	"net/netip"
+	"os"
+	"syscall"
+	"time"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+func dnsReadConfig(_ string) *dnsConfig {
+	conf := &dnsConfig{
+		ndots:    1,
+		timeout:  5 * time.Second,
+		attempts: 2,
+	}
+	defer func() {
+		if len(conf.servers) == 0 {
+			conf.servers = defaultNS
+		}
+	}()
+	aas, err := adapterAddresses()
+	if err != nil {
+		return nil
+	}
+
+	for _, aa := range aas {
+		// Only take interfaces whose OperStatus is IfOperStatusUp(0x01) into DNS configs.
+		if aa.OperStatus != windows.IfOperStatusUp {
+			continue
+		}
+
+		// Only take interfaces which have at least one gateway
+		if aa.FirstGatewayAddress == nil {
+			continue
+		}
+
+		for dns := aa.FirstDnsServerAddress; dns != nil; dns = dns.Next {
+			sa, err := dns.Address.Sockaddr.Sockaddr()
+			if err != nil {
+				continue
+			}
+			var ip netip.Addr
+			switch sa := sa.(type) {
+			case *syscall.SockaddrInet4:
+				ip = netip.AddrFrom4([4]byte{sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3]})
+			case *syscall.SockaddrInet6:
+				var addr16 [16]byte
+				copy(addr16[:], sa.Addr[:])
+				if addr16[0] == 0xfe && addr16[1] == 0xc0 {
+					// fec0/10 IPv6 addresses are site local anycast DNS
+					// addresses Microsoft sets by default if no other
+					// IPv6 DNS address is set. Site local anycast is
+					// deprecated since 2004, see
+					// https://datatracker.ietf.org/doc/html/rfc3879
+					continue
+				}
+				ip = netip.AddrFrom16(addr16)
+			default:
+				// Unexpected type.
+				continue
+			}
+			conf.servers = append(conf.servers, net.JoinHostPort(ip.String(), "53"))
+		}
+	}
+	return conf
+}
+
+//go:linkname defaultNS net.defaultNS
+var defaultNS []string
+
+func adapterAddresses() ([]*windows.IpAdapterAddresses, error) {
+	var b []byte
+	l := uint32(15000) // recommended initial size
+	for {
+		b = make([]byte, l)
+		const flags = windows.GAA_FLAG_INCLUDE_PREFIX | windows.GAA_FLAG_INCLUDE_GATEWAYS
+		err := windows.GetAdaptersAddresses(syscall.AF_UNSPEC, flags, 0, (*windows.IpAdapterAddresses)(unsafe.Pointer(&b[0])), &l)
+		if err == nil {
+			if l == 0 {
+				return nil, nil
+			}
+			break
+		}
+		if err.(syscall.Errno) != syscall.ERROR_BUFFER_OVERFLOW {
+			return nil, os.NewSyscallError("getadaptersaddresses", err)
+		}
+		if l <= uint32(len(b)) {
+			return nil, os.NewSyscallError("getadaptersaddresses", err)
+		}
+	}
+	var aas []*windows.IpAdapterAddresses
+	for aa := (*windows.IpAdapterAddresses)(unsafe.Pointer(&b[0])); aa != nil; aa = aa.Next {
+		aas = append(aas, aa)
+	}
+	return aas, nil
+}