Add dns transports

dns/transport_local.go

@@ -0,0 +1,79 @@
+package dns
+
+import (
+	"context"
+	"net"
+	"net/netip"
+	"os"
+	"sort"
+
+	"github.com/sagernet/sing/common"
+
+	C "github.com/sagernet/sing-box/constant"
+
+	"golang.org/x/net/dns/dnsmessage"
+)
+
+var LocalTransportConstructor func() Transport
+
+func NewLocalTransport() Transport {
+	if LocalTransportConstructor != nil {
+		return LocalTransportConstructor()
+	}
+	return &LocalTransport{}
+}
+
+var _ Transport = (*LocalTransport)(nil)
+
+type LocalTransport struct {
+	resolver net.Resolver
+}
+
+func (t *LocalTransport) Start() error {
+	return nil
+}
+
+func (t *LocalTransport) Close() error {
+	return nil
+}
+
+func (t *LocalTransport) Raw() bool {
+	return false
+}
+
+func (t *LocalTransport) Exchange(ctx context.Context, message *dnsmessage.Message) (*dnsmessage.Message, error) {
+	return nil, os.ErrInvalid
+}
+
+func (t *LocalTransport) Lookup(ctx context.Context, domain string, strategy C.DomainStrategy) ([]netip.Addr, error) {
+	var network string
+	switch strategy {
+	case C.DomainStrategyAsIS, C.DomainStrategyPreferIPv4, C.DomainStrategyPreferIPv6:
+		network = "ip"
+	case C.DomainStrategyUseIPv4:
+		network = "ip4"
+	case C.DomainStrategyUseIPv6:
+		network = "ip6"
+	}
+	addrs, err := t.resolver.LookupNetIP(ctx, network, domain)
+	if err != nil {
+		return nil, err
+	}
+	addrs = common.Map(addrs, func(it netip.Addr) netip.Addr {
+		if it.Is4In6() {
+			return netip.AddrFrom4(it.As4())
+		}
+		return it
+	})
+	switch strategy {
+	case C.DomainStrategyPreferIPv4:
+		sort.Slice(addrs, func(i, j int) bool {
+			return addrs[i].Is4() && addrs[j].Is6()
+		})
+	case C.DomainStrategyPreferIPv6:
+		sort.Slice(addrs, func(i, j int) bool {
+			return addrs[i].Is6() && addrs[j].Is4()
+		})
+	}
+	return addrs, nil
+}