Merge pull request #4806 from guggero/neutrino-tor-fix

Fix Onion v2 support for Neutrino backends

lnd.go

@@ -1508,12 +1508,43 @@ func initNeutrinoBackend(cfg *Config, chainDir string) (*neutrino.ChainService,
 		AddPeers:     cfg.NeutrinoMode.AddPeers,
 		ConnectPeers: cfg.NeutrinoMode.ConnectPeers,
 		Dialer: func(addr net.Addr) (net.Conn, error) {
+			dialAddr := addr
+			if tor.IsOnionFakeIP(addr) {
+				// Because the Neutrino address manager only
+				// knows IP addresses, we need to turn any fake
+				// tcp6 address that actually encodes an Onion
+				// v2 address back into the hostname
+				// representation before we can pass it to the
+				// dialer.
+				var err error
+				dialAddr, err = tor.FakeIPToOnionHost(addr)
+				if err != nil {
+					return nil, err
+				}
+			}
+
 			return cfg.net.Dial(
-				addr.Network(), addr.String(),
+				dialAddr.Network(), dialAddr.String(),
 				cfg.ConnectionTimeout,
 			)
 		},
 		NameResolver: func(host string) ([]net.IP, error) {
+			if tor.IsOnionHost(host) {
+				// Neutrino internally uses btcd's address
+				// manager which only operates on an IP level
+				// and does not understand onion hosts. We need
+				// to turn an onion host into a fake
+				// representation of an IP address to make it
+				// possible to connect to a block filter backend
+				// that serves on an Onion v2 hidden service.
+				fakeIP, err := tor.OnionHostToFakeIP(host)
+				if err != nil {
+					return nil, err
+				}
+
+				return []net.IP{fakeIP}, nil
+			}
+
 			addrs, err := cfg.net.LookupHost(host)
 			if err != nil {
 				return nil, err

tor/tor.go

@@ -1,6 +1,7 @@
 package tor
 
 import (
+	"bytes"
 	"crypto/rand"
 	"encoding/hex"
 	"fmt"
@@ -39,6 +40,15 @@ var (
 		22: "bad truncation",
 		23: "bad/missing server cookie",
 	}
+
+	// onionPrefixBytes is a special purpose IPv6 prefix to encode Onion v2
+	// addresses with. Because Neutrino uses the address manager of btcd
+	// which only understands net.IP addresses instead of net.Addr, we need
+	// to convert any .onion addresses into fake IPv6 addresses if we want
+	// to use a Tor hidden service as a Neutrino backend. This is the same
+	// range used by OnionCat, which is part part of the RFC4193 unique
+	// local IPv6 unicast address range.
+	onionPrefixBytes = []byte{0xfd, 0x87, 0xd8, 0x7e, 0xeb, 0x43}
 )
 
 // proxyConn is a wrapper around net.Conn that allows us to expose the actual
@@ -248,3 +258,60 @@ func IsOnionHost(host string) bool {
 
 	return true
 }
+
+// IsOnionFakeIP checks whether a given net.Addr is a fake IPv6 address that
+// encodes an Onion v2 address.
+func IsOnionFakeIP(addr net.Addr) bool {
+	_, err := FakeIPToOnionHost(addr)
+	return err == nil
+}
+
+// OnionHostToFakeIP encodes an Onion v2 address into a fake IPv6 address that
+// encodes the same information but can be used for libraries that operate on an
+// IP address base only, like btcd's address manager. For example, this will
+// turn the onion host ld47qlr6h2b7hrrf.onion into the ip6 address
+// fd87:d87e:eb43:58f9:f82e:3e3e:83f3:c625.
+func OnionHostToFakeIP(host string) (net.IP, error) {
+	if len(host) != V2Len {
+		return nil, fmt.Errorf("invalid onion v2 host: %v", host)
+	}
+
+	data, err := Base32Encoding.DecodeString(host[:V2Len-OnionSuffixLen])
+	if err != nil {
+		return nil, err
+	}
+
+	ip := make([]byte, len(onionPrefixBytes)+len(data))
+	copy(ip, onionPrefixBytes)
+	copy(ip[len(onionPrefixBytes):], data)
+	return ip, nil
+}
+
+// FakeIPToOnionHost turns a fake IPv6 address that encodes an Onion v2 address
+// back into its onion host address representation. For example, this will turn
+// the fake tcp6 address [fd87:d87e:eb43:58f9:f82e:3e3e:83f3:c625]:8333 back
+// into ld47qlr6h2b7hrrf.onion:8333.
+func FakeIPToOnionHost(fakeIP net.Addr) (net.Addr, error) {
+	tcpAddr, ok := fakeIP.(*net.TCPAddr)
+	if !ok {
+		return nil, fmt.Errorf("invalid fake onion IP address: %v",
+			fakeIP)
+	}
+
+	ip := tcpAddr.IP
+	if len(ip) != len(onionPrefixBytes)+V2DecodedLen {
+		return nil, fmt.Errorf("invalid fake onion IP address length: "+
+			"%v", fakeIP)
+	}
+
+	if !bytes.Equal(ip[:len(onionPrefixBytes)], onionPrefixBytes) {
+		return nil, fmt.Errorf("invalid fake onion IP address prefix: "+
+			"%v", fakeIP)
+	}
+
+	host := Base32Encoding.EncodeToString(ip[len(onionPrefixBytes):])
+	return &OnionAddr{
+		OnionService: host + ".onion",
+		Port:         tcpAddr.Port,
+	}, nil
+}

tor/tor_test.go

@@ -0,0 +1,36 @@
+package tor
+
+import (
+	"fmt"
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	testOnion  = "ld47qlr6h2b7hrrf.onion"
+	testFakeIP = "fd87:d87e:eb43:58f9:f82e:3e3e:83f3:c625"
+)
+
+// TestOnionHostToFakeIP tests that an onion host address can be converted into
+// a fake tcp6 address successfully.
+func TestOnionHostToFakeIP(t *testing.T) {
+	ip, err := OnionHostToFakeIP(testOnion)
+	require.NoError(t, err)
+	require.Equal(t, testFakeIP, ip.String())
+}
+
+// TestFakeIPToOnionHost tests that a fake tcp6 address can be converted back
+// into its original .onion host address successfully.
+func TestFakeIPToOnionHost(t *testing.T) {
+	tcpAddr, err := net.ResolveTCPAddr(
+		"tcp6", fmt.Sprintf("[%s]:8333", testFakeIP),
+	)
+	require.NoError(t, err)
+	require.True(t, IsOnionFakeIP(tcpAddr))
+
+	onionHost, err := FakeIPToOnionHost(tcpAddr)
+	require.NoError(t, err)
+	require.Equal(t, fmt.Sprintf("%s:8333", testOnion), onionHost.String())
+}