lntest/itest+lnwallet: add legacy chanrestore test

The test makes use of a nextRevocationProducer that is only used during
integration tests.

lnwallet/revocation_producer_itest.go

@@ -0,0 +1,77 @@
+// +build rpctest
+
+package lnwallet
+
+import (
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/lightningnetwork/lnd/shachain"
+)
+
+// nextRevocationProducer creates a new revocation producer, deriving the
+// revocation root by applying ECDH to a new key from our revocation root family
+// and the multisig key we use for the channel.
+func (l *LightningWallet) nextRevocationProducer(res *ChannelReservation,
+	keyRing keychain.KeyRing) (shachain.Producer, error) {
+
+	// Derive the next key in the revocation root family.
+	nextRevocationKeyDesc, err := keyRing.DeriveNextKey(
+		keychain.KeyFamilyRevocationRoot,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	// Within our itests, we want to make sure we can still restore channel
+	// backups created with the old revocation root derivation method. To
+	// create a channel in the legacy format during the test, we signal this
+	// by setting an explicit pending channel ID. The ID is the hex
+	// representation of the string "legacy-revocation".
+	itestLegacyFormatChanID := [32]byte{
+		0x6c, 0x65, 0x67, 0x61, 0x63, 0x79, 0x2d, 0x72, 0x65, 0x76,
+		0x6f, 0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e,
+	}
+	if res.pendingChanID == itestLegacyFormatChanID {
+		revocationRoot, err := l.DerivePrivKey(nextRevocationKeyDesc)
+		if err != nil {
+			return nil, err
+		}
+
+		// Once we have the root, we can then generate our shachain
+		// producer and from that generate the per-commitment point.
+		revRoot, err := chainhash.NewHash(revocationRoot.Serialize())
+		if err != nil {
+			return nil, err
+		}
+
+		return shachain.NewRevocationProducer(*revRoot), nil
+	}
+
+	// If the DeriveNextKey call returns the first key with Index 0, we need
+	// to re-derive the key as the keychain/btcwallet.go DerivePrivKey call
+	// special-cases Index 0.
+	if nextRevocationKeyDesc.Index == 0 {
+		nextRevocationKeyDesc, err = keyRing.DeriveNextKey(
+			keychain.KeyFamilyRevocationRoot,
+		)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	res.nextRevocationKeyLoc = nextRevocationKeyDesc.KeyLocator
+
+	// Perform an ECDH operation between the private key described in
+	// nextRevocationKeyDesc and our public multisig key. The result will be
+	// used to seed the revocation producer.
+	revRoot, err := l.ECDH(
+		nextRevocationKeyDesc, res.ourContribution.MultiSigKey.PubKey,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	// Once we have the root, we can then generate our shachain producer
+	// and from that generate the per-commitment point.
+	return shachain.NewRevocationProducer(revRoot), nil
+}