Merge pull request #3419 from Roasbeef/sign-create-key-if-not-found

lnwallet: when signing create account if not found

lnwallet/btcwallet/signer.go

@@ -83,6 +83,25 @@ func (b *BtcWallet) fetchOutputAddr(script []byte) (waddrmgr.ManagedAddress, err
 	return nil, lnwallet.ErrNotMine
 }
 
+// deriveFromKeyLoc attempts to derive a private key using a fully specified
+// KeyLocator.
+func deriveFromKeyLoc(scopedMgr *waddrmgr.ScopedKeyManager,
+	addrmgrNs walletdb.ReadWriteBucket,
+	keyLoc keychain.KeyLocator) (*btcec.PrivateKey, error) {
+
+	path := waddrmgr.DerivationPath{
+		Account: uint32(keyLoc.Family),
+		Branch:  0,
+		Index:   uint32(keyLoc.Index),
+	}
+	addr, err := scopedMgr.DeriveFromKeyPath(addrmgrNs, path)
+	if err != nil {
+		return nil, err
+	}
+
+	return addr.(waddrmgr.ManagedPubKeyAddress).PrivKey()
+}
+
 // deriveKeyByLocator attempts to derive a key stored in the wallet given a
 // valid key locator.
 func (b *BtcWallet) deriveKeyByLocator(keyLoc keychain.KeyLocator) (*btcec.PrivateKey, error) {
@@ -95,20 +114,31 @@ func (b *BtcWallet) deriveKeyByLocator(keyLoc keychain.KeyLocator) (*btcec.Priva
 	}
 
 	var key *btcec.PrivateKey
-	err = walletdb.View(b.db, func(tx walletdb.ReadTx) error {
-		addrmgrNs := tx.ReadBucket(waddrmgrNamespaceKey)
-
-		path := waddrmgr.DerivationPath{
-			Account: uint32(keyLoc.Family),
-			Branch:  0,
-			Index:   uint32(keyLoc.Index),
-		}
-		addr, err := scopedMgr.DeriveFromKeyPath(addrmgrNs, path)
-		if err != nil {
-			return err
+	err = walletdb.Update(b.db, func(tx walletdb.ReadWriteTx) error {
+		addrmgrNs := tx.ReadWriteBucket(waddrmgrNamespaceKey)
+
+		key, err = deriveFromKeyLoc(scopedMgr, addrmgrNs, keyLoc)
+		if waddrmgr.IsError(err, waddrmgr.ErrAccountNotFound) {
+			// If we've reached this point, then the account
+			// doesn't yet exist, so we'll create it now to ensure
+			// we can sign.
+			acctErr := scopedMgr.NewRawAccount(
+				addrmgrNs, uint32(keyLoc.Family),
+			)
+			if acctErr != nil {
+				return acctErr
+			}
+
+			// Now that we know the account exists, we'll attempt
+			// to re-derive the private key.
+			key, err = deriveFromKeyLoc(
+				scopedMgr, addrmgrNs, keyLoc,
+			)
+			if err != nil {
+				return err
+			}
 		}
 
-		key, err = addr.(waddrmgr.ManagedPubKeyAddress).PrivKey()
 		return err
 	})
 	if err != nil {

lnwallet/interface_test.go

@@ -2427,6 +2427,48 @@ func testCreateSimpleTx(r *rpctest.Harness, w *lnwallet.LightningWallet,
 	}
 }
 
+// testSignOutputCreateAccount tests that we're able to properly sign for an
+// output if the target account hasn't yet been created on disk. In this case,
+// we'll create the account, then sign.
+func testSignOutputCreateAccount(r *rpctest.Harness, w *lnwallet.LightningWallet,
+	_ *lnwallet.LightningWallet, t *testing.T) {
+
+	// First, we'll create a sign desc that references a non-default key
+	// family. Under the hood, key families are actually accounts, so this
+	// should force create of the account so we can sign with it.
+	fakeTx := wire.NewMsgTx(2)
+	fakeTx.AddTxIn(&wire.TxIn{
+		PreviousOutPoint: wire.OutPoint{
+			Hash:  chainhash.Hash{},
+			Index: 0,
+		},
+	})
+	signDesc := &input.SignDescriptor{
+		KeyDesc: keychain.KeyDescriptor{
+			KeyLocator: keychain.KeyLocator{
+				Family: 99,
+				Index:  1,
+			},
+		},
+		WitnessScript: []byte{},
+		Output: &wire.TxOut{
+			Value: 1000,
+		},
+		HashType:   txscript.SigHashAll,
+		SigHashes:  txscript.NewTxSigHashes(fakeTx),
+		InputIndex: 0,
+	}
+
+	// We'll now sign and expect this to succeed, as even though the
+	// account doesn't exist atm, it should be created in order to process
+	// the inbound signing request.
+	_, err := w.Cfg.Signer.SignOutputRaw(fakeTx, signDesc)
+	if err != nil {
+		t.Fatalf("unable to sign for output with non-existent "+
+			"account: %v", err)
+	}
+}
+
 type walletTestCase struct {
 	name string
 	test func(miner *rpctest.Harness, alice, bob *lnwallet.LightningWallet,
@@ -2493,6 +2535,10 @@ var walletTests = []walletTestCase{
 		name: "create simple tx",
 		test: testCreateSimpleTx,
 	},
+	{
+		name: "test sign create account",
+		test: testSignOutputCreateAccount,
+	},
 }
 
 func clearWalletStates(a, b *lnwallet.LightningWallet) error {