wallet: fix imported tapscript address behavior in watch-only mode

docs/release-notes/release-notes-0.19.3.md

@@ -25,6 +25,10 @@
   messages simultaneously. The fix ensures only a single goroutine processes the
   backlog at any given time using an atomic flag.
 
+- [Fixed a bug in `btcwallet` that caused issues with Tapscript addresses being
+  imported in a watch-only (e.g. remote-signing)
+  setup](https://github.com/lightningnetwork/lnd/pull/10119).
+
 # New Features
 
 ## Functional Enhancements
@@ -71,4 +75,5 @@
 # Contributors (Alphabetical Order)
 
 * Olaoluwa Osuntokun
+* Oliver Gugger
 * Yong Yu

go.mod

@@ -11,7 +11,7 @@ require (
 	github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0
 	github.com/btcsuite/btclog v0.0.0-20241003133417-09c4e92e319c
 	github.com/btcsuite/btclog/v2 v2.0.1-0.20250728225537-6090e87c6c5b
-	github.com/btcsuite/btcwallet v0.16.14
+	github.com/btcsuite/btcwallet v0.16.15-0.20250805011126-a3632ae48ab3
 	github.com/btcsuite/btcwallet/wallet/txauthor v1.3.5
 	github.com/btcsuite/btcwallet/wallet/txrules v1.2.2
 	github.com/btcsuite/btcwallet/walletdb v1.5.1

go.sum

@@ -64,8 +64,8 @@ github.com/btcsuite/btclog v0.0.0-20241003133417-09c4e92e319c/go.mod h1:w7xnGOhw
 github.com/btcsuite/btclog/v2 v2.0.1-0.20250728225537-6090e87c6c5b h1:MQ+Q6sDy37V1wP1Yu79A5KqJutolqUGwA99UZWQDWZM=
 github.com/btcsuite/btclog/v2 v2.0.1-0.20250728225537-6090e87c6c5b/go.mod h1:XItGUfVOxotJL8kkuk2Hj3EVow5KCugXl3wWfQ6K0AE=
 github.com/btcsuite/btcutil v0.0.0-20190425235716-9e5f4b9a998d/go.mod h1:+5NJ2+qvTyV9exUAL/rxXi3DcLg2Ts+ymUAY5y4NvMg=
-github.com/btcsuite/btcwallet v0.16.14 h1:CofysgmI1ednkLsXontAdBoXJkbiim7unXnFKhLLjnE=
-github.com/btcsuite/btcwallet v0.16.14/go.mod h1:H6dfoZcWPonM2wbVsR2ZBY0PKNZKdQyLAmnX8vL9JFA=
+github.com/btcsuite/btcwallet v0.16.15-0.20250805011126-a3632ae48ab3 h1:MAjNRpj3XhCOrhchq4wq0qI34TIBX/DCnT6OLWejx68=
+github.com/btcsuite/btcwallet v0.16.15-0.20250805011126-a3632ae48ab3/go.mod h1:H6dfoZcWPonM2wbVsR2ZBY0PKNZKdQyLAmnX8vL9JFA=
 github.com/btcsuite/btcwallet/wallet/txauthor v1.3.5 h1:Rr0njWI3r341nhSPesKQ2JF+ugDSzdPoeckS75SeDZk=
 github.com/btcsuite/btcwallet/wallet/txauthor v1.3.5/go.mod h1:+tXJ3Ym0nlQc/iHSwW1qzjmPs3ev+UVWMbGgfV1OZqU=
 github.com/btcsuite/btcwallet/wallet/txrules v1.2.2 h1:YEO+Lx1ZJJAtdRrjuhXjWrYsmAk26wLTlNzxt2q0lhk=

itest/lnd_psbt_test.go

@@ -1060,6 +1060,14 @@ func testFundPsbt(ht *lntest.HarnessTest) {
 	alice := ht.NewNodeWithCoins("Alice", nil)
 	bob := ht.NewNodeWithCoins("Bob", nil)
 
+	runFundPsbt(ht, alice, bob)
+}
+
+// runFundPsbt tests the FundPsbt RPC use case where we want to fund a PSBT
+// that already has an input specified. This is a pay-join scenario where Bob
+// wants to send Alice some coins, but he wants to do so in a way that doesn't
+// reveal the full amount he is sending.
+func runFundPsbt(ht *lntest.HarnessTest, alice, bob *node.HarnessNode) {
 	// We test a pay-join between Alice and Bob. Bob wants to send Alice
 	// 5 million Satoshis in a non-obvious way. So Bob selects a UTXO that's
 	// bigger than 5 million Satoshis and expects the change minus the send

itest/lnd_remote_signer_test.go

@@ -27,6 +27,10 @@ var remoteSignerTestCases = []*lntest.TestCase{
 		Name:     "account import",
 		TestFunc: testRemoteSignerAccountImport,
 	},
+	{
+		Name:     "tapscript import",
+		TestFunc: testRemoteSignerTapscriptImport,
+	},
 	{
 		Name:     "channel open",
 		TestFunc: testRemoteSignerChannelOpen,
@@ -228,6 +232,24 @@ func testRemoteSignerAccountImport(ht *lntest.HarnessTest) {
 	tc.fn(ht, watchOnly, carol)
 }
 
+func testRemoteSignerTapscriptImport(ht *lntest.HarnessTest) {
+	tc := remoteSignerTestCase{
+		name:      "tapscript import",
+		sendCoins: true,
+		fn: func(tt *lntest.HarnessTest, wo, carol *node.HarnessNode) {
+			testTaprootImportTapscriptFullTree(ht, wo)
+			testTaprootImportTapscriptPartialReveal(ht, wo)
+			testTaprootImportTapscriptRootHashOnly(ht, wo)
+			testTaprootImportTapscriptFullKey(ht, wo)
+
+			testTaprootImportTapscriptFullKeyFundPsbt(ht, wo)
+		},
+	}
+
+	_, watchOnly, carol := prepareRemoteSignerTest(ht, tc)
+	tc.fn(ht, watchOnly, carol)
+}
+
 func testRemoteSignerChannelOpen(ht *lntest.HarnessTest) {
 	tc := remoteSignerTestCase{
 		name:      "basic channel open close",
@@ -328,6 +350,11 @@ func testRemoteSignerPSBT(ht *lntest.HarnessTest) {
 			// that aren't in the wallet. But we also want to make
 			// sure we can fund and then sign PSBTs from our wallet.
 			runFundAndSignPsbt(ht, wo)
+
+			// We also have a more specific funding test that does
+			// a pay-join payment with Carol.
+			ht.FundCoins(btcutil.SatoshiPerBitcoin, carol)
+			runFundPsbt(ht, wo, carol)
 		},
 	}
 

itest/lnd_taproot_test.go

@@ -90,6 +90,8 @@ func testTaprootImportScripts(ht *lntest.HarnessTest) {
 	testTaprootImportTapscriptPartialReveal(ht, alice)
 	testTaprootImportTapscriptRootHashOnly(ht, alice)
 	testTaprootImportTapscriptFullKey(ht, alice)
+
+	testTaprootImportTapscriptFullKeyFundPsbt(ht, alice)
 }
 
 // testTaprootSendCoinsKeySpendBip86 tests sending to and spending from
@@ -1359,6 +1361,134 @@ func testTaprootImportTapscriptFullKey(ht *lntest.HarnessTest,
 	)
 }
 
+// testTaprootImportTapscriptFullKeyFundPsbt tests importing p2tr script
+// addresses for which we only know the full Taproot key. We also test that we
+// can use such an imported script to fund a PSBT.
+func testTaprootImportTapscriptFullKeyFundPsbt(ht *lntest.HarnessTest,
+	alice *node.HarnessNode) {
+
+	// For the next step, we need a public key. Let's use a special family
+	// for this.
+	_, internalKey, derivationPath := deriveInternalKey(ht, alice)
+
+	// Let's create a taproot script output now. This is a hash lock with a
+	// simple preimage of "foobar".
+	leaf1 := testScriptHashLock(ht.T, []byte("foobar"))
+
+	tapscript := input.TapscriptFullTree(internalKey, leaf1)
+	rootHash := leaf1.TapHash()
+	taprootKey, err := tapscript.TaprootKey()
+	require.NoError(ht, err)
+
+	// Import the scripts and make sure we get the same address back as we
+	// calculated ourselves.
+	req := &walletrpc.ImportTapscriptRequest{
+		InternalPublicKey: schnorr.SerializePubKey(taprootKey),
+		Script: &walletrpc.ImportTapscriptRequest_FullKeyOnly{
+			FullKeyOnly: true,
+		},
+	}
+	importResp := alice.RPC.ImportTapscript(req)
+
+	calculatedAddr, err := btcutil.NewAddressTaproot(
+		schnorr.SerializePubKey(taprootKey), harnessNetParams,
+	)
+	require.NoError(ht, err)
+	require.Equal(ht, calculatedAddr.String(), importResp.P2TrAddress)
+
+	// Send some coins to the generated tapscript address.
+	p2trOutpoint, p2trPkScript := sendToTaprootOutput(ht, alice, taprootKey)
+
+	p2trOutputRPC := &lnrpc.OutPoint{
+		TxidBytes:   p2trOutpoint.Hash[:],
+		OutputIndex: p2trOutpoint.Index,
+	}
+	ht.AssertUTXOInWallet(alice, p2trOutputRPC, "imported")
+	ht.AssertWalletAccountBalance(alice, "imported", testAmount, 0)
+
+	// We now fund a PSBT that spends the imported tapscript address.
+	utxo := &wire.TxOut{
+		Value:    testAmount,
+		PkScript: p2trPkScript,
+	}
+	_, sweepPkScript := newAddrWithScript(
+		ht, alice, lnrpc.AddressType_WITNESS_PUBKEY_HASH,
+	)
+
+	output := &wire.TxOut{
+		PkScript: sweepPkScript,
+		Value:    1,
+	}
+	packet, err := psbt.New(
+		[]*wire.OutPoint{&p2trOutpoint}, []*wire.TxOut{output}, 2, 0,
+		[]uint32{0},
+	)
+	require.NoError(ht, err)
+
+	// We have everything we need to know to sign the PSBT.
+	in := &packet.Inputs[0]
+	in.Bip32Derivation = []*psbt.Bip32Derivation{{
+		PubKey:    internalKey.SerializeCompressed(),
+		Bip32Path: derivationPath,
+	}}
+	in.TaprootBip32Derivation = []*psbt.TaprootBip32Derivation{{
+		XOnlyPubKey: schnorr.SerializePubKey(internalKey),
+		Bip32Path:   derivationPath,
+	}}
+	in.SighashType = txscript.SigHashDefault
+	in.TaprootMerkleRoot = rootHash[:]
+	in.WitnessUtxo = utxo
+
+	var buf bytes.Buffer
+	require.NoError(ht, packet.Serialize(&buf))
+
+	change := &walletrpc.PsbtCoinSelect_ExistingOutputIndex{
+		ExistingOutputIndex: 0,
+	}
+	fundResp := alice.RPC.FundPsbt(&walletrpc.FundPsbtRequest{
+		Template: &walletrpc.FundPsbtRequest_CoinSelect{
+			CoinSelect: &walletrpc.PsbtCoinSelect{
+				Psbt:         buf.Bytes(),
+				ChangeOutput: change,
+			},
+		},
+		Fees: &walletrpc.FundPsbtRequest_SatPerVbyte{
+			SatPerVbyte: 1,
+		},
+	})
+
+	// Sign the manually funded PSBT now.
+	signResp := alice.RPC.SignPsbt(&walletrpc.SignPsbtRequest{
+		FundedPsbt: fundResp.FundedPsbt,
+	})
+
+	signedPacket, err := psbt.NewFromRawBytes(
+		bytes.NewReader(signResp.SignedPsbt), false,
+	)
+	require.NoError(ht, err)
+
+	// We should be able to finalize the PSBT and extract the sweep TX now.
+	err = psbt.MaybeFinalizeAll(signedPacket)
+	require.NoError(ht, err)
+
+	sweepTx, err := psbt.Extract(signedPacket)
+	require.NoError(ht, err)
+
+	buf.Reset()
+	err = sweepTx.Serialize(&buf)
+	require.NoError(ht, err)
+
+	// Publish the sweep transaction and then mine it as well.
+	alice.RPC.PublishTransaction(&walletrpc.Transaction{
+		TxHex: buf.Bytes(),
+	})
+
+	// Mine one block which should contain the sweep transaction.
+	block := ht.MineBlocksAndAssertNumTxes(1, 1)[0]
+	sweepTxHash := sweepTx.TxHash()
+	ht.AssertTxInBlock(block, sweepTxHash)
+}
+
 // clearWalletImportedTapscriptBalance manually assembles and then attempts to
 // sign a TX to sweep funds from an imported tapscript address.
 func clearWalletImportedTapscriptBalance(ht *lntest.HarnessTest,