lnwallet: initialize first 255 accounts

This fixes lightninglabs/loop#437 by adding all accounts that are used
in liquidity products such as Loop or Pool. Since both of these products
use key families below 255, we can get by with that number.
The alternative to creating way too many accounts (which increases the
default wallet size by ~250kB) would be to hard code the exact accounts
used by Loop (99) and Pool (210). But that sounds like a bad idea given
that there could always be more accounts being added to those (or other)
products. By making sure the first 255 accounts exist, we have a lot
more flexibility in those products for choosing key families.

lntest/itest/lnd_remote_signer_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"github.com/btcsuite/btcutil"
+	"github.com/btcsuite/btcutil/hdkeychain"
 	"github.com/btcsuite/btcwallet/waddrmgr"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lnrpc"
@@ -39,76 +40,6 @@ var (
 		Xpub: "tpubDDWAWrSLRSFrG1KdqXMQQyTKYGSKLKaY7gxpvK7RdV3e3Dkhvu" +
 			"W2GgsFvsPN4RGmuoYtUgZ1LHZE8oftz7T4mzc1BxGt5rt8zJcVQi" +
 			"KTPPV",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyMultiSig),
-		Xpub: "tpubDDXFHr67Ro2tHKVWG2gNjjijKUH1Lyv5NKFYdJnuaLGVNBVwyV" +
-			"5AbykhR43iy8wYozEMbw2QfmAqZhb8gnuL5mm9sZh8YsR6FjGAbe" +
-			"w1xoT",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyRevocationBase),
-		Xpub: "tpubDDXFHr67Ro2tKkccDqNfDqZpd5wCs2n6XRV2Uh185DzCTbkDaE" +
-			"d9v7P837zZTYBNVfaRriuxgGVgxbGjDui4CKxyzBzwz4aAZxjn2P" +
-			"hNcQy",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyHtlcBase),
-		Xpub: "tpubDDXFHr67Ro2tNH4KH41i4oTsWfRjFigoH1Ee7urvHow51opH9x" +
-			"J7mu1qSPMPVtkVqQZ5tE4NTuFJPrbDqno7TQietyUDmPTwyVviJb" +
-			"GCwXk",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyPaymentBase),
-		Xpub: "tpubDDXFHr67Ro2tQj5Zvav2ALhkU6dRQAhEtNPnYJVBC8hs2U1A9e" +
-			"cqxRY3XTiJKBDD7e8tudhmTRs8aGWJAiAXJN5kXy3Hi6cmiwGWjX" +
-			"K5Cv5",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyDelayBase),
-		Xpub: "tpubDDXFHr67Ro2tSSR2LLBJtotxx2U45cuESLWKA72YT9td3SzVKH" +
-			"AptzDEx5chsUNZ4WRMY5h6HJxRSebjRatxQKX1uUsux1LvKS1wsf" +
-			"NJ2PH",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyRevocationRoot),
-		Xpub: "tpubDDXFHr67Ro2tTwzfWvNoMoPpZbxdMEfe1WhbXJxvXikGixPa4g" +
-			"gSRZeGx6T5yxVHTVT3rjVh35Veqsowj7emX8SZfXKDKDKcLduXCe" +
-			"WPUU3",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyNodeKey),
-		Xpub: "tpubDDXFHr67Ro2tYEDS2EByRedfsUoEwBtrzVbS1qdPrX6sAkUYGL" +
-			"rZWvMmQv8KZDZ4zd9r8WzM9bJ2nGp7XuNVC4w2EBtWg7i76gbrmu" +
-			"EWjQh",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyStaticBackup),
-		Xpub: "tpubDDXFHr67Ro2tYpwnFJEQaM8eAPM2UV5uY6gFgXeSzS5aC5T9Tf" +
-			"zXuawYKBbQMZJn8qHXLafY4tAutoda1aKP5h6Nbgy3swPbnhWbFj" +
-			"S5wnX",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyTowerSession),
-		Xpub: "tpubDDXFHr67Ro2tddKpAjUegXqt7EGxRXnHkeLbUkfuFMGbLJYgRp" +
-			"G4ew5pMmGg2nmcGmHFQ29w3juNhd8N5ZZ8HwJdymC4f5ukQLJ4yg" +
-			"9rEr3",
-	}, {
-		Purpose:  keychain.BIP0043Purpose,
-		CoinType: harnessNetParams.HDCoinType,
-		Account:  uint32(keychain.KeyFamilyTowerID),
-		Xpub: "tpubDDXFHr67Ro2tgE89V8ZdgMytC2Jq1iT9ttGhdzR1X7haQJNBmX" +
-			"t8kau6taC6DGASYzbrjmo9z9w6JQFcaLNqbhS2h2PVSzKf79j265" +
-			"Zi8hF",
 	}}
 )
 
@@ -181,7 +112,7 @@ func testRemoteSigner(net *lntest.NetworkHarness, t *harnessTest) {
 		password := []byte("itestpassword")
 		var (
 			signerNodePubKey  = nodePubKey
-			watchOnlyAccounts = accounts
+			watchOnlyAccounts = deriveCustomScopeAccounts(t.t)
 			signer            *lntest.HarnessNode
 			err               error
 		)
@@ -261,3 +192,55 @@ func testRemoteSigner(net *lntest.NetworkHarness, t *harnessTest) {
 		}
 	}
 }
+
+// deriveCustomScopeAccounts derives the first 255 default accounts of the custom lnd
+// internal key scope.
+func deriveCustomScopeAccounts(t *testing.T) []*lnrpc.WatchOnlyAccount {
+	allAccounts := make([]*lnrpc.WatchOnlyAccount, 0, 255+len(accounts))
+	allAccounts = append(allAccounts, accounts...)
+
+	extendedRootKey, err := hdkeychain.NewKeyFromString(rootKey)
+	require.NoError(t, err)
+
+	path := []uint32{
+		keychain.BIP0043Purpose + hdkeychain.HardenedKeyStart,
+		harnessNetParams.HDCoinType + hdkeychain.HardenedKeyStart,
+	}
+	coinTypeKey, err := derivePath(extendedRootKey, path)
+	require.NoError(t, err)
+	for idx := uint32(0); idx <= 255; idx++ {
+		accountPath := []uint32{idx + hdkeychain.HardenedKeyStart}
+		accountKey, err := derivePath(coinTypeKey, accountPath)
+		require.NoError(t, err)
+
+		accountXPub, err := accountKey.Neuter()
+		require.NoError(t, err)
+
+		allAccounts = append(allAccounts, &lnrpc.WatchOnlyAccount{
+			Purpose:  keychain.BIP0043Purpose,
+			CoinType: harnessNetParams.HDCoinType,
+			Account:  idx,
+			Xpub:     accountXPub.String(),
+		})
+	}
+
+	return allAccounts
+}
+
+// derivePath derives the given path from an extended key.
+func derivePath(key *hdkeychain.ExtendedKey, path []uint32) (
+	*hdkeychain.ExtendedKey, error) {
+
+	var (
+		currentKey = key
+		err        error
+	)
+	for _, pathPart := range path {
+		currentKey, err = currentKey.Derive(pathPart)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return currentKey, nil
+}