wallet: add dry run implementation of ImportAccount

This method returns the first N external and internal addresses, which
can be presented to users to confirm whether the account has been
imported correctly.

waddrmgr/scoped_manager.go

@@ -2270,3 +2270,11 @@ func (s *ScopedKeyManager) cloneKeyWithVersion(key *hdkeychain.ExtendedKey) (
 
 	return key.CloneWithVersion(versionBytes[:])
 }
+
+// InvalidateAccountCache invalidates the cache for the given account, forcing a
+// database read to retrieve the account information.
+func (s *ScopedKeyManager) InvalidateAccountCache(account uint32) {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+	delete(s.acctInfo, account)
+}

wallet/import.go

@@ -192,6 +192,24 @@ func (w *Wallet) ImportAccount(name string, accountPubKey *hdkeychain.ExtendedKe
 	masterKeyFingerprint uint32, addrType *waddrmgr.AddressType) (
 	*waddrmgr.AccountProperties, error) {
 
+	var accountProps *waddrmgr.AccountProperties
+	err := walletdb.Update(w.db, func(tx walletdb.ReadWriteTx) error {
+		ns := tx.ReadWriteBucket(waddrmgrNamespaceKey)
+		var err error
+		accountProps, err = w.importAccount(
+			ns, name, accountPubKey, masterKeyFingerprint, addrType,
+		)
+		return err
+	})
+	return accountProps, err
+}
+
+// importAccount is the internal implementation of ImportAccount -- one should
+// reference its documentation for this method.
+func (w *Wallet) importAccount(ns walletdb.ReadWriteBucket, name string,
+	accountPubKey *hdkeychain.ExtendedKey, masterKeyFingerprint uint32,
+	addrType *waddrmgr.AddressType) (*waddrmgr.AccountProperties, error) {
+
 	// Ensure we have a valid account public key.
 	if err := w.validateExtendedPubKey(accountPubKey, true); err != nil {
 		return nil, err
@@ -208,21 +226,80 @@ func (w *Wallet) ImportAccount(name string, accountPubKey *hdkeychain.ExtendedKe
 		return nil, err
 	}
 
-	// Store the account as watch-only within the database.
-	var accountProps *waddrmgr.AccountProperties
-	err = walletdb.Update(w.db, func(tx walletdb.ReadWriteTx) error {
-		ns := tx.ReadWriteBucket(waddrmgrNamespaceKey)
 	account, err := scopedMgr.NewAccountWatchingOnly(
-			ns, name, accountPubKey, masterKeyFingerprint,
-			addrSchema,
+		ns, name, accountPubKey, masterKeyFingerprint, addrSchema,
 	)
 	if err != nil {
-			return err
+		return nil, err
 	}
-		accountProps, err = scopedMgr.AccountProperties(ns, account)
-		return err
-	})
-	return accountProps, err
+	return scopedMgr.AccountProperties(ns, account)
+}
+
+// ImportAccountDryRun serves as a dry run implementation of ImportAccount. This
+// method also returns the first N external and internal addresses, which can be
+// presented to users to confirm whether the account has been imported
+// correctly.
+func (w *Wallet) ImportAccountDryRun(name string,
+	accountPubKey *hdkeychain.ExtendedKey, masterKeyFingerprint uint32,
+	addrType *waddrmgr.AddressType, numAddrs uint32) (
+	*waddrmgr.AccountProperties, []waddrmgr.ManagedAddress,
+	[]waddrmgr.ManagedAddress, error) {
+
+	// Start a database transaction that we'll never commit and always
+	// rollback.
+	tx, err := w.db.BeginReadWriteTx()
+	if err != nil {
+		return nil, nil, nil, err
+	}
+	defer func() {
+		_ = tx.Rollback()
+	}()
+	ns := tx.ReadWriteBucket(waddrmgrNamespaceKey)
+
+	// Import the account as usual.
+	accountProps, err := w.importAccount(
+		ns, name, accountPubKey, masterKeyFingerprint, addrType,
+	)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+
+	// Derive the external and internal addresses. Note that we could do
+	// this based on the provided accountPubKey alone, but we go through the
+	// ScopedKeyManager instead to ensure addresses will be derived as
+	// expected from the wallet's point-of-view.
+	manager, err := w.Manager.FetchScopedKeyManager(accountProps.KeyScope)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+
+	// The importAccount method above will cache the imported account within
+	// the scoped manager. Since this is a dry-run attempt, we'll want to
+	// invalidate the cache for it.
+	defer manager.InvalidateAccountCache(accountProps.AccountNumber)
+
+	externalAddrs, err := manager.NextExternalAddresses(
+		ns, accountProps.AccountNumber, numAddrs,
+	)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+	internalAddrs, err := manager.NextInternalAddresses(
+		ns, accountProps.AccountNumber, numAddrs,
+	)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+
+	// Refresh the account's properties after generating the addresses.
+	accountProps, err = manager.AccountProperties(
+		ns, accountProps.AccountNumber,
+	)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+
+	return accountProps, externalAddrs, internalAddrs, nil
 }
 
 // ImportPublicKey imports a single derived public key into the address manager.

wallet/import_test.go

@@ -178,6 +178,17 @@ func testImportAccount(t *testing.T, w *Wallet, tc *testCase, watchOnly bool,
 	acct3ExternalPub, err := acct3ExternalExtPub.ECPubKey()
 	require.NoError(t, err)
 
+	// Do a dry run import first and check that it results in the expected
+	// addresses being derived.
+	_, extAddrs, intAddrs, err := w.ImportAccountDryRun(
+		name+"1", acct1Pub, root.ParentFingerprint(), &tc.addrType, 1,
+	)
+	require.NoError(t, err)
+	require.Len(t, extAddrs, 1)
+	require.Equal(t, tc.expectedAddr, extAddrs[0].Address().String())
+	require.Len(t, intAddrs, 1)
+	require.Equal(t, tc.expectedChangeAddr, intAddrs[0].Address().String())
+
 	// Import the extended public keys into new accounts.
 	acct1, err := w.ImportAccount(
 		name+"1", acct1Pub, root.ParentFingerprint(), &tc.addrType,
@@ -228,12 +239,12 @@ func testImportAccount(t *testing.T, w *Wallet, tc *testCase, watchOnly bool,
 	require.Equal(t, uint32(0), acct2.ImportedKeyCount)
 
 	// Test address derivation.
-	addr, err := w.NewAddress(acct1.AccountNumber, tc.expectedScope)
+	extAddr, err := w.NewAddress(acct1.AccountNumber, tc.expectedScope)
 	require.NoError(t, err)
-	require.Equal(t, tc.expectedAddr, addr.String())
-	addr, err = w.NewChangeAddress(acct1.AccountNumber, tc.expectedScope)
+	require.Equal(t, tc.expectedAddr, extAddr.String())
+	intAddr, err := w.NewChangeAddress(acct1.AccountNumber, tc.expectedScope)
 	require.NoError(t, err)
-	require.Equal(t, tc.expectedChangeAddr, addr.String())
+	require.Equal(t, tc.expectedChangeAddr, intAddr.String())
 
 	// Make sure the key count was increased.
 	acct1, err = w.AccountProperties(tc.expectedScope, acct1.AccountNumber)
@@ -243,7 +254,7 @@ func testImportAccount(t *testing.T, w *Wallet, tc *testCase, watchOnly bool,
 	require.Equal(t, uint32(0), acct1.ImportedKeyCount)
 
 	// Make sure we can't get private keys for the imported accounts.
-	_, err = w.DumpWIFPrivateKey(addr)
+	_, err = w.DumpWIFPrivateKey(intAddr)
 	require.True(t, waddrmgr.IsError(err, waddrmgr.ErrWatchingOnly))
 
 	// Get the address info for the single key we imported.
@@ -258,13 +269,13 @@ func testImportAccount(t *testing.T, w *Wallet, tc *testCase, watchOnly bool,
 		witnessProg, err := txscript.PayToAddrScript(witnessAddr)
 		require.NoError(t, err)
 
-		addr, err = btcutil.NewAddressScriptHash(
+		intAddr, err = btcutil.NewAddressScriptHash(
 			witnessProg, &chaincfg.TestNet3Params,
 		)
 		require.NoError(t, err)
 
 	case waddrmgr.WitnessPubKey:
-		addr, err = btcutil.NewAddressWitnessPubKeyHash(
+		intAddr, err = btcutil.NewAddressWitnessPubKeyHash(
 			btcutil.Hash160(acct3ExternalPub.SerializeCompressed()),
 			&chaincfg.TestNet3Params,
 		)
@@ -274,7 +285,7 @@ func testImportAccount(t *testing.T, w *Wallet, tc *testCase, watchOnly bool,
 		t.Fatalf("unhandled address type %v", tc.addrType)
 	}
 
-	addrManaged, err := w.AddressInfo(addr)
+	addrManaged, err := w.AddressInfo(intAddr)
 	require.NoError(t, err)
 	require.Equal(t, true, addrManaged.Imported())
 }