cmd/lncli+walletrpc: add createwatchonly command

lnrpc/walletrpc/walletkit_util.go

@@ -0,0 +1,76 @@
+package walletrpc
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/lightningnetwork/lnd/lnrpc"
+)
+
+// AccountsToWatchOnly converts the accounts returned by the walletkit's
+// ListAccounts RPC into a struct that can be used to create a watch-only
+// wallet.
+func AccountsToWatchOnly(exported []*Account) ([]*lnrpc.WatchOnlyAccount,
+	error) {
+
+	result := make([]*lnrpc.WatchOnlyAccount, len(exported))
+	for idx, acct := range exported {
+		parsedPath, err := parseDerivationPath(acct.DerivationPath)
+		if err != nil {
+			return nil, fmt.Errorf("error parsing derivation path "+
+				"of account %d: %v", idx, err)
+		}
+		if len(parsedPath) < 3 {
+			return nil, fmt.Errorf("derivation path of account %d "+
+				"has invalid derivation path, need at least "+
+				"path of depth 3, instead has depth %d", idx,
+				len(parsedPath))
+		}
+
+		result[idx] = &lnrpc.WatchOnlyAccount{
+			Purpose:  parsedPath[0],
+			CoinType: parsedPath[1],
+			Account:  parsedPath[2],
+			Xpub:     acct.ExtendedPublicKey,
+		}
+	}
+
+	return result, nil
+}
+
+// parseDerivationPath parses a path in the form of m/x'/y'/z'/a/b into a slice
+// of [x, y, z, a, b], meaning that the apostrophe is ignored and 2^31 is _not_
+// added to the numbers.
+func parseDerivationPath(path string) ([]uint32, error) {
+	path = strings.TrimSpace(path)
+	if len(path) == 0 {
+		return nil, fmt.Errorf("path cannot be empty")
+	}
+	if !strings.HasPrefix(path, "m/") {
+		return nil, fmt.Errorf("path must start with m/")
+	}
+
+	// Just the root key, no path was provided. This is valid but not useful
+	// in most cases.
+	rest := strings.ReplaceAll(path, "m/", "")
+	if rest == "" {
+		return []uint32{}, nil
+	}
+
+	parts := strings.Split(rest, "/")
+	indices := make([]uint32, len(parts))
+	for i := 0; i < len(parts); i++ {
+		part := parts[i]
+		if strings.Contains(parts[i], "'") {
+			part = strings.TrimRight(parts[i], "'")
+		}
+		parsed, err := strconv.ParseInt(part, 10, 32)
+		if err != nil {
+			return nil, fmt.Errorf("could not parse part \"%s\": "+
+				"%v", part, err)
+		}
+		indices[i] = uint32(parsed)
+	}
+	return indices, nil
+}

lnrpc/walletrpc/walletkit_util_test.go

@@ -0,0 +1,74 @@
+package walletrpc
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseDerivationPath(t *testing.T) {
+	testCases := []struct {
+		name           string
+		path           string
+		expectedErr    string
+		expectedResult []uint32
+	}{{
+		name:        "empty path",
+		path:        "",
+		expectedErr: "path cannot be empty",
+	}, {
+		name:        "just whitespace",
+		path:        " \n\t\r",
+		expectedErr: "path cannot be empty",
+	}, {
+		name:        "incorrect prefix",
+		path:        "0/0",
+		expectedErr: "path must start with m/",
+	}, {
+		name:        "invalid number",
+		path:        "m/a'/0'",
+		expectedErr: "could not parse part \"a\": strconv.ParseInt",
+	}, {
+		name:        "double slash",
+		path:        "m/0'//",
+		expectedErr: "could not parse part \"\": strconv.ParseInt",
+	}, {
+		name:        "number too large",
+		path:        "m/99999999999999",
+		expectedErr: "could not parse part \"99999999999999\": strconv",
+	}, {
+		name:           "empty path",
+		path:           "m/",
+		expectedResult: []uint32{},
+	}, {
+		name:           "mixed path",
+		path:           "m/0'/1'/2'/3/4/5/6'/7'",
+		expectedResult: []uint32{0, 1, 2, 3, 4, 5, 6, 7},
+	}, {
+		name:           "short path",
+		path:           "m/0'",
+		expectedResult: []uint32{0},
+	}, {
+		name:           "plain path",
+		path:           "m/0/1/2",
+		expectedResult: []uint32{0, 1, 2},
+	}}
+
+	for _, tc := range testCases {
+		tc := tc
+
+		t.Run(tc.name, func(tt *testing.T) {
+			result, err := parseDerivationPath(tc.path)
+
+			if tc.expectedErr != "" {
+				require.Error(tt, err)
+				require.Contains(
+					tt, err.Error(), tc.expectedErr,
+				)
+			} else {
+				require.NoError(tt, err)
+				require.Equal(tt, tc.expectedResult, result)
+			}
+		})
+	}
+}