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
+}