walletrpc: Returns structured errors from FundPsbt

Converts errors likely to be thrown from string based errors to error
classes with returned grpc error codes

Author: arshbot

lnrpc/walletrpc/errors.go

@@ -0,0 +1,31 @@
+package walletrpc
+
+import (
+	"fmt"
+)
+
+// PSBTError wraps certain errors returned during the construction of partially
+// signed bitcoin transactions performed by FundPSBT
+type PSBTError struct {
+	error
+}
+
+var _ error = (*PSBTError)(nil)
+
+// ErrUnspentInputNotFound returns an error indicating that a specific unspent
+// input in a given list of non-locked UTXOs was not found, and the given
+// missing transaction index
+func ErrUnspentInputNotFound(idx int) PSBTError {
+	return PSBTError{
+		fmt.Errorf("input %d not found in list of non-"+
+			"locked UTXO", idx),
+	}
+}
+
+// ErrUnableToFund returns an error indicating that the FundPSBT method failed
+// along with the returned error message
+func ErrUnableToFund(err error) PSBTError {
+	return PSBTError{
+		fmt.Errorf("wallet couldn't fund PSBT: %v", err),
+	}
+}

lnrpc/walletrpc/psbt.go

@@ -11,6 +11,8 @@ import (
 	"github.com/btcsuite/btcutil/psbt"
 	"github.com/btcsuite/btcwallet/wtxmgr"
 	"github.com/lightningnetwork/lnd/lnwallet"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
 const (
@@ -36,8 +38,7 @@ func verifyInputsUnspent(inputs []*wire.TxIn, utxos []*lnwallet.Utxo) error {
 		}
 
 		if !found {
-			return fmt.Errorf("input %d not found in list of non-"+
-				"locked UTXO", idx)
+			return status.Error(codes.NotFound, ErrUnspentInputNotFound(idx).Error())
 		}
 	}
 

lnrpc/walletrpc/walletkit_server.go

@@ -34,6 +34,8 @@ import (
 	"github.com/lightningnetwork/lnd/macaroons"
 	"github.com/lightningnetwork/lnd/sweep"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 	"gopkg.in/macaroon-bakery.v2/bakery"
 )
 
@@ -1119,7 +1121,7 @@ func (w *WalletKit) FundPsbt(_ context.Context,
 			packet, feeSatPerKW, account,
 		)
 		if err != nil {
-			return fmt.Errorf("wallet couldn't fund PSBT: %v", err)
+			return status.Error(codes.FailedPrecondition, ErrUnableToFund(err).Error())
 		}
 
 		// Make sure we can properly serialize the packet. If this goes