rpcserver: populate features on lnrpc invoices

In the process, we also move the feature serialization into the
invoicesrpc package, so that it can be shared between the invoicesrpc
and main rpcserver.

lnrpc/invoicesrpc/utils.go

@@ -7,6 +7,7 @@ import (
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnrpc"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/zpay32"
 )
 
@@ -116,6 +117,7 @@ func CreateRPCInvoice(invoice *channeldb.Invoice,
 		AmtPaid:         int64(invoice.AmtPaid),
 		State:           state,
 		Htlcs:           rpcHtlcs,
+		Features:        CreateRPCFeatures(invoice.Terms.Features),
 	}
 
 	if preimage != channeldb.UnknownPreimage {
@@ -125,6 +127,22 @@ func CreateRPCInvoice(invoice *channeldb.Invoice,
 	return rpcInvoice, nil
 }
 
+// CreateRPCFeatures maps a feature vector into a list of lnrpc.Features.
+func CreateRPCFeatures(fv *lnwire.FeatureVector) []*lnrpc.Feature {
+	features := fv.Features()
+	rpcFeatures := make([]*lnrpc.Feature, 0, len(features))
+	for bit := range features {
+		rpcFeatures = append(rpcFeatures, &lnrpc.Feature{
+			Bit:        uint32(bit),
+			Name:       fv.Name(bit),
+			IsRequired: bit.IsRequired(),
+			IsKnown:    fv.IsKnown(bit),
+		})
+	}
+
+	return rpcFeatures
+}
+
 // CreateRPCRouteHints takes in the decoded form of an invoice's route hints
 // and converts them into the lnrpc type.
 func CreateRPCRouteHints(routeHints [][]zpay32.HopHint) []*lnrpc.RouteHint {