databroker: add support for field masks on Put (#3210)

* databroker: add support for field masks on Put

* return errors

* clean up go.mod

pkg/protoutil/mask.go

@@ -0,0 +1,31 @@
+package protoutil
+
+import (
+	"github.com/mennanov/fmutils"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/types/known/anypb"
+	"google.golang.org/protobuf/types/known/fieldmaskpb"
+)
+
+// MergeAnyWithFieldMask merges the data in src with the data in dst,
+// but only the fields identified by the given mask.
+func MergeAnyWithFieldMask(dst, src *anypb.Any, mask *fieldmaskpb.FieldMask) (*anypb.Any, error) {
+	if mask == nil {
+		return src, nil
+	}
+
+	srcMsg, err := src.UnmarshalNew()
+	if err != nil {
+		return nil, err
+	}
+
+	dstMsg, err := dst.UnmarshalNew()
+	if err != nil {
+		return nil, err
+	}
+
+	fmutils.Filter(srcMsg, mask.GetPaths())
+	proto.Merge(dstMsg, srcMsg)
+
+	return anypb.New(dstMsg)
+}