Add middleware.NextOrFailure (#462)

This checks if the next middleware to be called is nil, and if so returns
ServerFailure and an error. This makes the next calling more robust and
saves some lines of code.

Also prefix the error with the name of the middleware to aid in
debugging.

1 files changed, 2 insertions, 5 deletions

diff --git a/middleware/file/file.go b/middleware/file/file.go
index 6a171740f..13ef894d3 100644
--- a/middleware/file/file.go
+++ b/middleware/file/file.go
@@ -32,16 +32,13 @@ func (f File) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (i
 	state := request.Request{W: w, Req: r}
 
 	if state.QClass() != dns.ClassINET {
-		return dns.RcodeServerFailure, errors.New("can only deal with ClassINET")
+		return dns.RcodeServerFailure, middleware.Error(f.Name(), errors.New("can only deal with ClassINET"))
 	}
 	qname := state.Name()
 	// TODO(miek): match the qname better in the map
 	zone := middleware.Zones(f.Zones.Names).Matches(qname)
 	if zone == "" {
-		if f.Next != nil {
-			return f.Next.ServeDNS(ctx, w, r)
-		}
-		return dns.RcodeServerFailure, errors.New("no next middleware found")
+		return middleware.NextOrFailure(f.Name(), f.Next, ctx, w, r)
 	}
 
 	z, ok := f.Zones.Z[zone]