Extract/improve auth response check - it's common to all mechanisms.

src/xmpp/client.go

@@ -146,23 +146,30 @@ func authenticatePlain(stream *Stream, user, password string) error {
 	if err := stream.Send(&auth); err != nil {
 		return err
 	}
+	return authenticateResponse(stream)
+}
 
-	se, err := stream.Next(nil)
+func authenticateResponse(stream *Stream) error {
-	if err != nil {
+	if se, err := stream.Next(nil); err != nil {
 		return err
-	}
+	} else {
 		switch se.Name.Local {
 		case "success":
 			if err := stream.Skip(); err != nil {
 				return err
 			}
+			return nil
 		case "failure":
 			f := new(saslFailure)
-		stream.DecodeElement(f, se)
+			if err := stream.DecodeElement(f, se); err != nil {
-		return errors.New(fmt.Sprintf("Authentication failed: %s", f.Reason.Local))
+				return err
 			}
-
+			return fmt.Errorf("Authentication failed: %s", f.Reason.Local)
-	return nil
+		default:
+			return fmt.Errorf("Unexpected: %s", se.Name)
+		}
+	}
+	panic("unreachable")
 }
 
 type saslAuth struct {