From 25f453ce1a4461ef43c8b4a5ca3b32d4820736ca Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Wed, 3 Mar 2021 10:30:39 +0200
Subject: [PATCH] lib/promscrape/discovery/kubernetes: properly check for nil
 pointer inside interface

See https://mangatmodi.medium.com/go-check-nil-interface-the-right-way-d142776edef1

This fixes a panic when the ScrapeWork is filtered out in swcFunc.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1108
---
 lib/promscrape/discovery/kubernetes/api.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/promscrape/discovery/kubernetes/api.go b/lib/promscrape/discovery/kubernetes/api.go
index da858bd274..1d319a671a 100644
--- a/lib/promscrape/discovery/kubernetes/api.go
+++ b/lib/promscrape/discovery/kubernetes/api.go
@@ -12,6 +12,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"reflect"
 	"strconv"
 	"strings"
 	"sync"
@@ -380,7 +381,8 @@ func getScrapeWorkObjectsForLabels(swcFunc ScrapeWorkConstructorFunc, labelss []
 	swos := make([]interface{}, 0, len(labelss))
 	for _, labels := range labelss {
 		swo := swcFunc(labels)
-		if swo != nil {
+		// The reflect check is needed because of https://mangatmodi.medium.com/go-check-nil-interface-the-right-way-d142776edef1
+		if swo != nil && !reflect.ValueOf(swo).IsNil() {
 			swos = append(swos, swo)
 		}
 	}