check new line in target

Signed-off-by: Xiaochao Dong (@damnever) <the.xcdong@gmail.com>

model/relabel/relabel.go

@@ -269,6 +269,7 @@ func relabel(cfg *Config, lb *labels.Builder) (keep bool) {
 	case Replace:
 		// Fast path to add or delete label pair.
 		if val == "" && cfg.Regex == DefaultRelabelConfig.Regex &&
+			!containsNewLine(cfg.TargetLabel) &&
 			!varInRegexTemplate(cfg.TargetLabel) && !varInRegexTemplate(cfg.Replacement) {
 			if !model.LabelName(cfg.TargetLabel).IsValid() || cfg.Replacement == "" {
 				lb.Del(cfg.TargetLabel)
@@ -331,3 +332,7 @@ func relabel(cfg *Config, lb *labels.Builder) (keep bool) {
 func varInRegexTemplate(template string) bool {
 	return strings.Contains(template, "$")
 }
+
+func containsNewLine(s string) bool {
+	return strings.Contains(s, "\r\n") || strings.Contains(s, "\n")
+}

model/relabel/relabel_test.go

@@ -858,6 +858,8 @@ func BenchmarkRelabel_ReplaceAddLabel(b *testing.B) {
 		"wwwwww":       "wwwwww",
 		"xxxxxxxxx":    "xxxxxxxxx",
 		"yyyyyyyyyyyy": "yyyyyyyyyyyy",
+		"new\nline1":   "dropped",
+		"new\r\nline2": "dropped",
 		"${0}":         "dropped",
 		"dropped":      "${0}",
 	} {
@@ -905,7 +907,7 @@ func BenchmarkRelabel_ReplaceAddLabel(b *testing.B) {
 			labels.Label{Name: "abcdefg12", Value: "hijklmn12"},
 			labels.Label{Name: "abcdefg13", Value: "hijklmn13"},
 		}
-		_, _ = Process(lset, cfgs...)
-		// require.Equal(b, actual, expectLset)
+		actual, _ := Process(lset, cfgs...)
+		require.Equal(b, actual, expectLset)
 	}
 }