lib/promscrape: add promrelabel.GetLabelValueByName helper function

lib/promrelabel/relabel.go

@@ -280,3 +280,14 @@ func GetLabelByName(labels []prompbmarshal.Label, name string) *prompbmarshal.La
 	}
 	return nil
 }
+
+// GetLabelValueByName returns value for label with the given name from labels.
+//
+// It returns empty string for non-existing label.
+func GetLabelValueByName(labels []prompbmarshal.Label, name string) string {
+	label := GetLabelByName(labels, name)
+	if label == nil {
+		return ""
+	}
+	return label.Value
+}

lib/promscrape/config.go

@@ -191,11 +191,11 @@ func (cfg *Config) getFileSDScrapeWork(prev []ScrapeWork) []ScrapeWork {
 	swPrev := make(map[string][]ScrapeWork)
 	for i := range prev {
 		sw := &prev[i]
-		label := promrelabel.GetLabelByName(sw.Labels, "__vm_filepath")
-		if label == nil {
+		filepath := promrelabel.GetLabelValueByName(sw.Labels, "__vm_filepath")
+		if len(filepath) == 0 {
 			logger.Panicf("BUG: missing `__vm_filepath` label")
 		} else {
-			swPrev[label.Value] = append(swPrev[label.Value], *sw)
+			swPrev[filepath] = append(swPrev[filepath], *sw)
 		}
 	}
 	var dst []ScrapeWork
@@ -439,27 +439,21 @@ func appendScrapeWork(dst []ScrapeWork, swc *scrapeWorkConfig, target string, ex
 		return dst, nil
 	}
 	// See https://www.robustperception.io/life-of-a-label
-	schemeRelabeled := ""
-	if schemeLabel := promrelabel.GetLabelByName(labels, "__scheme__"); schemeLabel != nil {
-		schemeRelabeled = schemeLabel.Value
-	}
-	if schemeRelabeled == "" {
+	schemeRelabeled := promrelabel.GetLabelValueByName(labels, "__scheme__")
+	if len(schemeRelabeled) == 0 {
 		schemeRelabeled = "http"
 	}
-	addressLabel := promrelabel.GetLabelByName(labels, "__address__")
-	if addressLabel == nil || addressLabel.Name == "" {
+	addressRelabeled := promrelabel.GetLabelValueByName(labels, "__address__")
+	if len(addressRelabeled) == 0 {
 		// Drop target without scrape address.
 		return dst, nil
 	}
-	targetRelabeled := addMissingPort(schemeRelabeled, addressLabel.Value)
+	targetRelabeled := addMissingPort(schemeRelabeled, addressRelabeled)
 	if strings.Contains(targetRelabeled, "/") {
 		// Drop target with '/'
 		return dst, nil
 	}
-	metricsPathRelabeled := ""
-	if metricsPathLabel := promrelabel.GetLabelByName(labels, "__metrics_path__"); metricsPathLabel != nil {
-		metricsPathRelabeled = metricsPathLabel.Value
-	}
+	metricsPathRelabeled := promrelabel.GetLabelValueByName(labels, "__metrics_path__")
 	if metricsPathRelabeled == "" {
 		metricsPathRelabeled = "/metrics"
 	}

lib/promscrape/scrapework.go

@@ -62,11 +62,7 @@ type ScrapeWork struct {
 
 // Job returns job for the ScrapeWork
 func (sw *ScrapeWork) Job() string {
-	label := promrelabel.GetLabelByName(sw.Labels, "job")
-	if label == nil {
-		return ""
-	}
-	return label.Value
+	return promrelabel.GetLabelValueByName(sw.Labels, "job")
 }
 
 type scrapeWork struct {