[prometheusremotewrite] fix: counter name check

fixes  #2608

Ensure that the metric name is greater than the length of the
counter suffix ("_total") before checking if it contains the counter
suffix to prevent crashes for short (smaller or eq to the length of the
suffix) metric names.

The edge case where the metric name is "_total" is not handled (considered
not to have the suffix), but should not occur IRL.

Also fix the spelling of "delimiter".

Signed-off-by: naseemkullah <naseem@transit.app>

exporter/prometheusremotewriteexporter/helper.go

@@ -31,16 +31,16 @@ import (
 )
 
 const (
-	nameStr     = "__name__"
-	sumStr      = "_sum"
-	countStr    = "_count"
-	bucketStr   = "_bucket"
-	leStr       = "le"
-	quantileStr = "quantile"
-	pInfStr     = "+Inf"
-	totalStr    = "total"
-	delimeter   = "_"
-	keyStr      = "key"
+	nameStr       = "__name__"
+	sumStr        = "_sum"
+	countStr      = "_count"
+	bucketStr     = "_bucket"
+	leStr         = "le"
+	quantileStr   = "quantile"
+	pInfStr       = "+Inf"
+	counterSuffix = "_total"
+	delimiter     = "_"
+	keyStr        = "key"
 )
 
 // ByLabelName enables the usage of sort.Sort() with a slice of labels
@@ -188,14 +188,11 @@ func getPromMetricName(metric *otlp.Metric, ns string) string {
 	b.WriteString(ns)
 
 	if b.Len() > 0 {
-		b.WriteString(delimeter)
+		b.WriteString(delimiter)
 	}
 	name := metric.GetName()
 	b.WriteString(name)
 
-	// do not add the total suffix if the metric name already ends in "total"
-	isCounter = isCounter && name[len(name)-len(totalStr):] != totalStr
-
 	// Including units makes two metrics with the same name and label set belong to two different TimeSeries if the
 	// units are different.
 	/*
@@ -205,9 +202,12 @@ func getPromMetricName(metric *otlp.Metric, ns string) string {
 		}
 	*/
 
-	if b.Len() > 0 && isCounter {
-		b.WriteString(delimeter)
-		b.WriteString(totalStr)
+	counterSuffixLength := len(counterSuffix)
+	nameLength := len(name)
+	hasCounterSuffix := nameLength > counterSuffixLength && name[nameLength-counterSuffixLength:] == counterSuffix
+
+	if b.Len() > 0 && isCounter && !hasCounterSuffix {
+		b.WriteString(counterSuffix)
 	}
 	return sanitize(b.String())
 }
@@ -262,7 +262,7 @@ func sanitize(s string) string {
 	// See https://github.com/orijtech/prometheus-go-metrics-exporter/issues/4.
 	s = strings.Map(sanitizeRune, s)
 	if unicode.IsDigit(rune(s[0])) {
-		s = keyStr + delimeter + s
+		s = keyStr + delimiter + s
 	}
 	if s[0] == '_' {
 		s = keyStr + s

exporter/prometheusremotewriteexporter/helper_test.go

@@ -287,7 +287,7 @@ func Test_getPromMetricName(t *testing.T) {
 			"total_suffix",
 			validMetrics1[validIntSum],
 			ns1,
-			"test_ns_" + validIntSum + delimeter + totalStr,
+			"test_ns_" + validIntSum + counterSuffix,
 		},
 		{
 			"dirty_string",