Issue prometheus#13268: fix quality value in accept header

Signed-off-by: Kumar Kalpadiptya Roy <kalpadiptya.roy@outlook.com>

scrape/scrape.go

@@ -670,15 +670,26 @@ var errBodySizeLimit = errors.New("body size limit exceeded")
 func acceptHeader(sps []config.ScrapeProtocol) string {
 	var vals []string
 	weight := len(config.ScrapeProtocolsHeaders) + 1
+	normalisedWeight := normaliseWeightBetweenZeroAndOne(weight)
 	for _, sp := range sps {
-		vals = append(vals, fmt.Sprintf("%s;q=0.%d", config.ScrapeProtocolsHeaders[sp], weight))
+		vals = append(vals, fmt.Sprintf("%s;q=%f", config.ScrapeProtocolsHeaders[sp], normalisedWeight))
 		weight--
 	}
 	// Default match anything.
-	vals = append(vals, fmt.Sprintf("*/*;q=%d", weight))
+	vals = append(vals, fmt.Sprintf("*/*;q=%f", normalisedWeight))
 	return strings.Join(vals, ",")
 }
 
+func normaliseWeightBetweenZeroAndOne(weight int) float64 {
+	countDigits := 0
+	copy := weight
+	for copy > 0 {
+		countDigits++
+		copy /= 10
+	}
+	return float64(weight) / math.Pow(float64(10), float64(countDigits))
+}
+
 func acceptEncodingHeader(enableCompression bool) string {
 	if enableCompression {
 		return "gzip"