fixup! fixup! fixup! fixup! fixup! fixup! fixup! fixup! fix: fallback…

… to `gauge` for `protofmt`-based negotiations

pkg/metrics_store/metrics_writer.go

@@ -100,7 +100,7 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 				// Skip this step if we encounter a repeated header, as it will be removed.
 				if header != lastHeader && strings.HasPrefix(header, "# HELP") {
 
-					// If the requested content type was proto-based, replace "info" and "statesets" with "gauge", as they are not recognized by Prometheus' protobuf machinery.
+					// If the requested content type was proto-based (such as FmtProtoDelim, FmtProtoText, or FmtProtoCompact), replace "info" and "statesets" with "gauge", as they are not recognized by Prometheus' protobuf machinery.
 					if strings.HasPrefix(contentType, expfmt.ProtoType) {
 						infoTypeString := string(metric.Info)
 						stateSetTypeString := string(metric.StateSet)

pkg/metricshandler/metrics_handler.go

@@ -187,10 +187,9 @@ func (m *MetricsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	var writer io.Writer = w
 
 	contentType := expfmt.NegotiateIncludingOpenMetrics(r.Header)
-	gotContentType := contentType
 
-	// We do not support protobuf at the moment. Fall back to FmtText if the negotiated exposition format is not FmtOpenMetrics See: https://github.com/kubernetes/kube-state-metrics/issues/2022
-	if contentType != expfmt.FmtOpenMetrics_1_0_0 && contentType != expfmt.FmtOpenMetrics_0_0_1 {
+	// Assume text/plain if no Content-Type header is set.
+	if contentType == expfmt.FmtUnknown {
 		contentType = expfmt.FmtText
 	}
 	resHeader.Set("Content-Type", string(contentType))
@@ -209,7 +208,7 @@ func (m *MetricsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	m.metricsWriters = metricsstore.SanitizeHeaders(string(gotContentType), m.metricsWriters)
+	m.metricsWriters = metricsstore.SanitizeHeaders(string(contentType), m.metricsWriters)
 	for _, w := range m.metricsWriters {
 		err := w.WriteAll(writer)
 		if err != nil {