From ee2f53a2f103ad061b2e80182c07e25b6980d439 Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Wed, 13 Dec 2023 12:37:50 +0530
Subject: [PATCH 01/10] fix: fallback to `gauge` for `protofmt`-based
 negotiations

Fallback to `gauge` metric type when the negotiated content-type is
`protofmt`-based, since Prometheus' protobuf machinery does not
recognize all OpenMetrics types (`info` and `statesets` in this
context).

Signed-off-by: Pranshu Srivastava <rexagod@gmail.com>
---
 pkg/metrics_store/metrics_writer.go      | 20 ++++++++--
 pkg/metrics_store/metrics_writer_test.go | 47 ++++++++++++++++++++++++
 pkg/metricshandler/metrics_handler.go    |  3 +-
 3 files changed, 66 insertions(+), 4 deletions(-)

diff --git a/pkg/metrics_store/metrics_writer.go b/pkg/metrics_store/metrics_writer.go
index 77a9df6106..8a99705af1 100644
--- a/pkg/metrics_store/metrics_writer.go
+++ b/pkg/metrics_store/metrics_writer.go
@@ -19,6 +19,11 @@ package metricsstore
 import (
 	"fmt"
 	"io"
+	"strings"
+
+	"github.com/prometheus/common/expfmt"
+
+	"k8s.io/kube-state-metrics/v2/pkg/metric"
 )
 
 // MetricsWriterList represent a list of MetricsWriter
@@ -82,13 +87,22 @@ func (m MetricsWriter) WriteAll(w io.Writer) error {
 	return nil
 }
 
-// SanitizeHeaders removes duplicate headers from the given MetricsWriterList for the same family (generated through CRS).
-// These are expected to be consecutive since G** resolution generates groups of similar metrics with same headers before moving onto the next G** spec in the CRS configuration.
-func SanitizeHeaders(writers MetricsWriterList) MetricsWriterList {
+// SanitizeHeaders sanitizes the headers of the given MetricsWriterList.
+func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWriterList {
 	var lastHeader string
 	for _, writer := range writers {
 		if len(writer.stores) > 0 {
 			for i, header := range writer.stores[0].headers {
+				// If the requested content type was proto-based, replace the type with "gauge", as "info" and "statesets" are not recognized by Prometheus' protobuf machinery.
+				if strings.HasPrefix(contentType, expfmt.ProtoType) &&
+					strings.HasPrefix(header, "# HELP") &&
+					(strings.HasSuffix(header, " "+string(metric.Info)) || strings.HasSuffix(header, " "+string(metric.StateSet))) {
+					typeStringWithoutTypePaddedIndex := strings.LastIndex(header, " ")
+					typeStringWithoutType := header[:typeStringWithoutTypePaddedIndex]
+					writer.stores[0].headers[i] = typeStringWithoutType + " " + string(metric.Gauge)
+				}
+				// Removes duplicate headers from the given MetricsWriterList for the same family (generated through CRS).
+				// These are expected to be consecutive since G** resolution generates groups of similar metrics with same headers before moving onto the next G** spec in the CRS configuration.
 				if header == lastHeader {
 					writer.stores[0].headers[i] = ""
 				} else {
diff --git a/pkg/metrics_store/metrics_writer_test.go b/pkg/metrics_store/metrics_writer_test.go
index 73bf164765..d7e94c89de 100644
--- a/pkg/metrics_store/metrics_writer_test.go
+++ b/pkg/metrics_store/metrics_writer_test.go
@@ -18,6 +18,7 @@ package metricsstore_test
 
 import (
 	"fmt"
+	"github.com/prometheus/common/expfmt"
 	"strings"
 	"testing"
 
@@ -263,3 +264,49 @@ func TestWriteAllWithEmptyStores(t *testing.T) {
 		t.Fatalf("Unexpected output, got %q, want %q", result, "")
 	}
 }
+
+func BenchmarkSanitizeHeaders(b *testing.B) {
+	benchmarks := []struct {
+		name                      string
+		contentType               expfmt.Format
+		writersContainsDuplicates bool
+	}{
+		{
+			name:                      "text-format unique headers",
+			contentType:               expfmt.FmtText,
+			writersContainsDuplicates: false,
+		},
+		{
+			name:                      "text-format duplicate headers",
+			contentType:               expfmt.FmtText,
+			writersContainsDuplicates: true,
+		},
+		{
+			name:                      "proto-format unique headers",
+			contentType:               expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
+			writersContainsDuplicates: false,
+		},
+		{
+			name:                      "proto-format duplicate headers",
+			contentType:               expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
+			writersContainsDuplicates: true,
+		},
+	}
+
+	for _, benchmark := range benchmarks {
+		headers := []string{}
+		for j := 0; j < 10e4; j++ {
+			if benchmark.writersContainsDuplicates {
+				headers = append(headers, fmt.Sprintf("# HELP foo foo_help\n# TYPE foo info"))
+			} else {
+				headers = append(headers, fmt.Sprintf("# HELP foo_%d foo_help\n# TYPE foo_%d info", j, j))
+			}
+		}
+		writer := metricsstore.NewMetricsWriter(metricsstore.NewMetricsStore(headers, nil))
+		b.Run(benchmark.name, func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				metricsstore.SanitizeHeaders(string(benchmark.contentType), metricsstore.MetricsWriterList{writer})
+			}
+		})
+	}
+}
diff --git a/pkg/metricshandler/metrics_handler.go b/pkg/metricshandler/metrics_handler.go
index 911d24b161..4f2ddb530b 100644
--- a/pkg/metricshandler/metrics_handler.go
+++ b/pkg/metricshandler/metrics_handler.go
@@ -187,6 +187,7 @@ 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 {
@@ -208,7 +209,7 @@ func (m *MetricsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	m.metricsWriters = metricsstore.SanitizeHeaders(m.metricsWriters)
+	m.metricsWriters = metricsstore.SanitizeHeaders(string(gotContentType), m.metricsWriters)
 	for _, w := range m.metricsWriters {
 		err := w.WriteAll(writer)
 		if err != nil {

From 4be2ddf3f7027e0808457087d8b2ceac66d892f3 Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Fri, 15 Dec 2023 17:39:26 +0530
Subject: [PATCH 02/10] fixup! fix: fallback to `gauge` for `protofmt`-based
 negotiations

---
 pkg/customresourcestate/config.go             | 22 +++++-
 .../config_metrics_types.go                   | 10 ---
 .../custom_resource_metrics_test.go           |  8 ++-
 pkg/customresourcestate/registry_factory.go   |  8 +--
 pkg/metric/metric.go                          | 67 ++++++++++++++++---
 pkg/metric_generator/generator.go             |  2 +-
 pkg/metrics_store/metrics_writer.go           | 27 +++++---
 pkg/metrics_store/metrics_writer_test.go      |  5 +-
 8 files changed, 110 insertions(+), 39 deletions(-)

diff --git a/pkg/customresourcestate/config.go b/pkg/customresourcestate/config.go
index 385858b8ba..aaab8d8c83 100644
--- a/pkg/customresourcestate/config.go
+++ b/pkg/customresourcestate/config.go
@@ -20,6 +20,8 @@ import (
 	"fmt"
 	"strings"
 
+	"k8s.io/kube-state-metrics/v2/pkg/metric"
+
 	"github.com/gobuffalo/flect"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/klog/v2"
@@ -148,7 +150,7 @@ type Generator struct {
 type Metric struct {
 	// Type defines the type of the metric.
 	// +unionDiscriminator
-	Type MetricType `yaml:"type" json:"type"`
+	Type metric.Type `yaml:"type" json:"type"`
 
 	// Gauge defines a gauge metric.
 	// +optional
@@ -170,9 +172,16 @@ type ConfigDecoder interface {
 func FromConfig(decoder ConfigDecoder, discovererInstance *discovery.CRDiscoverer) (func() ([]customresource.RegistryFactory, error), error) {
 	var customResourceConfig Metrics
 	factoriesIndex := map[string]bool{}
+
+	// Decode the configuration.
 	if err := decoder.Decode(&customResourceConfig); err != nil {
 		return nil, fmt.Errorf("failed to parse Custom Resource State metrics: %w", err)
 	}
+
+	// Override the configuration with any custom overrides.
+	configOverrides(&customResourceConfig)
+
+	// Create a factory for each resource.
 	fn := func() (factories []customresource.RegistryFactory, err error) {
 		resources := customResourceConfig.Spec.Resources
 		// resolvedGVKPs will have the final list of GVKs, in addition to the resolved G** resources.
@@ -206,3 +215,14 @@ func FromConfig(decoder ConfigDecoder, discovererInstance *discovery.CRDiscovere
 	}
 	return fn, nil
 }
+
+// configOverrides applies overrides to the configuration.
+func configOverrides(config *Metrics) {
+	for i := range config.Spec.Resources {
+		for j := range config.Spec.Resources[i].Metrics {
+
+			// Override the metric type to lowercase, so the internals have a single source of truth for metric type definitions.
+			config.Spec.Resources[i].Metrics[j].Each.Type = metric.Type(strings.ToLower(string(config.Spec.Resources[i].Metrics[j].Each.Type)))
+		}
+	}
+}
diff --git a/pkg/customresourcestate/config_metrics_types.go b/pkg/customresourcestate/config_metrics_types.go
index 6e8e9167cd..25d63bfb69 100644
--- a/pkg/customresourcestate/config_metrics_types.go
+++ b/pkg/customresourcestate/config_metrics_types.go
@@ -16,16 +16,6 @@ limitations under the License.
 
 package customresourcestate
 
-// MetricType is the type of a metric.
-type MetricType string
-
-// Supported metric types.
-const (
-	MetricTypeGauge    MetricType = "Gauge"
-	MetricTypeStateSet MetricType = "StateSet"
-	MetricTypeInfo     MetricType = "Info"
-)
-
 // MetricMeta are variables which may used for any metric type.
 type MetricMeta struct {
 	// LabelsFromPath adds additional labels where the value of the label is taken from a field under Path.
diff --git a/pkg/customresourcestate/custom_resource_metrics_test.go b/pkg/customresourcestate/custom_resource_metrics_test.go
index 928f668ddd..31121de75c 100644
--- a/pkg/customresourcestate/custom_resource_metrics_test.go
+++ b/pkg/customresourcestate/custom_resource_metrics_test.go
@@ -21,6 +21,8 @@ import (
 	"reflect"
 	"testing"
 
+	"k8s.io/kube-state-metrics/v2/pkg/metric"
+
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/utils/ptr"
 )
@@ -55,7 +57,7 @@ func TestNewCustomResourceMetrics(t *testing.T) {
 						Name: "test_metrics",
 						Help: "metrics for testing",
 						Each: Metric{
-							Type: MetricTypeInfo,
+							Type: metric.Info,
 							Info: &MetricInfo{
 								MetricMeta: MetricMeta{
 									Path: []string{
@@ -117,7 +119,7 @@ func TestNewCustomResourceMetrics(t *testing.T) {
 						Name: "test_metrics",
 						Help: "metrics for testing",
 						Each: Metric{
-							Type: MetricTypeInfo,
+							Type: metric.Info,
 							Info: &MetricInfo{
 								MetricMeta: MetricMeta{
 									Path: []string{
@@ -180,7 +182,7 @@ func TestNewCustomResourceMetrics(t *testing.T) {
 						Name: "test_metrics",
 						Help: "metrics for testing",
 						Each: Metric{
-							Type: MetricTypeInfo,
+							Type: metric.Info,
 							Info: &MetricInfo{
 								MetricMeta: MetricMeta{
 									Path: []string{
diff --git a/pkg/customresourcestate/registry_factory.go b/pkg/customresourcestate/registry_factory.go
index a1ea43f962..d5f920e466 100644
--- a/pkg/customresourcestate/registry_factory.go
+++ b/pkg/customresourcestate/registry_factory.go
@@ -72,7 +72,7 @@ func compileCommon(c MetricMeta) (*compiledCommon, error) {
 func compileFamily(f Generator, resource Resource) (*compiledFamily, error) {
 	labels := resource.Labels.Merge(f.Labels)
 
-	if f.Each.Type == MetricTypeInfo && !strings.HasSuffix(f.Name, "_info") {
+	if f.Each.Type == metric.Info && !strings.HasSuffix(f.Name, "_info") {
 		klog.InfoS("Info metric does not have _info suffix", "gvk", resource.GroupVersionKind.String(), "name", f.Name)
 	}
 
@@ -153,7 +153,7 @@ type compiledMetric interface {
 // newCompiledMetric returns a compiledMetric depending on the given metric type.
 func newCompiledMetric(m Metric) (compiledMetric, error) {
 	switch m.Type {
-	case MetricTypeGauge:
+	case metric.Gauge:
 		if m.Gauge == nil {
 			return nil, errors.New("expected each.gauge to not be nil")
 		}
@@ -172,7 +172,7 @@ func newCompiledMetric(m Metric) (compiledMetric, error) {
 			NilIsZero:      m.Gauge.NilIsZero,
 			labelFromKey:   m.Gauge.LabelFromKey,
 		}, nil
-	case MetricTypeInfo:
+	case metric.Info:
 		if m.Info == nil {
 			return nil, errors.New("expected each.info to not be nil")
 		}
@@ -185,7 +185,7 @@ func newCompiledMetric(m Metric) (compiledMetric, error) {
 			compiledCommon: *cc,
 			labelFromKey:   m.Info.LabelFromKey,
 		}, nil
-	case MetricTypeStateSet:
+	case metric.StateSet:
 		if m.StateSet == nil {
 			return nil, errors.New("expected each.stateSet to not be nil")
 		}
diff --git a/pkg/metric/metric.go b/pkg/metric/metric.go
index 007eb9fa87..657bcbe29d 100644
--- a/pkg/metric/metric.go
+++ b/pkg/metric/metric.go
@@ -37,21 +37,68 @@ var (
 	}
 )
 
-// Type represents the type of a metric e.g. a counter. See
-// https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#metric-types.
+// Type represents the type of the metric. See https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#metric-types.
 type Type string
 
-// Gauge defines a OpenMetrics gauge.
-var Gauge Type = "gauge"
+// TypeN represents the type of the metric as an integer.
+type TypeN int
 
-// Info defines an OpenMetrics info.
-var Info Type = "info"
+// String returns the string representation of the metric type.
+func (i TypeN) String() Type {
+	return MetricTypeNMap[i]
+}
+
+// NString returns the string representation of the metric type as an integer.
+func (i TypeN) NString() string {
+	return strconv.Itoa(int(i))
+}
+
+// Supported metric types.
+const (
+	// GaugeN defines a OpenMetrics gauge.
+	GaugeN TypeN = iota
+
+	// InfoN defines an OpenMetrics info.
+	InfoN
+
+	// StateSetN defines an OpenMetrics stateset.
+	StateSetN
+
+	// CounterN defines a OpenMetrics counter.
+	CounterN
+)
 
-// StateSet defines an OpenMetrics stateset.
-var StateSet Type = "stateset"
+// Supported metric types.
+var (
+
+	// Gauge defines a OpenMetrics gauge.
+	Gauge Type = "gauge"
+
+	// Info defines an OpenMetrics info.
+	Info Type = "info"
+
+	// StateSet defines an OpenMetrics stateset.
+	StateSet Type = "stateset"
+
+	// Counter defines a OpenMetrics counter.
+	Counter Type = "counter"
 
-// Counter defines a OpenMetrics counter.
-var Counter Type = "counter"
+	// MetricTypeNMap is a map of MetricTypeN to MetricType.
+	MetricTypeNMap = map[TypeN]Type{
+		GaugeN:    Gauge,
+		InfoN:     Info,
+		StateSetN: StateSet,
+		CounterN:  Counter,
+	}
+
+	// MetricTypeMap is a map of MetricType to MetricTypeN.
+	MetricTypeMap = map[Type]TypeN{
+		Gauge:    GaugeN,
+		Info:     InfoN,
+		StateSet: StateSetN,
+		Counter:  CounterN,
+	}
+)
 
 // Metric represents a single time series.
 type Metric struct {
diff --git a/pkg/metric_generator/generator.go b/pkg/metric_generator/generator.go
index 2a2e30221f..4aaef6ce4e 100644
--- a/pkg/metric_generator/generator.go
+++ b/pkg/metric_generator/generator.go
@@ -90,7 +90,7 @@ func (g *FamilyGenerator) generateHeader() string {
 	header.WriteString("# TYPE ")
 	header.WriteString(g.Name)
 	header.WriteByte(' ')
-	header.WriteString(string(g.Type))
+	header.WriteString(metric.MetricTypeMap[g.Type].NString())
 
 	return header.String()
 }
diff --git a/pkg/metrics_store/metrics_writer.go b/pkg/metrics_store/metrics_writer.go
index 8a99705af1..e50f730803 100644
--- a/pkg/metrics_store/metrics_writer.go
+++ b/pkg/metrics_store/metrics_writer.go
@@ -93,20 +93,31 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 	for _, writer := range writers {
 		if len(writer.stores) > 0 {
 			for i, header := range writer.stores[0].headers {
-				// If the requested content type was proto-based, replace the type with "gauge", as "info" and "statesets" are not recognized by Prometheus' protobuf machinery.
-				if strings.HasPrefix(contentType, expfmt.ProtoType) &&
-					strings.HasPrefix(header, "# HELP") &&
-					(strings.HasSuffix(header, " "+string(metric.Info)) || strings.HasSuffix(header, " "+string(metric.StateSet))) {
-					typeStringWithoutTypePaddedIndex := strings.LastIndex(header, " ")
-					typeStringWithoutType := header[:typeStringWithoutTypePaddedIndex]
-					writer.stores[0].headers[i] = typeStringWithoutType + " " + string(metric.Gauge)
+
+				// Nothing to sanitize.
+				if len(header) == 0 {
+					continue
 				}
+
 				// Removes duplicate headers from the given MetricsWriterList for the same family (generated through CRS).
 				// These are expected to be consecutive since G** resolution generates groups of similar metrics with same headers before moving onto the next G** spec in the CRS configuration.
 				if header == lastHeader {
 					writer.stores[0].headers[i] = ""
-				} else {
+				} else if strings.HasPrefix(header, "# HELP") {
 					lastHeader = header
+
+					// If the requested content type was proto-based, replace the type with "gauge", as "info" and "statesets" are not recognized by Prometheus' protobuf machinery,
+					// else replace them by their respective string representations.
+					if strings.HasPrefix(contentType, expfmt.ProtoType) &&
+						(strings.HasSuffix(header, metric.InfoN.NString()) || strings.HasSuffix(header, metric.StateSetN.NString())) {
+						writer.stores[0].headers[i] = header[:len(header)-1] + string(metric.Gauge)
+					}
+
+					// Replace all remaining type enums with their string representations.
+					n := int(header[len(header)-1]) - '0'
+					if n >= 0 && n < len(metric.MetricTypeNMap) {
+						writer.stores[0].headers[i] = header[:len(header)-1] + string(metric.MetricTypeNMap[metric.TypeN(n)])
+					}
 				}
 			}
 		}
diff --git a/pkg/metrics_store/metrics_writer_test.go b/pkg/metrics_store/metrics_writer_test.go
index d7e94c89de..5939ac6958 100644
--- a/pkg/metrics_store/metrics_writer_test.go
+++ b/pkg/metrics_store/metrics_writer_test.go
@@ -18,10 +18,11 @@ package metricsstore_test
 
 import (
 	"fmt"
-	"github.com/prometheus/common/expfmt"
 	"strings"
 	"testing"
 
+	"github.com/prometheus/common/expfmt"
+
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -297,7 +298,7 @@ func BenchmarkSanitizeHeaders(b *testing.B) {
 		headers := []string{}
 		for j := 0; j < 10e4; j++ {
 			if benchmark.writersContainsDuplicates {
-				headers = append(headers, fmt.Sprintf("# HELP foo foo_help\n# TYPE foo info"))
+				headers = append(headers, "# HELP foo foo_help\n# TYPE foo info")
 			} else {
 				headers = append(headers, fmt.Sprintf("# HELP foo_%d foo_help\n# TYPE foo_%d info", j, j))
 			}

From bfa611dc51cb8792f6516a7477686693b05a3afb Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Tue, 19 Dec 2023 18:04:05 +0530
Subject: [PATCH 03/10] fixup! fixup! fix: fallback to `gauge` for
 `protofmt`-based negotiations

---
 pkg/metric/metric.go                | 20 ++++++++++----------
 pkg/metric_generator/generator.go   |  2 +-
 pkg/metrics_store/metrics_writer.go |  4 ++--
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/pkg/metric/metric.go b/pkg/metric/metric.go
index 657bcbe29d..0ee6a40bd5 100644
--- a/pkg/metric/metric.go
+++ b/pkg/metric/metric.go
@@ -44,8 +44,8 @@ type Type string
 type TypeN int
 
 // String returns the string representation of the metric type.
-func (i TypeN) String() Type {
-	return MetricTypeNMap[i]
+func (i TypeN) String() string {
+	return string(TypeNMap[i])
 }
 
 // NString returns the string representation of the metric type as an integer.
@@ -55,7 +55,7 @@ func (i TypeN) NString() string {
 
 // Supported metric types.
 const (
-	// GaugeN defines a OpenMetrics gauge.
+	// GaugeN defines an OpenMetrics gauge.
 	GaugeN TypeN = iota
 
 	// InfoN defines an OpenMetrics info.
@@ -64,14 +64,14 @@ const (
 	// StateSetN defines an OpenMetrics stateset.
 	StateSetN
 
-	// CounterN defines a OpenMetrics counter.
+	// CounterN defines an OpenMetrics counter.
 	CounterN
 )
 
 // Supported metric types.
 var (
 
-	// Gauge defines a OpenMetrics gauge.
+	// Gauge defines an OpenMetrics gauge.
 	Gauge Type = "gauge"
 
 	// Info defines an OpenMetrics info.
@@ -80,19 +80,19 @@ var (
 	// StateSet defines an OpenMetrics stateset.
 	StateSet Type = "stateset"
 
-	// Counter defines a OpenMetrics counter.
+	// Counter defines an OpenMetrics counter.
 	Counter Type = "counter"
 
-	// MetricTypeNMap is a map of MetricTypeN to MetricType.
-	MetricTypeNMap = map[TypeN]Type{
+	// TypeNMap is a map of MetricTypeN to MetricType.
+	TypeNMap = map[TypeN]Type{
 		GaugeN:    Gauge,
 		InfoN:     Info,
 		StateSetN: StateSet,
 		CounterN:  Counter,
 	}
 
-	// MetricTypeMap is a map of MetricType to MetricTypeN.
-	MetricTypeMap = map[Type]TypeN{
+	// TypeMap is a map of MetricType to MetricTypeN.
+	TypeMap = map[Type]TypeN{
 		Gauge:    GaugeN,
 		Info:     InfoN,
 		StateSet: StateSetN,
diff --git a/pkg/metric_generator/generator.go b/pkg/metric_generator/generator.go
index 4aaef6ce4e..53065d3d1a 100644
--- a/pkg/metric_generator/generator.go
+++ b/pkg/metric_generator/generator.go
@@ -90,7 +90,7 @@ func (g *FamilyGenerator) generateHeader() string {
 	header.WriteString("# TYPE ")
 	header.WriteString(g.Name)
 	header.WriteByte(' ')
-	header.WriteString(metric.MetricTypeMap[g.Type].NString())
+	header.WriteString(metric.TypeMap[g.Type].NString())
 
 	return header.String()
 }
diff --git a/pkg/metrics_store/metrics_writer.go b/pkg/metrics_store/metrics_writer.go
index e50f730803..75daea06be 100644
--- a/pkg/metrics_store/metrics_writer.go
+++ b/pkg/metrics_store/metrics_writer.go
@@ -115,8 +115,8 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 
 					// Replace all remaining type enums with their string representations.
 					n := int(header[len(header)-1]) - '0'
-					if n >= 0 && n < len(metric.MetricTypeNMap) {
-						writer.stores[0].headers[i] = header[:len(header)-1] + string(metric.MetricTypeNMap[metric.TypeN(n)])
+					if n >= 0 && n < len(metric.TypeNMap) {
+						writer.stores[0].headers[i] = header[:len(header)-1] + string(metric.TypeNMap[metric.TypeN(n)])
 					}
 				}
 			}

From 67f184cb1395d6d44ba328ab3fc21d9ad49f3ea8 Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Wed, 20 Dec 2023 05:03:40 +0530
Subject: [PATCH 04/10] fixup! fixup! fixup! fix: fallback to `gauge` for
 `protofmt`-based negotiations

---
 pkg/customresourcestate/registry_factory.go |  2 +-
 pkg/metric/metric.go                        | 43 +--------------------
 pkg/metric_generator/generator.go           |  2 +-
 pkg/metrics_store/metrics_writer.go         | 21 +++++-----
 4 files changed, 14 insertions(+), 54 deletions(-)

diff --git a/pkg/customresourcestate/registry_factory.go b/pkg/customresourcestate/registry_factory.go
index d5f920e466..907c786655 100644
--- a/pkg/customresourcestate/registry_factory.go
+++ b/pkg/customresourcestate/registry_factory.go
@@ -152,7 +152,7 @@ type compiledMetric interface {
 
 // newCompiledMetric returns a compiledMetric depending on the given metric type.
 func newCompiledMetric(m Metric) (compiledMetric, error) {
-	switch m.Type {
+	switch metric.Type(strings.ToLower(string(m.Type))) {
 	case metric.Gauge:
 		if m.Gauge == nil {
 			return nil, errors.New("expected each.gauge to not be nil")
diff --git a/pkg/metric/metric.go b/pkg/metric/metric.go
index 0ee6a40bd5..47787fe2df 100644
--- a/pkg/metric/metric.go
+++ b/pkg/metric/metric.go
@@ -40,34 +40,11 @@ var (
 // Type represents the type of the metric. See https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#metric-types.
 type Type string
 
-// TypeN represents the type of the metric as an integer.
-type TypeN int
-
 // String returns the string representation of the metric type.
-func (i TypeN) String() string {
-	return string(TypeNMap[i])
-}
-
-// NString returns the string representation of the metric type as an integer.
-func (i TypeN) NString() string {
-	return strconv.Itoa(int(i))
+func (t Type) String() string {
+	return string(t)
 }
 
-// Supported metric types.
-const (
-	// GaugeN defines an OpenMetrics gauge.
-	GaugeN TypeN = iota
-
-	// InfoN defines an OpenMetrics info.
-	InfoN
-
-	// StateSetN defines an OpenMetrics stateset.
-	StateSetN
-
-	// CounterN defines an OpenMetrics counter.
-	CounterN
-)
-
 // Supported metric types.
 var (
 
@@ -82,22 +59,6 @@ var (
 
 	// Counter defines an OpenMetrics counter.
 	Counter Type = "counter"
-
-	// TypeNMap is a map of MetricTypeN to MetricType.
-	TypeNMap = map[TypeN]Type{
-		GaugeN:    Gauge,
-		InfoN:     Info,
-		StateSetN: StateSet,
-		CounterN:  Counter,
-	}
-
-	// TypeMap is a map of MetricType to MetricTypeN.
-	TypeMap = map[Type]TypeN{
-		Gauge:    GaugeN,
-		Info:     InfoN,
-		StateSet: StateSetN,
-		Counter:  CounterN,
-	}
 )
 
 // Metric represents a single time series.
diff --git a/pkg/metric_generator/generator.go b/pkg/metric_generator/generator.go
index 53065d3d1a..9442c6554e 100644
--- a/pkg/metric_generator/generator.go
+++ b/pkg/metric_generator/generator.go
@@ -90,7 +90,7 @@ func (g *FamilyGenerator) generateHeader() string {
 	header.WriteString("# TYPE ")
 	header.WriteString(g.Name)
 	header.WriteByte(' ')
-	header.WriteString(metric.TypeMap[g.Type].NString())
+	header.WriteString(g.Type.String())
 
 	return header.String()
 }
diff --git a/pkg/metrics_store/metrics_writer.go b/pkg/metrics_store/metrics_writer.go
index 75daea06be..6e9386e18c 100644
--- a/pkg/metrics_store/metrics_writer.go
+++ b/pkg/metrics_store/metrics_writer.go
@@ -106,17 +106,16 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 				} else if strings.HasPrefix(header, "# HELP") {
 					lastHeader = header
 
-					// If the requested content type was proto-based, replace the type with "gauge", as "info" and "statesets" are not recognized by Prometheus' protobuf machinery,
-					// else replace them by their respective string representations.
-					if strings.HasPrefix(contentType, expfmt.ProtoType) &&
-						(strings.HasSuffix(header, metric.InfoN.NString()) || strings.HasSuffix(header, metric.StateSetN.NString())) {
-						writer.stores[0].headers[i] = header[:len(header)-1] + string(metric.Gauge)
-					}
-
-					// Replace all remaining type enums with their string representations.
-					n := int(header[len(header)-1]) - '0'
-					if n >= 0 && n < len(metric.TypeNMap) {
-						writer.stores[0].headers[i] = header[:len(header)-1] + string(metric.TypeNMap[metric.TypeN(n)])
+					// If the requested content type was proto-based, replace "info" and "statesets" with "gauge", as they are not recognized by Prometheus' protobuf machinery.
+					if strings.HasPrefix(contentType, expfmt.ProtoType) {
+						infoTypeString := metric.Info.String()
+						stateSetTypeString := metric.StateSet.String()
+						if strings.HasSuffix(header, infoTypeString) {
+							writer.stores[0].headers[i] = header[:len(header)-len(infoTypeString)] + string(metric.Gauge)
+						}
+						if strings.HasSuffix(header, stateSetTypeString) {
+							writer.stores[0].headers[i] = header[:len(header)-len(stateSetTypeString)] + string(metric.Gauge)
+						}
 					}
 				}
 			}

From 0e23fdbe5a905f4407a21cddfc49e8b96b1dfb90 Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Wed, 20 Dec 2023 06:33:03 +0530
Subject: [PATCH 05/10] fixup! fixup! fixup! fixup! fix: fallback to `gauge`
 for `protofmt`-based negotiations

---
 pkg/metrics_store/metrics_writer_test.go | 123 ++++++++++++++++++++---
 1 file changed, 110 insertions(+), 13 deletions(-)

diff --git a/pkg/metrics_store/metrics_writer_test.go b/pkg/metrics_store/metrics_writer_test.go
index 5939ac6958..b6fc7ff21c 100644
--- a/pkg/metrics_store/metrics_writer_test.go
+++ b/pkg/metrics_store/metrics_writer_test.go
@@ -14,21 +14,21 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package metricsstore_test
+package metricsstore
 
 import (
 	"fmt"
+	"github.com/google/go-cmp/cmp"
+	"github.com/prometheus/common/expfmt"
+	"reflect"
 	"strings"
 	"testing"
 
-	"github.com/prometheus/common/expfmt"
-
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
 	"k8s.io/kube-state-metrics/v2/pkg/metric"
-	metricsstore "k8s.io/kube-state-metrics/v2/pkg/metrics_store"
 )
 
 func TestWriteAllWithSingleStore(t *testing.T) {
@@ -62,7 +62,7 @@ func TestWriteAllWithSingleStore(t *testing.T) {
 
 		return []metric.FamilyInterface{&mf1, &mf2}
 	}
-	store := metricsstore.NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
+	store := NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
 	svcs := []v1.Service{
 		{
 			ObjectMeta: metav1.ObjectMeta{
@@ -86,7 +86,7 @@ func TestWriteAllWithSingleStore(t *testing.T) {
 		}
 	}
 
-	multiNsWriter := metricsstore.NewMetricsWriter(store)
+	multiNsWriter := NewMetricsWriter(store)
 	w := strings.Builder{}
 	err := multiNsWriter.WriteAll(&w)
 	if err != nil {
@@ -150,7 +150,7 @@ func TestWriteAllWithMultipleStores(t *testing.T) {
 
 		return []metric.FamilyInterface{&mf1, &mf2}
 	}
-	s1 := metricsstore.NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
+	s1 := NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
 	svcs1 := []v1.Service{
 		{
 			ObjectMeta: metav1.ObjectMeta{
@@ -190,7 +190,7 @@ func TestWriteAllWithMultipleStores(t *testing.T) {
 			},
 		},
 	}
-	s2 := metricsstore.NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
+	s2 := NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
 	for _, s := range svcs2 {
 		svc := s
 		if err := s2.Add(&svc); err != nil {
@@ -198,7 +198,7 @@ func TestWriteAllWithMultipleStores(t *testing.T) {
 		}
 	}
 
-	multiNsWriter := metricsstore.NewMetricsWriter(s1, s2)
+	multiNsWriter := NewMetricsWriter(s1, s2)
 	w := strings.Builder{}
 	err := multiNsWriter.WriteAll(&w)
 	if err != nil {
@@ -250,9 +250,9 @@ func TestWriteAllWithEmptyStores(t *testing.T) {
 
 		return []metric.FamilyInterface{&mf1, &mf2}
 	}
-	store := metricsstore.NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
+	store := NewMetricsStore([]string{"Info 1 about services", "Info 2 about services"}, genFunc)
 
-	multiNsWriter := metricsstore.NewMetricsWriter(store)
+	multiNsWriter := NewMetricsWriter(store)
 	w := strings.Builder{}
 	err := multiNsWriter.WriteAll(&w)
 	if err != nil {
@@ -266,6 +266,103 @@ func TestWriteAllWithEmptyStores(t *testing.T) {
 	}
 }
 
+// TODO: AFAIR empty headers are ignored by Prometheus? If not, we should remove them.
+func TestSanitizeHeaders(t *testing.T) {
+	boilerplateHeaders := []string{
+		"",
+		"",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"# HELP foo foo_help\n# TYPE foo info",
+		"# HELP foo foo_help\n# TYPE foo stateset",
+		"# HELP foo foo_help\n# TYPE foo counter",
+	}
+	duplicatedBoilerplateHeaders := []string{
+		"",
+		"",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"# HELP foo foo_help\n# TYPE foo info",
+		"# HELP foo foo_help\n# TYPE foo info",
+		"# HELP foo foo_help\n# TYPE foo stateset",
+		"# HELP foo foo_help\n# TYPE foo stateset",
+		"# HELP foo foo_help\n# TYPE foo counter",
+		"# HELP foo foo_help\n# TYPE foo counter",
+	}
+	dedepedBoilerplateHeaders := []string{
+		"",
+		"",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"",
+		"# HELP foo foo_help\n# TYPE foo info",
+		"",
+		"# HELP foo foo_help\n# TYPE foo stateset",
+		"",
+		"# HELP foo foo_help\n# TYPE foo counter",
+		"",
+	}
+	protoIngestibleHeaders := []string{
+		"",
+		"",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"# HELP foo foo_help\n# TYPE foo counter",
+	}
+	dedepedProtoIngestibleHeaders := []string{
+		"",
+		"",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"",
+		"# HELP foo foo_help\n# TYPE foo gauge",
+		"",
+		"# HELP foo foo_help\n# TYPE foo counter",
+		"",
+	}
+	testcases := []struct {
+		name            string
+		contentType     expfmt.Format
+		headers         []string
+		expectedHeaders []string
+	}{
+		{
+			name:            "text-format unique headers",
+			contentType:     expfmt.FmtText,
+			headers:         boilerplateHeaders,
+			expectedHeaders: boilerplateHeaders,
+		},
+		{
+			name:            "text-format consecutive duplicate headers",
+			contentType:     expfmt.FmtText,
+			headers:         duplicatedBoilerplateHeaders,
+			expectedHeaders: dedepedBoilerplateHeaders,
+		},
+		{
+			name:            "proto-format unique headers",
+			contentType:     expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
+			headers:         boilerplateHeaders,
+			expectedHeaders: protoIngestibleHeaders,
+		},
+		{
+			name:            "proto-format consecutive duplicate headers",
+			contentType:     expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
+			headers:         duplicatedBoilerplateHeaders,
+			expectedHeaders: dedepedProtoIngestibleHeaders,
+		},
+	}
+
+	for _, testcase := range testcases {
+		writer := NewMetricsWriter(NewMetricsStore(testcase.headers, nil))
+		t.Run(testcase.name, func(t *testing.T) {
+			SanitizeHeaders(string(testcase.contentType), MetricsWriterList{writer})
+			if !reflect.DeepEqual(testcase.expectedHeaders, writer.stores[0].headers) {
+				t.Fatalf("(-want, +got):\n%s", cmp.Diff(testcase.expectedHeaders, writer.stores[0].headers))
+			}
+		})
+	}
+}
+
 func BenchmarkSanitizeHeaders(b *testing.B) {
 	benchmarks := []struct {
 		name                      string
@@ -303,10 +400,10 @@ func BenchmarkSanitizeHeaders(b *testing.B) {
 				headers = append(headers, fmt.Sprintf("# HELP foo_%d foo_help\n# TYPE foo_%d info", j, j))
 			}
 		}
-		writer := metricsstore.NewMetricsWriter(metricsstore.NewMetricsStore(headers, nil))
+		writer := NewMetricsWriter(NewMetricsStore(headers, nil))
 		b.Run(benchmark.name, func(b *testing.B) {
 			for i := 0; i < b.N; i++ {
-				metricsstore.SanitizeHeaders(string(benchmark.contentType), metricsstore.MetricsWriterList{writer})
+				SanitizeHeaders(string(benchmark.contentType), MetricsWriterList{writer})
 			}
 		})
 	}

From 883296e9461aedcca62c7b6e8cb34fb4fe3b1078 Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Wed, 20 Dec 2023 06:33:54 +0530
Subject: [PATCH 06/10] fixup! fixup! fixup! fixup! fixup! fix: fallback to
 `gauge` for `protofmt`-based negotiations

---
 pkg/metrics_store/metrics_writer_test.go | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/pkg/metrics_store/metrics_writer_test.go b/pkg/metrics_store/metrics_writer_test.go
index b6fc7ff21c..890c1e0d6f 100644
--- a/pkg/metrics_store/metrics_writer_test.go
+++ b/pkg/metrics_store/metrics_writer_test.go
@@ -18,12 +18,13 @@ package metricsstore
 
 import (
 	"fmt"
-	"github.com/google/go-cmp/cmp"
-	"github.com/prometheus/common/expfmt"
 	"reflect"
 	"strings"
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
+	"github.com/prometheus/common/expfmt"
+
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -266,7 +267,8 @@ func TestWriteAllWithEmptyStores(t *testing.T) {
 	}
 }
 
-// TODO: AFAIR empty headers are ignored by Prometheus? If not, we should remove them.
+// TODO: AFFAIR empty headers are ignored by Prometheus? If not, we should remove them.
+// No two consecutive headers will be entirely the same. The cases used below are only for their suffixes.
 func TestSanitizeHeaders(t *testing.T) {
 	boilerplateHeaders := []string{
 		"",

From b6496c7fb4e6e2be8922278373fa71513f787f39 Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Wed, 20 Dec 2023 14:45:17 +0530
Subject: [PATCH 07/10] fixup! fixup! fixup! fixup! fixup! fixup! fix: fallback
 to `gauge` for `protofmt`-based negotiations

---
 pkg/metrics_store/metrics_writer.go      |  32 +++++-
 pkg/metrics_store/metrics_writer_test.go | 137 +++++++++++------------
 2 files changed, 94 insertions(+), 75 deletions(-)

diff --git a/pkg/metrics_store/metrics_writer.go b/pkg/metrics_store/metrics_writer.go
index 6e9386e18c..ff446e31ae 100644
--- a/pkg/metrics_store/metrics_writer.go
+++ b/pkg/metrics_store/metrics_writer.go
@@ -101,25 +101,45 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 
 				// Removes duplicate headers from the given MetricsWriterList for the same family (generated through CRS).
 				// These are expected to be consecutive since G** resolution generates groups of similar metrics with same headers before moving onto the next G** spec in the CRS configuration.
-				if header == lastHeader {
-					writer.stores[0].headers[i] = ""
-				} else if strings.HasPrefix(header, "# HELP") {
-					lastHeader = header
+				// 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 strings.HasPrefix(contentType, expfmt.ProtoType) {
 						infoTypeString := metric.Info.String()
 						stateSetTypeString := metric.StateSet.String()
 						if strings.HasSuffix(header, infoTypeString) {
-							writer.stores[0].headers[i] = header[:len(header)-len(infoTypeString)] + string(metric.Gauge)
+							header = header[:len(header)-len(infoTypeString)] + string(metric.Gauge)
+							writer.stores[0].headers[i] = header
 						}
 						if strings.HasSuffix(header, stateSetTypeString) {
-							writer.stores[0].headers[i] = header[:len(header)-len(stateSetTypeString)] + string(metric.Gauge)
+							header = header[:len(header)-len(stateSetTypeString)] + string(metric.Gauge)
+							writer.stores[0].headers[i] = header
 						}
 					}
 				}
+
+				// Nullify duplicate headers after the sanitization to not miss out on any new candidates.
+				if header == lastHeader {
+					writer.stores[0].headers[i] = ""
+				}
+
+				// Update the last header.
+				lastHeader = header
 			}
 		}
 	}
+
+	// Remove all empty headers.
+	for _, writer := range writers {
+		if len(writer.stores) > 0 {
+			for i := len(writer.stores[0].headers) - 1; i >= 0; i-- {
+				if writer.stores[0].headers[i] == "" {
+					writer.stores[0].headers = append(writer.stores[0].headers[:i], writer.stores[0].headers[i+1:]...)
+				}
+			}
+		}
+	}
+
 	return writers
 }
diff --git a/pkg/metrics_store/metrics_writer_test.go b/pkg/metrics_store/metrics_writer_test.go
index 890c1e0d6f..4d33a12369 100644
--- a/pkg/metrics_store/metrics_writer_test.go
+++ b/pkg/metrics_store/metrics_writer_test.go
@@ -267,61 +267,8 @@ func TestWriteAllWithEmptyStores(t *testing.T) {
 	}
 }
 
-// TODO: AFFAIR empty headers are ignored by Prometheus? If not, we should remove them.
 // No two consecutive headers will be entirely the same. The cases used below are only for their suffixes.
 func TestSanitizeHeaders(t *testing.T) {
-	boilerplateHeaders := []string{
-		"",
-		"",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"# HELP foo foo_help\n# TYPE foo info",
-		"# HELP foo foo_help\n# TYPE foo stateset",
-		"# HELP foo foo_help\n# TYPE foo counter",
-	}
-	duplicatedBoilerplateHeaders := []string{
-		"",
-		"",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"# HELP foo foo_help\n# TYPE foo info",
-		"# HELP foo foo_help\n# TYPE foo info",
-		"# HELP foo foo_help\n# TYPE foo stateset",
-		"# HELP foo foo_help\n# TYPE foo stateset",
-		"# HELP foo foo_help\n# TYPE foo counter",
-		"# HELP foo foo_help\n# TYPE foo counter",
-	}
-	dedepedBoilerplateHeaders := []string{
-		"",
-		"",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"",
-		"# HELP foo foo_help\n# TYPE foo info",
-		"",
-		"# HELP foo foo_help\n# TYPE foo stateset",
-		"",
-		"# HELP foo foo_help\n# TYPE foo counter",
-		"",
-	}
-	protoIngestibleHeaders := []string{
-		"",
-		"",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"# HELP foo foo_help\n# TYPE foo counter",
-	}
-	dedepedProtoIngestibleHeaders := []string{
-		"",
-		"",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"",
-		"# HELP foo foo_help\n# TYPE foo gauge",
-		"",
-		"# HELP foo foo_help\n# TYPE foo counter",
-		"",
-	}
 	testcases := []struct {
 		name            string
 		contentType     expfmt.Format
@@ -329,28 +276,80 @@ func TestSanitizeHeaders(t *testing.T) {
 		expectedHeaders []string
 	}{
 		{
-			name:            "text-format unique headers",
-			contentType:     expfmt.FmtText,
-			headers:         boilerplateHeaders,
-			expectedHeaders: boilerplateHeaders,
+			name:        "text-format unique headers",
+			contentType: expfmt.FmtText,
+			headers: []string{
+				"",
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
+			expectedHeaders: []string{
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
 		},
 		{
-			name:            "text-format consecutive duplicate headers",
-			contentType:     expfmt.FmtText,
-			headers:         duplicatedBoilerplateHeaders,
-			expectedHeaders: dedepedBoilerplateHeaders,
+			name:        "text-format consecutive duplicate headers",
+			contentType: expfmt.FmtText,
+			headers: []string{
+				"",
+				"",
+				"",
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo counter",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
+			expectedHeaders: []string{
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
 		},
 		{
-			name:            "proto-format unique headers",
-			contentType:     expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
-			headers:         boilerplateHeaders,
-			expectedHeaders: protoIngestibleHeaders,
+			name:        "proto-format unique headers",
+			contentType: expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
+			headers: []string{
+				"",
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
+			expectedHeaders: []string{
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
 		},
 		{
-			name:            "proto-format consecutive duplicate headers",
-			contentType:     expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
-			headers:         duplicatedBoilerplateHeaders,
-			expectedHeaders: dedepedProtoIngestibleHeaders,
+			name:        "proto-format consecutive duplicate headers",
+			contentType: expfmt.ProtoFmt, // Prometheus ProtoFmt is the only proto-based format we check for.
+			headers: []string{
+				"",
+				"",
+				"",
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo info",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo stateset",
+				"# HELP foo foo_help\n# TYPE foo counter",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
+			expectedHeaders: []string{
+				"# HELP foo foo_help\n# TYPE foo gauge",
+				"# HELP foo foo_help\n# TYPE foo counter",
+			},
 		},
 	}
 

From e0c3e8384aba73dc55257cdd3725c0276d4360bb Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Mon, 15 Jan 2024 01:49:38 +0530
Subject: [PATCH 08/10] fixup! fixup! fixup! fixup! fixup! fixup! fixup! fix:
 fallback to `gauge` for `protofmt`-based negotiations

---
 pkg/customresourcestate/config.go           |  1 +
 pkg/customresourcestate/config_test.go      |  1 +
 pkg/customresourcestate/registry_factory.go |  2 +-
 pkg/metric/metric.go                        |  5 ----
 pkg/metric_generator/generator.go           |  2 +-
 pkg/metrics_store/metrics_writer.go         | 29 +++++++--------------
 pkg/metricshandler/metrics_handler.go       |  4 +--
 7 files changed, 16 insertions(+), 28 deletions(-)

diff --git a/pkg/customresourcestate/config.go b/pkg/customresourcestate/config.go
index aaab8d8c83..873591372f 100644
--- a/pkg/customresourcestate/config.go
+++ b/pkg/customresourcestate/config.go
@@ -222,6 +222,7 @@ func configOverrides(config *Metrics) {
 		for j := range config.Spec.Resources[i].Metrics {
 
 			// Override the metric type to lowercase, so the internals have a single source of truth for metric type definitions.
+			// This is done as a convenience measure for users, so they don't have to remember the exact casing.
 			config.Spec.Resources[i].Metrics[j].Each.Type = metric.Type(strings.ToLower(string(config.Spec.Resources[i].Metrics[j].Each.Type)))
 		}
 	}
diff --git a/pkg/customresourcestate/config_test.go b/pkg/customresourcestate/config_test.go
index 7ae11985f2..6927b3c211 100644
--- a/pkg/customresourcestate/config_test.go
+++ b/pkg/customresourcestate/config_test.go
@@ -32,6 +32,7 @@ var testData string
 func Test_Metrics_deserialization(t *testing.T) {
 	var m Metrics
 	assert.NoError(t, yaml.NewDecoder(strings.NewReader(testData)).Decode(&m))
+	configOverrides(&m)
 	assert.Equal(t, "active_count", m.Spec.Resources[0].Metrics[0].Name)
 
 	t.Run("can create resource factory", func(t *testing.T) {
diff --git a/pkg/customresourcestate/registry_factory.go b/pkg/customresourcestate/registry_factory.go
index 907c786655..d5f920e466 100644
--- a/pkg/customresourcestate/registry_factory.go
+++ b/pkg/customresourcestate/registry_factory.go
@@ -152,7 +152,7 @@ type compiledMetric interface {
 
 // newCompiledMetric returns a compiledMetric depending on the given metric type.
 func newCompiledMetric(m Metric) (compiledMetric, error) {
-	switch metric.Type(strings.ToLower(string(m.Type))) {
+	switch m.Type {
 	case metric.Gauge:
 		if m.Gauge == nil {
 			return nil, errors.New("expected each.gauge to not be nil")
diff --git a/pkg/metric/metric.go b/pkg/metric/metric.go
index 47787fe2df..d138b240a4 100644
--- a/pkg/metric/metric.go
+++ b/pkg/metric/metric.go
@@ -40,11 +40,6 @@ var (
 // Type represents the type of the metric. See https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#metric-types.
 type Type string
 
-// String returns the string representation of the metric type.
-func (t Type) String() string {
-	return string(t)
-}
-
 // Supported metric types.
 var (
 
diff --git a/pkg/metric_generator/generator.go b/pkg/metric_generator/generator.go
index 9442c6554e..2a2e30221f 100644
--- a/pkg/metric_generator/generator.go
+++ b/pkg/metric_generator/generator.go
@@ -90,7 +90,7 @@ func (g *FamilyGenerator) generateHeader() string {
 	header.WriteString("# TYPE ")
 	header.WriteString(g.Name)
 	header.WriteByte(' ')
-	header.WriteString(g.Type.String())
+	header.WriteString(string(g.Type))
 
 	return header.String()
 }
diff --git a/pkg/metrics_store/metrics_writer.go b/pkg/metrics_store/metrics_writer.go
index ff446e31ae..960f350eb1 100644
--- a/pkg/metrics_store/metrics_writer.go
+++ b/pkg/metrics_store/metrics_writer.go
@@ -92,12 +92,8 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 	var lastHeader string
 	for _, writer := range writers {
 		if len(writer.stores) > 0 {
-			for i, header := range writer.stores[0].headers {
-
-				// Nothing to sanitize.
-				if len(header) == 0 {
-					continue
-				}
+			for i := 0; i < len(writer.stores[0].headers); {
+				header := writer.stores[0].headers[i]
 
 				// Removes duplicate headers from the given MetricsWriterList for the same family (generated through CRS).
 				// These are expected to be consecutive since G** resolution generates groups of similar metrics with same headers before moving onto the next G** spec in the CRS configuration.
@@ -106,8 +102,8 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 
 					// If the requested content type was proto-based, replace "info" and "statesets" with "gauge", as they are not recognized by Prometheus' protobuf machinery.
 					if strings.HasPrefix(contentType, expfmt.ProtoType) {
-						infoTypeString := metric.Info.String()
-						stateSetTypeString := metric.StateSet.String()
+						infoTypeString := string(metric.Info)
+						stateSetTypeString := string(metric.StateSet)
 						if strings.HasSuffix(header, infoTypeString) {
 							header = header[:len(header)-len(infoTypeString)] + string(metric.Gauge)
 							writer.stores[0].headers[i] = header
@@ -121,22 +117,17 @@ func SanitizeHeaders(contentType string, writers MetricsWriterList) MetricsWrite
 
 				// Nullify duplicate headers after the sanitization to not miss out on any new candidates.
 				if header == lastHeader {
-					writer.stores[0].headers[i] = ""
+					writer.stores[0].headers = append(writer.stores[0].headers[:i], writer.stores[0].headers[i+1:]...)
+
+					// Do not increment the index, as the next header is now at the current index.
+					continue
 				}
 
 				// Update the last header.
 				lastHeader = header
-			}
-		}
-	}
 
-	// Remove all empty headers.
-	for _, writer := range writers {
-		if len(writer.stores) > 0 {
-			for i := len(writer.stores[0].headers) - 1; i >= 0; i-- {
-				if writer.stores[0].headers[i] == "" {
-					writer.stores[0].headers = append(writer.stores[0].headers[:i], writer.stores[0].headers[i+1:]...)
-				}
+				// Move to the next header.
+				i++
 			}
 		}
 	}
diff --git a/pkg/metricshandler/metrics_handler.go b/pkg/metricshandler/metrics_handler.go
index 4f2ddb530b..0b61a16d63 100644
--- a/pkg/metricshandler/metrics_handler.go
+++ b/pkg/metricshandler/metrics_handler.go
@@ -178,8 +178,8 @@ func (m *MetricsHandler) Run(ctx context.Context) error {
 	return ctx.Err()
 }
 
-// ServeHTTP implements the http.Handler interface. It writes all generated
-// metrics to the response body.
+// ServeHTTP implements the http.Handler interface. It writes all generated metrics to the response body.
+// Note that all operations defined within this procedure are performed at every request.
 func (m *MetricsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	m.mtx.RLock()
 	defer m.mtx.RUnlock()

From 8e7b38d516296dcf40fbc7cf23366ee99f16acd6 Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Tue, 26 Mar 2024 23:47:53 +0530
Subject: [PATCH 09/10] fixup! fixup! fixup! fixup! fixup! fixup! fixup! fixup!
 fix: fallback to `gauge` for `protofmt`-based negotiations

---
 pkg/metrics_store/metrics_writer.go   | 2 +-
 pkg/metricshandler/metrics_handler.go | 7 +++----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/pkg/metrics_store/metrics_writer.go b/pkg/metrics_store/metrics_writer.go
index 960f350eb1..0e263e4654 100644
--- a/pkg/metrics_store/metrics_writer.go
+++ b/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)
diff --git a/pkg/metricshandler/metrics_handler.go b/pkg/metricshandler/metrics_handler.go
index 0b61a16d63..29e7c88e89 100644
--- a/pkg/metricshandler/metrics_handler.go
+++ b/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 {

From 2a06c450615c4f4a908df043a54eba9f54cb459d Mon Sep 17 00:00:00 2001
From: Pranshu Srivastava <rexagod@gmail.com>
Date: Wed, 27 Mar 2024 23:53:23 +0530
Subject: [PATCH 10/10] fixup! fixup! fixup! fixup! fixup! fixup! fixup! fixup!
 fixup! fix: fallback to `gauge` for `protofmt`-based negotiations

---
 pkg/metricshandler/metrics_handler.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pkg/metricshandler/metrics_handler.go b/pkg/metricshandler/metrics_handler.go
index 29e7c88e89..8cee50b4f5 100644
--- a/pkg/metricshandler/metrics_handler.go
+++ b/pkg/metricshandler/metrics_handler.go
@@ -188,8 +188,8 @@ func (m *MetricsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	contentType := expfmt.NegotiateIncludingOpenMetrics(r.Header)
 
-	// Assume text/plain if no Content-Type header is set.
-	if contentType == expfmt.FmtUnknown {
+	// 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 {
 		contentType = expfmt.FmtText
 	}
 	resHeader.Set("Content-Type", string(contentType))