add label value validation to NewConstMetric and friends

prometheus/histogram.go

@@ -430,8 +430,8 @@ func NewConstHistogram(
 	buckets map[float64]uint64,
 	labelValues ...string,
 ) (Metric, error) {
-	if len(desc.variableLabels) != len(labelValues) {
-		return nil, errInconsistentCardinality
+	if err := validateLabelValues(labelValues, len(desc.variableLabels)); err != nil {
+		return nil, err
 	}
 	return &constHistogram{
 		desc:       desc,

prometheus/summary.go

@@ -543,8 +543,8 @@ func NewConstSummary(
 	quantiles map[float64]float64,
 	labelValues ...string,
 ) (Metric, error) {
-	if len(desc.variableLabels) != len(labelValues) {
-		return nil, errInconsistentCardinality
+	if err := validateLabelValues(labelValues, len(desc.variableLabels)); err != nil {
+		return nil, err
 	}
 	return &constSummary{
 		desc:       desc,

prometheus/value.go

@@ -158,8 +158,8 @@ func (v *valueFunc) Write(out *dto.Metric) error {
 // the Collect method. NewConstMetric returns an error if the length of
 // labelValues is not consistent with the variable labels in Desc.
 func NewConstMetric(desc *Desc, valueType ValueType, value float64, labelValues ...string) (Metric, error) {
-	if len(desc.variableLabels) != len(labelValues) {
-		return nil, errInconsistentCardinality
+	if err := validateLabelValues(labelValues, len(desc.variableLabels)); err != nil {
+		return nil, err
 	}
 	return &constMetric{
 		desc:       desc,

prometheus/value_test.go

@@ -0,0 +1,48 @@
+package prometheus
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestNewConstMetricInvalidLabelValues(t *testing.T) {
+	testCases := []struct {
+		desc   string
+		labels Labels
+	}{
+		{
+			desc:   "non utf8 label value",
+			labels: Labels{"a": "\xFF"},
+		},
+		{
+			desc:   "not enough label values",
+			labels: Labels{},
+		},
+		{
+			desc:   "too many label values",
+			labels: Labels{"a": "1", "b": "2"},
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			metricDesc := NewDesc(
+				"sample_value",
+				"sample value",
+				[]string{"a"},
+				Labels{},
+			)
+
+			expectPanic(t, func() {
+				MustNewConstMetric(metricDesc, CounterValue, 0.3, "\xFF")
+			}, fmt.Sprintf("WithLabelValues: expected panic because: %s", test.desc))
+
+			if _, err := NewConstMetric(metricDesc, CounterValue, 0.3, "\xFF"); err == nil {
+				t.Errorf("NewConstMetric: expected error because: %s", test.desc)
+			}
+		})
+	}
+}

prometheus/vec.go

@@ -207,7 +207,7 @@ func (m *metricVec) Reset() {
 }
 
 func (m *metricVec) hashLabelValues(vals []string) (uint64, error) {
-	if err := validateLabelValues(m.desc, vals); err != nil {
+	if err := validateLabelValues(vals, len(m.desc.variableLabels)); err != nil {
 		return 0, err
 	}
 
@@ -220,7 +220,7 @@ func (m *metricVec) hashLabelValues(vals []string) (uint64, error) {
 }
 
 func (m *metricVec) hashLabels(labels Labels) (uint64, error) {
-	if err := validateLabels(m.desc, labels); err != nil {
+	if err := validateLabels(labels, len(m.desc.variableLabels)); err != nil {
 		return 0, err
 	}