Add suffix collision checks during gathering

So far, if a gauge was named `xxx_count`, and a summary or histogram
`xxx`, this would have led to a legal protobuf exposition but would
have created a name collision on `xxx_count` in the text format and
within the Prometheus server.

Signed-off-by: beorn7 <beorn@soundcloud.com>

prometheus/registry.go

@@ -19,6 +19,7 @@ import (
 	"os"
 	"runtime"
 	"sort"
+	"strings"
 	"sync"
 	"unicode/utf8"
 
@@ -542,7 +543,7 @@ func processMetric(
 		return fmt.Errorf("error collecting metric %v: %s", desc, err)
 	}
 	metricFamily, ok := metricFamiliesByName[desc.fqName]
-	if ok {
+	if ok { // Existing name.
 		if metricFamily.GetHelp() != desc.help {
 			return fmt.Errorf(
 				"collected metric %s %s has help %q but should have %q",
@@ -589,7 +590,7 @@ func processMetric(
 		default:
 			panic("encountered MetricFamily with invalid type")
 		}
-	} else {
+	} else { // New name.
 		metricFamily = &dto.MetricFamily{}
 		metricFamily.Name = proto.String(desc.fqName)
 		metricFamily.Help = proto.String(desc.help)
@@ -608,6 +609,9 @@ func processMetric(
 		default:
 			return fmt.Errorf("empty metric collected: %s", dtoMetric)
 		}
+		if err := checkSuffixCollisions(metricFamily, metricFamiliesByName); err != nil {
+			return err
+		}
 		metricFamiliesByName[desc.fqName] = metricFamily
 	}
 	if err := checkMetricConsistency(metricFamily, dtoMetric, metricHashes); err != nil {
@@ -688,6 +692,10 @@ func (gs Gatherers) Gather() ([]*dto.MetricFamily, error) {
 				existingMF.Name = mf.Name
 				existingMF.Help = mf.Help
 				existingMF.Type = mf.Type
+				if err := checkSuffixCollisions(existingMF, metricFamiliesByName); err != nil {
+					errs = append(errs, err)
+					continue
+				}
 				metricFamiliesByName[mf.GetName()] = existingMF
 			}
 			for _, m := range mf.Metric {
@@ -767,6 +775,66 @@ func normalizeMetricFamilies(metricFamiliesByName map[string]*dto.MetricFamily)
 	return result
 }
 
+// checkSuffixCollisions checks for collisions with the “magic” suffixes the
+// Prometheus text format and the internal metric representation of the
+// Prometheus server add while flattening Summaries and Histograms.
+func checkSuffixCollisions(mf *dto.MetricFamily, mfs map[string]*dto.MetricFamily) error {
+	var (
+		newName              = mf.GetName()
+		newType              = mf.GetType()
+		newNameWithoutSuffix = ""
+	)
+	switch {
+	case strings.HasSuffix(newName, "_count"):
+		newNameWithoutSuffix = newName[:len(newName)-6]
+	case strings.HasSuffix(newName, "_sum"):
+		newNameWithoutSuffix = newName[:len(newName)-4]
+	case strings.HasSuffix(newName, "_bucket"):
+		newNameWithoutSuffix = newName[:len(newName)-7]
+	}
+	if newNameWithoutSuffix != "" {
+		if existingMF, ok := mfs[newNameWithoutSuffix]; ok {
+			switch existingMF.GetType() {
+			case dto.MetricType_SUMMARY:
+				if !strings.HasSuffix(newName, "_bucket") {
+					return fmt.Errorf(
+						"collected metric named %q collides with previously collected summary named %q",
+						newName, newNameWithoutSuffix,
+					)
+				}
+			case dto.MetricType_HISTOGRAM:
+				return fmt.Errorf(
+					"collected metric named %q collides with previously collected histogram named %q",
+					newName, newNameWithoutSuffix,
+				)
+			}
+		}
+	}
+	if newType == dto.MetricType_SUMMARY || newType == dto.MetricType_HISTOGRAM {
+		if _, ok := mfs[newName+"_count"]; ok {
+			return fmt.Errorf(
+				"collected histogram or summary named %q collides with previously collected metric named %q",
+				newName, newName+"_count",
+			)
+		}
+		if _, ok := mfs[newName+"_sum"]; ok {
+			return fmt.Errorf(
+				"collected histogram or summary named %q collides with previously collected metric named %q",
+				newName, newName+"_sum",
+			)
+		}
+	}
+	if newType == dto.MetricType_HISTOGRAM {
+		if _, ok := mfs[newName+"_bucket"]; ok {
+			return fmt.Errorf(
+				"collected histogram named %q collides with previously collected metric named %q",
+				newName, newName+"_bucket",
+			)
+		}
+	}
+	return nil
+}
+
 // checkMetricConsistency checks if the provided Metric is consistent with the
 // provided MetricFamily. It also hashes the Metric labels and the MetricFamily
 // name. If the resulting hash is already in the provided metricHashes, an error

prometheus/registry_test.go

@@ -250,6 +250,63 @@ metric: <
 	expectedMetricFamilyInvalidLabelValueAsText := []byte(`An error has occurred during metrics gathering:
 
 collected metric "name" { label:<name:"constname" value:"\377" > label:<name:"labelname" value:"different_val" > counter:<value:42 > } has a label named "constname" whose value is not utf8: "\xff"
+`)
+
+	summary := prometheus.NewSummary(prometheus.SummaryOpts{
+		Name: "complex",
+		Help: "A metric to check collisions with _sum and _count.",
+	})
+	summaryAsText := []byte(`# HELP complex A metric to check collisions with _sum and _count.
+# TYPE complex summary
+complex{quantile="0.5"} NaN
+complex{quantile="0.9"} NaN
+complex{quantile="0.99"} NaN
+complex_sum 0
+complex_count 0
+`)
+	histogram := prometheus.NewHistogram(prometheus.HistogramOpts{
+		Name: "complex",
+		Help: "A metric to check collisions with _sun, _count, and _bucket.",
+	})
+	externalMetricFamilyWithBucketSuffix := &dto.MetricFamily{
+		Name: proto.String("complex_bucket"),
+		Help: proto.String("externaldocstring"),
+		Type: dto.MetricType_COUNTER.Enum(),
+		Metric: []*dto.Metric{
+			{
+				Counter: &dto.Counter{
+					Value: proto.Float64(1),
+				},
+			},
+		},
+	}
+	externalMetricFamilyWithBucketSuffixAsText := []byte(`# HELP complex_bucket externaldocstring
+# TYPE complex_bucket counter
+complex_bucket 1
+`)
+	externalMetricFamilyWithCountSuffix := &dto.MetricFamily{
+		Name: proto.String("complex_count"),
+		Help: proto.String("externaldocstring"),
+		Type: dto.MetricType_COUNTER.Enum(),
+		Metric: []*dto.Metric{
+			{
+				Counter: &dto.Counter{
+					Value: proto.Float64(1),
+				},
+			},
+		},
+	}
+	bucketCollisionMsg := []byte(`An error has occurred during metrics gathering:
+
+collected metric named "complex_bucket" collides with previously collected histogram named "complex"
+`)
+	summaryCountCollisionMsg := []byte(`An error has occurred during metrics gathering:
+
+collected metric named "complex_count" collides with previously collected summary named "complex"
+`)
+	histogramCountCollisionMsg := []byte(`An error has occurred during metrics gathering:
+
+collected metric named "complex_count" collides with previously collected histogram named "complex"
 `)
 
 	type output struct {
@@ -513,7 +570,7 @@ collected metric "name" { label:<name:"constname" value:"\377" > label:<name:"la
 		},
 		{ // 17
 			headers: map[string]string{
-				"Accept": "application/json",
+				"Accept": "text/plain",
 			},
 			out: output{
 				headers: map[string]string{
@@ -523,6 +580,72 @@ collected metric "name" { label:<name:"constname" value:"\377" > label:<name:"la
 			},
 			collector: uncheckedCollector{metricVec},
 		},
+		{ // 18
+			headers: map[string]string{
+				"Accept": "text/plain",
+			},
+			out: output{
+				headers: map[string]string{
+					"Content-Type": `text/plain; charset=utf-8`,
+				},
+				body: histogramCountCollisionMsg,
+			},
+			collector: histogram,
+			externalMF: []*dto.MetricFamily{
+				externalMetricFamilyWithCountSuffix,
+			},
+		},
+		{ // 19
+			headers: map[string]string{
+				"Accept": "text/plain",
+			},
+			out: output{
+				headers: map[string]string{
+					"Content-Type": `text/plain; charset=utf-8`,
+				},
+				body: bucketCollisionMsg,
+			},
+			collector: histogram,
+			externalMF: []*dto.MetricFamily{
+				externalMetricFamilyWithBucketSuffix,
+			},
+		},
+		{ // 20
+			headers: map[string]string{
+				"Accept": "text/plain",
+			},
+			out: output{
+				headers: map[string]string{
+					"Content-Type": `text/plain; charset=utf-8`,
+				},
+				body: summaryCountCollisionMsg,
+			},
+			collector: summary,
+			externalMF: []*dto.MetricFamily{
+				externalMetricFamilyWithCountSuffix,
+			},
+		},
+		{ // 21
+			headers: map[string]string{
+				"Accept": "text/plain",
+			},
+			out: output{
+				headers: map[string]string{
+					"Content-Type": `text/plain; version=0.0.4; charset=utf-8`,
+				},
+				body: bytes.Join(
+					[][]byte{
+						summaryAsText,
+						externalMetricFamilyWithBucketSuffixAsText,
+					},
+					[]byte{},
+				),
+			},
+			collector: summary,
+			externalMF: []*dto.MetricFamily{
+				externalMetricFamilyWithBucketSuffix,
+			},
+		},
 	}
 	for i, scenario := range scenarios {
 		registry := prometheus.NewPedanticRegistry()