Make mapper cache respect metric type

- Statsd allows users to provide a metric with the same name but
  differing types (counter, gauge, timer)
- The exporter allows this by letting users specify a
  "match_metric_type" in the mapping config
- However the mapper cache does not look at the metric type so it would
  return a MetricMapperCacheResult for the type of the first metric with
that name that the exporter saw
- Add MetricType to the signature for the cache and format the metric
  name with the type to provide unique keys for a metric with the same
name but differing type

Signed-off-by: Andy Paine <andy.paine@digital.cabinet-office.gov.uk>

pkg/mapper/mapper.go

@@ -237,7 +237,7 @@ func (m *MetricMapper) InitCache(cacheSize int) {
 func (m *MetricMapper) GetMapping(statsdMetric string, statsdMetricType MetricType) (*MetricMapping, prometheus.Labels, bool) {
 	m.mutex.RLock()
 	defer m.mutex.RUnlock()
-	result, cached := m.cache.Get(statsdMetric)
+	result, cached := m.cache.Get(statsdMetric, statsdMetricType)
 	if cached {
 		return result.Mapping, result.Labels, result.Matched
 	}
@@ -253,12 +253,12 @@ func (m *MetricMapper) GetMapping(statsdMetric string, statsdMetricType MetricTy
 				labels[result.labelKeys[index]] = formatter.Format(captures)
 			}
 
-			m.cache.AddMatch(statsdMetric, result, labels)
+			m.cache.AddMatch(statsdMetric, statsdMetricType, result, labels)
 
 			return result, labels, true
 		} else if !m.doRegex {
 			// if there's no regex match type, return immediately
-			m.cache.AddMiss(statsdMetric)
+			m.cache.AddMiss(statsdMetric, statsdMetricType)
 			return nil, nil, false
 		}
 	}
@@ -291,11 +291,11 @@ func (m *MetricMapper) GetMapping(statsdMetric string, statsdMetricType MetricTy
 			labels[label] = string(value)
 		}
 
-		m.cache.AddMatch(statsdMetric, &mapping, labels)
+		m.cache.AddMatch(statsdMetric, statsdMetricType, &mapping, labels)
 
 		return &mapping, labels, true
 	}
 
-	m.cache.AddMiss(statsdMetric)
+	m.cache.AddMiss(statsdMetric, statsdMetricType)
 	return nil, nil, false
 }

pkg/mapper/mapper_cache.go

@@ -14,6 +14,7 @@
 package mapper
 
 import (
+	"fmt"
 	"github.com/hashicorp/golang-lru"
 	"github.com/prometheus/client_golang/prometheus"
 )
@@ -34,9 +35,9 @@ type MetricMapperCacheResult struct {
 }
 
 type MetricMapperCache interface {
-	Get(metricString string) (*MetricMapperCacheResult, bool)
-	AddMatch(metricString string, mapping *MetricMapping, labels prometheus.Labels)
-	AddMiss(metricString string)
+	Get(metricString string, metricType MetricType) (*MetricMapperCacheResult, bool)
+	AddMatch(metricString string, metricType MetricType, mapping *MetricMapping, labels prometheus.Labels)
+	AddMiss(metricString string, metricType MetricType)
 }
 
 type MetricMapperLRUCache struct {
@@ -57,42 +58,46 @@ func NewMetricMapperCache(size int) (*MetricMapperLRUCache, error) {
 	return &MetricMapperLRUCache{cache: cache}, nil
 }
 
-func (m *MetricMapperLRUCache) Get(metricString string) (*MetricMapperCacheResult, bool) {
-	if result, ok := m.cache.Get(metricString); ok {
+func (m *MetricMapperLRUCache) Get(metricString string, metricType MetricType) (*MetricMapperCacheResult, bool) {
+	if result, ok := m.cache.Get(formatKey(metricString, metricType)); ok {
 		return result.(*MetricMapperCacheResult), true
 	} else {
 		return nil, false
 	}
 }
 
-func (m *MetricMapperLRUCache) AddMatch(metricString string, mapping *MetricMapping, labels prometheus.Labels) {
+func (m *MetricMapperLRUCache) AddMatch(metricString string, metricType MetricType, mapping *MetricMapping, labels prometheus.Labels) {
 	go m.trackCacheLength()
-	m.cache.Add(metricString, &MetricMapperCacheResult{Mapping: mapping, Matched: true, Labels: labels})
+	m.cache.Add(formatKey(metricString, metricType), &MetricMapperCacheResult{Mapping: mapping, Matched: true, Labels: labels})
 }
 
-func (m *MetricMapperLRUCache) AddMiss(metricString string) {
+func (m *MetricMapperLRUCache) AddMiss(metricString string, metricType MetricType) {
 	go m.trackCacheLength()
-	m.cache.Add(metricString, &MetricMapperCacheResult{Matched: false})
+	m.cache.Add(formatKey(metricString, metricType), &MetricMapperCacheResult{Matched: false})
 }
 
 func (m *MetricMapperLRUCache) trackCacheLength() {
 	cacheLength.Set(float64(m.cache.Len()))
 }
 
+func formatKey(metricString string, metricType MetricType) string {
+	return fmt.Sprintf("%s.%s", string(metricType), metricString)
+}
+
 func NewMetricMapperNoopCache() *MetricMapperNoopCache {
 	cacheLength.Set(0)
 	return &MetricMapperNoopCache{}
 }
 
-func (m *MetricMapperNoopCache) Get(metricString string) (*MetricMapperCacheResult, bool) {
+func (m *MetricMapperNoopCache) Get(metricString string, metricType MetricType) (*MetricMapperCacheResult, bool) {
 	return nil, false
 }
 
-func (m *MetricMapperNoopCache) AddMatch(metricString string, mapping *MetricMapping, labels prometheus.Labels) {
+func (m *MetricMapperNoopCache) AddMatch(metricString string, metricType MetricType, mapping *MetricMapping, labels prometheus.Labels) {
 	return
 }
 
-func (m *MetricMapperNoopCache) AddMiss(metricString string) {
+func (m *MetricMapperNoopCache) AddMiss(metricString string, metricType MetricType) {
 	return
 }