Allow help text to be customized (#87)

* Updated mappings to accept custom help text in YAML config
* Updated exporter to display configured help messages
* Update README to reflect aditional configurability
* Removed inaccurate comment

* Removed some cruft from a rebase

README.md

@@ -128,6 +128,17 @@ follows:
      => test_web__server_foo_bar{}
 
 
+If the default metric help text is insufficient for your needs you may use the YAML
+configuration to specify a custom help text for each mapping:
+```yaml
+mappings:
+- match: http.request.*
+  help: "Total number of http requests"
+  labels:
+    name: "http_requests_total"
+    code: "$1"
+```
+
 In the configuration, one may also set the timer type to "histogram". The 
 default is "summary" as in the plain text configuration format.  For example,
 to set the timer type for a single metric:

exporter.go

@@ -71,13 +71,13 @@ func NewCounterContainer() *CounterContainer {
 	}
 }
 
-func (c *CounterContainer) Get(metricName string, labels prometheus.Labels) (prometheus.Counter, error) {
+func (c *CounterContainer) Get(metricName string, labels prometheus.Labels, help string) (prometheus.Counter, error) {
 	hash := hashNameAndLabels(metricName, labels)
 	counter, ok := c.Elements[hash]
 	if !ok {
 		counter = prometheus.NewCounter(prometheus.CounterOpts{
 			Name:        metricName,
-			Help:        defaultHelp,
+			Help:        help,
 			ConstLabels: labels,
 		})
 		if err := prometheus.Register(counter); err != nil {
@@ -98,13 +98,13 @@ func NewGaugeContainer() *GaugeContainer {
 	}
 }
 
-func (c *GaugeContainer) Get(metricName string, labels prometheus.Labels) (prometheus.Gauge, error) {
+func (c *GaugeContainer) Get(metricName string, labels prometheus.Labels, help string) (prometheus.Gauge, error) {
 	hash := hashNameAndLabels(metricName, labels)
 	gauge, ok := c.Elements[hash]
 	if !ok {
 		gauge = prometheus.NewGauge(prometheus.GaugeOpts{
 			Name:        metricName,
-			Help:        defaultHelp,
+			Help:        help,
 			ConstLabels: labels,
 		})
 		if err := prometheus.Register(gauge); err != nil {
@@ -125,14 +125,14 @@ func NewSummaryContainer() *SummaryContainer {
 	}
 }
 
-func (c *SummaryContainer) Get(metricName string, labels prometheus.Labels) (prometheus.Summary, error) {
+func (c *SummaryContainer) Get(metricName string, labels prometheus.Labels, help string) (prometheus.Summary, error) {
 	hash := hashNameAndLabels(metricName, labels)
 	summary, ok := c.Elements[hash]
 	if !ok {
 		summary = prometheus.NewSummary(
 			prometheus.SummaryOpts{
 				Name:        metricName,
-				Help:        defaultHelp,
+				Help:        help,
 				ConstLabels: labels,
 			})
 		if err := prometheus.Register(summary); err != nil {
@@ -155,7 +155,7 @@ func NewHistogramContainer(mapper *metricMapper) *HistogramContainer {
 	}
 }
 
-func (c *HistogramContainer) Get(metricName string, labels prometheus.Labels, mapping *metricMapping) (prometheus.Histogram, error) {
+func (c *HistogramContainer) Get(metricName string, labels prometheus.Labels, help string, mapping *metricMapping) (prometheus.Histogram, error) {
 	hash := hashNameAndLabels(metricName, labels)
 	histogram, ok := c.Elements[hash]
 	if !ok {
@@ -166,7 +166,7 @@ func (c *HistogramContainer) Get(metricName string, labels prometheus.Labels, ma
 		histogram = prometheus.NewHistogram(
 			prometheus.HistogramOpts{
 				Name:        metricName,
-				Help:        defaultHelp,
+				Help:        help,
 				ConstLabels: labels,
 				Buckets:     buckets,
 			})
@@ -244,10 +244,19 @@ func (b *Exporter) Listen(e <-chan Events) {
 			return
 		}
 		for _, event := range events {
+			var help string
 			metricName := ""
 			prometheusLabels := event.Labels()
 
 			mapping, labels, present := b.mapper.getMapping(event.MetricName())
+			if mapping == nil {
+				mapping = &metricMapping{}
+			}
+			if mapping.HelpText == "" {
+				help = defaultHelp
+			} else {
+				help = mapping.HelpText
+			}
 			if present {
 				metricName = labels["name"]
 				for label, value := range labels {
@@ -273,6 +282,7 @@ func (b *Exporter) Listen(e <-chan Events) {
 				counter, err := b.Counters.Get(
 					metricName,
 					prometheusLabels,
+					help,
 				)
 				if err == nil {
 					counter.Add(event.Value())
@@ -287,6 +297,7 @@ func (b *Exporter) Listen(e <-chan Events) {
 				gauge, err := b.Gauges.Get(
 					metricName,
 					prometheusLabels,
+					help,
 				)
 
 				if err == nil {
@@ -316,6 +327,7 @@ func (b *Exporter) Listen(e <-chan Events) {
 					histogram, err := b.Histograms.Get(
 						metricName,
 						prometheusLabels,
+						help,
 						mapping,
 					)
 					if err == nil {
@@ -330,6 +342,7 @@ func (b *Exporter) Listen(e <-chan Events) {
 					summary, err := b.Summaries.Get(
 						metricName,
 						prometheusLabels,
+						help,
 					)
 					if err == nil {
 						summary.Observe(event.Value())

mapper.go

@@ -52,6 +52,7 @@ type metricMapping struct {
 	TimerType timerType         `yaml:"timer_type"`
 	Buckets   []float64         `yaml:"buckets"`
 	MatchType matchType         `yaml:"match_type"`
+	HelpText  string            `yaml:"help"`
 }
 
 func (m *metricMapper) initFromYAMLString(fileContents string) error {