Resolves prometheus#77 add cmdline flag to drop unmapped

* Adds `-statsd.drop-unmapped` cmdline flag which causes statsd metrics
  that don't match a mapping to be dropped. New flag defaults to "false"

Add test for dropUnmapped behavior

Convert dropUnmapped to a attribute of the Exporter

  * Removed references to dropUnmapped global var in favor of a boolean
    attribute of `Exporter`
  * Updated tests to reflect refactor
  * Reordered command line options per PR review

exporter.go

@@ -218,11 +218,12 @@ func (c *TimerEvent) Labels() map[string]string { return c.labels }
 type Events []Event
 
 type Exporter struct {
-	Counters   *CounterContainer
-	Gauges     *GaugeContainer
-	Summaries  *SummaryContainer
-	Histograms *HistogramContainer
-	mapper     *metricMapper
+	Counters     *CounterContainer
+	Gauges       *GaugeContainer
+	Summaries    *SummaryContainer
+	Histograms   *HistogramContainer
+	mapper       *metricMapper
+	dropUnmapped bool
 }
 
 func escapeMetricName(metricName string) string {
@@ -257,6 +258,9 @@ func (b *Exporter) Listen(e <-chan Events) {
 				}
 			} else {
 				eventsUnmapped.Inc()
+				if b.dropUnmapped == true {
+					continue
+				}
 				metricName = escapeMetricName(event.MetricName())
 			}
 
@@ -351,13 +355,14 @@ func (b *Exporter) Listen(e <-chan Events) {
 	}
 }
 
-func NewExporter(mapper *metricMapper) *Exporter {
+func NewExporter(mapper *metricMapper, dropUnmapped bool) *Exporter {
 	return &Exporter{
-		Counters:   NewCounterContainer(),
-		Gauges:     NewGaugeContainer(),
-		Summaries:  NewSummaryContainer(),
-		Histograms: NewHistogramContainer(mapper),
-		mapper:     mapper,
+		Counters:     NewCounterContainer(),
+		Gauges:       NewGaugeContainer(),
+		Summaries:    NewSummaryContainer(),
+		Histograms:   NewHistogramContainer(mapper),
+		mapper:       mapper,
+		dropUnmapped: dropUnmapped,
 	}
 }
 

exporter_test.go

@@ -44,7 +44,30 @@ func TestNegativeCounter(t *testing.T) {
 		},
 	}
 	events <- c
-	ex := NewExporter(&metricMapper{})
+	ex := NewExporter(&metricMapper{}, false)
+
+	// Close channel to signify we are done with the listener after a short period.
+	go func() {
+		time.Sleep(time.Millisecond * 100)
+		close(events)
+	}()
+
+	ex.Listen(events)
+}
+
+// TestDropUnmapped validates that the dropUnmapped global will prevent unmapped
+// metrics from being recorded when set true and that they are recorded when set
+// false.
+func TestDropUnmapped(t *testing.T) {
+	events := make(chan Events, 1)
+	c := Events{
+		&CounterEvent{
+			metricName: "foo",
+			value:      1,
+		},
+	}
+	events <- c
+	ex := NewExporter(&metricMapper{}, true, true)
 
 	// Close channel to signify we are done with the listener after a short period.
 	go func() {
@@ -53,14 +76,29 @@ func TestNegativeCounter(t *testing.T) {
 	}()
 
 	ex.Listen(events)
+	if len(ex.Counters.Elements) != 0 {
+		t.Fatalf("Unmapped metric recorded inspite of dropUnmapped being set true")
+	}
+	ex = NewExporter(&metricMapper{}, true, false)
+	events = make(chan Events, 1)
+	events <- c
+	// Close channel to signify we are done with the listener after a short period.
+	go func() {
+		time.Sleep(time.Millisecond * 100)
+		close(events)
+	}()
+	ex.Listen(events)
+	if len(ex.Counters.Elements) != 1 {
+		t.Fatalf("Unmapped metric not recorded inspite of dropUnmapped being set false")
+	}
 }
 
 // TestInvalidUtf8InDatadogTagValue validates robustness of exporter listener
 // against datadog tags with invalid tag values.
 // It sends the same tags first with a valid value, then with an invalid one.
 // The exporter should not panic, but drop the invalid event
 func TestInvalidUtf8InDatadogTagValue(t *testing.T) {
-	ex := NewExporter(&metricMapper{})
+	ex := NewExporter(&metricMapper{}, false)
 	for _, l := range []statsDPacketHandler{&StatsDUDPListener{}, &mockStatsDTCPListener{}} {
 		events := make(chan Events, 2)
 

main.go

@@ -40,6 +40,7 @@ var (
 	mappingConfig       = flag.String("statsd.mapping-config", "", "Metric mapping configuration file name.")
 	readBuffer          = flag.Int("statsd.read-buffer", 0, "Size (in bytes) of the operating system's transmit read buffer associated with the UDP connection. Please make sure the kernel parameters net.core.rmem_max is set to a value greater than the value specified.")
 	showVersion         = flag.Bool("version", false, "Print version information.")
+	dropUnmapped        = flag.Bool("statsd.drop-unmapped", false, "Drop statsd metrics which have no matched mapping configured.")
 )
 
 func serveHTTP() {
@@ -194,6 +195,6 @@ func main() {
 		}
 		go watchConfig(*mappingConfig, mapper)
 	}
-	exporter := NewExporter(mapper)
+	exporter := NewExporter(mapper, *dropUnmapped)
 	exporter.Listen(events)
 }