metricsbp: add MetricsLabels type (reddit#93)

This is a `map[string]string` typedef that allows you to define StatsD labels in a simple way and provides a method to convert itself to the format that the StatsD client expects.

metricsbp/statsd.go

@@ -75,6 +75,26 @@ type Statsd struct {
 	histogramSampleRate float64
 }
 
+// MetricsLabels allows you to specify labels as a convenient map and
+// provides helpers to convert them into other formats.
+type MetricsLabels map[string]string
+
+// AsStatsdLabels returns the labels in the format expected by the
+// statsd metrics client, that is a slice of strings.
+//
+// This method is nil-safe and will just return nil if the receiver is
+// nil.
+func (l MetricsLabels) AsStatsdLabels() []string {
+	if l == nil {
+		return nil
+	}
+	labels := make([]string, 0, len(l)*2)
+	for k, v := range l {
+		labels = append(labels, k, v)
+	}
+	return labels
+}
+
 // StatsdConfig is the configs used in NewStatsd.
 type StatsdConfig struct {
 	// Prefix is the common metrics path prefix shared by all metrics managed by
@@ -111,7 +131,7 @@ type StatsdConfig struct {
 	// Labels are the labels/tags to be attached to every metrics created
 	// from this Statsd object. For labels/tags only needed by some metrics,
 	// use Counter/Gauge/Timing.With() instead.
-	Labels map[string]string
+	Labels MetricsLabels
 }
 
 // counterSampleRate treats 0 (abs(rate) < epsilon) as 1, and <-epsilon as 0.
@@ -136,10 +156,7 @@ func NewStatsd(ctx context.Context, cfg StatsdConfig) *Statsd {
 	if prefix != "" && !strings.HasSuffix(prefix, ".") {
 		prefix = prefix + "."
 	}
-	labels := make([]string, 0, len(cfg.Labels)*2)
-	for k, v := range cfg.Labels {
-		labels = append(labels, k, v)
-	}
+	labels := cfg.Labels.AsStatsdLabels()
 	st := &Statsd{
 		Statsd:              influxstatsd.New(prefix, log.KitLogger(cfg.LogLevel), labels...),
 		ctx:                 ctx,

metricsbp/statsd_test.go

@@ -3,6 +3,7 @@ package metricsbp_test
 import (
 	"bytes"
 	"context"
+	"reflect"
 	"strings"
 	"testing"
 
@@ -247,3 +248,39 @@ func BenchmarkStatsd(b *testing.B) {
 		},
 	)
 }
+
+func TestMetricsLabels(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name     string
+		labels   metricsbp.MetricsLabels
+		expected []string
+	}{
+		{
+			name:     "nil",
+			labels:   nil,
+			expected: nil,
+		},
+		{
+			name:     "one",
+			labels:   metricsbp.MetricsLabels{"key": "value"},
+			expected: []string{"key", "value"},
+		},
+	}
+
+	for _, _c := range cases {
+		c := _c
+		t.Run(c.name, func(t *testing.T) {
+			t.Parallel()
+
+			asStatsd := c.labels.AsStatsdLabels()
+			if len(asStatsd) != len(c.labels)*2 {
+				t.Fatalf("wrong size: %#v", asStatsd)
+			}
+			if !reflect.DeepEqual(c.expected, asStatsd) {
+				t.Fatalf("labels do not match, expected %#v, got %#v", c.expected, asStatsd)
+			}
+		})
+	}
+}

thriftclient/client_pool.go

@@ -42,7 +42,7 @@ type ClientPoolConfig struct {
 
 	// Any labels that should be applied to metrics logged by the ClientPool.
 	// This includes the optional pool stats.
-	MetricsLabels map[string]string
+	MetricsLabels metricsbp.MetricsLabels
 
 	// ReportPoolStats signals to the ClientPool that it should report
 	// statistics on the underlying clientpool.Pool in a background
@@ -61,16 +61,6 @@ type ClientPoolConfig struct {
 	PoolGaugeInterval time.Duration
 }
 
-// getMetricLabels returns c.MetricsLabels as a slice of strings, appropriate
-// for passing to a metrics client.
-func (c ClientPoolConfig) getMetricLabels() []string {
-	labels := make([]string, len(c.MetricsLabels)*2)
-	for k, v := range c.MetricsLabels {
-		labels = append(labels, k, v)
-	}
-	return labels
-}
-
 // Client is a client object that implements both the clientpool.Client and
 // thrift.TCLient interfaces.
 //
@@ -187,7 +177,7 @@ func NewCustomClientPool(cfg ClientPoolConfig, genAddr AddressGenerator, clientF
 }
 
 func newClientPool(cfg ClientPoolConfig, genAddr AddressGenerator, clientFact ClientFactory, protoFact thrift.TProtocolFactory) (*clientPool, error) {
-	labels := cfg.getMetricLabels()
+	labels := cfg.MetricsLabels.AsStatsdLabels()
 	pool, err := clientpool.NewChannelPool(
 		cfg.InitialConnections,
 		cfg.MaxConnections,