Add low card provider for optionally skipping labels

go-kit/metrics/lowcard/low_cardinality.go

@@ -0,0 +1,120 @@
+package lowcard
+
+import (
+	"github.com/go-kit/kit/metrics"
+	xmetrics "github.com/heroku/x/go-kit/metrics"
+)
+
+// NewLowCardinalityWrappedProvider is a wrapper around metrics.Provider
+// that ignores any added labels via metric.With() call.
+func NewLowCardinalityWrappedProvider(p xmetrics.Provider, labels []string) xmetrics.Provider {
+	return lowCardinalityWrappedProvider{
+		Provider:        p,
+		labelsToInclude: labels,
+	}
+}
+
+type lowCardinalityWrappedProvider struct {
+	xmetrics.Provider
+	// Labels that will be added to instruments.
+	labelsToInclude []string
+}
+
+type counter struct {
+	metrics.Counter
+	// Labels that will be added to counters.
+	labelsToInclude []string
+}
+
+// NewCounter wraps counter around metrics.Counter.
+func (p lowCardinalityWrappedProvider) NewCounter(name string) metrics.Counter {
+	return counter{
+		Counter:         p.Provider.NewCounter(name),
+		labelsToInclude: p.labelsToInclude,
+	}
+}
+
+// With noops and returns counter if the passed labelValues
+// do not start with a label that has been designated for inclusion.
+func (c counter) With(labelValues ...string) metrics.Counter {
+	c.Counter = c.Counter.With(sanitizeLabels(c.labelsToInclude, labelValues)...)
+	return c
+}
+
+type gauge struct {
+	metrics.Gauge
+	// Labels that will be added to gauges.
+	labelsToInclude []string
+}
+
+// NewGauge wraps gauge around metrics.Gauge.
+func (p lowCardinalityWrappedProvider) NewGauge(name string) metrics.Gauge {
+	return gauge{
+		Gauge:           p.Provider.NewGauge(name),
+		labelsToInclude: p.labelsToInclude,
+	}
+}
+
+// With noops and returns gauge if the passed labelValues
+// do not start with a label that has been designated for inclusion.
+func (g gauge) With(labelValues ...string) metrics.Gauge {
+	g.Gauge = g.Gauge.With(sanitizeLabels(g.labelsToInclude, labelValues)...)
+	return g
+}
+
+type histogram struct {
+	metrics.Histogram
+	// Labels that will be added to histograms.
+	labelsToInclude []string
+}
+
+// With noops and returns histogram if the passed labelValues
+// do not start with a label that has been designated for inclusion.
+func (p lowCardinalityWrappedProvider) NewHistogram(name string, buckets int) metrics.Histogram {
+	return histogram{
+		Histogram:       p.Provider.NewHistogram(name, buckets),
+		labelsToInclude: p.labelsToInclude,
+	}
+}
+
+// With noops and returns histogram if the passed labelValues
+// do not start with a label that has been designated for inclusion.
+func (p lowCardinalityWrappedProvider) NewExplicitHistogram(name string, fn xmetrics.DistributionFunc) metrics.Histogram {
+	return histogram{
+		Histogram:       p.Provider.NewExplicitHistogram(name, fn),
+		labelsToInclude: p.labelsToInclude,
+	}
+}
+
+// With noops and returns histogram.
+func (h histogram) With(labelValues ...string) metrics.Histogram {
+	h.Histogram = h.Histogram.With(sanitizeLabels(h.labelsToInclude, labelValues)...)
+	return h
+}
+
+func sanitizeLabels(labelsToInclude, labelValues []string) []string {
+	sanitized := []string{}
+
+	// The instrument expects an even number of values
+	// since they represent key-value pairs. If there
+	// are not an even number, we assume labels are malformed.
+	// If malformed, the labels are not added.
+	if len(labelValues)%2 != 0 {
+		return []string{}
+	}
+	for i := 0; i <= len(labelValues)-2; i += 2 {
+		if contains(labelsToInclude, labelValues[i]) {
+			sanitized = append(sanitized, labelValues[i], labelValues[i+1])
+		}
+	}
+	return sanitized
+}
+
+func contains(strs []string, str string) bool {
+	for _, s := range strs {
+		if s == str {
+			return true
+		}
+	}
+	return false
+}