Metrics interface and Prometheus implementation (#1929)

* Metrics interface

* Prometheus implementation

* NoOp implementation

Co-authored-by: chris <chris@Profanity.local>

metrics/noop/reporter.go

@@ -0,0 +1,37 @@
+package noop
+
+import (
+	"time"
+
+	log "github.com/micro/go-micro/v3/logger"
+	"github.com/micro/go-micro/v3/metrics"
+)
+
+// Reporter is an implementation of metrics.Reporter:
+type Reporter struct {
+	options metrics.Options
+}
+
+// New returns a configured noop reporter:
+func New(opts ...metrics.Option) *Reporter {
+	log.Info("Metrics/NoOp - not doing anything")
+
+	return &Reporter{
+		options: metrics.NewOptions(opts...),
+	}
+}
+
+// Count implements the metrics.Reporter interface Count method:
+func (r *Reporter) Count(metricName string, value int64, tags metrics.Tags) error {
+	return nil
+}
+
+// Gauge implements the metrics.Reporter interface Gauge method:
+func (r *Reporter) Gauge(metricName string, value float64, tags metrics.Tags) error {
+	return nil
+}
+
+// Timing implements the metrics.Reporter interface Timing method:
+func (r *Reporter) Timing(metricName string, value time.Duration, tags metrics.Tags) error {
+	return nil
+}

metrics/noop/reporter_test.go

@@ -0,0 +1,20 @@
+package noop
+
+import (
+	"testing"
+
+	"github.com/micro/go-micro/v3/metrics"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNoopReporter(t *testing.T) {
+
+	// Make a Reporter:
+	reporter := New(metrics.Path("/noop"))
+	assert.NotNil(t, reporter)
+	assert.Equal(t, "/noop", reporter.options.Path)
+
+	// Check that our implementation is valid:
+	assert.Implements(t, new(metrics.Reporter), reporter)
+}