Metrics interface and Prometheus implementation (#1929)

* Metrics interface

* Prometheus implementation

* NoOp implementation

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

metrics/prometheus/reporter.go

@@ -0,0 +1,69 @@
+package prometheus
+
+import (
+	"net/http"
+	"strings"
+
+	log "github.com/micro/go-micro/v3/logger"
+	"github.com/micro/go-micro/v3/metrics"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// Reporter is an implementation of metrics.Reporter:
+type Reporter struct {
+	options            metrics.Options
+	prometheusRegistry *prometheus.Registry
+	metrics            metricFamily
+}
+
+// New returns a configured prometheus reporter:
+func New(opts ...metrics.Option) (*Reporter, error) {
+	options := metrics.NewOptions(opts...)
+
+	// Make a prometheus registry (this keeps track of any metrics we generate):
+	prometheusRegistry := prometheus.NewRegistry()
+	prometheusRegistry.Register(prometheus.NewGoCollector())
+	prometheusRegistry.Register(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{Namespace: "goruntime"}))
+
+	// Make a new Reporter:
+	newReporter := &Reporter{
+		options:            options,
+		prometheusRegistry: prometheusRegistry,
+	}
+
+	// Add metrics families for each type:
+	newReporter.metrics = newReporter.newMetricFamily()
+
+	// Handle the metrics endpoint with prometheus:
+	log.Infof("Metrics/Prometheus [http] Listening on %s%s", options.Address, options.Path)
+	http.Handle(options.Path, promhttp.HandlerFor(prometheusRegistry, promhttp.HandlerOpts{ErrorHandling: promhttp.ContinueOnError}))
+	go http.ListenAndServe(options.Address, nil)
+
+	return newReporter, nil
+}
+
+// convertTags turns Tags into prometheus labels:
+func (r *Reporter) convertTags(tags metrics.Tags) prometheus.Labels {
+	labels := prometheus.Labels{}
+	for key, value := range tags {
+		labels[key] = r.stripUnsupportedCharacters(value)
+	}
+	return labels
+}
+
+// listTagKeys returns a list of tag keys (we need to provide this to the Prometheus client):
+func (r *Reporter) listTagKeys(tags metrics.Tags) (labelKeys []string) {
+	for key := range tags {
+		labelKeys = append(labelKeys, key)
+	}
+	return
+}
+
+// stripUnsupportedCharacters cleans up a metrics key or value:
+func (r *Reporter) stripUnsupportedCharacters(metricName string) string {
+	valueWithoutDots := strings.Replace(metricName, ".", "_", -1)
+	valueWithoutCommas := strings.Replace(valueWithoutDots, ",", "_", -1)
+	valueWIthoutSpaces := strings.Replace(valueWithoutCommas, " ", "", -1)
+	return valueWIthoutSpaces
+}