Metrics interface and Prometheus implementation (#1929)

* Metrics interface

* Prometheus implementation

* NoOp implementation

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

metrics/wrapper/metrics_wrapper.go

@@ -0,0 +1,51 @@
+package wrapper
+
+import (
+	"time"
+
+	"context"
+
+	"github.com/micro/go-micro/v3/metrics"
+	"github.com/micro/go-micro/v3/server"
+)
+
+// Wrapper provides a HandlerFunc for metrics.Reporter implementations:
+type Wrapper struct {
+	reporter metrics.Reporter
+}
+
+// New returns a *Wrapper configured with the given metrics.Reporter:
+func New(reporter metrics.Reporter) *Wrapper {
+	return &Wrapper{
+		reporter: reporter,
+	}
+}
+
+// HandlerFunc instruments handlers registered to a service:
+func (w *Wrapper) HandlerFunc(handlerFunction server.HandlerFunc) server.HandlerFunc {
+	return func(ctx context.Context, req server.Request, rsp interface{}) error {
+
+		// Build some tags to describe the call:
+		tags := metrics.Tags{
+			"method": req.Method(),
+		}
+
+		// Start the clock:
+		callTime := time.Now()
+
+		// Run the handlerFunction:
+		err := handlerFunction(ctx, req, rsp)
+
+		// Add a result tag:
+		if err != nil {
+			tags["result"] = "failure"
+		} else {
+			tags["result"] = "failure"
+		}
+
+		// Instrument the result (if the DefaultClient has been configured):
+		w.reporter.Timing("service.handler", time.Since(callTime), tags)
+
+		return err
+	}
+}