add feature/metrics

docs/protoapi_metrics.md

@@ -0,0 +1,56 @@
+# protoapi metrics
+
+## Usage
+
+Import middleware and use in echo.
+
+example:
+```go
+package main
+
+import (
+	"github.com/labstack/echo"
+	"github.com/yoozoo/protoapi/protoapigo/metrics"
+	"code/generated/by/protoapi/demo"
+)
+
+type Service struct{}
+
+var _ demo.DemoService = &Service{}
+
+func main() {
+    e := echo.New()
+
+    service := &Service{}
+	calsvr.RegisterCalcService(e, c)
+
+    // use metrics middleware
+    m := metrics.MetricsFunc()
+    e.Use(m)
+
+	e.Logger.Fatal(e.Start(":8080"))
+}
+```
+
+## Metrics endpoint
+
+By default, echo server exports metrics under the `/metrics` path on its client port.
+
+The metrics can be fetched with `curl`:
+
+```sh
+$ curl -L http://localhost:8080/metrics
+```
+## More Options
+Function `metrics.MetricsFunc()` can have `Option` parameters.
+```go
+package metrics
+
+func Registry(r prometheus.Registerer) Option {}
+
+func MetricsPath(v string) Option {}
+
+func Namespace(v string) Option {}
+
+func Subsystem(v string) Option {}
+```