add metrics

metrics/service/service.go

@@ -0,0 +1,65 @@
+package service
+
+import (
+	"net"
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+const (
+	DefaultPath = "/metrics"
+)
+
+type options struct {
+	path string
+}
+
+type Option func(*options)
+
+func PathOption(path string) Option {
+	return func(o *options) {
+		o.path = path
+	}
+}
+
+type Service struct {
+	s  *http.Server
+	ln net.Listener
+}
+
+func NewService(addr string, opts ...Option) (*Service, error) {
+	ln, err := net.Listen("tcp", addr)
+	if err != nil {
+		return nil, err
+	}
+
+	var options options
+	for _, opt := range opts {
+		opt(&options)
+	}
+	if options.path == "" {
+		options.path = DefaultPath
+	}
+
+	mux := http.NewServeMux()
+	mux.Handle(options.path, promhttp.Handler())
+	return &Service{
+		s: &http.Server{
+			Handler: mux,
+		},
+		ln: ln,
+	}, nil
+}
+
+func (s *Service) Serve() error {
+	return s.s.Serve(s.ln)
+}
+
+func (s *Service) Addr() net.Addr {
+	return s.ln.Addr()
+}
+
+func (s *Service) Close() error {
+	return s.s.Close()
+}