add RegisterCheck web server option for internal health checks

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

web/options.go

@@ -25,6 +25,9 @@ type Options struct {
 	RegisterTTL      time.Duration
 	RegisterInterval time.Duration
 
+	// RegisterCheck runs a check function before registering the service
+	RegisterCheck func(context.Context) error
+
 	Server  *http.Server
 	Handler http.Handler
 
@@ -62,6 +65,10 @@ func newOptions(opts ...Option) Options {
 		o(&opt)
 	}
 
+	if opt.RegisterCheck == nil {
+		opt.RegisterCheck = DefaultRegisterCheck
+	}
+
 	return opt
 }
 
@@ -225,3 +232,10 @@ func StaticDir(d string) Option {
 		o.StaticDir = d
 	}
 }
+
+// RegisterCheck run func before registry service
+func RegisterCheck(fn func(context.Context) error) Option {
+	return func(o *Options) {
+		o.RegisterCheck = fn
+	}
+}

web/service.go

@@ -123,6 +123,13 @@ func (s *service) register() error {
 	srv := s.genSrv()
 	srv.Endpoints = s.srv.Endpoints
 	s.srv = srv
+
+	// use RegisterCheck func before register
+	if err := s.opts.RegisterCheck(s.opts.Context); err != nil {
+		log.Logf("Server %s-%s register check error: %s", s.opts.Name, s.opts.Id, err)
+		return err
+	}
+
 	return r.Register(s.srv, registry.RegisterTTL(s.opts.RegisterTTL))
 }
 

web/web.go

@@ -2,6 +2,7 @@
 package web
 
 import (
+	"context"
 	"net/http"
 	"time"
 
@@ -33,6 +34,7 @@ var (
 
 	// static directory
 	DefaultStaticDir     = "html"
+	DefaultRegisterCheck = func(context.Context) error { return nil }
 )
 
 // NewService returns a new web.Service