add RegisterCheck server option for internal health checks

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

server/options.go

@@ -25,6 +25,8 @@ type Options struct {
 	HdlrWrappers []HandlerWrapper
 	SubWrappers  []SubscriberWrapper
 
+	// RegisterCheck runs a check function before registering the service
+	RegisterCheck func(context.Context) error
 	// The register expiry time
 	RegisterTTL time.Duration
 	// The interval on which to register
@@ -67,6 +69,10 @@ func newOptions(opt ...Option) Options {
 		opts.DebugHandler = debug.DefaultDebugHandler
 	}
 
+	if opts.RegisterCheck == nil {
+		opts.RegisterCheck = DefaultRegisterCheck
+	}
+
 	if len(opts.Address) == 0 {
 		opts.Address = DefaultAddress
 	}
@@ -163,6 +169,13 @@ func Metadata(md map[string]string) Option {
 	}
 }
 
+// RegisterCheck run func before registry service
+func RegisterCheck(fn func(context.Context) error) Option {
+	return func(o *Options) {
+		o.RegisterCheck = fn
+	}
+}
+
 // Register the service with a TTL
 func RegisterTTL(t time.Duration) Option {
 	return func(o *Options) {