DrainXXX options for nats broker and subscriber

nats.go

@@ -19,11 +19,13 @@ type nbroker struct {
 	conn  *nats.Conn
 	opts  broker.Options
 	nopts nats.Options
+	drain bool
 }
 
 type subscriber struct {
 	s     *nats.Subscription
 	opts  broker.SubscribeOptions
+	drain bool
 }
 
 type publication struct {
@@ -56,6 +58,9 @@ func (n *subscriber) Topic() string {
 }
 
 func (n *subscriber) Unsubscribe() error {
+	if n.drain {
+		return n.s.Drain()
+	}
 	return n.s.Unsubscribe()
 }
 
@@ -121,7 +126,11 @@ func (n *nbroker) Connect() error {
 
 func (n *nbroker) Disconnect() error {
 	n.RLock()
+	if n.drain {
+		n.conn.Drain()
+	} else {
 		n.conn.Close()
+	}
 	n.RUnlock()
 	return nil
 }
@@ -155,12 +164,18 @@ func (n *nbroker) Subscribe(topic string, handler broker.Handler, opts ...broker
 
 	opt := broker.SubscribeOptions{
 		AutoAck: true,
+		Context: context.Background(),
 	}
 
 	for _, o := range opts {
 		o(&opt)
 	}
 
+	var drain bool
+	if _, ok := opt.Context.Value(drainSubscriptionKey{}).(bool); ok {
+		drain = true
+	}
+
 	fn := func(msg *nats.Msg) {
 		var m broker.Message
 		if err := n.opts.Codec.Unmarshal(msg.Data, &m); err != nil {
@@ -182,7 +197,7 @@ func (n *nbroker) Subscribe(topic string, handler broker.Handler, opts ...broker
 	if err != nil {
 		return nil, err
 	}
-	return &subscriber{s: sub, opts: opt}, nil
+	return &subscriber{s: sub, opts: opt, drain: drain}, nil
 }
 
 func (n *nbroker) String() string {
@@ -205,6 +220,11 @@ func NewBroker(opts ...broker.Option) broker.Broker {
 		natsOpts = n
 	}
 
+	var drain bool
+	if _, ok := options.Context.Value(drainSubscriptionKey{}).(bool); ok {
+		drain = true
+	}
+
 	// broker.Options have higher priority than nats.Options
 	// only if Addrs, Secure or TLSConfig were not set through a broker.Option
 	// we read them from nats.Option
@@ -224,6 +244,7 @@ func NewBroker(opts ...broker.Option) broker.Broker {
 		opts:  options,
 		nopts: natsOpts,
 		addrs: setAddrs(options.Addrs),
+		drain: drain,
 	}
 
 	return nb

options.go

@@ -6,8 +6,20 @@ import (
 )
 
 type optionsKey struct{}
+type drainConnectionKey struct{}
+type drainSubscriptionKey struct{}
 
 // Options accepts nats.Options
 func Options(opts nats.Options) broker.Option {
 	return setBrokerOption(optionsKey{}, opts)
 }
+
+// DrainConnection will drain subscription on close
+func DrainConnection() broker.Option {
+	return setBrokerOption(drainConnectionKey{}, true)
+}
+
+// DrainSubscription will drain pending messages when unsubscribe
+func DrainSubscription() broker.SubscribeOption {
+	return setSubscribeOption(drainSubscriptionKey{}, true)
+}