Add callback prior to reconnection attempt

client.go

@@ -345,6 +345,9 @@ func (c *client) reconnect() {
 	)
 
 	for rc != 0 && atomic.LoadUint32(&c.status) != disconnected {
+		if nil != c.options.OnReconnecting {
+			c.options.OnReconnecting(c, &c.options)
+		}
 		for _, broker := range c.options.Servers {
 			cm := newConnectMsgFromOptions(&c.options, broker)
 			DEBUG.Println(CLI, "about to write new connect msg")

options.go

@@ -46,6 +46,10 @@ type ConnectionLostHandler func(Client, error)
 // at initial connection and on reconnection
 type OnConnectHandler func(Client)
 
+// ReconnectHandler is invoked prior to reconnecting after
+// the initial connection is lost
+type ReconnectHandler func(Client, *ClientOptions)
+
 // ClientOptions contains configurable options for an Client.
 type ClientOptions struct {
 	Servers                 []*url.URL
@@ -72,6 +76,7 @@ type ClientOptions struct {
 	DefaultPublishHandler   MessageHandler
 	OnConnect               OnConnectHandler
 	OnConnectionLost        ConnectionLostHandler
+	OnReconnecting          ReconnectHandler
 	WriteTimeout            time.Duration
 	MessageChannelDepth     uint
 	ResumeSubs              bool
@@ -297,6 +302,13 @@ func (o *ClientOptions) SetConnectionLostHandler(onLost ConnectionLostHandler) *
 	return o
 }
 
+// SetReconnectingHandler sets the OnReconnecting callback to be executed prior
+// to the client attempting a reconnect to the MQTT broker.
+func (o *ClientOptions) SetReconnectingHandler(cb ReconnectHandler) *ClientOptions {
+	o.OnReconnecting = cb
+	return o
+}
+
 // SetWriteTimeout puts a limit on how long a mqtt publish should block until it unblocks with a
 // timeout error. A duration of 0 never times out. Default 30 seconds
 func (o *ClientOptions) SetWriteTimeout(t time.Duration) *ClientOptions {