Add OnPacketIDExhausted hook (#211)

README.md

@@ -304,6 +304,7 @@ The function signatures for all the hooks and `mqtt.Hook` interface can be found
 | OnQosPublish | Called when a publish packet with Qos >= 1 is issued to a subscriber. | 
 | OnQosComplete | Called when the Qos flow for a message has been completed. | 
 | OnQosDropped | Called when an inflight message expires before completion. | 
+| OnPacketIDExhausted | Called when a client runs out of unused packet ids to assign. | 
 | OnWill | Called when a client disconnects and intends to issue a will message. Allows packet modification. | 
 | OnWillSent | Called when an LWT message has been issued from a disconnecting client. | 
 | OnClientExpired | Called when a client session has expired and should be deleted. | 

hooks.go

@@ -44,6 +44,7 @@ const (
 	OnQosPublish
 	OnQosComplete
 	OnQosDropped
+	OnPacketIDExhausted
 	OnWill
 	OnWillSent
 	OnClientExpired
@@ -93,6 +94,7 @@ type Hook interface {
 	OnQosPublish(cl *Client, pk packets.Packet, sent int64, resends int)
 	OnQosComplete(cl *Client, pk packets.Packet)
 	OnQosDropped(cl *Client, pk packets.Packet)
+	OnPacketIDExhausted(cl *Client, pk packets.Packet)
 	OnWill(cl *Client, will Will) (Will, error)
 	OnWillSent(cl *Client, pk packets.Packet)
 	OnClientExpired(cl *Client)
@@ -447,6 +449,16 @@ func (h *Hooks) OnQosDropped(cl *Client, pk packets.Packet) {
 	}
 }
 
+// OnPacketIDExhausted is called when the client runs out of unused packet ids to
+// assign to a packet.
+func (h *Hooks) OnPacketIDExhausted(cl *Client, pk packets.Packet) {
+	for _, hook := range h.GetAll() {
+		if hook.Provides(OnPacketIDExhausted) {
+			hook.OnPacketIDExhausted(cl, pk)
+		}
+	}
+}
+
 // OnWill is called when a client disconnects and publishes an LWT message. This method
 // differs from OnWillSent in that it allows you to modify the LWT message before it is
 // published. The return values of the hook methods are passed-through in the order
@@ -754,6 +766,9 @@ func (h *HookBase) OnQosComplete(cl *Client, pk packets.Packet) {}
 // OnQosDropped is called the Qos flow for a message expires.
 func (h *HookBase) OnQosDropped(cl *Client, pk packets.Packet) {}
 
+// OnPacketIDExhausted is called when the client runs out of unused packet ids to assign to a packet.
+func (h *HookBase) OnPacketIDExhausted(cl *Client, pk packets.Packet) {}
+
 // OnWill is called when a client disconnects and publishes an LWT message.
 func (h *HookBase) OnWill(cl *Client, will Will) (Will, error) {
 	return will, nil

hooks_test.go

@@ -241,6 +241,7 @@ func TestHooksNonReturns(t *testing.T) {
 			h.OnQosPublish(cl, packets.Packet{}, time.Now().Unix(), 0)
 			h.OnQosComplete(cl, packets.Packet{})
 			h.OnQosDropped(cl, packets.Packet{})
+			h.OnPacketIDExhausted(cl, packets.Packet{})
 			h.OnWillSent(cl, packets.Packet{})
 			h.OnClientExpired(cl)
 			h.OnRetainedExpired("a/b/c")