Add method to handle OptIn messages (#21)

actions.go

@@ -16,4 +16,6 @@ const (
 	ReadAction
 	// PostBackAction represents post call back
 	PostBackAction
+	// OptInAction represents opting in through the Send to Messenger button
+	OptInAction
 )

messenger.go

@@ -47,6 +47,9 @@ type ReadHandler func(Read, *Response)
 // PostBackHandler is a handler used postback callbacks.
 type PostBackHandler func(PostBack, *Response)
 
+// OptInHandler is a handler used to handle opt-ins.
+type OptInHandler func(OptIn, *Response)
+
 // Messenger is the client which manages communication with the Messenger Platform API.
 type Messenger struct {
 	mux              *http.ServeMux
@@ -54,6 +57,7 @@ type Messenger struct {
 	deliveryHandlers []DeliveryHandler
 	readHandlers     []ReadHandler
 	postBackHandlers []PostBackHandler
+	optInHandlers    []OptInHandler
 	token            string
 	verifyHandler    func(http.ResponseWriter, *http.Request)
 }
@@ -91,6 +95,12 @@ func (m *Messenger) HandleDelivery(f DeliveryHandler) {
 	m.deliveryHandlers = append(m.deliveryHandlers, f)
 }
 
+// HandleOptIn adds a new OptInHandler to the Messenger which will be triggered
+// once a user opts in to communicate with the bot.
+func (m *Messenger) HandleOptIn(f OptInHandler) {
+	m.optInHandlers = append(m.optInHandlers, f)
+}
+
 // HandleRead adds a new DeliveryHandler to the Messenger which will be triggered
 // when a previously sent message is read by the recipient.
 func (m *Messenger) HandleRead(f ReadHandler) {
@@ -277,6 +287,14 @@ func (m *Messenger) dispatch(r Receive) {
 					message.Time = time.Unix(info.Timestamp/int64(time.Microsecond), 0)
 					f(message, resp)
 				}
+			case OptInAction:
+				for _, f := range m.optInHandlers {
+					message := *info.OptIn
+					message.Sender = info.Sender
+					message.Recipient = info.Recipient
+					message.Time = time.Unix(info.Timestamp/int64(time.Microsecond), 0)
+					f(message, resp)
+				}
 			}
 		}
 	}
@@ -325,6 +343,8 @@ func (m *Messenger) classify(info MessageInfo, e Entry) Action {
 		return ReadAction
 	} else if info.PostBack != nil {
 		return PostBackAction
+	} else if info.OptIn != nil {
+		return OptInAction
 	}
 	return UnknownAction
 }

receiving.go

@@ -1,5 +1,7 @@
 package messenger
 
+import "time"
+
 // Receive is the format in which webhook events are sent.
 type Receive struct {
 	// Object should always be `page`. (I don't quite understand why)
@@ -37,6 +39,19 @@ type MessageInfo struct {
 	PostBack *PostBack `json:"postback"`
 
 	Read *Read `json:"read"`
+
+	OptIn *OptIn `json:"optin"`
+}
+
+type OptIn struct {
+	// Sender is the sender of the message
+	Sender Sender `json:"-"`
+	// Recipient is who the message was sent to.
+	Recipient Recipient `json:"-"`
+	// Time is when the message was sent.
+	Time time.Time `json:"-"`
+	// Ref is the reference as given
+	Ref string `json:"ref"`
 }
 
 // Sender is who the message was sent from.