Adds the Referral webhook and PostBacks's referral structure (#26)

actions.go

@@ -18,4 +18,6 @@ const (
 	PostBackAction
 	// OptInAction represents opting in through the Send to Messenger button
 	OptInAction
+	// ReferralAction represents ?ref parameter in m.me URLs
+	ReferralAction
 )

message.go

@@ -56,6 +56,8 @@ type PostBack struct {
 	Time time.Time `json:"-"`
 	// PostBack ID
 	Payload string `json:"payload"`
+	// Optional referral info
+	Referral Referral `json:"referral"`
 }
 
 // Watermark is the RawWatermark timestamp rendered as a time.Time.

messenger.go

@@ -50,6 +50,9 @@ type PostBackHandler func(PostBack, *Response)
 // OptInHandler is a handler used to handle opt-ins.
 type OptInHandler func(OptIn, *Response)
 
+// ReferralHandler is a handler used postback callbacks.
+type ReferralHandler func(ReferralMessage, *Response)
+
 // Messenger is the client which manages communication with the Messenger Platform API.
 type Messenger struct {
 	mux              *http.ServeMux
@@ -58,6 +61,7 @@ type Messenger struct {
 	readHandlers     []ReadHandler
 	postBackHandlers []PostBackHandler
 	optInHandlers    []OptInHandler
+	referralHandlers []ReferralHandler
 	token            string
 	verifyHandler    func(http.ResponseWriter, *http.Request)
 }
@@ -112,6 +116,11 @@ func (m *Messenger) HandlePostBack(f PostBackHandler) {
 	m.postBackHandlers = append(m.postBackHandlers, f)
 }
 
+// HandleReferral adds a new ReferralHandler to the Messenger
+func (m *Messenger) HandleReferral(f ReferralHandler) {
+	m.referralHandlers = append(m.referralHandlers, f)
+}
+
 // Handler returns the Messenger in HTTP client form.
 func (m *Messenger) Handler() http.Handler {
 	return m.mux
@@ -295,6 +304,14 @@ func (m *Messenger) dispatch(r Receive) {
 					message.Time = time.Unix(info.Timestamp/int64(time.Microsecond), 0)
 					f(message, resp)
 				}
+			case ReferralAction:
+				for _, f := range m.referralHandlers {
+					message := *info.ReferralMessage
+					message.Sender = info.Sender
+					message.Recipient = info.Recipient
+					message.Time = time.Unix(info.Timestamp/int64(time.Microsecond), 0)
+					f(message, resp)
+				}
 			}
 		}
 	}
@@ -345,6 +362,8 @@ func (m *Messenger) classify(info MessageInfo, e Entry) Action {
 		return PostBackAction
 	} else if info.OptIn != nil {
 		return OptInAction
+	} else if info.ReferralMessage != nil {
+		return ReferralAction
 	}
 	return UnknownAction
 }

receiving.go

@@ -41,6 +41,8 @@ type MessageInfo struct {
 	Read *Read `json:"read"`
 
 	OptIn *OptIn `json:"optin"`
+
+	ReferralMessage *ReferralMessage `json:"referral"`
 }
 
 type OptIn struct {
@@ -54,6 +56,28 @@ type OptIn struct {
 	Ref string `json:"ref"`
 }
 
+// ReferralMessage represents referral endpoint
+type ReferralMessage struct {
+	*Referral
+
+	// 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:"-"`
+}
+
+// Referral represents referral info
+type Referral struct {
+	// Data originally passed in the ref param
+	Ref string `json:"ref"`
+	// Source type
+	Source string `json:"source"`
+	// The identifier dor the referral
+	Type string `json:"type"`
+}
+
 // Sender is who the message was sent from.
 type Sender struct {
 	ID int64 `json:"id,string"`