Switch to sending data messages only

Handling of notification messages is quite inconsistent (at least on
android). Send the payload in data only and let the app handle the
notification locally.

Add pageTime to data payload (Unix epoch UTC).

fcm.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"strings"
 	tmpltext "text/template"
+	"time"
 
 	"github.com/prometheus/alertmanager/template"
 	"golang.org/x/net/context"
@@ -59,18 +60,15 @@ func NewMessaging() (*messaging.Client, error) {
 	return client, err
 }
 
-// NewMessage returns a new FCM message struct
-func NewMessage(topic, title, body string) *messaging.Message {
+func NewDataMessage(topic, title, body string) *messaging.Message {
+	unixMillisecondsUTC := time.Now().UTC().UnixNano() / 1000000
+	data := map[string]string{
+		"title":    title,
+		"body":     body,
+		"pageTime": string(unixMillisecondsUTC),
+	}
 	return &messaging.Message{
-		Notification: &messaging.Notification{
-			Title: title,
-			Body:  body,
-		},
-		Data: map[string]string{
-			"title":        title,
-			"body":         body,
-			"click_action": "FLUTTER_NOTIFICATION_CLICK",
-		},
+		Data:  data,
 		Topic: topic,
 		// https://firebase.google.com/docs/cloud-messaging/concept-options#setting-the-priority-of-a-message
 		Android: &messaging.AndroidConfig{
@@ -79,7 +77,18 @@ func NewMessage(topic, title, body string) *messaging.Message {
 	}
 }
 
-// NewMessageFromAlertmanagerDats returns a new FCM message from alertmanager POST data
+// NewNoficationMessage returns a new FCM message including notificaton data
+func NewNoficationMessage(topic, title, body string) *messaging.Message {
+	message := NewDataMessage(topic, title, body)
+	message.Notification = &messaging.Notification{
+		Title: title,
+		Body:  body,
+	}
+	message.Data["click_action"] = "FLUTTER_NOTIFICATION_CLICK"
+	return message
+}
+
+// NewMessageFromAlertmanagerDats returns a new FCM data message from alertmanager POST data
 func NewMessageFromAlertmanagerData(topic string, m *template.Data) (*messaging.Message, error) {
 	title, err := tmpltextExecuteToString(tmplTitle, m)
 	if err != nil {
@@ -91,7 +100,7 @@ func NewMessageFromAlertmanagerData(topic string, m *template.Data) (*messaging.
 		return nil, &TemplateError{Type: "body", Err: err}
 	}
 
-	return NewMessage(topic, title, body), nil
+	return NewDataMessage(topic, title, body), nil
 }
 
 func tmpltextExecuteToString(tmpl *tmpltext.Template, data interface{}) (string, error) {

handler.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"strconv"
 
+	"firebase.google.com/go/messaging"
 	"github.com/julienschmidt/httprouter"
 	"github.com/prometheus/alertmanager/template"
 )
@@ -19,8 +20,9 @@ type JSONResponse struct {
 }
 
 type genericJSONRequest struct {
-	Title string
-	Body  string
+	Title        string
+	Body         string
+	Notification bool
 }
 
 func indexHandler(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
@@ -36,6 +38,7 @@ func indexHandler(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
 }
 
 func genericHandler(w http.ResponseWriter, req *http.Request, ps httprouter.Params) {
+	var message *messaging.Message
 	data, err := readGenericRequestBody(req)
 	if err != nil {
 		log.Printf("Error parsing request body: %v", err)
@@ -44,7 +47,11 @@ func genericHandler(w http.ResponseWriter, req *http.Request, ps httprouter.Para
 	}
 
 	topic := getParamTopic(ps)
-	message := NewMessage(topic, data.Title, data.Body)
+	if data.Notification {
+		message = NewNoficationMessage(topic, data.Title, data.Body)
+	} else {
+		message = NewDataMessage(topic, data.Title, data.Body)
+	}
 	msg, err := fcmClient.Send(req.Context(), message)
 	fcmMessages.WithLabelValues(ps.MatchedRoutePath(), topic).Inc()
 
@@ -60,13 +67,6 @@ func genericHandler(w http.ResponseWriter, req *http.Request, ps httprouter.Para
 	)
 }
 
-func readGenericRequestBody(req *http.Request) (*genericJSONRequest, error) {
-	defer req.Body.Close()
-	data := genericJSONRequest{}
-	err := json.NewDecoder(req.Body).Decode(&data)
-	return &data, err
-}
-
 func alertHandler(w http.ResponseWriter, req *http.Request, ps httprouter.Params) {
 	templateData, err := readAlertRequestBody(req)
 	if err != nil {
@@ -99,6 +99,13 @@ func getParamTopic(ps httprouter.Params) string {
 	return topic
 }
 
+func readGenericRequestBody(req *http.Request) (*genericJSONRequest, error) {
+	defer req.Body.Close()
+	data := genericJSONRequest{}
+	err := json.NewDecoder(req.Body).Decode(&data)
+	return &data, err
+}
+
 func readAlertRequestBody(req *http.Request) (*template.Data, error) {
 	defer req.Body.Close()
 	data := template.Data{}