Fix FCM custom data handling

README.md

@@ -580,13 +580,27 @@ pushNotifications.send(tokens, notifications, (error, result) => {
 });
 ```
 
-`fcm_notification` - object that will be passed to
+`fcm_notification` - object that will be **merged** with the notification fields. This allows you to override specific notification properties (like `channelId`, `ttl`, etc.) without duplicating standard fields like `title` and `body`.
 
+For example, to set a channel ID for Android:
 ```js
-  new gcm.Message({ ..., notification: data.fcm_notification })
+const data = {
+  title: 'My Title',
+  body: 'My Message',
+  fcm_notification: {
+    channelId: 'my-channel-id'
+  },
+  custom: { id: 123 }
+};
+```
+
+The `fcm_notification` object will be passed to
+
+```js
+  new gcm.Message({ ..., notification: { ...builtNotification, ...data.fcm_notification } })
 ```
 
-Fcm object that will be sent to provider ([Fcm message format](https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages?authuser=0#Message)) :
+FCM object that will be sent to provider ([FCM message format](https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages?authuser=0#Message)) :
 
 ```json
 {

src/utils/fcmMessage.js

@@ -28,7 +28,9 @@ class FcmMessage {
   }
 
   static buildAndroidMessage(params, options) {
-    const message = buildGcmMessage(params, options);
+    // Mark as FCM so buildGcmMessage doesn't pollute custom data
+    const fcmOptions = { ...options, fcm: true };
+    const message = buildGcmMessage(params, fcmOptions);
 
     const androidMessage = message.toJson();
 

src/utils/tools.js

@@ -87,7 +87,7 @@ const containsValidRecipients = (obj) => {
 };
 
 const buildGcmNotification = (data) => {
-  const notification = data.fcm_notification || {
+  const notification = {
     title: data.title,
     body: data.body,
     icon: data.icon,
@@ -107,6 +107,11 @@ const buildGcmNotification = (data) => {
     notification_count: data.notificationCount || data.badge,
   };
 
+  // Merge with fcm_notification overrides if provided
+  if (data.fcm_notification) {
+    return { ...notification, ...data.fcm_notification };
+  }
+
   return notification;
 };
 
@@ -126,11 +131,15 @@ const buildGcmMessage = (data, options) => {
     };
   }
 
-  custom.title = custom.title || data.title;
-  custom.message = custom.message || data.body;
-  custom.sound = custom.sound || data.sound;
-  custom.icon = custom.icon || data.icon;
-  custom.msgcnt = custom.msgcnt || data.badge;
+  // Only add notification fields to custom data for GCM (not FCM)
+  // FCM uses separate notification and data fields
+  if (!options.fcm) {
+    custom.title = custom.title || data.title;
+    custom.message = custom.message || data.body;
+    custom.sound = custom.sound || data.sound;
+    custom.icon = custom.icon || data.icon;
+    custom.msgcnt = custom.msgcnt || data.badge;
+  }
   if (options.phonegap === true && data.contentAvailable) {
     custom['content-available'] = 1;
   }

test/send/sendFCM.js

@@ -79,4 +79,68 @@ describe('push-notifications-fcm', () => {
         .catch(done);
     });
   });
+
+  describe('send push notifications with custom data', () => {
+    const customDataMessage = {
+      title: 'Notification Title',
+      body: 'Notification Body',
+      custom: {
+        userId: '12345',
+        actionId: 'action-001',
+        deepLink: 'app://section/item',
+      },
+    };
+
+    let customDataSendMethod;
+
+    function sendCustomDataMethod() {
+      return sinon.stub(
+        fbMessaging.prototype,
+        'sendEachForMulticast',
+        function sendFCMWithCustomData(firebaseMessage) {
+          const { custom } = customDataMessage;
+
+          // Verify custom data is preserved in top-level data field
+          expect(firebaseMessage.data).to.deep.equal(custom);
+
+          // Verify custom data does NOT pollute the notification
+          // Note: normalizeDataParams converts all values to strings (FCM requirement)
+          expect(firebaseMessage.android.data).to.deep.equal(custom);
+          expect(firebaseMessage.android.data).to.not.have.property('title');
+          expect(firebaseMessage.android.data).to.not.have.property('body');
+
+          // Verify notification has proper fields (separate from data)
+          expect(firebaseMessage.android.notification).to.include({
+            title: customDataMessage.title,
+            body: customDataMessage.body,
+          });
+
+          return Promise.resolve({
+            successCount: 1,
+            failureCount: 0,
+            responses: [{ error: null }],
+          });
+        }
+      );
+    }
+
+    before(() => {
+      customDataSendMethod = sendCustomDataMethod();
+    });
+
+    after(() => {
+      customDataSendMethod.restore();
+    });
+
+    it('custom data should be preserved and not mixed with notification fields', (done) => {
+      pn.send(regIds, customDataMessage)
+        .then((results) => {
+          expect(results).to.be.an('array');
+          expect(results[0].method).to.equal('fcm');
+          expect(results[0].success).to.equal(1);
+          done();
+        })
+        .catch(done);
+    });
+  });
 });

test/send/sendGCM.js

@@ -910,6 +910,53 @@ describe('push-notifications-gcm', () => {
     });
   });
 
+  describe('fcm_notification partial override (merge)', () => {
+    before(() => {
+      sendMethod = sinon.stub(
+        gcm.Sender.prototype,
+        'send',
+        (message, recipients, retries, cb) => {
+          expect(recipients).to.be.instanceOf(Object);
+          expect(message).to.be.instanceOf(gcm.Message);
+          // Verify that title and body from main data are preserved
+          expect(message.params.notification.title).to.equal(data.title);
+          expect(message.params.notification.body).to.equal(data.body);
+          // Verify that fcm_notification overrides are applied
+          expect(message.params.notification.color).to.equal('#FF0000');
+          // Verify custom data is present
+          expect(message.params.data.sender).to.equal(data.custom.sender);
+
+          cb(null, {
+            multicast_id: 'abc',
+            success: recipients.registrationTokens.length,
+            failure: 0,
+            results: recipients.registrationTokens.map((token) => ({
+              message_id: '',
+              registration_id: token,
+              error: null,
+            })),
+          });
+        }
+      );
+    });
+
+    after(() => {
+      sendMethod.restore();
+    });
+
+    it('should merge fcm_notification overrides with base notification', (done) => {
+      const androidData = {
+        ...data,
+        fcm_notification: {
+          color: '#FF0000', // Override only the color
+        },
+      };
+      pn.send(regIds, androidData, (err, results) =>
+        testSuccess(err, results, done)
+      );
+    });
+  });
+
   describe('send push notifications in phonegap-push compatibility mode', () => {
     const pushPhoneGap = new PN({
       gcm: {