From 65a1bfc50f3c5f4acde7b2c8ce147abf5412c12d Mon Sep 17 00:00:00 2001
From: Alexander Friedl <mail@alexanderfriedl.com>
Date: Thu, 27 Nov 2025 23:29:44 +0100
Subject: [PATCH] Fix FCM custom data handling

---
 src/utils/fcmMessage.js |  4 ++-
 src/utils/tools.js      | 14 +++++----
 test/send/sendFCM.js    | 64 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+), 6 deletions(-)

diff --git a/src/utils/fcmMessage.js b/src/utils/fcmMessage.js
index e9907f7..0141f9e 100644
--- a/src/utils/fcmMessage.js
+++ b/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();
 
diff --git a/src/utils/tools.js b/src/utils/tools.js
index b5a06a8..4b9259c 100644
--- a/src/utils/tools.js
+++ b/src/utils/tools.js
@@ -126,11 +126,15 @@ 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;
   }
diff --git a/test/send/sendFCM.js b/test/send/sendFCM.js
index 35ae46b..d61f1a9 100644
--- a/test/send/sendFCM.js
+++ b/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);
+    });
+  });
 });