expose sync user subscribe in the c-api

Author: nicola-cab

src/realm.h

@@ -3495,9 +3495,14 @@ typedef enum realm_flx_sync_subscription_set_state {
 typedef void (*realm_sync_on_subscription_state_changed_t)(realm_userdata_t userdata,
                                                            realm_flx_sync_subscription_set_state_e state);
 
+typedef void (*realm_user_changed_callback_t)(realm_userdata_t userdata, realm_user_state s);
+
+
 typedef struct realm_async_open_task_progress_notification_token realm_async_open_task_progress_notification_token_t;
 typedef struct realm_sync_session_connection_state_notification_token
     realm_sync_session_connection_state_notification_token_t;
+typedef struct realm_sync_user_subscription_token
+    realm_sync_user_subscription_token_t;
 
 /**
  * Callback function invoked by the async open task once the realm is open and fully synchronized.
@@ -3894,6 +3899,13 @@ RLM_API realm_sync_session_connection_state_notification_token_t* realm_sync_ses
     realm_sync_session_t*, realm_sync_progress_func_t, realm_sync_progress_direction_e, bool is_streaming,
     realm_userdata_t userdata, realm_free_userdata_func_t userdata_free) RLM_API_NOEXCEPT;
 
+
+//register callback for tracking user status.
+RLM_API realm_sync_user_subscription_token_t*
+realm_sync_user_state_change_register_callback(
+    realm_user_t*, realm_user_changed_callback_t, realm_userdata_t userdata,
+    realm_free_userdata_func_t userdata_free);
+
 /**
  * Register a callback that will be invoked when all pending downloads have completed.
  */

src/realm/object-store/c_api/app.cpp

@@ -750,6 +750,21 @@ RLM_API realm_app_t* realm_user_get_app(const realm_user_t* user) noexcept
     return nullptr;
 }
 
+
+RLM_API realm_sync_user_subscription_token_t*
+realm_sync_user_state_change_register_callback(realm_user_t* user, realm_user_changed_callback_t callback,
+                                               realm_userdata_t userdata, realm_free_userdata_func_t userdata_free)
+{
+    return wrap_err([&] {
+        auto cb = [callback,
+                   userdata = SharedUserdata{userdata, FreeUserdata(userdata_free)}](const SyncUser& sync_user) {
+            callback(userdata.get(), realm_user_state_e(sync_user.state()););
+        };
+        auto token = (*user)->subscribe(std::move(cb));
+        return new realm_sync_user_subscription_token_t{user, token.value()};
+    };
+}
+
 template <typename T>
 inline util::Optional<T> convert_to_optional(T data)
 {

src/realm/object-store/c_api/sync.cpp

@@ -40,6 +40,11 @@ realm_sync_session_connection_state_notification_token::~realm_sync_session_conn
     session->unregister_connection_change_callback(token);
 }
 
+realm_sync_user_subscription_token::~realm_sync_user_subscription_token()
+{
+    user->unsubscribe({user.get(), token});
+}
+
 namespace realm::c_api {
 
 static_assert(realm_sync_client_metadata_mode_e(SyncClientConfig::MetadataMode::NoEncryption) ==

src/realm/object-store/c_api/types.hpp

@@ -569,6 +569,18 @@ struct realm_results : realm::c_api::WrapC, realm::Results {
 };
 
 #if REALM_ENABLE_SYNC
+
+struct realm_sync_user_subscription_token : realm::c_api::WrapC {
+    realm_sync_user_subscription_token(std::shared_ptr<realm::SyncUser> user, uint64_t token)
+        : user(user)
+        , token(token)
+    {
+    }
+    ~realm_sync_user_subscription_token();
+    std::shared_ptr<realm::SyncUser> user;
+    uint64_t token;
+};
+
 struct realm_async_open_task_progress_notification_token : realm::c_api::WrapC {
     realm_async_open_task_progress_notification_token(std::shared_ptr<realm::AsyncOpenTask> task, uint64_t token)
         : task(task)

test/object-store/c_api/c_api.cpp

@@ -602,6 +602,9 @@ TEST_CASE("C API (non-database)", "[c_api]") {
         realm_user_t* sync_user;
         auto user_data_free = [](realm_userdata_t) {};
 
+        realm_sync_user_state_change_register_callback(
+            sync_user, [](realm_user_state_e state) {}, nullptr, nullptr);
+
         // Verify the values above are included in the login request
         auto credentials = cptr(realm_app_credentials_new_anonymous(true));
         realm_app_log_in_with_credentials(