expose sync user subscribe in the c-api (#7302)

* expose sync user subscribe in the c-api

Author: nicola-cab

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Enhancements
 * <New feature description> (PR [#????](https://github.com/realm/realm-core/pull/????))
+* Add support in the C API for receiving a notification when sync user state changes. ([#7302](https://github.com/realm/realm-core/pull/7302))
 * Allow the query builder to construct >, >=, <, <= queries for string constants. This is a case sensitive lexicographical comparison. Improved performance of RQL (parsed) queries on a non-linked string property using: >, >=, <, <=, operators and fixed behaviour that a null string should be evaulated as less than everything, previously nulls were not matched. ([#3939](https://github.com/realm/realm-core/issues/3939), this is a prerequisite for https://github.com/realm/realm-swift/issues/8008).
 
 ### Fixed

src/realm.h

@@ -3495,9 +3495,13 @@ 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_sync_on_user_state_changed_t)(realm_userdata_t userdata, realm_user_state_e 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 +3898,15 @@ 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;
 
+
+/**
+ * @return a notification token object. Dispose it to stop receiving notifications.
+ */
+RLM_API realm_sync_user_subscription_token_t*
+realm_sync_user_on_state_change_register_callback(realm_user_t*, realm_sync_on_user_state_changed_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_on_state_change_register_callback(realm_user_t* user, realm_sync_on_user_state_changed_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, std::move(token)};
+    });
+}
+
 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(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 +569,19 @@ struct realm_results : realm::c_api::WrapC, realm::Results {
 };
 
 #if REALM_ENABLE_SYNC
+
+struct realm_sync_user_subscription_token : realm::c_api::WrapC {
+    using Token = realm::Subscribable<realm::SyncUser>::Token;
+    realm_sync_user_subscription_token(std::shared_ptr<realm::SyncUser> user, Token&& token)
+        : user(user)
+        , token(std::move(token))
+    {
+    }
+    ~realm_sync_user_subscription_token();
+    std::shared_ptr<realm::SyncUser> user;
+    Token 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

@@ -615,6 +615,12 @@ TEST_CASE("C API (non-database)", "[c_api]") {
             },
             &sync_user, user_data_free);
 
+        auto user_state = [](realm_userdata_t, realm_user_state_e state) {
+            CHECK(state == RLM_USER_STATE_LOGGED_IN);
+        };
+        auto token =
+            realm_sync_user_on_state_change_register_callback(sync_user, user_state, nullptr, user_data_free);
+
         auto check_base_url = [&](std::string expected) {
             CHECK(transport->get_location_called());
             auto app_base_url = realm_app_get_base_url(test_app.get());
@@ -653,6 +659,7 @@ TEST_CASE("C API (non-database)", "[c_api]") {
         update_and_check_base_url("", default_base_url);
 
         realm_release(sync_user);
+        realm_release(token);
     }
 #endif // REALM_ENABLE_SYNC
 }