Add schema version to flexible sync client BIND message (#6863)

* Send schema version as part of BIND messages

* Update comment

* Changelog

CHANGELOG.md

@@ -137,6 +137,7 @@
 * Add baas-network-tests nightly task for testing sync client operation with non-ideal network conditions. ([PR #6852](https://github.com/realm/realm-core/pull/6852))
 * Added non-ideal network conditions and network fault tests to the evergreen nightly test runs. ([PR #7063](https://github.com/realm/realm-core/pull/7063))
 * Updated baas tests to run with dev mode disabled by default. ([PR #6852](https://github.com/realm/realm-core/pull/6852))
+* Add schema version to flexible sync client BIND message. ([#6840](https://github.com/realm/realm-core/issues/6840))
 
 ----------------------------------------------
 

src/realm/sync/client.cpp

@@ -167,6 +167,8 @@ class SessionWrapper final : public util::AtomicRefCountBase, DB::CommitListener
 
     SessionReason m_session_reason;
 
+    const uint64_t m_schema_version;
+
     std::shared_ptr<SubscriptionStore> m_flx_subscription_store;
     int64_t m_flx_active_version = 0;
     int64_t m_flx_last_seen_version = 0;
@@ -714,6 +716,13 @@ SessionReason SessionImpl::get_session_reason() noexcept
     return m_wrapper.m_session_reason;
 }
 
+uint64_t SessionImpl::get_schema_version() noexcept
+{
+    // Can only be called if the session is active or being activated
+    REALM_ASSERT_EX(m_state == State::Active || m_state == State::Unactivated, m_state);
+    return m_wrapper.m_schema_version;
+}
+
 void SessionImpl::initiate_integrate_changesets(std::uint_fast64_t downloadable_bytes, DownloadBatchState batch_state,
                                                 const SyncProgress& progress, const ReceivedChangesets& changesets)
 {
@@ -1140,6 +1149,7 @@ SessionWrapper::SessionWrapper(ClientImpl& client, DBRef db, std::shared_ptr<Sub
     , m_proxy_config{config.proxy_config} // Throws
     , m_debug_hook(std::move(config.on_sync_client_event_hook))
     , m_session_reason(config.session_reason)
+    , m_schema_version(config.schema_version)
     , m_flx_subscription_store(std::move(flx_sub_store))
     , m_migration_store(std::move(migration_store))
 {
@@ -2012,7 +2022,7 @@ void Client::voluntary_disconnect_all_connections()
 
 bool Client::wait_for_session_terminations_or_client_stopped()
 {
-    return m_impl.get()->wait_for_session_terminations_or_client_stopped();
+    return m_impl->wait_for_session_terminations_or_client_stopped();
 }
 
 

src/realm/sync/client.hpp

@@ -353,6 +353,11 @@ class Session {
         ///
         /// Note: Currently only used in FLX sync.
         SessionReason session_reason = SessionReason::Sync;
+
+        /// Schema version
+        ///
+        /// Note: Currently set only for FLX sync.
+        uint64_t schema_version = -1; // = ObjectStore::NotVersioned
     };
 
     /// \brief Start a new session for the specified client-side Realm.

src/realm/sync/noinst/client_impl_base.cpp

@@ -206,10 +206,8 @@ ClientImpl::ClientImpl(ClientConfig config)
     REALM_ASSERT_EX(m_socket_provider, "Must provide socket provider in sync Client config");
 
     if (m_one_connection_per_session) {
-        // FIXME: Re-enable this warning when the load balancer is able to handle
-        // multiplexing.
-        //        logger.warn("Testing/debugging feature 'one connection per session' enabled - "
-        //            "never do this in production");
+        logger.warn("Testing/debugging feature 'one connection per session' enabled - "
+                    "never do this in production");
     }
 
     if (config.disable_upload_activation_delay) {
@@ -1873,6 +1871,7 @@ void Session::send_bind_message()
             bind_json_data["migratedPartition"] = *migrated_partition;
         }
         bind_json_data["sessionReason"] = static_cast<uint64_t>(get_session_reason());
+        bind_json_data["schema_version"] = get_schema_version();
         if (logger.would_log(util::Logger::Level::debug)) {
             std::string json_data_dump;
             if (!bind_json_data.empty()) {

src/realm/sync/noinst/client_impl_base.hpp

@@ -908,6 +908,9 @@ class ClientImpl::Session {
     // - Client reset state means the session is going to be used to download a fresh realm.
     SessionReason get_session_reason() noexcept;
 
+    /// Returns the schema version the synchronization session connects with to the server.
+    uint64_t get_schema_version() noexcept;
+
     /// \brief Initiate the integration of downloaded changesets.
     ///
     /// This function must provide for the passed changesets (if any) to