Try really hard to make sync RPC finish

src/connection.cpp

@@ -241,8 +241,27 @@ void ConnectionLoader::doAutoConnect()
             syncTimer->deleteLater();
             // When sync is done, set the connection
             this->doRPCSetConnection(connection);
-        }, [=](auto) {
+        }, [=](auto) mutable {
             DEBUG("sync rpc error! server=" << config->server);
+            // continually retry sync RPC until it succeeds
+            // change server each time it fails
+            bool failed = true;
+            do {
+                config->server = Settings::getRandomServer();
+                auto connection = makeConnection(config);
+                DEBUG("changed server to " << config->server);
+                connection->doRPC("sync", "", [=](auto) mutable {
+                    DEBUG("sync success with server=" << config->server);
+                    failed = false;
+                    isSyncing->store(false);
+                    // Cancel the timer
+                    syncTimer->deleteLater();
+                    // When sync is done, set the connection
+                    this->doRPCSetConnection(connection);
+                }, [=](auto) {
+                    DEBUG("sync failed with server=" << config->server << " . continuing sync loop" );
+                });
+            } while (failed);
         });
 
         // While it is syncing, we'll show the status updates while it is alive.
@@ -261,12 +280,11 @@ void ConnectionLoader::doAutoConnect()
                     }
                     },
                     [=](QString err) {
-                        DEBUG("Sync error" << err);
+                        DEBUG("syncstatus error" << err);
                     });
                 } catch (const std::exception& e)  {
                     DEBUG("caught exception from syncstatus: " << e.what());
                 }
-
             }
         });