midb: resolve "inside a readonly TXN" warnings during message deletion

An implicitly started transaction stays open until the cursors have
reached the end of the data set. Just like e.g. fread(3), it is not
sufficient to read the exact number of rows/bytes — it really takes
that final step()/fread() call for the end-of-data/end-of-file flag
to be set.

Fixes: gromox-2.17-23-g24e7d57eb
Fixes: gromox-2.17-117-g5fb5e9a20
References: GXL-524, GXF-1738, GXF-1769, DESK-2301, DESK-2311
References: DESK-2402, DESK-2421, DESK-2436, DESK-2449

Author: jengelh

exch/midb/mail_engine.cpp

@@ -4191,7 +4191,7 @@ static void mail_engine_modify_notification_message(
 }
 
 static void mail_engine_notification_proc(const char *dir,
-	BOOL b_table, uint32_t notify_id, const DB_NOTIFY *pdb_notify)
+    BOOL b_table, uint32_t notify_id, const DB_NOTIFY *pdb_notify) try
 {
 	uint64_t parent_id = 0, folder_id = 0, message_id = 0;
 	char temp_buff[1280];
@@ -4240,8 +4240,12 @@ static void mail_engine_notification_proc(const char *dir,
 		auto stm = gx_sql_prep(pidb->psqlite, sql_string);
 		if (stm == nullptr || stm.step() != SQLITE_ROW)
 			return;
+		std::string name = znul(stm.col_text(0));
+		/* end implicit transaction since we have not attempted to read
+		 * past the last row yet */
+		stm.finalize();
 		mail_engine_delete_notification_message(pidb.get(), folder_id,
-			message_id, pidb->username, stm.col_text(0));
+			message_id, pidb->username, name.c_str());
 		folder_id = 0;
 		break;
 	}
@@ -4275,8 +4279,10 @@ static void mail_engine_notification_proc(const char *dir,
 		auto stm = gx_sql_prep(pidb->psqlite, sql_string);
 		if (stm == nullptr || stm.step() != SQLITE_ROW)
 			return;
+		std::string name = znul(stm.col_text(0));
+		stm.finalize();
 		mail_engine_delete_notification_message(pidb.get(), folder_id,
-			message_id, pidb->username, stm.col_text(0));
+			message_id, pidb->username, name.c_str());
 		folder_id = n->folder_id;
 		message_id = n->message_id;
 		mail_engine_add_notification_message(pidb.get(), folder_id,
@@ -4309,10 +4315,14 @@ static void mail_engine_notification_proc(const char *dir,
 		auto stm = gx_sql_prep(pidb->psqlite, sql_string);
 		if (stm == nullptr || stm.step() != SQLITE_ROW)
 			return;
+		std::string name = znul(stm.col_text(0));
+		stm.finalize();
 		snprintf(temp_buff, std::size(temp_buff), "FOLDER-TOUCH %s %s",
-			pidb->username.c_str(), stm.col_text(0));
+			pidb->username.c_str(), name.c_str());
 		system_services_broadcast_event(temp_buff);
 	}
+} catch (const std::bad_alloc &) {
+	mlog(LV_ERR, "E-2346: ENOMEM");
 }
 
 void mail_engine_init(const char *default_charset, const char *org_name,