MDEV-39788 CHANGE MASTER savefiles read and write one line to many

mysql-test/main/rpl_info_file_line_count.result

@@ -0,0 +1,8 @@
+CHANGE MASTER TO master_host='127.0.0.1';
+# restart: --skip-slave-start
+Master_SSL_Key = ''
+Using_Gtid = 'Current_Pos'
+SQL_Delay = '0'
+RESET SLAVE ALL;
+Warnings:
+Note	4190	RESET SLAVE is implicitly changing the value of 'Using_Gtid' from 'Current_Pos' to 'Slave_Pos'

mysql-test/main/rpl_info_file_line_count.test

@@ -0,0 +1,74 @@
+# Line count / upgrading test for `@@master_info_file` & `@@relay_log_info_file`
+#
+# This regression test reminds that the line count includes the line count line.
+#
+# Reference:
+# MDEV-39788 CHANGE MASTER savefiles read and write one line to many
+
+--source include/have_binlog_format_mixed.inc # format-agnostic
+CHANGE MASTER TO master_host='127.0.0.1'; # have_info_files
+
+--let $MYSQLD_DATADIR= `SELECT @@datadir`
+
+
+# `using_gtid` is the key-value section, not the 33rd option.
+--remove_file $MYSQLD_DATADIR/master.info
+--write_file $MYSQLD_DATADIR/master.info
+33
+
+4
+127.0.0.1
+root
+
+3306
+60
+1
+
+
+
+
+
+1
+60.000
+
+0
+
+100000
+
+
+
+
+
+
+
+
+
+
+
+
+
+using_gtid=1
+EOF
+
+# This file does not have the 6th option
+# (neither does the current `@@relay_log_info_file`).
+--remove_file $MYSQLD_DATADIR/relay-log.info
+--write_file $MYSQLD_DATADIR/relay-log.info
+6
+./mysqld-relay-bin.000001
+4
+
+0
+0
+EOF
+
+
+--let $restart_parameters= --skip-slave-start
+--source include/restart_mysqld.inc
+
+--let $status_items= Master_SSL_Key, Using_Gtid, SQL_Delay
+--source include/show_slave_status.inc
+
+
+# Reset
+RESET SLAVE ALL;

sql/rpl_info_file.h

@@ -294,9 +294,9 @@ struct Info_file
     auto &line1= dynamic_cast<String_value<> &>(values[0](this));
     if (line1.load_from(&file))
       return true;
-    char *end= str2int(line1.buf, 10, 0, INT32_MAX, &val);
+    char *end= str2int(line1.buf, 10, 1, INT32_MAX, &val);
     /**
-      If this first line was not a number - the line count,
+      If this first line was not a positive number - the line count,
       then it was the first value for real,
       so the for loop should then skip over it, the index 0 of the list.
     */
@@ -305,7 +305,8 @@ struct Info_file
       Set the default after parsing: While std::from_chars() does not replace
       the output if it failed, it does replace if the line is not fully spent.
     */
-    size_t line_count= i ? default_line_count: static_cast<size_t>(val);
+    size_t line_count= i ? default_line_count :
+      static_cast<size_t>(val - 1); // remove the line count line from the count
     for (; i < line_count; ++i)
     {
       int c;
@@ -355,10 +356,11 @@ struct Info_file
     }
     /*
       Pad additional reserved lines:
-      (1 for the line count line + line count) inclusive -> max line inclusive
-       = line count exclusive <- max line inclusive
+      (1 for the line count line + line count) exclusive -> max line inclusive
+       = line count exclusive -> max line exclusive
     */
-    for (; total_line_count > size; --total_line_count)
+    // Pad additional reserved lines
+    while ((++size) < total_line_count)
       my_b_write_byte(&file, '\n');
   }