MDEV-16372 ER_BASE64_DECODE_ERROR upon replaying binary log via mysqlbinlog --verbose

(This commit is exclusively for 10.2 branch. Do not merge it to 10.3)

In case of a pattern of non-STMT_END-marked Rows-log-event (A) followed by
a STMT_END marked one (B) mysqlbinlog mixes up the base64 encoded rows events
with their pseudo sql representation produced by the verbose option:
      BINLOG '
        base64 encoded data for A
        ### verbose section for A
        base64 encoded data for B
        ### verbose section for B
      '/*!*/;
In effect the produced BINLOG '...' query is not valid and is rejected with the error.
Examples of this way malformed BINLOG could have been found in binlog_row_annotate.result
that gets corrected with the patch.

The issue is fixed with introduction an auxiliary IO_CACHE to hold on the verbose
comments until the terminal STMT_END event is found. The new cache is emptied
out after two pre-existing ones are done at that time.
The correctly produced output now for the above case is as the following:
      BINLOG '
        base64 encoded data for A
        base64 encoded data for B
      '/*!*/;
        ### verbose section for A
        ### verbose section for B

Thanks to Alexey Midenkov for the problem recognition and attempt to tackle,
and to Venkatesh Duggirala who produced a patch for the upstream whose
idea is exploited here, as well as to MDEV-23077 reporter LukeXwang who
also contributed a piece of a patch aiming at this issue.

1 files changed, 8 insertions, 3 deletions

diff --git a/client/mysqlbinlog.cc b/client/mysqlbinlog.cc
index 13a92c0b581..4e28876cdf6 100644
--- a/client/mysqlbinlog.cc
+++ b/client/mysqlbinlog.cc
@@ -891,7 +891,8 @@ static bool print_base64(PRINT_EVENT_INFO *print_event_info, Log_event *ev)
   ev->print(result_file, print_event_info);
   return
     print_event_info->head_cache.error == -1 ||
-    print_event_info->body_cache.error == -1;
+    print_event_info->body_cache.error == -1 ||
+    print_event_info->tail_cache.error == -1;
 }
 
 
@@ -962,8 +963,12 @@ static bool print_row_event(PRINT_EVENT_INFO *print_event_info, Log_event *ev,
         my_b_printf(body_cache, "'%s\n", print_event_info->delimiter);
 
       // flush cache
-      if ((copy_event_cache_to_file_and_reinit(&print_event_info->head_cache, result_file) ||
-          copy_event_cache_to_file_and_reinit(&print_event_info->body_cache, result_file)))
+      if ((copy_event_cache_to_file_and_reinit(&print_event_info->head_cache,
+                                               result_file) ||
+           copy_event_cache_to_file_and_reinit(&print_event_info->body_cache,
+                                               result_file) ||
+           copy_event_cache_to_file_and_reinit(&print_event_info->tail_cache,
+                                               result_file)))
         return 1;
     }
   }