PG-2540 Fix bug with overread after comment end in extraction

After the end of a comment we skipped one extra byte ahead accidentally
causing a potential buffer overread if that comment was at the very end
and otherwise potentially missing a comment if we had two comments next
to eachother.

Author: jeltz

src/pg_stat_monitor.c

@@ -3220,8 +3220,10 @@ extract_query_comments(const char *query, char *comments, size_t buf_len)
 				q_iter++;
 			}
 		}
-
-		q_iter++;
+		else
+		{
+			q_iter++;
+		}
 	}
 
 	comments[curr_len] = '\0';

t/003_settings_pgms_extract_comments.pl

@@ -59,6 +59,18 @@
 	extra_params => [ '-a', '-Pformat=aligned', '-Ptuples_only=off' ]);
 PGSM::append_to_file($stdout);
 
+($cmdret, $stdout, $stderr) = $node->psql(
+	'postgres',
+	'SELECT 1 /* a *//* b */, 2, 3',
+	extra_params => [ '-a', '-Pformat=aligned', '-Ptuples_only=off' ]);
+PGSM::append_to_file($stdout);
+
+($cmdret, $stdout, $stderr) = $node->psql(
+	'postgres',
+	'SELECT 1, 2, 3, 4 /* x */',
+	extra_params => [ '-a', '-Pformat=aligned', '-Ptuples_only=off' ]);
+PGSM::append_to_file($stdout);
+
 ($cmdret, $stdout, $stderr) = $node->psql(
 	'postgres',
 	'SELECT query, comments FROM pg_stat_monitor ORDER BY query COLLATE "C";',

t/expected/003_settings_pgms_extract_comments.out

@@ -23,14 +23,28 @@ SELECT 1 /* xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
         1 |        2
 (1 row)
 
+SELECT 1 /* a *//* b */, 2, 3
+ ?column? | ?column? | ?column? 
+----------+----------+----------
+        1 |        2 |        3
+(1 row)
+
+SELECT 1, 2, 3, 4 /* x */
+ ?column? | ?column? | ?column? | ?column? 
+----------+----------+----------+----------
+        1 |        2 |        3 |        4
+(1 row)
+
 SELECT query, comments FROM pg_stat_monitor ORDER BY query COLLATE "C";
                                                                                                                                        query                                                                                                                                        |                                                                                                                            comments                                                                                                                             
 ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ SELECT 1 /* a *//* b */, 2, 3                                                                                                                                                                                                                                                      | /* a */
  SELECT 1 /* xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx */, 2 | /* xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  SELECT 1 AS num /* First comment */, 'John' AS name /* Second comment*/                                                                                                                                                                                                            | /* First comment */, /* Second comment*/
+ SELECT 1, 2, 3, 4 /* x */                                                                                                                                                                                                                                                          | /* x */
  SELECT name, setting, unit, context, vartype, source, min_val, max_val, enumvals, boot_val, reset_val, pending_restart FROM pg_settings WHERE name = 'pg_stat_monitor.pgsm_extract_comments'                                                                                       | 
  SELECT pg_stat_monitor_reset()                                                                                                                                                                                                                                                     | 
-(4 rows)
+(6 rows)
 
 SELECT pg_stat_monitor_reset();
  pg_stat_monitor_reset