Reconnect in do() if uses on a disconnected dbh

This is because calling mysql_stmt_prepare() after calling mysql_close()
is not safe and is causing segfaults when running with MariaDB 10.3 libs.

Author: dveeden

dbdimp.c

@@ -5318,6 +5318,16 @@ int mysql_db_reconnect(SV* h)
   else
     imp_dbh= (imp_dbh_t*) imp_xxh;
 
+  /* reconnect a closed connection, used in do() for implicit reconnect */
+  if (!DBIc_has(imp_dbh, DBIcf_ACTIVE) && DBIc_has(imp_dbh, DBIcf_AutoCommit)) {
+    if (my_login(aTHX_ h, imp_dbh)) {
+      DBIc_ACTIVE_on(imp_dbh);
+      DBIc_set(imp_dbh, DBIcf_AutoCommit, TRUE);
+      return TRUE;
+    }
+    return FALSE;
+  }
+
   if (mysql_errno(imp_dbh->pmysql) != CR_SERVER_GONE_ERROR &&
           mysql_errno(imp_dbh->pmysql) != CR_SERVER_LOST)
     /* Other error */

mysql.xs

@@ -272,6 +272,9 @@ do(dbh, statement, attr=Nullsv, ...)
   MYSQL_BIND      *bind= NULL;
 #endif
     ASYNC_CHECK_XS(dbh);
+    if ((!DBIc_has(imp_dbh, DBIcf_ACTIVE)) &&
+        (!mysql_db_reconnect(dbh)))
+      XSRETURN_UNDEF;
 #if MYSQL_VERSION_ID >= MULTIPLE_RESULT_SET_VERSION
     while (mysql_next_result(imp_dbh->pmysql)==0)
     {

t/15reconnect.t

@@ -16,7 +16,7 @@ eval {$dbh = DBI->connect($test_dsn, $test_user, $test_password,
 if ($@) {
   plan skip_all => "no database connection";
 }
-plan tests => 8 * 2;
+plan tests => 13 * 2;
 
 for my $mysql_server_prepare (0, 1) {
 $dbh= DBI->connect("$test_dsn;mysql_server_prepare=$mysql_server_prepare;mysql_server_prepare_disable_fallback=1", $test_user, $test_password,
@@ -38,5 +38,13 @@ ok($dbh->do("SELECT 1"), "implicitly reconnecting handle with 'do'");
 
 ok($dbh->{Active}, "checking for reactivated handle");
 
-$dbh->disconnect();
+ok(!($dbh->{AutoCommit} = 0), "disabling autocommit");
+
+ok($dbh->disconnect(), "disconnecting active handle");
+
+ok(!$dbh->{Active}, "checking for inactive handle");
+
+ok(!$dbh->do("SELECT 1"), "implicitly reconnecting handle with 'do'");
+
+ok(!$dbh->{Active}, "checking for reactivated handle");
 }