Description:
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(This is related to mysqlnd in general, not only to mysqli).

When connection gets broken while store_result()/query() is transferring data, "Empty row packet body" warning is generated, but errno/error are not set. Any following mysql-network-related function generates 2006/"MySQL server has gone away" and correctly sets errno/error. Expected behaviour: store_result()/query() to set errno/error immediately after an error happened.


More digging details below.

store_result() generates one Warning ("Empty row packet body"), but query() generates two:

Warning: Empty row packet body in 1.php on line 5
Warning: mysqli::query(): (00000/0):  in 1.php on line 5

And neither of them sets errno/error.

I added CONN_SET_STATE(conn, CONN_QUIT_SENT) and SET_CLIENT_ERROR(*conn->error_info, ...) to php_mysqlnd_read_row_ex() in mysqlnd_wireprotocol.c (similarly to PACKET_READ_HEADER_AND_BODY macro), and found another problem: errors from mysqlnd_wireprotocol.c are set to *conn->error_info, but store_result_fetch_data() in mysqlnd_result.c expects errors in row_packet->error_info. It seems that errors generated in mysqlnd_wireprotocol.c are never actually used in mysqlnd_result.c. Furthermore, connection state set in mysqlnd_wireprotocol.c is always overwritten in mysqlnd_result.c with either CONN_NEXT_RESULT_PENDING or CONN_READY.

I ended up with the following patch to at least set correct errno/error on store_result()/query(), so the script can get aware about lost connections timely. However this patch is definitely not a complete solution, it doesn't fix neither double warning nor connection state (and it looks like it's not the only place where warnings are raised but errno/error are not set).

Test script:
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<?php

// connect to a remote server, slow connection is preferrable (so you'll have more time to kill the connection)
// while script is performing $mysqli->query(), kill the connection using mysql "kill" command (killall -9 mysqld would work too :))

$mysqli = new mysqli('remote-host', 'user', 'password');
$mysqli->query('set global max_allowed_packet=' . 60e6); // 60M
// echo "Do this in mysql shell: kill {$mysqli->threadid}\n";
$mysqli->query('select repeat("0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789", 500000)'); // ~50M packet
echo "errno={$mysqli->errno}, error={$mysqli->error}\n";

Expected result:
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Warning: mysqli::query(): (HY000/2006): MySQL server has gone away in 1.php on line 9
errno=2006, error=MySQL server has gone away

Actual result:
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Warning: Empty row packet body in 1.php on line 9
Warning: mysqli::query(): (00000/0):  in 1.php on line 9
errno=0, error=