php hangs when auth_socket is set for the user

[jonashrem]

Description

The following code:

<?php
$mysqli = new mysqli("localhost", "root", "...", "mysql");

echo $mysqli->host_info . "\n";

with a local MySQL 8.4 User like this:

*************************** 6. row ***************************
                    Host: localhost
                    User: root
...
                  plugin: auth_socket

Results in php hanging until MySQL timeouts instead of connecting to MySQL

Changing the auth plugin to caching_sha2_password solves the situation. I did not test what happens when I don't set the password or explicitly use the socket.

PHP Version

PHP 8.4.1 (cli) (built: Nov 25 2024 18:04:19) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.1, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.1, Copyright (c), by Zend Technologies

Operating System

Ubuntu 24.04

[nielsdos]

I created a user authenticated via auth_socket.
Then I tried connecting with the unix domain socket (/var/run/mysqld/mysqld.sock), and it works fine.
Then I tried connecting via localhost without the mysqlnd socket specified in the constructor, and it correctly throws a mysqli_sql_exception.
So I can't reproduce the behaviour.
Something is probably off in your setup.
Also please note that PHP 8.4.1 is very outdated. Please retry on a more recent version.

[jonashrem]

ah sorry regarding the php version. It is the same in 8.4.10. I downgraded it to test if this can be reproduced in older versions.

I didn't explictly specify the socket but a username and password.

As my my.cnf contained the socket

# CLIENT #
[client]
port                           = 3306
socket                         = /var/run/mysqld/mysqld.sock

'localhost' is automatically rewritten to using the socket through here but I'd still expected getting an error not a timeout.

[nielsdos]

Not specifying the socket also worked for me fine: I get an error instead of a timeout.
Please check the mysqli.default-socket php.ini setting.
Also please check if explicitly specifying the socket works, and double check your environment settings.
If nothing stands out, you can try running php under strace (i.e. strace php script.php) to see all the system calls being executed and see where it hangs.

[jonashrem]

Here is the relevant part from strace. Looks for me like php is trying to authenticate with caching_sha2_password while already logged in through socket.

Did you name your account the same as your local username? With a different user I get an error as well.

connect(4, {sa_family=AF_UNIX, sun_path="/var/run/mysqld/mysqld.sock"}, 29) = 0
fcntl(4, F_SETFL, O_RDWR)               = 0
poll([{fd=4, events=POLLIN|POLLERR|POLLHUP}], 1, 86400000) = 1 ([{fd=4, revents=POLLIN}])
recvfrom(4, "I\0\0\0\n8.4.5\0[\0\0\0\35\26-\10p\16Z\"\0\377\377\340\2\0\377\337\25\0\0\0\0\0\0\0\0\0\0YaV+:4[#a\35\25\27\0caching_sha2_password\0", 32768, MSG_DONTWAIT, NULL, NULL) = 77
sendto(4, "\217\0\0\1\215\242\32\0\0\0\0\300\340\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0root\0 !.\324\350\347\226\"\4\252\322\20\246\r7\303\367^zTX\324\335:\315+\363\343>h\17)8mysql\0caching_sha2_password\0,\f_client_name\7mysqlnd\f_server_host\tlocalhost", 147, MSG_DONTWAIT, NULL, 0) = 147
poll([{fd=4, events=POLLIN|POLLERR|POLLHUP}], 1, 86400000) = 1 ([{fd=4, revents=POLLIN}])
recvfrom(4, "\7\0\0\2\0\0\0\2\0\0\0", 32768, MSG_DONTWAIT, NULL, NULL) = 11
poll([{fd=4, events=POLLIN|POLLERR|POLLHUP}], 1, 86400000