server.php

<?php

$log = fn ($message) => print '['.number_format(microtime(true), 4, '.', '').'] '.$message.PHP_EOL;

$bail = function ($reason = null) use ($log) {
    $reason ??= socket_strerror(socket_last_error());

    $log($reason);

    exit(1);
};

$socket = @socket_create(AF_INET, SOCK_STREAM, SOL_TCP);

$socket || $bail();

pcntl_async_signals(true);
pcntl_signal(SIGINT, fn () => exit(1), false);
register_shutdown_function(function () use ($socket, $log) {
    socket_close($socket);

    $log('Socket closed');
});

@socket_bind($socket, 'localhost', 1234) || $bail();

@socket_listen($socket, backlog: 1) || $bail();

socket_set_nonblock($socket) || $bail('Unable to set socket to non-blocking');

$log('Ready for incoming connections');

while (true) {
    $log('Waiting for an incoming connection');

    $read = [$socket];
    $write = [];
    $except = [];
    $changes = @socket_select($read, $write, $except, 10);

    $changes === false && $bail();

    if ($changes === 0) {
        continue;
    }

    $connection = @socket_accept($socket);

    $connection || $bail();

    $log('Connection received');

    socket_set_nonblock($connection) || $bail('Unable to set socket to non-blocking');

    $log('Connection set to non-blocking');

    $message = '';

    do {
        $log('Reading from the socket');

        $message .= $read = socket_read($connection, 10_000, PHP_BINARY_READ);
    } while ($read !== false);

    $log("Received\n=======\n{$message}=======");

    $written = socket_write($connection, <<< 'HTTP_RESPONSE'
        HTTP/1.0 200 OK

        Hello world
        HTTP_RESPONSE);

    $written === false && $bail();

    $log('Response sent');

    socket_shutdown($connection);
    socket_close($connection);

    $connection = null;

    $log('Socket closed');
}