PHP send message to socket server (netcat)

nc.php

<?php
$payload = 'hello world';
$stream = stream_socket_client("tcp://127.0.0.1:5555", $errno, $errstr);
if (!$stream) {
  echo "{$errno}: {$errstr}\n";
  die();
}

fwrite($stream, $payload);
stream_socket_shutdown($stream, STREAM_SHUT_WR);
$contents = stream_get_contents($stream);
fclose($stream);
echo $contents;
?>

server.sh

nc -k -l 5555

FROM alpine
RUN apk add netcat-openbsd