PHP array mysterious behavior as "Undefined index" - php

Question

I am practicing socket programming using stream methods in PHP.
I am using PHP 7.3.11.
I found very unexpected error message which says "undefined index " error where
Here is my server side code
<?php
error_reporting(E_ALL);
/* allow the script to hang around waiting for connection.*/
set_time_limit(0);
$address = '127.0.0.1';
$port = 9016;
$server = stream_socket_server($address .":". $port, $errno, $errorMessage);
$req = array( "R004"=>"R004 exist"
, "R001" => "R001 Ruccess"
, "R002"=>"R002Rcontinue"
, "R003"=>"R003 lRquit"
, "R005"=>"R005 hello");
$res = array("TT","SOO1", "S002", "S003");
if ($server === false)
{
throw new UnexpectedValueException("Could not bind to socket: $errorMessage");
}
echo json_encode($req);
while($socket = stream_socket_accept($server)){
$rand = rand(1,3);
$peer = stream_socket_get_name($socket, true);
$pkt = stream_socket_recvfrom($socket, 1500, 0,$peer);
if( !empty($pkt)){
$pkt = trim(preg_replace('/\s+/','',$pkt));
echo "pkt[{$pkt}]";
echo "EXITS:".array_key_exists($pkt, $req)."\n";
echo "pkt[{$pkt}]".PHP_EOL;
echo $req[$pkt].PHP_EOL;
stream_socket_sendto($socket, $res[$rand], 0, $peer);
}
fclose($socket);
usleep(1000);
}
stream_socket_shutdown($server, \STREAM_SHUT_RDWR);
and here is my client side code
error_reporting(E_ALL);
set_time_limit(0);
$address = '127.0.0.1';
$port = 9016;
$local = "tcp://{$address}:{$port}";
$socket = stream_socket_client($local, $errno, $errstr, 30);
$c_res = array("S001" => "Success", "S002" => "continue", "S003" => "quit");
$c_req = array("ROO3", "R005", "R002", "R001", "R004");
while ($socket = stream_socket_client($local, $errno, $errstr, 30)) {
$rand = rand(1, 4);
// echo "SEND[$c_req[$rand]]" . PHP_EOL;
$sent = stream_socket_sendto($socket, $c_req[$rand] . PHP_EOL);
if ($sent > 0) {
usleep(1000);
$s_res = stream_socket_recvfrom($socket, 1500, 0, $peer);
// $s_res = fread($socket, 4096);
$s_res = trim(preg_replace('/\s+/', '', $s_res));
echo "c_res[{$s_res}]";
echo "EXITS:" . array_key_exists($s_res, $c_res) . "\n";
echo "c_res[{$s_res}]" . PHP_EOL;
echo $c_res[$s_res] . PHP_EOL;
}
}
stream_socket_shutdown($socket, STREAM_SHUT_RDWR);
when I ran this code both server and client ( server runs first and thereafter does client)
I found this kind of error message
PHP Notice: Undefined index: SOO1 in E:\xampp\htdocs\mave_gen\www\adm\client.php on line 29
I do not understand this error message at all because all other references prints out OK except S001.
Obviously, there is S001 is defined in the code.
Do I miss something here ?
Thank you in advance.

Answer 1

The line SOO1 should be S001 in $res = array("TT","SOO1", "S002", "S003"); in the server side code. You have entered letter "O" in SOO1 but it should be "0" (zero) according to the rest of your code.
And in the client side code modify the following line of code
if ($sent > 0) {
usleep(1000);
$s_res = stream_socket_recvfrom($socket, 1500, 0, $peer);
// $s_res = fread($socket, 4096);
$s_res = trim(preg_replace('/\s+/', '', $s_res));
echo "c_res[{$s_res}]";
echo "EXITS:" . array_key_exists($s_res, $c_res) . "\n";
echo "c_res[{$s_res}]" . PHP_EOL;
echo $c_res[$s_res] . PHP_EOL;
}
to the following line
if ($sent > 0) {
usleep(1000);
$s_res = stream_socket_recvfrom($socket, 1500, 0, $peer);
if(!empty($s_res))
{
// $s_res = fread($socket, 4096);
$s_res = trim(preg_replace('/\s+/', '', $s_res));
echo "c_res[{$s_res}]";
echo "EXITS:" . array_key_exists($s_res, $c_res) . "\n";
echo "c_res[{$s_res}]" . PHP_EOL;
echo $c_res[$s_res] . PHP_EOL;
}
}
After these changes it should work.