Create a network service that sits on TCP port 12321, which accepts connections on that port, and which echoes complete lines (using a carriage-return/line-feed sequence as line separator) back to clients. No error handling is required. For the purposes of testing, it is only necessary to support connections from localhost (127.0.0.1 or perhaps ::1). Logging of connection information to standard output is recommended.

The implementation must be able to handle simultaneous connections from multiple clients. A multi-threaded or multi-process solution may be used. Each connection must be able to echo more than a single line.

The implementation must not stop responding to other clients if one client sends a partial line or stops reading responses.

$socket = socket_create(AF_INET,SOCK_STREAM,SOL_TCP);
socket_bind($socket, '127.0.0.1', 12321);
socket_listen($socket);
 
$client_count = 0;
while (true){
  if (($client = socket_accept($socket)) === false) continue;
  $client_count++;
 
  $client_name = 'Unknown';
  socket_getpeername($client, $client_name);
  echo "Client {$client_count} ({$client_name}) connected\n";
  $pid = pcntl_fork();
  if($pid == -1) die('Could not fork');
  if($pid){
    pcntl_waitpid(-1, $status, WNOHANG);
    continue;
  }
 
  //In a child process
  while(true){
    if($input = socket_read($client, 1024)){
      socket_write($client, $input);
    } else {
      socket_shutdown($client);
      socket_close($client);
      echo "Client {$client_count} ({$client_name}) disconnected\n";
      exit();
    }
  }
}