PHP Guacamole string encoder and decoder

<?php
namespace Guacamole;
// why does php not have a built in slice method?
function str_slice() {
    $args = func_get_args();
    $str        = $args[0];
    $str_length = strlen($str);
    $start      = $args[1];
    $end        = $args[2];
    if ($start >= $str_length) {
        return "";
    }
    if ($start < 0) {
        if ($start < - $str_length) {
            $start = 0;
        } else {
            $start = $str_length - abs($start);
        }
    }
    if ($end <= $start) {
        return "";
    }
    if ($end > $str_length) {
        $end = $str_length;
    }
    $length = $end - $start;
    return substr($str, $start, $length);
}

function decodeResponse($str) {
  $pos=-1;
  $sections = [];

  for(;;) {
      $len = strpos($str,'.',$pos+1);
      if($len==-1) {break;}
      $pos = intval(str_slice($str,$pos+1,$len))+$len+1;
      array_push($sections, str_slice($str,$len+1,$pos));
      if(str_slice($str,$pos,$pos+1)==';'){
        break;
      }
  }
  return $sections;
}

function encodeGuac($cypher) {
    $command='';
    for($i=0;$i<count($cypher);$i++){
        $current=$cypher[$i];
        $command.=strval(strlen($current)).".".$current;
        $command.=($i<count($cypher)-1?',':';');
    }
    return $command;
}
?>