How to make services node output of file to use external URL instead of public:// URI
There is parse_url

Like 

&lt;?php
$url = file_create_url($field[0]['uri']);
$url = parse_url($url);
$path = $url['path'];
?&gt;


OR  file_create_url

$usablepath = file_create_url($filesyspath);


OR

$path = str_replace('public:/', variable_get('file_public_path', 'sites/default/files'), $uri);