curl重写php file_get_contents

file_get_contents在连接不上的时候会提示Connection refused，有时候会带来不便；另外，curl的性能比file_get_contents高，所以用curl重写file_get_contents

function _file_get_contents($s) {
    $ret = "";
    $ch = curl_init($s);
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_FRESH_CONNECT, true);
    curl_setopt($ch, CURLOPT_TIMEOUT, 0);
    $buffer = curl_exec($ch);
    curl_close($ch);

    if ($buffer === false || empty($buffer)) {
        $ret = "";
    } else {
        $ret = $buffer;
    }

    return $ret;
}