fetch 不知哪里错误，请高手看看

    <?php  
    /* 
     * 
     * @desc URL安全形式的base64编码 
     * @param string $str 
     * @return string 
     */  


    function urlsafe_base64_encode($str){  
        $find = array("+","/");  
        $replace = array("-", "_");  
        return str_replace($find, $replace, base64_encode($str));  
    }  

    /** 
     * generate_access_token 
     * 
     * @desc 签名运算 
     * @param string $access_key 
     * @param string $secret_key 
     * @param string $url 
     * @param array  $params 
     * @return string 
     */  
    function generate_access_token($access_key, $secret_key, $url, $params = ''){  
        $parsed_url = parse_url($url);  
        $path = $parsed_url['path'];  
        $access = $path;  
        if (isset($parsed_url['query'])) {  
            $access .= "?" . $parsed_url['query'];  
        }  
        $access .= "\n";  
        if($params){  
            if (is_array($params)){  
                $params = http_build_query($params);  
            }  
            $access .= $params;  
        }  
        $digest = hash_hmac('sha1', $access, $secret_key, true);  
        return $access_key.':'.urlsafe_base64_encode($digest);  
    }  

    /** 
     * 测试 
     */  

    $access_key = 'NxGwvMPpIlusCqG8yBUBfsmy5DX4SBSsrMP1ftD0';  
    $secret_key = 'b1t0-1PsoWRpFMpDlLGQi761KnCeuFtG3d6VhRm-';  



    $fetch = urlsafe_base64_encode('http://maxcdn.thedesigninspiration.com/wp-content/uploads/2015/07/Sharks-s.jpg');  
    $to = urlsafe_base64_encode('allun:11.jpg');  

    $url  = 'http://iovip.qbox.me/fetch/'. $fetch .'/to/' . $to;  

    $access_token = generate_access_token($access_key, $secret_key, $url);  

    $header[] = 'Content-Type: application/json';  
    $header[] = 'Authorization: QBox '. $access_token;  


    $con = send('iovip.qbox.me/fetch/'.$fetch.'/to/'.$to, $header);  
    var_dump($con);  

    function send($url, $header = '') {  
        $curl = curl_init($url);  
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);  
        curl_setopt($curl, CURLOPT_HEADER,1);  
        curl_setopt($curl, CURLOPT_HTTPHEADER, $header);  
        curl_setopt($curl, CURLOPT_POST, 1);  

        $con = curl_exec($curl);  

        if ($con === false) {  
            echo 'CURL ERROR: ' . curl_error($curl);  
        } else {  
            return $con;  
        }  
    }  
    ?>  

以上代码不知哪里错误，老是报400错误， 请求报文格式错误