save base64 images alongside entity creation

Question

I need to save and edit entities via services like {user, nodes, products ...etc}

the problem comes with images posted form mobile apps encoded base64.

I saved the file and stored the object in session to be used in hook_services_request_postprocess_alter to be added to the entity saved by loading it again and assign the value to the field

// in preprocess
$_SESSION['file'] = file_save_data(base64_decode($args[0]['image']),'public://test.png');

// in postprocess
$product = entity_load('commerce_product', array($result->product_id));
$wrapper = entity_metadata_wrapper('commerce_product', $product);

//$wrapper->field_field_user_avatar->file->set($_SESSION['file']);
//$wrapper->field_field_user_avatar['und'][0]['value']=(array)$_SESSION['file']; 
//$wrapper->save();   
entity_save('commerce_product', $product);

what missing here I have tried many answers either adding the file object to the field when creating the field nor entity saving

Answer 1

It works after getting file mime type here is the code sample

$data = base64_decode($args[1]['avatar']);    
$finfo = finfo_open();
        $mime_type = finfo_buffer($finfo, $data, FILEINFO_MIME_TYPE);
        finfo_close($finfo);
        // get file type png. jpg
        $ext = $mime_type ? str_replace('image/', '', $mime_type) : 'png';
        $file_name = str_replace(' ', '-', $args[1]['name']);

then you we save the file using

$file = file_save_data($data, 'public://users/'.$file_name.'.'.$ext, FILE_EXISTS_REPLACE);

    $args[1]['field_field_user_picture'] = array(
        'fid' => $file->fid,
        'width' => 100,
        'height' => 100,
        'alt' => $args[1]['name'],
        'title' => $args[1]['name']
    );