hook_file_download not triggered

Question

I set the private file system to /system/files/export , I create a file in private directory programmatically and it not belong to any field ,and show link to user , I implement Hook_file_download , I want check some condition in it but when user click on link to download the file created in private path it return me Forbidden and mymodule_file_download not tirggered ( I put some code to it , even die but never called). I clear cache but noting changes, the link that showed for user is http://localhost/mytestdrupal/system/files/export/Export-couponcards-1393307265.csv where is problem?

Part of my code to create file in submit

function mymodule_export_form_submit($form, $form_state) {
    $temp1 = variable_get('file_private_path');
    if (!file_prepare_directory($temp1, FILE_CREATE_DIRECTORY)) {
        drupal_set_message(t('Problem in write file in directory'), 'error');
        return;
    }
    $filename = 'Export-file'. '.csv';
    $filepath = $temp1 . '/' . $filename;
    $df = fopen($filepath, 'w');
    if (!$df) {
        drupal_set_message(t('Can not write file in') . $filepath, 'error');
        return;
    }
            fputcsv($df, array('code', 'name'));
            fputcsv($df, array('test','test'));

    fclose($df);
    $path = file_create_url($filepath);
    drupal_set_message(t('Export done. ') . '<a href="' . $path . '">' . t('Download export file') . '</a>');
}

Answer 1

hook_file_download working perfectly, List of steps which worked for me

1. I made File System to Private
2. Created a File Field in Article Content Type and marked it as Private In Settings
3. Uploaded a PDF File
4. Link to file is something link below

http://example.com/d7/system/files/**.pdf

Created a custom module with hook_file_download, When ever i access above URL and visit any page i can see drupal set message "Hi"

function drup_custom_file_download($uri) {
  drupal_set_message("Hi");
}

Answer 2

First you need to verify your file is being saved to the correct place.

You say you want to save to a sub-directory 'export' but that is not what your code is doing.

You should be saving to the private file system, not the public one. So variable_get('file_private_path', '') instead of variable_get('file_public_path').

Then append you export directory, so it would be:

$temp1 = variable_get('file_private_path', '') . '/export';

Then if you file is successfully saved at /sites/default/files/private/export (or wherever your private files should be), then you are ready for the next step.

When making the link to the file you have to pass in a uri, so

$path = file_create_url($filepath);

should be something like:

$path = file_create_url('private://export/' . $filename);

Using the 'private' stream wrapper means that internal links match to /sites/default/files/private (or whatever you have variable_get('file_private_path', '') set to) and external links generate like www.example.com/system/files/...

For more information see: DrupalPrivateStreamWrapper