Force download csv file don't works always

Question

This is my function for writing a csv file and then downloading it. I have a dropdown menu $_REQUEST['page_start_date'] and $_REQUEST['page_end_date']. In some options file download, in other options it doesn't. The problem is this part always works correct

foreach ( $employees as $employee ) {
   fputcsv( $file, $employee );
}   

And i write file content on the local server. That's why I don't get it why the file sometimes download and sometimes don't.

function crb_export_employees() {
$start_date = $_REQUEST['page_start_date'];
$end_date   = $_REQUEST['page_end_date'];

$employees = crb_get_employees_started_in_date_range( $start_date, $end_date 
);
$filePath = CRB_THEME_DIR . 'employees.csv';

$file = fopen( $filePath, 'w+');
foreach ( $employees as $employee ) {
    fputcsv( $file, $employee );
}

fclose( $file );

header( 'Cache-Control: public' );
header( "Content-type: application/x-msdownload", true, 200 );
header( 'Content-Disposition: attachment; File Transfer' );
header( 'Content-Disposition: attachment; filename="employees.csv"' );
header( "Pragma: no-cache");
header( "Expires: 0");

readfile( $filePath );

wp_safe_redirect( wp_get_referer() );
exit;
}

Answer 1

I think if the filesize is relatively small a single call to readfile generally works but if the file is larger then reading the file in chunks is more reliable. The portion of code below is what I have used for a while to force the download of csv files - it reads in small chunks until the eof marker is reached.

function crb_export_employees() {
    $start_date = $_REQUEST['page_start_date'];
    $end_date   = $_REQUEST['page_end_date'];

    $employees = crb_get_employees_started_in_date_range( $start_date, $end_date );
    $filepath = CRB_THEME_DIR . 'employees.csv';

    $file = fopen( $filepath, 'w+');
    foreach ( $employees as $employee ) {
        fputcsv( $file, $employee );
    }
    fclose( $file );



    if( !is_file( $filepath ) or connection_status()!=0 ) return FALSE;

    header("Cache-Control: no-store, no-cache, must-revalidate");
    header("Pragma: no-cache");
    header("Expires: 0");
    header("Content-Type: application/octet-stream");
    header("Content-Length: ".(string)( filesize( $filepath ) ) );
    header("Content-Disposition: inline; filename=employee.csv");
    header("Content-Transfer-Encoding: binary\n");

    if( $file = @fopen( $filepath, 'rb' ) ) {
        while( !@feof( $file ) and ( connection_status()==0 ) ) {
            print( fread( $file, 1024*8 ) );
            flush();
        }
        @fclose( $file );
    }

    wp_safe_redirect( wp_get_referer() );

    return( ( connection_status()==0 ) and !connection_aborted() );
}