How to download CSV file from function in WordPress plugin?

/** * Query For Top Title Row */

$results = $wpdb->get_results("SHOW COLUMNS FROM $table" );if(count($results) > 0){    foreach($results as $result){        $csv_output .= str_replace('_',' ',$result->Field).", "; // , or ;          }}$csv_output .= "\n";

/** * Query For All Required Data */

$results = $wpdb->get_results("SELECT * FROM $table",ARRAY_A );if(count($results) > 0){    foreach($results as $result){        $result = array_values($result);        $result = implode(", ", $result);        $csv_output .= $result."\n";     }}

/** * Prepare Filename And CSV File to export */

$filename = $file."_".date("Y-m-d_H-i",time());header("Content-type: application/vnd.ms-excel");header("Content-disposition: csv" . date("Y-m-d") . ".csv");header( "Content-disposition: filename=".$filename.".csv");print $csv_output;exit;

Putting this all in a function should do the trick

Try this:

<?phpclass CSVExport{/** * Constructor */public function __construct(){    if(isset($_GET['download_report']))    {        $csv = $this->generate_csv();        header("Pragma: public");        header("Expires: 0");        header("Cache-Control: must-revalidate, post-check=0, pre-check=0");        header("Cache-Control: private", false);        header("Content-Type: application/octet-stream");        header("Content-Disposition: attachment; filename=\"report.csv\";" );        header("Content-Transfer-Encoding: binary");        echo $csv;        exit;    }    // Add extra menu items for admins    add_action('admin_menu', array($this, 'admin_menu'));    // Create end-points    add_filter('query_vars', array($this, 'query_vars'));    add_action('parse_request', array($this, 'parse_request'));}/** * Add extra menu items for admins */public function admin_menu(){    add_menu_page('Download Report', 'Download Report', 'manage_options', 'download_report', array($this, 'download_report'));}/** * Allow for custom query variables */public function query_vars($query_vars){    $query_vars[] = 'download_report';    return $query_vars;}/** * Parse the request */public function parse_request(&$wp){    if(array_key_exists('download_report', $wp->query_vars))    {        $this->download_report();        exit;    }}/** * Download report */public function download_report(){    echo '<div class="wrap">';    echo '<div id="icon-tools" class="icon32"></div>';    echo '<h2>Download Report</h2>';    //$url = site_url();    echo '<p><a href="site_url()/wp-admin/admin.php?page=download_report&download_report">Export the Subscribers</a>';}/** * Converting data to CSV */public function generate_csv(){    $csv_output = '';    $table = 'users';    $result = mysql_query("SHOW COLUMNS FROM ".$table."");    $i = 0;    if (mysql_num_rows($result) > 0) {        while ($row = mysql_fetch_assoc($result)) {            $csv_output = $csv_output . $row['Field'].",";            $i++;        }    }    $csv_output .= "\n";    $values = mysql_query("SELECT * FROM ".$table."");    while ($rowr = mysql_fetch_row($values)) {        for ($j=0;$j<$i;$j++) {            $csv_output .= $rowr[$j].",";        }        $csv_output .= "\n";    }    return $csv_output;}}// Instantiate a singleton of this plugin$csvExport = new CSVExport();

You'll need to change some header information

header('Content-Type: text/csv');header('Content-Disposition: attachment;filename="report.csv"');header('Cache-Control: max-age=0');// If you're serving to IE 9, then the following may be neededheader('Cache-Control: max-age=1');// If you're serving to IE over SSL, then the following may be neededheader ('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); // Date in the pastheader ('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT'); // always modifiedheader ('Cache-Control: cache, must-revalidate'); // HTTP/1.1header ('Pragma: public'); // HTTP/1.0

After that make use of php://output for providing the data directly to the browser, this will prevent the blank page.

for example:

$outstream = fopen("php://output", "w");foreach($result as $result){    fputcsv($outstream, $result);}fclose($outstream);exit();

php://output is a read only stream that allows you provide data directly to the requester.

EDIT: Also you should make use of $wpdb