Creating FPDF directly in the browser using template_rediect

Question

I am trying to create a pdf using fpdf, which opens in a browser window. Ultimately, the data will be passed from a form submit to a non-existent WP page called pdf.

I am checking for this in template_redirect hook, so if it is pdf being requested, it will generate the pdf, and exit, otherwise will continue for normal WP processes.

This works in Firefox, but in Chrome, an alert : Failed to open PDF document. If I call a page with just this code in, it also works in Chrome.

add_action("template_redirect", "checkRedirect");

function checkRedirect() {
    $url = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on' ? "https" : "http") . "://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]";
    $slug = strtolower(basename($url));

    if ($slug == "pdf") {
        require_once(getPath() . "fpdf.php");

        $pdf = new \FPDF;
        $pdf->AddPage();
        $pdf->SetFont('Arial','B',16);
        $pdf->Cell(40,10,'Hello World!');
        $pdf->Output(); 
        die(); // to stop WP processing
    } 
}

Using the template_redirect hook, I believe WP has not output any data, so not sure what the problem is, and it works in Firefox.

Answer 1

Use ob_start();, ob_clean(); before outputting the PDF to make any uwanted content is not written while cretaing PDF.

add_action("template_redirect", "checkRedirect");

function checkRedirect() {
    $url = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on' ? "https" : "http") . "://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]";
    $slug = strtolower(basename($url));

    if ($slug == "pdf") {
        ob_start();
        require_once(getPath() . "fpdf.php");
        $pdf = new \FPDF;
        $pdf->AddPage();
        $pdf->SetFont('Arial','B',16);
        $pdf->Cell(40,10,'Hello World!');
        ob_clean();
        $pdf->Output(); 
        exit; // this better then die
    } 
}

Answer 2

It is not ideal, but I have found a workaround. Instead of outputting directly, I am saving the pdf file, and then doing a redirection to it.

I will write a process to remove the files created so that they do not build up uncontrollably.

add_action("template_redirect", "checkRedirect");

function checkRedirect() {
    $url = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on' ? "https" : "http") . "://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]";
    $slug = strtolower(basename($url));

    if ($slug == "pdf") {
        require_once(getPath() . "fpdf.php");

        $filePath = getPath() . "pdf/test.pdf";
        $fileUrl = getUrl() . "pdf/test.pdf";

        $pdf = new \FPDF;
        $pdf->AddPage();
        $pdf->SetFont('Arial','B',16);
        $pdf->Cell(40,10,'Hello World!');
        $pdf->Output("F",$filePath); 

        header('Location: '. $fileUrl);

        exit(); // to stop WP processing
    } 
}