PDFKIT not starting streaming on http response till I call doc.end()

Question

I am using pdfkit to generate pdf at runtime and returning this in http response for download. I am able to download the file at browser end but the download dialog is not opening immediately. Instead its waiting till doc.end is called. I guess pdfkit is unable to push the stream efficiently. Has anybody else faced this? If yes, please guide.

Here is the sample code which I am trying

exports.testPdfKit = functions.https.onRequest((request, response) => {
    //create pdf document
    doc.pipe(response);

    response.set('Content-Disposition', `attachment;filename=testpdfstream.pdf`);
    response.writeHead(200, { 'Content-Type': 'application/pdf' })

    const bigText = "some big text"

    for (var i = 0; i < 1000; i++) {
        console.log('inside iteration -',i)
        doc.text(bigText);
        doc.addPage();
    }
    doc.end()
});

I am implementing this functionality on firebase functions which uses expressjs internally for processing http requests. To generate bigger files at my end, streaming is must for me.

Answer 1

HTTP functions can not stream the input or output of the function. The entire request is delivered in one chunk of memory, and the response is collection and send back to the client in one chunk. The maximum size of both is 10MB. There are not workarounds for this limitation of Cloud Functions (but it does help you system scale better).

If you need streaming or websockets, you'll need to use a different product, such as app engine or compute engine.