设置“ Content-disposition”而不设置“ Content-Length”是否可以接受？

Question

I have a simple Express.js route:

app.get('/db/csv', function (req, res) {
    db.users.find({}, { _id: 0 }, function (err, docs) {
        var csv = /* compute from docs */;

        res.setHeader('Content-disposition', 'attachment; filename=users.csv');
        res.send(csv);
    });
});

I use this route to download a CSV version of my "users" database. Setting the Content-disposition HTTP response header will trigger the "Save as…" dialog in the browser.

Should I also set a Content-Length header? I've seen it in an example and I'm not sure if it's required here. If it's required, how would I calculate the size value from the csv variable (which is a JavaScript string)?

(Btw, the functionality in the browser works without Content-Length .)

Answer 1

It's not required, it's perfectly fine to set just Content-Disposition . For instance, there's nothing in RFC2616 or RFC6266 requiring you combine them.

If it's required, how would I calculate the size value from the csv variable (which is a JavaScript string)?

It isn't, but that doesn't mean it's not nice to include. :-) I haven't done this with NodeJS, but I'd say convert it to a buffer with the appropriate encoding (eg, the encoding you're including in charset ) and get the size of the buffer in bytes. Since you're then going to send that buffer as the content, and the buffer's told you how big it is, that should be accurate.

Answer 2

Content-Length and Content-Disposition are orthogonal.

If you don't send Content-Length, you'll have to use Transfer-Encoding chunked. (Usually, your HTTP library will do this for you)