NodeJS将图像流转换为base64会提供无效数据

Question

I'm trying to generate a QR code and then return it as a Base64-encoded data URL. I know that there's a module ( https://github.com/cmanzana/qrcode-npm ) which is supposed to be able to do this directly, but I'm having trouble installing the canvas module dependency. I'm still working on that front but for now, my attempted workaround is to generate an image stream with an alternate module, then convert it to Base64. This is what I have so far:

var qrBase64 = '';
var qrImg = qr.image(qrText, { type: 'png', ec_level: 'L' });

qrImg.on('readable', function () {
    qrBase64 += qrImg.read().toString('base64');
});

qrImg.on('end', function () {
    qrBase64 = "data:image/png;base64," + qrBase64;
    return res.json({
        success: true,
        qrBase64: qrBase64
    });
});

It seems to work in that it gives me a string which resembles a Base64-encoded string. However, if I try to view it in a browser, I get an invalid URL error. If I pipe the qrImg to a file and then use an online tool to convert it to Base64, the result (which is valid and works in a browser) does not match my Node result.

Answer 1

You need to base64 encode all of the image data at once. Concatenating chunks before and after base64 encoding usually doesn't yield the same result. Take a look at this example:

btoa("12" + "34")         -> "MTIzNA=="

btoa("12") + btoa("34")   -> "MTI=MzQ="