Google Drive API sending PDF attachments in emails - node.js

Question

I have some node.js code that reads in a PDF file using Google Drive API drive.files.get()... (it's a file that is sourced on our Google team/shared drives). I convert the returned stream to a single base64 data chunk with something like this:
// read using drive.files.get() into 'pdfStream'
//...
let pdf64 = '';
pdfSream.on('readable', function () {
var chunk = pdfStream.read();
if (chunk != null) {
var chunk64 = chunk.toString('base64');
pdf64 += chunk64;
}
});
pdfStream.on('end', function () {
// Do SendGrid email with pdf64 as attachment
});
Note that the final goal is to send an email with the PDF. I haven't included much of the code because this all works great - as long as the email recipient is on our company's domain. For external email recipients, the PDF attachment is unviewable and cannot be downloaded - at least this is what the situation appears to be.
I didn't think that access-restrictions and permissions would stay with data that is read directly using drive.files.get(). Is this a thing? I would suspect SendGrid except that we send attachments in other areas of our code with no issue.
Thoughts anyone? Much appreciated!
~Bob

Answer 1

I was able to fix it. The permissions thing was a red herring - the pdf attachments were corrupt and our company email system was just more lenient with the errors than others (like Gmail). I refactored the above code to first create a complete array of data, then converted that array to base64:
// read using drive.files.get() into 'pdfStream'
//...
let pdfChunks = [];
// Read through stream chunks and concat them together
pdfStream.on('readable', function () {
var chunk = pdfStream.read();
if (chunk != null) {
pdfChunks.push(chunk);
}
});
// On the end of the stream, convert to base64 and email the Pdf
pdfStream.once('end', function () {
let pdfBin = Buffer.concat(pdfChunks);
let pdf64 = pdfBin.toString('base64');
//...
// Do SendGrid email with pdf64 as attachment
});
Cheers!
~Bob