pdf.js and protected files not otherwise viewable - file

Question

I am using the PDF.js library to display PDf files within my site (using the pdf_viewer.js to display documents on-screen), but the PDF files I am displaying are confidential and I need to be able to show them within the site but block non-authorized public folks from being able to view the same files just by typing in theie URLs and seeing them show up right in their browser.
I tried to add the Deny from all line in my htaccess file, but that also of courfse blocked the viewer from showing the docs, so that seems to be a no-go. Clearly anyone could simply look at inspector and see the pdf file that is being read by the viewer, so it seems a direct URL is not going to be secure in any way.
I did read about PDF.js being able to read binary data, but I have no knowledge of how I might read in a PDF in my own file system and prep it for use by the library, eveen if that means it is all a bit slower in loading to get the file contents and prep it on the fly.
Anyone have a solution that allows PDFJS to work without revealing the source PDF URL, or to otherwise read the file using local file calls?

Answer 1

Okay, after some testing, the solution is very easy:
Get the PDF data using an Ajax-called function that can figure out what actual file is to be viewed.
In that PHP file...
Read the file into memory, using fopen and fread normally.
Convert to base64 using the base64_encode
Pass that string back to the calling Javascript.
In the original calling function, use the following to convert the string to a Uint array and then pass that to the PDFJS library...
## The function that turns the base64 string into whatever a Uint8 array is...
function base64ToUint8Array(base64) {
var raw = atob(base64);
var uint8Array = new Uint8Array(raw.length);
for (var i = 0; i < raw.length; i++) {
uint8Array[i] = raw.charCodeAt(i);
}
return uint8Array;
}
## the guts that gets the file data, calls the above function to convert it, and then calls PDF.JS to display it
$.ajax({
type: "GET",
data: {file: <a file id or whatever distinguishes this PDF>},
url: 'getFilePDFdata.php', (the PHP file that reads the data and returns it encoded)
success: function(base64Data){
var pdfData = base64ToUint8Array(base64Data);
## Loading document.
PDFJS.getDocument(pdfData).then(function (pdfDocument) {
## Document loaded, specifying document for the viewer and
## the (optional) linkService.
pdfViewer.setDocument(pdfDocument);
pdfLinkService.setDocument(pdfDocument, null);
});
}
});