在浏览器中解码 Base64 编码的 PDF 内容

Question

We transform HTML to PDF in the backend (PHP) using dompdf . The generated output from dompdf is Base64 encoded with

$output = $dompdf->output();
base64_encode($output);

This Base64 encoded content is saved as a file on the server. When we decode this file content like this:

cat /tmp/55acbaa9600f4 | base64 -D > test.pdf

we get a proper PDF file.

But when we transfer the Base64 content to the client as a string value inside a JSON object (the server provides a RESTful API...):

{
  "file_data": "...the base64 string..."
}

And decode it with atob() and then create a Blob object to download the file later on, the PDF is always "empty"/broken.

$scope.downloadFileData = function(doc) {
  DocumentService.getFileData(doc).then(function(data) {
    var decodedFileData = atob(data.file_data);
    var file = new Blob([decodedFileData], { type: doc.file_type });
    saveAs(file, doc.title + '.' + doc.extension);
  });
};

When we log the decoded content, it seems that the content is "broken", because several symbols are not the same as when we decode the content on the server using base64 -D.

When we encode/decode the content of simple text/plain documents, it's working as expected. But all binary (or not ASCII formats) are not working.

We have searched the web for many hours, but didn't find a solution for this that works for us. Does anyone have the same problem and can provide us with a working solution? Thanks in advance!

This is a example for a on the server Base64 encoded content of a PDF document:

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 IGYgCjAwMDAwMDAwMDggMDAwMDAgbiAKMDAwMDAwMDA3MyAwMDAwMCBuIAowMDAwMDAwMTE5IDAwMDAwIG4gCjAwMDAwMDAyNzMgMDAwMDAgbiAKMDAwMDAwMDMwMiAwMDAwMCBuIAowMDAwMDAwNDE2IDAwMDAwIG4gCjAwMDAwMDA0NzkgMDAwMDAgbiAKMDAwMDAwMDYxNiAwMDAwMCBuIAp0cmFpbGVyCjw8Ci9TaXplIDkKL1Jvb3QgMSAwIFIKL0luZm8gNSAwIFIKPj4Kc3RhcnR4cmVmCjcyNQolJUVPRgo=

If you atob() this, you don't get the same result as on the console with base64 -D. Why?

Answer 1

Your issue looks identical to the one I needed to solve recently.

Here is what worked for me:

const binaryImg = atob(base64String);
const length = binaryImg.length;
const arrayBuffer = new ArrayBuffer(length);
const uintArray = new Uint8Array(arrayBuffer);

for (let i = 0; i < length; i++) {
    uintArray[i] = binaryImg.charCodeAt(i);
}

const fileBlob = new Blob([uintArray], { type: 'application/pdf' });

saveAs(fileBlob, 'filename.pdf');

It seems that only doing a base64 decode is not enough...you need to put the result into a Uint8Array. Otherwise, the pdf pages appear blank.

I found this solution here: https://github.com/sayanee/angularjs-pdf/issues/110#issuecomment-579988190

Answer 2

You can use btoa() and atob() work in some browsers: For Exa.

var enc = btoa("this is some text");
alert(enc);
alert(atob(enc));

To JSON and base64 are completely independent.

Here's a JSON stringifier/parser (and direct GitHub link ).

Here's a base64 Q&A . Here's another one .