Google-App-Script base64 vs javascript base64 decode

Question

Please, help with GoogleApps Script Base 64 Decode

-- Google Apps Script

  var tmp_base64 = "EXezAAA=";
  var byte_base64 = Utilities.base64Decode(tmp_base64);

  return ContentService.createTextOutput('\''+ tmp_base64 + '\' => \''+byte_base64 +'\'' );

return : 'EXezAAA=' => '17,119,-77,0,0'

-- javascript

function _base64ToArrayBuffer(base64) {
    var binary_string = window.atob(base64);
    var len = binary_string.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
        bytes[i] = binary_string.charCodeAt(i);
    }
    return bytes;
}
_base64ToArrayBuffer('EXezAAA=');

return : Uint8Array(5) [ 17, 119, 179, 0, 0 ]

correctly converted javascript, but why does Google Apps Script convert to wrong bytes?

How to solve this problem ?

Tanaike · Accepted Answer · 2022-03-23 12:18:28Z

2

When the document of "Uint8Array" is seen, it says as follows. Ref

The Uint8Array typed array represents an array of 8-bit unsigned integers.

By this, your _base64ToArrayBuffer returns [17, 119, 179, 0, 0].

On the other hand, at Google Apps Script, the byte array uses "twos-complement 8-bit signed integers" as the default. By this, Utilities.base64Decode("EXezAAA=") returns [17, 119, -77, 0, 0].

This is the reason for your current situation.

For example, when you want to retrieve the same value, in Javascript, please modify it as follows.

From:

var bytes = new Uint8Array(len);

To:

var bytes = new Int8Array(len);

By this, your _base64ToArrayBuffer returns [17, 119, -77, 0, 0].

When you want to retrieve the value of [17, 119, 179, 0, 0] at Google Apps Script, please modify it as follows.

From:

var byte_base64 = Utilities.base64Decode(tmp_base64);

To:

var byte_base64 = [...Uint8Array.from(Utilities.base64Decode(tmp_base64))];

By this, your _base64ToArrayBuffer returns [17, 119, 179, 0, 0].

References:

Uint8Array
Int8Array
- When the document of "Int8Array" is seen, it says as follows. Ref
The Int8Array typed array represents an array of twos-complement 8-bit signed integers.

answered Mar 23, 2022 at 12:18

Tanaike

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1 Comment

NightEye Over a year ago

a very clear answer.

Erique Bomfim · Accepted Answer · 2024-11-27 15:58:53Z

1

Another approach is to use Utilities.newBlob() feature. It can be easily converted to a String using .getDataAsString() method.

var tmp_base64 = "EXezAAA=";
var byte_base64 = Utilities.base64Decode(tmp_base64);
var data64Blob = Utilities.newBlob(byte_base64);
var data64String = data64Blob.getDataAsString();

return ContentService.createTextOutput('\''+ tmp_base64 + '\' => \''+data64String +'\'' );

answered Nov 27, 2024 at 15:58

Erique Bomfim

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