修复此Mozilla Base64字节编码器

Question

I am using https://developer.mozilla.org/en-US/Add-ons/Code_snippets/StringView

to do some base64 conversions. It occurs to me that there is a bug, but I am not sure how to fix it.

In my testing, if I do

var name = new StringView("ZipFile.zip").toBase64();
console.log("Original Text = " + StringView.makeFromBase64(name));

I do not get back my original text - I get "ZipFile.zi"

I think the library is calculating the padding wrong, but I am unsure how to fix it - The method bytesToBase64() generates a string for this input that is WmlwRmlsZS56aXAA and then has a regex lookahead that replaces the last two values to give the result WmlwRmlsZS56aX== when the correct value should be WmlwRmlsZS56aXA=

Below is encoding function - with the regex at the end:

/* Base64 string to array encoding */

StringView.bytesToBase64 = function (aBytes) {

  var sB64Enc = "";

  for (var nMod3, nLen = aBytes.length, nUint24 = 0, nIdx = 0; nIdx < nLen; nIdx++) {
    nMod3 = nIdx % 3;
    nUint24 |= aBytes[nIdx] << (16 >>> nMod3 & 24);
    if (nMod3 === 2 || aBytes.length - nIdx === 1) {
      sB64Enc += String.fromCharCode(StringView.uint6ToB64(nUint24 >>> 18 & 63), StringView.uint6ToB64(nUint24 >>> 12 & 63), StringView.uint6ToB64(nUint24 >>> 6 & 63), StringView.uint6ToB64(nUint24 & 63));
      nUint24 = 0;
    }
  }

  return sB64Enc.replace(/A(?=A$|$)/g, "=");

};

I have tried to figure out how to fix the problem, but I am not sure if it is the regex, or the way that the encoding library is generating the sB64Enc value before it ever gets that far.

Is the problem that the line sB64Enc.replace(/A(?=A$|$)/g, "="); should not be global -ie sB64Enc.replace(/A(?=A$|$)/, "=");

Answer 1

I'm the author of the library. Thanks for reporting the bug!

The bug has been fixed now, and the code has been published also on GitHub .