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Encode an ArrayBuffer as a base64 string
// Converts an ArrayBuffer directly to base64, without any intermediate 'convert to string then
// use window.btoa' step. According to my tests, this appears to be a faster approach:
// http://jsperf.com/encoding-xhr-image-data/5
/*
MIT LICENSE
Copyright 2011 Jon Leighton
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
function base64ArrayBuffer(arrayBuffer) {
var base64 = ''
var encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
var bytes = new Uint8Array(arrayBuffer)
var byteLength = bytes.byteLength
var byteRemainder = byteLength % 3
var mainLength = byteLength - byteRemainder
var a, b, c, d
var chunk
// Main loop deals with bytes in chunks of 3
for (var i = 0; i < mainLength; i = i + 3) {
// Combine the three bytes into a single integer
chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2]
// Use bitmasks to extract 6-bit segments from the triplet
a = (chunk & 16515072) >> 18 // 16515072 = (2^6 - 1) << 18
b = (chunk & 258048) >> 12 // 258048 = (2^6 - 1) << 12
c = (chunk & 4032) >> 6 // 4032 = (2^6 - 1) << 6
d = chunk & 63 // 63 = 2^6 - 1
// Convert the raw binary segments to the appropriate ASCII encoding
base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d]
}
// Deal with the remaining bytes and padding
if (byteRemainder == 1) {
chunk = bytes[mainLength]
a = (chunk & 252) >> 2 // 252 = (2^6 - 1) << 2
// Set the 4 least significant bits to zero
b = (chunk & 3) << 4 // 3 = 2^2 - 1
base64 += encodings[a] + encodings[b] + '=='
} else if (byteRemainder == 2) {
chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1]
a = (chunk & 64512) >> 10 // 64512 = (2^6 - 1) << 10
b = (chunk & 1008) >> 4 // 1008 = (2^6 - 1) << 4
// Set the 2 least significant bits to zero
c = (chunk & 15) << 2 // 15 = 2^4 - 1
base64 += encodings[a] + encodings[b] + encodings[c] + '='
}
return base64
}

tsenart commented Jun 7, 2011

I kind of need the reverse. A base64 encoded utf8 string to an ArrayBuffer. How can I do that?

Owner

jonleighton commented Jun 7, 2011

I guess you would need to write this function sort of in reverse. So iterate over each 4 characters, converting them to three bytes which you append to the ArrayBuffer, and then with special handling for the padding at the end. I don't have code for that though :)

n1k0 commented Sep 10, 2011

As you just saved my life, I just wanted to say THANK YOU

joscha commented Jan 18, 2013

kinda late, but here is the reverse

joscha commented Jan 18, 2013

And CryptoJS has a method to transform to a WordArray as well: CryptoJS.enc.Base64.parse

@joscha, the "reverse" (see comment https://gist.github.com/jonleighton/958841/#comment-733469) seems to be 3x slower than atob in my tests.

This is a pretty nifty method! Is there any chance you might add a license to it? I would really like to include it in a project of mine but am not allowed to do so without a proper license ;-)

lapsio commented Oct 20, 2013

It's amazing, I'm working on >10 000 000 arrays (audio files) and performance was serious bottleneck, thanks

This function is flaw. Everything turns out as "AAAAAAAAA" for small number like [0.000354254885, -0.521365849254, 0.002453687924].

gfranko commented May 28, 2014

Thank you very much, works like a charm! Would you mind adding a license to this?

Thank you for this useful script. Which license is this? GPL? BSD?

You made my day.

You are my hero!

Boom, thanks.

Thanks a lot! Would be awesome if you could state under which license you published this.

+1 for a license statement.

Thank you. It's works.

A question.
How max limit about arrayBuffer length ? Thanks again.

wmaciel commented Aug 5, 2016

Soooo, license?

hookenz commented Aug 24, 2016

I tried this this just now on Chrome 52.0 thinking your approach would be faster. It's not, but it may once have been. Interestingly it's about 40ms slower than other approaches I tried. The most simplistic implementation is now very fast. Perhaps modern browsers have optimised certain routines more.

This is actually faster.

function uint8ToBase64(buffer) {
     var binary = '';
     var len = buffer.byteLength;
     for (var i = 0; i < len; i++) {
         binary += String.fromCharCode(buffer[i]);
     }
     return window.btoa( binary );
}

For those of you looking for an ES6 version

export function base64ArrayBuffer(arrayBuffer) {
  let base64 = '';
  const encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

  const bytes = new Uint8Array(arrayBuffer);
  const byteLength = bytes.byteLength;
  const byteRemainder = byteLength % 3;
  const mainLength = byteLength - byteRemainder;

  let a;
  let b;
  let c;
  let d;
  let chunk;

  // Main loop deals with bytes in chunks of 3
  for (let i = 0; i < mainLength; i += 3) {
    // Combine the three bytes into a single integer
    chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2];

    // Use bitmasks to extract 6-bit segments from the triplet
    a = (chunk & 16515072) >> 18; // 16515072 = (2^6 - 1) << 18
    b = (chunk & 258048) >> 12; // 258048   = (2^6 - 1) << 12
    c = (chunk & 4032) >> 6; // 4032     = (2^6 - 1) << 6
    d = chunk & 63;        // 63       = 2^6 - 1

    // Convert the raw binary segments to the appropriate ASCII encoding
    base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d];
  }

  // Deal with the remaining bytes and padding
  if (byteRemainder === 1) {
    chunk = bytes[mainLength];

    a = (chunk & 252) >> 2; // 252 = (2^6 - 1) << 2

    // Set the 4 least significant bits to zero
    b = (chunk & 3) << 4; // 3   = 2^2 - 1

    base64 += `${encodings[a]}${encodings[b]}==`;
  } else if (byteRemainder === 2) {
    chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1];

    a = (chunk & 64512) >> 10; // 64512 = (2^6 - 1) << 10
    b = (chunk & 1008) >> 4; // 1008  = (2^6 - 1) << 4

    // Set the 2 least significant bits to zero
    c = (chunk & 15) << 2; // 15    = 2^4 - 1

    base64 += `${encodings[a]}${encodings[b]}${encodings[c]}=`;
  }

  return base64;
}

I was looking to pure conversion from BufferArray to base64 (non-browser usage) and this has hit the spot perfectly. Much appreciated.

Cheers,
Ilay

hookenz commented Mar 2, 2017

@Grantlyk - that's better but still slower than the code I posted above.

Thank you very much, this helped me get around the btoa() error "String contains an invalid character"!

otaroo commented Sep 26, 2017

Thank you very much

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