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I have a base64 string that represents binary data (e.g. not a nice readable string after you decode it or UTF-8 data otherwise this answer would help me -- Using Javascript's atob to decode base64 doesn't properly decode utf-8 strings). My JS Is

var byteCharacters = atob(base64str);

which results in

InvalidCharacterError: Failed to execute 'atob' on 'WorkerGlobalScope': The string to be decoded contains characters outside of the Latin1 range.

How do I decode a base 64 string that is not ASCII (or even UTF-8 data)?

Edit: Here's an example of the type of string I'm talking about. Using Mac, I can base64 encode a file like so

openssl base64 -in ~/Downloads/star.jpg -out ~/Downloads/star.base64

Here's the resulting base64 string. If you can decode this with JS tools, you've solved the problem. Got the below by doing "cat myfile.base64" so hopefully "cat" or my cutting and pasting didn't introduce any weird characters here.

iVBORw0KGgoAAAANSUhEUgAAAQMAAADCCAMAAAB6zFdcAAAAulBMVEUNKlK+vr7/
///FxMMAJU/BwcAAFUgAIU1BUGoAHEsAIE0AI04AHkyztbgAGEkJKFEAEEXU2N48
T27JzNMAAEGGjZhye4urrrKkqa6doqgRLlYAE0c2SGaQlp8AAD99hZJfaHyYnKMb
NFkACkNKWXHs7vFncYPh5OgmPF4UM1tWY3ior7uSmqmAh5ROXHS7wcotQGGKlKR1
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nO1dC3vaOLP2RcLYsiVCuF+ScAkh2YaSJm1P9+v+/791NCPJFzAFHFpwnXl2nwZs
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AABJRU5ErkJggg==
Dave
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  • Is the string sharable, or are you able to provide a minimal working example? – Matt Way May 25 '18 at 21:51
  • You're probably not decoding with the same character set that the binary data was encoded with. They must match. Do you know which character set was used for encoding? – Victor Stoddard May 25 '18 at 21:55
  • @VictorStoddard, The original data that was encoded wasn't a readable string. It was like PDF data or image data or something like that. Does the decoding depend on the original file type? Is there just a generic binary decode? – Dave May 25 '18 at 22:01
  • If the result should be binary data why do you call it a string? What is an appropriate data type for the result? – Tom Blodget May 27 '18 at 14:33
  • @TomBlodget, I want my quesiton to be clear. The item "base64str" is indeed a string, since base 64 encoded entitties are all strings, from what I have been told. What it represents is not. Where in my question do I refer to the entity that was encoded as a string? I want to make this quesiton clear before it goes to its inevitable bounty. – Dave May 27 '18 at 16:38
  • So, the task is to convert from data as base64 in a `String` to bytes in, say, a `Uint8Array`? – Tom Blodget May 27 '18 at 16:42
  • Sure Uint8Array would be just fine. Or an ArrayBuffer. As long as teh binary data is returned to its original form. – Dave May 28 '18 at 13:30
  • The real problem lies in generation of base64 string. How are you getting the base64 string? The string may be getting corrupted. I tried with uint8Array and an image Here is the code for Uint8Array ar = [1,2,3]; uar = Uint8Array.from(ar) base64str = btoa(uar) byteCharacters = atob(base64str) // "1,2,3" //No errors were encountered. – Sreeragh A R May 29 '18 at 16:14
  • @SreeraghAR, added an example into my question. The file was base64 encoded using the command "openssl base64 -in ~/Downloads/star.jpg -out ~/Downloads/star.base64" If this is a faulty way of base64 encoding something, I'm open to suggestions for encoding to allow a JS decode function to work. – Dave May 31 '18 at 14:38
  • ok.. I have posted an answer. – Sreeragh A R Jun 01 '18 at 08:54

3 Answers3

0

Last edit: More publicity should made of this sentence from the 2015 related SO answer

The original solution (deprecated)

When mentioning atob, btoa, base64js and other libraries functions: save your time with a library and deprecate atob and btoa

Try base64.js.toByteArray with your data. Follow the link to the library Github Readme: it says it does exactly what you want, well, only that from and to.

Tested @1.3.0 succesfully with your data base64js.min.js on Chrome 66.0.3359.181

Tested @1.3.0 succesfully with your data in Nodejs @4.4.7

quote from the README:

base64js has three exposed functions, byteLength, toByteArray and fromByteArray, which both take a single argument.

  1. byteLength - Takes a base64 string and returns length of byte array
  2. toByteArray - Takes a base64 string and returns a byte array
  3. fromByteArray - Takes a byte array and returns a base64 string

I would also test original binary data against whatever file type/structure it is supposed to be/have, if you can access it.

Did you test the base64 string against base64, at first, is it a proper base64 string?

To be fair a code Example link and more information in the Github repo, when included as script in the client, use:

var byteArray = base64js.toByteArray(myBase64Str)

In Node, you would do:

var fs = require('fs')
var base64js =  require('base64-js')
fs.readFile('pathToMyBase64File', 'utf8', (err, data) => { // here 'utf8' is mandatory
  if (err) throw err;
  var byteArray = base64js.toByteArray(data)
  console.log(base64js.byteLength(data) == byteArray.length)
})

Important, myBase64File should be encoded with utf-8 w/BOM or it won´t work.

P.S. : I am not any contributor to this library, just a good tool for everybody to know, LICENSE MIT.

lucchi
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  • Can you elaborate a little more with a code sample? Are you saying "base64.js.toByteArray" will decode my base64 string taht was origianlly a binary data file? – Dave May 31 '18 at 14:12
  • This example taht you linekd to -- is this for a NodeJS script or for an in-browser application of the tool? I'm more interested in the in-browser application. – Dave May 31 '18 at 14:54
  • Both of them, for the moment I´ve been able to test your data with C# .NET and I get a length 5722 Array so data is OK. When I get an environment I´ll try with the JS lib – lucchi May 31 '18 at 15:22
  • I've just pated base64js.min.js in my console then called toByteArray over the pasted data and I got a beautiful Uint8Array(5722) [137, 80,... – lucchi May 31 '18 at 16:04
  • Ah this is good news. How did you invoke the toByteArray function? When I included "" on my page and then called "b64.toByteArray(myBase64Str)" using the example you posted, I get the error, "Uncaught TypeError: Cannot read property 'toByteArray' of undefined" – Dave May 31 '18 at 16:19
  • I agree it might not be the easiest example from the repo – lucchi May 31 '18 at 16:28
  • Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/172177/discussion-between-lucchi-and-dave). – lucchi May 31 '18 at 16:29
0

As I already mentioned in the comments, the problem is with encoding. Your shared base64 string has a lot of newlines('\n') in it. Newlines are added (by cat) for user readability. But they cause troubles while decoding. If you try after removing all '\n' in your string and try atob(), it should be working.

To get base64 string without spaces or '\n'

In Linux 

$ base64 -w 0 ~/Downloads/star.jpg >~/Downloads/star.base64

In Mac, you may try -A option in openssl.

$ openssl base64 -A -in ~/Downloads/star.jpg -out ~/Downloads/star.base64

Please try atob() with the resulting string (Copy directly from file not from cat output).

Note:I'm not a Mac user

Sreeragh A R
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-1

You could try the following code: 

function decode_base64(s) {
  var b=l=0, r='',
  m='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
  s.split('').forEach(function (v) {
    b=(b<<6)+m.indexOf(v); l+=6;
    if (l>=8) r+=String.fromCharCode((b>>>(l-=8))&0xff);
  });
  return r;
}

Then you can create an async function that can do your job: 

function decode_base64_async(s, cb) {
  setTimeout(function () { cb(decode_base64(s)); }, 0);
}

P.S: I've not checked this code for non-ASCII characters, so you need to try it

Ajay Kulkarni
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    THis only works if the thing that was encoed was originally a string, right? The thing I have encoded to a base64 string was binary data (think an image file). – Dave May 27 '18 at 16:39