How to convert an array of bytes into string with Node.js?

Question

I need a random sequence of bytes for making a password hash. In Ruby, this would look like:

 File.open("/dev/urandom").read(20).each_byte{|x| rand << sprintf("%02x",x)}

In Node.js, I can get a sequence of random bytes with:

 var randomSource = RandBytes.urandom.getInstance();
 var bytes = randomSource.getRandomBytesAsync(20);

But the problem is, how to convert these to a String?

Also, I need to have them wrapped in promisses. Would this work:

   get_rand()
   .then(function(bytes) {
     authToken = bytes;
   })

Andrew · Accepted Answer · 2013-11-29 09:32:12Z

31

Try this:

new Buffer(bytes).toString('ascii');

More details here: http://nodejs.org/api/buffer.html

edited Nov 29, 2013 at 9:32

answered Nov 29, 2013 at 9:16

Andrew

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3 Comments

poseid Over a year ago

I like your answer since you mention the place to learn about this... however, I get: <Buffer b8 92 17 4c f1 11 35 d2 04 2a 7b 94 03 5c 9c 1a d0 9d 6a 43> - why is this not something as "saDasdkn2"

poseid Over a year ago

hmm.. maybe it is the promise library I am using, I filed an issue here: github.com/petkaantonov/bluebird/issues/34

袁文涛 Over a year ago

new Buffer(bytes) was deprecated, you can use new Buffer.from(bytes) now

Esailija · Accepted Answer · 2013-11-29 13:51:28Z

4

You can just use crypto that comes with node:

var Promise = require("bluebird");
var crypto = Promise.promisifyAll(require("crypto"));

crypto.randomBytesAsync(20).then(function(bytes){
    console.log('random byte string:', bytes.toString("hex"));
});

Logs:

random byte string: 39efc98a75c87fd8d5172bbb1f291de1c6064849

answered Nov 29, 2013 at 13:51

Esailija

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1 Comment

j03m Over a year ago

This seems like the correct answer actually. Not sure of the benefit of using randbytes these days. It definitely doesn't work on windows. (not that anyone cares... ;) )

robertklep · Accepted Answer · 2013-11-29 09:29:24Z

2

randbytes works asynchronously. If you want to combine it with promises, you need to use a Promises-lib as well. I'm using when as an example:

var when          = require('when');
var RandBytes     = require('randbytes');
var randomSource  = RandBytes.urandom.getInstance();

function get_rand() {
  var dfd = when.defer();
  randomSource.getRandomBytes(20, function(bytes) {
    dfd.resolve( bytes.toString('hex') ); // convert to hex string
  });
  return dfd.promise;
}

// example call:
get_rand().then(function(bytes) {
  console.log('random byte string:', bytes);
});

answered Nov 29, 2013 at 9:29

robertklep

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2 Comments

poseid Over a year ago

this answer is very good too, small detail, I am using the bluebird library, and maybe my problem is there, I referenced to your answer here: github.com/petkaantonov/bluebird/issues/34

j03m Over a year ago

I think @Esailija's answer is actually the correct one.

9me · Accepted Answer · 2020-10-06 09:42:44Z

2

If you are using ES6 then its also easy

String.fromCharCode(...bytes)
Promise.resolve(String.fromCharCode(...bytes)) // Promise

or

String.fromCharCode.apply(null, bytes)
Promise.resolve(String.fromCharCode.apply(null, bytes)) // Promise

answered Oct 6, 2020 at 9:42

9me

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Comments

Ginden · Accepted Answer · 2013-11-29 09:24:23Z

0

Do you want to conver it to ASCII? If not, this is my code (1 minute of work):

  var z;
 randomSource.getRandomBytes(20, function(){z=arguments[0]})
 z
<Buffer c8 64 03 d1 2d 27 7d 8e 8f 14 ec 48 e2 97 46 84 5a d7 c7 2f>
 String(z)
'�d\u0003�-\'}��\u0014�H��F�Z��/'

answered Nov 29, 2013 at 9:24

Ginden

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