NodeJS - How to retrieve original data from a Buffer after use JSON.parse(JSON.stringify())

Question

I am working with crypto library to send a POST request to update some data and for some reason I get as if I used JSON.parse(JSON.stringify(myBufferData)) to a Buffer data. I want to recover the original data.

How you can replicate my situation:

var buf = Buffer.from('abc');
var parsedBuf = JSON.parse(JSON.stringify(buf)); -> I faced with this result at some point.

buf.toString() -> Give the expected result ('abc').
parsedBuf.toString() -> Doesn't retrieve original data ('[object Object]').

How can I retrieve the original data from parsedBuf ?

Answer 1

Solution

Use Buffer(parsedBuf).toString() instead of parsedBuf.toString() to retrieve original data.

---

Explanation

Checking the Buffer docs, I found out that its toString method is not Javascript's built-in. You can simply check it's source wherever you want by calling buf.[method].toString(). In this case:

• buf.toString.toString()

• JSON.parse(JSON.stringify(buf)).toString.toString()

So it revealed me somehow their source code:

// Buffer's toString method
function () {
  let result;
  if (arguments.length === 0) {
    result = this.utf8Slice(0, this.length);
  } else {
    result = slowToString.apply(this, arguments);
  }
  if (result === undefined)
    throw new Error('"toString()" failed');
  return result;
}

// Javascript's built-in
function toString() { [native code] } // I haven't sought to find it out

It turns out that whenever you do JSON.parse(JSON.stringify(buf)) you are actually transforming your Buffer into a Javascript object. For example:

{ type: 'Buffer', data: [ 61, 62, 63] }.

So another toString() on it will run native JS function (not Buffer's) which returns by default [object Object].