Decode Base64 string in node.js

Question

I'm trying to decode a base64 string representing an image stored in a db. I tried many libraries and solutions provided on SO, but I'm still unable to decode the image correctly. In particular, using the following code:

var img = new Buffer(b64, 'base64').toString('ascii');

I get a similar binary representation, except for the first bytes. This is the initial part of the base64 string:

/9j/4RxVRXhpZgAASUkqAAgAAAANADIBAgAUAAAAqgAAACWIBAABAAAAiwYAABABAgAIAAAAvgAA

Here are the first 50 bytes of the original image:

ffd8ffe11c5545786966000049492a00080000000d003201020014000000aa00000025880400010000008b06000010010200

And here are the first 50 bytes of the string I get with javascript:

7f587f611c5545786966000049492a00080000000d0032010200140000002a00000025080400010000000b06000010010200

How you can see, the two strings are identical except for the fisrt 3 bytes and some few bytes in the middle.
Can somebody help me understand why this is happening and how to solve it? Thanks

Answer 1

The problem is that you're trying to convert binary data to ASCII, which most likely than not, will mean loss of data since ASCII only consists of values 0x00-0x7F. So when the conversion takes place, all bytes > 0x7F are capped at 0x7F.

If you do this instead, you can see the data matches your first 50 bytes of the original image:

console.log(Buffer.from(b64, 'base64').toString('hex'));

But if you want to keep the binary data intact, just keep it as a Buffer instance without calling .toString(), as many functions that work with binary data can deal with Buffers (e.g. fs core module).