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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

SimoV8
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    possible duplicate of [NodeJS: How to decode base64 encoded string back to binary?](http://stackoverflow.com/questions/14573001/nodejs-how-to-decode-base64-encoded-string-back-to-binary) – Vidul Sep 06 '15 at 17:21
  • No, it's not a duplicate. I already tried that solution and doesn't work for me. – SimoV8 Sep 06 '15 at 17:36

1 Answers1

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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).

mscdex
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    I thought it was a character encryption problem but I was sure ascii values could arrive till 0xFF. However replacing `.toString('hex')` doesn't work for me (I get a completely different string), but removing the `.toString()` call did the work, thank you! – SimoV8 Sep 06 '15 at 17:47
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    Please be aware that new Buffer has been depreciated, you should see a warning in your logs: "DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead. " In mscdex example above use Buffer.from(b64, 'base64').toString('hex') – user2677034 Dec 22 '19 at 00:02