Develop Reference

What is that nonsense string we get when requesting binary data, and how do we convert it into a proper buffer?

When using a library to request some non-ASCII/UTF8 data, we often get back a string full of nonsense. Example:
const got = require("got");
got("http://twemoji.maxcdn.com/16x16/1f525.png")
.then(response => console.log(response.body))
This is the output:
�PNG
IHD��aaIDAT8�c`��L�fEb��?��8�-���#���5�!� ���|bQ\�$�� �ׁX�y�xT
���y#< �c�i��6$�K$
L÷���w��������_��Ϡ���d��?�j��2��� ��hX��cn������e"L����x�3�
��Y�f�N���
mt:����2e�f��N���~{'̀x�ȿ �;�m
�
�PIEND�B`� �vZ�]�dX<R�\�Y:������`�A�A��ӂƟ}�����#A�\�n����|�A� u83����,�{������#�#4��#��D�
Curiously, that is the same thing we see when downloading the image and using:
cat 1f525.png
What, exactly, is that string, why it looks like this, and how do we convert it to a proper Buffer object?

That's a PNG image which is not text data, but just basic binary data. It doesn't make sense to interpret it as a string.
got will return string, buffer, readableStream, or object. console.log is converting your stream into a string which is not what you want. cat deals with text, not binary data.
Also the response from http://twemoji.maxcdn.com/16x16/1f525.png does not include the Content-Type header which could be throwing off the got library.

It's not really strange that you see the same output from cat - that is how a PNG image looks like when interpreted as a string.
According to the got documentation, it should return a buffer when you specify the encoding as null. Perhaps console.log is converting the buffer to a string, or you could try to set the encoding to image/png.
Did you actually try to save to image to file? Perhaps it'll just work.

By default, got will fetch you a string. It assumes you want UTF-8 text data by default, since that's probably the most common case, people fetching HTML documents. From the documentation:
encoding
Type: string, null
Default: 'utf8'
Encoding to be used on setEncoding of the response data. If null, the body is returned as a Buffer.
If you want binary data instead, specify {encoding: null}:
const got = require("got");
got("http://twemoji.maxcdn.com/16x16/1f525.png", {encoding:null})
.then(response => console.log(response.body))
Then response.body will be a Buffer.

Unable to decode base64 from req.header.authorization

In express I am grabbing the basic auth from:
req.headers.authorization
From that I get back
dXNlcm5hbWU6cGFzc3dvcmQ=
I say "hey that looks like base64". I quickly go to one of those base64 sites and decode it and it turns out to be 'username:password'. So I google how to decode base64 in express 4. I wind up with this code:
console.log(new Buffer(req.headers.authorization.toString(), 'base64').toString('ascii'));
That is returning:
+"qUMI95iAMM]=I
Which is not username:password. I also tried this with the utf8 setting and that did not work either. I also tried this without toString() on the req.headers.authorization. How do I properly decode base64 with expressjs?

In case anyone is as stupid as I am and didn't realize that the string that is returned from req.headers.authorization is the word Basic followed by the base64 encoded string, you must split the string before decoding.
console.log(new Buffer(req.headers.authorization.split(" ")[1], 'base64').toString())
req.headers.authorization returned for me: Basic dXNlcm5hbWU6cGFzc3dvcmQ=. Not just the base64 string.

Using the new Buffer API it is now
console.log(Buffer.from(req.headers.authorization.split(" ")[1], 'base64').toString())
Else you will get deprecated warnings.

Saving Base64 String as .PNG not working

I have a base64 string that I got from using Google Charts.
The project is being written in Python/Django/Javascript if that helps.
chartStr = chart.getImageURI()
I want to save this string as a .png on my server.
I've tried
with open('foo.png',"wb") as f:
f.write(chartStr.decode('base64'))
but I get an incorrect padding error. I fix this by adding a '=' at the end of the string chartStr. WHen I do that, the foo.png image is created but when I try to open it I get an error that says
Fatal error reading PNG image file: Not a PNG file
Any advice?
Thanks!

When you added the = to the string the returned string from .decode("base64") was the same as the input string minus the appended =.
To write the .png to a file you need to do the following:
head, data = chartStr.split(",", 1)
with open('foo.png',"wb") as f:
f.write(data.decode('base64'))
This removes the data:image/png;base64, stuff and leaves you with some base64 encoded data.

Convert Base64 to image file with javascript

Does anyone know of any simple javascript that I can use to turn a base64 string into an image (jpg format preferably), so that I can save the image to a file? This is for a signature pad application. I can get the signature into a base64 format, but need to save the signature as an image file to use for embedding into a Crystal Report.

I have tried this method in a JSP page to print the image from a base64 string, I guess this should hold good for javascript too. Do not have sample data for now to verify, but here's how I would try it.
var oImg=document.createElement("img");
var baseString = null; //the base64 string you have
var imsc = 'data:image/jpg;base64, '+baseString;
oImg.setAttribute('src', imsc);
document.body.appendChild(oImg);

Convert cryptic string to a readable one with JavaScript (UTF-8)

I found out that when I save this distorted string ("Äußerungen üben") as an ANSI text file, then open it with Firefox and choose in the Firefox menu "Unicode", it turns it into a readable german format ("Äußerungen üben").
The same thing is possible with my text editor (Notepad++).
Is there any way to achieve this with JavaScript? E.g. the following would be nice:
var output = makeReadable("Äußerungen üben");
Unfortunately, I get this kind of distorted strings from an external source which doesn't care about UTF-8 and provides all data as ANSI.
PS: Saving the file as UTF-8 and setting the charset as UTF-8 in the META Tag has no effect.
Edit:
Now I solved it through making a list of all common UTF8/ANSI distortions (more than 1300) and wrote a function replacing all wrong character combinations with the right character. It works fine :-) .

I think the encoding of the "distorted string" in your question got munged further by posting it here. But a quick Google search for "javascript convert from utf-8" returns this blog post as the top hit:
http://ecmanaut.blogspot.com/2006/07/encoding-decoding-utf8-in-javascript.html
So it turns out that encoding and decoding UTF-8 in JavaScript is really easy. This works great for me:
var original = "Äußerungen üben";
var utf8 = unescape(encodeURIComponent(original));
//return utf8; // something like "ÃuÃerungen üben"
var output = decodeURIComponent(escape(utf8));
return output;