Re: [GNU-linux-libre] youtube-dl might be running non-free software from

[rain1]

I haved audited the JSInterpreter class in youtube-dl. Here are my 
findings:

* You can crash it by doing an infinite loop: function loop(){loop();}
* It is NOT turing complete (because there is no 'if' or ability to 
create 'if' by passing functions as values)

I believe that all the jsinterpreter can do is run a fixed call tree of 
functions which pass numbers, characters and strings as arguments. And 
apply a small set of built in functions on them like +, -, reverse, 
slice, array indexing.

Originally youtube-dl used to reverse engineer a certain 'signature' 
function from the youtube base.js file. This function had to be updated 
more and more often, a primitive version of jsinterpreter was used by 
the developers to do this quickly. Eventually they automated that 
completely.

So this a little bit of a fuzzy issue. Here are a summary of the points 
to weigh up:

* The javascript file is source-available but not libre.
* The javascript snippet used would be classified as trivial by 
librejs[1] and not require license
* The "language" implemented can do small computations but is branchless 
and sub-turing
* Youtube terms of service[2] say that you do not have permission 
download youtube videos

[1] 
https://www.gnu.org/software/librejs/manual/librejs.html#JavaScript-Detection
[2] https://www.youtube.com/static?template=terms

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Those are the technical details, Now here's my opinion:

Richard Stallman has stated (at FOSDEM 2016, I think) that it is ok to 
use non-free software if it is to further the use of free-software: For 
example using a non-free system to print out leaflets to advertise a 
free software convention. Related link 
<https://www.gnu.org/philosophy/is-ever-good-use-nonfree-program.en.html>

I think youtube-dl fits under a similar situation, there is a wealth of 
enriching information on there including educational materials about 
free software. It is wonderful when people upload them to mediagoblin 
but not everything is there. Secondly, the youtube site seems to want 
the user to be executing their (non-libre) js and youtube-dl is actually 
avoiding this and working around it in a clever way - in fact it is not 
even executing a turing complete language, it simply extracts the cipher 
it needs to get around that. Of course this is not ideal, in a perfect 
world you wouldn't want your programs to access or parse non-libre 
javascript.

So, while youtube-dl is an invaluable tool.. it is not exactly clear to 
me whether it can be considered free libre software.
* The source code is available and it is permissively licensed[4]
* The program munges nonfree javascript, allowing the user to accomplish 
a task without executing it.
* The program is used to violate TOS, but software freedom 0 says we 
have the right to use a program for any purpose.

[4] https://github.com/rg3/youtube-dl/blob/master/LICENSE

What would a completely libre version of youtube-dl look it? I think 
that it would only work on sites whose TOS support downloading videos, 
and only does so for videos which have some kind of creative 
commons/free culture license.