Re: [PATCH] Try URI quoting for embedded TAB and LF in pathnames

From: Linus Torvalds <torvalds@osdl.org>
Date: Oct 12, 2005, 21:05 UTC
Message-ID: <Pine.LNX.4.64.0510121355280.15297@g5.osdl.org>
In-Reply-To: <87vf02qy79.fsf@penguin.cs.ucla.edu>

On Wed, 12 Oct 2005, Paul Eggert wrote:

> 
> Your email message suggests that we need to be cautious here.
> That message contained UTF-8 text but its header said "Content-Type:
> TEXT/PLAIN; charset=ISO-8859-1".

Well, my email message was wrong and evil, because it _mixed_ two different encodings in the same text. No sane client could have shown them both at the same time - but especially with a stupid client, you could have changed your terminal to show either one or the other by switching from utf-8 to latin1 encoding and doing a refresh.

In other words, my email really was a nasty case of not one or the other, but both.

Now, I believe patches can actually be that way - it's not at all impossible to have a diff where the _filename_ is utf-8, but the content of the patch itself is some byte-encoding like latin1. Or the other way around.

> If we're still having problems like this in 2005 then I guess we need
> to deal with them.  This suggests we should be escaping every
> non-ASCII byte, at least for patches designed to be emailed robustly.

I find that email is very robust - it's basically 8-bit clean. No character encoding, no crap. Just a byte stream. It really _is_ the most reliable format.

Now, a lot of email clients are really weak in _showing_ it, and as mentioned, the email that mixed both is fundamentally not something you really even _can_ show sanely. But who cares? What matters is not what it looks like, but what it _saves_ as. If you save the email message, it should come out as the same reliable 8-bit byte stream, or your client is actively corrupting messages rather than just showing them.

This is really what my argument boils down to: character set encoding should _not_ EVER affect the _transfer_ of the data. It doesn't matter if something is latin1 or utf-8, the only thing that matters is the byte sequence. Only when you _display_ it should you try to figure out what the byte sequence possibly means.

So I repeat: 
 - escape as little as possible
 - make the _viewer_ decide how to view it.

Yes, if people use "cat" to view patches, it can be dangerous. But that's _their_ problem.

		Linus