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Date:   Tue, 6 Aug 2019 14:50:08 -0400
From:   "J. Bruce Fields" <bfields@redhat.com>
To:     Andy Shevchenko <andriy.shevchenko@intel.com>
Cc:     linux-nfs@vger.kernel.org
Subject: Re: [PATCH 08/16] nfsd: escape high characters in binary data
Message-ID: <20190806185008.GC9456@parsley.fieldses.org>
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On Tue, Aug 06, 2019 at 03:19:31PM +0300, Andy Shevchenko wrote:
> On Thu, Jun 20, 2019 at 10:51:07AM -0400, J. Bruce Fields wrote:
> > From: "J. Bruce Fields" <bfields@redhat.com>
> > 
> > I'm exposing some information about NFS clients in pseudofiles.  I
> > expect to eventually have simple tools to help read those pseudofiles.
> > 
> > But it's also helpful if the raw files are human-readable to the extent
> > possible.  It aids debugging and makes them usable on systems that don't
> > have the latest nfs-utils.
> > 
> > A minor challenge there is opaque client-generated protocol objects like
> > state owners and client identifiers.  Some clients generate those to
> > include handy information in plain ascii.  But they may also include
> > arbitrary byte sequences.
> > 
> > I think the simplest approach is to limit to isprint(c) && isascii(c)
> > and escape everything else.
> > 
> > That means you can just cat the file and get something that looks OK.
> > Also, I'm trying to keep these files legal YAML, which requires them to
> > UTF-8, and this is a simple way to guarantee that.
> 
> Two questions:
> - why can't be original function extended to cover this case
>   (using additional flags, maybe)?

I found the ESCAPE_NP/"only" logic made it a little difficult to extend
string_escape_mem().

So, I wrote a patch series that removes the string_escape_mem flags that
aren't used, simplifies it a bit, then separates the flags into two
different types: those that select which characters to escape
(non-printable, non-ascii, whitespace, etc.) and those that choose a
style of escaping to use (octal, hex, or \\).  That seems to make the
code a little easier to extend while still covering the cases people
actually use.  I'll try to get those out this week and you can tell me
what you think.

> - where are the test cases?

I didn't write a test case.  I agree that it would be a good idea--I'll
work on it.

--b.