Re: [libvirt] [PATCH] Add a virStrSplitQuoted for splitting quoted strings
On 03/14/2012 10:50 AM, Daniel P. Berrange wrote:
> This looks like it is repeating some of the code in
> virsh.c:vshCommandStringGetArg; any chance we can combine them? In
> particular, the ability to mimic shell handling of \ escapes, as well as
> the difference in behavior of \ inside "" vs. '', seems like it
will
> come in handy.
Ah I had forgotten about that code. Can you clarify the difference
in \ handling. I guess you mean that inside '', \ can only be used
for \\ and \', while inside "", it can do all the standard shell
escapes like \t, \n, etc ?
Inside '', \ has no special meaning. (There's no way to escape ' inside
of ').
Inside "", \ escapes the next byte (important for " and \, but works on
any byte.
Outside quotes, \ escapes the next byte.
And most importantly: concatenating two forms of quoted materials is
permitted. Thus:
foo"b'ar\" "\'' blah\'
on input becomes this on output:
foob'ar" ' blah\
>
> What you have here does neither; although I didn't spot any flaw in the
> code, I don't know if it's the algorithm we want to be using.
I should have sent this paired with my other patch for <cmdline>
handling in LXC. That is the intended use case for this function.
I'm not sure that anyone has ever clearly defined what escaping
syntax is used for /proc/cmdline (which is what <cmdline> is
representing.
Hmm, good point. If it is /bin/sh doing the parsing, then we know the
rules (and virsh matches them); but it if is a custom parser in the
kernel, the we have to match that custom parser.
> A point in your favor, for at least testing what you parse! If
we
> change our mind to mimic shell or C parsing, then we'd have to update
> these tests.
Yes, escaping rules blow my mind unless I can test them :-)
You're not the only one - I added loads of tests when I added shell
parsing to virsh.
> Overall, I like the idea of the new function, but I'm worried
that
> introducing yet another parser could hurt us (users will be asking "now
> which escape style is in effect here, and how does it differ from
> standardized escape styles that I'm used to?").
I think that perhaps we should have virStrSplitQuoted just return
the split pieces, with *no* unescaping. And then have separate
functions to escape/unescape individual string pieces after the
fact.
Except that you then have to know what quoting styles were in use to
know whether \ was a literal or an escape.
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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