[Libguestfs] [PATCH nbdkit v3 3/6] common/utils: Add C string quoting function

[Richard W.M. Jones]

On Tue, May 09, 2023 at 01:18:13PM -0500, Eric Blake wrote:
> On Tue, May 09, 2023 at 03:51:18PM +0100, Richard W.M. Jones wrote:
> > eg. { '\r', '\n' } -> { '\\', 'n', '\\', 'r' }
> > ---
> >  common/utils/utils.h |  1 +
> >  common/utils/quote.c | 58 ++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 59 insertions(+)
> > 
> 
> > +
> > +/* Print str to fp, quoting in a way similar to C strings, for example
> > + * '\n' -> "\n".
> > + *
> > + * Note that we do not emit quotes around the string, and double
> > + * quotes within the string are not escaped.
> > + */
> > +void
> > +c_string_quote (const char *str, FILE *fp)
> > +{
> > +  size_t i;
> > +  char c;
> > +
> > +  for (i = 0; c = str[i], c != '\0'; ++i) {
> > +    if (ascii_isprint (c))
> > +      fputc (c, fp);
> 
> ascii_isprint('\\') returns true, which means you output just one
> backslash; but that's one where you really want to output two.
> Otherwise, you can't tell the difference on the output from the
> C-string input of one-byte "\a" vs. two-byte "\\a".  :(
> 
> > +    else {
> > +      switch (c) {
> ...
> > +      default:
> > +        fputc ('\\', fp);
> > +        fputc ('x', fp);
> > +        fputc (hexchar (c >> 4), fp);
> > +        fputc (hexchar (c), fp);
> > +      }
> 
> You mentioned in the commit message that not escaping " is
> intentional; and I can live with that for this patch.  But if we need
> to add it in the future, it will be easier to rejigger the loop as
> (abbreviated, but you get the idea):
> 
> for (i = 0; c = str[i], c != '\0'; ++i) {
>   switch (c) {
>   case '\\': fputc ('\\'); fputc ('\\'); break;
>   case '\a': fputc ('\\'); fputc ('a'); break;
>   ...
>   default:
>     if (isprint (c)
>       fputc (c);
>     else {
>       // output \xXX
>     }
>   }
> }

Yes this is a good idea anyway, I will make a change like this.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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