[Libguestfs] [PATCH nbdkit v2 3/4] common/utils: Add C string quoting function

[Richard W.M. Jones]

On Tue, May 09, 2023 at 02:28:40PM +0200, Laszlo Ersek wrote:
> On 5/9/23 11:51, 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(+)
> > 
> > diff --git a/common/utils/utils.h b/common/utils/utils.h
> > index 42288a5cd..1e6d8972b 100644
> > --- a/common/utils/utils.h
> > +++ b/common/utils/utils.h
> > @@ -35,6 +35,7 @@
> >  
> >  extern void shell_quote (const char *str, FILE *fp);
> >  extern void uri_quote (const char *str, FILE *fp);
> > +extern void c_string_quote (const char *str, FILE *fp);
> >  extern int exit_status_to_nbd_error (int status, const char *cmd);
> >  extern int set_cloexec (int fd);
> >  extern int set_nonblock (int fd);
> > diff --git a/common/utils/quote.c b/common/utils/quote.c
> > index 863e08a8e..877035387 100644
> > --- a/common/utils/quote.c
> > +++ b/common/utils/quote.c
> > @@ -37,6 +37,9 @@
> >  #include <string.h>
> >  #include <unistd.h>
> >  
> > +#include "ascii-ctype.h"
> > +#include "hexdigit.h"
> > +
> >  /* Print str to fp, shell quoting if necessary.  This comes from
> >   * libguestfs, but was written by me so I'm relicensing it to a BSD
> >   * license for nbdkit.
> > @@ -98,3 +101,58 @@ uri_quote (const char *str, FILE *fp)
> >        fprintf (fp, "%%%02X", str[i] & 0xff);
> >    }
> >  }
> > +
> > +/* 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) {
> 
> For the controlling expression, do we like
> 
>   (c = str[i]) != '\0'
> 
> more?

I think they're both a bit awkward :-/

> Another question regarding brace style:
> 
> 
> > +    if (ascii_isprint (c))
> > +      fputc (c, fp);
> > +    else {
> > +      switch (c) {
> > +      case '\a':
> > +        fputc ('\\', fp);
> > +        fputc ('a', fp);
> > +        break;
> > +      case '\b':
> > +        fputc ('\\', fp);
> > +        fputc ('b', fp);
> > +        break;
> > +      case '\f':
> > +        fputc ('\\', fp);
> > +        fputc ('f', fp);
> > +        break;
> > +      case '\n':
> > +        fputc ('\\', fp);
> > +        fputc ('n', fp);
> > +        break;
> > +      case '\r':
> > +        fputc ('\\', fp);
> > +        fputc ('r', fp);
> > +        break;
> > +      case '\t':
> > +        fputc ('\\', fp);
> > +        fputc ('t', fp);
> > +        break;
> > +      case '\v':
> > +        fputc ('\\', fp);
> > +        fputc ('v', fp);
> > +        break;
> > +      default:
> > +        fputc ('\\', fp);
> > +        fputc ('x', fp);
> > +        fputc (hexchar (c >> 4), fp);
> > +        fputc (hexchar (c), fp);
> > +      }
> > +    }
> > +  }
> 
> In theory, we don't have to use any brace characters here except within
> the "switch" statement -- the "for" and "else" parts don't need braces.
> libnbd / nbdkit usually (?) forbids using braces unless we *must*
> braces. But this looks like an exception. What's the rule?
> 
> (Sorry if I asked the same question before -- I don't remember exactly,
> but I might have. It just doesn't congeal into a consistent rule for me.)

I don't think there's really a hard rule, whatever makes the
code clearer I guess ...

> Looks OK otherwise of course.
> 
> Thanks!
> Laszlo

Thanks,

Rich.

-- 
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