[Slirp] [PATCH 1/6] util: add slirp_fmt() helpers

[Daniel P. Berrangé]

On Mon, Jan 27, 2020 at 10:43:36AM +0100, Philippe Mathieu-Daudé wrote:
> On 1/27/20 10:24 AM, marcandre.lureau at redhat.com wrote:
> > From: Marc-André Lureau <marcandre.lureau at redhat.com>
> > 
> > Various calls to snprintf() in libslirp assume that snprintf() returns
> > "only" the number of bytes written (excluding terminating NUL).
> > 
> > https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html#tag_16_159_04
> > 
> > "Upon successful completion, the snprintf() function shall return the
> > number of bytes that would be written to s had n been sufficiently
> > large excluding the terminating null byte."
> > 
> > Introduce slirp_fmt() that handles several pathological cases the
> > way libslirp usually expect:
> > 
> > - treat error as fatal (instead of silently returning -1)
> > 
> > - fmt0() will always \0 end
> > 
> > - return the number of bytes actually written (instead of what would
> > have been written, which would usually result in OOB later), including
> > the ending \0 for fmt0()

> > diff --git a/src/util.c b/src/util.c
> > index e596087..e3b6257 100644
> > --- a/src/util.c
> > +++ b/src/util.c
> > @@ -364,3 +364,65 @@ void slirp_pstrcpy(char *buf, int buf_size, const char *str)
> >       }
> >       *q = '\0';
> >   }
> > +
> > +static int slirp_vsnprintf(char *str, size_t size,
> > +                           const char *format, va_list args)
> > +{
> > +    int rv = vsnprintf(str, size, format, args);

Should use g_vsnprintf()

The GLib impl guarantees GNU compatible format strings, which fixes
the horror of Windows platform format strings.

> > diff --git a/src/util.h b/src/util.h
> > index e9c3073..5530c46 100644
> > --- a/src/util.h
> > +++ b/src/util.h
> > @@ -181,4 +181,7 @@ static inline int slirp_socket_set_fast_reuse(int fd)
> >   void slirp_pstrcpy(char *buf, int buf_size, const char *str);
> > +int slirp_fmt(char *str, size_t size, const char *format, ...);
> > +int slirp_fmt0(char *str, size_t size, const char *format, ...);

Ought to annotate with the  "gnu_printf" attribute so that the compilers
can check for various format string mistakes.

Regards,
Daniel
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