Re: [PATCH v4 02/11] lib/charset: add u16_strlcat() function

[Masahisa Kojima <masahisa.kojima@linaro.org>]

Hi Heinrich,

On Mon, 18 Apr 2022 at 16:47, Masahisa Kojima
<masahisa.kojima@linaro.org> wrote:
>
> On Sat, 16 Apr 2022 at 16:32, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> >
> > On 3/24/22 14:54, Masahisa Kojima wrote:
> > > Provide u16 string version of strlcat().
> > >
> > > Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
> > > Reviewed-by: Simon Glass <sjg@chromium.org>
> > > ---
> > > Changes in v4:
> > > - add blank line above the return statement
> > >
> > > Changes in v2:
> > > - implement u16_strlcat(with the destination buffer size in argument)
> > >    instead of u16_strcat
> > >
> > >   include/charset.h | 15 +++++++++++++++
> > >   lib/charset.c     | 21 +++++++++++++++++++++
> > >   2 files changed, 36 insertions(+)
> > >
> > > diff --git a/include/charset.h b/include/charset.h
> > > index b93d023092..dc5fc275ec 100644
> > > --- a/include/charset.h
> > > +++ b/include/charset.h
> > > @@ -259,6 +259,21 @@ u16 *u16_strcpy(u16 *dest, const u16 *src);
> > >    */
> > >   u16 *u16_strdup(const void *src);
> > >
> > > +/**
> > > + * u16_strlcat() - Append a length-limited, %NUL-terminated string to another
> > > + *
> > > + * Append the src string to the dest string, overwriting the terminating
> > > + * null word at the end of dest, and then adds a terminating null word.
> > > + * It will append at most size - u16_strlen(dst) - 1 bytes, NUL-terminating the result.
> >
> > Why "- 1"?
>
> It is my mistake, it should be 2.
>
> >
> > If size is even, we append up to size - u16_strlen(dst) - 2 bytes. The
> > two extra bytes used for 0x0000.
> > If size is odd, we append up to size - u16_strlen(dst) - 3 bytes leaving
> > one byte of the buffer unused.

To make behavior simple, I update the meaning of the 3rd parameter
from buffer size to u16 string count.
It is the same behavior as other u16_strxxx functions in U-boot.

Thanks,
Masahisa Kojima
>
> Thanks, It clearly explains the behavior.
>
> >
> > > + *
> > > + * @dest:            destination buffer (null terminated)
> > > + * @src:             source buffer (null terminated)
> > > + * @size:            destination buffer size in bytes
> >
> > s/$/ including the trailing 0x0000/
>
> OK, I will update "(null terminated)" to the suggested one.
>
> >
> > > + * Return:           total size of the created string in bytes.
> > > + *                   If return value >= size, truncation occurred.
> > > + */
> > > +size_t u16_strlcat(u16 *dest, const u16 *src, size_t size);
> > > +
> > >   /**
> > >    * utf16_to_utf8() - Convert an utf16 string to utf8
> > >    *
> > > diff --git a/lib/charset.c b/lib/charset.c
> > > index f44c58d9d8..47997eca7d 100644
> > > --- a/lib/charset.c
> > > +++ b/lib/charset.c
> > > @@ -428,6 +428,27 @@ u16 *u16_strdup(const void *src)
> > >       return new;
> > >   }
> > >
> > > +size_t u16_strlcat(u16 *dest, const u16 *src, size_t size)
> > > +{
> >
> > If you start the function with
> >
> >      size >>= 1;
> >
> > or
> >
> >      size /= sizeof(u16);
> >
> > this might simplify the code.
>
> In u16_strlcat(), there are two size definitions, u16 string size and
> buffer size.
> I will rename some of the variables to clearly identify the meaning.
>
> >
> > > +     size_t dstrlen = u16_strnlen(dest, size >> 1);
> > > +     size_t dlen = dstrlen * sizeof(u16);
> > > +     size_t len = u16_strlen(src) * sizeof(u16);
> > > +     size_t ret = dlen + len;
> >
> > This misses the  trailing 0x0000.
>
> Strlcat() is not the C standard function, but the linux implementation
> of strlcat() does not include trailing 0x00[1],
> also the same for openbsd.
> [1] https://github.com/torvalds/linux/blob/master/lib/string.c#L319.
>
> The current U-Boot strlcat() contains trailing 0x00, I think it needs
> to be updated.
>
> Thanks,
> Masahisa Kojima
>
> >
> > Best regards
> >
> > Heinrich
> >
> > > +
> > > +     if (dlen >= size)
> > > +             return ret;
> > > +
> > > +     dest += dstrlen;
> > > +     size -= dlen;
> > > +     if (len >= size)
> > > +             len = size - sizeof(u16);
> > > +
> > > +     memcpy(dest, src, len);
> > > +     dest[len >> 1] = u'\0';
> > > +
> > > +     return ret;
> > > +}
> > > +
> > >   /* Convert UTF-16 to UTF-8.  */
> > >   uint8_t *utf16_to_utf8(uint8_t *dest, const uint16_t *src, size_t size)
> > >   {
> >