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Re: [Libvir] [PATCH] Enhance virBuffer code



On Fri, Dec 14, 2007 at 11:53:35PM +0100, Jim Meyering wrote:
> "Daniel P. Berrange" <berrange redhat com> wrote:
> > On Fri, Dec 14, 2007 at 08:34:13AM +0100, Jim Meyering wrote:
> >> Daniel Veillard <veillard redhat com> wrote:
> >> > On Thu, Dec 13, 2007 at 11:21:31PM +0100, Jim Meyering wrote:
> >> >> "Richard W.M. Jones" <rjones redhat com> wrote:
> >> >> ...
> >> >> > + * virBufferURIEncodeString:
> >> >> > + * @buf:  the buffer to append to
> >> >> > + * @str:  the string argument which will be URI-encoded
> >> >> > + *
> >> >> > + * Append the string to the buffer.  The string will be URI-encoded
> >> >> > + * during the append (ie any non alpha-numeric characters are replaced
> >> >> > + * with '%xx' hex sequences).
> >> >> > + *
> >> >> > + * Returns 0 successful, -1 in case of internal or API error.
> >> >> > + */
> >> >> > +int
> >> >> > +virBufferURIEncodeString (virBufferPtr buf, const char *str)
> >> >> > +{
> >> >> > +    int grow_size = 0;
> >> >> > +    const char *p;
> >> >> > +    unsigned char uc;
> >> >> > +    const char *hex = "0123456789abcdef";
> >> >> > +
> >> >> > +    for (p = str; *p; ++p) {
> >> >> > +        /* Want to leave only strict 7 bit ASCII alphanumerics ... */
> >> >> > +        if ((*p >= '0' && *p <= '9') ||
> >> >> > +            (*p >= 'a' && *p <= 'z') ||
> >> >> > +            (*p >= 'A' && *p <= 'Z'))
> >> >> ...
> >> >> > +    for (p = str; *p; ++p) {
> >> >> > +        if ((*p >= '0' && *p <= '9') ||
> >> >> > +            (*p >= 'a' && *p <= 'z') ||
> >> >> > +            (*p >= 'A' && *p <= 'Z'))
> >> >>
> >> >> Hi Rich,
> >> >>
> >> >> What do you think of using this?
> >> >>
> >> >>   isascii (*p) && isalnum (*p)
> >> >
> >> >   I have learned to be very cautious of the is* macros because they
> >> > tend to be local dependant whichis usually really not what you would
> >> > like or expect. In that case this may work, but explicit ranges
> >> > are 100% clear about what you intend to accept or not, that's why I
> >> > usually prefer them.
> >>
> >> You're right that we shouldn't use isalnum here.
> >> However, we shouldn't use inequality comparisons, either.
> >> While 0 <= c <= 9 is guaranteed to be ok for the digits, the
> >> a..z and A..Z ranges need not be contiguous, i.e., with EBCDIC:
> >
> > Seriously who gives a damn about EBCDIC anymore.
> 
> Daniel and Daniel,
> 
> Personally, I don't care at all, but I suspect that people using z/OS
> and OS/390 care, among others.  Some might even be Red Hat customers.
> What's wrong with making the code portable, just in case?

Portability while certainly worthwhile isn't absolute - we only have finite
development time. While we could spend that time worrying about EBCDIC and
other platforms we're not likely to encounter any time soon, there is a
tradeoff to be made at some point where we have to get back to actually
developing features that matter to the 99.99999% of our userbase who isn't
EBCDIC.  I'm not saying we should go out of our way to break other platforms,
but there's a cost/benefit tradeoff to be had.

> > This just makes it totally unreadable.
> 
> This just makes *what* totally unreadable?

The giant switch statements is what I was referring to.

> I proposed to do this:
> 
>     for (p = str; *p; ++p) {
>         is_alphanum (*p)
>     ...
> 
>     for (p = str; *p; ++p) {
>         is_alphanum (*p)

I've no objection to this - just the giant switch statement.

Dan.
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