Re: Resolution differences for getaddrinfo versus host/dig/delv

[Mark Andrews]

Mark Andrews writes:
>       
> And whomever added underscorechar() to that should be shot.  There
> are good reasons to be able to distingish hostnames from other sorts
> of text.  Adding '_' doesn't help one do that as it is impossible to
> distinguish underscored text from underscored hostnames. 
> 
>       This_is_a_title

Lets try the example again.

        _T_h_i_s__i_s__a__t_i_t_l_e
 
> Mark
>       
> In message <20151118212633.ga18...@sources.org>, Stephane Bortzmeyer writes:
> > On Wed, Nov 18, 2015 at 12:19:57PM +0000,
> >  Phil Mayers <p.may...@imperial.ac.uk> wrote
> >  a message of 44 lines which said:
> >
> > > I suspect getaddrinfo isn't parsing the DNS response for some reason.
> > ...
> > > Obviously the *.thing on the RHS of the first CNAME is weird, but is it
> > > illegal?
> >
> > Yes, for a *host* name (no for a *domain* name). See Tony Finch's
> > explanation.
> >
> > In the GNU libc, the relevant code is in resolv/res_comp.c and
> > includes this function, which tests that a *host* name is
> > a-z0-9\.\-+:
> >
> > #define alphachar(c) (((c) >= 0x41 && (c) <= 0x5a) \
> >                || ((c) >= 0x61 && (c) <= 0x7a))
> > #define digitchar(c) ((c) >= 0x30 && (c) <= 0x39)
> >
> > #define borderchar(c) (alphachar(c) || digitchar(c))
> > #define middlechar(c) (borderchar(c) || hyphenchar(c) ||
> > underscorechar(c))
> > #define     domainchar(c) ((c) > 0x20 && (c) < 0x7f)
> >
> > int
> > res_hnok(const char *dn) {
> >     int pch = PERIOD, ch = *dn++;
> >
> >     while (ch != '\0') {
> >             int nch = *dn++;
> >
> >             if (periodchar(ch)) {
> >                     (void)NULL;
> >             } else if (periodchar(pch)) {
> >                     if (!borderchar(ch))
> >                             return (0);
> >             } else if (periodchar(nch) || nch == '\0') {
> >                     if (!borderchar(ch))
> >                             return (0);
> >             } else {
> >                     if (!middlechar(ch))
> >                             return (0);
> >             }
> >             pch = ch, ch = nch;
> >     }
> >     return (1);
> > }   
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> 
> -- 
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                 INTERNET: ma...@isc.org
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: ma...@isc.org
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