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

[Mark Andrews]

        
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

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
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