Re: [9fans] csipinfo

[rog]

i don't know if it's any help, but here's some code that
i have used in the past to do a reverse dns lookup. it was under inferno and
the code's in limbo, but i think that /net/dns probably works
the same in both inferno and plan 9, so it should be cross-applicable.

it expects a host address of the form "123.45.67.89!9999" (as found in the
remote file) and returns the dns name.

hostname(addr: string): string
{
        (nil, toks) := sys->tokenize(addr, "!");
        if(len toks != 2)
                return addr;
        addr = hd toks;
        if(NoDNS)
                return addr;
        a := addr2arpa(addr);
        if(a == nil)
                return addr;
        fd := sys->open("/net/dns", Sys->ORDWR);
        if(fd == nil)
                return addr;
        if(sys->fprint(fd, "%s ptr", a) < 0){
                err := sys->sprint("%r");
                log(sys->sprint("dnslookup failed %q %q", addr, err));
                return addr;
        }
        buf := array[1024] of byte;
        sys->seek(fd, big 0, 0);
        n := sys->read(fd, buf, len buf);
        if(n <= 0)
                return addr;
        a = string buf[0:n];
        for(i := 0; i < len a; i++)
                if(a[i] == '\t')
                        break;
        if(i == len a)
                return addr;
        i++;
        # return address of the form:
        # 68.1.1.200.in-addr.arpa ptr   presto.vitanuova.com(0)
        for(j := len a - 1; j > i; j--)
                if(a[j] == '(')
                        return a[i:j];
        return a[i:];
}

addr2arpa(a: string): string
{
        addr := "in-addr.arpa";
        for(toks := sys->tokenize(a, ".").t1; toks != nil; toks = tl toks)
                addr = hd toks + "." + addr;
        return addr;
}