Re: [idn] length restrictions on IDN label

[Soobok Lee <lsb@postel.co.kr>]

Mark.Andrews@isc.org wrote:

>> Most applications programmer have been reserving 256 bytes for any LDH
>>
>>FQDN buffer space .
>>    
>>
>
>	Most applications will use NS_MAXDNAME or MAXDNAME to store
>	a domain name today as that is enough to cover all the
>	potential expansions from wire to RFC 1034 presentation
>	format.  Have a look at NS_MAXDNAME in <arpa/nameser.h>.
>	Unless you have a really old OS it will be at least (250*4
>	+ 5) (minimum number of label that can appear in a full
>	length domain name is 4 labels + root, all 4 periods +
>	null).
>
If you have a linux (Redhat) box, "chdir /usr/include; grep MAXHOST */*".
Then you will get the enclosed header lists.
Many applications headers use 64/65/257 except for resolver/network
libraries headers which
use 1024/1025 for FQDN. If you have openssh 3.4p1 sources, you can find
that it uses MAXHOSTNAMELEN (64) in
some place in addition to 1025 in other places. of course, 64 is for a
hostname label length.
See rpc/* headers.


asm/param.h:#define MAXHOSTNAMELEN 64 /* max length of hostname */
imap/mail.h:#define NETMAXHOST 65
imap/mail.h: char host[NETMAXHOST]; /* host name (may be canonicalized) */
imap/mail.h: char orighost[NETMAXHOST]; /* host name before
canonicalization */
lwres/netdb.h:#undef NI_MAXHOST
lwres/netdb.h:#define NI_MAXHOST 1025
mozilla/plresolv.h:#define PL_RESOLVE_MAXHOSTENTBUF 1024
protocols/timed.h: char tsp_name[MAXHOSTNAMELEN];
rpcsvc/rusers.h:#define RUSERS_MAXHOSTLEN 257
rpcsvc/rusers.x:const RUSERS_MAXHOSTLEN = 257;
rpcsvc/rusers.x: string ut_host<RUSERS_MAXHOSTLEN>; /* host user logged
on from */
rpc/types.h:#ifndef MAXHOSTNAMELEN
rpc/types.h:#define MAXHOSTNAMELEN 64
w3c-libwww/wwwsys.h:#ifndef MAXHOSTNAMELEN
w3c-libwww/wwwsys.h:#define MAXHOSTNAMELEN 64 /* Any better ideas? */
X11/Xos_r.h: char h_name[MAXHOSTNAMELEN];


>
>	As I said what you are talking about is NOT new.  These
>	issues have existed for years.
>
yes, for presentation formats, it is not new. But for protocol elements,
it is new. isn't it ?

Soobok Lee