One document matched: draft-josefsson-getaddrinfo-idn-00.txt
Network Working Group S. Josefsson
Internet-Draft SJD AB
Expires: December 17, 2010 June 15, 2010
Internationalized Domain Names support in POSIX getaddrinfo
draft-josefsson-getaddrinfo-idn-00
Abstract
This document describes an extension for Internationalized Domain
Names support in the POSIX getaddrinfo function.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 17, 2010.
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Table of Contents
1. Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Alternative Approaches . . . . . . . . . . . . . . . . . . . . 3
4. What I propose . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8. Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
9. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
12. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Preface
This document was originally written in 2003 and published and
implemented as part of GNU Libidn. This is a copy of the memo but in
IETF form. The document was written informally, and does not (yet?)
follow typical IETF document formats. The intention is to make the
IETF community aware of this work, to see if there are interest in
the ideas.
2. Background
Libidn is a package for internationalized string handling based on
the Stringprep, Punycode and Internationalized Domain Names in
Applications (IDNA) specifications. It can be used by applications
directly by linking to it, as is done by, e.g., Gnus, KDE, and Mutt.
Having each and every application link with and perform its own IDN
handling is not a good idea. It bloats the code and makes things
unnecessarily complex. Only few applications, such as web browsers
and mail clients, will need to do this in the future, to provide good
user interfaces for internationalization.
See http://josefsson.org/libidn/ for more information.
3. Alternative Approaches
There are implementation that modify gethostbyname() to accept UTF-8
strings and perform the IDNA ToASCII operation within
gethostbyname().
There are even implementations that assume gethostbyname (on the
client host) perform no validation of the string and will send UTF-8
strings out to the DNS server, and perform the IDN-conversion on the
DNS server.
Some doubts can be raised whether this is an approach that is likely
to be standardized. It also lack in functionality: it only provide
black-box ToASCII functionality. The application cannot extract the
output from the ToASCII operation. More important, there is no way
to perform a ToUnicode operation that applications may want to use
for display purposes. Furthermore, while the first can support
locale specific character sets (e.g., ISO-8859-1), the second
approach is bound to either guess the character set, or always use
UTF-8.
See also the thread rooted in <iluel7n6bmu.fsf@latte.josefsson.org>
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posted to libc-alpha@sources.redhat.com on 08 Jan 2003.
4. What I propose
The getaddrinfo() API should have two new flags, AI_IDN and
AI_CANONIDN. Roughly they correspond to IDNA ToASCII and IDNA
ToUnicode, but there are several details. Note that strings are
still 'char*', i.e. it does not use the "wide" character type, and
that the encoding of non-ASCII strings are the current locale's
character set (i.e., nl_langinfo(CODESET)).
An application that uses AI_IDN signal to the getaddrinfo()
implementation that the input host name may be non-ASCII and that the
appropriate IDNA ToASCII steps should be carried out on the input,
and the output from the ToASCII operation (if any) should be used in
the lookup using the current resolver processing.
An application that uses AI_CANONIDN signal to the getaddrinfo()
implementation that the input host name should be put through the
IDNA ToUnicode steps, and the output of that placed in the
'ai_canonname' field of the resulting structure. Normal resolver
processing applies to the input string, of course.
Consequently, an application that uses AI_IDN|AI_CANONIDN signal to
the getaddrinfo() implementation that the input host name may be non-
ASCII and should be put through the IDNA ToASCII steps before run
through the resolver, and that the input string should also be run
through the IDNA ToUnicode steps and the output of that placed in the
'ai_canonname' field.
The semantics of AI_CANONNAME|AI_CANONIDN is that instead of running
the ToUnicode IDNA steps on the input string, the canonical host name
as returned by the resolver for the input string should be used in
the ToUnicode IDNA step.
5. Details
Four new flags has been proposed; AI_IDN_ALLOW_UNASSIGNED,
AI_IDN_USE_STD3_ASCII_RULES for getaddrinfo, and
NI_IDN_ALLOW_UNASSIGNED, NI_IDN_USE_STD3_ASCII_RULES for getnameinfo.
The implementation is simple, if specified those flag will set the
appropriate flag in the call to the IDNA functions. See the RFC for
the meaning of those flags.
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6. Status
The AI_IDN flag has been implemented and shipped as a proof-of-
concept patch for GNU Libc with GNU Libidn since January 2003.
Binary libc packages with the patch exists for (at least) two GNU/
Linux distributions. The AI_CANONIDN flag is not yet implemented.
As of March 2004, Libidn has been integrated as an add-on in the GNU
Libc CVS repository. The AI_CANONIDN flag has been implemented. The
AllowUnassigned and UseSTD3ASCIIRules flags were added.
7. Future
Allow non-ASCII in gethostname (and similar functions), if
administrator has supplied, e.g., 'option idn' in /etc/resolv.conf?
8. Feedback
This document is a work-in-progress and the details may change.
Contact me at simon@josefsson.org to discuss changes.
9. Security Considerations
TBA.
10. IANA Considerations
TBA.
11. Acknowledgements
Ulrich Drepper integrated the work in GNU Libc.
12. Normative References
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Author's Address
Simon Josefsson
SJD AB
Email: simon@josefsson.org
Josefsson Expires December 17, 2010 [Page 6]
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