Network Working Group J. Klensin
Internet-Draft November 30, 2010
Updates: 959 (if approved)
Intended status: Standards Track
Expires: June 3, 2011
FTP Extension for Internationalized Text
draft-ietf-ftpext2-typeu-00.txt
Abstract
The original FTP protocol supported TYPE values for ASCII and EBCDIC
text, plus binary ("IMAGE") transmission. As the Internet becomes
more international, there is a growing requirement to be able to
transmit textual data, encoded in Unicode, in a way that is
independent of the coding and line representation forms of particular
operating systems. This memo specifies a new FTP TYPE value for
Unicode data.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Context and Overview . . . . . . . . . . . . . . . . . . . 3
1.2. Summary of History of Internationalization of FTP . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4. Discussion List . . . . . . . . . . . . . . . . . . . . . . 3
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Existing TYPEs . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Unicode TYPE . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Data Structure . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Feature Negotiation . . . . . . . . . . . . . . . . . . . . 5
3. Net-Unicode Format for FTP . . . . . . . . . . . . . . . . . . 5
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. New Version and File Name:
draft-ietf-ftpext2-unicode-00 . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
1.1. Context and Overview
The original FTP protocol [RFC0959] supported TYPE values for ASCII
and EBCDIC text, plus binary ("IMAGE") transmission. The Host
Requirements specification [RFC1123] made other changes to FTP, but
did not alter the TYPE environment.
As the Internet becomes more international, there is a growing
requirement to be able to transmit textual data, encoded in Unicode
[Unicode52], in a way that is independent of the coding and line
representation forms of particular operating systems. This memo
specifies a new FTP TYPE value for Unicode data.
1.2. Summary of History of Internationalization of FTP
RFC 2640 [RFC2640] is described as providing internationalization of
FTP, but only addresses the use of FTP in internationalized (non-
ASCII or extended ASCII [ASCII]) file systems. Its facilities were
slightly enhanced in a more general extensions specification
[RFC3659], which builds on a more general FTP extension mechanism
[RFC2389]. The specification in this document addresses the transfer
of non-ASCII text files only, building on the TYPE command of the
original FTP specification [RFC0959].
1.3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document assumes that the reader is familiar with the
terminology of RFC 959. Those terms, especially reply, server-FTP
process, user-FTP process, server-PI, user-PI, logical byte size, and
user, if used here, are used in the same way. It also uses the ABNF
of [RFC2389] and [RFC5234] in preference to the BNF of RFC 959. For
the convenience of contemporary readers, the terms "client" and
"server" are used interchangeably with the historic terms "user-FTP
process" and "server-FTP process". The document also assumes the
termology and changes in the updates to FTP specified in RFC 1123 and
RFC 2389.
1.4. Discussion List
[[anchor5: RFC Editor: please remove this section before
publication.]]
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This proposal is being discussed in the IETF FTPEXT2 Working Group.
Its mailing list is at ftpext@ietf.org.
2. Specification
2.1. Existing TYPEs
The FTP TYPE command, described in [RFC0959] accepts four possible
first argument values, as described below. Note that these
descriptions are provided for the reader's convenience; the
definitions in RFC 959 remain normative.
A The data are expected to be in, and are transformed by the server
if needed to, an ASCII [ASCII] data stream conforming to the "NVT"
specification (See RFC 959 [RFC0959] and Appendix B of RFC 5198
[RFC5198] for more information).
E The data are expected to be in, and are transformed by the server
if needed to, an EBCDIC data stream as specified in RFC 959.
I The data are transferred in "image" form, i.e., exactly as they
appear in the server. Because it is the only TYPE form in which
true binary data can be transferred, TYPE I is often referred to
as "binary" or "binary transfer".
L The data are transmitted in logical bytes of a size specified in
an additional argument. See RFC 959.
Any of these four argument variations to TYPE except "TYPE A" (with
non-print format) MAY be rejected by the server-FTP process with a
504 response code if it does not support that type and the necessary
conversions.
2.2. Unicode TYPE
The client-PI MAY transmit TYPE U to the server-PI as an alternative
to other TYPE commands and arguments. If it does, the server MAY
return reply-code 504, indicating that the TYPE U feature is not
supported (unchanged from RFC 959) or MUST respond to any data
retrieval request (e.g., GET) by sending the data in a stream
conformant to the Net-Unicode format specified in Section 3.
Similarly, if the client-PI sends TYPE U and the server accepts it,
the client MUST send any data streams in that format while the option
is in effect. No second parameter is used or permitted for TYPE U.
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2.3. Data Structure
The default and only permitted data structure for TYPE U is "file
structure". Use of the STRU command SHOULD be avoided. If is used,
its argument MUST be "F".
2.4. Feature Negotiation
RFC 2389 [RFC2389] specifies a feature negotiation mechanism for new
extensions to FTP. Since the TYPE command is a required part of the
base FTP specification, the client-PI is not required to issue the
FEAT command prior to issuing TYPE U. However, it MAY do so and
Server-FTP implementations that include TYPE U SHOULD support FEAT as
described below. If the FEAT command is transmitted from the
client-PI to the server-PI, and this extension and FEAT are
supported, the response MUST include a TYPE line that lists all TYPE
values supported by the server (including the required ones). For
example, if an FTP-server supports all of TYPEs A, E, I, and U, the
FEAT response line would contain each of the possible arguments
separated by semicolons, e.g.,
TYPE A;E;I;U
This specification does not change either RFC 959 or RFC 2389. In
particular, no FEAT response line is required for TYPE unless this,
or some other, extension to TYPE is supported by the FTP-server.
3. Net-Unicode Format for FTP
This section specifies a profile of Net-Unicode [RFC5198] for use
with FTP TYPE U.
Unicode characters must be transmitted in UTF-8 as specified for Net-
Unicode. Because FTP is used in data transmission, the characters
and sequences that are discouraged in Section 2 of RFC 5198 are
permitted to be transported by FTP. However, line-ending sequences
MUST conform to the CRLF convention specified there. Consistent with
Paragraph 4 of that Section, strings SHOULD be normalized before
transmission if at all possible.
The implicit logical byte size for this transmission type is eight
bits.
4. Acknowledgments
This document draws heavily on RFC 959; appreciation is expressed to
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its authors and to the authors of RFC 2398. The work of Mark P.
Peterson and Douglas J. Papenthien on other FTP extensions finally
motivated production of this document in 2008 after a long delay;
that contribution is appreciated as well.
5. IANA Considerations
When this specification is approved, an entry for "TYPE U" that
refers to it should be incorporated into the FTP Extensions Registry
established by RFC 5797 [RFC5797].
6. Security Considerations
This specification makes no substantive change to the FTP command
stream but only alters the presentation of data in the data stream.
Consequently, it should have no negative security implications that
are not already present in the earlier FTP specifications described
in Section 1 and in the Net-Unicode specification [RFC5198]. By
specifying an exact canonical form for the identification and
transfer of Unicode strings, it may eliminate some problems that
might be encountered when such strings are transmitted without
identification or without restrictions.
7. Change Log
RFC Editor: Please remove this section
7.1. New Version and File Name: draft-ietf-ftpext2-unicode-00
This version of the document is a slight update to
draft-klensin-ftp-typeu-00, posted in July 2008). It includes some
updated references to work completed in the interim, information
about the FTPEXT2 WG, a new Security Considerations section (omitted
from the prior draft), and a few other minor corrections.
8. References
8.1. Normative References
[ASCII] American National Standards Institute (formerly United
States of America Standards Institute), "USA Code for
Information Interchange", ANSI X3.4-1968, 1968.
ANSI X3.4-1968 has been replaced by newer versions with
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slight modifications, but the 1968 version remains
definitive for the Internet.
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2389] Hethmon, P. and R. Elz, "Feature negotiation mechanism for
the File Transfer Protocol", RFC 2389, August 1998.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, March 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[Unicode52]
The Unicode Consortium. The Unicode Standard, Version
5.2.0, defined by:, "The Unicode Standard, Version 5.2.0",
(Mountain View, CA: The Unicode Consortium, 2009. ISBN
978-1-936213-00-9).,
<http://www.unicode.org/versions/Unicode5.2.0/>.
8.2. Informative References
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC2640] Curtin, B., "Internationalization of the File Transfer
Protocol", RFC 2640, July 1999.
[RFC3659] Hethmon, P., "Extensions to FTP", RFC 3659, March 2007.
[RFC5797] Klensin, J. and A. Hoenes, "FTP Command and Extension
Registry", RFC 5797, March 2010.
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Author's Address
John C Klensin
1770 Massachusetts Ave, Ste 322
Cambridge, MA 02140
USA
Phone: +1 617 245 1457
Email: john+ietf@jck.com
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