Internet DRAFT - draft-ietf-ftpext2-typeu
draft-ietf-ftpext2-typeu
FTPEXT2 J. Klensin
Internet-Draft March 12, 2012
Updates: 959 (if approved)
Intended status: Standards Track
Expires: September 13, 2012
FTP TYPE Extension for Internationalized Text
draft-ietf-ftpext2-typeu-03
Abstract
The traditional FTP protocol includes a TYPE command to specify the
data representation. That command has 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 representation TYPE
value for Unicode data.
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 September 13, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Context and Overview . . . . . . . . . . . . . . . . . . . 4
1.2. Summary of History of Internationalization of FTP . . . . 4
1.3. History of the TYPE Command . . . . . . . . . . . . . . . 4
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.5. Discussion List . . . . . . . . . . . . . . . . . . . . . 6
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Existing TYPEs . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Unicode TYPE . . . . . . . . . . . . . . . . . . . . . . . 7
2.3. Data Structure . . . . . . . . . . . . . . . . . . . . . . 7
2.4. Feature Negotiation . . . . . . . . . . . . . . . . . . . 7
3. Net-Unicode Format for FTP . . . . . . . . . . . . . . . . . . 8
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 10
A.1. New Version and File Name: draft-ietf-ftpext2-typeu-00 . . 10
A.2. Version -01 . . . . . . . . . . . . . . . . . . . . . . . 10
A.3. Version -02 . . . . . . . . . . . . . . . . . . . . . . . 10
A.4. Version -03 . . . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
1.1. Context and Overview
The traditional FTP protocol, as documented in RFC 959 [RFC0959],
includes a TYPE command to specify the data representation. That
command was originally specified as having 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 command or the environment for which it
provided.
As the Internet becomes more international, there is a growing
requirement to be able to transmit textual data, encoded in Unicode
[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.
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. History of the TYPE Command
[[Note in Draft: AppsAWG: please decide whether this subsection
should be included in the final version as informative or dropped as
surplus text that doesn't contribute to an implementer understanding
of what should be done.]]
When the FTP protocol was first defined in 1971 [RFC0114], hosts on
the ARPANET were extremely diverse. ASCII and EBCDIC were both in
active use, as were several completely different character encodings,
and ASCII was encoded in a variety of different forms inside
different systems (TENEX/TOPS-20, Multics, Unix on 16 and then 32 bit
architectures, and the original IBM ASCII all used different
encodings. In mid-1972, the late John McCarthy described some
aspects of the issues [RFC0373]. Within a relatively short period of
time, it was understood that expecting every system to adapt to the
formats of every other system -- a fairly large n-squared problem --
was crazy. At least for text, the solution was to expect all FTP-
supporting hosts to convert between their local formats and a
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network-standard ASCII encoding and, optionally, to also identify,
and permit, EBCBIC files to be transferred in canonical form. The
TYPE command was incorporated into FTP to support client
specification of those forms for on-the-wire transfer and also to
support a pair of TYPEs to support transferring data in forms that
were likely to be operating system and hardware specific (see
Section 2.1 for more details).
Because of the need to handle these different text character sets and
encoding forms without that n-squared problem, TYPE was very commonly
used unless it was known that the sending and receiving systems were
homogeneous. Several arrangements for single-line FTP commands did
not make explicit provision for TYPE specifications, but they tended
to make exactly that homogeneity assumption.
By the late 1980s, the ARPANET was converging toward a single basic
host system architecture. Almost all significant computer systems
used 32 bit architectures or felt an obligation to be able to
simulate them. EBCDIC had fallen into disuse on the network. ASCII,
encoded right-justified in eight bits with a leading zero, had become
pervasive. An Image transfer among diverse systems might well
encounter differences with line termination or, occasionally, record
structures rather than stream ones (both of which TYPE A would have
smoothed out), but the character encodings were almost certain to be
the same. So, with allowances for those line termination problems --
which have been a large issue in many cases -- Image ("binary") and
ASCII transfers were almost equivalent and the TYPE command became
less-used. Some client FTP implementations also adopted an
"automatic" mode in which they tried to determine heuristically,
based on either file names or content inspection, whether the
relevant file consisted of ASCII characters or binary information and
to send the appropriate TYPE command without user intervention.
Because there were usually only two choices in practice, they often
(but not always) got it right.
However, migration to Unicode has reintroduced many of the old
issues. When Unicode is used inside a system, it can be used with
several different encodings (e.g., UTF-8 and several variations on
UTF-16 (possibly with surrogate pairs), different assumptions about
normalization (see "Terminology for Use in Internationalization"
[i18n-terms] for more discussion) and even new variations on line
termination conventions. When those files are transferred to another
system with Image type, the result may be completely uninterpretable
on the target system. This specification extends to non-ASCII
character transfers the early concept of having a very small number
of common/ canonical network transfer formats for characters, having
systems able to convert to or from them. By doing so, it avoids a
Unicode version of the n-squared problems and the general confusion
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that led to the definition of TYPE.
1.4. 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. 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
[RFC2389].
1.5. Discussion List
[[anchor5: RFC Editor: please remove this section before
publication.]]
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 the
descriptions in this subsection 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".
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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., RETR) 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.
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.
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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 [RFC3629] 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
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. Specific useful comments
on this draft or its immediate predecessors were provided by the late
and much-lamented Mike Padlipsky and by Mykyta Yevstifeyev.
5. IANA Considerations
When this specification is approved, IANA is requested to add an
additional table to the FTP Extensions Registry established by RFC
5797 [RFC5797]. That table should be titled "TYPE command arguments"
and should include "A (m) RFC 959", "E (o) RFC 959", "I (o) RFC 959",
"L (o) RFC 959", and "U (o) RFCNNNN".
6. Security Considerations
This specification makes no substantive change to the FTP command
stream (the argument to the standard TYPE command is changed). It
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
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identification or without restrictions (e.g., using TYPE I to obtain
a "binary" transfer).
7. References
7.1. 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
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.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, March 2008.
[Unicode] The Unicode Consortium. The Unicode Standard, Version
6.0.0, defined by:, "The Unicode Standard, Version 6.0.0",
(Mountain View, CA: The Unicode Consortium, 2011. ISBN
978-1-936213-01-6).,
<http://www.unicode.org/versions/Unicode6.0.0/>.
7.2. Informative References
[RFC0114] Bhushan, A., "File Transfer Protocol", RFC 114,
April 1971.
[RFC0373] McCarthy, J., "Arbitrary Character Sets", RFC 373,
July 1972.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
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[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.
[i18n-terms]
Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", June 2011, <https://
datatracker.ietf.org/doc/draft-ietf-appsawg-rfc3536bis/>.
Appendix A. Change Log
[[anchor13: RFC Editor: Please remove this section]]
A.1. New Version and File Name: draft-ietf-ftpext2-typeu-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.
A.2. Version -01
o Corrected a typographical error in the -00 change log entry and
made a cosmetic change to that section.
o Added additional metadata.
o Added a new introductory subsection (Section 1.3) to clarify the
relationship of this spec to FTP's development and some other
ongoing discussions in the IETF.
A.3. Version -02
o Changed title per suggestion from Mykyta Yevstifeyev
o Removed reference to ABNF since it turned out to be possible to
write the document without it.
o Rewrote the IANA Considerations to specify a table for TYPE
argument values.
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o Made a number of other relatively minor corrections and
clarifications.
o Updated Unicode reference to 6.0.
o Moved this section to an appendix for easier handling later.
A.4. Version -03
o Draft reissued to reactivate it.
o Many small editorial changes and clarifications with no
substantive change to the specification itself.
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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