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2 FTPEXT2 J. Klensin
3 Internet-Draft July 10, 2011
4 Updates: 959 (if approved)
5 Intended status: Standards Track
6 Expires: January 11, 2012
8 FTP TYPE Extension for Internationalized Text
9 draft-ietf-ftpext2-typeu-02
11 Abstract
13 The traditional FTP protocol includes a TYPE command to specify the
14 data representation. That command has values for ASCII and EBCDIC
15 text, plus binary ("IMAGE") transmission. As the Internet becomes
16 more international, there is a growing requirement to be able to
17 transmit textual data, encoded in Unicode, in a way that is
18 independent of the coding and line representation forms of particular
19 operating systems. This memo specifies a new FTP representation TYPE
20 value for Unicode data.
22 Status of this Memo
24 This Internet-Draft is submitted in full conformance with the
25 provisions of BCP 78 and BCP 79.
27 Internet-Drafts are working documents of the Internet Engineering
28 Task Force (IETF). Note that other groups may also distribute
29 working documents as Internet-Drafts. The list of current Internet-
30 Drafts is at http://datatracker.ietf.org/drafts/current/.
32 Internet-Drafts are draft documents valid for a maximum of six months
33 and may be updated, replaced, or obsoleted by other documents at any
34 time. It is inappropriate to use Internet-Drafts as reference
35 material or to cite them other than as "work in progress."
37 This Internet-Draft will expire on January 11, 2012.
39 Copyright Notice
41 Copyright (c) 2011 IETF Trust and the persons identified as the
42 document authors. All rights reserved.
44 This document is subject to BCP 78 and the IETF Trust's Legal
45 Provisions Relating to IETF Documents
46 (http://trustee.ietf.org/license-info) in effect on the date of
47 publication of this document. Please review these documents
48 carefully, as they describe your rights and restrictions with respect
49 to this document. Code Components extracted from this document must
50 include Simplified BSD License text as described in Section 4.e of
51 the Trust Legal Provisions and are provided without warranty as
52 described in the Simplified BSD License.
54 This document may contain material from IETF Documents or IETF
55 Contributions published or made publicly available before November
56 10, 2008. The person(s) controlling the copyright in some of this
57 material may not have granted the IETF Trust the right to allow
58 modifications of such material outside the IETF Standards Process.
59 Without obtaining an adequate license from the person(s) controlling
60 the copyright in such materials, this document may not be modified
61 outside the IETF Standards Process, and derivative works of it may
62 not be created outside the IETF Standards Process, except to format
63 it for publication as an RFC or to translate it into languages other
64 than English.
66 Table of Contents
68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
69 1.1. Context and Overview . . . . . . . . . . . . . . . . . . . 4
70 1.2. Summary of History of Internationalization of FTP . . . . 4
71 1.3. History of the TYPE Command . . . . . . . . . . . . . . . 4
72 1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
73 1.5. Discussion List . . . . . . . . . . . . . . . . . . . . . 6
74 2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 6
75 2.1. Existing TYPEs . . . . . . . . . . . . . . . . . . . . . . 6
76 2.2. Unicode TYPE . . . . . . . . . . . . . . . . . . . . . . . 7
77 2.3. Data Structure . . . . . . . . . . . . . . . . . . . . . . 7
78 2.4. Feature Negotiation . . . . . . . . . . . . . . . . . . . 7
79 3. Net-Unicode Format for FTP . . . . . . . . . . . . . . . . . . 8
80 4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
81 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
82 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
83 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
84 7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
85 7.2. Informative References . . . . . . . . . . . . . . . . . . 9
86 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 10
87 A.1. New Version and File Name: draft-ietf-ftpext2-typeu-00 . . 10
88 A.2. Version -01 . . . . . . . . . . . . . . . . . . . . . . . 10
89 A.3. Version -02 . . . . . . . . . . . . . . . . . . . . . . . 10
90 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
92 1. Introduction
94 1.1. Context and Overview
96 The traditional FTP protocol, as documented in RFC 959 [RFC0959],
97 includes a TYPE command to specify the data representation. That
98 command was originally specified as having values for ASCII and
99 EBCDIC text, plus binary ("IMAGE") transmission. The Host
100 Requirements specification [RFC1123] made other changes to FTP, but
101 did not alter the TYPE command or the environment for which it
102 provided.
104 As the Internet becomes more international, there is a growing
105 requirement to be able to transmit textual data, encoded in Unicode
106 [Unicode52], in a way that is independent of the coding and line
107 representation forms of particular operating systems. This memo
108 specifies a new FTP TYPE value for Unicode data.
110 1.2. Summary of History of Internationalization of FTP
112 RFC 2640 [RFC2640] is described as providing internationalization of
113 FTP, but only addresses the use of FTP in internationalized (non-
114 ASCII or extended ASCII [ASCII]) file systems. Its facilities were
115 slightly enhanced in a more general extensions specification
116 [RFC3659], which builds on a more general FTP extension mechanism
117 [RFC2389]. The specification in this document addresses the transfer
118 of non-ASCII text files only, building on the TYPE command of the
119 original FTP specification [RFC0959].
121 1.3. History of the TYPE Command
123 [[Note in Draft: AppsAWG: please decide whether this subsection
124 should be included in the final version as informative or dropped as
125 surplus text that doesn't contribute to an implementer understanding
126 of what should be done.]]
128 When the FTP protocol was first defined in 1971 [RFC0114], hosts on
129 the ARPANET were extremely diverse. ASCII and EBCDIC were both in
130 active use, as were several completely different character encodings,
131 and ASCII was encoded in a variety of different forms inside
132 different systems (TENEX/TOPS-20, Multics, Unix on 16 and then 32 bit
133 architectures, and the original IBM ASCII all used different
134 encodings. In mid-1972, John McCarthy described some aspects of the
135 issues [RFC0373]. Within a relatively short period of time, it was
136 understood that expecting every system to adapt to the formats of
137 every other system -- a fairly large n-squared problem -- was crazy
138 and, at least for text, the solution was to expect all FTP-supporting
139 hosts to convert between their local formats and a network-standard
140 ASCII encoding and, optionally, to also identify, and permit, EBCBIC
141 files to be transferred in canonical form. The TYPE command was
142 incorporated into FTP to support client specification of those forms
143 for on-the-wire transfer and also to support a pair of TYPEs to
144 support transferring data in forms that were likely to be operating
145 system and hardware specific (see Section 2.1 for more details).
147 Because of the need to handle these different text character sets and
148 encoding forms without that n-squared problem, TYPE was very commonly
149 used unless it was known that the sending and receiving systems were
150 homogeneous. Several arrangements for single-line FTP commands did
151 not make explicit provision for TYPE specifications, but they tended
152 to make exactly that homogeneity assumption.
154 By the late 1980s, the ARPANET was converging toward a single host
155 system architecture. Almost all significant computer systems used 32
156 bit architectures or felt an obligation to be able to simulate them.
157 EBCDIC had fallen into disuse on the network. ASCII, encoded right-
158 justified in eight bits with a leading zero, had become pervasive.
159 An Image transfer among diverse systems might well encounter
160 differences with line termination or, occasionally, record structures
161 rather than stream ones (both of which TYPE A would have smoothed
162 out), but the character encodings were almost certain to be the same.
163 So, with allowances for those line termination problems -- which have
164 been a large issue in many cases -- Image ("binary") and ASCII
165 transfers were almost equivalent and the TYPE command became less-
166 used. Some client FTP implementations also adopted an "automatic"
167 mode in which they tried to determine heuristically, based on either
168 file names or content inspection, whether the relevant file consisted
169 of ASCII characters or binary information. When there were only two
170 choices, they often (but not always) got it right.
172 However, migration to Unicode has reintroduced many of the old
173 issues. When Unicode is used inside a system, it can be used with
174 several different encodings and different assumptions about
175 normalization (see "Terminology for Use in Internationalization"
176 [i18n-terms] for more discussion). When those files are transferred
177 to another system with Image type, the result may be completely
178 uninterpretable on the target system. This specification extends to
179 non-ASCII character transfers the early concept of having a very
180 small number of common/ canonical network transfer formats for
181 characters, having systems able to convert to or from them. By doing
182 so, it avoids a Unicode version of the n-squared problems and general
183 confusion that led to the definition of TYPE.
185 1.4. Terminology
187 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
188 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
189 document are to be interpreted as described in [RFC2119].
191 This document assumes that the reader is familiar with the
192 terminology of RFC 959. Those terms, especially reply, server-FTP
193 process, user-FTP process, server-PI, user-PI, logical byte size, and
194 user, if used here, are used in the same way. For the convenience of
195 contemporary readers, the terms "client" and "server" are used
196 interchangeably with the historic terms "user-FTP process" and
197 "server-FTP process". The document also assumes the termology and
198 changes in the updates to FTP specified in RFC 1123 and RFC 2389
199 [RFC2389].
201 1.5. Discussion List
203 [[anchor5: RFC Editor: please remove this section before
204 publication.]]
206 This proposal is being discussed in the IETF FTPEXT2 Working Group.
207 Its mailing list is at ftpext@ietf.org.
209 2. Specification
211 2.1. Existing TYPEs
213 The FTP TYPE command, described in [RFC0959] accepts four possible
214 first argument values, as described below. Note that these
215 descriptions are provided for the reader's convenience; the
216 definitions in RFC 959 remain normative.
218 A The data are expected to be in, and are transformed by the server
219 if needed to, an ASCII [ASCII] data stream conforming to the "NVT"
220 specification (See RFC 959 [RFC0959] and Appendix B of RFC 5198
221 [RFC5198] for more information).
223 E The data are expected to be in, and are transformed by the server
224 if needed to, an EBCDIC data stream as specified in RFC 959.
226 I The data are transferred in "image" form, i.e., exactly as they
227 appear in the server. Because it is the only TYPE form in which
228 true binary data can be transferred, TYPE I is often referred to
229 as "binary" or "binary transfer".
231 L The data are transmitted in logical bytes of a size specified in
232 an additional argument. See RFC 959.
234 Any of these four argument variations to TYPE except "TYPE A" (with
235 non-print format) MAY be rejected by the server-FTP process with a
236 504 response code if it does not support that type and the necessary
237 conversions.
239 2.2. Unicode TYPE
241 The client-PI MAY transmit TYPE U to the server-PI as an alternative
242 to other TYPE commands and arguments. If it does, the server MAY
243 return reply-code 504, indicating that the TYPE U feature is not
244 supported (unchanged from RFC 959) or MUST respond to any data
245 retrieval request (e.g., RETR) by sending the data in a stream
246 conformant to the Net-Unicode format specified in Section 3.
247 Similarly, if the client-PI sends TYPE U and the server accepts it,
248 the client MUST send any data streams in that format while the option
249 is in effect. No second parameter is used or permitted for TYPE U.
251 2.3. Data Structure
253 The default and only permitted data structure for TYPE U is "file
254 structure". Use of the STRU command SHOULD be avoided. If is used,
255 its argument MUST be "F".
257 2.4. Feature Negotiation
259 RFC 2389 [RFC2389] specifies a feature negotiation mechanism for new
260 extensions to FTP. Since the TYPE command is a required part of the
261 base FTP specification, the client-PI is not required to issue the
262 FEAT command prior to issuing TYPE U. However, it MAY do so and
263 Server-FTP implementations that include TYPE U SHOULD support FEAT as
264 described below. If the FEAT command is transmitted from the
265 client-PI to the server-PI, and this extension and FEAT are
266 supported, the response MUST include a TYPE line that lists all TYPE
267 values supported by the server (including the required ones). For
268 example, if an FTP-server supports all of TYPEs A, E, I, and U, the
269 FEAT response line would contain each of the possible arguments
270 separated by semicolons, e.g.,
272 TYPE A;E;I;U
274 This specification does not change either RFC 959 or RFC 2389. In
275 particular, no FEAT response line is required for TYPE unless this,
276 or some other, extension to TYPE is supported by the FTP-server.
278 3. Net-Unicode Format for FTP
280 This section specifies a profile of Net-Unicode [RFC5198] for use
281 with FTP TYPE U.
283 Unicode characters must be transmitted in UTF-8 [RFC3629] as
284 specified for Net-Unicode. Because FTP is used in data transmission,
285 the characters and sequences that are discouraged in Section 2 of RFC
286 5198 are permitted to be transported by FTP. However, line-ending
287 sequences MUST conform to the CRLF convention specified there.
288 Consistent with Paragraph 4 of that Section, strings SHOULD be
289 normalized before transmission if at all possible.
291 The implicit logical byte size for this transmission type is eight
292 bits.
294 4. Acknowledgments
296 This document draws heavily on RFC 959; appreciation is expressed to
297 its authors and to the authors of RFC 2398. The work of Mark P.
298 Peterson and Douglas J. Papenthien on other FTP extensions finally
299 motivated production of this document in 2008 after a long delay;
300 that contribution is appreciated as well. Specific useful comments
301 on this draft or its immediate predecessors were provided by the late
302 and much-lamented Mike Padlipsky and by Mykyta Yevstifeyev.
304 5. IANA Considerations
306 When this specification is approved, IANA is requested to add an
307 additional table to the FTP Extensions Registry established by RFC
308 5797 [RFC5797]. That table should be titled "TYPE command arguments"
309 and should include "A (m) RFC 959", "E (o) RFC 959", "I (o) RFC 959",
310 "L (o) RFC 959", and "U (o) RFCNNNN".
312 6. Security Considerations
314 This specification makes no substantive change to the FTP command
315 stream but only alters the presentation of data in the data stream.
316 Consequently, it should have no negative security implications that
317 are not already present in the earlier FTP specifications described
318 in Section 1 and in the Net-Unicode specification [RFC5198]. By
319 specifying an exact canonical form for the identification and
320 transfer of Unicode strings, it may eliminate some problems that
321 might be encountered when such strings are transmitted without
322 identification or without restrictions.
324 7. References
326 7.1. Normative References
328 [ASCII] American National Standards Institute (formerly United
329 States of America Standards Institute), "USA Code for
330 Information Interchange", ANSI X3.4-1968, 1968.
332 ANSI X3.4-1968 has been replaced by newer versions with
333 slight modifications, but the 1968 version remains
334 definitive for the Internet.
336 [RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
337 STD 9, RFC 959, October 1985.
339 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
340 Requirement Levels", BCP 14, RFC 2119, March 1997.
342 [RFC2389] Hethmon, P. and R. Elz, "Feature negotiation mechanism for
343 the File Transfer Protocol", RFC 2389, August 1998.
345 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
346 10646", STD 63, RFC 3629, November 2003.
348 [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
349 Interchange", RFC 5198, March 2008.
351 [Unicode52]
352 The Unicode Consortium. The Unicode Standard, Version
353 6.0.0, defined by:, "The Unicode Standard, Version 6.0.0",
354 (Mountain View, CA: The Unicode Consortium, 2011. ISBN
355 978-1-936213-01-6).,
356 .
358 7.2. Informative References
360 [RFC0114] Bhushan, A., "File Transfer Protocol", RFC 114,
361 April 1971.
363 [RFC0373] McCarthy, J., "Arbitrary Character Sets", RFC 373,
364 July 1972.
366 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application
367 and Support", STD 3, RFC 1123, October 1989.
369 [RFC2640] Curtin, B., "Internationalization of the File Transfer
370 Protocol", RFC 2640, July 1999.
372 [RFC3659] Hethmon, P., "Extensions to FTP", RFC 3659, March 2007.
374 [RFC5797] Klensin, J. and A. Hoenes, "FTP Command and Extension
375 Registry", RFC 5797, March 2010.
377 [i18n-terms]
378 Hoffman, P. and J. Klensin, "Terminology Used in
379 Internationalization in the IETF", June 2011, .
382 Appendix A. Change Log
384 [[anchor13: RFC Editor: Please remove this section]]
386 A.1. New Version and File Name: draft-ietf-ftpext2-typeu-00
388 This version of the document is a slight update to
389 draft-klensin-ftp-typeu-00, posted in July 2008). It includes some
390 updated references to work completed in the interim, information
391 about the FTPEXT2 WG, a new Security Considerations section (omitted
392 from the prior draft), and a few other minor corrections.
394 A.2. Version -01
396 o Corrected a typographical error in the -00 change log entry and
397 made a cosmetic change to that section.
399 o Added additional metadata.
401 o Added a new introductory subsection (Section 1.3) to clarify the
402 relationship of this spec to FTP's development and some other
403 ongoing discussions in the IETF.
405 A.3. Version -02
407 o Changed title per suggestion from Mykyta Yevstifeyev
409 o Removed reference to ABNF since it turned out to be possible to
410 write the document without it.
412 o Rewrote the IANA Considerations to specify a table for TYPE
413 argument values.
415 o Made a number of other relatively minor corrections and
416 clarifications.
418 o Updated Unicode reference to 6.0.
420 o Moved this section to an appendix for easier handling later.
422 Author's Address
424 John C Klensin
425 1770 Massachusetts Ave, Ste 322
426 Cambridge, MA 02140
427 USA
429 Phone: +1 617 245 1457
430 Email: john+ietf@jck.com