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2 Network Working Group J. Klensin
3 Internet-Draft March 30, 2012
4 Updates: 959 (if approved)
5 Intended status: Standards Track
6 Expires: October 1, 2012
8 FTP TYPE Extension for Internationalized Text
9 draft-klensin-ftpext-typeu-00
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 October 1, 2012.
39 Copyright Notice
41 Copyright (c) 2012 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 A.4. Version -03 . . . . . . . . . . . . . . . . . . . . . . . 11
91 A.5. New Version and File Name:
92 draft-klensin-ftpext-typeu-00 . . . . . . . . . . . . . . 11
93 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
95 1. Introduction
97 1.1. Context and Overview
99 The traditional FTP protocol, as documented in RFC 959 [RFC0959],
100 includes a TYPE command to specify the data representation. That
101 command was originally specified as having values for ASCII and
102 EBCDIC text, plus binary ("IMAGE") transmission. The Host
103 Requirements specification [RFC1123] made other changes to FTP, but
104 did not alter the TYPE command or the environment for which it
105 provided.
107 As the Internet becomes more international, there is a growing
108 requirement to be able to transmit textual data, encoded in Unicode
109 [Unicode], in a way that is independent of the coding and line
110 representation forms of particular operating systems. This memo
111 specifies a new FTP TYPE value for Unicode data.
113 1.2. Summary of History of Internationalization of FTP
115 RFC 2640 [RFC2640] is described as providing internationalization of
116 FTP, but only addresses the use of FTP in internationalized (non-
117 ASCII or extended ASCII [ASCII]) file systems. Its facilities were
118 slightly enhanced in a more general extensions specification
119 [RFC3659], which builds on a more general FTP extension mechanism
120 [RFC2389]. The specification in this document addresses the transfer
121 of non-ASCII text files only, building on the TYPE command of the
122 original FTP specification [RFC0959].
124 1.3. History of the TYPE Command
126 [[Note in Draft: AppsAWG: please decide whether this subsection
127 should be included in the final version as informative or dropped as
128 surplus text that doesn't contribute to an implementer understanding
129 of what should be done.]]
131 When the FTP protocol was first defined in 1971 [RFC0114], hosts on
132 the ARPANET were extremely diverse. ASCII and EBCDIC were both in
133 active use, as were several completely different character encodings,
134 and ASCII was encoded in a variety of different forms inside
135 different systems (TENEX/TOPS-20, Multics, Unix on 16 and then 32 bit
136 architectures, and the original IBM ASCII all used different
137 encodings. In mid-1972, the late John McCarthy described some
138 aspects of the issues [RFC0373]. Within a relatively short period of
139 time, it was understood that expecting every system to adapt to the
140 formats of every other system -- a fairly large n-squared problem --
141 was crazy. At least for text, the solution was to expect all FTP-
142 supporting hosts to convert between their local formats and a
143 network-standard ASCII encoding and, optionally, to also identify,
144 and permit, EBCBIC files to be transferred in canonical form. The
145 TYPE command was incorporated into FTP to support client
146 specification of those forms for on-the-wire transfer and also to
147 support a pair of TYPEs to support transferring data in forms that
148 were likely to be operating system and hardware specific (see
149 Section 2.1 for more details).
151 Because of the need to handle these different text character sets and
152 encoding forms without that n-squared problem, TYPE was very commonly
153 used unless it was known that the sending and receiving systems were
154 homogeneous. Several arrangements for single-line FTP commands did
155 not make explicit provision for TYPE specifications, but they tended
156 to make exactly that homogeneity assumption.
158 By the late 1980s, the ARPANET was converging toward a single basic
159 host system architecture. Almost all significant computer systems
160 used 32 bit architectures or felt an obligation to be able to
161 simulate them. EBCDIC had fallen into disuse on the network. ASCII,
162 encoded right-justified in eight bits with a leading zero, had become
163 pervasive. An Image transfer among diverse systems might well
164 encounter differences with line termination or, occasionally, record
165 structures rather than stream ones (both of which TYPE A would have
166 smoothed out), but the character encodings were almost certain to be
167 the same. So, with allowances for those line termination problems --
168 which have been a large issue in many cases -- Image ("binary") and
169 ASCII transfers were almost equivalent and the TYPE command became
170 less-used. Some client FTP implementations also adopted an
171 "automatic" mode in which they tried to determine heuristically,
172 based on either file names or content inspection, whether the
173 relevant file consisted of ASCII characters or binary information and
174 to send the appropriate TYPE command without user intervention.
175 Because there were usually only two choices in practice, they often
176 (but not always) got it right.
178 However, migration to Unicode has reintroduced many of the old
179 issues. When Unicode is used inside a system, it can be used with
180 several different encodings (e.g., UTF-8 and several variations on
181 UTF-16 (possibly with surrogate pairs), different assumptions about
182 normalization (see "Terminology for Use in Internationalization"
183 [i18n-terms] for more discussion) and even new variations on line
184 termination conventions. When those files are transferred to another
185 system with Image type, the result may be completely uninterpretable
186 on the target system. This specification extends to non-ASCII
187 character transfers the early concept of having a very small number
188 of common/ canonical network transfer formats for characters, having
189 systems able to convert to or from them. By doing so, it avoids a
190 Unicode version of the n-squared problems and the general confusion
191 that led to the definition of TYPE.
193 1.4. Terminology
195 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
196 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
197 document are to be interpreted as described in [RFC2119].
199 This document assumes that the reader is familiar with the
200 terminology of RFC 959. Those terms, especially reply, server-FTP
201 process, user-FTP process, server-PI, user-PI, logical byte size, and
202 user, if used here, are used in the same way. For the convenience of
203 contemporary readers, the terms "client" and "server" are used
204 interchangeably with the historic terms "user-FTP process" and
205 "server-FTP process". The document also assumes the termology and
206 changes in the updates to FTP specified in RFC 1123 and RFC 2389
207 [RFC2389].
209 1.5. Discussion List
211 [[anchor5: RFC Editor: please remove this section before
212 publication.]]
214 This proposal is being discussed on the IETF FTP Extensions mailing
215 list at ftpext@ietf.org. Subscription and other information is
216 available from https://www.ietf.org/mailman/listinfo/ftpext.
218 2. Specification
220 2.1. Existing TYPEs
222 The FTP TYPE command, described in [RFC0959] accepts four possible
223 first argument values, as described below. Note that the
224 descriptions in this subsection are provided for the reader's
225 convenience; the definitions in RFC 959 remain normative.
227 A The data are expected to be in, and are transformed by the server
228 if needed to, an ASCII [ASCII] data stream conforming to the "NVT"
229 specification (See RFC 959 [RFC0959] and Appendix B of RFC 5198
230 [RFC5198] for more information).
232 E The data are expected to be in, and are transformed by the server
233 if needed to, an EBCDIC data stream as specified in RFC 959.
235 I The data are transferred in "image" form, i.e., exactly as they
236 appear in the server. Because it is the only TYPE form in which
237 true binary data can be transferred, TYPE I is often referred to
238 as "binary" or "binary transfer".
240 L The data are transmitted in logical bytes of a size specified in
241 an additional argument. See RFC 959.
243 Any of these four argument variations to TYPE except "TYPE A" (with
244 non-print format) MAY be rejected by the server-FTP process with a
245 504 response code if it does not support that type and the necessary
246 conversions.
248 2.2. Unicode TYPE
250 The client-PI MAY transmit TYPE U to the server-PI as an alternative
251 to other TYPE commands and arguments. If it does, the server MAY
252 return reply-code 504, indicating that the TYPE U feature is not
253 supported (unchanged from RFC 959) or MUST respond to any data
254 retrieval request (e.g., RETR) by sending the data in a stream
255 conformant to the Net-Unicode format specified in Section 3.
256 Similarly, if the client-PI sends TYPE U and the server accepts it,
257 the client MUST send any data streams in that format while the option
258 is in effect. No second parameter is used or permitted for TYPE U.
260 2.3. Data Structure
262 The default and only permitted data structure for TYPE U is "file
263 structure". Use of the STRU command SHOULD be avoided. If is used,
264 its argument MUST be "F".
266 2.4. Feature Negotiation
268 RFC 2389 [RFC2389] specifies a feature negotiation mechanism for new
269 extensions to FTP. Since the TYPE command is a required part of the
270 base FTP specification, the client-PI is not required to issue the
271 FEAT command prior to issuing TYPE U. However, it MAY do so and
272 Server-FTP implementations that include TYPE U SHOULD support FEAT as
273 described below. If the FEAT command is transmitted from the
274 client-PI to the server-PI, and this extension and FEAT are
275 supported, the response MUST include a TYPE line that lists all TYPE
276 values supported by the server (including the required ones). For
277 example, if an FTP-server supports all of TYPEs A, E, I, and U, the
278 FEAT response line would contain each of the possible arguments
279 separated by semicolons, e.g.,
280 TYPE A;E;I;U
282 This specification does not change either RFC 959 or RFC 2389. In
283 particular, no FEAT response line is required for TYPE unless this,
284 or some other, extension to TYPE is supported by the FTP-server.
286 3. Net-Unicode Format for FTP
288 This section specifies a profile of Net-Unicode [RFC5198] for use
289 with FTP TYPE U.
291 Unicode characters must be transmitted in UTF-8 [RFC3629] as
292 specified for Net-Unicode. Because FTP is used in data transmission,
293 the characters and sequences that are discouraged in Section 2 of RFC
294 5198 are permitted to be transported by FTP. However, line-ending
295 sequences MUST conform to the CRLF convention specified there.
296 Consistent with Paragraph 4 of that Section, strings SHOULD be
297 normalized before transmission if at all possible.
299 The implicit logical byte size for this transmission type is eight
300 bits.
302 4. Acknowledgments
304 This document draws heavily on RFC 959; appreciation is expressed to
305 its authors and to the authors of RFC 2398. The work of Mark P.
306 Peterson and Douglas J. Papenthien on other FTP extensions finally
307 motivated production of this document in 2008 after a long delay;
308 that contribution is appreciated as well. Specific useful comments
309 on this draft or its immediate predecessors were provided by the late
310 and much-lamented Mike Padlipsky and by Mykyta Yevstifeyev.
312 5. IANA Considerations
314 When this specification is approved, IANA is requested to add an
315 additional table to the FTP Extensions Registry established by RFC
316 5797 [RFC5797]. That table should be titled "TYPE command arguments"
317 and should include "A (m) RFC 959", "E (o) RFC 959", "I (o) RFC 959",
318 "L (o) RFC 959", and "U (o) RFCNNNN".
320 6. Security Considerations
322 This specification makes no substantive change to the FTP command
323 stream (the argument to the standard TYPE command is changed). It
324 only alters the presentation of data in the data stream.
325 Consequently, it should have no negative security implications that
326 are not already present in the earlier FTP specifications described
327 in Section 1 and in the Net-Unicode specification [RFC5198]. By
328 specifying an exact canonical form for the identification and
329 transfer of Unicode strings, it may eliminate some problems that
330 might be encountered when such strings are transmitted without
331 identification or without restrictions (e.g., using TYPE I to obtain
332 a "binary" transfer).
334 7. References
336 7.1. Normative References
338 [ASCII] American National Standards Institute (formerly United
339 States of America Standards Institute), "USA Code for
340 Information Interchange", ANSI X3.4-1968, 1968.
342 ANSI X3.4-1968 has been replaced by newer versions with
343 slight modifications, but the 1968 version remains
344 definitive for the Internet.
346 [RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
347 STD 9, RFC 959, October 1985.
349 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
350 Requirement Levels", BCP 14, RFC 2119, March 1997.
352 [RFC2389] Hethmon, P. and R. Elz, "Feature negotiation mechanism for
353 the File Transfer Protocol", RFC 2389, August 1998.
355 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
356 10646", STD 63, RFC 3629, November 2003.
358 [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
359 Interchange", RFC 5198, March 2008.
361 [Unicode] The Unicode Consortium. The Unicode Standard, Version
362 6.0.0, defined by:, "The Unicode Standard, Version 6.0.0",
363 (Mountain View, CA: The Unicode Consortium, 2011. ISBN
364 978-1-936213-01-6).,
365 .
367 7.2. Informative References
369 [RFC0114] Bhushan, A., "File Transfer Protocol", RFC 114,
370 April 1971.
372 [RFC0373] McCarthy, J., "Arbitrary Character Sets", RFC 373,
373 July 1972.
375 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application
376 and Support", STD 3, RFC 1123, October 1989.
378 [RFC2640] Curtin, B., "Internationalization of the File Transfer
379 Protocol", RFC 2640, July 1999.
381 [RFC3659] Hethmon, P., "Extensions to FTP", RFC 3659, March 2007.
383 [RFC5797] Klensin, J. and A. Hoenes, "FTP Command and Extension
384 Registry", RFC 5797, March 2010.
386 [i18n-terms]
387 Hoffman, P. and J. Klensin, "Terminology Used in
388 Internationalization in the IETF", June 2011, .
391 Appendix A. Change Log
393 [[anchor13: RFC Editor: Please remove this section]]
395 A.1. New Version and File Name: draft-ietf-ftpext2-typeu-00
397 This version of the document is a slight update to
398 draft-klensin-ftp-typeu-00, posted in July 2008). It includes some
399 updated references to work completed in the interim, information
400 about the FTPEXT2 WG, a new Security Considerations section (omitted
401 from the prior draft), and a few other minor corrections.
403 A.2. Version -01
405 o Corrected a typographical error in the -00 change log entry and
406 made a cosmetic change to that section.
408 o Added additional metadata.
410 o Added a new introductory subsection (Section 1.3) to clarify the
411 relationship of this spec to FTP's development and some other
412 ongoing discussions in the IETF.
414 A.3. Version -02
416 o Changed title per suggestion from Mykyta Yevstifeyev
417 o Removed reference to ABNF since it turned out to be possible to
418 write the document without it.
420 o Rewrote the IANA Considerations to specify a table for TYPE
421 argument values.
423 o Made a number of other relatively minor corrections and
424 clarifications.
426 o Updated Unicode reference to 6.0.
428 o Moved this section to an appendix for easier handling later.
430 A.4. Version -03
432 o Draft reissued to reactivate it.
434 o Many small editorial changes and clarifications with no
435 substantive change to the specification itself.
437 A.5. New Version and File Name: draft-klensin-ftpext-typeu-00
439 This version of the document is identical, except for the date, file
440 name and updated mailing list information, to
441 draft-ietf-ftpext2-typeu-03, posted on 12 July 2012. This return the
442 draft to individual submission status after the shutdown of the
443 FTPEXT2 WG.
445 Author's Address
447 John C Klensin
448 1770 Massachusetts Ave, Ste 322
449 Cambridge, MA 02140
450 USA
452 Phone: +1 617 245 1457
453 Email: john+ietf@jck.com