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2 FTPEXT2 J. Klensin
3 Internet-Draft March 12, 2012
4 Updates: 959 (if approved)
5 Intended status: Standards Track
6 Expires: September 13, 2012
8 FTP TYPE Extension for Internationalized Text
9 draft-ietf-ftpext2-typeu-03
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 September 13, 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 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
93 1. Introduction
95 1.1. Context and Overview
97 The traditional FTP protocol, as documented in RFC 959 [RFC0959],
98 includes a TYPE command to specify the data representation. That
99 command was originally specified as having values for ASCII and
100 EBCDIC text, plus binary ("IMAGE") transmission. The Host
101 Requirements specification [RFC1123] made other changes to FTP, but
102 did not alter the TYPE command or the environment for which it
103 provided.
105 As the Internet becomes more international, there is a growing
106 requirement to be able to transmit textual data, encoded in Unicode
107 [Unicode], in a way that is independent of the coding and line
108 representation forms of particular operating systems. This memo
109 specifies a new FTP TYPE value for Unicode data.
111 1.2. Summary of History of Internationalization of FTP
113 RFC 2640 [RFC2640] is described as providing internationalization of
114 FTP, but only addresses the use of FTP in internationalized (non-
115 ASCII or extended ASCII [ASCII]) file systems. Its facilities were
116 slightly enhanced in a more general extensions specification
117 [RFC3659], which builds on a more general FTP extension mechanism
118 [RFC2389]. The specification in this document addresses the transfer
119 of non-ASCII text files only, building on the TYPE command of the
120 original FTP specification [RFC0959].
122 1.3. History of the TYPE Command
124 [[Note in Draft: AppsAWG: please decide whether this subsection
125 should be included in the final version as informative or dropped as
126 surplus text that doesn't contribute to an implementer understanding
127 of what should be done.]]
129 When the FTP protocol was first defined in 1971 [RFC0114], hosts on
130 the ARPANET were extremely diverse. ASCII and EBCDIC were both in
131 active use, as were several completely different character encodings,
132 and ASCII was encoded in a variety of different forms inside
133 different systems (TENEX/TOPS-20, Multics, Unix on 16 and then 32 bit
134 architectures, and the original IBM ASCII all used different
135 encodings. In mid-1972, the late John McCarthy described some
136 aspects of the issues [RFC0373]. Within a relatively short period of
137 time, it was understood that expecting every system to adapt to the
138 formats of every other system -- a fairly large n-squared problem --
139 was crazy. At least for text, the solution was to expect all FTP-
140 supporting hosts to convert between their local formats and a
141 network-standard ASCII encoding and, optionally, to also identify,
142 and permit, EBCBIC files to be transferred in canonical form. The
143 TYPE command was incorporated into FTP to support client
144 specification of those forms for on-the-wire transfer and also to
145 support a pair of TYPEs to support transferring data in forms that
146 were likely to be operating system and hardware specific (see
147 Section 2.1 for more details).
149 Because of the need to handle these different text character sets and
150 encoding forms without that n-squared problem, TYPE was very commonly
151 used unless it was known that the sending and receiving systems were
152 homogeneous. Several arrangements for single-line FTP commands did
153 not make explicit provision for TYPE specifications, but they tended
154 to make exactly that homogeneity assumption.
156 By the late 1980s, the ARPANET was converging toward a single basic
157 host system architecture. Almost all significant computer systems
158 used 32 bit architectures or felt an obligation to be able to
159 simulate them. EBCDIC had fallen into disuse on the network. ASCII,
160 encoded right-justified in eight bits with a leading zero, had become
161 pervasive. An Image transfer among diverse systems might well
162 encounter differences with line termination or, occasionally, record
163 structures rather than stream ones (both of which TYPE A would have
164 smoothed out), but the character encodings were almost certain to be
165 the same. So, with allowances for those line termination problems --
166 which have been a large issue in many cases -- Image ("binary") and
167 ASCII transfers were almost equivalent and the TYPE command became
168 less-used. Some client FTP implementations also adopted an
169 "automatic" mode in which they tried to determine heuristically,
170 based on either file names or content inspection, whether the
171 relevant file consisted of ASCII characters or binary information and
172 to send the appropriate TYPE command without user intervention.
173 Because there were usually only two choices in practice, they often
174 (but not always) got it right.
176 However, migration to Unicode has reintroduced many of the old
177 issues. When Unicode is used inside a system, it can be used with
178 several different encodings (e.g., UTF-8 and several variations on
179 UTF-16 (possibly with surrogate pairs), different assumptions about
180 normalization (see "Terminology for Use in Internationalization"
181 [i18n-terms] for more discussion) and even new variations on line
182 termination conventions. When those files are transferred to another
183 system with Image type, the result may be completely uninterpretable
184 on the target system. This specification extends to non-ASCII
185 character transfers the early concept of having a very small number
186 of common/ canonical network transfer formats for characters, having
187 systems able to convert to or from them. By doing so, it avoids a
188 Unicode version of the n-squared problems and the general confusion
189 that led to the definition of TYPE.
191 1.4. Terminology
193 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
194 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
195 document are to be interpreted as described in [RFC2119].
197 This document assumes that the reader is familiar with the
198 terminology of RFC 959. Those terms, especially reply, server-FTP
199 process, user-FTP process, server-PI, user-PI, logical byte size, and
200 user, if used here, are used in the same way. For the convenience of
201 contemporary readers, the terms "client" and "server" are used
202 interchangeably with the historic terms "user-FTP process" and
203 "server-FTP process". The document also assumes the termology and
204 changes in the updates to FTP specified in RFC 1123 and RFC 2389
205 [RFC2389].
207 1.5. Discussion List
209 [[anchor5: RFC Editor: please remove this section before
210 publication.]]
212 This proposal is being discussed in the IETF FTPEXT2 Working Group.
213 Its mailing list is at ftpext@ietf.org.
215 2. Specification
217 2.1. Existing TYPEs
219 The FTP TYPE command, described in [RFC0959] accepts four possible
220 first argument values, as described below. Note that the
221 descriptions in this subsection are provided for the reader's
222 convenience; the definitions in RFC 959 remain normative.
224 A The data are expected to be in, and are transformed by the server
225 if needed to, an ASCII [ASCII] data stream conforming to the "NVT"
226 specification (See RFC 959 [RFC0959] and Appendix B of RFC 5198
227 [RFC5198] for more information).
229 E The data are expected to be in, and are transformed by the server
230 if needed to, an EBCDIC data stream as specified in RFC 959.
232 I The data are transferred in "image" form, i.e., exactly as they
233 appear in the server. Because it is the only TYPE form in which
234 true binary data can be transferred, TYPE I is often referred to
235 as "binary" or "binary transfer".
237 L The data are transmitted in logical bytes of a size specified in
238 an additional argument. See RFC 959.
240 Any of these four argument variations to TYPE except "TYPE A" (with
241 non-print format) MAY be rejected by the server-FTP process with a
242 504 response code if it does not support that type and the necessary
243 conversions.
245 2.2. Unicode TYPE
247 The client-PI MAY transmit TYPE U to the server-PI as an alternative
248 to other TYPE commands and arguments. If it does, the server MAY
249 return reply-code 504, indicating that the TYPE U feature is not
250 supported (unchanged from RFC 959) or MUST respond to any data
251 retrieval request (e.g., RETR) by sending the data in a stream
252 conformant to the Net-Unicode format specified in Section 3.
253 Similarly, if the client-PI sends TYPE U and the server accepts it,
254 the client MUST send any data streams in that format while the option
255 is in effect. No second parameter is used or permitted for TYPE U.
257 2.3. Data Structure
259 The default and only permitted data structure for TYPE U is "file
260 structure". Use of the STRU command SHOULD be avoided. If is used,
261 its argument MUST be "F".
263 2.4. Feature Negotiation
265 RFC 2389 [RFC2389] specifies a feature negotiation mechanism for new
266 extensions to FTP. Since the TYPE command is a required part of the
267 base FTP specification, the client-PI is not required to issue the
268 FEAT command prior to issuing TYPE U. However, it MAY do so and
269 Server-FTP implementations that include TYPE U SHOULD support FEAT as
270 described below. If the FEAT command is transmitted from the
271 client-PI to the server-PI, and this extension and FEAT are
272 supported, the response MUST include a TYPE line that lists all TYPE
273 values supported by the server (including the required ones). For
274 example, if an FTP-server supports all of TYPEs A, E, I, and U, the
275 FEAT response line would contain each of the possible arguments
276 separated by semicolons, e.g.,
278 TYPE A;E;I;U
280 This specification does not change either RFC 959 or RFC 2389. In
281 particular, no FEAT response line is required for TYPE unless this,
282 or some other, extension to TYPE is supported by the FTP-server.
284 3. Net-Unicode Format for FTP
286 This section specifies a profile of Net-Unicode [RFC5198] for use
287 with FTP TYPE U.
289 Unicode characters must be transmitted in UTF-8 [RFC3629] as
290 specified for Net-Unicode. Because FTP is used in data transmission,
291 the characters and sequences that are discouraged in Section 2 of RFC
292 5198 are permitted to be transported by FTP. However, line-ending
293 sequences MUST conform to the CRLF convention specified there.
294 Consistent with Paragraph 4 of that Section, strings SHOULD be
295 normalized before transmission if at all possible.
297 The implicit logical byte size for this transmission type is eight
298 bits.
300 4. Acknowledgments
302 This document draws heavily on RFC 959; appreciation is expressed to
303 its authors and to the authors of RFC 2398. The work of Mark P.
304 Peterson and Douglas J. Papenthien on other FTP extensions finally
305 motivated production of this document in 2008 after a long delay;
306 that contribution is appreciated as well. Specific useful comments
307 on this draft or its immediate predecessors were provided by the late
308 and much-lamented Mike Padlipsky and by Mykyta Yevstifeyev.
310 5. IANA Considerations
312 When this specification is approved, IANA is requested to add an
313 additional table to the FTP Extensions Registry established by RFC
314 5797 [RFC5797]. That table should be titled "TYPE command arguments"
315 and should include "A (m) RFC 959", "E (o) RFC 959", "I (o) RFC 959",
316 "L (o) RFC 959", and "U (o) RFCNNNN".
318 6. Security Considerations
320 This specification makes no substantive change to the FTP command
321 stream (the argument to the standard TYPE command is changed). It
322 only alters the presentation of data in the data stream.
323 Consequently, it should have no negative security implications that
324 are not already present in the earlier FTP specifications described
325 in Section 1 and in the Net-Unicode specification [RFC5198]. By
326 specifying an exact canonical form for the identification and
327 transfer of Unicode strings, it may eliminate some problems that
328 might be encountered when such strings are transmitted without
329 identification or without restrictions (e.g., using TYPE I to obtain
330 a "binary" transfer).
332 7. References
334 7.1. Normative References
336 [ASCII] American National Standards Institute (formerly United
337 States of America Standards Institute), "USA Code for
338 Information Interchange", ANSI X3.4-1968, 1968.
340 ANSI X3.4-1968 has been replaced by newer versions with
341 slight modifications, but the 1968 version remains
342 definitive for the Internet.
344 [RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
345 STD 9, RFC 959, October 1985.
347 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
348 Requirement Levels", BCP 14, RFC 2119, March 1997.
350 [RFC2389] Hethmon, P. and R. Elz, "Feature negotiation mechanism for
351 the File Transfer Protocol", RFC 2389, August 1998.
353 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
354 10646", STD 63, RFC 3629, November 2003.
356 [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
357 Interchange", RFC 5198, March 2008.
359 [Unicode] The Unicode Consortium. The Unicode Standard, Version
360 6.0.0, defined by:, "The Unicode Standard, Version 6.0.0",
361 (Mountain View, CA: The Unicode Consortium, 2011. ISBN
362 978-1-936213-01-6).,
363 .
365 7.2. Informative References
367 [RFC0114] Bhushan, A., "File Transfer Protocol", RFC 114,
368 April 1971.
370 [RFC0373] McCarthy, J., "Arbitrary Character Sets", RFC 373,
371 July 1972.
373 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application
374 and Support", STD 3, RFC 1123, October 1989.
376 [RFC2640] Curtin, B., "Internationalization of the File Transfer
377 Protocol", RFC 2640, July 1999.
379 [RFC3659] Hethmon, P., "Extensions to FTP", RFC 3659, March 2007.
381 [RFC5797] Klensin, J. and A. Hoenes, "FTP Command and Extension
382 Registry", RFC 5797, March 2010.
384 [i18n-terms]
385 Hoffman, P. and J. Klensin, "Terminology Used in
386 Internationalization in the IETF", June 2011, .
389 Appendix A. Change Log
391 [[anchor13: RFC Editor: Please remove this section]]
393 A.1. New Version and File Name: draft-ietf-ftpext2-typeu-00
395 This version of the document is a slight update to
396 draft-klensin-ftp-typeu-00, posted in July 2008). It includes some
397 updated references to work completed in the interim, information
398 about the FTPEXT2 WG, a new Security Considerations section (omitted
399 from the prior draft), and a few other minor corrections.
401 A.2. Version -01
403 o Corrected a typographical error in the -00 change log entry and
404 made a cosmetic change to that section.
406 o Added additional metadata.
408 o Added a new introductory subsection (Section 1.3) to clarify the
409 relationship of this spec to FTP's development and some other
410 ongoing discussions in the IETF.
412 A.3. Version -02
414 o Changed title per suggestion from Mykyta Yevstifeyev
416 o Removed reference to ABNF since it turned out to be possible to
417 write the document without it.
419 o Rewrote the IANA Considerations to specify a table for TYPE
420 argument values.
422 o Made a number of other relatively minor corrections and
423 clarifications.
425 o Updated Unicode reference to 6.0.
427 o Moved this section to an appendix for easier handling later.
429 A.4. Version -03
431 o Draft reissued to reactivate it.
433 o Many small editorial changes and clarifications with no
434 substantive change to the specification itself.
436 Author's Address
438 John C Klensin
439 1770 Massachusetts Ave, Ste 322
440 Cambridge, MA 02140
441 USA
443 Phone: +1 617 245 1457
444 Email: john+ietf@jck.com