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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