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1 FTPEXT Working Group R. Elz
2 Internet Draft University of Melbourne
3 Expiration Date: April 2000
4 P. Hethmon
5 Hethmon Brothers
7 October 1999
10 Extensions to FTP
13 draft-ietf-ftpext-mlst-08.txt
15 Status of this Memo
17 This document is an Internet-Draft and is NOT offered in accordance
18 with Section 10 of RFC2026, and the author does not provide the IETF
19 with any rights other than to publish as an Internet-Draft.
21 Internet-Drafts are working documents of the Internet Engineering
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34 To view the list Internet-Draft Shadow Directories, see
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37 This entire section has been prepended to this document automatically
38 during formatting without any direct involvement by the author(s) of
39 this draft.
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58 Abstract
60 In order to overcome the problems caused by the undefined format of
61 the current FTP LIST command output, a new command is needed to
62 transfer standardized listing information from Server-FTP to User-
63 FTP. Commands to enable this are defined in this document.
65 In order to allow consenting clients and servers to interact more
66 freely, a quite basic, and optional, virtual file store structure is
67 defined.
69 This proposal also extends the FTP protocol to allow character sets
70 other than US-ASCII[1] by allowing the transmission of 8-bit
71 characters and the recommended use of UTF-8[2] encoding.
73 Much implemented, but long undocumented, mechanisms to permit
74 restarts of interrupted data transfers in STREAM mode, are also
75 included here.
77 Lastly, the HOST command has been added to allow a style of "virtual
78 site" to be constructed.
80 Changed in this version of this document: Minor corrections as
81 discussed on the mailing list, including fixing many typographical
82 errors; Additional examples. This paragraph will be deleted from the
83 final version of this document.
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117 Table of Contents
119 Abstract ................................................ 2
120 1 Introduction ............................................ 4
121 2 Document Conventions .................................... 4
122 2.1 Basic Tokens ............................................ 5
123 2.2 Pathnames ............................................... 5
124 2.3 Times ................................................... 7
125 2.4 Server Replies .......................................... 8
126 3 File Modification Time (MDTM) ........................... 8
127 3.1 Syntax .................................................. 9
128 3.2 Error responses ......................................... 9
129 3.3 FEAT response for MDTM .................................. 9
130 3.4 MDTM Examples ........................................... 10
131 4 File SIZE ............................................... 11
132 4.1 Syntax .................................................. 11
133 4.2 Error responses ......................................... 11
134 4.3 FEAT response for SIZE .................................. 12
135 4.4 Size Examples ........................................... 12
136 5 Restart of Interrupted Transfer (REST) .................. 13
137 5.1 Restarting in STREAM Mode ............................... 13
138 5.2 Error Recovery and Restart .............................. 14
139 5.3 Syntax .................................................. 14
140 5.4 FEAT response for REST .................................. 16
141 5.5 REST Example ............................................ 16
142 6 Virtual FTP servers ..................................... 16
143 6.1 The HOST command ........................................ 18
144 6.2 Syntax of the HOST command .............................. 18
145 6.3 HOST command semantics .................................. 19
146 6.4 HOST command errors ..................................... 21
147 6.5 FEAT response for HOST command .......................... 22
148 7 A Trivial Virtual File Store (TVFS) ..................... 23
149 7.1 TVFS File Names ......................................... 23
150 7.2 TVFS Path Names ......................................... 24
151 7.3 FEAT Response for TVFS .................................. 25
152 7.4 OPTS for TVFS ........................................... 26
153 7.5 TVFS Examples ........................................... 26
154 8 Listings for Machine Processing (MLST and MLSD) ......... 28
155 8.1 Format of MLSx Requests ................................. 29
156 8.2 Format of MLSx Response ................................. 29
157 8.3 Filename encoding ....................................... 32
158 8.4 Format of Facts ......................................... 33
159 8.5 Standard Facts .......................................... 33
160 8.6 System Dependent and Local Facts ........................ 41
161 8.7 MLSx Examples ........................................... 42
162 8.8 FEAT response for MLSx .................................. 50
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172 8.9 OPTS parameters for MLST ................................ 51
173 9 Impact On Other FTP Commands ............................ 55
174 10 Character sets and Internationalization ................. 56
175 11 IANA Considerations ..................................... 56
176 11.1 The OS specific fact registry ........................... 56
177 11.2 The OS specific filetype registry ....................... 57
178 12 Security Considerations ................................. 57
179 13 References .............................................. 58
180 Acknowledgments ......................................... 59
181 Copyright ............................................... 60
182 Editors' Addresses ...................................... 60
187 1. Introduction
189 This document amends the File Transfer Protocol (FTP) [3]. Five new
190 commands are added: "SIZE", "HOST", "MDTM", "MLST", and "MLSD". The
191 existing command "REST" is modified. Of those, the "SIZE" and "MDTM"
192 commands, and the modifications to "REST" have been in wide use for
193 many years. The others are new.
195 These commands allow a client to restart an interrupted transfer in
196 transfer modes not previously supported in any documented way, to
197 support the notion of virtual hosts, and to obtain a directory
198 listing in a machine friendly, predictable, format.
200 An optional structure for the server's file store (NVFS) is also
201 defined, allowing servers that support such a structure to convey
202 that information to clients in a standard way, thus allowing clients
203 more certainty in constructing and interpreting path names.
205 2. Document Conventions
207 This document makes use of the document conventions defined in BCP14
208 [4]. That provides the interpretation of capitalized imperative
209 words like MUST, SHOULD, etc.
211 This document also uses notation defined in STD 9 [3]. In
212 particular, the terms "reply", "user", "NVFS", "file", "pathname",
213 "FTP commands", "DTP", "user-FTP process", "user-PI", "user-DTP",
214 "server-FTP process", "server-PI", "server-DTP", "mode", "type",
215 "NVT", "control connection", "data connection", and "ASCII", are all
216 used here as defined there.
218 Syntax required is defined using the Augmented BNF defined in [5].
219 Some general ABNF definitions are required throughout the document,
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229 those will be defined later in this section. At first reading, it
230 may be wise to simply recall that these definitions exist here, and
231 skip to the next section.
233 2.1. Basic Tokens
235 This document imports the core definitions given in Appendix A of
236 [5]. There definitions will be found for basic ABNF elements like
237 ALPHA, DIGIT, SP, etc. To that, the following terms are added for
238 use in this document.
240 TCHAR = VCHAR / SP / HTAB ; visible plus white space
241 RCHAR = ALPHA / DIGIT / "," / "." / ":" / "!" /
242 "@" / "#" / "$" / "%" / "^" /
243 "&" / "(" / ")" / "-" / "_" /
244 "+" / "?" / "/" / "\" / "'" /
245 DQUOTE ; <"> -- double quote character (%x22)
247 The VCHAR (from [5]), TCHAR, and RCHAR types give basic character
248 types from varying sub-sets of the ASCII character set for use in
249 various commands and responses.
251 token = 1*RCHAR
253 A "token" is a string whose precise meaning depends upon the context
254 in which it is used. In some cases it will be a value from a set of
255 possible values maintained elsewhere. In others it might be a string
256 invented by one party to an FTP conversation from whatever sources it
257 finds relevant.
259 Note that in ABNF, string literals are case insensitive. That
260 convention is preserved in this document, and implies that FTP
261 commands added by this specification have names that can be
262 represented in any case. That is, "MDTM" is the same as "mdtm",
263 "Mdtm" and "MdTm" etc. However note that ALPHA, in particular, is
264 case sensitive. That implies that a "token" is a case sensitive
265 value. That implication is correct.
267 2.2. Pathnames
269 Various FTP commands take pathnames as arguments, or return pathnames
270 in responses. When the MLST command is supported, as indicated in
271 the response to the FEAT command [6], pathnames are to be transferred
272 in one of the following two formats.
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286 pathname = utf-8-name / raw
287 utf-8-name = <a UTF-8 encoded Unicode string>
288 raw = <any string not being a valid UTF-8 encoding>
290 Which format is used is at the option of the user-PI or server-PI
291 sending the pathname. UTF-8 encodings [2] contain enough internal
292 structure that it is always, in practice, possible to determine
293 whether a UTF-8 or raw encoding has been used, in those cases where
294 it matters. While it is useful for the user-PI to be able to
295 correctly display a pathname received from the server-PI to the user,
296 it is far more important for the user-PI to be able to retain and
297 retransmit the identical pathname when required. Implementations are
298 advised against converting a UTF-8 pathname to a local encoding, and
299 then attempting to invert the encoding later. Note that ASCII is a
300 subset of UTF-8.
302 Unless otherwise specified, the pathname is terminated by the CRLF
303 that terminates the FTP command, or by the CRLF that ends a reply.
304 Any trailing spaces preceding that CRLF form part of the name.
305 Exactly one space will precede the pathname and serve as a separator
306 from the preceding syntax element. Any additional spaces form part
307 of the pathname. See [7] for a fuller explanation of the character
308 encoding issues. All implementations supporting MLST MUST support
309 [7].
311 Implementations should also beware that the control connection uses
312 Telnet NVT conventions [8], and that the Telnet IAC character, if
313 part of a pathname sent over the control connection, MUST be
314 correctly escaped as defined by the Telnet protocol.
316 Implementors should also be aware that although Telnet NVT
317 conventions are used over the control connections, Telnet option
318 negotiation MUST NOT be attempted. See section 4.1.2.12 of [9].
320 2.2.1. Pathname Syntax
322 Except where TVFS is supported (see section 7) this specification
323 imposes no syntax upon pathnames. Nor does it restrict the character
324 set from which pathnames are created. This does not imply that the
325 NVFS is required to make sense of all possible pathnames. Server-PIs
326 may restrict the syntax of valid pathnames in their NVFS in any
327 manner appropriate to their implementation or underlying file system.
328 Similarly, a server-PI may parse the pathname, and assign meaning to
329 the components detected.
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343 2.2.2. Wildcarding
345 For the commands defined in this specification, all pathnames are to
346 be treated literally. That is, for a pathname given as a parameter
347 to a command, the file whose name is identical to the pathname given
348 is implied. No characters from the pathname may be treated as
349 special or "magic", thus no pattern matching (other than for exact
350 equality) between the pathname given and the files present in the
351 NVFS of the Server-FTP is permitted.
353 Clients that desire some form of pattern matching functionality must
354 obtain a listing of the relevant directory, or directories, and
355 implement their own filename selection procedures.
357 2.3. Times
359 The syntax of a time value is:
361 time-val = 14DIGIT [ "." 1*DIGIT ]
363 The leading, mandatory, fourteen digits are to be interpreted as, in
364 order from the leftmost, four digits giving the year, with a range of
365 1000-9999, two digits giving the month of the year, with a range of
366 01-12, two digits giving the day of the month, with a range of 01-31,
367 two digits giving the hour of the day, with a range of 00-23, two
368 digits giving minutes past the hour, with a range of 00-59, and
369 finally, two digits giving seconds past the minute, with a range of
370 00-60 (with 60 being used only at a leap second). Years in the tenth
371 century, and earlier, cannot be expressed. This is not considered a
372 serious defect of the protocol.
374 The optional digits, which are preceded by a period, give decimal
375 fractions of a second. These may be given to whatever precision is
376 appropriate to the circumstance, however implementations MUST NOT add
377 precision to time-vals where that precision does not exist in the
378 underlying value being transmitted.
380 Symbolically, a time-val may be viewed as
382 YYYYMMDDHHMMSS.sss
384 The "." and subsequent digits ("sss") are optional. However the "."
385 MUST NOT appear unless at least one following digit also appears.
387 Time values are always represented in UTC (GMT), and in the Gregorian
388 calendar regardless of what calendar may have been in use at the date
389 and time indicated at the location of the server-PI.
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400 The technical differences between GMT, TAI, UTC, UT1, UT2, etc, are
401 not considered here. A server-FTP process should always use the same
402 time reference, so the times it returns will be consistent. Clients
403 are not expected to be time synchronized with the server, so the
404 possible difference in times that might be reported by the different
405 time standards is not considered important.
407 2.4. Server Replies
409 Section 4.2 of [3] defines the format and meaning of replies by the
410 server-PI to FTP commands from the user-PI. Those reply conventions
411 are used here without change.
413 error-response = error-code SP *TCHAR CRLF
414 error-code = ("4" / "5") 2DIGIT
416 Implementors should note that the ABNF syntax (which was not used in
417 [3]) used in this document, and other FTP related documents,
418 sometimes shows replies using the one line format. Unless otherwise
419 explicitly stated, that is not intended to imply that multi-line
420 responses are not permitted. Implementors should assume that, unless
421 stated to the contrary, any reply to any FTP command (including QUIT)
422 may be of the multi-line format described in [3].
424 Throughout this document, replies will be identified by the three
425 digit code that is their first element. Thus the term "500 reply"
426 means a reply from the server-PI using the three digit code "500".
428 3. File Modification Time (MDTM)
430 The FTP command, MODIFICATION TIME (MDTM), can be used to determine
431 when a file in the server NVFS was last modified. This command has
432 existed in many FTP servers for many years, as an adjunct to the REST
433 command for STREAM mode, thus is widely available. However, where
434 supported, the "modify" fact which can be provided in the result from
435 the new MLST command is recommended as a superior alternative.
437 When attempting to restart a RETRieve, if the User-FTP makes use of
438 the MDTM command, or "modify" fact, it can check and see if the
439 modification time of the source file is more recent than the
440 modification time of the partially transferred file. If it is, then
441 most likely the source file has changed and it would be unsafe to
442 restart the previously incomplete file transfer.
444 When attempting to restart a STORe, the User FTP can use the MDTM
445 command to discover the modification time of the partially
446 transferred file. If it is older than the modification time of the
447 file that is about to be STORed, then most likely the source file has
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457 changed and it would be unsafe to restart the file transfer.
459 Note that using MLST (described below) where available, can provide
460 this information, and much more, thus giving an even better
461 indication that a file has changed, and that restarting a transfer
462 would not give valid results.
464 Note that this is applicable to any RESTart attempt, regardless of
465 the mode of the file transfer.
467 3.1. Syntax
469 The syntax for the MDTM command is:
471 mdtm = "MdTm" SP pathname CRLF
473 As with all FTP commands, the "MDTM" command label is interpreted in
474 a case insensitive manner.
476 The "pathname" specifies an object in the NVFS which may be the
477 object of a RETR command. Attempts to query the modification time of
478 files that are unable to be retrieved generate undefined responses.
480 The server-PI will respond to the MDTM command with a 213 reply
481 giving the last modification time of the file whose pathname was
482 supplied, or a 550 reply if the file does not exist, the modification
483 time is unavailable, or some other error has occurred.
485 mdtm-response = "213" SP time-val CRLF /
486 error-response
488 3.2. Error responses
490 Where the command is correctly parsed, but the modification time is
491 not available, either because the pathname identifies no existing
492 entity, or because the information is not available for the entity
493 named, then a 550 reply should be sent. Where the command cannot be
494 correctly parsed, a 500 or 501 reply should be sent, as specified in
495 [3].
497 3.3. FEAT response for MDTM
499 When replying to the FEAT command [6], an FTP server process that
500 supports the MDTM command MUST include a line containing the single
501 word "MDTM". This MAY be sent in upper or lower case, or a mixture
502 of both (it is case insensitive) but SHOULD be transmitted in upper
503 case only. That is, the response SHOULD be
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514 C> Feat
515 S> 211- <any descriptive text>
516 S> ...
517 S> MDTM
518 S> ...
519 S> 211 End
521 The ellipses indicate place holders where other features may be
522 included, and are not required. The one space indentation of the
523 feature lines is mandatory [6].
525 3.4. MDTM Examples
527 If we assume the existence of three files, A B and C, and a directory
528 D, and no other files at all, then the MTDM command may behave as
529 indicated. The "C>" lines are commands from user-PI to server-PI,
530 the "S>" lines are server-PI replies.
532 C> MDTM A
533 S> 213 19980615100045.014
534 C> MDTM B
535 S> 213 19980615100045.014
536 C> MDTM C
537 S> 213 19980705132316
538 C> MDTM D
539 S> 550 D is not retrievable
540 C> MDTM E
541 S> 550 No file named "E"
542 C> mdtm file6
543 S> 213 19990929003355
544 C> MdTm 19990929043300 File6
545 S> 213 19991005213102
546 C> MdTm 19990929043300 file6
547 S> 550 19990929043300 file6: No such file or directory.
549 From that we can conclude that both A and B were last modified at the
550 same time (to the nearest millisecond), and that C was modified 21
551 days and several hours later.
553 The times are in GMT, so file A was modified on the 15th of June,
554 1998, at approximately 11am in London (summer time was then in
555 effect), or perhaps at 8pm in Melbourne, Australia, or at 6am in New
556 York. All of those represent the same absolute time of course. The
557 location where the file was modified, and consequently the local wall
558 clock time at that location, is not available.
560 There is no file named "E" in the current directory, but there are
561 files named both "file6" and "19990929043300 File6". The
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571 modification times of those files were obtained. There is no file
572 named "19990929043300 file6".
574 4. File SIZE
576 The FTP command, SIZE OF FILE (SIZE), is used to obtain the transfer
577 size of a file from the server-FTP process. That is, the exact
578 number of octets (8 bit bytes) which would be transmitted over the
579 data connection should that file be transmitted. This value will
580 change depending on the current STRUcture, MODE and TYPE of the data
581 connection, or a data connection which would be created were one
582 created now. Thus, the result of the SIZE command is dependent on
583 the currently established STRU, MODE and TYPE parameters.
585 The SIZE command returns how many octets would be transferred if the
586 file were to be transferred using the current transfer structure,
587 mode and type. This command is normally used in conjunction with the
588 RESTART (REST) command. The server-PI might need to read the
589 partially transferred file, do any appropriate conversion, and count
590 the number of octets that would be generated when sending the file in
591 order to correctly respond to this command. Estimates of the file
592 transfer size MUST NOT be returned, only precise information is
593 acceptable.
595 4.1. Syntax
597 The syntax of the SIZE command is:
599 size = "Size" SP pathname CRLF
601 The server-PI will respond to the SIZE command with a 213 reply
602 giving the transfer size of the file whose pathname was supplied, or
603 an error response if the file does not exist, the size is
604 unavailable, or some other error has occurred. The value returned is
605 in a format suitable for use with the RESTART (REST) command for mode
606 STREAM, provided the transfer mode and type are not altered.
608 size-response = "213" SP 1*DIGIT CRLF /
609 error-response
611 4.2. Error responses
613 Where the command is correctly parsed, but the size is not available,
614 either because the pathname identifies no existing entity, or because
615 the entity named cannot be transferred in the current MODE and TYPE
616 (or at all), then a 550 reply should be sent. Where the command
617 cannot be correctly parsed, a 500 or 501 reply should be sent, as
618 specified in [3].
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628 4.3. FEAT response for SIZE
630 When replying to the FEAT command [6], an FTP server process that
631 supports the SIZE command MUST include a line containing the single
632 word "SIZE". This word is case insensitive, and MAY be sent in any
633 mixture of upper or lower case, however it SHOULD be sent in upper
634 case. That is, the response SHOULD be
636 C> FEAT
637 S> 211- <any descriptive text>
638 S> ...
639 S> SIZE
640 S> ...
641 S> 211 END
643 The ellipses indicate place holders where other features may be
644 included, and are not required. The one space indentation of the
645 feature lines is mandatory [6].
647 4.4. Size Examples
649 Consider a text file "Example" stored on a Unix(TM) server where each
650 end of line is represented by a single octet. Assume the file
651 contains 112 lines, and 1830 octets total. Then the SIZE command
652 would produce:
654 C> TYPE I
655 S> 200 Type set to I.
656 C> size Example
657 S> 213 1830
658 C> TYPE A
659 S> 200 Type set to A.
660 C> Size Example
661 S> 213 1942
663 Notice that with TYPE=A the SIZE command reports an extra 112 octets.
664 Those are the extra octets that need to be inserted, one at the end
665 of each line, to provide correct end of line semantics for a transfer
666 using TYPE=A. Other systems might need to make other changes to the
667 transfer format of files when converting between TYPEs and MODEs.
668 The SIZE command takes all of that into account.
670 Since calculating the size of a file with this degree of precision
671 may take considerable effort on the part of the server-PI, user-PIs
672 should not used this command unless this precision is essential (such
673 as when about to restart an interrupted transfer). For other uses,
674 the "Size" fact of the MLST command (see section 8.5.7) ought be
675 requested.
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685 5. Restart of Interrupted Transfer (REST)
687 To avoid having to resend the entire file if the file is only
688 partially transferred, both sides need some way to be able to agree
689 on where in the data stream to restart the data transfer.
691 The FTP specification [3] includes three modes of data transfer,
692 Stream, Block and Compressed. In Block and Compressed modes, the
693 data stream that is transferred over the data connection is
694 formatted, allowing the embedding of restart markers into the stream.
695 The sending DTP can include a restart marker with whatever
696 information it needs to be able to restart a file transfer at that
697 point. The receiving DTP can keep a list of these restart markers,
698 and correlate them with how the file is being saved. To restart the
699 file transfer, the receiver just sends back that last restart marker,
700 and both sides know how to resume the data transfer. Note that there
701 are some flaws in the description of the restart mechanism in RFC 959
702 [3]. See section 4.1.3.4 of RFC 1123 [9] for the corrections.
704 5.1. Restarting in STREAM Mode
706 In Stream mode, the data connection contains just a stream of
707 unformatted octets of data. Explicit restart markers thus cannot be
708 inserted into the data stream, they would be indistinguishable from
709 data. For this reason, the FTP specification [3] did not provide the
710 ability to do restarts in stream mode. However, there is not really
711 a need to have explicit restart markers in this case, as restart
712 markers can be implied by the octet offset into the data stream.
714 Because the data stream defines the file in STREAM mode, a different
715 data stream would represent a different file. Thus, an offset will
716 always represent the same position within a file. On the other hand,
717 in other modes than STREAM, the same file can be transferred using
718 quite different octet sequences, and yet be reconstructed into the
719 one identical file. Thus an offset into the data stream in transfer
720 modes other than STREAM would not give an unambiguous restart point.
722 If the data representation TYPE is IMAGE, and the STRUcture is File,
723 for many systems the file will be stored exactly in the same format
724 as it is sent across the data connection. It is then usually very
725 easy for the receiver to determine how much data was previously
726 received, and notify the sender of the offset where the transfer
727 should be restarted. In other representation types and structures
728 more effort will be required, but it remains always possible to
729 determine the offset with finite, but perhaps non-negligible, effort.
730 In the worst case an FTP process may need to open a data connection
731 to itself, set the appropriate transfer type and structure, and
732 actually transmit the file, counting the transmitted octets.
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742 If the user-FTP process is intending to restart a retrieve, it will
743 directly calculate the restart marker, and send that information in
744 the RESTart command. However, if the user-FTP process is intending
745 to restart sending the file, it needs to be able to determine how
746 much data was previously sent, and correctly received and saved. A
747 new FTP command is needed to get this information. This is the
748 purpose of the SIZE command, as documented in section 4.
750 5.2. Error Recovery and Restart
752 STREAM MODE transfers with FILE STRUcture may be restarted even
753 though no restart marker has been transferred in addition to the data
754 itself. This is done by using the SIZE command, if needed, in
755 combination with the RESTART (REST) command, and one of the standard
756 file transfer commands.
758 When using TYPE ASCII or IMAGE, the SIZE command will return the
759 number of octets that would actually be transferred if the file were
760 to be sent between the two systems. I.e. with type IMAGE, the SIZE
761 normally would be the number of octets in the file. With type ASCII,
762 the SIZE would be the number of octets in the file including any
763 modifications required to satisfy the TYPE ASCII CR-LF end of line
764 convention.
766 5.3. Syntax
768 The syntax for the REST command when the current transfer mode is
769 STREAM is:
771 rest = "Rest" SP 1*DIGIT CRLF
773 The numeric value gives the number of octets of the immediately
774 following transfer to not actually send, effectively causing the
775 transmission to be restarted at a later point. A value of zero
776 effectively disables restart, causing the entire file to be
777 transmitted. The server-PI will respond to the REST command with a
778 350 reply, indicating that the REST parameter has been saved, and
779 that another command, which should be either RETR or STOR, should
780 then follow to complete the restart.
782 rest-response = "350" SP *TCHAR CRLF /
783 error-response
785 Server-FTP processes may permit transfer commands other than RETR and
786 STOR, such as APPE and STOU, to complete a restart, however, this is
787 not recommended. STOU (store unique) is undefined in this usage, as
788 storing the remainder of a file into a unique filename is rarely
789 going to be useful. If APPE (append) is permitted, it MUST act
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799 identically to STOR when a restart marker has been set. That is, in
800 both cases, octets from the data connection are placed into the file
801 at the location indicated by the restart marker value.
803 The REST command is intended to complete a failed transfer. Use with
804 RETR is comparatively well defined in all cases, as the client bears
805 the responsibility of merging the retrieved data with the partially
806 retrieved file. If it chooses to use the data obtained other than to
807 complete an earlier transfer, or if it chooses to re-retrieve data
808 that had been retrieved before, that is its choice. With STOR,
809 however, the server must insert the data into the file named. The
810 results are undefined if a client uses REST to do other than restart
811 to complete a transfer of a file which had previously failed to
812 completely transfer. In particular, if the restart marker set with a
813 REST command is not at the end of the data currently stored at the
814 server, as reported by the server, or if insufficient data are
815 provided in a STOR that follows a REST to extend the destination file
816 to at least its previous size, then the effects are undefined.
818 The REST command must be the last command issued before the data
819 transfer command which is to cause a restarted rather than complete
820 file transfer. The effect of issuing a REST command at any other
821 time is undefined. The server-PI may react to a badly positioned
822 REST command by issuing an error response to the following command,
823 not being a restartable data transfer command, or it may save the
824 restart value and apply it to the next data transfer command, or it
825 may silently ignore the inappropriate restart attempt. Because of
826 this, a user-PI that has issued a REST command, but which has not
827 successfully transmitted the following data transfer command for any
828 reason, should send another REST command before the next data
829 transfer command. If that transfer is not to be restarted, then
830 "REST 0" should be issued.
832 An error-response will follow a REST command only when the server
833 does not implement the command, or the restart marker value is
834 syntactically invalid for the current transfer mode. That is, in
835 STREAM mode, if something other than one or more digits appears in
836 the parameter to the REST command. Any other errors, including such
837 problems as restart marker out of range, should be reported when the
838 following transfer command is issued. Such errors will cause that
839 transfer request to be rejected with an error indicating the invalid
840 restart attempt.
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856 5.4. FEAT response for REST
858 Where a server-FTP process supports RESTart in STREAM mode, as
859 specified here, it MUST include in the response to the FEAT command
860 [6], a line containing exactly the string "REST STREAM". This string
861 is not case sensitive, but SHOULD be transmitted in upper case.
862 Where REST is not supported at all, or supported only in block or
863 compressed modes, the REST line MUST NOT be included in the FEAT
864 response. Where required, the response SHOULD be
866 C> feat
867 S> 211- <any descriptive text>
868 S> ...
869 S> REST STREAM
870 S> ...
871 S> 211 end
873 The ellipses indicate place holders where other features may be
874 included, and are not required. The one space indentation of the
875 feature lines is mandatory [6].
877 5.5. REST Example
879 Assume that the transfer of a largish file has previously been
880 interrupted after 802816 octets had been received, that the previous
881 transfer was with TYPE=I, and that it has been verified that the file
882 on the server has not since changed.
884 C> TYPE I
885 S> 200 Type set to I.
886 C> PORT 127,0,0,1,15,107
887 S> 200 PORT command successful.
888 C> REST 802816
889 S> 350 Restarting at 802816. Send STORE or RETRIEVE
890 C> RETR cap60.pl198.tar
891 S> 150 Opening BINARY mode data connection
892 [...]
893 S> 226 Transfer complete.
895 6. Virtual FTP servers
897 It has become common in the Internet for many domain names to be
898 allocated to a single IP address. This has introduced the concept of
899 a "virtual host", where a host appears to exist as an independent
900 entity, but in reality shares all of its resources with one, or more,
901 other such hosts.
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913 Such an arrangement presents some problems for FTP Servers, as all
914 the FTP Server can detect is an incoming FTP connection to a
915 particular IP address. That is, all domain names which share the IP
916 address also share the FTP server, and more importantly, its NVFS.
917 This means that the various virtual hosts cannot offer different
918 virtual file systems to clients, nor can they offer different
919 authentication systems.
921 No scheme can overcome this without modifications of some kind to the
922 user-PI and the user-FTP process. That process is the only entity
923 that knows which virtual host is required. It has performed the
924 domain name to IP address translation, and thus has the original
925 domain name available.
927 One method which could be used to allow a style of virtual host would
928 be for the client to simply send a "CWD" command after connecting,
929 using the virtual host name as the argument to the CWD command. This
930 would allow the server-FTP process to implement the file stores of
931 the virtual hosts as sub-directories in its NVFS. This is simple,
932 and supported by essentially all server-FTP implementations without
933 requiring any code changes.
935 While that method is simple to describe, and to implement, it suffers
936 from several drawbacks. First, the "CWD" command is available only
937 after the user-PI has authenticated itself to the server-FTP process.
938 Thus, all virtual hosts would be required to share a common
939 authentication scheme. Second, either the server-FTP process needs
940 to be modified to understand the special nature of this first CWD
941 command, negating most of the advantage of this scheme, or all users
942 must see the same identical NVFS view upon connecting (they must
943 connect in the same initial directory) or the NVFS must implement the
944 full set of virtual host directories at each possible initial
945 directory for any possible user, or the virtual host will not be
946 truly transparent. Third, and again unless the server is specially
947 modified, a user connecting this way to a virtual host would be able
948 to trivially move to any other virtual host supported at the same
949 server-FTP process, exposing the nature of the virtual host.
951 Other schemes overloading other existing FTP commands have also been
952 proposed. None of those have sufficient merit to be worth
953 discussion.
955 The conclusion from the examination of the possibilities seems to be
956 that to obtain an adequate emulation of "real" FTP servers, server
957 modifications to support virtual hosts are required. A new command
958 seems most likely to provide the support required.
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967 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
970 6.1. The HOST command
972 A new command "HOST" is added to the FTP command set to allow
973 server-FTP process to determine to which of possibly many virtual
974 hosts the client wishes to connect. This command is intended to be
975 issued before the user is authenticated, allowing the authentication
976 scheme, and set of legal users, to be dependent upon the virtual host
977 chosen. Server-FTP processes may, if they desire, permit the HOST
978 command to be issued after the user has been authenticated, or may
979 treat that as an erroneous sequence of commands. The behavior of the
980 server-FTP process which does allow late HOST commands is undefined.
981 One reasonable interpretation would be for the user-PI to be returned
982 to the state that existed after the TCP connection was first
983 established, before user authentication.
985 Servers should note that the response to the HOST command is a
986 sensible time to send their "welcome" message. This allows the
987 message to be personalized for any virtual hosts that are supported,
988 and also allows the client to have determined supported languages, or
989 representations, for the message, and other messages, via the FEAT
990 response, and selected an appropriate one via the LANG command. See
991 [7] for more information.
993 6.2. Syntax of the HOST command
995 The HOST command is defined as follows.
997 host-command = "Host" SP hostname CRLF
998 hostname = 1*DNCHAR 1*( "." 1*DNCHAR ) [ "." ]
999 DNCHAR = ALPHA / DIGIT / "-" / "_" / "$" /
1000 "!" / "%" / "[" / "]" / ":"
1001 host-response = host-ok / error-response
1002 host-ok = "220" [ SP *TCHAR ] CRLF
1004 As with all FTP commands, the "host" command word is case
1005 independent, and may be specified in any character case desired.
1007 The "hostname" given as a parameter specifies the virtual host to
1008 which access is desired. It should normally be the same name that
1009 was used to obtain the IP address to which the FTP control connection
1010 was made, after any client conversions to convert an abbreviated or
1011 local alias to a complete (fully qualified) domain name, but before
1012 resolving a DNS alias (owner of a CNAME resource record) to its
1013 canonical name.
1015 If the client was given a network literal address, and consequently
1016 was not required to derive it from a hostname, it should send the
1017 HOST command with the network address, as specified to it, enclosed
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1027 in brackets (after eliminating any syntax, which might also be
1028 brackets, but is not required to be, from which the server deduced
1029 that a literal address had been specified.) That is, for example
1031 HOST [10.1.2.3]
1033 should be sent if the client had been instructed to connect to
1034 "10.1.2.3", or "[10.1.2.3]", or perhaps even IPv4:10.1.2.3. The
1035 method of indicating to a client that a literal address is to be used
1036 is beyond the scope of this specification.
1038 The parameter is otherwise to be treated as a "complete domain name",
1039 as that term is defined in section 3.1 of RFC 1034 [10]. That
1040 implies that the name is to be treated as a case independent string,
1041 in that upper case ASCII characters are to be treated as equivalent
1042 to the corresponding lower case ASCII characters, but otherwise
1043 preserved as given. It also implies some limits on the length of the
1044 parameter and of the components that create its internal structure.
1045 Those limits are not altered in any way here.
1047 RFC 1034 imposes no other restrictions upon what kinds of names can
1048 be stored in the DNS. Nor does RFC 1035. This specification,
1049 however, allows only a restricted set of names for the purposes of
1050 the HOST command. Those restrictions can be inferred from the ABNF
1051 grammar given for the "hostname".
1053 6.3. HOST command semantics
1055 Upon receiving the HOST command, before authenticating the user-PI, a
1056 server-FTP process should validate that the hostname given represents
1057 a valid virtual host for that server, and if so, establish the
1058 appropriate environment for that virtual host. The meaning of that
1059 is not specified here, and may range from doing nothing at all, or
1060 performing a simple change of working directory, to much more
1061 elaborate state changes, as required.
1063 If the hostname specified is unknown at the server, or if the server
1064 is otherwise unwilling to treat the particular connection as a
1065 connection to the hostname specified, the server will respond with a
1066 504 reply.
1068 Note: servers may require that the name specified is in some sense
1069 equivalent to the particular network address that was used to reach
1070 the server.
1072 If the hostname specified would normally be acceptable, but for any
1073 reason is temporarily unavailable, the server SHOULD reply to the
1074 HOST command with a 434 reply.
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1084 The "220" reply code for the HOST command is the same as the code
1085 used on the initial connection established "welcome" message. This
1086 is done deliberately so as to allow the implementation to implement
1087 the front end FTP server as a wrapper which simply waits for the HOST
1088 command, and then invokes an older, RFC959 compliant, server in the
1089 appropriate environment for the particular hostname received.
1091 6.3.1. The REIN command
1093 As specified in [3], the REIN command returns the state of the
1094 connection to that it was immediately after the transport connection
1095 was opened. That is not changed here. The effect of a HOST command
1096 will be lost if a REIN command is performed, a new HOST command must
1097 be issued.
1099 Implementors of user-FTP should be aware that server-FTP
1100 implementations which implement the HOST command as a wrapper around
1101 older implementations will be unable to correctly implement the REIN
1102 command. In such an implementation, REIN will typically return the
1103 server-FTP to the state that existed immediately after the HOST
1104 command was issued, instead of to the state immediately after the
1105 connection was opened.
1107 6.3.2. User-PI usage of HOST
1109 A user-PI that conforms to this specification, MUST send the HOST
1110 command after opening the transport connection, or after any REIN
1111 command, before attempting to authenticate the user with the USER
1112 command.
1114 The following state diagram shows a typical sequence of flow of
1115 control, where the "B" (begin) state is assumed to occur after the
1116 transport connection has opened, or a REIN command has succeeded.
1117 Other commands (such as FEAT [6]) which require no authentication may
1118 have intervened. This diagram is modeled upon (and largely borrowed
1119 from) the similar diagram in section 6 of [3].
1121 In this diagram, a three digit reply indicates that precise server
1122 reply code, a single digit on a reply path indicates any server reply
1123 beginning with that digit, other than any three digit replies that
1124 might take another path.
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1138 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
1142 +---+ HOST +---+ 1,3,5
1143 | B |---------->| W |-----------------
1144 +---+ +---+ |
1145 | | |
1146 2,500,502 | | 4,501,503,504 |
1147 -------------- ------------- |
1148 | | |
1149 V 1 | V
1150 +---+ USER +---+-------------->+---+
1151 | |---------->| W | 2 ----->| E |
1152 +---+ +---+------ | --->+---+
1153 | | | | | |
1154 3 | | 4,5 | | | |
1155 -------------- ----- | | | |
1156 | | | | | |
1157 | | | | | |
1158 | --------- | |
1159 | 1| | | | |
1160 V | | | | |
1161 +---+ PASS +---+ 2 | ------->+---+
1162 | |---------->| W |-------------->| S |
1163 +---+ +---+ ----------->+---+
1164 | | | | | |
1165 3 | |4,5| | | |
1166 -------------- -------- | |
1167 | | | | | ----
1168 | | | | | |
1169 | ----------- |
1170 | 1,3| | | | |
1171 V | 2| | | V
1172 +---+ ACCT +---+-- | ------>+---+
1173 | |---------->| W | 4,5 --------->| F |
1174 +---+ +---+-------------->+---+
1176 6.4. HOST command errors
1178 The server-PI shall reply with a 500 or 502 reply if the HOST command
1179 is unrecognized or unimplemented. A 503 reply may be sent if the
1180 HOST command is given after a previous HOST command, or after a user
1181 has been authenticated. Alternately, the server may accept the
1182 command at such a time, with server defined behavior. A 501 reply
1183 should be sent if the hostname given is syntactically invalid, and a
1184 504 reply if a syntactically valid hostname is not a valid virtual
1185 host name for the server.
1187 In all such cases the server-FTP process should act as if no HOST
1188 command had been given.
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1198 A user-PI receiving a 500 or 502 reply should assume that the
1199 server-PI does not implement the HOST command style virtual server.
1200 It may then proceed to login as if the HOST command had succeeded,
1201 and perhaps, attempt a CWD command to the hostname after
1202 authenticating the user.
1204 A user-PI receiving some other error reply should assume that the
1205 virtual HOST is unavailable, and terminate communications.
1207 A server-PI that receives a USER command, beginning the
1208 authentication sequence, without having received a HOST command
1209 SHOULD NOT reject the USER command. Clients conforming to earlier
1210 FTP specifications do not send HOST commands. In this case the
1211 server may act as if some default virtual host had been explicitly
1212 selected, or may enter an environment different from that of all
1213 supported virtual hosts, perhaps one in which a union of all
1214 available accounts exists, and which presents a NVFS which appears to
1215 contain sub-directories containing the NVFS for all virtual hosts
1216 supported.
1218 6.5. FEAT response for HOST command
1220 A server-FTP process that supports the host command, and virtual FTP
1221 servers, MUST include in the response to the FEAT command [6], a
1222 feature line indicating that the HOST command is supported. This
1223 line should contain the single word "HOST". This MAY be sent in
1224 upper or lower case, or a mixture of both (it is case insensitive)
1225 but SHOULD be transmitted in upper case only. That is, the response
1226 SHOULD be
1228 C> Feat
1229 S> 211- <any descriptive text>
1230 S> ...
1231 S> HOST
1232 S> ...
1233 S> 211 End
1235 The ellipses indicate place holders where other features may be
1236 included, and are not required. The one space indentation of the
1237 feature lines is mandatory [6].
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1255 7. A Trivial Virtual File Store (TVFS)
1257 Traditionally, FTP has placed almost no constraints upon the file
1258 store (NVFS) provided by a server. This specification does not alter
1259 that. However, it has become common for servers to attempt to
1260 provide at least file system naming conventions modeled loosely upon
1261 those of the UNIX(TM) file system. That is, a tree structured file
1262 system, built of directories, each of which can contain other
1263 directories, or other kinds of files, or both. Each file and
1264 directory has a file name relative to the directory that contains it,
1265 except for the directory at the root of the tree, which is contained
1266 in no other directory, and hence has no name of its own.
1268 That which has so far been described is perfectly consistent with the
1269 standard FTP NVFS and access mechanisms. The "CWD" command is used
1270 to move from one directory to an embedded directory. "CDUP" may be
1271 provided to return to the parent directory, and the various file
1272 manipulation commands ("RETR", "STOR", the rename commands, etc) are
1273 used to manipulate files within the current directory.
1275 However, it is often useful to be able to reference files other than
1276 by changing directories, especially as FTP provides no guaranteed
1277 mechanism to return to a previous directory. The Trivial Virtual
1278 File Store (TVFS), if implemented, provides that mechanism.
1280 7.1. TVFS File Names
1282 Where a server implements the TVFS, no elementary filename shall
1283 contain the character "/". Where the underlying natural file store
1284 permits files, or directories, to contain the "/" character in their
1285 names, a server-PI implementing TVFS must encode that character in
1286 some manner whenever file or directory names are being returned to
1287 the user-PI, and reverse that encoding whenever such names are being
1288 accepted from the user-PI.
1290 The encoding method to be used is not specified here. Where some
1291 other character is illegal in file and directory names in the
1292 underlying file store, a simple transliteration may be sufficient.
1293 Where there is no suitable substitute character a more complex
1294 encoding scheme, possibly using an escape character, is likely to be
1295 required.
1297 With the one exception of the unnamed root directory, a TVFS file
1298 name may not be empty. That is, all other file names contain at
1299 least one character.
1301 With the sole exception of the "/" character, any valid IS10646
1302 character [11] may be used in a TVFS filename. When transmitted,
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1309 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
1312 file name characters are encoded using the UTF-8 encoding [2].
1314 7.2. TVFS Path Names
1316 A TVFS "Path Name" combines the file or directory name of a target
1317 file or directory, with the directory names of zero or more enclosing
1318 directories, so as to allow the target file or directory to be
1319 referenced other than when the server's "current working directory"
1320 is the directory directly containing the target file or directory.
1322 By definition, every TVFS file or directory name is also a TVFS path
1323 name. Such a path name is valid to reference the file from the
1324 directory containing the name, that is, when that directory is the
1325 server-FTP's current working directory.
1327 Other TVFS path names are constructed by prefixing a path name by a
1328 name of a directory from which the path is valid, and separating the
1329 two with the "/" character. Such a path name is valid to reference
1330 the file or directory from the directory containing the newly added
1331 directory name.
1333 Where a path name has been extended to the point where the directory
1334 added is the unnamed root directory, the path name will begin with
1335 the "/" character. Such a path is known as a fully qualified path
1336 name. Fully qualified paths may, obviously, not be further extended,
1337 as, by definition, no directory contains the root directory. Being
1338 unnamed, it cannot be represented in any other directory. A fully
1339 qualified path name is valid to reference the named file or directory
1340 from any location (that is, regardless of what the current working
1341 directory may be) in the virtual file store.
1343 Any path name which is not a fully qualified path name may be
1344 referred to as a "relative path name" and will only correctly
1345 reference the intended file when the current working directory of the
1346 server-FTP is a directory from which the relative path name is valid.
1348 As a special case, the path name "/" is defined to be a fully
1349 qualified path name referring to the root directory. That is, the
1350 root directory does not have a directory (or file) name, but does
1351 have a path name. This special path name may be used only as is as a
1352 reference to the root directory. It may not be combined with other
1353 path names using the rules above, as doing so would lead to a path
1354 name containing two consecutive "/" characters, which is an undefined
1355 sequence.
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1369 7.2.1. Notes
1371 + It is not required, or expected, that there be only one fully
1372 qualified path name that will reference any particular file or
1373 directory.
1374 + As a caveat, though the TVFS file store is basically tree
1375 structured, there is no requirement that any file or directory
1376 have only one parent directory.
1377 + As defined, no TVFS path name will ever contain two consecutive
1378 "/" characters. Such a name is not illegal however, and may be
1379 defined by the server for any purpose that suits it. Clients
1380 implementing this specification should not assume any semantics
1381 at all for such names.
1382 + Similarly, other than the special case path that refers to the
1383 root directory, no TVFS path name constructed as defined here
1384 will ever end with the "/" character. Such names are also not
1385 illegal, but are undefined.
1386 + While any legal IS10646 character is permitted to occur in a TVFS
1387 file or directory name, other than "/", server FTP
1388 implementations are not required to support all possible IS10646
1389 characters. The subset supported is entirely at the discretion
1390 of the server. The case (where it exists) of the characters that
1391 make up file, directory, and path names may be significant.
1392 Unless determined otherwise by means unspecified here, clients
1393 should assume that all such names are comprised of characters
1394 whose case is significant. Servers are free to treat case (or
1395 any other attribute) of a name as irrelevant, and hence map two
1396 names which appear to be distinct onto the same underlying file.
1397 + There are no defined "magic" names, like ".", ".." or "C:".
1398 Servers may implement such names, with any semantics they choose,
1399 but are not required to do so.
1400 + TVFS imposes no particular semantics or properties upon files,
1401 guarantees no access control schemes, or any of the other common
1402 properties of a file store. Only the naming scheme is defined.
1404 7.3. FEAT Response for TVFS
1406 In response to the FEAT command [6] a server that wishes to indicate
1407 support for the TVFS as defined here will include a line that begins
1408 with the four characters "TVFS" (in any case, or mixture of cases,
1409 upper case is not required). Servers SHOULD send upper case.
1411 Such a response to the FEAT command MUST NOT be returned unless the
1412 server implements TVFS as defined here.
1414 Later specifications may add to the TVFS definition. Such additions
1415 should be notified by means of additional text appended to the TVFS
1416 feature line. Such specifications, if any, will define the extra
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1423 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
1426 text.
1428 Until such a specification is defined, servers should not include
1429 anything after "TVFS" in the TVFS feature line. Clients, however,
1430 should be prepared to deal with arbitrary text following the four
1431 defined characters, and simply ignore it if unrecognized.
1433 A typical response to the FEAT command issued by a server
1434 implementing only this specification would be:
1436 C> feat
1437 S> 211- <any descriptive text>
1438 S> ...
1439 S> TVFS
1440 S> ...
1441 S> 211 end
1443 The ellipses indicate place holders where other features may be
1444 included, and are not required. The one space indentation of the
1445 feature lines is mandatory [6], and is not counted as one of the
1446 first four characters for the purposes of this feature listing.
1448 The TVFS feature adds no new commands to the FTP command repertoire.
1450 7.4. OPTS for TVFS
1452 There are no options in this TVFS specification, and hence there is
1453 no OPTS command defined.
1455 7.5. TVFS Examples
1457 Assume a TVFS file store is comprised of a root directory, which
1458 contains two directories (A and B) and two non-directory files (X and
1459 Y). The A directory contains two directories (C and D) and one other
1460 file (Z). The B directory contains just two non-directory files (P
1461 and Q) and the C directory also two non-directory files (also named P
1462 and Q, by chance). The D directory is empty, that is, contains no
1463 files or directories.
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1480 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
1483 This structure may depicted graphically as...
1485 (unnamed root)
1486 / | \ \
1487 / | \ \
1488 A X B Y
1489 /|\ / \
1490 / | \ / \
1491 C D Z P Q
1492 / \
1493 / \
1494 P Q
1496 Given this structure, the following fully qualified path names exist.
1498 /
1499 /A
1500 /B
1501 /X
1502 /Y
1503 /A/C
1504 /A/D
1505 /A/Z
1506 /A/C/P
1507 /A/C/Q
1508 /B/P
1509 /B/Q
1511 It is clear that none of the paths / /A /B or /A/D refer to the same
1512 directory, as the contents of each is different. Nor do any of / /A
1513 /A/C or /A/D. However /A/C and /B might be the same directory, there
1514 is insufficient information given to tell. Any of the other path
1515 names (/X /Y /A/Z /A/C/P /A/C/Q /B/P and /B/Q) may refer to the same
1516 underlying files, in almost any combination.
1518 If the current working directory of the server-FTP is /A then the
1519 following path names, in addition to all the fully qualified path
1520 names, are valid
1522 C
1523 D
1524 Z
1525 C/P
1526 C/Q
1528 These all refer to the same files or directories as the corresponding
1529 fully qualified path with "/A/" prepended.
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1540 That those path names all exist does not imply that the TVFS sever
1541 will necessarily grant any kind of access rights to the named paths,
1542 or that access to the same file via different path names will
1543 necessarily be granted equal rights.
1545 None of the following relative paths are valid when the current
1546 directory is /A
1548 A
1549 B
1550 X
1551 Y
1552 B/P
1553 B/Q
1554 P
1555 Q
1557 Any of those could be made valid by changing the server-FTP's current
1558 working directory to the appropriate directory. Note that the paths
1559 "P" and "Q" might refer to different files depending upon which
1560 directory is selected to cause those to become valid TVFS relative
1561 paths.
1563 8. Listings for Machine Processing (MLST and MLSD)
1565 The MLST and MLSD commands are intended to standardize the file and
1566 directory information returned by the Server-FTP process. These
1567 commands differ from the LIST command in that the format of the
1568 replies is strictly defined although extensible.
1570 Two commands are defined, MLST which provides data about exactly the
1571 object named on its command line, and no others. MLSD on the other
1572 hand will list the contents of a directory if a directory is named,
1573 otherwise a 501 reply will be returned. In either case, if no object
1574 is named, the current directory is assumed. That will cause MLST to
1575 send a one line response, describing the current directory itself,
1576 and MLSD to list the contents of the current directory.
1578 In the following, the term MLSx will be used wherever either MLST or
1579 MLSD may be inserted.
1581 The MLST and MLSD commands also extend the FTP protocol as presented
1582 in RFC 959 [3] and RFC 1123 [9] to allow that transmission of 8-bit
1583 data over the control connection. Note this is not specifying
1584 character sets which are 8-bit, but specifying that FTP
1585 implementations are to specifically allow the transmission and
1586 reception of 8-bit bytes, with all bits significant, over the control
1587 connection. That is, all 256 possible octet values are permitted.
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1594 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
1597 The MLSx command allows both UTF-8/Unicode and "raw" forms as
1598 arguments, and in responses both to the MLST and MLSD commands, and
1599 all other FTP commands which take pathnames as arguments.
1601 8.1. Format of MLSx Requests
1603 The MLST and MLSD commands each allow a single optional argument.
1604 This argument may be either a directory name or, for MLST only, a
1605 filename. For these purposes, a "filename" is the name of any entity
1606 in the server NVFS which is not a directory. Where TVFS is
1607 supported, any TVFS relative path name valid in the current working
1608 directory, or any TVFS fully qualified path name, may be given. If a
1609 directory name is given then MLSD must return a listing of the
1610 contents of the named directory, otherwise it issues a 501 reply, and
1611 does not open a data connection. In all cases for MLST, a single set
1612 of fact lines (usually a single fact line) containing the information
1613 about the named file or directory shall be returned over the control
1614 connection, without opening a data connection.
1616 If no argument is given then MLSD must return a listing of the
1617 contents of the current working directory, and MLST must return a
1618 listing giving information about the current working directory
1619 itself. For these purposes, the contents of a directory are whatever
1620 filenames (not pathnames) the server-PI will allow to be referenced
1621 when the current working directory is the directory named, and which
1622 the server-PI desires to reveal to the user-PI.
1624 No title, header, or summary, lines, or any other formatting, other
1625 than as is specified below, is ever returned in the output of an MLST
1626 or MLSD command.
1628 If the Client-FTP sends an invalid argument, the Server-FTP MUST
1629 reply with an error code of 501.
1631 The syntax for the MLSx command is:
1633 mlst = "MLst" [ SP pathname ] CRLF
1634 mlsd = "MLsD" [ SP pathname ] CRLF
1636 8.2. Format of MLSx Response
1638 The format of a response to an MLSx command is as follows:
1640 mlst-response = control-response / error-response
1641 mlsd-response = ( initial-response final-response ) /
1642 error-response
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1651 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
1654 control-response = "250-" [ response-message ] CRLF
1655 1*( SP entry CRLF )
1656 "250" [ SP response-message ] CRLF
1658 initial-response = "150" [ SP response-message ] CRLF
1659 final-response = "226" SP response-message CRLF
1661 response-message = *TCHAR
1663 data-response = *( entry CRLF )
1665 entry = [ facts ] SP pathname
1666 facts = 1*( fact ";" )
1667 fact = factname "=" value
1668 factname = "Size" / "Modify" / "Create" /
1669 "Type" / "Unique" / "Perm" /
1670 "Lang" / "Media-Type" / "CharSet" /
1671 os-depend-fact / local-fact
1672 os-depend-fact = <IANA assigned OS name> "." token
1673 local-fact = "X." token
1674 value = *RCHAR
1676 Upon receipt of a MLSx command, the server will verify the parameter,
1677 and if invalid return an error-response. For this purpose, the
1678 parameter should be considered to be invalid if the client issuing
1679 the command does not have permission to perform the request
1680 operation.
1682 If valid, then for an MLST command, the server-PI will send the first
1683 (leading) line of the control response, the entry for the pathname
1684 given, or the current directory if no pathname was provided, and the
1685 terminating line. Normally exactly one entry would be returned, more
1686 entries are permitted only when required to represent a file that is
1687 to have multiple "Type" facts returned.
1689 Note that for MLST the fact set is preceded by a space. That is
1690 provided to guarantee that the fact set cannot be accidentally
1691 interpreted as the terminating line of the control response, but is
1692 required even when that would not be possible. Exactly one space
1693 exists between the set of facts and the pathname. Where no facts are
1694 present, there will be exactly two leading spaces before the
1695 pathname. No spaces are permitted in the facts, any other spaces in
1696 the response are to be treated as being a part of the pathname.
1698 If the command was an MLSD command, the server will open a data
1699 connection as indicated in section 3.2 of RFC959 [3]. If that fails,
1700 the server will return an error-response. If all is OK, the server
1701 will return the initial-response, send the appropriate data-response
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1708 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
1711 over the new data connection, close that connection, and then send
1712 the final-response over the control connection. The grammar above
1713 defines the format for the data-response, which defines the format of
1714 the data returned over the data connection established.
1716 The data connection opened for a MLSD response shall be a connection
1717 as if the "TYPE L 8", "MODE S", and "STRU F" commands had been given,
1718 whatever FTP transfer type, mode and structure had actually been set,
1719 and without causing those settings to be altered for future commands.
1720 That is, this transfer type shall be set for the duration of the data
1721 connection established for this command only. While the content of
1722 the data sent can be viewed as a series of lines, implementations
1723 should note that there is no maximum line length defined.
1724 Implementations should be prepared to deal with arbitrarily long
1725 lines.
1727 The facts part of the specification would contain a series of "file
1728 facts" about the file or directory named on the same line. Typical
1729 information to be presented would include file size, last
1730 modification time, creation time, a unique identifier, and a
1731 file/directory flag.
1733 The complete format for a successful reply to the MLSD command would
1734 be:
1736 facts SP pathname CRLF
1737 facts SP pathname CRLF
1738 facts SP pathname CRLF
1739 ...
1741 Note that the format is intended for machine processing, not human
1742 viewing, and as such the format is very rigid. Implementations MUST
1743 NOT vary the format by, for example, inserting extra spaces for
1744 readability, replacing spaces by tabs, including header or title
1745 lines, or inserting blank lines, or in any other way alter this
1746 format. Exactly one space is always required after the set of facts
1747 (which may be empty). More spaces may be present on a line if, and
1748 only if, the file name presented contains significant spaces. The
1749 set of facts must not contain any spaces anywhere inside it. Facts
1750 should be provided in each output line only if they both provide
1751 relevant information about the file named on the same line, and they
1752 are in the set requested by the user-PI. There is no requirement
1753 that the same set of facts be provided for each file, or that the
1754 facts presented occur in the same order for each file.
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1768 8.3. Filename encoding
1770 An FTP implementation supporting the MLSx commands must be 8-bit
1771 clean. This is necessary in order to transmit UTF-8 encoded
1772 filenames. This specification recommends the use of UTF-8 encoded
1773 filenames. FTP implementations SHOULD use UTF-8 whenever possible to
1774 encourage the maximum interoperability.
1776 Filenames are not restricted to UTF-8, however treatment of arbitrary
1777 character encodings is not specified by this standard. Applications
1778 are encouraged to treat non-UTF-8 encodings of filenames as octet
1779 sequences.
1781 Note that this encoding is unrelated to that of the contents of the
1782 file, even if the file contains character data.
1784 Further information about filename encoding for FTP may be found in
1785 "Internationalization of the File Transfer Protocol" [7].
1787 8.3.1. Notes about the Filename
1789 The filename returned in the MLST response should be the same name as
1790 was specified in the MLST command, or, where TVFS is supported, a
1791 fully qualified TVFS path naming the same file. Where no argument
1792 was given to the MLST command, the server-PI may either include an
1793 empty filename in the response, or it may supply a name that refers
1794 to the current directory, if such a name is available. Where TVFS is
1795 supported, a fully qualified path name of the current directory
1796 SHOULD be returned.
1798 Filenames returned in the output from an MLSD command SHOULD be
1799 unqualified names within the directory named, or the current
1800 directory if no argument was given. That is, the directory named in
1801 the MLSD command SHOULD NOT appear as a component of the filenames
1802 returned.
1804 If the server-FTP process is able, and the "type" fact is being
1805 returned, it MAY return in the MLSD response, an entry whose type is
1806 "cdir", which names the directory from which the contents of the
1807 listing were obtained. Where TVFS is supported, the name MAY be the
1808 fully qualified path name of the directory, or MAY be any other path
1809 name which is valid to refer to that directory from the current
1810 working directory of the server-FTP. Where more than one name
1811 exists, multiple of these entries may be returned. In a sense, the
1812 "cdir" entry can be viewed as a heading for the MLSD output.
1813 However, it is not required to be the first entry returned, and may
1814 occur anywhere within the listing.
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1825 When TVFS is supported, a user-PI can refer to any file or directory
1826 in the listing by combining a type "cdir" name, with the appropriate
1827 name from the directory listing using the procedure defined in
1828 section 7.2.
1830 Alternatively, whether TVFS is supported or not, the user-PI can
1831 issue a CWD command ([3]) giving a name of type "cdir" from the
1832 listing returned, and from that point reference the files returned in
1833 the MLSD response from which the cdir was obtained by using the
1834 filename components of the listing.
1836 8.4. Format of Facts
1838 The "facts" for a file in a reply to a MLSx command consist of
1839 information about that file. The facts are a series of keyword=value
1840 pairs each followed by semi-colon (";") characters. An individual
1841 fact may not contain a semi-colon in its name or value. The complete
1842 series of facts may not contain the space character. See the
1843 definition or "RCHAR" in section 2.1 for a list of the characters
1844 that can occur in a fact value. Not all are applicable to all facts.
1846 A sample of a typical series of facts would be: (spread over two
1847 lines for presentation here only)
1849 size=4161;lang=en-US;modify=19970214165800;create=19961001124534;
1850 type=file;x.myfact=foo,bar;
1852 8.5. Standard Facts
1854 This document defines a standard set of facts as follows:
1856 size -- Size in octets
1857 modify -- Last modification time
1858 create -- Creation time
1859 type -- Entry type
1860 unique -- Unique id of file/directory
1861 perm -- File permissions, whether read, write, execute is
1862 allowed for the login id.
1863 lang -- Language of the filename per IANA[12] registry.
1864 media-type -- MIME media-type of file contents per IANA registry.
1865 charset -- Character set per IANA registry (if not UTF-8)
1867 Fact names are case-insensitive. Size, size, SIZE, and SiZe are the
1868 same fact.
1870 Further operating system specific keywords could be specified by
1871 using the IANA operating system name as a prefix (examples only):
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1882 OS/2.ea -- OS/2 extended attributes
1883 MACOS.rf -- MacIntosh resource forks
1884 UNIX.mode -- Unix file modes (permissions)
1886 Implementations may define keywords for experimental, or private use.
1887 All such keywords MUST begin with the two character sequence "x.".
1888 As type names are case independent, "x." and "X." are equivalent.
1889 For example:
1891 x.ver -- Version information
1892 x.desc -- File description
1893 x.type -- File type
1895 8.5.1. The type Fact
1897 The type fact needs a special description. Part of the problem with
1898 current practices is deciding when a file is a directory. If it is a
1899 directory, is it the current directory, a regular directory, or a
1900 parent directory? The MLST specification makes this unambiguous
1901 using the type fact. The type fact given specifies information about
1902 the object listed on the same line of the MLST response.
1904 Five values are possible for the type fact:
1906 file -- a file entry
1907 cdir -- the listed directory
1908 pdir -- a parent directory
1909 dir -- a directory or sub-directory
1910 OS.name=type -- an OS or file system dependent file type
1912 The syntax is defined to be:
1914 type-fact = type-label "=" type-val
1915 type-label = "Type"
1916 type-val = "File" / "cdir" / "pdir" / "dir" /
1917 os-type
1919 8.5.1.1. type=file
1921 The presence of the type=file fact indicates the listed entry is a
1922 file containing non-system data. That is, it may be transferred from
1923 one system to another of quite different characteristics, and perhaps
1924 still be meaningful.
1926 8.5.1.2. type=cdir
1928 The type=cdir fact indicates the listed entry contains a pathname of
1929 the directory whose contents are listed. An entry of this type will
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1939 only be returned as a part of the result of an MLSD command when the
1940 type fact is included, and provides a name for the listed directory,
1941 and facts about that directory. In a sense, it can be viewed as
1942 representing the title of the listing, in a machine friendly format.
1943 It may appear at any point of the listing, it is not restricted to
1944 appearing at the start, though frequently may do so, and may occur
1945 multiple times. It MUST NOT be included if the type fact is not
1946 included, or there would be no way for the user-PI to distinguish the
1947 name of the directory from an entry in the directory.
1949 Where TVFS is supported by the server-FTP, this name may be used to
1950 construct path names with which to refer to the files and directories
1951 returned in the same MLSD output (see section 7.2). These path names
1952 are only expected to work when the server-PI's position in the NVFS
1953 file tree is the same as its position when the MLSD command was
1954 issued, unless a fully qualified path name results.
1956 Where TVFS is not supported, the only defined semantics associated
1957 with a "type=cdir" entry are that, provided the current working
1958 directory of the server-PI has not been changed, a pathname of type
1959 "cdir" may be used as an argument to a CWD command, which will cause
1960 the current directory of the server-PI to change so that the
1961 directory which was listed in its current working directory.
1963 8.5.1.3. type=dir
1965 If present, the type=dir entry gives the name of a directory. Such
1966 an entry typically cannot be transferred from one system to another
1967 using RETR, etc, but should (permissions permitting) be able to be
1968 the object of an MLSD command.
1970 8.5.1.4. type=pdir
1972 If present, which will occur only in the response to a MLSD command
1973 when the type fact is included, the type=pdir entry represents a
1974 pathname of the parent directory of the listed directory. As well as
1975 having the properties of a type=dir, a CWD command that uses the
1976 pathname from this entry should change the user to a parent directory
1977 of the listed directory. If the listed directory is the current
1978 directory, a CDUP command may also have the effect of changing to the
1979 named directory. User-FTP processes should note not all responses
1980 will include this information, and that some systems may provide
1981 multiple type=pdir responses.
1983 Where TVFS is supported, a "type=pdir" name may be a relative path
1984 name, or a fully qualified path name. A relative path name will be
1985 relative to the directory being listed, not to the current directory
1986 of the server-PI at the time.
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1996 For the purposes of this type value, a "parent directory" is any
1997 directory in which there is an entry of type=dir which refers to the
1998 directory in which the type=pdir entity was found. Thus it is not
1999 required that all entities with type=pdir refer to the same
2000 directory. The "unique" fact (if supported) can be used to determine
2001 whether there is a relationship between the type=pdir entries or not.
2003 8.5.1.5. System defined types
2005 Files types that are specific to a specific operating system, or file
2006 system, can be encoded using the "OS." type names. The format is:
2008 os-type = "OS." os-name "=" os-type
2009 os-name = <an IANA registered operating system name>
2010 os-type = token
2012 The "os-name" indicates the specific system type which supports the
2013 particular localtype. OS specific types are registered by the IANA
2014 using the procedures specified in section 11. The "os-type" provides
2015 the system dependent information as to the type of the file listed.
2016 The os-name and os-type strings in an os-type are case independent.
2017 "OS.unix=block" and "OS.Unix=BLOCK" represent the same type (or
2018 would, if such a type were registered.)
2020 Note: Where the underlying system supports a file type which is
2021 essentially an indirect pointer to another file, the NVFS
2022 representation of that type should normally be to represent the file
2023 which the reference indicates. That is, the underlying basic file
2024 will appear more than once in the NVFS, each time with the "unique"
2025 fact (see immediately following section) containing the same value,
2026 indicating that the same file is represented by all such names.
2027 User-PIs transferring the file need then transfer it only once, and
2028 then insert their own form of indirect reference to construct
2029 alternate names where desired, or perhaps even copy the local file if
2030 that is the only way to provide two names with the same content. A
2031 file which would be a reference to another file, if only the other
2032 file actually existed, may be represented in any OS dependent manner
2033 appropriate, or not represented at all.
2035 8.5.1.6. Multiple types
2037 Where a file is such that it may validly, and sensibly, treated by
2038 the server-PI as being of more than one of the above types, then
2039 multiple entries should be returned, each with its own "Type" fact of
2040 the appropriate type, and each containing the same pathname. This
2041 may occur, for example, with a structured file, which may contain
2042 sub-files, and where the server-PI permits the structured file to be
2043 treated as a unit, or treated as a directory allowing the sub-files
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2050 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2053 within it to be referenced.
2055 8.5.2. The unique Fact
2057 The unique fact is used to present a unique identifier for a file or
2058 directory in the NVFS accessed via a server-FTP process. The value
2059 of this fact should be the same for any number of pathnames that
2060 refer to the same underlying file. The fact should have different
2061 values for names which reference distinct files. The mapping between
2062 files, and unique fact tokens should be maintained, and remain
2063 consistent, for at least the lifetime of the control connection from
2064 user-PI to server-PI.
2066 unique-fact = "Unique" "=" token
2068 This fact would be expected to be used by Server-FTPs whose host
2069 system allows things such as symbolic links so that the same file may
2070 be represented in more than one directory on the server. The only
2071 conclusion that should be drawn is that if two different names each
2072 have the same value for the unique fact, they refer to the same
2073 underlying object. The value of the unique fact (the token) should
2074 be considered an opaque string for comparison purposes, and is a case
2075 dependent value. The tokens "A" and "a" do not represent the same
2076 underlying object.
2078 8.5.3. The modify Fact
2080 The modify fact is used to determine the last time the content of the
2081 file (or directory) indicated was modified. Any change of substance
2082 to the file should cause this value to alter. That is, if a change
2083 is made to a file such that the results of a RETR command would
2084 differ, then the value of the modify fact should alter. User-PIs
2085 should not assume that a different modify fact value indicates that
2086 the file contents are necessarily different than when last retrieved.
2087 Some systems may alter the value of the modify fact for other
2088 reasons, though this is discouraged wherever possible. Also a file
2089 may alter, and then be returned to its previous content, which would
2090 often be indicated as two incremental alterations to the value of the
2091 modify fact.
2093 For directories, this value should alter whenever a change occurs to
2094 the directory such that different filenames would (or might) be
2095 included in MLSD output of that directory.
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2107 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2110 modify-fact = "Modify" "=" time-val
2112 8.5.4. The create Fact
2114 The create fact indicates when a file, or directory, was first
2115 created. Exactly what "creation" is for this purpose is not
2116 specified here, and may vary from server to server. About all that
2117 can be said about the value returned is that it can never indicate a
2118 later time than the modify fact.
2120 create-fact = "Create" "=" time-val
2122 Implementation Note: Implementors of this fact on UNIX(TM) systems
2123 should note that the unix "stat" "st_ctime" field does not give
2124 creation time, and that unix file systems do not record creation
2125 time at all. Unix (and POSIX) implementations will normally not
2126 include this fact.
2128 8.5.5. The perm Fact
2130 The perm fact is used to indicate access rights the current FTP user
2131 has over the object listed. Its value is always an unordered
2132 sequence of alphabetic characters.
2134 perm-fact = "Perm" "=" *pvals
2135 pvals = "a" / "c" / "d" / "e" / "f" /
2136 "l" / "m" / "p" / "r" / "w"
2138 There are ten permission indicators currently defined. Many are
2139 meaningful only when used with a particular type of object. The
2140 indicators are case independent, "d" and "D" are the same indicator.
2142 The "a" permission applies to objects of type=file, and indicates
2143 that the APPE (append) command may be applied to the file named.
2145 The "c" permission applies to objects of type=dir (and type=pdir,
2146 type=cdir). It indicates that files may be created in the directory
2147 named. That is, that a STOU command is likely to succeed, and that
2148 STOR and APPE commands might succeed if the file named did not
2149 previously exist, but is to be created in the directory object that
2150 has the "c" permission. It also indicates that the RNTO command is
2151 likely to succeed for names in the directory.
2153 The "d" permission applies to all types. It indicates that the
2154 object named may be deleted, that is, that the RMD command may be
2155 applied to it if it is a directory, and otherwise that the DELE
2156 command may be applied to it.
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2167 The "e" permission applies to the directory types. When set on an
2168 object of type=dir, type=cdir, or type=pdir it indicates that a CWD
2169 command naming the object should succeed, and the user should be able
2170 to enter the directory named. For type=pdir it also indicates that
2171 the CDUP command may succeed (if this particular pathname is the one
2172 to which a CDUP would apply.)
2174 The "f" permission for objects indicates that the object named may be
2175 renamed - that is, may be the object of an RNFR command.
2177 The "l" permission applies to the directory file types, and indicates
2178 that the listing commands, LIST, NLST, and MLSD may be applied to the
2179 directory in question.
2181 The "m" permission applies to directory types, and indicates that the
2182 MKD command may be used to create a new directory within the
2183 directory under consideration.
2185 The "p" permission applies to directory types, and indicates that
2186 objects in the directory may be deleted, or (stretching naming a
2187 little) that the directory may be purged. Note: it does not indicate
2188 that the RMD command may be used to remove the directory named
2189 itself, the "d" permission indicator indicates that.
2191 The "r" permission applies to type=file objects, and for some
2192 systems, perhaps to other types of objects, and indicates that the
2193 RETR command may be applied to that object.
2195 The "w" permission applies to type=file objects, and for some
2196 systems, perhaps to other types of objects, and indicates that the
2197 STOR command may be applied to the object named.
2199 Note: That a permission indicator is set can never imply that the
2200 appropriate command is guaranteed to work - just that it might.
2201 Other system specific limitations, such as limitations on
2202 available space for storing files, may cause an operation to
2203 fail, where the permission flags may have indicated that it was
2204 likely to succeed. The permissions are a guide only.
2206 Implementation note: The permissions are described here as they apply
2207 to FTP commands. They may not map easily into particular
2208 permissions available on the server's operating system. Servers
2209 are expected to synthesize these permission bits from the
2210 permission information available from operating system. For
2211 example, to correctly determine whether the "D" permission bit
2212 should be set on a directory for a server running on the
2213 UNIX(TM) operating system, the server should check that the
2214 directory named is empty, and that the user has write permission
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2221 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2224 on both the directory under consideration, and its parent
2225 directory.
2227 Some systems may have more specific permissions than those
2228 listed here, such systems should map those to the flags defined
2229 as best they are able. Other systems may have only more broad
2230 access controls. They will generally have just a few possible
2231 permutations of permission flags, however they should attempt to
2232 correctly represent what is permitted.
2234 8.5.6. The lang Fact
2236 The lang fact describes the natural language of the filename for use
2237 in display purposes. Values used here should be taken from the
2238 language registry of the IANA. See [13] for the syntax, and
2239 procedures, related to language tags.
2241 lang-fact = "Lang" "=" token
2243 Server-FTP implementations MUST NOT guess language values. Language
2244 values must be determined in an unambiguous way such as file system
2245 tagging of language or by user configuration. Note that the lang
2246 fact provides no information at all about the content of a file, only
2247 about the encoding of its name.
2249 8.5.7. The size Fact
2251 The size fact applies to non-directory file types and should always
2252 reflect the approximate size of the file. This should be as accurate
2253 as the server can make it, without going to extraordinary lengths,
2254 such as reading the entire file. The size is expressed in units of
2255 octets of data in the file.
2257 Given limitations in some systems, Client-FTP implementations must
2258 understand this size may not be precise and may change between the
2259 time of a MLST and RETR operation.
2261 Clients that need highly accurate size information for some
2262 particular reason should use the SIZE command as defined in section
2263 4. The most common need for this accuracy is likely to be in
2264 conjunction with the REST command described in section 5. The size
2265 fact, on the other hand, should be used for purposes such as
2266 indicating to a human user the approximate size of the file to be
2267 transferred, and perhaps to give an idea of expected transfer
2268 completion time.
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2278 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2281 size-fact = "Size" "=" 1*DIGIT
2283 8.5.8. The media-type Fact
2285 The media-type fact represents the IANA media type of the file named,
2286 and applies only to non-directory types. The list of values used
2287 must follow the guidelines set by the IANA registry.
2289 media-type = "Media-Type" "=" <per IANA guidelines>
2291 Server-FTP implementations MUST NOT guess media type values. Media
2292 type values must be determined in an unambiguous way such as file
2293 system tagging of media-type or by user configuration. This fact
2294 gives information about the content of the file named. Both the
2295 primary media type, and any appropriate subtype should be given,
2296 separated by a slash "/" as is traditional.
2298 8.5.9. The charset Fact
2300 The charset fact provides the IANA character set name, or alias, for
2301 the encoded pathnames in a MLSx response. The default character set
2302 is UTF-8 unless specified otherwise. FTP implementations SHOULD use
2303 UTF-8 if possible to encourage maximum interoperability. The value
2304 of this fact applies to the pathname only, and provides no
2305 information about the contents of the file.
2307 charset-type = "Charset" "=" token
2309 8.5.10. Required facts
2311 Servers are not required to support any particular set of the
2312 available facts. However, servers SHOULD, if conceivably possible,
2313 support at least the type, perm, size, unique, and modify facts.
2315 8.6. System Dependent and Local Facts
2317 By using an system dependent fact, or a local fact, a server-PI may
2318 communicate to the user-PI information about the file named which is
2319 peculiar to the underlying file system.
2321 8.6.1. System Dependent Facts
2323 System dependent fact names are labeled by prefixing a label
2324 identifying the specific information returned by the name of the
2325 appropriate operating system from the IANA maintained list of
2326 operating system names.
2332 Elz & Hethmon [Expires April 2000] [Page 41]
2335 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2338 The value of an OS dependent fact may be whatever is appropriate to
2339 convey the information available. It must be encoded as a "token" as
2340 defined in section 2.1 however.
2342 In order to allow reliable interoperation between users of system
2343 dependent facts, the IANA will maintain a registry of system
2344 dependent fact names, their syntax, and the interpretation to be
2345 given to their values. Registrations of system dependent facts are
2346 to be accomplished according to the procedures of section 11.
2348 8.6.2. Local Facts
2350 Implementations may also make available other facts of their own
2351 choosing. As the method of interpretation of such information will
2352 generally not be widely understood, server-PIs should be aware that
2353 clients will typically ignore any local facts provided. As there is
2354 no registration of locally defined facts, it is entirely possible
2355 that different servers will use the same local fact name to provide
2356 vastly different information. Hence user-PIs should be hesitant
2357 about making any use of any information in a locally defined fact
2358 without some other specific assurance that the particular fact is one
2359 that they do comprehend.
2361 Local fact names all begin with the sequence "X.". The rest of the
2362 name is a "token" (see section 2.1). The value of a local fact can
2363 be anything at all, provided it can be encoded as a "token".
2365 8.7. MLSx Examples
2367 The following examples are all taken from dialogues between existing
2368 FTP clients and servers. Because of this, not all possible
2369 variations of possible response formats are shown in the examples.
2370 This should not be taken as limiting the options of other server
2371 implementors. Where the examples show OS dependent information, that
2372 is to be treated as being purely for the purposes of demonstration of
2373 some possible OS specific information that could be defined. As at
2374 the time of the writing of this document, no OS specific facts or
2375 file types have been defined, the examples shown here should not be
2376 treated as in any way to be preferred over other possible similar
2377 definitions. Consult the IANA registries to determine what types and
2378 facts have been defined.
2380 In the examples shown, only relevant commands and responses have been
2381 included. This is not to imply that other commands (including
2382 authentication, directory modification, PORT or PASV commands, or
2383 similar) would not be present in an actual connection, or were not,
2384 in fact, actually used in the examples before editing. Note also
2385 that the formats shown are those that are transmitted between client
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2392 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2395 and server, not formats which would normally ever be reported to the
2396 user of the client.
2398 In the examples, lines that begin "C> " were sent over the control
2399 connection from the client to the server, lines that begin "S> " were
2400 sent over the control connection from the server to the client, and
2401 lines that begin "D> " were sent from the server to the client over a
2402 data connection created just to send those lines and closed
2403 immediately after. No examples here show data transferred over a
2404 data connection from the client to the server. In all cases, the
2405 prefixes shown above, including the one space, have been added for
2406 the purposes of this document, and are not a part of the data
2407 exchanged between client and server.
2409 8.7.1. Simple MLST
2411 C> PWD
2412 S> 257 "/tmp" is current directory.
2413 C> MLst cap60.pl198.tar.gz
2414 S> 250- Listing cap60.pl198.tar.gz
2415 S> Type=file;Size=1024990;Perm=r; /tmp/cap60.pl198.tar.gz
2416 S> 250 End
2418 The client first asked to be told the current directory of the
2419 server. This was purely for the purposes of clarity of this example.
2420 The client then requested facts about a specific file. The server
2421 returned the "250-" first control-response line, followed by a single
2422 line of facts about the file, followed by the terminating "250 "
2423 line. The text on the control-response line and the terminating line
2424 can be anything the server decides to send. Notice that the fact
2425 line is indented by a single space. Notice also that there are no
2426 spaces in the set of facts returned, until the single space before
2427 the filename. The filename returned on the fact line is a fully
2428 qualified pathname of the file listed. The facts returned show that
2429 the line refers to a file, that file contains approximately 1024990
2430 bytes, though more or less than that may be transferred if the file
2431 is retrieved, and a different number may be required to store the
2432 file at the client's file store, and the connected user has
2433 permission to retrieve the file but not to do anything else
2434 particularly interesting.
2436 8.7.2. MLST of a directory
2438 C> PWD
2439 S> 257 "/" is current directory.
2440 C> MLst tmp
2441 S> 250- Listing tmp
2442 S> Type=dir;Modify=19981107085215;Perm=el; /tmp
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2449 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2452 S> 250 End
2454 Again the PWD is just for the purposes of demonstration for the
2455 example. The MLST fact line this time shows that the file listed is
2456 a directory, that it was last modified at 08:52:15 on the 7th of
2457 November, 1998 UTC, and that the user has permission to enter the
2458 directory, and to list its contents, but not to modify it in any way.
2459 Again, the fully qualified path name of the directory listed is
2460 given.
2462 8.7.3. MLSD of a directory
2464 C> MLSD tmp
2465 S> 150 BINARY connection open for MLSD tmp
2466 D> Type=cdir;Modify=19981107085215;Perm=el; tmp
2467 D> Type=cdir;Modify=19981107085215;Perm=el; /tmp
2468 D> Type=pdir;Modify=19990112030508;Perm=el; ..
2469 D> Type=file;Size=25730;Modify=19940728095854;Perm=; capmux.tar.z
2470 D> Type=file;Size=1830;Modify=19940916055648;Perm=r; hatch.c
2471 D> Type=file;Size=25624;Modify=19951003165342;Perm=r; MacIP-02.txt
2472 D> Type=file;Size=2154;Modify=19950501105033;Perm=r; uar.netbsd.patch
2473 D> Type=file;Size=54757;Modify=19951105101754;Perm=r; iptnnladev.1.0.sit.hqx
2474 D> Type=file;Size=226546;Modify=19970515023901;Perm=r; melbcs.tif
2475 D> Type=file;Size=12927;Modify=19961025135602;Perm=r; tardis.1.6.sit.hqx
2476 D> Type=file;Size=17867;Modify=19961025135602;Perm=r; timelord.1.4.sit.hqx
2477 D> Type=file;Size=224907;Modify=19980615100045;Perm=r; uar.1.2.3.sit.hqx
2478 D> Type=file;Size=1024990;Modify=19980130010322;Perm=r; cap60.pl198.tar.gz
2479 S> 226 MLSD completed
2481 In this example notice that there is no leading space on the fact
2482 lines returned over the data connection. Also notice that two lines
2483 of "type=cdir" have been given. These show two alternate names for
2484 the directory listed, one a fully qualified pathname, and the other a
2485 local name relative to the servers current directory when the MLSD
2486 was performed. Note that all other filenames in the output are
2487 relative to the directory listed, though the server could, if it
2488 chose, give a fully qualified path name for the "type=pdir" line.
2489 This server has chosen not to. The other files listed present a
2490 fairly boring set of files that are present in the listed directory.
2491 Note that there is no particular order in which they are listed.
2492 They are not sorted by filename, by size, or by modify time. Note
2493 also that the "perm" fact has an empty value for the file
2494 "capmux.tar.z" indicating that the connected user has no permissions
2495 at all for that file. This server has chosen to present the "cdir"
2496 and "pdir" lines before the lines showing the content of the
2497 directory, it is not required to do so. The "size" fact does not
2498 provide any meaningful information for a directory, so is not
2499 included in the fact lines for the directory types shown.
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2506 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2509 8.7.4. A more complex example
2511 C> MLst test
2512 S> 250- Listing test
2513 S> Type=dir;Perm=el;Unique=keVO1+ZF4 test
2514 S> 250 End
2515 C> MLSD test
2516 S> 150 BINARY connection open for MLSD test
2517 D> Type=cdir;Perm=el;Unique=keVO1+ZF4; test
2518 D> Type=pdir;Perm=e;Unique=keVO1+d?3; ..
2519 D> Type=OS.unix=slink:/foobar;Perm=;Unique=keVO1+4G4; foobar
2520 D> Type=OS.unix=chr-13/29;Perm=;Unique=keVO1+5G4; device
2521 D> Type=OS.unix=blk-11/108;Perm=;Unique=keVO1+6G4; block
2522 D> Type=file;Perm=awr;Unique=keVO1+8G4; writable
2523 D> Type=dir;Perm=cpmel;Unique=keVO1+7G4; promiscuous
2524 D> Type=dir;Perm=;Unique=keVO1+1t2; no-exec
2525 D> Type=file;Perm=r;Unique=keVO1+EG4; two words
2526 D> Type=file;Perm=r;Unique=keVO1+IH4; leading space
2527 D> Type=file;Perm=r;Unique=keVO1+1G4; file1
2528 D> Type=dir;Perm=cpmel;Unique=keVO1+7G4; incoming
2529 D> Type=file;Perm=r;Unique=keVO1+1G4; file2
2530 D> Type=file;Perm=r;Unique=keVO1+1G4; file3
2531 D> Type=file;Perm=r;Unique=keVO1+1G4; file4
2532 S> 226 MLSD completed
2533 C> MLSD test/incoming
2534 S> 150 BINARY connection open for MLSD test/incoming
2535 D> Type=cdir;Perm=cpmel;Unique=keVO1+7G4; test/incoming
2536 D> Type=pdir;Perm=el;Unique=keVO1+ZF4; ..
2537 D> Type=file;Perm=awdrf;Unique=keVO1+EH4; bar
2538 D> Type=file;Perm=awdrf;Unique=keVO1+LH4;
2539 D> Type=file;Perm=rf;Unique=keVO1+1G4; file5
2540 D> Type=file;Perm=rf;Unique=keVO1+1G4; file6
2541 D> Type=dir;Perm=cpmdelf;Unique=keVO1+!s2; empty
2542 S> 226 MLSD completed
2544 For the purposes of this example the fact set requested has been
2545 modified to delete the "size" and "modify" facts, and add the
2546 "unique" fact. First, facts about a filename have been obtained via
2547 MLST. Note that no fully qualified path name was given this time.
2548 That was because the server was unable to determine that information.
2549 Then having determined that the filename represents a directory, that
2550 directory has been listed. That listing also shows no fully
2551 qualified path name, for the same reason, thus has but a single
2552 "type=cdir" line. This directory (which was created especially for
2553 the purpose) contains several interesting files. There are some with
2554 OS dependent file types, several sub-directories, and several
2555 ordinary files.
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2563 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2566 Not much can be said here about the OS dependent file types, as none
2567 of the information shown there should be treated as any more than
2568 possibilities. It can be seen that the OS type of the server is
2569 "unix" though, which is one of the OS types in the IANA registry of
2570 Operating System names.
2572 Of the three directories listed, "no-exec" has no permission granted
2573 to this user to access at all. From the "Unique" fact values, it can
2574 be determined that "promiscuous" and "incoming" in fact represent the
2575 same directory. Its permissions show that the connected user has
2576 permission to do essentially anything other than to delete the
2577 directory. That directory was later listed. It happens that the
2578 directory can not be deleted because it is not empty.
2580 Of the normal files listed, two contain spaces in their names. The
2581 file called " leading space" actually contains two spaces in its
2582 name, one before the "l" and one between the "g" and the "s". The
2583 two spaces that separate the facts from the visible part of the path
2584 name make that clear. The file "writable" has the "a" and "w"
2585 permission bits set, and consequently the connected user should be
2586 able to STOR or APPE to that file.
2588 The other four file names, "file1", "file2", "file3", and "file4" all
2589 represent the same underlying file, as can be seen from the values of
2590 the "unique" facts of each. It happens that "file1" and "file2" are
2591 Unix "hard" links, and that "file3" and "file4" are "soft" or
2592 "symbolic" links to the first two. None of that information is
2593 available via standard MLST facts, it is sufficient for the purposes
2594 of FTP to note that all represent the same file, and that the same
2595 data would be fetched no matter which of them was retrieved, and that
2596 all would be simultaneously modified were data stored in any.
2598 Finally, the sub-directory "incoming" is listed. Since "promiscuous"
2599 is the same directory there would be no point listing it as well. In
2600 that directory, the files "file5" and "file6" represent still more
2601 names for the "file1" file we have seen before. Notice the entry
2602 between that for "bar" and "file5". Though it is not possible to
2603 easily represent it in this document, that shows a file with a name
2604 comprising exactly three spaces (" "). A client will have no
2605 difficulty determining that name from the output presented to it
2606 however. The directory "empty" is, as its name implies, empty,
2607 though that is not shown here. It can, however, be deleted, as can
2608 file "bar" and the file whose name is three spaces. All the files
2609 that reside in this directory can be renamed. This is a consequence
2610 of the UNIX semantics of the directory that contains them being
2611 modifiable.
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2620 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2623 8.7.5. More accurate time information
2625 C> MLst file1
2626 S> 250- Listing file1
2627 S> Type=file;Modify=19990929003355.237; file1
2628 S> 250 End
2630 In this example, the server-FTP is indicating that "file1" was last
2631 modified 237 milliseconds after 00:33:55 UTC on the 29th of
2632 September, 1999.
2634 8.7.6. A different server
2636 C> MLST
2637 S> 250-Begin
2638 S> type=dir;unique=AQkAAAAAAAABCAAA; /
2639 S> 250 End.
2640 C> MLSD .
2641 S> 150 Opening ASCII mode data connection for MLS.
2642 D> type=cdir;unique=AQkAAAAAAAABCAAA; /
2643 D> type=dir;unique=AQkAAAAAAAABEAAA; bin
2644 D> type=dir;unique=AQkAAAAAAAABGAAA; etc
2645 D> type=dir;unique=AQkAAAAAAAAB8AwA; halflife
2646 D> type=dir;unique=AQkAAAAAAAABoAAA; incoming
2647 D> type=dir;unique=AQkAAAAAAAABIAAA; lib
2648 D> type=dir;unique=AQkAAAAAAAABWAEA; linux
2649 D> type=dir;unique=AQkAAAAAAAABKAEA; ncftpd
2650 D> type=dir;unique=AQkAAAAAAAABGAEA; outbox
2651 D> type=dir;unique=AQkAAAAAAAABuAAA; quake2
2652 D> type=dir;unique=AQkAAAAAAAABQAEA; winstuff
2653 S> 226 Listing completed.
2654 C> MLSD linux
2655 S> 150 Opening ASCII mode data connection for MLS.
2656 D> type=cdir;unique=AQkAAAAAAAABWAEA; /linux
2657 D> type=pdir;unique=AQkAAAAAAAABCAAA; /
2658 D> type=dir;unique=AQkAAAAAAAABeAEA; firewall
2659 D> type=file;size=12;unique=AQkAAAAAAAACWAEA; helo_world
2660 D> type=dir;unique=AQkAAAAAAAABYAEA; kernel
2661 D> type=dir;unique=AQkAAAAAAAABmAEA; scripts
2662 D> type=dir;unique=AQkAAAAAAAABkAEA; security
2663 S> 226 Listing completed.
2664 C> MLSD linux/kernel
2665 S> 150 Opening ASCII mode data connection for MLS.
2666 D> type=cdir;unique=AQkAAAAAAAABYAEA; /linux/kernel
2667 D> type=pdir;unique=AQkAAAAAAAABWAEA; /linux
2668 D> type=file;size=6704;unique=AQkAAAAAAAADYAEA; k.config
2669 D> type=file;size=7269221;unique=AQkAAAAAAAACYAEA; linux-2.0.36.tar.gz
2670 D> type=file;size=12514594;unique=AQkAAAAAAAAEYAEA; linux-2.1.130.tar.gz
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2677 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2680 S> 226 Listing completed.
2682 Note that this server returns its "unique" fact value in quite a
2683 different format. It also returns fully qualified path names for the
2684 "pdir" entry.
2686 8.7.7. Some IANA files
2688 C> MLSD .
2689 S> 150 BINARY connection open for MLSD .
2690 D> Type=cdir;Modify=19990219183438; /iana/assignments
2691 D> Type=pdir;Modify=19990112030453; ..
2692 D> Type=dir;Modify=19990219073522; media-types
2693 D> Type=dir;Modify=19990112033515; character-set-info
2694 D> Type=dir;Modify=19990112033529; languages
2695 D> Type=file;Size=44242;Modify=19990217230400; character-sets
2696 D> Type=file;Size=1947;Modify=19990209215600; operating-system-names
2697 S> 226 MLSD completed
2698 C> MLSD media-types
2699 S> 150 BINARY connection open for MLSD media-types
2700 D> Type=cdir;Modify=19990219073522; media-types
2701 D> Type=cdir;Modify=19990219073522; /iana/assignments/media-types
2702 D> Type=pdir;Modify=19990219183438; ..
2703 D> Type=dir;Modify=19990112033045; text
2704 D> Type=dir;Modify=19990219183442; image
2705 D> Type=dir;Modify=19990112033216; multipart
2706 D> Type=dir;Modify=19990112033254; video
2707 D> Type=file;Size=30249;Modify=19990218032700; media-types
2708 S> 226 MLSD completed
2709 C> MLSD character-set-info
2710 S> 150 BINARY connection open for MLSD character-set-info
2711 D> Type=cdir;Modify=19990112033515; character-set-info
2712 D> Type=cdir;Modify=19990112033515; /iana/assignments/character-set-info
2713 D> Type=pdir;Modify=19990219183438; ..
2714 D> Type=file;Size=1234;Modify=19980903020400; windows-1251
2715 D> Type=file;Size=4557;Modify=19980922001400; tis-620
2716 D> Type=file;Size=801;Modify=19970324130000; ibm775
2717 D> Type=file;Size=552;Modify=19970320130000; ibm866
2718 D> Type=file;Size=922;Modify=19960505140000; windows-1258
2719 S> 226 MLSD completed
2720 C> MLSD languages
2721 S> 150 BINARY connection open for MLSD languages
2722 D> Type=cdir;Modify=19990112033529; languages
2723 D> Type=cdir;Modify=19990112033529; /iana/assignments/languages
2724 D> Type=pdir;Modify=19990219183438; ..
2725 D> Type=file;Size=2391;Modify=19980309130000; default
2726 D> Type=file;Size=943;Modify=19980309130000; tags
2727 D> Type=file;Size=870;Modify=19971026130000; navajo
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2734 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2737 D> Type=file;Size=699;Modify=19950911140000; no-bok
2738 S> 226 MLSD completed
2739 C> PWD
2740 S> 257 "/iana/assignments" is current directory.
2742 This example shows some of the IANA maintained files that are
2743 relevant for this specification in MLSD format. Note that these
2744 listings have been edited by deleting many entries, the actual
2745 listings are much longer.
2747 8.7.8. A stress test of case (in)dependence
2749 The following example is intended to make clear some cases where case
2750 dependent strings are permitted in the MLSx commands, and where case
2751 independent strings are required.
2753 C> MlsD .
2754 S> 150 BINARY connection open for MLSD .
2755 D> Type=pdir;Modify=19990929011228;Perm=el;Unique=keVO1+ZF4; ..
2756 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+Bd8; FILE2
2757 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+aG8; file3
2758 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+ag8; FILE3
2759 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+bD8; file1
2760 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+bD8; file2
2761 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+Ag8; File3
2762 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+bD8; File1
2763 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+Bd8; File2
2764 D> Type=file;Size=4096;Modify=19990929011440;Perm=r;Unique=keVO1+bd8; FILE1
2765 S> 226 MLSD completed
2767 Note first that the "MLSD" command, shown here as "MlsD" is case
2768 independent. Clients may issue this command in any case, or
2769 combination of cases, they desire. This is the case for all FTP
2770 commands.
2772 Next, notice the labels of the facts. These are also case
2773 independent strings, Server-FTP is permitted to return them in any
2774 case they desire. User-FTP must be prepared to deal with any case,
2775 though it may do this by mapping the labels to a common case if
2776 desired.
2778 Then, notice that there are nine objects of "type" file returned. In
2779 a case independent NVFS these would represent three different file
2780 names, "file1", "file2", and "file3". With a case dependent NVFS all
2781 nine represent different file names. Either is possible, server-FTPs
2782 may implement a case dependent or a case independent NVFS. User-FTPs
2783 must allow for case dependent selection of files to manipulate on the
2784 server.
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2791 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2794 Lastly, notice that the value of the "unique" fact is case dependent.
2795 In the example shown, "file1", "File1", and "file2" all have the same
2796 "unique" fact value "keVO1+bD8", and thus all represent the same
2797 underlying file. On the other hand, "FILE1" has a different "unique"
2798 fact value ("keVO1+bd8") and hence represents a different file.
2799 Similarly, "FILE2" and "File2" are two names for the same underlying
2800 file, whereas "file3", "File3" and "FILE3" all represent different
2801 underlying files.
2803 That the approximate sizes ("size" fact) and last modification times
2804 ("modify" fact) are the same in all cases might be no more than a
2805 coincidence.
2807 It is not suggested that the operators of server-FTPs create NVFS
2808 which stress the protocols to this extent, however both user and
2809 server implementations must be prepared to deal with such extreme
2810 examples.
2812 8.8. FEAT response for MLSx
2814 When responding to the FEAT command, a server-FTP process that
2815 supports MLST, and MLSD, plus internationalization of pathnames, MUST
2816 indicate that this support exists. It does this by including a MLST
2817 feature line. As well as indicating the basic support, the MLST
2818 feature line indicates which MLST facts are available from the
2819 server, and which of those will be returned if no subsequent "OPTS
2820 MLST" command is sent.
2822 mlst-feat = SP "MLST" [SP factlist] CRLF
2823 factlist = 1*( factname ["*"] ";" )
2825 The initial space shown in the mlst-feat response is that required by
2826 the FEAT command, two spaces are not permitted. If no factlist is
2827 given, then the server-FTP process is indicating that it supports
2828 MLST, but implements no facts. Only pathnames can be returned. This
2829 would be a minimal MLST implementation, and useless for most
2830 practical purposes. Where the factlist is present, the factnames
2831 included indicate the facts supported by the server. Where the
2832 optional asterisk appears after a factname, that fact will be
2833 included in MLST format responses, until an "OPTS MLST" is given to
2834 alter the list of facts returned. After that, subsequent FEAT
2835 commands will return the asterisk to show the facts selected by the
2836 most recent "OPTS MLST".
2838 Note that there is no distinct FEAT output for MLSD. The presence of
2839 the MLST feature indicates that both MLST and MLSD are supported.
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2848 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2851 8.8.1. Examples
2853 C> Feat
2854 S> 211- Features supported
2855 S> REST STREAM
2856 S> MDTM
2857 S> SIZE
2858 S> TVFS
2859 S> UTF8
2860 S> MLST Type*;Size*;Modify*;Perm*;Unique*;UNIX.mode;UNIX.chgd;X.hidden;
2861 S> 211 End
2863 Aside from some features irrelevant here, this server indicates that
2864 it supports MLST including several, but not all, standard facts, all
2865 of which it will send by default. It also supports two OS dependent
2866 facts, and one locally defined fact. The latter three must be
2867 requested expressly by the client for this server to supply them.
2869 C> Feat
2870 S> 211-Extensions supported:
2871 S> CLNT
2872 S> MDTM
2873 S> MLST type*;size*;modify*;UNIX.mode*;UNIX.owner;UNIX.group;unique;
2874 S> PASV
2875 S> REST STREAM
2876 S> SIZE
2877 S> TVFS
2878 S> Compliance Level: 19981201 (IETF mlst-05)
2879 S> 211 End.
2881 Again, in addition to some irrelevant features here, this server
2882 indicates that it supports MLST, four of the standard facts, one of
2883 which ("unique") is not enabled by default, and several OS dependent
2884 facts, one of which is provided by the server by default. This
2885 server actually supported more OS dependent facts. Others were
2886 deleted for the purposes of this document to comply with document
2887 formatting restrictions.
2889 8.9. OPTS parameters for MLST
2891 For the MLSx commands, the Client-FTP may specify a list of facts it
2892 wishes to be returned in all subsequent MLSx commands until another
2893 OPTS MLST command is sent. The format is specified by:
2902 Elz & Hethmon [Expires April 2000] [Page 51]
2905 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2908 mlst-opts = "OPTS" SP "MLST"
2909 [ SP 1*( factname ";" ) ]
2911 By sending the "OPTS MLST" command, the client requests the server to
2912 include only the facts listed as arguments to the command in
2913 subsequent output from MLSx commands. Facts not included in the
2914 "OPTS MLST" command MUST NOT be returned by the server. Facts that
2915 are included should be returned for each entry returned from the MLSx
2916 command where they meaningfully apply. Facts requested that are not
2917 supported, or which are inappropriate to the file or directory being
2918 listed should simply be omitted from the MLSx output. This is not an
2919 error. Note that where no factname arguments are present, the client
2920 is requesting that only the file names be returned. In this case,
2921 and in any other case where no facts are included in the result, the
2922 space that separates the fact names and their values from the file
2923 name is still required. That is, the first character of the output
2924 line will be a space, (or two characters will be spaces when the line
2925 is returned over the control connection,) and the file name will
2926 start immediately thereafter.
2928 Clients should note that generating values for some facts can be
2929 possible, but very expensive, for some servers. It is generally
2930 acceptable to retrieve any of the facts that the server offers as its
2931 default set before any "OPTS MLST" command has been given, however
2932 clients should use particular caution before requesting any facts not
2933 in that set. That is, while other facts may be available from the
2934 server, clients should refrain from requesting such facts unless
2935 there is a particular operational requirement for that particular
2936 information, which ought be more significant than perhaps simply
2937 improving the information displayed to an end user.
2939 Note, there is no "OPTS MLSD" command, the fact names set with the
2940 "OPTS MLST" command apply to both MLST and MLSD commands.
2942 Servers are not required to accept "OPTS MLST" commands before
2943 authentication of the user-PI, but may choose to permit them.
2945 8.9.1. OPTS MLST Response
2947 The "response-message" from [6] to a successful OPTS MLST command has
2948 the following syntax.
2950 mlst-opt-resp = "MLST OPTS" [ SP 1*( factname ";" ) ]
2952 This defines the "response-message" as used in the "opts-good"
2953 message in RFC2389 [6].
2959 Elz & Hethmon [Expires April 2000] [Page 52]
2962 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
2965 The facts named in the response are those which the server will now
2966 include in MLST (and MLSD) response, after the processing of the
2967 "OPTS MLST" command. Any facts from the request not supported by the
2968 server will be omitted from this response message. If no facts will
2969 be included, the list of facts will be empty. Note that the list of
2970 facts returned will be the same as those marked by a trailing
2971 asterisk ("*") in a subsequent FEAT command response. There is no
2972 requirement that the order of the facts returned be the same as that
2973 in which they were requested, or that in which they will be listed in
2974 a FEAT command response, or that in which facts are returned in MLST
2975 responses. The fixed string "MLST OPTS" in the response may be
2976 returned in any case, or mixture of cases.
2978 8.9.2. Examples
2980 C> Feat
2981 S> 211- Features supported
2982 S> MLST Type*;Size;Modify*;Perm;Unique;UNIX.mode;UNIX.chgd;X.hidden;
2983 S> 211 End
2984 C> OptS Mlst Type;UNIX.mode;Perm;
2985 S> 201 MLST OPTS Type;Perm;UNIX.mode;
2986 C> Feat
2987 S> 211- Features supported
2988 S> MLST Type*;Size;Modify;Perm*;Unique;UNIX.mode*;UNIX.chgd;X.hidden;
2989 S> 211 End
2990 C> opts MLst lang;type;charset;create;
2991 S> 201 MLST OPTS Type;
2992 C> Feat
2993 S> 211- Features supported
2994 S> MLST Type*;Size;Modify;Perm;Unique;UNIX.mode;UNIX.chgd;X.hidden;
2995 S> 211 End
2996 C> OPTS mlst size;frogs;
2997 S> 201 MLST OPTS Size;
2998 C> Feat
2999 S> 211- Features supported
3000 S> MLST Type;Size*;Modify;Perm;Unique;UNIX.mode;UNIX.chgd;X.hidden;
3001 S> 211 End
3002 C> opts MLst unique type;
3003 S> 501 Invalid MLST options
3004 C> Feat
3005 S> 211- Features supported
3006 S> MLST Type;Size*;Modify;Perm;Unique;UNIX.mode;UNIX.chgd;X.hidden;
3007 S> 211 End
3009 For the purposes of this example, features other than MLST have been
3010 deleted from the output to avoid clutter. The example shows the
3011 initial default feature output for MLST. The facts requested are
3012 then changed by the client. The first change shows facts that are
3016 Elz & Hethmon [Expires April 2000] [Page 53]
3019 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
3022 available from the server being selected. Subsequent FEAT output
3023 shows the altered features as being returned. The client then
3024 attempts to select some standard features which the server does not
3025 support. This is not an error, however the server simply ignores the
3026 requests for unsupported features, as the FEAT output that follows
3027 shows. Then, the client attempts to request a non-standard, and
3028 unsupported, feature. The server ignores that, and selects only the
3029 supported features requested. Lastly, the client sends a request
3030 containing a syntax error (spaces cannot appear in the factlist.) The
3031 server-FTP sends an error response and completely ignores the
3032 request, leaving the fact set selected as it had been previously.
3034 Note that in all cases, except the error response, the response lists
3035 the facts that have been selected.
3037 C> Feat
3038 S> 211- Features supported
3039 S> MLST Type*;Size*;Modify*;Perm*;Unique*;UNIX.mode;UNIX.chgd;X.hidden;
3040 S> 211 End
3041 C> Opts MLST
3042 S> 201 MLST OPTS
3043 C> Feat
3044 S> 211- Features supported
3045 S> MLST Type;Size;Modify;Perm;Unique;UNIX.mode;UNIX.chgd;X.hidden;
3046 S> 211 End
3047 C> MLst tmp
3048 S> 250- Listing tmp
3049 S> /tmp
3050 S> 250 End
3051 C> OPTS mlst unique;size;
3052 S> 201 MLST OPTS Size;Unique;
3053 C> MLst tmp
3054 S> 250- Listing tmp
3055 S> Unique=keVO1+YZ5; /tmp
3056 S> 250 End
3057 C> OPTS mlst unique;type;modify;
3058 S> 201 MLST OPTS Type;Modify;Unique;
3059 C> MLst tmp
3060 S> 250- Listing tmp
3061 S> Type=dir;Modify=19990930152225;Unique=keVO1+YZ5; /tmp
3062 S> 250 End
3063 C> OPTS mlst fish;cakes;
3064 S> 201 MLST OPTS
3065 C> MLst tmp
3066 S> 250- Listing tmp
3067 S> /tmp
3068 S> 250 End
3069 C> OptS Mlst Modify;Unique;
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3076 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
3079 S> 201 MLST OPTS Modify;Unique;
3080 C> MLst tmp
3081 S> 250- Listing tmp
3082 S> Modify=19990930152225;Unique=keVO1+YZ5; /tmp
3083 S> 250 End
3084 C> opts MLst fish cakes;
3085 S> 501 Invalid MLST options
3086 C> MLst tmp
3087 S> 250- Listing tmp
3088 S> Modify=19990930152225;Unique=keVO1+YZ5; /tmp
3089 S> 250 End
3091 This example shows the effect of changing the facts requested upon
3092 subsequent MLST commands. Notice that a syntax error leaves the set
3093 of selected facts unchanged. Also notice exactly two spaces
3094 preceding the pathname when no facts were selected, either
3095 deliberately, or because none of the facts requested were available.
3097 9. Impact On Other FTP Commands
3099 Along with the introduction of MLST, traditional FTP commands must be
3100 extended to allow for the use of more than US-ASCII or EBCDIC
3101 character sets. In general, the support of MLST requires support for
3102 arbitrary character sets wherever filenames and directory names are
3103 allowed. This applies equally to both arguments given to the
3104 following commands and to the replies from them, as appropriate.
3106 CWD
3107 RETR
3108 STOR
3109 STOU
3110 APPE
3111 RNFR
3112 RNTO
3113 DELE
3114 RMD
3115 MKD
3116 PWD
3117 STAT
3119 The arguments to all of these commands should be processed the same
3120 way that MLST commands and responses are processed with respect to
3121 handling embedded spaces, CRs and NULs. See section 2.2.
3130 Elz & Hethmon [Expires April 2000] [Page 55]
3133 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
3136 10. Character sets and Internationalization
3138 FTP commands are protocol elements, and are always expressed in
3139 ASCII. FTP responses are composed of the numeric code, which is a
3140 protocol element, and a message, which is often expected to convey
3141 information to the user. It is not expected that users normally
3142 interact directly with the protocol elements, rather the user FTP-
3143 process constructs the commands, and interprets the results, in the
3144 manner best suited for the particular user. Explanatory text in
3145 responses generally has no particular meaning to the protocol. The
3146 numeric codes provide all necessary information. Server-PIs are free
3147 to provide the text in any language that can be adequately
3148 represented in ASCII, or where an alternative language and
3149 representation has been negotiated (see [7]) in that language and
3150 representation.
3152 Pathnames are expected to be encoded in UTF-8 allowing essentially
3153 any character to be represented in a pathname. Meaningful pathnames
3154 are defined by the server NVFS.
3156 No restrictions at all are placed upon the contents of files
3157 transferred using the FTP protocols. Unless the "media-type" fact is
3158 provided in a MLSx response nor is any advice given here which would
3159 allow determining the content type. That information is assumed to
3160 be obtained via other means.
3162 11. IANA Considerations
3164 This specification makes use of some lists of values currently
3165 maintained by the IANA, and creates two new lists for the IANA to
3166 maintain. It does not add any values to any existing registries.
3168 The existing IANA registries used by this specification are modified
3169 using mechanisms specified elsewhere.
3171 11.1. The OS specific fact registry
3173 A registry of OS specific fact names shall be maintained by the IANA.
3174 The OS names for the OS portion of the fact name must be taken from
3175 the IANA's list of registered OS names. To add a fact name to this
3176 OS specific registry of OS specific facts, an applicant must send to
3177 the IANA a request, in which is specified the OS name, the OS
3178 specific fact name, a definition of the syntax of the fact value,
3179 which must conform to the syntax of a token as given in this
3180 document, and a specification of the semantics to be associated with
3181 the particular fact and its values. Upon receipt of such an
3182 application, and if the combination of OS name and OS specific fact
3183 name has not been previously defined, the IANA will add the
3187 Elz & Hethmon [Expires April 2000] [Page 56]
3190 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
3193 specification to the registry.
3195 Any examples of OS specific facts found in this document are to be
3196 treated as examples of possible OS specific facts, and do not form a
3197 part of the IANA's registry merely because of being included in this
3198 document.
3200 11.2. The OS specific filetype registry
3202 A registry of OS specific file types shall be maintained by the IANA.
3203 The OS names for the OS portion of the fact name must be taken from
3204 the IANA's list of registered OS names. To add a file type to this
3205 OS specific registry of OS specific file types, an applicant must
3206 send to the IANA a request, in which is specified the OS name, the OS
3207 specific file type, a definition of the syntax of the fact value,
3208 which must conform to the syntax of a token as given in this
3209 document, and a specification of the semantics to be associated with
3210 the particular fact and its values. Upon receipt of such an
3211 application, and if the combination of OS name and OS specific file
3212 type has not been previously defined, the IANA will add the
3213 specification to the registry.
3215 Any examples of OS specific file types found in this document are to
3216 be treated as potential OS specific file types only, and do not form
3217 a part of the IANA's registry merely because of being included in
3218 this document.
3220 12. Security Considerations
3222 This memo does not directly concern security. It is not believed
3223 that any of the mechanisms documented here impact in any particular
3224 way upon the security of FTP.
3226 Implementing the SIZE command, and perhaps some of the facts of the
3227 MDLx commands, may impose a considerable load on the server, which
3228 could lead to denial of service attacks. Servers have, however,
3229 implemented this for many years, without significant reported
3230 difficulties.
3232 With the introduction of virtual hosts to FTP, and the possible
3233 accompanying multiple authentication environments, server
3234 implementors will need to take some care to ensure that integrity is
3235 maintained.
3237 The FEAT and OPTS commands may be issued before the FTP
3238 authentication has occurred [6]. This allows unauthenticated clients
3239 to determine which of the features defined here are supported, and to
3240 negotiate the fact list for MLSx output. No actual MLSx commands may
3244 Elz & Hethmon [Expires April 2000] [Page 57]
3247 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
3250 be issued however, and no problems with permitting the selection of
3251 the format prior to authentication are foreseen.
3253 A general discussion of issues related to the security of FTP can be
3254 found in [14].
3256 13. References
3258 [1] Coded Character Set--7-bit American Standard Code for Information
3259 Interchange, ANSI X3.4-1986.
3261 [2] Yergeau, F., "UTF-8, a transformation format of Unicode and ISO
3262 10646", RFC 2044, October 1996.
3264 [3] Postel, J., Reynolds, J., "File Transfer Protocol (FTP)",
3265 STD 9, RFC 959, October 1985
3267 [4] Bradner, S., "Key words for use in RFCs to Indicate
3268 Requirement Levels", BCP 14, RFC 2119, March 1997
3270 [5] Crocker, D., Overell, P., "Augmented BNF for Syntax
3271 Specifications: ABNF", RFC 2234, November 1997
3273 [6] Hethmon, P., Elz, R., "Feature negotiation mechanism for the
3274 File Transfer Protocol", RFC 2389, August 1998
3276 [7] Curtin, W., "Internationalization of the File Transfer Protocol",
3277 RFC 2640, July 1999
3279 [8] Postel, J., Reynolds, J., "Telnet protocol Specification"
3280 STD 8, RFC 854, May 1983
3282 [9] Braden, R,. "Requirements for Internet Hosts -- Application
3283 and Support", STD 3, RFC 1123, October 1989
3285 [10] Mockapetris, P., "Domain Names - Concepts and Facilities"
3286 STD 13, RFC 1034, November 1987
3288 [11] ISO/IEC 10646-1:1993 "Universal multiple-octet coded character set
3289 (UCS) -- Part 1: Architecture and basic multilingual plane",
3290 International Standard -- Information Technology, 1993
3292 [12] Internet Assigned Numbers Authority. http://www.iana.org
3293 Email: iana@iana.org.
3295 [13] Alvestrand, H., "Tags for the Identification of Languages"
3296 RFC 1766, March 1995
3301 Elz & Hethmon [Expires April 2000] [Page 58]
3304 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
3307 [14] Allman, M., Ostermann, S., "FTP Security Considerations"
3308 RFC 2577, May 1999
3310 Acknowledgments
3312 This document is a product of the FTPEXT working group of the IETF.
3314 The following people are among those who have contributed to this
3315 document:
3317 Alex Belits
3318 D. J. Bernstein
3319 Dave Cridland
3320 Martin J. Duerst
3321 Mike Gleason
3322 Mark Harris
3323 Alun Jones
3324 James Matthews
3325 Luke Mewburn
3326 Jan Mikkelsen
3327 Keith Moore
3328 Buz Owen
3329 Mark Symons
3330 Stephen Tihor
3331 and the entire FTPEXT working group of the IETF.
3333 Apologies are offered to any inadvertently omitted.
3335 Bernhard Rosenkraenzer suggested the HOST command, and initially
3336 described it.
3338 The description of the modifications to the REST command and the MDTM
3339 and SIZE commands comes from a set of modifications suggested for
3340 RFC959 by Rick Adams in 1989. A draft containing just those
3341 commands, edited by David Borman, has been merged with this document.
3343 Mike Gleason provided access to the FTP server used in some of the
3344 examples.
3346 All of the examples in this document are taken from actual
3347 client/server exchanges, though some have been edited for brevity, or
3348 to meet document formatting requirements.
3358 Elz & Hethmon [Expires April 2000] [Page 59]
3361 Internet Draft draft-ietf-ftpext-mlst-08.txt October 1999
3364 Copyright
3366 This document is in the public domain. Any and all copyright
3367 protection that might apply in any jurisdiction is expressly
3368 disclaimed.
3370 Editors' Addresses
3372 Robert Elz
3373 University of Melbourne
3374 Department of Computer Science
3375 Parkville, Vic 3052
3376 Australia
3378 Email: kre@munnari.OZ.AU
3381 Paul Hethmon
3382 Hethmon Brothers
3383 2305 Chukar Road
3384 Knoxville, TN 37923 USA
3386 Phone: +1 423 690 8990
3387 Email: phethmon@hethmon.com
3415 Elz & Hethmon [Expires April 2000] [Page 60]