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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 3659

FTPEXT Working Group                                              R. Elz
Internet Draft                                   University of Melbourne
Expiration Date: December 1997
                                                              P. Hethmon
                                                        Hethmon Brothers

                                                               June 1997


        Extended Directory Listing and Restart Mechanism for FTP


                     draft-ietf-ftpext-mlst-01.txt

Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   To learn the current status of any Internet-Draft, please check the
   "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
   munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
   ftp.isi.edu (US West Coast).

Abstract

   In order to overcome the problems caused by the undefined format of
   the current FTP LIST command output, a new command is needed to
   transfer standardized listing information from Server-FTP to Client-
   FTP.  Commands to enable this are defined in this document.

   This proposal also extends the FTP protocol to allow character sets
   other than US-ASCII[1] by allowing the transmission of 8-bit
   characters and the recommended use of UTF-8[2] encoding.

   Much implemented, but long undocumented, mechanisms to permit
   restarts of interrupted data transfers in STREAM mode, are also
   included here.





Elz & Hethmon                                                   [Page 1]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


   This version contains changes as agreed at the 38th IETF, Memphis,
   April 1997.  In particular: the SIZE MDTM and modified REST draft has
   been folded into this doc, (and the FEAT and OPTS commands have been
   moved out to a separate draft).  Almost everything that was case
   dependent no longer is, MLST/MLSD no longer send replies on the
   control connection but the ancient STAT command has been revitalised.
   Files of type "link" are no longer reported, and the 'x' permission
   indicator has gone to meet its maker.  The draft has also be
   editorially updated in some significant ways.  This paragraph will be
   deleted from the final version of this document.









































Elz & Hethmon                                                   [Page 2]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997




Table of Contents

          Status of this Memo  .....................................   1
          Abstract  ................................................   1
    1     Introduction  ............................................   4
    2     Document Conventions  ....................................   4
    2.1   Basic Tokens  ............................................   4
    2.2   Pathnames  ...............................................   5
    2.3   Times  ...................................................   6
    2.4   Server Replies  ..........................................   7
    3     File Modification Time (MDTM)  ...........................   7
    3.1   Syntax  ..................................................   8
    3.2   Error responses  .........................................   8
    3.3   FEAT response for MTDM  ..................................   8
    4     File SIZE  ...............................................   9
    4.1   Syntax  ..................................................   9
    4.2   Error responses  .........................................   9
    4.3   FEAT response for SIZE  ..................................  10
    5     Restart of Interrupted Transfer (REST)  ..................  10
    5.1   Restarting in STREAM Mode  ...............................  10
    5.2   ERROR RECOVER AND RESTART  ...............................  11
    5.3   Syntax  ..................................................  11
    5.4   FEAT response for REST  ..................................  12
    6     Machine Parseable Listings (MLST and MLSD)  ..............  13
    6.1   Format of MLST Request  ..................................  13
    6.2   Format of MLST Response  .................................  14
    6.3   Filename encoding  .......................................  15
    6.4   Format of Facts  .........................................  16
    6.5   Standard Facts  ..........................................  16
    6.6   FEAT response for MLST  ..................................  23
    6.7   OPTS parameters for MLST  ................................  23
    7     Interpretation of STAT command output  ...................  24
    7.1   FEAT response for STAT  ..................................  24
    8     Impact On Other FTP Commands  ............................  24
    8.1   Impact on Pathnames and Filenames  .......................  25
    9     Character sets and Internationalisation  .................  25
   10     Security  ................................................  25
   11     References  ..............................................  25
          Acknowledgements  ........................................  26
          Editors' Addresses  ......................................  27









Elz & Hethmon                                                   [Page 3]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


1. Introduction

   This document amends the File Transfer Protocol (FTP) [6].  Four new
   commands are added: "SIZE", "MDTM", "MLST", and "MLSD".  Two existing
   commands are modified, those are "REST" and "STAT".  Of those, the
   "SIZE" and "MDTM" commands, and the modifications to "REST" have been
   in wide use for many years.  The others are new.

   These commands allow a client to restart an interrupted transfer in
   transfer modes not previously supported in any documented way, and to
   obtain a directory listing in a machine friendly, predictable,
   format.

2. Document Conventions

   This document makes use of the document conventions defined in
   RFC2119 [10].  That provides the interpretation of capitalized
   imperative words like MUST, SHOULD, etc.

   This document also uses notation defined in STD 9 [6].  In
   particular, the terms "reply", "user", "NVFS", "file", "pathname",
   "FTP commands", "DTP", "user-FTP process", "user-PI", "user-DTP",
   "server-FTP process", "server-PI", "server-DTP", "mode", "type",
   "NVT", "control connection", "data connection", and "ASCII", are all
   used here as defined there.

   Syntax required is defined using the Augmented BNF defined in [9].
   Some general ABNF definitions are required throughout the document,
   those will be defined later in this section.  At first reading, it
   may be wise to simply recall that these definitions exist here, and
   skip to the next section.

2.1. Basic Tokens

   This document imports the definitions given in Appendix A of [9].
   There definitions will be found for basic ABNF elements like ALPHA,
   DIGIT, SP, etc.  To that, the following terms are added for use in
   this document.

        PCHAR          = %x21-7e          ; a printing character, ! to ~
        TCHAR          = PCHAR / SP / %x08   ; printing plus white space
        ltext          = ALPHA / DIGIT / "," / "." / ":" / "!" /
                         "@" / "#" / "$" / "%" / "^" /
                         "&" / "(" / ")" / "-" / "_" /
                         "+" / "?" / "/" / "\" / "'" /
                         %x22            ; <"> -- double quote character





Elz & Hethmon                                                   [Page 4]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


   The PCHAR, TCHAR, and ltext types give basic character types from
   varying sub-sets of the ASCII character set for use in various
   commands and responses.

        token          = 1*ltext

   A "token" is a string whose precise meaning depends upon the context
   in which it is used.  In some cases it will be a value from a set of
   possible values maintained elsewhere.  In others it might be a string
   invented by one party to an FTP conversation from whatever sources it
   finds relevant.

        error-response = error-code SP *TCHAR CRLF
        error-code     = ("4" / "5") 2DIGIT

   Note that in ABNF, string literals are case insensitive.  That
   convention is preserved in this document.  However note that ALPHA,
   in particular, is case sensitive.  That implies that a "token" is a
   case sensitive value.  That implication is correct.

2.2. Pathnames

   Various FTP commands take pathnames as arguments, or return pathnames
   in responses.  When the MLST command is supported, as indicated in
   the response to the FEAT command [11], pathnames are to be
   transferred in one of the following two formats.

        utf-8-name     = <a UTF-8 encoded Unicode string>
        raw            = <any string not being a valid UTF-8 encoding>

   Which format is used is at the option of the user-PI or server-PI
   sending the pathname.  UTF-8 encodings contain enough internal
   structure that it is always, in practice, possible to determine
   whether a UTF-8 or raw encoding has been used, in the cases where it
   matters.  Note that ASCII is a subset of UTF-8.

   Unless otherwise specified, the pathname is terminated by the CRLF
   that terminates the FTP command, or by the CRLF that ends a reply.
   Any trailing spaces preceding that CRLF form part of the name.
   Exactly one space will precede the pathname from the preceding syntax
   element, any additional spaces form part of the pathname.  See [4]
   for a fuller explanation of the character encoding issues.  All
   implementations supporting MLST MUST support [4].

   Implementations should also beware that the control connection uses
   Telnet NVT conventions [12], and that the Telnet IAC character, if
   part of a pathname, MUST be correctly escaped as defined by the
   Telnet protocol.



Elz & Hethmon                                                   [Page 5]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


2.3. Times

   The syntax of a time value is:

        time-val       = 12DIGIT [ "." 1*DIGIT ]

   The leading, mandatory, twelve digits are to be interpreted as, in
   order from the leftmost, four digits giving the year, with a range of
   1000-9999, two digits giving the month of the year, with a range of
   01-12, two digits giving the day of the month, with a range of 01-31,
   two digits giving the hour of the day, with a range of 00-23, two
   digits giving minutes past the hour, with a range of 00-59, and
   finally, two digits giving seconds past the minute, with a range of
   00-60 (with 60 being used only at a leap second).  Years in the tenth
   century, and earlier, cannot be expressed.  This is not considered a
   serious defect of the protocol.

               [ Ed-Note: Should we permit 12*DIGIT (or maybe
               12*13DIGIT) so times in the 101st century and beyond can
               be represented? ]

   The optional digits, which must be preceded by a period, give decimal
   fractions of a second.  These may be given to whatever precision is
   appropriate to the circumstance, however implementations MUST NOT add
   precision to time-vals where that precision does not exist in the
   underlying value being transmitted.

   Symbolically, a time-val may be viewed as

        YYYYMMDDHHMMSS.sss

   The "." and subsequent digits are optional.

   Time values are always represented in UTC (GMT), and in the Gregorian
   calendar regardless of what calendar may have been in use at the date
   and time indicated at the location of the server-PI.

   The technical differences between GMT, UTC, UT1, UT2, etc, are not
   considered here.  A server-FTP process should always use the same
   time reference, so the times it returns will be consistent.  Clients
   are not expected to be time synchronised with the server, so the
   possible difference in times that might be reported by the different
   time standards is not considered important.








Elz & Hethmon                                                   [Page 6]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


2.4. Server Replies

   Section 4.2 of [6] defines the format and meaning of replies by the
   server-PI to FTP commands from the user-PI.  Those reply conventions
   are used here without change.  Implementors should note that the ABNF
   syntax (which was not used in [6]) in this document, and other FTP
   related documents, sometimes shows replies using the one line format.
   Unless otherwise explicitly stated, that is not intended to imply
   that multi-line responses are not permitted.  Implementors should
   assume that, unless stated to the contrary, any reply to any FTP
   command (including QUIT) may be of the multiline format described in
   [6].

   Throughout this document, replies will be identified by the three
   digit code that is their first element.  Thus the term "500 reply"
   means a reply from the server-PI using the three digit code "500".

3. File Modification Time (MDTM)

   The FTP command, MODIFICATION TIME (MDTM), can be used to determine
   when a file in the server NVFS was last modified.  This command has
   existed in many FTP servers for many years, as an adjunct to the REST
   command for STEAM mode, thus is widely available.  However, where
   supported the "mtime" fact which can be provided in the result from
   the new MLST command is recommended as a superior alternative.

   When attempting to restart a RETRieve, if the User FTP makes use of
   the MDTM command, it can check and see if the modification time of
   the source file is more recent than the modification time of the
   partially transferred file.  If it is, then most likely the source
   file has changed and it would be unsafe to restart in the middle of
   the file transfer.

   When attempting to restart a STORe, the User FTP can use the MDTM
   command to discover the modification time of the partially
   transferred file.  If it is older than the modification time of the
   file that is about to be STORed, then most likely the source file has
   changed and it would be unsafe to restart in the middle of the file
   transfer.

   Using MLST can provide this information, and much more, thus giving
   an even better indication that a file has changed, and that
   restarting a transfer would not give valid results.

   Note that this is applicable to any RESTart attempt, regardless of
   the mode of the file transfer.





Elz & Hethmon                                                   [Page 7]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


3.1. Syntax

   The syntax for the MDTM command is:

        mdtm          = "MdTm" SP ( utf-8-name / raw ) CRLF

   The server-PI will respond to the MDTM command with a 213 reply
   giving the last modification time of the file whose pathname was
   supplied, or an error response if the file does not exist, the
   modification time is unavailable, or some other error has occurred.

        mdtm-response = "213" SP time-val CRLF /
                        error-response

3.2. Error responses

   Where the command is correctly parsed, but the modification time is
   not available, either because the pathname identifies no existing
   entity, or because the information is not available for the entity
   named, then a 550 reply should be sent.  Where the command cannot be
   correctly parsed, a 500 or 501 reply should be sent, as specified in
   [6].

3.3. FEAT response for MTDM

   When replying to the FEAT command [11], a FTP server process that
   supports the MTDM command MUST include a line containing the single
   word "MDTM" (in upper case, and without the quotes).  That is, the
   response MUST be

        C> FEAT
        S> 211- <any descriptive text>
        S>  ...
        S>  MDTM
        S>  ...
        S> 211 End

   The ellipses indicate placeholders where other features may be
   included, and are not required.  The one space indentation of the
   feature lines is mandatory.











Elz & Hethmon                                                   [Page 8]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


4. File SIZE

   The FTP command, SIZE OF FILE (SIZE), is used to obtain the transfer
   size of a file from the server-FTP process.  That is, the exact
   number of bytes (or octets) which would be transmitted over the data
   connection should that file be transmitted.  This value will change
   depending on the current STRUcture, MODE and TYPE of the data
   connection, or a data connection which would be created were one
   created now.  Thus, the result of the SIZE command is dependent on
   the currently established STRU, MODE and TYPE parameters.

   The SIZE command returns how many bytes would be transferred if the
   file were to be transferred using the current transfer structure,
   mode and type.  This command is normally used in conjunction with the
   RESTART (REST) command.  The server-PI might need to read the
   partially transferred file, do any appropriate conversion, and count
   the number of bytes that would be generated when sending the file in
   order to correctly respond to this command.  Estimates of the file
   transfer size MUST NOT be returned, only precise information is
   acceptable.

4.1. Syntax

   The syntax of the SIZE command is:

        size          = "Size" SP ( utf-8-name / raw ) CRLF

   The server-PI will respond to the SIZE command with a 213 reply
   giving the transfer size of the file whose pathname was supplied, or
   an error response if the file does not exist, the size is
   unavailable, or some other error has occurred.  The value returned is
   in a format suitable for use with the RESTART (REST) command for mode
   STREAM, provided the transfer mode and type are not altered.

        size-response = "213" SP 1*DIGIT CRLF /
                        error-response

4.2. Error responses

   Where the command is correctly parsed, but the size is not available,
   either because the pathname identifies no existing entity, or because
   the entity named cannot be transferred in the current MODE and TYPE
   (or at all), then a 550 reply should be sent.  Where the command
   cannot be correctly parsed, a 500 or 501 reply should be sent, as
   specified in [6].






Elz & Hethmon                                                   [Page 9]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


4.3. FEAT response for SIZE

   When replying to the FEAT command [11], a FTP server process that
   supports the SIZE command MUST include a line containing the single
   word "SIZE" (in upper case, and without the quotes).  That is, the
   response MUST be

        C> FEAT
        S> 211- <any descriptive text>
        S>  ...
        S>  SIZE
        S>  ...
        S> 211 End

   The ellipses indicate placeholders where other features may be
   included, and are not required.  The one space indentation of the
   feature lines is mandatory.

5. Restart of Interrupted Transfer (REST)

   To avoid having to resend the entire file if the file is only
   partially transferred, both sides need some way to be able to agree
   on where in the data stream to restart the data transfer.

   The FTP specification [6] includes three modes of data transfer,
   Stream, Block and Compressed.  In Block and Compressed modes, the
   data stream that is transferred over the data connection is
   formatted, allowing the embedding of restart markers into the stream.
   The sending DTP can include a restart marker with whatever
   information it needs to be able to restart a file transfer at that
   point.  The receiving DTP can keep a list of these restart markers,
   and correlate them with how the file is being saved.  To restart the
   file transfer, the receiver just sends back that last restart marker,
   and both sides know how to resume the data transfer.  Note that there
   are some flaws in the description of the restart mechanism in RFC 959
   [6], see section 4.1.3.4 of RFC 1123 [7] for the corrections.

5.1. Restarting in STREAM Mode

   In Stream mode, the data connection contains just a stream of
   unformatted bytes of data.  Explicit restart markers thus cannot be
   inserted into the data stream, they would be indistinguishable from
   data.  For this reason, the FTP specification [6] did not provide the
   ability to do restarts in stream mode.  However, there is not really
   a need to have explicit restart markers in this case, as restart
   markers can be implied by the byte offset into the data stream.





Elz & Hethmon                                                  [Page 10]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


   If the data representation TYPE is IMAGE, and the STRUcture is File,
   for many systems the file will be stored exactly in the same format
   as it is sent across the data connection.  It is then very easy for
   the receiver to determine how much data was previously received, and
   notify the sender the byte offset where the transfer should be
   restarted.  In other representation types and structures more effort
   will be required, but it remains always possible to determine the
   byte offset with finite, but perhaps non-negligible, effort.  In the
   worst case an FTP process may need to open a data connection to
   itself, set the appropriate transfer type and structure, and actually
   transmit the file, counting the transmitted bytes.

   If the user-FTP process is intending to restart a retrieve, it will
   directly calculate the restart marker, and send that information in
   the RESTart command.  However, if the user-FTP process is intending
   to restart sending the file, it needs to be able to determine how
   much data was previously sent, and correctly received and saved.  A
   new FTP command is needed to get this information.  This is the
   purpose of the SIZE command, as documented in section 4.

5.2. ERROR RECOVER AND RESTART

   STREAM MODE transfers with FILE STRUcture may be restarted even
   though no restart marker has been transferred in addition to the data
   itself.  This is done by perhaps using the SIZE command in
   combination with the RESTART (REST) command.

   When using TYPE ASCII or IMAGE, the SIZE command will return the
   number of bytes that would actually be transferred if the file were
   to be sent between the two systems.  I.e. with type IMAGE, the SIZE
   normally would be the number of octets in the file.  With type ASCII,
   the SIZE would be the number of characters in the file INCLUDING any
   characters that would be inserted during the CR-LF expansion.

5.3. Syntax

   The syntax for the REST command when the current transfer mode is
   STREAM is:

        rest          = "Rest" SP 1*DIGIT CRLF

   The numeric value gives the number of octets of the immediately
   following transfer to not actually send, effectively causing the
   transmission to be restarted at a later point.  The server-PI will
   respond to the REST command with a 350 reply, indicating that the
   REST parameter has been saved, and that another command, which should
   be either RETR or STOR, should then follow to complete the restart.




Elz & Hethmon                                                  [Page 11]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


        rest-response = "350" SP *TCHAR CRLF /
                        error-response

   Server-FTP processes may permit transfer commands other than RETR and
   STOR, such as APPE and STOU, to complete a restart, however, this is
   not recommended.  STOU (store unique) is undefined in this usage, as
   storing the remainder of a file into a unique filename is rarely
   going to be useful.  If APPE (append) is permitted, it MUST act
   identically to STOR when a restart marker has been set.  That is, in
   both cases, octets from the data connection are placed into the file
   at the location indicated by the restart marker value.

   An error-response will follow a REST command only when the server
   does not implement the command, or the restart marker value is
   syntactically invalid for the current transfer mode.  That is, in
   STREAM mode, if something other than one or more digits appears in
   the parameter to the REST command.  Any other errors, including such
   problems as restart marker out of range, should be reported when the
   following transfer command is issued.

5.4. FEAT response for REST

   Where a server-FTP process supports RESTart in STREAM mode, as
   specified here, it MUST include in the response to the FEAT command
   [11], a line containing exactly the string "REST STREAM" (in upper
   case, and without the quotes).  Where REST is not supported at all,
   or supported only in block or compressed modes, the REST command MUST
   NOT be included in the FEAT response.  Where required, the response
   MUST be

        C> FEAT
        S> 211- <any descriptive text>
        S>  ...
        S>  REST STREAM
        S>  ...
        S> 211 End

   The ellipses indicate placeholders where other features may be
   included, and are not required.  The one space indentation of the
   feature lines is mandatory.











Elz & Hethmon                                                  [Page 12]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


6. Machine Parseable Listings (MLST and MLSD)

   The MLST and MLSD commands are intended to standardize the file and
   directory information returned by the Server-FTP process.  These
   commands differ from the LIST and NLST commands in that the format of
   the replies is strictly defined although extensible.

   Two commands are defined, MLST which provides data about exactly the
   object named on its command line, and no others.  MLSD on the other
   hand will list the contents of a directory if a directory is named,
   otherwise it is identical to MLST.  In either case, if no object is
   named, the current directory is assumed.  That will cause MLST to
   send a one line response, and MLSD to list the contents of the
   current directory.

               [ Ed-Note: An alternative would be to have MLSD fail if
               the argument is not a directory.  Which is better? ]

   In the sequel only MLST will be described, other than as previously
   mentioned, MLSD is identical.

   The MLST and MLSD commands also extend the FTP protocol as presented
   in RFC 959 [6] and RFC 1123 [7] to allow that transmission of 8-bit
   data.  Note this is not specifying character sets which are 8-bit,
   but specifying that FTP implementations are to specifically allow the
   transmission and reception of 8-bit bytes over the control
   connection.  That is, all 256 possible octet values are permitted.
   The MLST command allows both UTF-8/Unicode and "raw" forms as
   arguments, and in responses.

6.1. Format of MLST Request

   The MLST and MLSD commands each allow a single optional argument.
   This argument may be either a directory name or a filename.  If a
   directory name is given then MLSD must return a listing of the
   contents of the named directory.  If the argument is not a directory,
   and the command is MLSD, and in all cases for MLST, then only a
   single fact line containing the information about the named file or
   directory shall be returned.

   If no argument is given then MLSD must return a listing of the
   contents of the current working directory, and MLST must return a
   listing giving information about the current working directory
   itself.

   If the Client-FTP sends an invalid argument, the Server-FTP MUST
   reply with an error code of 501.




Elz & Hethmon                                                  [Page 13]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


   The syntax for the MLST command is:

        mlst       = "MLst" [ SP ( utf-8-name / raw ) ] CRLF
        utf-8-name = <a UTF-8 encoded Unicode string>
        raw        = <any string not being a valid UTF-8 encoding>

6.2. Format of MLST Response

   The format of a response to the MLST command is as follows:

        mlst-response         = initial-response final-response
        initial-response      = "150" [ SP response-message ] CRLF /
                                error-response
        response-message      = *TCHAR
        final-response        = "226" SP response-message CRLF

        data-response         = *( entry CRLF )
        entry                 = [ facts ] SP ( utf-8-name / raw )
        facts                 = fact *( ";" fact )
        fact                  = factname "=" value
        factname              = 1*ltext
        value                 = 1*ltext
        end-token             = "End"

   Upon receipt of a MLST or MLSD command, the server will verify the
   parameter, and if invalid return an error-response.  If valid, the
   server will open a data connection as indicated in section 3.2 of
   RFC959.  If that fails, the server will return an error-response.  If
   all is OK, the server will return the initial-response, send the
   appropriate data-response over the new data connection, close that
   connection, and then send the final-response.

   The data connection opened for a MLST or MLSD response shall be
   connection as if the "TYPE L 8", "MODE S", and "STRU F" commands had
   been given, whatever FTP transfer type, mode and structure had
   actually been set, and without causing those settings to be altered
   for future commands.  That is, this transfer type shall be set for
   the duration of the data connection established for this command
   only.  While the content of the data sent can be viewed as a series
   of lines, implementations should note that there is no maximum line
   length defined.  Implementations should be prepared to deal with
   arbitrarily long lines.

   The facts part of the specification would contain a series of "file
   facts" about the file/directory named on the same line.  Typical
   information to be presented would include file size, last
   modification time, creation time, a unique identifier, and a
   file/directory flag.



Elz & Hethmon                                                  [Page 14]


Internet Draft       draft-ietf-ftpext-mlst-01.txt             June 1997


   The complete format for a successful reply to the MLST command would
   be:

        facts SP utf-8-name CRLF
        facts SP utf-8-name CRLF
        facts SP utf-8-name CRLF
        ...

   Note that the format is intended for machine processing, not human
   viewing, and as such the format is very rigid.  Implementations must
   not vary the format by, for example, inserting extra spaces for
   readability, or inserting blank lines, or in any other way alter this
   format.  Exactly one space is always required after the set of facts
   (which may be empty).  More spaces may be present on a line if, and
   only if, the file name presented contains significant spaces.  The
   set of facts must not contain any spaces anywhere inside it.

6.3. Filename encoding

   A FTP implementation using the MLST command must be 8-bit clean.
   This is necessary in order to transmit UTF-8 encoded filenames.  This
   specification recommends the use of UTF-8 encoded filenames.  FTP
   implementations SHOULD use UTF-8 whenever possible to encourage the
   maximum interoperability.

   Filenames are not restricted to UTF-8, however treatment of arbitrary
   character encodings is not specified by this standard.  Applications
   are encouraged to treat non-UTF-8 encodings of filenames as octet
   sequences.

   Note that this encoding is unrelated to that of the contents of the
   file, even if the file contains character data.

   Further information about filename encoding for FTP may be found in
   "Internationalization of the File Transfer Protocol" [4].

6.3.1. Notes about the Filename

   The filename returned in the MLST response should be the same name as
   was specified in the MLST command.  Filenames returned in the output
   from an MLSD command should be unqualified names within the directory
   named.  That is, the directory named in the MLSD command should not
   appear as a component of the filenames returned.

   If the server-FTP process is able, it MAY return in the MLSD
   response, an entry whose type is "cdir", which names the directory
   from which the contents of the listing were obtained.  Where more
   than one name exists, multiple of these entries may be returned.  The



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   server MUST return type "cdir" names in a format such that if the
   user-PI takes a name of type "cdir", and appends a name of type which
   is not "cdir", and which appeared in the same MLSD response as the
   type=cdir name, with no intervening separators, then a valid pathname
   will be produced, using which the user-PI can reference the file
   indicated from its current working directory.

   Alternatively, the user-PI can issue a CWD command ([6]) giving the
   name of type "cdir", and from that point reference the files returned
   in the MLSD response from which the cdir was obtained by using the
   filename components of the listing.  Once having attempted any CWD
   command however, it is no longer guaranteed that a file can be
   referenced by the combination of type "cdir" and other names, whether
   using CWD or name concatenation.

6.3.2. Examples

   Once upon a (future) time, examples existed here.

6.4. Format of Facts

   The "facts" for a file in a reply to a MLST command consist of
   information about that file.  The facts are a series of keyword=value
   pairs separated by a semi-colon (";") character.  The complete series
   of facts may not contain the space character.

   A sample of a typical series of facts would be: (spread over two
   lines for presentation only)

        size=4161;lang=en-us;modify=19970214165800;create=19961001124534;
        type=file;x.myfact=foo,bar

6.5. Standard Facts

   This document defines a standard set of facts as follows:

        size       -- Size in bytes
        modify     -- Last modification time
        create     -- Creation time
        type       -- Entry type
        unique     -- Unique id of file/directory
        perm       -- File permissions, whether read, write, execute is
                      allowed for the login id.
        lang       -- Language of the filename per IANA[5] registry.
        media-type -- MIME media-type of file contents per IANA registry.
        charset    -- Character set per IANA registry (if not UTF-8)





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   Fact names are case-insensitive.  Size, size, SIZE, and SiZe are the
   same fact.

   Further operating system specific keywords could be specified by
   using the IANA operating system name as a prefix (examples only):

        OS/2.ea   -- OS/2 extended attributes
        MACOS.rf  -- MacIntosh resource forks
        UNIX.mode -- Unix file modes (permissions)

   Implementations may define keywords for experimental, or private use.
   All such keywords MUST begin with the two character sequence "x.".
   As type names are case independent, "x." and "X." are equivalent.
   For example:

        x.ver  -- Version information
        x.desc -- File description
        x.type -- File type

6.5.1. The type Fact

   The type fact needs a special description.  Part of the problem with
   current practices is deciding when a file is a directory.  If it is a
   directory, is it the current directory, a regular directory, or a
   parent directory?  The MLST specification makes this unambiguous
   using the type fact.  The type fact given specifies information about
   the object listed on the same line of the MLST response.

   Five values are possible for the type fact:

        file        -- a file entry
        cdir        -- the current directory
        pdir        -- the parent directory
        dir         -- a directory or sub-directory
        OSname=type -- an OS or file system dependent file type

   The syntax is defined to be:

        type-fact       = type-label "=" type-val
        type-label      = "Type"
        type-val        = "File" / "cdir" / "pdir" / "dir" /
                          sys-depend-type
        sys-depend-type = "OS" 1*ltext "=" 1*ltext

6.5.1.1. type=file

   The presence of the type=file fact indicates the listed entry is a
   file containing non-system data.  That is, it may be transferred from



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   one system to another of quite different characteristics, and perhaps
   still be meaningful.

6.5.1.2. type=cdir

   The type=cdir fact indicates the listed entry is the pathname of the
   directory whose contents are listed.  The value of this entry (the
   filename part) plus the value of a type=file entry from the same MLSD
   listing together should represent a complete pathname suitable for a
   RETR command.  The value for the type=cdir entry should include any
   necessary system delimiters used between path components.  An example
   would be the forward slash "/" on a UNIX(TM) system, or a back slash
   "\" on an OS/2 or Windows system.

6.5.1.3. type=dir

   If present, the type=dir entry is the name of a directory.  When
   executed with the current directory in the same place in the NVFS as
   it was when the MLST or MLSD command was issued, a CWD with its
   argument being the formed by appending the name with type=pdir to a
   name with type-cdir should succeed (assuming the user has the
   appropriate access rights).

6.5.1.4. type=pdir

   If present, which will occur only in the response to a MLSD command,
   the type=pdir entry represents a pathname of the parent directory of
   the listed directory.  As well as having the properties of a
   type=dir, a CWD command with the appropriate value should change the
   user to the parent directory of the listed directory.  User-FTP
   processes should note not all responses will include this
   information.

6.5.2. The unique Fact

   The unique fact is used to present a unique identifier for a file or
   directory in the NVFS accessed via a server-FTP process.  The value
   of this fact should be the same for any number of filenames that
   refer to the same underlying file.  The fact should have different
   values for names which reference distinct files.  The mapping between
   files, and unique fact tokens should be maintained, and remain
   consistent, for at least the lifetime of the control connection from
   user-PI to server-PI.








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        unique-fact  = "Unique" "=" token

   This fact would be expected to be used by Server-FTPs whose host
   system allows things such as symbolic links so that the same file may
   be represented in more than one directory on the server.  The value
   of the unique fact should be considered an opaque string for
   comparison purposes.  The only conclusion that should be drawn is
   that if two different names each have the same value for the unique
   fact, they refer to the same underlying object.

6.5.3. The modify Fact

   The modify fact is used to determine the last time the content of the
   file (or directory) indicated was modified.  Any change of substance
   to the file should cause this value to alter.  Changes which merely
   alter access rights, and similar attributes, which do not affect the
   content or meaning of the data contained in a file, should not cause
   this value to alter.

   For directories, this value should alter whenever a change occurs to
   the directory such that different filenames would (or might) be
   included in MLSD output of that directory.

        modify-fact  = "Modify" "=" time-val

6.5.4. The create Fact

   The create fact indicates when a file, or directory, was first
   created.  Exactly what "creation" is for this purpose is not
   specified here, and may vary from server to server.  About all that
   can be said about the value returned is that it can never indicate a
   later time than the mtime fact.

        create-fact  = "Create" "=" time-val

   Implementation Note: Implementors of this fact on UNIX(TM) systems
        should note that the unix "stat" "st_ctime" field does not give
        creation time, and that unix filesystems do not record creation
        time at all.  Unix (and POSIX) implementations will normally not
        include this fact.

6.5.5. The perm Fact

   The perm fact is used to indicate access rights the current FTP user
   has over the object listed.  Its value is always an unordered
   sequence of alphabetic characters.





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        perm-fact    = "Perm" "=" pvals
        pvals        = *ALPHA

   There are ten permission indicators currently defined.  Many are
   meaningful only when used with a particular type of object.  The ten
   characters currently defined are:

        a c d e f l m p r w

               [ Ed-Note: should these be case dependent or independent
               ? ]

   The "a" permission applies to objects of type=file, and indicates
   that the APPE (append) command may be applied to the file named.

   The "c" permission applies to objects of type=dir (and type=pdir,
   type=cdir).  It indicates that files may be created in the directory
   named.  That is, that a STOU command is likely to succeed, and that
   STOR and APPE commands might succeed if the file named did not
   previously exist, but is to be created in the directory object that
   has the "c" permission.  It also indicates that the RNTO command is
   likely to succeed for names in the directory.

   The "d" permission applies to all types.  For type=file it indicates
   that the file may be deleted, that is, that the DELE command may be
   applied to it.  For the directory types it indicates that (some)
   files in the directory may be deleted.

   The "e" permission applies to the directory types.  When set on an
   object of type=dir, type=cdir, or type=pdir it indicates that a CWD
   command naming the object should succeed, and the user should be able
   to enter the directory named.  For type=pdir it also indicates that
   the CDUP command should succeed.

   The "f" permission for objects indicates that the object named may be
   renamed - that is, may be the object of an RNFR command.

   The "l" permission applies to the directory file types, and indicates
   that the listing commands, LIST, NLST, and MLSD may be applied to the
   directory in question, and that MLST, LIST, NLST, and STAT may be
   applied to objects in the directory.

   The "m" permission applies to directory types, and indicates that the
   MKD command may be used to create a new directory within the
   directory under consideration.

   The "p" permission applies to directory types, and indicates that the
   RMD command may be used to remove (purge) the directory named.



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   The "r" permission applies to type=file objects, and indicates that
   the RETR command may be applied to that object.

   The "w" permission applies to type=file objects, and indicates that
   the STOR command may be applied to the object named.

   Note: That a permission indicator is set can never imply that the
        appropriate command is guaranteed to work - just that it might.
        Other system specific limitations, such as limitations on
        available space for storing files, may cause an operation to
        fail, where the permission flags may have indicated that it was
        likely to succeed.  The permissions are a guide only.

   Implementation note: The permissions are described here as they apply
        to FTP commands.  They may not map easily into particular
        permissions available on the server's operating system.  Servers
        are expected to synthesize these permission bits from the
        permission information available from operating system.  For
        example, to correctly determine whether the "p" permission bit
        should be set on a directory for a server running on the
        UNIX(TM) operating system, the server should check that the
        directory named is empty, and that the user has write permission
        on both the directory under consideration, and its parent
        directory.

        Some systems may have more specific permissions than those
        listed here, such systems should map those to the flags defined
        as best they are able.  Other systems may have only more broad
        access controls.  They will generally have just a few possible
        permutations of permission flags, however they should attempt to
        correctly represent what is permitted.

6.5.6. The lang Fact

   The lang fact describes the natural language of the filename for use
   in display purposes.  Values used here should be taken from the
   language registry of the IANA.

        lang-fact  = "Lang" "=" token

   Server-FTP implementations MUST NOT guess language values.  Language
   values must be determined in an unambiguous way such as filesystem
   tagging of language or by user configuration.








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6.5.7. The size Fact

   The size should always reflect the approximate size of the file.
   This should be as accurate as the server can make it, without going
   to extraordinary lengths, such as reading the entire file.  The size
   is expressed in units of octets.

   Given limitations in some systems, Client-FTP implementations must
   understand this size may not be precise and may change between the
   time of a MLST and RETR operation.

   Clients that need highly accurate size information for some
   particular reason should use the SIZE command as defined in section
   4.  The most common need for this accuracy is likely to be in
   conjunction with the REST command described in section 5.  The size
   fact, on the other hand, should be used for purposes such as
   indicating to a human user the approximate size of the file to be
   transferred, and perhaps to give an idea of expected transfer
   completion time.

        size-fact  = "Size" "=" 1*DIGIT

6.5.8. The media-type Fact

   The media-type fact represents the IANA media type of the file.  The
   list of values used must follow the guidelines set by the IANA
   registry.

        media-type  = "Media-Type" "=" <per IANA guidelines>

   Server-FTP implementations MUST NOT guess media type values.  Media
   type values must be determined in an unambiguous way such as
   filesystem tagging of media-type or by user configuration.

6.5.9. The charset Fact

   The charset fact represents the IANA character set name for the
   encoded names in a MLST response.  The default character set is UTF-8
   unless specified otherwise.  FTP implementations SHOULD use UTF-8 if
   possible to encourage maximum interoperability.

        charset-type  = "Charset" "=" token









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6.6. FEAT response for MLST

   When responding to the FEAT command, a server-FTP process that
   supports MLST, and related commands, MLSD, and the modified STAT,
   plus internationalisation of pathnames, MUST indicate that this
   support exists.  It does this by including a MLST feature line.  As
   well as indicating the basic support, the MLST feature line indicates
   which MLST facts are available from the server, and which of those
   will be returned if no subsequent "OPTS MLST" command is sent.

        mlst-feat     = SP "MLST" [SP factlist] CRLF
        factlist      = factname ["*"] *( ";" factname ["*"] )

   The initial space shown in the mlst-feat response is that required by
   the FEAT command, two spaces are not permitted.  If no factlist is
   given, then the server-FTP process is indicating that it supports
   MLST, but implements no facts.  Only pathnames can be returned.  This
   would be a minimal MLST implementation, and useless for most
   practical purposes.  Where the factlist is present, the factnames
   included indicate the facts supported by the server.  Where the
   optional asterisk appears after a factname, that fact will be
   included in MLST format responses, until an "OPTS MLST" is given to
   alter the list of facts returned.

               [ Ed-Note: Perhaps the sense of the "*" should be
               reversed?  That is, make the asterisk indicate those
               facts not returned? ]

6.7. OPTS parameters for MLST

   For the MLST command, the Client-FTP may specify a list of facts it
   wishes to be returned in all subsequent MLST commands until another
   OPTS MLST command is sent.  The format is specified by:

        mlst-opts     = "OPTS" SP "MLST"
                        [ SP factname *(";" factname) ]

   By sending the "OPTS MLST" command, the client requests the server to
   include only the facts listed as arguments to the command in
   subsequent output from MLST commands.  Facts not included in the
   "OPTS MLST" command must not be returned by the server.  Facts that
   are included should be returned for each entry returned from the MLST
   command where they apply.  Facts requested that are not supported, or
   which are inappropriate to the file or directory being listed should
   simply be omitted from the MLST output.  This is not an error.  Note
   that where no factname arguments are present, the client is
   requesting that only the file names be returned.  In this case, and
   in any other case where no facts are included in the result, the



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   space that separates the fact names and their values from the file
   name is still required.  That is, the first character of the output
   line will be a space, and the file name will start immediately
   thereafter.

   Note, there is no "OPTS MLSD" command, the fact names set with the
   TS MLST" command apply to both MLST and MLSD commands, and to the
   STAT command when used with a file name argument and no transfer in
   progress.

7. Interpretation of STAT command output

   Where a server-FTP process supports the MLST and MLST commands, the
   format of the output from the STAT command ([6] section 4.1.3) when
   given with the optional pathname argument, permitted only when there
   is no file transfer operation in progress, is hereby specified to be
   the same as that of the MLST command, with just the following
   modifications, required because the output is sent over the control
   connection.

   More text comes here, eventually, setting out exactly what the STAT
   response will look like.  Most of it will be borrowed from the
   original definition of MLST output, from the days when it was
   permitted over the control connection.

7.1. FEAT response for STAT

   There is no output in the FEAT command that specifically indicates
   that the STAT command behaves as described above.  Implementations
   must infer this from support of the MLST command by the server, which
   is indicated in the FEAT output.

8. Impact On Other FTP Commands

   Along with the introduction of MLST, traditional FTP commands must be
   extended to allow for the use of more than US-ASCII or EBCDIC
   character sets.  In general, the support of MLST requires support for
   arbitrary character sets wherever filenames and directory names are
   allowed.  This applies equally to both arguments given to the
   following commands and to the replies from them, as appropriate.

        CWD
        RETR
        STOR
        STOU
        APPE
        RNFR
        RNTO



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        DELE
        RMD
        MKD
        PWD
        STAT

   The arguments to all of these commands should be processed the same
   way that MLST commands and responses are processed with respect to
   handling embedded CRs and NULs.  See section 2.2.

8.1. Impact on Pathnames and Filenames

   The design of MLST requires the Server-FTP to allow concatenation of
   certain elements of a MLST response.  Specifically, a typical
   response would include an element which indicates the current
   directory and one or more elements which are files in the indicated
   directory.  A Server-FTP must be able to accept a simple
   concatenation of these two names even if the underlying operating
   system does not accept a simple concatenation.  The Server-FTP must
   perform any translation of the concatenated name to local
   equivalents.

9. Character sets and Internationalisation

   This section will set out just what is going on with char sets, what
   data is part of the protocol, and always appears exactly as is
   specified (and could almost as easily be numbers, or any other kind
   of encoding), and what is text for users, which should be able to
   appear in their language of choice, or otherwise be handled in some
   kind of rational way.  That is, it will once it is written.  This is
   merely a placeholder.

10. Security

   This memo does not yet discuss security.  It is possible that no new
   security concerns are raised in this memo above what already exists
   within the FTP protocol.  However, the working group needs to
   consider this carefully.

11. References

   [1]  Coded Character Set--7-bit American Standard Code for Information
        Interchange, ANSI X3.4-1986.

   [2]  F. Yergeau, "UTF-8, a transformation format of Unicode and ISO
        10646", RFC 2044, Alis Technologies, October 1996.





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   [3]  D. Crocker, "Augmented BNF for Syntax Specifications: ABNF",
        Work In Progress <draft-ietf-drums-abnf-02.txt>, Internet
        Mail Consortium, March 1997.

   [4]  W. Curtin, "Internationalization of the File Transfer Protocol",
        Work In Progress <draft-ietf-ftpext-itln-02.txt>, Defense
        Information Systems Agency, November 1996.

   [5]  Internet Assigned Numbers Authority. http://www.isi.edu/div7/iana/
        Email: iana@iana.org.

   [6]  J. Postel, J. Reynolds, "File Transfer Protocol (FTP)",
        STD 9 (RFC 959), ISI, October 1985

   [7]  R. Braden, "Requirements for Internet Hosts -- Application
        and Support", STD 3 (RFC 1123), October 1989

   [8]  ISO 3307 (need a citation for this please!)

   [9]  D. Crocker, "Augmented BNF for Syntax Specifications: ABNF",
        Work In Progress <draft-ietf-drums-abnf-NN.txt>, Internet
        Mail Consortium, March 1997.

   [10] S. Bradner, "Key words for use in RFCs to Indicate
        Requirement Levels", BCP 14 (RFC 2119), Harvard University,
        March 1997

   [11] P. Hethmon, R. Elz, "Feature negotiation mechanism for the
        File Transfer Protocol",  Work in progress,
        <draft-ietf-ftpext-feat-00.txt> Hethmon Bros, University of Melbourne,
        June 1997.

   [12] J. Postel, J. Reynolds, "Telnet protocol Specification"
        STD 8 (RFC 854), ISI, May 1983

Acknowledgements

   The following people have contributed to this document:

        Alex Belits
        D. J. Berstein
        Martin J. Duerst
        Mark Harris
        Alun Jones
        James Matthews
        Keith Moore
        and the entire FTPEXT working group of the IETF.




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   The description of the modifications to the REST command and the MDTM
   and SIZE commands comes from a set of modifications suggested for
   RFC959 by Rick Adams in 1989.  A draft containing just those
   commands, edited by David Borman, has been merged with this document.

Editors' Addresses

   Robert Elz
   University of Melbourne
   Department of Computer Science
   Parkville, Vic   3052
   Australia

   Email: kre@munnari.OZ.AU


   Paul Hethmon
   Hethmon Brothers
   2305 Chukar Road
   Knoxville, TN 37923 USA

   Phone: +1-423-690-8990
   Email: phethmon@hethmon.com




























Elz & Hethmon                                                  [Page 27]


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