          RFC 775          Directory oriented FTP commands        Page 1

                           DIRECTORY ORIENTED FTP COMMANDS

                             David Mankins (dm@bbn-unix)
                             Dan Franklin (dan@bbn-unix)
                              A. D. Owen (ADOwen@bbnd)

          As a part of the Remote Site Maintenance (RSM) project for  ARPA,
          BBN  has installed and maintains the software of several DEC PDP-
          11s running the Unix operating system.  Since Unix  has  a  tree-
          like  directory  structure,  in  which directories are as easy to
          manipulate as ordinary files, we  have  found  it  convenient  to
          expand  the  FTP  servers  on  these machines to include commands
          which deal with the creation of  directories.   Since  there  are
          other  hosts  on  the  ARPA net which have tree-like directories,
          including Tops-20 and  Multics,  we  have  tried  to  make  these
          commands as general as possible.

          We have added four commands to our server:

               XMKD child
                             Make a directory with the name "child".

               XRMD child
                             Remove the directory with the name "child".

               XPWD
                             Print the current working directory.

               XCUP
                             Change to the parent of  the  current  working
                             directory.

          The  "child"  argument  should  be   created   (removed)   as   a
          subdirectory of the current working directory, unless the "child"
          string contains sufficient information to  specify  otherwise  to
          the server, e.g., "child" is an absolute pathname (in Multics and
          Unix), or child is something like "<abso.lute.path>" to Tops-20.

    RFC 775          Directory oriented FTP commands        Page 2

                                     REPLY CODES

          The XCUP command is a special case of XCWD, and  is  included  to
          simplify   the   implementation   of  programs  for  transferring
          directory  trees  between  operating  systems  having   different
          syntaxes for naming the parent directory.  Therefore we recommend
          that the reply codes for XCUP be identical to the reply codes  of
          XCWD.

          Similarly,  we  recommend  that  the  reply  codes  for  XRMD  be
          identical to the reply codes for its file analogue, DELE.

          The reply codes for XMKD, however, are a bit more complicated.  A
          freshly created directory will probably be the object of a future
          XCWD command.  Unfortunately, the argument to XMKD may not always
          be  a suitable argument for XCWD.  This is the case, for example,
          when a  Tops-20  subdirectory  is  created  by  giving  just  the
          subdirectory  name.   That  is,  with  a  Tops-20 server FTP, the
          command sequence

                                     XMKD MYDIR
                                     XCWD MYDIR

          will fail.  The new directory may only  be  referred  to  by  its
          "absolute"  name;  e.g.,  if  the  XMKD command above were issued
          while  connected  to   the   directory   <DFRANKLIN>,   the   new
          subdirectory   could   only   be   referred   to   by   the  name
          <DFRANKLIN.MYDIR>.

          Even on Unix and Multics, however, the argument given to XMKD may
          not  be  suitable.   If  it  is a "relative" pathname (that is, a
          pathname which is interpreted relative to the current directory),
          the  user would need to be in the same current directory in order
          to reach the subdirectory.  Depending on  the  application,  this
          may be inconvenient.  It is not very robust in any case.

          To solve these problems, upon successful completion  of  an  XMKD
          command, the server should return a line of the form:

                   257<space>"<directory-name>"<space><commentary>

          That is, the server will tell the user what string  to  use  when
          referring  to  the  created  directory.   The  directory name can
          contain any character; embedded double-quotes should  be  escaped

    RFC 775          Directory oriented FTP commands        Page 3

          by double-quotes (the "quote-doubling" convention).

          For example, a  user  connects  to  the  directory  /usr/dm,  and
          creates a subdirectory, named child:

                      XCWD /usr/dm
                      200 directory changed to /usr/dm
                      XMKD child
                      257 "/usr/dm/child" directory created

          An example with an embedded double quote:

                      XMKD foo"bar
                      257 "/usr/dm/foo""bar" directory created
                      XCWD /usr/dm/foo"bar
                      200 directory changed to /usr/dm/foo"bar

          We  feel that the prior existence of a subdirectory with the same
          name  should be interpreted as an error, and have implemented our
          server to give an "access denied" error reply in  that case.

                      CWD /usr/dm
                      200 directory changed to /usr/dm
                      XMKD child
                      521-"/usr/dm/child" directory already exists;
                      521    taking no action.

          We recommend that failure replies for XMKD be  analogous  to  its
          file  creating  cousin, STOR.  Also, we recommend that an "access
          denied" return be given if a file name with the same name as  the
          subdirectory  will conflict with the creation of the subdirectory
          (this is a problem on Unix, but shouldn't be one on Tops-20).

          Essentially because the XPWD command returns  the  same  type  of
          information  as  the successful XMKD command, we have implemented
          the successful XPWD command to use the 257 reply code as well.

          We present here a summary of the proposed  reply  codes  for  the
          experimental  commands.   The codes given outside parentheses are
          consistent with RFC 691; i.e.,  are  for  the  old  protocol,  as
          updated  by  the  suggestions  in  that RFC.  The server and user
          programs at BBN-Unix currently implement these codes.  Reply  257
          is  the  only new code.  Reply codes shown within parentheses are
          for the "new" ftp protocol, most recently documented in RFC  765.

    RFC 775          Directory oriented FTP commands        Page 4

          The invented code for the RFC 765 Protocol is 251.

          Command:

                  reply code      explanation

          XMKD                    create directory

                  257 (251) "pathname" created
                  521 (450) "pathname" already exists
                  506 (502) action not implemented
                  521 (450) access denied
                  550 (501) bad pathname syntax or ambiguous
                  425 (451) random file system error

          XCUP                    change directory to
                                          superior of current one

                  200 (200) working directory changed
                  506 (502) action not implemented
                  507 (551) no superior directory
                  521 (450) access denied
                  425 (451) random file system error

          XRMD                    remove directory

                  224 (250) deleted ok
                  506 (502) action not implemented
                  521 (450) access denied
                  550 (501) bad pathname syntax or ambiguous
                  425 (451) random file system error

          XPWD                    print current working
                                          directory

                  257 (251) "pathname"
                  425 (451) random file system error
                  506 (502) action not implemented

    RFC 775          Directory oriented FTP commands        Page 5

                                     SUBTLETIES

          Because these  commands  will  be  most  useful  in  transferring
          subtrees  from  one  machine  to another, we must stress the fact
          that the argument to XMKD is to be interpreted as a sub-directory
          of  the  current  working  directory,  unless  it contains enough
          information for  the  destination  host  to  tell  otherwise.   A
          hypothetical example of its use in the Tops-20 world:

                      XCWD <some.where>
                  200 Working directory changed
                      XMKD overrainbow
                      257 "<some.where.overrainbow>" directory created
                      XCWD overrainbow
                      431 No such directory
                      XCWD <some.where.overrainbow>
                      200 Working directory changed

                      XCWD <some.where>
                      200 Working directory changed to <some.where>
                      XMKD <unambiguous>
                      257 "<unambiguous>" directory created
                      XCWD <unambiguous>

          Note that the first example results  in  a  subdirectory  of  the
          connected  directory.   In  contrast,  the argument in the second
          example contains enough information for Tops-20 to tell that  the
          <unambiguous> directory is a top-level directory.  Note also that
          in  the  first  example  the  user  "violated"  the  protocol  by
          attempting  to  access  the freshly created directory with a name
          other than the one returned  by  Tops-20.   Problems  could  have
          resulted  in this case had there been an <overrainbow> directory;
          this is an ambiguity inherent in  some  Tops-20  implementations.
          Similar  considerations  apply to the XRMD command.  The point is
          this: except where to do so would violate  a  host's  conventions
          for  denoting relative versus absolute pathnames, the host should
          treat  the  operands  of  the   XMKD   and   XRMD   commands   as
          subdirectories.   The  257  reply to the XMKD command must always
          contain the absolute pathname of the created directory.

                                     References

          File Transfer Protocol (RFC 765), Postel,  J., June 1980

    RFC 775          Directory oriented FTP commands        Page 6

          CWD Command of FTP (RFC 697), Lieb, J., NIC 32963, 14 July 1975
          One More Try on the FTP (RFC 691), Harvey, B., NIC 32700, 28  May
          1975
          Revised FTP Reply Codes (RFC 640),  Postel,  J.,  N.  Neigus,  K.
          Pogran, NIC 30843, 5 June 1974
          File Transfer Protocol (RFC 542), Neigus, N., NIC 17759,  12 July
          1977