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rfc:rfc640
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Revised FTP Reply Codes
                                                         Jon Postel
                                                          19 JUN 75
                        Revised FTP Reply Codes                          1
  This document describes a revised set of reply codes for the File
  Transfer Protocol.                                                     2
  The aim of this revision is to satisfy the goal of using reply
  codes to enable the command issuing process to easily determine
  the outcome of each command. The user protocol interpreter should
  be able to determine the success or failure of a command by
  examining the first digit of the reply code.                           3
  An important change in the sequencing of commands and replies
  which may not be obvious in the following documents concerns the
  establishment of the data connection.                                  4
     In the previous FTP specifications when an actual transfer
     command (STOR, RETR, APPE, LIST, NLIST, MLFL) was issued the
     preliminary reply was sent after the data connection was
     established. This presented a problem for some user protocol
     interpreters which had difficulty monitoring two connections
     asynchronously.                                                    4a
     The current specification is that the preliminary reply to the
     actual transfer commands indicates that the file can be
     transferred and either the connection was previously
     established or an attempt is about to be made to establish the
     data connection.                                                   4b
  This reply code revision is a modification of the protocol in
  described in RFC 542, that is to say that the protocol
  implementation associated with socket number 21 (decimal) is the
  protocol specified by the combination of RFC 542 and this RFC.         5
  A note of thanks to those who contributed to this work: Ken
  Pogran, Mark Krilanovich, Wayne Hathway, and especially Nancy
  Neigus.                                                                6
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  
                                                       Nancy Neigus
                                                         Ken Pogran
                                                         Jon Postel
                                                          19 JUN 75
                   A New Schema for FTP Reply Codes                      7
  Replies to File Transfer Protocol commands were devised to ensure
  the synchronization of requests and actions in the process of
  file transfer, and to guarantee that the user process always
  knows the state of the Server. Every command must generate at
  least one reply, although there may be more than one; in the
  latter case, the multiple replies must be easily distinguished.
  In addition, some commands occur in sequential groups, such as
  USER, PASS and ACCT, or RNFR and RNTO.  The replies show the
  existence of an intermediate state if all preceding commands have
  been successful.  A failure at any point in the sequence
  necessitates the repetition of the entire sequence from the
  beginning.                                                             8
     Details of the command-reply sequence will be made explicit in
     a state diagram.                                                   8a
  An FTP reply consists of a three digit number (transmitted as
  three alphanumeric characters) followed by some text.  The number
  is intended for use by automata to determine what state to enter
  next; the text is intended for the human user.  It is intended
  that the three digits contain enough encoded information that the
  user-process (the User-PI described in RFC 542) will not need to
  examine the text and may either discard it or pass it on to the
  user, as appropriate.  In particular, the text may be
  server-dependent, so there are likely to be varying texts for
  each reply code.                                                       9
  Formally, a reply is defined to contain the 3-digit code,
  followed by Space <SP>, followed by one line of text (where some
  maximum line length has been specified), and terminated by the
  TELNET end-of-line code.  There will be cases, however, where the
  text is longer than a single line.  In these cases the complete
  text must be bracketed so the User-process knows when it may stop
  reading the reply (i.e. stop processing input on the TELNET
  connection) and go do other things.  This requires a special
  format on the first line to indicate that more than one line is
  coming, and another on the last line to designate it as the last.
  At least one of these must contain the appropriate reply code to
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                       FTP Reply Codes  [3]
  indicate the state of the transaction.  To satisfy all factions
  it was decided that both the first and last line codes should be
  the same.                                                             10
     Thus the format for multi-line replies is that the first line
     will begin with the exact required reply code, followed
     immediately by a Hyphen, "-" (also known as Minus), followed
     by text.  The last line will begin with the same code,
     followed immediately by Space <SP>, optionally some text, and
     TELNET <eol>.                                                     10a
        For example:
                             123-First line
                             Second line
                               234 A line beginning with numbers
                             123 The last line                        10a1
     The user-process then simply needs to search for the second
     occurrence of the same reply code, followed by <SP> (Space),
     at the beginning of a line, and ignore all intermediary lines.
     If an intermediary line begins with a 3-digit number, the
     Server must pad the front to avoid confusion.                     10b
        This scheme allows standard system routines to be used for
        reply information (such as for the STAT reply), with
        "artificial" first and last lines tacked on.  In the rare
        cases where these routines are able to generate three
        digits and a Space at the beginning of any line, the
        beginning of each text line should be offset by some
        neutral text, like Space.                                     10b1
     This scheme assumes that multi-line replies may not be nested.
     We  have found that, in general, nesting of replies will not
     occur, except for random system messages (called spontaneous
     replies in the previous FTP incarnations) which may interrupt
     another reply.  Spontaneous replies are no longer defined;
     system messages (i.e. those not processed by the FTP server)
     will NOT carry reply codes and may occur anywhere in the
     command-reply sequence.  They may be ignored by the
     User-process as they are only information for the human user.     10c
  The three digits of the reply each have a special significance.
  This is intended to allow a range of very simple to very
  sophisticated response by the user-process.  The first digit
  denotes whether the response is good, bad or incomplete.
  (Referring to the state diagram) an unsophisticated user-process
  will be able to determine its next action (proceed as planned,
  redo, retrench, etc.) by simply examining this first digit.  A
  user-process that wants to know approximately what kind of error
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                       FTP Reply Codes  [4]
  occurred (e.g. file system error, command syntax error) may
  examine the second digit, reserving the third digit for the
  finest gradation of information (e.g. RNTO command without a
  preceding RNFR.)                                                      11
     There are four values for the first digit of the reply code:      11a
     1yz   Positive Preliminary reply                                  11b
        The requested action is being initiated; expect another
        reply before proceeding with a new command.  (The
        user-process sending another command before the  completion
        reply would be in violation of protocol; but server-FTP
        processes should queue any commands that arrive while a
        preceeding command is in progress.)  This type of reply can
        be used to indicate that the command was accepted and the
        user-process may now pay attention to the data connections,
        for implementations where simultaneous monitoring is
        difficult.                                                    11b1
     2yz   Positive Completion reply                                   11c
        The requested action has been successfully completed.  A
        new request may be initiated.                                 11c1
     3yz   Positive Intermediate reply                                 11d
        The command has been accepted, but the requested action is
        being held in abeyance, pending receipt of further
        information.  The user should send another command
        specifying this information.  This reply is used in command
        sequence groups.                                              11d1
     4yz   Transient Negative Completion reply                         11e
        The command was not accepted and the requested action did
        not take place, but the error condition is temporary and
        the action may be requested again.  The user should return
        to the beginning of the command sequence, if any.  It is
        difficult to assign a meaning to "transient", particularly
        when two distinct sites (Server and User-processes) have to
        agree on the interpretation.  Each reply in the 4yz
        category might have a slightly different time value, but
        the intent is that the user-process is encouraged to try
        again.  A rule of thumb in determining if a reply fits into
        the 4yz or the 5yz (Permanent Negative) category is that
        replies are 4yz if the commands can be repeated without any
        change in command form or in properties of the User or
        Server (e.g. the command is spelled the same with the same
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                       FTP Reply Codes  [5]
        arguments used; the user does not change his file access or
        user name; the server does not put up a new
        implementation.)                                              11e1
     5yz   Permanent Negative Completion reply                         11f
        The command was not accepted and the requested action did
        not take place.  The User-process is discouraged from
        repeating the exact request (in the same sequence).  Even
        some "permanent" error conditions can be corrected, so the
        human user may want to direct his User-process to
        reinitiate the command sequence by direct action at some
        point in the future (e.g. after the spelling has been
        changed, or the user has altered his directory status.)       11f1
     The following function groupings are encoded in the second
     digit:                                                            11g
        x0z   Syntax - These replies refer to syntax errors,
                syntactically correct  commands that don't fit any
                functional category, unimplemented or superfluous
                commands.                                             11g1
        x1z   Information -  These are replies to requests for
                information, such as status or help.                  11g2
        x2z   Connections - Replies referring to the TELNET and
                data connections.                                     11g3
        x3z   Authentication and accounting - Replies for the logon
                process and accounting procedures.                    11g4
        x4z   Unspecified as yet                                      11g5
        x5z   File system - These replies indicate the status of
                the Server file system vis-a-vis the requested
                transfer or other file system action.                 11g6
     The third digit gives a finer gradation of meaning in each of
     the function categories, specified by the second digit.  The
     list of replies below will illustrate this.  Note that the
     text associated with each reply is suggestive, rather than
     mandatory, and may even change according to the command with
     which it is associated.  The reply codes, on the other hand,
     should strictly follow the specifications in the last section;
     that is, Server implementations should not invent new codes
     for situations that are only slightly different from the ones
     described here, but rather should adapt codes already defined.
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                       FTP Reply Codes  [6]
     If additional codes are found to be necessary, the details
     should be submitted to the FTP committee, through Jon Postel.     11h
        A command such as TYPE or ALLO whose successful execution
        does not offer the user-process any new information will
        cause a 200 reply to be returned.  If the command is not
        implemented by a particular Server-FTP process because it
        has no relevance to that computer system, for example ALLO
        at a TENEX site, a Positive Completion reply is still
        desired so that the simple User-process knows it can
        proceed with its course of action.  A 202 reply is used in
        this case with, for example, the reply text:  "No storage
        allocation necessary."  If, on the other hand, the command
        requests a non-site-specific action and is unimplemented,
        the response is 502.  A refinement of that is the 504 reply
        for a command that IS implemented, but that requests an
        unimplemented parameter.                                      11h1
                                                                       11i
        200  Command okay                                             11i1
        500  Syntax error, command unrecognized
                [This may include errors such as command line too
                long.]                                                11i2
        501  Syntax error in parameters or arguments                  11i3
        202  Command not imlemented, superfluous at this site.        11i4
        502  Command not implemented                                  11i5
        503  Bad sequence of commands                                 11i6
        504  Command not implemented for that parameter               11i7
                                                                       11j
        110  Restart marker reply.
                In this case the text is exact and not left to the
                particular implementation; it must read:
                             MARK yyyy = mmmm
                where yyyy is User-process data stream marker, and
                mmmm is Server's equivalent marker.  (note the
                spaces between the markers and "=".)                  11j1
        211  System status, or system help reply                      11j2
        212  Directory status                                         11j3
        213  File status                                              11j4
        214  Help message (on how to use the server or the meaning
                of a particular non-standard command.  This reply
                is useful only to the human user.)                    11j5
                                                                       11k
        120  Service ready in nnn minutes                             11k1
        220  Service ready for new user                               11k2
        221  Service closing TELNET connection (logged off if
                appropriate)                                          11k3
        421  Service not available, closing TELNET connection.
                [This may be a reply to any command if the service
                knows it must shut down.]                             11k4
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                       FTP Reply Codes  [7]
        125  Data connection already open; transfer starting          11k5
        225  Data connection open; no transfer in progress            11k6
        425  Can't open data connection                               11k7
        226  Closing data connection; requested file action
                successful (for example, file transfer or file
                abort.)                                               11k8
        426  Connection trouble, closed; transfer aborted.            11k9
        227  Entering [passive, active] mode                         11k10
                                                                       11l
        230  User logged on, proceed                                  11l1
        530  Not logged in                                            11l2
        331  User name okay, need password                            11l3
        332  Need account for login                                   11l4
        532  Need account for storing files                           11l5
                                                                       11m
        150  File status okay; about to open data connection.         11m1
        250  Requested file action okay, completed.                   11m2
        350  Requested file action pending further information        11m3
        450  Requested file action not taken: file unavailable
                (e.g. file not found, no access)                      11m4
        550  Requested action not taken:  file unavailable (e.g.
                file busy)                                            11m5
        451  Requested action aborted: local error in processing      11m6
        452  Requested action not taken:  insufficient storage
                space in system                                       11m7
        552  Requested file action aborted:  exceeded storage
                allocation (for current directory or dataset)         11m8
        553  Requested action not taken: file name not allowed        11m9
        354  Start mail input; end with <CR><LF>.<CR><LF>            11m10
                        Command-Reply Sequences                         12
   In this section, the command-reply sequence is presented.  Each
  command is listed with its possible replies; command groups are
  listed together.  Preliminary replies are listed first (with
  their succeeding replies under them), then positive and negative
  completion, and finally intermediary replies with the remaining
  commands from the sequence following.  This listing forms the
  basis for the state diagrams, which will be presented separately.     13
     ICP                                                               13a
        120                                                           13a1
           220                                                       13a1a
        220                                                           13a2
        421                                                           13a3
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                       FTP Reply Codes  [8]
     Logon                                                             13b
        USER                                                          13b1
           230                                                       13b1a
           530                                                       13b1b
           500, 501, 421                                             13b1c
           331, 332                                                  13b1d
        PASS                                                          13b2
           230                                                       13b2a
           202                                                       13b2b
           530                                                       13b2c
           500, 501, 503, 421                                        13b2d
           332                                                       13b2e
        ACCT                                                          13b3
           230                                                       13b3a
           202                                                       13b3b
           530                                                       13b3c
           500, 501, 503, 421                                        13b3d
     Logoff                                                            13c
        QUIT                                                          13c1
           221                                                       13c1a
           500                                                       13c1b
        REIN                                                          13c2
           120                                                       13c2a
              220                                                   13c2a1
           220                                                       13c2b
           421                                                       13c2c
           500, 502                                                  13c2d
     Transfer parameters                                               13d
        SOCK                                                          13d1
           200                                                       13d1a
           500, 501, 421, 530                                        13d1b
        PASV                                                          13d2
           227                                                       13d2a
           500, 501, 502, 421, 530                                   13d2b
        ACTV                                                          13d3
           227                                                       13d3a
           202                                                       13d3b
           500, 501, 421, 530                                        13d3c
        BYTE, MODE, TYPE, STRU                                        13d4
           200                                                       13d4a
           500, 501, 504, 421, 530                                   13d4b
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                       FTP Reply Codes  [9]
     File action commands                                              13e
        ALLO                                                          13e1
           200                                                       13e1a
           202                                                       13e1b
           500, 501, 504, 421, 530                                   13e1c
        REST                                                          13e2
           500, 501, 502, 421, 530                                   13e2a
           350                                                       13e2b
        STOR                                                          13e3
           125, 150                                                  13e3a
              (110)                                                 13e3a1
              226, 250                                              13e3a2
              425, 426, 451, 552                                    13e3a3
           532, 450, 452, 553                                        13e3b
           500, 501, 421, 530                                        13e3c
        RETR                                                          13e4
           125, 150                                                  13e4a
              (110)                                                 13e4a1
              226, 250                                              13e4a2
              425, 426, 451                                         13e4a3
           450, 550                                                  13e4b
           500, 501, 421, 530                                        13e4c
        LIST, NLST                                                    13e5
           125, 150                                                  13e5a
              226, 250                                              13e5a1
              425, 426, 451                                         13e5a2
           450                                                       13e5b
           500, 501, 502, 421, 530                                   13e5c
        APPE                                                          13e6
           125, 150                                                  13e6a
              (110)                                                 13e6a1
              226, 250                                              13e6a2
              425, 426, 451, 552                                    13e6a3
           532, 450, 550, 452, 553                                   13e6b
           500, 501, 502, 421, 530                                   13e6c
        MLFL                                                          13e7
           125, 150                                                  13e7a
              226, 250                                              13e7a1
              425, 426, 451, 552                                    13e7a2
           532, 450, 550, 452, 553                                   13e7b
           500, 501, 502, 421, 530                                   13e7c
        RNFR                                                          13e8
           450, 550                                                  13e8a
           500, 501, 502, 421, 530                                   13e8b
           350                                                       13e8c
        RNTO                                                          13e9
           250                                                       13e9a
           532, 553                                                  13e9b
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Neigus                                      FTP Reply Codes  [10]
           500, 501, 502, 503, 421, 530                              13e9c
        DELE                                                         13e10
           250                                                      13e10a
           450, 550                                                 13e10b
           500, 501, 502, 421, 530                                  13e10c
        ABOR                                                         13e11
           225, 226                                                 13e11a
           500, 501, 502, 421                                       13e11b
        MAIL                                                         13e12
           354                                                      13e12a
              250                                                  13e12a1
              451, 552                                             13e12a2
           450, 550, 452, 553                                       13e12b
           500, 501, 502, 421, 530                                  13e12c
     Informational commands                                            13f
        STAT                                                          13f1
           211, 212, 213                                             13f1a
           450                                                       13f1b
           500, 501, 502, 421, 530                                   13f1c
        HELP                                                          13f2
           211, 214                                                  13f2a
           500, 501, 502, 421                                        13f2b
     Miscellaneous commands                                            13g
        SITE                                                          13g1
           200                                                       13g1a
           202                                                       13g1b
           500, 501, 530                                             13g1c
        NOOP                                                          13g2
           200                                                       13g2a
           500                                                       13g2b
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
                                                         Jon Postel
                                                          19 JUN 75
                          FTP State Diagrams                            14
  Here we present state diagrams for a very simple minded FTP
  implementation. Only the first digit of the reply codes is used.
  There is one state diagram for each group of FTP commands or
  command sequences.                                                    15
  The command groupings were determined by constructing a model for
  each command then collecting together the commands with
  structurally identical models.                                        16
  For each command or command sequence there are three possible
  outcomes: success (S), failure (F), and error (E). In the state
  diagrams below we use the symbol B for "begin", and the symbol W
  for "wait for reply".                                                 17
  We first present the diagram that represents the largest group of
  FTP commands:                                                         18
     
                              1,3    +---+
                         ----------->! E !
                        !            +---+
                        !
     +---+    cmd    +---+    2      +---+
     ! B !---------->! W !---------->! S !
     +---+           +---+           +---+
                        !
                        !     4,5    +---+
                         ----------->! F !
                                     +---+
                                                                       18a
     This diagram models the commands:                                 18b
        ABOR, ACTV, ALLO, BYTE, DELE, HELP, MODE, NOOP, PASV, QUIT,
        SITE, SOCK, STAT, STRU, TYPE.                                 18b1
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Postel                                    FTP State Diagrams [12]
  The other large group of commands is represented by a very
  similar diagram:                                                      19
     
                              3      +---+
                         ----------->! E !
                        !            +---+
                        !
     +---+    cmd    +---+    2      +---+
     ! B !---------->! W !---------->! S !
     +---+       --->+---+           +---+
                !     ! !
                !     ! !     4,5    +---+
                !  1  !  ----------->! F !
                 -----               +---+
                                                                       19a
     This diagram models the commands:                                 19b
        APPE, (ICP), LIST, MLFL, NLST, REIN, RETR, STOR.              19b1
  Note that this second model could also be used to represent the
  first group of commands, the only difference being that in the
  first group the 100 series replies are unexpected and therefore
  treated as error, while the second group expects (some may
  require) 100 series replies.                                          20
  The remaining diagrams model command sequences, perhaps the
  simplest of these is the rename sequence:                             21
     
     +---+   RNFR    +---+    1,2    +---+
     ! B !---------->! W !---------->! E !
     +---+           +---+        -->+---+
                      ! !        !
               3      ! ! 4,5    !
        --------------  ------   !
       !                      !  !   +---+
       !               ------------->! S !
       !              !   1,3 !  !   +---+
       !             2!  --------
       !              ! !     !
       V              ! !     !
     +---+   RNTO    +---+ 4,5 ----->+---+
     !   !---------->! W !---------->! F !
     +---+           +---+           +---+
                                                                       21a
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Postel                                    FTP State Diagrams [13]
  A very similar diagram models the Mail command:                       22
     
     +---+   MAIL    +---+    1,2    +---+
     ! B !---------->! W !---------->! E !
     +---+           +---+        -->+---+
                      ! !        !
               3      ! ! 4,5    !
        --------------  ------   !
       !                      !  !   +---+
       !               ------------->! S !
       !              !   1,3 !  !   +---+
       !             2!  --------
       !              ! !     !
       V              ! !     !
     +---+   text    +---+ 4,5 ----->+---+
     !   !---------->! W !---------->! F !
     +---+           +---+           +---+
                                                                       22a
     Note that the "text" here is a series of lines sent from the
     user to the server with no response expected until the last
     line is sent, recall that the last line must consist only of a
     single period.                                                    22b
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Postel                                    FTP State Diagrams [14]
  The next diagram is a simple model of the Restart command:            23
     
     +---+   REST    +---+    1,2    +---+
     ! B !---------->! W !---------->! E !
     +---+           +---+        -->+---+
                      ! !        !
               3      ! ! 4,5    !
        --------------  ------   !
       !                      !  !   +---+
       !               ------------->! S !
       !              !   3   !  !   +---+
       !             2!  --------
       !              ! !     !
       V              ! !     !
     +---+   cmd     +---+ 4,5 ----->+---+
     !   !---------->! W !---------->! F !
     +---+        -->+---+           +---+
                 !      !
                 !  1   !
                  ------
                                                                       23a
        Where "cmd" is APPE, STOR, RETR, or MLFL.                     23a1
  We note that the above three models are similar, in fact the Mail
  diagram and the Rename diagram are structurally identical. The
  Restart differs from the other two only in the treatment of 100
  series replies at the second stage.                                   24
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Postel                                    FTP State Diagrams [15]
  The most complicated diagram is for the Logon sequence:               25
     
                           1
     +---+   USER    +---+------------->+---+
     ! B !---------->! W ! 2       ---->! E !
     +---+           +---+------  !  -->+---+
                      ! !       ! ! !
                    3 ! ! 4,5   ! ! !
        --------------   -----  ! ! !
       !                      ! ! ! !
       !                      ! ! ! !
       !                 ---------  !
       !               1!     ! !   !
       V                !     ! !   !
     +---+   PASS    +---+ 2  !  ------>+---+
     !   !---------->! W !------------->! S !
     +---+           +---+   ---------->+---+
                      ! !   ! !     !
                    3 ! !4,5! !     !
        --------------   --------   !
       !                    ! !  !  !
       !                    ! !  !  !
       !                 -----------
       !             1,3!   ! !  !
       V                !  2! !  !
     +---+   ACCT    +---+--  !   ----->+---+
     !   !---------->! W ! 4,5 -------->! F !
     +---+           +---+------------->+---+
                                                                       25a
  NWG/RFC# 640                               JBP NJN 5-JUN-74 16:07  30843
  Postel                                    FTP State Diagrams [16]
  Finally we present a generalized diagram that could be used to
  model the command and reply interchange:                              26
     
              ------------------------------------
             !                                    !
     Begin   !                                    !
       !     V                                    !
       !   +---+  cmd   +---+ 2         +---+     !
        -->!   !------->!   !---------->!   !     !
           !   !        ! W !           ! S !-----!
        -->!   !     -->!   !-----      !   !     !
       !   +---+    !   +---+ 4,5 !     +---+     !
       !     !      !    ! !      !               !
       !     !      !   1! !3     !     +---+     !
       !     !      !    ! !      !     !   !     !
       !     !       ----  !       ---->! F !-----
       !     !             !            !   !
       !     !             !            +---+
        -------------------
             !
             !
             V
            End
                                                                       26a
/data/webs/external/dokuwiki/data/pages/rfc/rfc640.txt · Last modified: 1992/10/15 21:52 by 127.0.0.1

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