rfc640.txt

RFC 相关的技术文档

          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