rfc765.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

                                                                        
IEN 149                                                        J. Postel
RFC 765                                                              ISI
                                                               June 1980

                         FILE TRANSFER PROTOCOL


INTRODUCTION

   The objectives of FTP are 1) to promote sharing of files (computer
   programs and/or data), 2) to encourage indirect or implicit (via
   programs) use of remote computers, 3) to shield a user from
   variations in file storage systems among Hosts, and 4) to transfer
   data reliably and efficiently.  FTP, though usable directly by a user
   at a terminal, is designed mainly for use by programs.

   The attempt in this specification is to satisfy the diverse needs of
   users of maxi-Hosts, mini-Hosts, and TIPs, with a simple, and easily
   implemented protocol design.

   This paper assumes knowledge of the following protocols described in
   the ARPA Internet Protocol Handbook.

      The Transmission Control Protocol

      The TELNET Protocol

DISCUSSION

   In this section, the terminology and the FTP model are discussed.
   The terms defined in this section are only those that have special
   significance in FTP.  Some of the terminology is very specific to the
   FTP model; some readers may wish to turn to the section on the FTP
   model while reviewing the terminology.

   TERMINOLOGY

      ASCII

         The ASCII character set as defined in the ARPA Internet
         Protocol Handbook.  In FTP, ASCII characters are defined to be
         the lower half of an eight-bit code set (i.e., the most
         significant bit is zero).

      access controls

         Access controls define users' access privileges to the use of a
         system, and to the files in that system.  Access controls are
         necessary to prevent unauthorized or accidental use of files.
         It is the prerogative of a server-FTP process to invoke access
         controls.




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June 1980                                                        IEN 149
File Transfer Protocol                                           RFC 765



      byte size

         There are two byte sizes of interest in FTP:  the logical byte
         size of the file, and the transfer byte size used for the
         transmission of the data.  The transfer byte size is always 8
         bits.  The transfer byte size is not necessarily the byte size
         in which data is to be stored in a system, nor the logical byte
         size for interpretation of the structure of the data.

      data connection

         A simplex connection over which data is transferred, in a
         specified mode and type. The data transferred may be a part of
         a file, an entire file or a number of files.  The path may be
         between a server-DTP and a user-DTP, or between two
         server-DTPs.

      data port

         The passive data transfer process "listens" on the data port
         for a connection from the active transfer process in order to
         open the data connection.

      EOF

         The end-of-file condition that defines the end of a file being
         transferred.

      EOR

         The end-of-record condition that defines the end of a record
         being transferred.

      error recovery

         A procedure that allows a user to recover from certain errors
         such as failure of either Host system or transfer process.  In
         FTP, error recovery may involve restarting a file transfer at a
         given checkpoint.

      FTP commands

         A set of commands that comprise the control information flowing
         from the user-FTP to the server-FTP process.






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IEN 149                                                        June 1980
RFC 765                                           File Transfer Protocol



      file

         An ordered set of computer data (including programs), of
         arbitrary length, uniquely identified by a pathname.

      mode

         The mode in which data is to be transferred via the data
         connection. The mode defines the data format during transfer
         including EOR and EOF.  The transfer modes defined in FTP are
         described in the Section on Transmission Modes.

      NVT

         The Network Virtual Terminal as defined in the TELNET Protocol.

      NVFS

         The Network Virtual File System.  A concept which defines a
         standard network file system with standard commands and
         pathname conventions.  FTP only partially implements the NVFS
         concept at this time.

      page

         A file may be structured as a set of independent parts called
         pages.  FTP supports the transmission of discontinuous files as
         independent indexed pages.

      pathname

         Pathname is defined to be the character string which must be
         input to a file system by a user in order to identify a file.
         Pathname normally contains device and/or directory names, and
         file name specification.  FTP does not yet specify a standard
         pathname convention.  Each user must follow the file naming
         conventions of the file systems involved in the transfer.

      record

         A sequential file may be structured as a number of contiguous
         parts called records.  Record structures are supported by FTP
         but a file need not have record structure.







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June 1980                                                        IEN 149
File Transfer Protocol                                           RFC 765



      reply

         A reply is an acknowledgment (positive or negative) sent from
         server to user via the TELNET connections in response to FTP
         commands.  The general form of a reply is a completion code
         (including error codes) followed by a text string.  The codes
         are for use by programs and the text is usually intended for
         human users.

      server-DTP

         The data transfer process, in its normal "active" state,
         establishes the data connection with the "listening" data port,
         sets up parameters for transfer and storage, and transfers data
         on command from its PI.  The DTP can be placed in a "passive"
         state to listen for, rather than initiate a, connection on the
         data port.

      server-FTP process

         A process or set of processes which perform the function of
         file transfer in cooperation with a user-FTP process and,
         possibly, another server.  The functions consist of a protocol
         interpreter (PI) and a data transfer process (DTP).

      server-PI

         The protocol interpreter "listens" on Port L for a connection
         from a user-PI and establishes a TELNET communication
         connection.  It receives standard FTP commands from the
         user-PI, sends replies, and governs the server-DTP.

      TELNET connections

         The full-duplex communication path between a user-PI and a
         server-PI, operating according to the TELNET Protocol.

      type

         The data representation type used for data transfer and
         storage.  Type implies certain transformations between the time
         of data storage and data transfer.  The representation types
         defined in FTP are described in the Section on Establishing
         Data Connections.






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IEN 149                                                        June 1980
RFC 765                                           File Transfer Protocol



      user

         A human being or a process on behalf of a human being wishing
         to obtain file transfer service.  The human user may interact
         directly with a server-FTP process, but use of a user-FTP
         process is preferred since the protocol design is weighted
         towards automata.

      user-DTP

         The data transfer process "listens" on the data port for a
         connection from a server-FTP process.  If two servers are
         transferring data between them, the user-DTP is inactive.

      user-FTP process

         A set of functions including a protocol interpreter, a data
         transfer process and a user interface which together perform
         the function of file transfer in cooperation with one or more
         server-FTP processes.  The user interface allows a local
         language to be used in the command-reply dialogue with the
         user.

      user-PI

         The protocol interpreter initiates the TELNET connection from
         its port U to the server-FTP process, initiates FTP commands,
         and governs the user-DTP if that process is part of the file
         transfer.





















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June 1980                                                        IEN 149
File Transfer Protocol                                           RFC 765



   THE FTP MODEL

      With the above definitions in mind, the following model (shown in
      Figure 1) may be diagrammed for an FTP service.

                                            -------------
                                            |/---------\|
                                            ||   User  ||    --------
                                            ||Interface|<--->| User |
                                            |\----:----/|    --------
                  ----------                |     V     |
                  |/------\|  FTP Commands  |/---------\|
                  ||Server|<---------------->|   User  ||
                  ||  PI  ||   FTP Replies  ||    PI   ||
                  |\--:---/|                |\----:----/|
                  |   V    |                |     V     |
      --------    |/------\|      Data      |/---------\|    --------
      | File |<--->|Server|<---------------->|  User   |<--->| File |
      |System|    || DTP  ||   Connection   ||   DTP   ||    |System|
      --------    |\------/|                |\---------/|    --------
                  ----------                -------------

                  Server-FTP                   User-FTP