rfc959.txt

RFC 相关的技术文档

                                                                        
Network Working Group                                          J. Postel
Request for Comments: 959                                    J. Reynolds
                                                                     ISI
Obsoletes RFC: 765 (IEN 149)                                October 1985

                      FILE TRANSFER PROTOCOL (FTP)


Status of this Memo

   This memo is the official specification of the File Transfer
   Protocol (FTP).  Distribution of this memo is unlimited.

   The following new optional commands are included in this edition of
   the specification:

      CDUP (Change to Parent Directory), SMNT (Structure Mount), STOU
      (Store Unique), RMD (Remove Directory), MKD (Make Directory), PWD
      (Print Directory), and SYST (System).

   Note that this specification is compatible with the previous edition.

1.  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, personal workstations, and TACs,
   with a simple, and easily implemented protocol design.

   This paper assumes knowledge of the Transmission Control Protocol
   (TCP) [2] and the Telnet Protocol [3].  These documents are contained
   in the ARPA-Internet protocol handbook [1].

2.  OVERVIEW

   In this section, the history, 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.







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File Transfer Protocol


   2.1.  HISTORY

      FTP has had a long evolution over the years.  Appendix III is a
      chronological compilation of Request for Comments documents
      relating to FTP.  These include the first proposed file transfer
      mechanisms in 1971 that were developed for implementation on hosts
      at M.I.T. (RFC 114), plus comments and discussion in RFC 141.

      RFC 172 provided a user-level oriented protocol for file transfer
      between host computers (including terminal IMPs).  A revision of
      this as RFC 265, restated FTP for additional review, while RFC 281
      suggested further changes.  The use of a "Set Data Type"
      transaction was proposed in RFC 294 in January 1982.

      RFC 354 obsoleted RFCs 264 and 265.  The File Transfer Protocol
      was now defined as a protocol for file transfer between HOSTs on
      the ARPANET, with the primary function of FTP defined as
      transfering files efficiently and reliably among hosts and
      allowing the convenient use of remote file storage capabilities.
      RFC 385 further commented on errors, emphasis points, and
      additions to the protocol, while RFC 414 provided a status report
      on the working server and user FTPs.  RFC 430, issued in 1973,
      (among other RFCs too numerous to mention) presented further
      comments on FTP.  Finally, an "official" FTP document was
      published as RFC 454.

      By July 1973, considerable changes from the last versions of FTP
      were made, but the general structure remained the same.  RFC 542
      was published as a new "official" specification to reflect these
      changes.  However, many implementations based on the older
      specification were not updated.

      In 1974, RFCs 607 and 614 continued comments on FTP.  RFC 624
      proposed further design changes and minor modifications.  In 1975,
      RFC 686 entitled, "Leaving Well Enough Alone", discussed the
      differences between all of the early and later versions of FTP.
      RFC 691 presented a minor revision of RFC 686, regarding the
      subject of print files.

      Motivated by the transition from the NCP to the TCP as the
      underlying protocol, a phoenix was born out of all of the above
      efforts in RFC 765 as the specification of FTP for use on TCP.

      This current edition of the FTP specification is intended to
      correct some minor documentation errors, to improve the
      explanation of some protocol features, and to add some new
      optional commands.


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File Transfer Protocol


      In particular, the following new optional commands are included in
      this edition of the specification:

         CDUP - Change to Parent Directory

         SMNT - Structure Mount

         STOU - Store Unique

         RMD - Remove Directory

         MKD - Make Directory

         PWD - Print Directory

         SYST - System

      This specification is compatible with the previous edition.  A
      program implemented in conformance to the previous specification
      should automatically be in conformance to this specification.

   2.2.  TERMINOLOGY

      ASCII

         The ASCII character set is 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.

      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.



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      control connection

         The communication path between the USER-PI and SERVER-PI for
         the exchange of commands and replies.  This connection follows
         the Telnet Protocol.

      data connection

         A full duplex 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.

      DTP

         The data transfer process establishes and manages the data
         connection.  The DTP can be passive or active.

      End-of-Line

         The end-of-line sequence defines the separation of printing
         lines.  The sequence is Carriage Return, followed by Line Feed.

      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.



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File Transfer Protocol


      FTP commands

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

      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.

      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.

      PI

         The protocol interpreter.  The user and server sides of the
         protocol have distinct roles implemented in a user-PI and a
         server-PI.


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      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.

      reply

         A reply is an acknowledgment (positive or negative) sent from
         server to user via the control connection 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.
         It 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.