rfc354.txt

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and interpreting FTP commands, sending replies, setting up the data
connection, and transferring data.

IV.A FTP Commands

    FTP commands are ASCII terminated by the ASCII
character sequence CRLF (Carriage Return follow by Line Feed).  The
command codes themselves are ASCII alpabetic characters terminated by
the ASCII character 'space' (code = 32.). For convenience, the command
codes are defined to be four (or less) ASCII alphanumeric characters
(including both upper and lower case alphabetic characters). The command
codes and the semantics of commands are described in this section, but
the detailed syntax of commands is specified in Section V.b, the reply
sequence are discussed in Section V.C, and scenarios illustrating the
use of commands are provided in Section V.D.

    FTP commands may be partitioned as those specifying
access-control identifiers, data transfer parameters, or FTP service
requests.








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IV.A.1 Access Control Commands

The following commands specify access control identifiers
       (command codes are shown in parentheses).

       User name (USER) - The argument field is an ASCII string
       identifying the user. The user identification is that wich is
       required by the server for access to its file system. This
       command will normally be the first command transmitted by the
       user after the TELNET connections are made (some servers may
       require this). Additional identification information in the form
       of pasword command may also be required by some servers.

       Password (PASS) - The argument field is an ASCII string
       identifying the user's password. This command must be immediately
       preceded by the user name command, and together it completes the
       user's identifecation for access control.

IV.A.2 Data Transfer Commands

       All data transfer parameters have default values, and the
       commands specifying data transfer parameters are required only if
       the default parameter values are to be changed.  The default
       value is teh last specified value, or if no value has been
       specified, the standard default value specified here. This
       implies that the server must "remember" the applicable default
       values. The commands may be in any order except that they must
       precede the FTP service request. The following commands specify
       data transfer parameters.

       Byte size (BYTE) - The argument is an ASCII-represented decimal
       integer (1 through 255), specifying the byte size for the data
       connection for local byte and image representation types. The
       default byte size is 8 bits.  The byte size is always 8 bits in
       the ASCII and Print file representation types. A server may
       reject specific byte size/type combinations by sending an
       appropriate reply.

       Data socket (SOCK) - The argument is a HOST-socket specification
       for the data socket to be used in data connection. There may be
       two data sockets, one from server to user and the other for user
       to server data transfer. An odd socket number defines a send
       socket and an even socket number defines a receive socket. The
       default HOST is the user HOST to which TELNET connections are
       made. The default data sockets are (U+4) and (U+5) where U is the
       socket number used in the TELNET ICP and the TELNET connections
       are on sockets (U+2) and (U+3).




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       Representation Type (TYPE) - The argument is a single ASCII
       character code specifying the representation types described in
       section III.B. The following codes are assigned for type:

          A - ASCII
          I - Image
          L - Local Byte
          P - Print file in ASCII
          E - EBCDIC print file

       The default representation type is ASCII

       File Structure (STRU) - The argument is a single ASCII character
       code specifying file structure described in section III.C. The
       following codes are assigned for structure:

          F - File (no record structure)
          R - Record structure

       The default structure is File (i.e., no records).

       Transfer Mode (MODE) - The argument is a single ASCII character
       code specifying the data transfer modes described in Section
       III.C. The following codes are assigned for transfer modes:

          S - Stream (bytes, close is EOF)
          B - Block (Header with descriptor and count)
          T - Text (TELNET control mode for EOR, EOF)
          H - Hasp (specially formatted compressed data)

       The default transfer mode is Stream.

IV.A.3 FTP Service Commands.

       The FTP service commands define the file transfer or the file
       system function requested by the user. The argument of an FTP
       service command will normally be a pathname.  the syntax of
       pathnames must conform to server site conventions (with standard
       defaults applicable), except that ASCII characters must be used
       (in conformance with the TELNET Protool). The suggested default
       handling is to use the last specified device directory or file
       name, or the standard default defined for local users. The
       commands may be in any order except that a "rename from" command,
       must be followed by a "rename to" command, and some servers may
       require an "allocate" command before a "store" command. The data
       when transferred in response to FTP service commands shall always
       be over the data connection. The following commands specify FTP
       service requests:



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       Retrieve (RETR) - This command achieves the transfer of a copy of
       file specified in pathname, from server to user site. The status
       and contents of a file at server site shall be unaffected.

       Store (STOR) - This command achieves the transfer of a copy of
       file from user to server site. If file specified in pathname
       exists at the server site, then its contents shall be replaced by
       the contents of the file being transferred. A new file is created
       at the server site if the file specified in pathname does not
       already exist.

       Append (with create) (APPE) - This command achieves the transfer
       of data from using to serving site. If file specified in pathname
       exists at the server site, then the data transferred shall be
       appended to that file, otherwise the file specified in pathname
       shall be created at the server site.

       Rename from (RNFR) - This command specifies the file which is to
       be renamed. This command must be immediately followed by a
       "rename to" command specifying the new file pathname.

       Delete (DELE) - This command causes teh file specified in
       pathname to be deleted at the server site. If an extra level of
       protection is desired (such as the query, "Do you really wish to
       delete?"), it should be provided by the user-FTP process.

       List (LIST) - This command causes a list to be sent from server
       to user site. If pathname specifies a directory, the server
       should transfer a list of files in the specified directory. If
       pathname specifies a file then server should send current
       information on the file. This command may be used to obtain the
       contents of a file directory (the response should be sent in
       ASCII type) or test the existence of a file and its current
       status.

       Allocate (ALLO) - This command my be required by some servers to
       reserve sufficient storage to accomodate the new file to be
       transferred. The command field shall be a decimal integer
       representing the number of bytes (of size specified by the byte
       size command) of storage to be reserved for the file. This
       command shall be followed by a store or append command. The ALLO
       command should be treated as a NO-OP (no operation) by thuse
       servers which do not require that the maximum size of the file be
       declared beforehand.

       Restart (REST) - The argument field represents the server marker
       at which file transfer is to be restarted. This command does not
       cause file transfer but "spaces" over the file to the specified



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       data checkpoint. This command shall be immediately followed by
       the appropriate FTP service command which shall cause file
       transfer to resume.

       Status (STAT) - This command shall cause a status response to be
       sent over the TELNET connection in form of a reply.  The command
       may have an argument field such as a pathname.  if the argument
       is a pathname, the command is analogous to the "list" command
       except that data shall be transferred in ASCII on the TELNET
       connection. If no argument is specified, the server should return
       general status information about the server FTP process. This may
       include service availability, the current settings for the
       relevant FTP parameters (including default settings), and the
       status of command execution and connections.

       Abort (ABOR) - This command indicates to the server to abort the
       previous FTP service command and any associated transfer of data.
       The abort command should be preceded by the TELNET SYNCH
       condition (indicated by the combination of the DATA MARK and the
       INS). No action is to be taken if the previous command has been
       completed (including data transfer). The TELNET connections is
       not to be closed by the server, but the data connection may be
       closed. An appropriate reply should be sent by the server.

       Logout (BYE) - This command terminates a USER and if file
       transfer is not in progress, closes the TELNET connection.  If
       file transfer is in progress, the connection will remain open for
       result response and will then close.  During the interim a new
       USER command (and no other command) is acceptable.

       An unexpected close on TELNET connection will cause the server to
       take the effective action of an abort (ABOR) and a logout (BYE).

IV.B FTP Replies

    The server sends FTP replies to user over the TELNET
connections in response to FTP commands. The FTP replies constitute the
acknowledgement or completion code (including errors). The FTP-server
replies are formatted for human or program interpretation. The replies
consist of a leading three digit numeric code followed by a space
followed by a text explanation of the code. The numeric codes are
assigned by groups and for ease of interpretation by programs in a
manner consistent with other protocols such as the RJE protocol. The
three digits of the code are to be interpredet as follows:







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a) The first digit specifies type of response as indicated below:

   000 These replies are purely informative and constitute
       neither a positive nor a negative acknowledgement.

   1xx informative replies to status inrequiries. These constitute
       a positive acknowledgment to the status command.

   2xx Positive acknowledgment of previous command or other
       successful action.

   3xx Incomplete information. Activity cannot proceed without
       further specification and input.

   4xx Unsuccessful reply. The request is correctly specified
       but the server is unsuccessful in corretly fulfilling
       it.

   5xx Incorrect or illegal command. The command or its
       parameters were invalid or incomplete from a syntactic
       viewpoint, or the command its inconsistent with a previous
       command. The command in question has been completely
       ignored.

   6xx - 9xx Reserved for future expansion.

b) The second digit specifies the general category to which
   the response refers:

   x00-x29 General purpose replies, not assignable to other
       categories.

   x30 Primary access. Informative replies to the "log-on"
       attempt.

   x40 Secondary access. The primary server is commenting on its
       ability to access a secondary service.

   x5x FTP results.

   x6x RJE resutls.

   x7x-x9x Reserved for future expansion.








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c) the final digit specifies a particular message type. Since the code
is designed for an automaton process to interpret, it is not necessary
for every variation of a reply to have a unique number. Only the basic
meaning of replies need have unique numbers. The text of a reply can
explain the specific reason for that reply to a human user.

    Each TELNET line (ended by CRLF) from the server is intended
to be a complete reply message. if it is necessary to continue the text
of a reply onto following lines, then those continuation replies contain
the special reply code of three spaces. It should be noted that text of
replies are intended for a human user. Only the reply codes and in some
instances the first line of text are intended for programs.

    The assigned reply codes relating to FTP are:

000 General information message (site, time of day, etc.)
030 Server availibility information.
050 FTP commentary or user information.
100 System status reply.
150 File status reply.
151 Directory listing reply.
200 Last command received correctly.
201 An ABORT has terminated activity, as requested.
202 Abort request ignored, no activity in progress.
230 User is "logged in". may proceed.
231 User is "logged out". Service terminated.
232 Logout command noted, will complete when transfer done.
250 FTP file transfer started correctly.
251 FTP Restart-marker reply
          Text is: MARK yyyy  =  mmmm
          where yyyy is user's data stream marker (yours)
          and mmmm is server's equivalent marker (mine)
          (Note the spaces between the markers and '=').
252 FTP transfer completed correctly.
253 Rename completed.
254 Delete completed.
255 FTP server data socket reply
          Text is: SOCK nnnn
          where nnnn is decimal integer representing