SIFT/UFT: Sender-Initiated/Unsolicited File Transfer

Network Working Group                                           R. Troth
Request for Comments: 1440                               Rice University
                                                               July 1993


          SIFT/UFT: Sender-Initiated/Unsolicited File Transfer

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard.  Discussion and
   suggestions for improvement are requested.  Please refer to the
   current edition of the "IAB Official Protocol Standards" for the
   standardization state and status of this protocol.  Distribution of
   this memo is unlimited.

1.  Introduction

   This document describes a Sender-Initiated File Transfer (SIFT)
   protocol, also commonly called Unsolicited File Transfer (UFT)
   protocol.  The acronyms SIFT and UFT are synonymous throughout this
   document.  The term "unsolicited" does not imply that the file is
   unwanted, but that the receiver did not initiate the transaction.

   Sender-Initiated File Transfer contrasts with other file transfer
   methods in that the sender need not have an account or any
   registration on the target host system, and the receiving user may
   have less steps to take to retrieve the file(s) sent.  Unlike
   traditional file transfer, UFT lends itself handily to background or
   deferred operation, though it may be carried out immediately, even
   interactively.

2.  Rationale

   In certain non-IP networks, notably NJE based networks such as
   BITNET, it is possible to send a file to another user outside of the
   realm of "mail".  The effect is that the file sent is not perceived
   as correspondence and not processed by a mail user agent.  This
   convenient service is missed in the standard TCP/IP suite.  The
   author maintains that traditional electronic mail is not suited to
   non-correspondence file transfer.  There should be a means of sending
   non-mail, analogous to the sending of parcels rather than surface
   mail.  Several groups and individuals have shown an interest in this
   type of service.

3.  Specification

   We define sender-initiated file transfer for IP as a TCP service as
   follows: a receiver program (the server or "daemon") listens on port
   608 for inbound connections.  Client programs connect to this port
   and send a sequence of commands followed by a stream of data.  The
   entire job stream may be thought of as the concatenation of two
   files, 1) a control file, and 2) a data file, where the control file
   is plain text and the data file may be any of several formats, but is
   stored and sent as binary.  After each command, the receiver either
   ACKs (signals positive acknowledgement) or NAKs (signals negative
   acknowledgement).  The target host may reject a file for various
   reasons, most obvious being 1) that there is no local user matching
   the intended user, or 2) that there is not enough space to hold the
   incoming file.

   Most UFT commands are parametric.  That is, they don't necessarily
   invoke an action as much as change parameters of the one action,
   transfer of the file(s) being sent.  This means that UFT is suitable
   for encapsulation in some higher-level "envelope", such as mail.
   However, the obvious prefered medium for UFT is TCP.

   When files arrive at the destination host, they are kept in a public
   area, say /usr/spool/uft, until accepted or rejected by the recipient
   user or discarded for age by the system.  This staging area is public
   in the sense of shared space, not unrestricted access.  Exactly how
   long files may remain unprocessed and exactly how large these
   transient files may be is a local administrative or implementation
   decision.

   But not all hosts have IP connectivity; not all hosts will want to
   put up yet another server; not all hosts will be on the unrestricted
   side of a "fire wall" that only passes mail.  In such cases, UFT may
   be transported via MIME (Multipurpose Internet Mail Extensions) as
   Content-Type: application/octet-stream.  UFT commands then become
   parameters to the Content-Type field and the data file is carried as
   the mail body.  While the data file is carried in raw (binary) form
   over TCP, it is encoded in BASE64 when carried by mail.

   UFT supports several representation types.  The receiving host should
   accept any file type sent.  If the representation type is not
   meaningful to the target host system, then it should be treated as
   "binary" (image).  The data file (body) should be processed as little
   as possible until the target user (recipient) acts to accept
   (receive) it.  The commands from the client may be stored in the form
   of a plain-text file so that processing otherwise foreign to the
   receiver may be off-loaded from the TCP listener.  So there are
   actually two files: the command sequence and the file body.

   Job Entry capability:

      The target "user" may actually be no user at all, but may be the
      name of some software service engine.  An example of this is the
      job entry queue available as a pseudo-user on many NJE networked
      hosts.

4.  Essential commands and Syntax:

        FILE    size    sender    [auth]
        USER    recipient

        TYPE    type   [parm]

        Representation Types:

        TYPE        A           ASCII, CR/LF (0D/0A)
                    B           binary (image; octet stream)

                    C           ASCII, CC, CR/LF (ASA print)

                    U           unformatted (binary; image)
                    V           var-length records (16 bit)
                    W           wide var-len records (32 bit)
                    X           extra-wide var-length (64 bit)

                    I           image (binary; octet stream)
                    E           EBCDIC, NL (15)
                    F  reclen   fixed-length records (binary)

                    N           NETDATA
                    M           ASCII, mail

        Additional Parameters:

        NAME    filename
        DATE    date    time    [time-zone]

        CLASS   class
        FORM    paper-form-code  or  print-stock-code
        DEST    destination

        DIST | BIN | BOX        distribution-code  or  mail-stop
        FCB | CTAPE             forms-control-buffer  or  carriage-tape
        UCS | CHARSET | TRAIN   print-train  or  character-set

        LRECL           logical-record-length
        RECFM           record-format
        BLKSIZE         block-size

        MODE            file access permissions

        File disposition commands:

        DATA  [burst-size]

        EOF
        ABORT

        QUIT

5.  Details:

   Commands consist of command words, possibly followed by tokens
   delimited by white space.  Command lines are ASCII terminated by
   CR/LF.  White space may be composed of any mixture of blanks or tab
   characters, but use of ordinary blank space (ASCII 0x20) is strongly
   recommended.

   One connection (one socket) is used for both commands and data.
   While a data burst is being received, command interpretation is
   suspended.  Command lines are read until CR/LF; data bursts are read
   until burst-size number of octets are received, at which point
   command interpretation is resumed.  After data transmission has
   begun, the only commands valid are DATA, EOF, ABORT and QUIT.  EOF
   causes the server to close the file at the receiving end and return
   to normal command processing.  ABORT signals that the client wishes
   to discard a file partially transmitted.  QUIT closes any open file,
   closes the connection, and can appear anywhere in the job.

   For the daring, a "fast" mode is available.  If the burst-size token
   is omitted from the DATA command, processing switches to data mode
   and the stream is read until the client closes the connection.  In
   this case there is no EOF or QUIT command sent.  NOTE: with the
   former mode of operation, the connection may remain open indefinitely
   passing multiple files, while in this latter case the connection must
   close to terminate the transaction.

   Acknowledgement is by simple "NULL ACK".  A server accepts a command
   by sending a single packet back to the client that starts with a NULL
   character, decimal 0.  Anything else may be considered negative
   acknowledgement, and the client should close the connection.  Any
   characters following the NULL may be ignored.  An ACK response packet
   may signal only one acknowledgement.

   When a client first connects to a server, the server immediately
   sends a herald of the form:

                xxx hostname UFT 1.0 server-version xxx

   where "xxx" represents arbitrary data.  The first "xxx" must be a
   single blank delimited token.  1.0 is the protocol version.  Hostname
   is the IP name of the host where this server is running.  Server-
   version is the name and level of UFT server code on this host.

   A US English server might send:

                100 ricevm1.rice.edu UFT 1.0 VM/CMS-0.9.2 ready.

   The purpose of this herald is partly for client/server
   synchronization, but mainly for protocol agreement.  There may be
   future versions of UFT beyond 1.0 which support more features than
   are outlined here.  The herald indicates what level of UFT the server
   will accept.

   The FILE Command:

                FILE    size    from    [auth]

   The size is in bytes and may be followed by an 'M', 'K', or 'G',
   indicating Mega, Kilo, or Giga.  Size may be an inexact value (the
   data file will be read until one of the above end-of-file indications
   is received).  The size specified is used to answer the question, "is
   there room for it?"

   The from token is the login name of the user sending this file.

   The auth token is an unimplemented authentication ticket.
   Authentication is not ensured in the protocol as described.  There
   are several ways that it might be added to UFT over TCP, but this
   author will wait for authentication developments by others to come to
   fruition before implementing any.  When UFT is piggy-backed on mail,
   authentication is left to the mail transfer system.

   The FILE command is required in any transaction.

   The USER Command:

                USER    recipient

   The recipient is a valid local user or service name.

   The USER command is required in any transaction.  Without it, the
   destination of the file is unknown.

   The TYPE Command:

                TYPE    type   [parm]

   Some representation types need additional specification.  As an
   example, the type "F" (fixed length, record oriented) obviously needs
   more qualification.  How long are these fixed length records?  A
   record length in ASCII decimal should follow the "F" resulting in a
   command like "TYPE F 80".

   UFT types V, W, X use a tape model for file transfer.  Files in
   transit consist of blocks that vary in size based on the range of
   sizes specifiable with 16, 32, or 64 bits, respectively.  Whether the
   blocking is significant to the recipient is the decision of the
   recipient, but if the file originally had some kind of blocking, it
   is preserved without additional processing.  In the stream, the 16,
   32, or 64-bit block length is prepended to each record in TCP/IP
   network order.

   Type N (NETDATA) is an IBM representation common on NJE networks.

   The TYPE command is required in any transaction.

   The NAME Command:

                NAME    filename


   A name should typically be associated with the file being sent,
   although this is not mandatory.   This is a mixed case token
   delimitted by white space.   If the filename contains blanks or white
   space, it must be quoted.   Quotation is not valid within the
   filename. ASCII control characters (hex 00 thru 1F and 80 thru 9F)
   are not valid as part of the filename.  Some characters may have
   special meaning to the receiving operating system and their effect is
   not guaranteed.

   The NAME command is optional.

   The DATE Command:

                DATE    date    time    [time-zone]

   The time stamp on the file as it appears at the sending site may be
   sent and applied to the copy at the receiving site.  The form is US
   mm/dd/yy and hh:mm:ss.  A time zone is optional.  If the time zone is
   omitted, local time is assumed.  If the DATE command is omitted, time
   and date of arrival are assumed.

   The DATE command is optional.

   The DATA Command:

                DATA  [burst-size]

   If no data bursts have yet been received since the connection was
   opened or since an EOF or ABORT was received, the server opens a new
   file on the receiving end and writes this burst of data to it.  The
   file may have already been created by a prior DATA command.  There
   can be any number of DATA commands; most files will be sent using
   many data bursts.  If burst-size is supplied, then burst-size number
   of octets are read and appended to the open file on the receiving end
   and the server returns to the command state.  If no burst-size
   parameter is given, then the TCP stream is read until it is closed.
   (this is the "fast" mode mentioned above)

   The DATA command must come after FILE, USER, TYPE, and any other
   parametric commands and must come before any EOF or ABORT command.
   The file need not be complete before an ABORT can be received and
   carried out, but the DATA command must have completed (burst-size
   number of octets must have been read), thus ABORT is not possible in
   "fast" mode.

   The EOF Command:

                EOF

   This signals the server that the entire file has been sent.  The
   server then closes the file and ensures that it is disposed of
   appropriately, usually just placing it where a user-level application
   can retrieve it later.

   The ABORT Command:

                ABORT

   This signals the server that the client is unable or unwilling to
   finish the job.  The file should be discarded and the server should
   return to normal command processing.

   The QUIT Command:

                QUIT

   This signals the server that all work is complete.  Any open file
   should be closed and delivered.  The TCP stream will be closed.

        Other commands:

        CLASS       class
        FORM        paper-form-code  or  print-stock-code
        DEST        destination
        DIST        distribution-code  or  mail-stop
        FCB         forms-control-buffer  or  carriage-tape
        CHARSET     print-train  or  character-set

        The above are relevant to print jobs sent to a print server.

        LRECL       logical-record-length
        RECFM       record-format
        BLKSIZE     block-size
        MODE        file access permissions

6.  References

        NJE        --   Network Job Entry; IBM publication SC23-0070,
                        "Network Job Entry; Formats and Protocols"

        NETDATA    --   see IBM publication aann-nnnn (SC24-5461);
                        VM/ESA: CMS Application Development Reference
                        for Assembler

        BITNET     --   "Because It's Time"; academic network
                        based on NJE protocol

        MIME       --   RFC 1341; Multipurpose Internet Mail Extensions;
                        Borenstein & Freed

        FTP        --   File Transfer Protocol; STD 9, RFC 959;
                        Postel & Reynolds

        SMTP       --   STD 10, RFC 821; Simple Mail Transfer
                        Protocol; Postel

        LPR        --   UNIX Programmer's Manual, LPD(8);
                        4.2BSD Line Printer Spooler Manual

7.  Security Considerations

   Security issues are not discussed in this memo.

8.  Author's Address

   Rick Troth
   Rice University
   Information Systems
   Houston, Texas 77251

   Phone: (713) 285-5148
   Fax: (713) 527-6099
   EMail: troth@rice.edu