RFC 743 (rfc743) - Page 2 of 8

FTP extension: XRSQ/XRCP

NWG/RFC# 743                                  KLH 30-Dec-77 08:39  42759
An Extension to FTP



   an XRSQ with no argument must always return a 200 reply and restore
   the default state of having no scheme selected.  Any other reply
   implies that XRSQ and hence XRCP are not understood or cannot be
   performed correctly.

   The second is that the use of "?" as a  asks the FTP server
   to return a 215 reply in which the server specifies a "preferred"
   scheme.  The format of this reply is simple:

      215  [] 

      Any other reply (e.g. 4xx or 5xx) implies that XRSQ and XRCP are
      not implemented, because "?" must always be implemented if XRSQ
      is.

   The third important thing about XRSQ is that it always has the side
   effect of resetting all schemes to their initial state.  This reset
   must be done no matter what the reply will be - 200, 215, or 501.
   The actions necessary for a reset will be explained when discussing
   how each scheme actually works.

Message Text Specification: MAIL/MLFL

   Regardless of which scheme (if any) has been selected, a MAIL or MLFL
   with a non-null argument will behave exactly as before; this
   extension has no effect on them.  However, such normal MAIL/MLFL
   commands do have the same side effect as XRSQ; they "reset" the
   current scheme to its initial state.

   It is only when the argument is null (e.g. MAIL or MLFL)
   that the particular scheme being used is important, because rather
   than producing an error (as most servers currently do), the server
   will accept message text for this "null" specification; what it does
   with it depends on which scheme is in effect, and will be described
   in "Scheme Mechanics".

Recipient specification: XRCP

   In order to specify recipient names and receive some acknowledgement
   (or refusal) for each name, the following new command is also
   defined:

      XRCP 

      Reply for no scheme:
         507 No scheme specified yet; use XRSQ.
      Replies for scheme T are identical to those for MAIL/MLFL.