RFC 743 (rfc743) - Page 2 of 8
FTP extension: XRSQ/XRCP
Alternative Format: Original Text Document
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.