📄 rfc1756.txt
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Network Working Group T. Rinne
Request for Comments: 1756 HUT
Category: Experimental January 1995
REMOTE WRITE PROTOCOL - VERSION 1.0
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. This memo does not specify an Internet standard of any
kind. Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
1. Background
It is often convenient to use electronic communication somewhat
lighter than electronic mail. Sometimes even the use of the talk(1)
*) program seems like overkill. We like to offer to user something
like UNIX **) command write(1) ***) except that it can also pass
messages through the network instead of the single host.
There have been few programs offering this kind of service, but they
have either based on SUN-RPC protocol or used a strictly undocumented
protocol.
This document describes a simple Remote Write Protocol (RWP) that
should have been documented at least 10 years ago. But late is
better than never. Version number of the RWP protocol in this
document is 1.0.
2. Overview
RWP is a simple protocol that can be used to relay short messages
through the network to other users. RWP looks pretty much like
Simple Mail Transfer Protocol (SMTP) ****) though it is a bit more
complicated due to the interactive nature of the RWP session.
The idea behind the RWP session is that client program that is
relaying message to the host in which the target user is logged in
opens the tcp or udp connection to the server program running in the
target machine Then the client gives the sender's and recipient's
identification (usually login ids), actual message body and tells the
server to deliver a message to the user. On tcp-connection server
returns a status from each action taken. On udp-connection no
responses are sent. RWP sessions through udp are implemented to
support message broadcasting.
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RFC 1756 Remote Write Protocol January 1995
Message delivering methods are not defined within this document, but
the basic method could be a simple write to users terminal. This is
basically what UNIX command write(1) does. Depending on server
implementation, the delivery method could be configurable personally
by each user.
3. Description
Server program answers to each command submitted by a response. All
responses have two parts: three number unique response code and a
short textual explanation of the response. Also whenever the server
is ready to accept new commands a notification is submitted to the
client.
There are three kinds of commands in RWP. The first group is for
querying a status of the server. The second group is actual message
handling commands and the last set of commands are for RWP session
control.
When the server is ready to receive a command from the client, it
sends a message code 100 to the client. This message is for example
as follows:
100 Ready.
Server commands are as follows:
Status Query
HELP Gives a short help message that contains legal
RWP commands. Help lines have code 510. Example RWP
implementation *****) gives a following response to
HELP command:
510 Valid commands are:
510 BYE, DATA, HELP, HELO,
510 RSET, SEND, PROT, QUIT,
510 VRFY, VER
510 FROM senderlogin
510 FHST senderhost
510 TO recipentlogin [tty]
510 FWDS current_hop_count
HELO Says hello to the server. Server response to HELO
command has code 500. For example:
500 Hello remote.host. This is local.host speaking.
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RFC 1756 Remote Write Protocol January 1995
PROT Asks the RWP protocol version from the server.
Response code to PROT command is 502. Protocol
version described in this document is RWP 1.0 and the
response is as follows:
502 RWP version 1.0.
VRFY After the recipient of the message is set by to command
described later, the possibility of message delivery
can be queried by VRFY command. If message can be
delivered the response code is 108. If message is
about to be forwarded the response code is 110 and
message is either form:
110 Recipient ok to forward.
or if the server can tell the destination of the
forwarding:
110 Recipient ok to forward <user@host.domain>.
Other possible response codes are 669, 670, 671, 674
and 677 and they all indicate that message delivery is
by one way or another currently impossible.
Description of the codes is later in this document.
After the SEND command the server may also give
autoreply from the remote user before the actual
response code. Autoreply lines are ones of code 300.
VER Asks the version of the server program. Response code
to VER command is 501 and the textual part of the
response is the name and the version number of the RWP
server, for example:
501 Rwrited version 1.0.
Message Handling:
FROM senderlogin
Tells the server the identification information of the
sender of the message. Usually this id information is
user's login id. Response code to successful FROM
command is 105, for example:
105 Sender ok.
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RFC 1756 Remote Write Protocol January 1995
TO recipentlogin [tty]
Tells the server the identification information of the
intended recipient of the message. Usually this id
information is user's login id. If tty is submitted,
the message is delivered to that tty. If tty is
submitted between brackets '[]' the tty given is
treated as a hint only. Response code to successful
TO command is 106.
FHST original.host [forwarder1.host forwarder2.host ...]
Tells the server the host name that the message
originates to and the path of the hosts that has
forwarded the message. The host name of the machine
that is currently submitting the message to the server
should not be in the path list.
This information is relevant if message is forwarded
and it is not originally coming from the host that is
forwarding it. Response code to successful FHST
command is 111.
DATA Tells the server to start receive the body of the
message. Response code to DATA command is 200, for
example:
200 Enter message. Single dot '.' on line terminates.
After response 200 the message lines are submitted to
the server one after another. Message is terminated
by the line that contains a single dot '.'. The
termination of the message is acknowledged by the
server with the response code 107. Server does not
notify client about receiving the single message
lines. If empty message is submitted (i.e. single dot
is on the first line) the response code is 672 and
DATA command only cancels possible previous DATA
command. Because of this all dots or at least dots
that are standing alone in the line have to be quoted.
SEND Sends the message. If commands FROM, TO and DATA are
successfully given before SEND command, the message is
delivered to the target user. If delivery is
successful the response code is 103. If message is
not delivered directly to the target user but instead
forwarded to another host the response code is 104.
Response codes 669, 670 and 671, 677 indicate an error
on message delivery and codes 673, 674, 675 indicate
that either command FROM, TO or DATA has not been
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RFC 1756 Remote Write Protocol January 1995
successfully given before SEND command. After the
SEND command the server may also give autoreply from
the remote user before the actual response code.
Autoreply lines are ones of code 300.
FWDS n Tells the server that message has been forwarded n
times. If the server forwards the message to the
another server, it increments the counter and tells
the remote server the current count of forwards.
Response code to the FWDS command is 110 if n is less
than the server specific forward limit. If this limit
is exceeded the response code is 676. If the response
code is 676 the client can either quit the session and
fail the message or it can give the message to the
server despite the fact that the forward limit is
exceeded. If the message is given when forward limit
is exceeded, the server tries to deliver it, but does
not forward it to another server. If forward count is
given as -1, the message is considered as a autoreply
and never forwarded.
Session Control:
RSET Resets the RWP session. FROM, TO and DATA -commands
that are given before are canceled and they have to
be given again before SEND command can be used. Also
possible FWDS and FHST commands are canceled.
BYE Terminates the RWP session. Server gives a response
code 101 and closes the connection.
QUIT Is the synonym to bye, but it's a lot more impolite.
Response code is however 101 as in bye.
Server specific command:
QUOTE command
Relay a command to the server. If the QUOTE command
is successfully completed response code 112 is
returned. If QUOTE command is failed the response
code is 678. If RWP server doesn't recognize the
given QUOTE command the response code is 679.
Currently reserved QUOTE commands are AGENT, CHARSET,
IDENT, KEY and KEYID.
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RFC 1756 Remote Write Protocol January 1995
4. Response Codes
Here are all legal response codes of RWP server followed by short
textual explanation. Only the numeral codes are important and texts
can contain practically anything, however in response code 110 there
is possibly useful information between '<' and '>' characters. No
characters '<' or '>' should be present in other responses. Also
response 502 has possibly interesting information about the RWP
protocol version the server supports.
100 Ready.
The RWP server is ready to accept next command.
101 Goodbye.
The RWP server is closing connection.
103 Message delivered.
The SEND command is successfully completed and the message is
delivered directly to its destination.
104 Message forwarded.
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