Internet Relay Chat: Client-to-Client Protocol (CTCP)
draft-oakley-irc-ctcp-01

Network Working Group                                       M. Mikulenas
Internet-Draft                                               Independent
Updates: 1459, 2812 (if approved)                              D. Oakley
Intended status: Informational                                   ircdocs
Expires: January 19, 2018                                  July 18, 2017

         Internet Relay Chat: Client-to-Client Protocol (CTCP)
                        draft-oakley-irc-ctcp-01

Abstract

   This document describes the Client-to-Client Protocol (CTCP), which
   lets Internet Relay Chat (IRC) clients send each other messages that
   get displayed or responded to in special ways.  CTCP has been widely
   implemented, with most clients supporting it natively.  This document
   outlines how to implement CTCP and the most common messages used.

   It updates RFC 1459 and RFC 2812.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 19, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Message Syntax  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Message Types . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Extended formatting . . . . . . . . . . . . . . . . . . .   4
     3.2.  Metadata Query  . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Extended Query  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Messages  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Message List . . . . . . . . . . . . . . . . . . . .   6
     A.1.  ACTION  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     A.2.  CLIENTINFO  . . . . . . . . . . . . . . . . . . . . . . .   7
     A.3.  DCC . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     A.4.  FINGER  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     A.5.  PING  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     A.6.  SOURCE  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     A.7.  TIME  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     A.8.  VERSION . . . . . . . . . . . . . . . . . . . . . . . . .   9
     A.9.  USERINFO  . . . . . . . . . . . . . . . . . . . . . . . .  10
   Appendix B.  Change History [RFC Editor: Please remove this
                section] . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The core Internet Relay Chat (IRC) protocol as described in [RFC1459]
   and [RFC2812] only has a single command for regular user messages,
   and does not provide a way for clients to exchange information
   directly.  Client-to-Client Protocol (CTCP) messages let clients
   exchange messages that get displayed or responded to in special ways.
   Some examples of how CTCP is used is to request special formatting on
   messages, query other clients for metadata, and help initiate file
   transfers with other clients.

   This document goes over the subset of CTCP which is commonly
   implemented, and is compatible with clients implementing CTCP as
   described by older documents.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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2.  Message Syntax

   CTCP queries are sent with the PRIVMSG IRC command, and CTCP replies
   are sent with NOTICE command.  To indicate a CTCP query or reply, the
   body of the message (the second parameter) begins with the CTCP
   delimiter.  The ABNF [RFC5234] for this message body is as follows:

        delim    = %x01

        command  = 1*( %x02-09 / %x0B-0C / %x0E-1F / %x21-FF )
                      ; any octet except NUL, delim, CR, LF, and " "

        params   = 1*( %x02-09 / %x0B-0C / %x0E-FF )
                      ; any octet except NUL, delim, CR, and LF

        body     = delim command [ SPACE params ] [ delim ]

   Commands are case-insensitive.  When creating new CTCP commands,
   authors SHOULD use only alphanumeric characters for ease of
   implementation.

   The final CTCP delimiter SHOULD be sent on outgoing messages for
   compatibility reasons, and software MUST accept incoming messages
   which lack it.  This is due to how servers implement message
   truncation and certain clients implement message splitting.

   Queries MAY be sent to channels.  When these queries are responded
   to, the responses are sent to the querying client rather than the
   channel which the query was originally sent to.

   Many servers implement optional filtering so that only the ACTION
   CTCP message can be sent to channels.  When this is done, it can
   typically be enabled or disabled by channel operators with a channel
   mode.

   Here are two examples of CTCP queries and replies:

     :alice!a@localhost PRIVMSG bob :\x01VERSION\x01
     :bob!b@localhost NOTICE alice :\x01VERSION Snak for Mac 4.13\x01

     :alice!a@localhost PRIVMSG #ircv3 :\x01PING 1473523796 918320\x01
     :bob!b@localhost NOTICE alice :\x01PING 1473523796 918320\x01

3.  Message Types

   CTCP messages generally take on one of these types.  These message
   types are defined here to simplify understanding, and aren't
   differentiated by the protocol itself.

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3.1.  Extended formatting

   This type of CTCP is used to request special formatting of a user-
   visible message.  That is, to send a user-visible message that should
   be displayed differently from regular messages - e.g. as an action, a
   whisper, an announcement.

   Extended formatting messages are sent as a PRIVMSG, and are expected
   to be used in channels as well as between clients.  There is no
   automatic response to this message type, as it is not a query nor
   reply.

   These messages are sent as a PRIVMSG and can have parameters, but
   generate no reply.

   Example:

     :dan!u@localhost PRIVMSG #ircv3 :\x01ACTION writes some specs!\x01

3.2.  Metadata Query

   This type of CTCP is used to provide relatively static information
   about the target client, user or connection.

   This CTCP takes the form of a query and a response (as a PRIVMSG and
   NOTICE, respectively).  Due to how bouncers interact with multiple
   clients, there may sometimes be multiple responses to queries.

   Metadata queries MUST NOT require the recipient to implement any side
   effects (beyond sending the reply itself); if a CTCP message causes
   side effects by design, it should be categorized as an extended query
   instead.

   Metadata queries do not have any parameters, but expect a reply with
   parameters as the response data.

   Example:

     :alice!a@localhost PRIVMSG bob :\x01VERSION\x01
     :bob!b@localhost NOTICE alice :\x01VERSION SaberChat 27.5\x01

3.3.  Extended Query

   This type of CTCP is used to provide dynamic information or invoke
   actions from the client.

   This CTCP takes the form of a query and a response (as a PRIVMSG and
   NOTICE, respectively).

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   Queries sent to a channel always generate private replies.

   Extended queries and replies may have parameters.

   Example:

     :alice!a@localhost PRIVMSG bob :\x01PING 1473523796 918320\x01
     :bob!b@localhost NOTICE alice :\x01PING 1473523796 918320\x01

4.  Messages

   CTCP messages themselves are not standardised.  Clients that receive
   either unexpected messages or known messages with unexpected values
   SHOULD ignore them and produce no response to the sending user.
   Clients MAY receive more than one response per user for a query they
   send, due to multiple clients being connected behind an IRC bouncer.

5.  Acknowledgements

   Thanks to the IRCv3 group for giving feedback on this specification,
   and to Khaled for advice on client flood protection.

   Thanks to Michael Sandrof for creating CTCP, Troy Rollo for creating
   the related DCC protocol, as well as Klaus Zeuge and Ben Mesander who
   wrote and revised related specifications.

   Special thanks to dequis, Peter Powell and James Wheare for help with
   this and related work.

6.  Security Considerations

   CTCP messages are completely untrusted data, and clients MUST NOT
   assume that they are well-formed or complete.

   Older CTCP specifications describe quoting methods which are complex
   and not widely implemented.  Implementations SHOULD NOT implement
   "low-level quoting" or "CTCP-level quoting" when parsing messages.

   Older CTCP specifications describe including more than one CTCP
   message inside a single PRIVMSG or NOTICE command.  Implementations
   SHOULD NOT implement this form of CTCP parsing as it is not widely-
   implemented and may result in an implementation that can be more
   easily flooded off the server they are connected to.

   CTCP requests can be abused to flood clients off the server they are
   connected to.  Clients may ignore or delay excessive incoming
   requests to protect against this.

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7.  IANA Considerations

   This document has no actions for IANA.

8.  Normative References

   [RFC1459]  Oikarinen, J. and D. Reed, "Internet Relay Chat Protocol",
              RFC 1459, DOI 10.17487/RFC1459, May 1993,
              <http://www.rfc-editor.org/info/rfc1459>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2812]  Kalt, C., "Internet Relay Chat: Client Protocol",
              RFC 2812, DOI 10.17487/RFC2812, April 2000,
              <http://www.rfc-editor.org/info/rfc2812>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <http://www.rfc-editor.org/info/rfc5322>.

Appendix A.  Message List

   This section is not exhaustive, and only lists those CTCP messages
   which are widely implemented across the IRC ecosystem.

   The reply and parameter lines below use a simplified syntax that
   represents variables by surrounding them with angle brackets.

A.1.  ACTION

   Type:    Extended Formatting
   Params:  ACTION <text>

   This extended formatting message shows that <text> should be
   displayed as a third-person action or emote; in clients, it's
   generally activated with the command "/me".

   If <text> is empty, clients SHOULD still include a single space after
   "ACTION" (i.e. an empty params section) to help compatibility.

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   Clients SHOULD correctly parse incoming ACTION messages with or
   without the params section.

   ACTION is universally implemented and very commonly used.  Clients
   MUST implement this CTCP message to effectively use IRC.

   Examples:

     Raw:        :dan!user@host PRIVMSG #ircv3 :\x01ACTION does it!\x01

     Formatted:  * dan does it!

     Raw:        :dan!user@host PRIVMSG #ircv3 :\x01ACTION \x01

     Formatted:  * dan

     Raw:        :dan!user@host PRIVMSG #ircv3 :\x01ACTION\x01

     Formatted:  * dan

A.2.  CLIENTINFO

   Type:   Extended Query
   Reply:  CLIENTINFO <tokens>

   This extended query returns a list of the CTCP messages that this
   client supports and implements, delimited by a single ASCII space.

   CLIENTINFO is widely implemented.  Clients SHOULD implement this CTCP
   message.

   Example:

     Query:     CLIENTINFO
     Response:  CLIENTINFO ACTION DCC CLIENTINFO PING TIME VERSION

A.3.  DCC

   Type:    Extended Query
   Params:  DCC <type> <argument> <host> <port>

   This extended query is used to setup and control connections that go
   directly between clients, bypassing the IRC server.  This is
   typically used for features that require a large amount of traffic
   between clients or simply wish to bypass the server itself such as
   file transfer and direct chat.

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   The Direct Client-to-Client (DCC) Protocol requires its own
   specification, and is not described in-depth here.

   DCC is widely implemented.  Clients MAY implement this CTCP message.

A.4.  FINGER

   Type:   Metadata Query
   Reply:  FINGER <info>

   This metadata query returns miscellaneous info about the user,
   typically the same information that's held in their realname field.

   However, some implementations return the client name and version
   instead.

   FINGER is largely obsolete.  Clients MAY implement this CTCP message.

   Example:

     Query:     FINGER
     Response:  FINGER WeeChat 1.8-dev

A.5.  PING

   Type:    Extended Query
   Params:  PING <info>

   This extended query is used to confirm reachability with other
   clients and to check latency.  When receiving a CTCP PING, the reply
   MUST contain exactly the same parameters as the original query.

   PING is universally implemented.  Clients SHOULD implement this CTCP
   message.

   Example:

     Query:     PING 1473523721 662865
     Response:  PING 1473523721 662865

     Query:     PING foo bar baz
     Response:  PING foo bar baz

A.6.  SOURCE

   Type:   Metadata Query
   Reply:  SOURCE <info>

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   This metadata query is used to return the location of the source code
   for the client.

   SOURCE is rarely implemented.  Clients MAY implement this CTCP
   message.

   Example:

     Query:     SOURCE
     Response:  SOURCE https://weechat.org/download

A.7.  TIME

   Type:    Extended Query
   Params:  TIME <timestring>

   This extended query is used to return the client's local time in an
   unspecified human-readable format.  In practice, both the format
   output by ctime() and the format described in Section 3.3 of
   [RFC5322] are common.  Earlier specifications recommended to prefix
   the time string with a colon, but this is no longer recommended.

   New implementations MAY default to UTC time for privacy reasons.

   TIME is almost universally implemented.  Clients SHOULD implement
   this CTCP message.

   Example:

     Query:     TIME
     Response:  TIME Mon, 08 May 2017 09:15:29 GMT

A.8.  VERSION

   Type:   Metadata Query
   Reply:  VERSION <verstring>

   This metadata query is used to return the name and version of the
   client software in use.  There is no specified format for the version
   string.

   Clients may allow users to customise the response value for this
   query.

   VERSION is universally implemented.  Clients SHOULD implement this
   CTCP message.

   Example:

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     Query:     VERSION
     Response:  VERSION WeeChat 1.8-dev (git: v1.7-329-g22f2fd03a)

A.9.  USERINFO

   Type:   Metadata Query
   Reply:  USERINFO <info>

   This metadata query returns miscellaneous info about the user,
   typically the same information that's held in their realname field.

   However, some implementations return "<nickname> (<realname>)"
   instead.

   USERINFO is largely obsolete.  Clients MAY implement this CTCP
   message.

   Example:

     Query:     USERINFO
     Response:  USERINFO fred (Fred Foobar)

Appendix B.  Change History [RFC Editor: Please remove this section]

   Changes from draft 0 (May 29, 2017)

   o  Added note about servers truncating CTCP messages (thanks Peter).

   o  Fixed misspellings and added note to TIME about previously-
      recommended prefix (thanks Patrick).

   o  Mentioned how to parse/send empty ACTION messages (thanks dequis
      and the crew).

Authors' Addresses

   Mantas Mikulenas
   Independent

   Email: grawity@gmail.com

   Daniel Oakley
   ircdocs

   Email: daniel@danieloaks.net

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