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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Mikulenas & Oakley Expires January 19, 2018 [Page 1] Internet-Draft IRC Client-to-Client Protocol July 2017 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]. Mikulenas & Oakley Expires January 19, 2018 [Page 2] Internet-Draft IRC Client-to-Client Protocol July 2017 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. Mikulenas & Oakley Expires January 19, 2018 [Page 3] Internet-Draft IRC Client-to-Client Protocol July 2017 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). Mikulenas & Oakley Expires January 19, 2018 [Page 4] Internet-Draft IRC Client-to-Client Protocol July 2017 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. Mikulenas & Oakley Expires January 19, 2018 [Page 5] Internet-Draft IRC Client-to-Client Protocol July 2017 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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2812] Kalt, C., "Internet Relay Chat: Client Protocol", RFC 2812, DOI 10.17487/RFC2812, April 2000, . [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008, . 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 This extended formatting message shows that should be displayed as a third-person action or emote; in clients, it's generally activated with the command "/me". If is empty, clients SHOULD still include a single space after "ACTION" (i.e. an empty params section) to help compatibility. Mikulenas & Oakley Expires January 19, 2018 [Page 6] Internet-Draft IRC Client-to-Client Protocol July 2017 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 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 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. Mikulenas & Oakley Expires January 19, 2018 [Page 7] Internet-Draft IRC Client-to-Client Protocol July 2017 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 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 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 Mikulenas & Oakley Expires January 19, 2018 [Page 8] Internet-Draft IRC Client-to-Client Protocol July 2017 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 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 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: Mikulenas & Oakley Expires January 19, 2018 [Page 9] Internet-Draft IRC Client-to-Client Protocol July 2017 Query: VERSION Response: VERSION WeeChat 1.8-dev (git: v1.7-329-g22f2fd03a) A.9. USERINFO Type: Metadata Query Reply: USERINFO This metadata query returns miscellaneous info about the user, typically the same information that's held in their realname field. However, some implementations return " ()" 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 Mikulenas & Oakley Expires January 19, 2018 [Page 10]