protocol

irc message protocol stack

        MODE    - Change the channel's mode
        INVITE  - Invite a client to an invite-only channel (mode +i)
        TOPIC   - Change the channel topic in a mode +t channel




Oikarinen & Reed                                                [Page 6]

RFC 1459              Internet Relay Chat Protocol              May 1993


   A channel operator is identified by the '@' symbol next to their
   nickname whenever it is associated with a channel (ie replies to the
   NAMES, WHO and WHOIS commands).

2. The IRC Specification

2.1 Overview

   The protocol as described herein is for use both with server to
   server and client to server connections.  There are, however, more
   restrictions on client connections (which are considered to be
   untrustworthy) than on server connections.

2.2 Character codes

   No specific character set is specified. The protocol is based on a a
   set of codes which are composed of eight (8) bits, making up an
   octet.  Each message may be composed of any number of these octets;
   however, some octet values are used for control codes which act as
   message delimiters.

   Regardless of being an 8-bit protocol, the delimiters and keywords
   are such that protocol is mostly usable from USASCII terminal and a
   telnet connection.

   Because of IRC's scandanavian origin, the characters {}| are
   considered to be the lower case equivalents of the characters []\,
   respectively. This is a critical issue when determining the
   equivalence of two nicknames.

2.3 Messages

   Servers and clients send eachother messages which may or may not
   generate a reply.  If the message contains a valid command, as
   described in later sections, the client should expect a reply as
   specified but it is not advised to wait forever for the reply; client
   to server and server to server communication is essentially
   asynchronous in nature.

   Each IRC message may consist of up to three main parts: the prefix
   (optional), the command, and the command parameters (of which there
   may be up to 15).  The prefix, command, and all parameters are
   separated by one (or more) ASCII space character(s) (0x20).

   The presence of a prefix is indicated with a single leading ASCII
   colon character (':', 0x3b), which must be the first character of the
   message itself.  There must be no gap (whitespace) between the colon
   and the prefix.  The prefix is used by servers to indicate the true



Oikarinen & Reed                                                [Page 7]

RFC 1459              Internet Relay Chat Protocol              May 1993


   origin of the message.  If the prefix is missing from the message, it
   is assumed to have originated from the connection from which it was
   received.  Clients should not use prefix when sending a message from
   themselves; if they use a prefix, the only valid prefix is the
   registered nickname associated with the client.  If the source
   identified by the prefix cannot be found from the server's internal
   database, or if the source is registered from a different link than
   from which the message arrived, the server must ignore the message
   silently.

   The command must either be a valid IRC command or a three (3) digit
   number represented in ASCII text.

   IRC messages are always lines of characters terminated with a CR-LF
   (Carriage Return - Line Feed) pair, and these messages shall not
   exceed 512 characters in length, counting all characters including
   the trailing CR-LF. Thus, there are 510 characters maximum allowed
   for the command and its parameters.  There is no provision for
   continuation message lines.  See section 7 for more details about
   current implementations.

2.3.1 Message format in 'pseudo' BNF

   The protocol messages must be extracted from the contiguous stream of
   octets.  The current solution is to designate two characters, CR and
   LF, as message separators.   Empty  messages  are  silently  ignored,
   which permits  use  of  the  sequence  CR-LF  between  messages
   without extra problems.

   The extracted message is parsed into the components <prefix>,
   <command> and list of parameters matched either by <middle> or
   <trailing> components.

   The BNF representation for this is:


<message>  ::= [':' <prefix> <SPACE> ] <command> <params> <crlf>
<prefix>   ::= <servername> | <nick> [ '!' <user> ] [ '@' <host> ]
<command>  ::= <letter> { <letter> } | <number> <number> <number>
<SPACE>    ::= ' ' { ' ' }
<params>   ::= <SPACE> [ ':' <trailing> | <middle> <params> ]

<middle>   ::= <Any *non-empty* sequence of octets not including SPACE
               or NUL or CR or LF, the first of which may not be ':'>
<trailing> ::= <Any, possibly *empty*, sequence of octets not including
                 NUL or CR or LF>

<crlf>     ::= CR LF



Oikarinen & Reed                                                [Page 8]

RFC 1459              Internet Relay Chat Protocol              May 1993


NOTES:

  1)    <SPACE> is consists only of SPACE character(s) (0x20).
        Specially notice that TABULATION, and all other control
        characters are considered NON-WHITE-SPACE.

  2)    After extracting the parameter list, all parameters are equal,
        whether matched by <middle> or <trailing>. <Trailing> is just
        a syntactic trick to allow SPACE within parameter.

  3)    The fact that CR and LF cannot appear in parameter strings is
        just artifact of the message framing. This might change later.

  4)    The NUL character is not special in message framing, and
        basically could end up inside a parameter, but as it would
        cause extra complexities in normal C string handling. Therefore
        NUL is not allowed within messages.

  5)    The last parameter may be an empty string.

  6)    Use of the extended prefix (['!' <user> ] ['@' <host> ]) must
        not be used in server to server communications and is only
        intended for server to client messages in order to provide
        clients with more useful information about who a message is
        from without the need for additional queries.

   Most protocol messages specify additional semantics and syntax for
   the extracted parameter strings dictated by their position in the
   list.  For example, many server commands will assume that the first
   parameter after the command is the list of targets, which can be
   described with:

   <target>     ::= <to> [ "," <target> ]
   <to>         ::= <channel> | <user> '@' <servername> | <nick> | <mask>
   <channel>    ::= ('#' | '&') <chstring>
   <servername> ::= <host>
   <host>       ::= see RFC 952 [DNS:4] for details on allowed hostnames
   <nick>       ::= <letter> { <letter> | <number> | <special> }
   <mask>       ::= ('#' | '$') <chstring>
   <chstring>   ::= <any 8bit code except SPACE, BELL, NUL, CR, LF and
                     comma (',')>

   Other parameter syntaxes are:

   <user>       ::= <nonwhite> { <nonwhite> }
   <letter>     ::= 'a' ... 'z' | 'A' ... 'Z'
   <number>     ::= '0' ... '9'
   <special>    ::= '-' | '[' | ']' | '\' | '`' | '^' | '{' | '}'



Oikarinen & Reed                                                [Page 9]

RFC 1459              Internet Relay Chat Protocol              May 1993


   <nonwhite>   ::= <any 8bit code except SPACE (0x20), NUL (0x0), CR
                     (0xd), and LF (0xa)>

2.4 Numeric replies

   Most of the messages sent to the server generate a reply of some
   sort.  The most common reply is the numeric reply, used for both
   errors and normal replies.  The numeric reply must be sent as one
   message consisting of the sender prefix, the three digit numeric, and
   the target of the reply.  A numeric reply is not allowed to originate
   from a client; any such messages received by a server are silently
   dropped. In all other respects, a numeric reply is just like a normal
   message, except that the keyword is made up of 3 numeric digits
   rather than a string of letters.  A list of different replies is
   supplied in section 6.

3. IRC Concepts.

   This section is devoted to describing the actual concepts behind  the
   organization  of  the  IRC  protocol and how the current
   implementations deliver different classes of messages.



                          1--\
                              A        D---4
                          2--/ \      /
                                B----C
                               /      \
                              3        E

   Servers: A, B, C, D, E         Clients: 1, 2, 3, 4

                    [ Fig. 2. Sample small IRC network ]

3.1 One-to-one communication

   Communication on a one-to-one basis is usually only performed by
   clients, since most server-server traffic is not a result of servers
   talking only to each other.  To provide a secure means for clients to
   talk to each other, it is required that all servers be able to send a
   message in exactly one direction along the spanning tree in order to
   reach any client.  The path of a message being delivered is the
   shortest path between any two points on the spanning tree.

   The following examples all refer to Figure 2 above.





Oikarinen & Reed                                               [Page 10]

RFC 1459              Internet Relay Chat Protocol              May 1993


Example 1:
     A message between clients 1 and 2 is only seen by server A, which
     sends it straight to client 2.

Example 2:
     A message between clients 1 and 3 is seen by servers A & B, and
     client 3.  No other clients or servers are allowed see the message.

Example 3:
     A message between clients 2 and 4 is seen by servers A, B, C & D
     and client 4 only.

3.2 One-to-many

   The main goal of IRC is to provide a  forum  which  allows  easy  and
   efficient  conferencing (one to many conversations).  IRC offers
   several means to achieve this, each serving its own purpose.

3.2.1 To a list

   The least efficient style of one-to-many conversation is through
   clients talking to a 'list' of users.  How this is done is almost
   self explanatory: the client gives a list of destinations to which
   the message is to be delivered and the server breaks it up and
   dispatches a separate copy of the message to each given destination.
   This isn't as efficient as using a group since the destination list
   is broken up and the dispatch sent without checking to make sure
   duplicates aren't sent down each path.

3.2.2 To a group (channel)

   In IRC the channel has a role equivalent to that of the multicast
   group; their existence is dynamic (coming and going as people join
   and leave channels) and the actual conversation carried out on a
   channel is only sent to servers which are supporting users on a given
   channel.  If there are multiple users on a server in the same
   channel, the message text is sent only once to that server and then
   sent to each client on the channel.  This action is then repeated for
   each client-server combination until the original message has fanned
   out and reached each member of the channel.

   The following examples all refer to Figure 2.

Example 4:
     Any channel with 1 client in it. Messages to the channel go to the
     server and then nowhere else.





Oikarinen & Reed                                               [Page 11]

RFC 1459              Internet Relay Chat Protocol              May 1993


Example 5:
     2 clients in a channel. All messages traverse a path as if they
     were private messages between the two clients outside a channel.

Example 6:
     Clients 1, 2 and 3 in a channel.  All messages to the channel are
     sent to all clients and only those servers which must be traversed
     by the message if it were a private message to a single client.  If
     client 1 sends a message, it goes back to client 2 and then via
     server B to client 3.

3.2.3 To a host/server mask

   To provide IRC operators with some mechanism to send  messages  to  a
   large body of related users, host and server mask messages are
   provided.  These messages are sent to users whose host or server
   information  match that  of  the mask.  The messages are only sent to
   locations where users are, in a fashion similar to that of channels.

3.3 One-to-all

   The one-to-all type of message is better described as a broadcast
   message, sent to all clients or servers or both.  On a large network
   of users and servers, a single message can result in a lot of traffic
   being sent over the network in an effort to reach all of the desired
   destinations.

   For some messages, there is no option but to broadcast it to all
   servers so that the state information held by each server is
   reasonably consistent between servers.

3.3.1 Client-to-Client

   There is no class of message which, from a single message, results in
   a message being sent to every other client.

3.3.2 Client-to-Server