rfc2811.txt

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        m - toggle the moderated channel;
        n - toggle the no messages to channel from clients on the
            outside;
        q - toggle the quiet channel flag;
        p - toggle the private channel flag;
        s - toggle the secret channel flag;
        r - toggle the server reop channel flag;
        t - toggle the topic settable by channel operator only flag;

        k - set/remove the channel key (password);
        l - set/remove the user limit to channel;

        b - set/remove ban mask to keep users out;
        e - set/remove an exception mask to override a ban mask;
        I - set/remove an invitation mask to automatically override
            the invite-only flag;

   Unless mentioned otherwise below, all these modes can be manipulated
   by "channel operators" by using the MODE command defined in "IRC
   Client Protocol" [IRC-CLIENT].

4.1 Member Status

   The modes in this category take a channel member nickname as argument
   and affect the privileges given to this user.

4.1.1 "Channel Creator" Status

   The mode 'O' is only used in conjunction with "safe channels" and
   SHALL NOT be manipulated by users.  Servers use it to give the user
   creating the channel the status of "channel creator".






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4.1.2 Channel Operator Status

   The mode 'o' is used to toggle the operator status of a channel
   member.

4.1.3 Voice Privilege

   The mode 'v' is used to give and take voice privilege to/from a
   channel member.  Users with this privilege can talk on moderated
   channels.  (See section 4.2.3 (Moderated Channel Flag).

4.2 Channel Flags

   The modes in this category are used to define properties which
   affects how channels operate.

4.2.1 Anonymous Flag

   The channel flag 'a' defines an anonymous channel.  This means that
   when a message sent to the channel is sent by the server to users,
   and the origin is a user, then it MUST be masked.  To mask the
   message, the origin is changed to "anonymous!anonymous@anonymous."
   (e.g., a user with the nickname "anonymous", the username "anonymous"
   and from a host called "anonymous.").  Because of this, servers MUST
   forbid users from using the nickname "anonymous".  Servers MUST also
   NOT send QUIT messages for users leaving such channels to the other
   channel members but generate a PART message instead.

   On channels with the character '&' as prefix, this flag MAY be
   toggled by channel operators, but on channels with the character '!'
   as prefix, this flag can be set (but SHALL NOT be unset) by the
   "channel creator" only.  This flag MUST NOT be made available on
   other types of channels.

   Replies to the WHOIS, WHO and NAMES commands MUST NOT reveal the
   presence of other users on channels for which the anonymous flag is
   set.

4.2.2 Invite Only Flag

   When the channel flag 'i' is set, new members are only accepted if
   their mask matches Invite-list (See section 4.3.2) or they have been
   invited by a channel operator.  This flag also restricts the usage of
   the INVITE command (See "IRC Client Protocol" [IRC-CLIENT]) to
   channel operators.






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4.2.3 Moderated Channel Flag

   The channel flag 'm' is used to control who may speak on a channel.
   When it is set, only channel operators, and members who have been
   given the voice privilege may send messages to the channel.

      This flag only affects users.

4.2.4 No Messages To Channel From Clients On The Outside

   When the channel flag 'n' is set, only channel members MAY send
   messages to the channel.

      This flag only affects users.

4.2.5 Quiet Channel

   The channel flag 'q' is for use by servers only.  When set, it
   restricts the type of data sent to users about the channel
   operations: other user joins, parts and nick changes are not sent.
   From a user's point of view, the channel contains only one user.

   This is typically used to create special local channels on which the
   server sends notices related to its operations.  This was used as a
   more efficient and flexible way to replace the user mode 's' defined
   in RFC 1459 [IRC].

4.2.6 Private and Secret Channels

   The channel flag 'p' is used to mark a channel "private" and the
   channel flag 's' to mark a channel "secret".  Both properties are
   similar and conceal the existence of the channel from other users.

   This means that there is no way of getting this channel's name from
   the server without being a member.  In other words, these channels
   MUST be omitted from replies to queries like the WHOIS command.

   When a channel is "secret", in addition to the restriction above, the
   server will act as if the channel does not exist for queries like the
   TOPIC, LIST, NAMES commands.  Note that there is one exception to
   this rule: servers will correctly reply to the MODE command.
   Finally, secret channels are not accounted for in the reply to the
   LUSERS command (See "Internet Relay Chat: Client Protocol" [IRC-
   CLIENT]) when the <mask> parameter is specified.







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   The channel flags 'p' and 's' MUST NOT both be set at the same time.
   If a MODE message originating from a server sets the flag 'p' and the
   flag 's' is already set for the channel, the change is silently
   ignored.  This should only happen during a split healing phase
   (mentioned in the "IRC Server Protocol" document [IRC-SERVER]).

4.2.7 Server Reop Flag

   The channel flag 'r' is only available on channels which name begins
   with the character '!' and MAY only be toggled by the "channel
   creator".

   This flag is used to prevent a channel from having no channel
   operator for an extended period of time.  When this flag is set, any
   channel that has lost all its channel operators for longer than the
   "reop delay" period triggers a mechanism in servers to reop some or
   all of the channel inhabitants.  This mechanism is described more in
   detail in section 5.2.4 (Channel Reop Mechanism).

4.2.8 Topic

   The channel flag 't' is used to restrict the usage of the TOPIC
   command to channel operators.

4.2.9 User Limit

   A user limit may be set on channels by using the channel flag 'l'.
   When the limit is reached, servers MUST forbid their local users to
   join the channel.

   The value of the limit MUST only be made available to the channel
   members in the reply sent by the server to a MODE query.

4.2.10 Channel Key

   When a channel key is set (by using the mode 'k'), servers MUST
   reject their local users request to join the channel unless this key
   is given.

   The channel key MUST only be made visible to the channel members in
   the reply sent by the server to a MODE query.

4.3 Channel Access Control

   The last category of modes is used to control access to the channel,
   they take a mask as argument.





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   In order to reduce the size of the global database for control access
   modes set for channels, servers MAY put a maximum limit on the number
   of such modes set for a particular channel.  If such restriction is
   imposed, it MUST only affect user requests.  The limit SHOULD be
   homogeneous on a per IRC network basis.

4.3.1 Channel Ban and Exception

   When a user requests to join a channel, his local server checks if
   the user's address matches any of the ban masks set for the channel.
   If a match is found, the user request is denied unless the address
   also matches an exception mask set for the channel.

   Servers MUST NOT allow a channel member who is banned from the
   channel to speak on the channel, unless this member is a channel
   operator or has voice privilege. (See Section 4.1.3 (Voice
   Privilege)).

   A user who is banned from a channel and who carries an invitation
   sent by a channel operator is allowed to join the channel.

4.3.2 Channel Invitation

   For channels which have the invite-only flag set (See Section 4.2.2
   (Invite Only Flag)), users whose address matches an invitation mask
   set for the channel are allowed to join the channel without any
   invitation.

5. Current Implementations

   The only current implementation of these rules as part of the IRC
   protocol is the IRC server, version 2.10.

   The rest of this section deals with issues that are mostly of
   importance to those who wish to implement a server but some parts may
   also be of interest for client writers.

5.1 Tracking Recently Used Channels

   This mechanism is commonly known as "Channel Delay" and generally
   only applies to channels which names is prefixed with the character
   '#' (See Section 3.1 "Standard channels").

   When a network split occurs, servers SHOULD keep track of which
   channels lost a "channel operator" as the result of the break.  These
   channels are then in a special state which lasts for a certain period
   of time.  In this particular state, the channels cannot cease to




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   exist.  If all the channel members leave the channel, the channel
   becomes unavailable: the server local clients cannot join the channel
   as long as it is empty.

   Once a channel is unavailable, it will become available again either
   because a remote user has joined the channel (most likely because the
   network is healing), or because the delay period has expired (in
   which case the channel ceases to exist and may be re-created).

   The duration for which a channel death is delayed SHOULD be set
   considering many factors among which are the size (user wise) of the
   IRC network, and the usual duration of network splits.  It SHOULD be
   uniform on all servers for a given IRC network.

5.2 Safe Channels

   This document introduces the notion of "safe channels".  These
   channels have a name prefixed with the character '!' and great effort
   is made to avoid collisions in this name space.  Collisions are not
   impossible, however they are very unlikely.

5.2.1 Channel Identifier

   The channel identifier is a function of the time.  The current time
   (as defined under UNIX by the number of seconds elapsed since
   00:00:00 GMT, January 1, 1970) is converted in a string of five (5)
   characters using the following base:
   "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890" (each character has a decimal
   value starting from 0 for 'A' to 35 for '0').

   The channel identifier therefore has a periodicity of 36^5 seconds
   (about 700 days).

5.2.2 Channel Delay

   These channels MUST be subject to the "channel delay" mechanism
   described in section 5.1 (Channel Delay).  However, the mechanism is
   slightly adapted to fit better.

   Servers MUST keep track of all such channels which lose members as
   the result of a network split, no matter whether the user is a
   "channel operator" or not.

   However, these channels do NOT ever become unavailable, it is always
   possible to join them even when they are empty.






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5.2.3 Abuse Window

   Because the periodicity is so long, attacks on a particular channel
   (name) may only occur once in a very long while.  However, with luck
   and patience, it is still possible for a user to cause a channel
   collision.  In order to avoid this, servers MUST "look in the future"
   and keep a list of channel names which identifier is about to be used
   (in the coming few days for example). Such list should remain small,
   not be a burden for servers to maintain and be used to avoid channel
   collisions by preventing the re-creation of such channel for a longer
   period of time than channel delay does.

   Eventually a server MAY choose to extend this procedure to forbid
   creation of channels with the same shortname only (then ignoring the
   channel identifier).

5.2.4 Preserving Sanity In The Name Space

   The combination of the mechanisms described in sections 5.2.2 and
   5.2.3 makes it quite difficult for a user to create a channel
   collision. However, another type of abuse consists of creating many
   channels having the same shortname, but different identifiers.  To
   prevent this from happening, servers MUST forbid the creation of a
   new channel which has the same shortname of a channel currently
   existing.

5.2.5 Server Reop Mechanism

   When a channel has been opless for longer than the "reop delay"
   period and has the channel flag 'r' set (See Section 4.2.7 (Server
   Reop Flag)), IRC servers are responsible for giving the channel
   operator status randomly to some of the members.

   The exact logic used for this mechanism by the current implementation