construct/doc/features/modeg.txt

                         User Mode +g Documentation

Support of this specification is indicated by the CALLERID token in
RPL_ISUPPORT (005).  This token takes an optional parameter, of the letter
of the user mode.  If no parameter is specified, the user mode is g.  A
typical token would be: CALLERID=g
The rest of this specification will assume the user mode is g, as
implemented in hybrid, ratbox and charybdis.

Hybrid 7 includes a new and power feature that all users can take advantage
of to help prevent flooding and unwanted messages.  This new feature is 
invoked by setting user mode +g.  When a client is set +g, that user will
be in "Caller ID" mode.  Any user that messages a +g client will receive
a notice saying that they are in +g (server side ignore) mode.  The target
client (who is set +g) will also receive a notice saying that so and so
messaged them, and that they are in +g mode.

The target of the message will only receive one notification per minute, from
any client, in order to help prevent flooding.  The sender will NOT have the
rate limit, and will receive a numeric saying the target is in +g mode every
time they send a message.  Note that this behavior is similar to the way AWAY
messages are done.

There are numerous benefits for both opers and regular users, including the
ability to stop spambot messages from ever reaching your client, stopping
private message and CTCP floods, and being able to sit on IRC in privacy.

One question that arises is how to message specific users, while blocking
out everyone else.  The command ACCEPT is your answer.  To add a user to
your accept list, issue the raw command ACCEPT <nick>,<nick>,<nick>,...

You will not receive a reply from the ACCEPT command if it is succesful,
only if an error has occured.  There are three possible errors, shown by
numerics:

   ERR_ACCEPTFULL (456): :irc.server 456 client :Accept list is full
     - This is sent when an accept list is full.
   ERR_ACCEPTEXIST (457): :irc.server 457 client target :already exists
     - This is sent when a client tries to add a user to the accept list
       that already exists there
   ERR_ACCEPTNOT (458): :irc.server 458 client target :doesnt exist
     - This is sent when a client tries to remove a user from their accept
       list who is not on the accept list.

That user will now be able to send messages to your client until the
association is broken.

Associations break in one of the following situations:  when an accepted user
QUIT's (or is on the other side of a split), you QUIT, or the accepted user
changes their nick.  The reason why a remote user's nick change will remove
them from your accept list is so that you cannot track a user after they
changed their nick.

Viewing the accept list is also very easy.  Issue the raw command ACCEPT *.
Removing a user from your accept list is also simple.  Issue the command
ACCEPT -<nick>.  

The ACCEPT command can be used whether or not +g is enabled at the time.
Setting -g does not clear the accept list.

Some users (in particular IRC operators and services) may be exempt from
CallerID, and able to message a +g user without being on their accept list.

Being on the accept list may allow a user to bypass more than +g (for example,
a +R user can use the ACCEPT command to receive messages from unidentified
users in charybdis).

                              Sample Session

The easiest way to see how this works is by experiencing it.  Seeing a sample
session can help understand what goes on though.

Client Hwy-LL is set +g initially.
Client Hwy101 wants to message Hwy-LL

Note that some clients may have to use /quote ACCEPT instead of /accept.

--

Client Hwy101:  /msg Hwy-LL hi
Hwy101 will see:  -!- Hwy-LL is in +g mode (server-side ignore.)
                  -!- Hwy-LL has been informed that you messaged them.

Hwy-LL will see:  -!- Hwy101 wcampbel@admin.irc.monkie.org is messaging you, and you have umode +g.

--

If Hwy101 sends another message to Hwy-LL (before the minute expires), he will
see:  -!- Hwy-LL is in +g mode (server-side ignore.)
and will not receive the second notice

Hwy-LL will NOT see any notice. This also applies if the second message comes
from a different user.

--

Hwy-LL now wishes to see messages from Hwy101 and SpamBot

Client Hwy-LL:  /accept Hwy101,SpamBot

Neither side will be told of the change in the accept list, Hwy-LL should
presume that the accept was succesful if no error occurs.

Now Hwy-LL can see messages from Hwy101 and SpamBot without any blockage.
If Hwy101 was also set +g, then he would have to issue /accept Hwy-LL
before he would be able to see messages from Hwy-LL.

--

Hwy-LL now wants to see who is on his accept list.

Client Hwy-LL:  /accept *

Hwy-LL will see:
  irc.server 281 Hwy-LL Hwy101 SpamBot
  irc.server 282 Hwy-LL :End of /ACCEPT list

The replies are in numeric form to help parsing by scripts.
--

Hwy-LL realises he added a spambot to his list, and wants to remove it, and
allow messages from services

Client Hwy-LL:  /accept -SpamBot,services

Hwy-LL will now only accept messages from Hwy101 and services.

--

The nicks to be added can be in ANY order, however you cannot add or remove
AND list.  
    /ACCEPT x,y,-z,f,-a would be acceptable.
    /ACCEPT x,y,-z,* would ignore the * and generate an invalid nick
                     response.

Like Dalnet and Undernet's SILENCE system, the accept list only exists while
you are connected to IRC.  In order for you to have the same accept list
every time you come onto IRC, you must put the accept commands into your 
client's auto-perform, or manually issue the commands each time.  

This system may seem similar to the SILENCE system, but it is actually a
reverse SILENCE.  SILENCE ignores certain users and allows the rest.  Mode
+g ignores all users except certain ones (on your accept list.)  Both systems
have their place, but the mode +g in Hybrid 7 is what the developers thought
would be most useful for clients.

The goals of this user mode is to provide protection from flooding and
spamming, and to provide users with a means to keep their privacy.

We hope that these goals are obtained.

Numeric replies
---------------

280 - RPL_ACCEPTLIST
--------------------
:<server> 280 <nick> <accepted1> <accepted2> ...

This numeric is used to indicate to a client the list of nicknames they are
accepting. At most 15 accepted nicknames may be included; if this is exceeded
multiple RPL_ACCEPTLIST must be sent.

281 - RPL_ENDOFACCEPT
---------------------
:<server> 281 <nick> :End of /ACCEPT list.

This numeric is used to indicate to a client the end of an accept list.

456 - ERR_ACCEPTFULL
--------------------
:<server> 456 <nick> :Accept list is full

This numeric is used to indicate to a client that their accept list is full
and one or more nicks could not be added.

457 - ERR_ACCEPTEXIST
---------------------
:<server> 457 <nick> <target> :is already on your accept list

This numeric is used to indicate to a client that the given nick was already
on their accept list.

458 - ERR_ACCEPTNOT
-------------------
:<server> 458 <nick> <target> :is not on your accept list

This numeric is used to indicate to a client that the given nick was not on
their accept list.

716 - ERR_TARGUMODEG
--------------------
:<server> 716 <nick> <target> :is in +g mode (server-side ignore.)

This numeric is used to indicate that a message (PRIVMSG) the client sent
could not be delivered because of CallerID restrictions. The <target>
parameter is the target user's nick.

717 - RPL_TARGNOTIFY
--------------------
:<server> 717 <nick> <target> :has been informed that you messaged them.

This numeric is sent after 716 if the target user was notified of the message.

718 - RPL_UMODEGMSG
-------------------
:<server> 718 <nick> <target> <user>@<host> :is messaging you, and you have umode +g.

This numeric is sent when a message (PRIVMSG or NOTICE) sent to the user is
blocked by CallerID, at most once per minute.

Problem: hybrid uses the following form instead
:<server> 718 <nick> <target>[<user>@<host>] :is messaging you, and you have umode +g.
which is ambiguous if the user may contain a [ and in the author's opinion ugly.

--
W. Campbell
updated by J. Tjoelker