# Assignment 3: Channels and Modes¶

In this part of the project, your main goal will be to add support for channels and modes. You will now have to deal with the fact that messages may be relayed to multiple users, sometimes across multiple channels.

The parts of this assignment are presented in suggested order of implementation. Nonetheless, once you’ve implemented channels (JOIN, PART, and sending messages to channels), implementing modes and the remaining messages are all fairly independent of each other.

## JOIN¶

Implement the JOIN command, as described in [RFC2812 §3.2.1], with the following exceptions:

• The command must accept a single parameter: a channel name.
• You must only support the RPL_TOPIC, RPL_NAMREPLY, and ERR_NEEDMOREPARAMS replies.

Take into account the following:

• You must only send a RPL_TOPIC reply if the channel has a topic (you will implement the TOPIC message later). Otherwise, that reply is skipped.

• Although not stated explicitly in [RFC2812 §3.2.1], the RPL_NAMREPLY reply must be followed by a RPL_ENDOFNAMES. Basically, you are sending the same replies generated when a NAMES message (with this channel as a parameter) is received.

• The first automated tests for JOIN will check that the RPL_NAMREPLY and RPL_ENDOFNAMES replies are sent, but won’t validate their contents. So, you can get away with just sending the following replies (substituting nick with the recipient nick):

:hostname 353 nick = #foobar :foobar1 foobar2 foobar3
:hostname 366 nick #foobar :End of NAMES list


Once you implement the NAMES message, you can simply substitute this with a call to the same code that handles the NAMES message. Note that, until you implement NAMES correctly, most IRC clients will show your channels as having the three users in your hardcoded NAMES reply (foobar1, foobar2, and foobar3)

## PRIVMSG and NOTICE to channels¶

Extend your implementation of PRIVMSG and NOTICE from the previous assignment to support sending messages to a channel.

Until you implement modes, you will not need to support any additional replies in PRIVMSG. However, take into account the following:

• Despite its name, the ERR_NOSUCHNICK is also the appropriate reply when a non-existent channel is specified.
• Users cannot send PRIVMSG and NOTICE messages to channels they have not joined. When this happens, a ERR_CANNOTSENDTOCHAN reply must be sent back (only in the case of PRIVMSG messages).
• Once you have implement modes, there may be additional cases where a message will be denied if the user has insufficient privileges to speak on a channel.

## PART¶

Implement the PART command, as described in [RFC2812 §3.2.2], with the following exceptions:

• The command must accept either one parameter (a channel name) or two parameters (a channel name and a parting message)
• You must only support the ERR_NOTONCHANNEL, ERR_NOSUCHCHANNEL, and ERR_NEEDMOREPARAMS replies.

Take into account the following:

• Once all users in a channel have left that channel, the channel must be destroyed.

## TOPIC¶

Implement the TOPIC command, as described in [RFC2812 §3.2.4], with the following exceptions:

• You only need to support the ERR_NOTONCHANNEL, RPL_NOTOPIC, RPL_TOPIC, and ERR_NEEDMOREPARAMS replies.
• You will not need to support the ERR_CHANOPRIVSNEEDED reply until you implement modes.

## User and channel modes¶

In IRC, users can have certain modes assigned to them. Modes are identified by a single letter, and they are binary: a user either has a mode, or he doesn’t. The possible user modes are described in [RFC2812 §3.1.5], and we will be implementing only the following modes:

• a – The away mode. Users with this mode are considered to be “away from IRC”. Besides being displayed as such on an IRC client, it will also affect how certain messages directed to a user will be processed.
• o – The operator mode. Users with this mode have administrative privileges on the IRC server, and have access to certain commands available only to operators.

The above two modes are global modes: they have effect across the entire server. Users can also have channel-specific modes (or member status modes, see [RFC2811 §4.1]). We will be implementing the following member status modes:

• o – The channel operator mode. Users with this mode on a channel have special privileges on that channel.
• v – The voice mode. Users with this mode are able to send messages to moderated channels (described below).

Finally, channels themselves can also have modes (see [RFC2811 §4]). We will be implementing the following modes:

• m – The moderated mode. When a channel has this mode, only certain users are allowed to send messages to the channel.
• t – The topic mode. When a channel has this mode, only a channel operator can set the channel’s topic.

These modes are managed with the OPER, MODE, and AWAY commands. For now, we will focus on the first two.

You must implement the OPER message as described in [RFC2812 §3.1.4], with the following exceptions:

• You must only support the RPL_YOUREOPER, ERR_PASSWDMISMATCH, and ERR_NEEDMOREPARAMS.

Take into account that you should expect a <user> parameter but will ignore its content; the password expected by the OPER command is the one specified in the -o command-line parameter to the chirc executable.

You must implement the MODE message as described in [RFC2812 §3.1.5] (for user modes) and [RFC2812 §3.2.3] (for member status and channel modes), with the following exceptions:

• For user modes:

• You only need to support two (and only two) parameters: the nick and the mode string. The mode string will always be two characters long: a plus or minus character, followed by a letter.

• You only need to support the ERR_UMODEUNKNOWNFLAG and ERR_USERSDONTMATCH replies.

• If there are no errors, the reply to the MODE message will be a relay of the message, prefixed by the user’s nick and with the mode string in a long parameter. So, if a user sends this message:

MODE jrandom -o


:jrandom MODE jrandom :-o

• For channel modes:

• When only a single parameter (a channel name) is used, the only error condition you must support is the ERR_NOSUCHCHANNEL reply (although this is not included in the specification for MODE). If the command is successful, return a RPL_CHANNELMODEIS reply (in this reply, the <mode> parameter must be a plus sign followed by the channel modes; you must omit the <mode params> parameter).
• When two parameters (a channel name and a mode string) are used, you must support the following error replies: ERR_NOSUCHCHANNEL, ERR_CHANOPRIVSNEEDED, and ERR_UNKNOWNMODE. If the command is successful, the message is relayed back to the user and to all the users in the channel.
• For member status modes:

• You only need to support three parameters: the channel, the mode string, and the nick.
• You must support the following error replies: ERR_NOSUCHCHANNEL, ERR_CHANOPRIVSNEEDED, ERR_UNKNOWNMODE, and ERR_USERNOTINCHANNEL.
• If the command is successful, the message is relayed back to the user and to all the users in the channel.

You must observe the following rules when dealing with modes:

• The OPER message is the only way for a user to gain operator status (the o user mode). As indicated in the specification, a request for +o by a non-operator should be ignored.
• The a user mode cannot be toggled using the MODE command. Only the AWAY message can manipulate that mode. Requests to change it should be ignored.
• When a channel is created (when the first user enters that channel), that user is automatically granted the channel operator mode.
• In a channel, only a channel operator can change the channel modes.
• In a channel, only a channel operator can change the member status modes of users in that channel.
• When a channel has the m mode, only channel operators and users with the v member status can send PRIVMSG and NOTICE messages to that channel. Other users will receive an ERR_CANNOTSENDTOCHAN reply.
• When a channel has the t mode, only channel operators can change the channel’s topic. Other users will receive a ERR_CHANOPRIVSNEEDED reply.
• In terms of permissions, server operators (i.e., with user mode o) are assumed to have the same privileges as a channel operator. However, a server operator does not explicitly receive the o member status upon joining a channel (the user will simply have, implicitly, the same privileges as a channel operator).

## AWAY¶

Implement the AWAY command, as described in [RFC2812 §4.1].

## NAMES¶

Implement the NAMES command, as described in [RFC2812 §3.2.5], with the following exceptions:

• We are not supporting invisible, private, or secret channels, so you can consider that all channels are visible to a user sending the NAMES command.
• You only need to support NAMES messages with no parameters or with a single parameter.
• When no parameters are specified, you must return a RPL_NAMREPLY reply for each channel. Since we are not supporting invisible users, the final RPL_NAMREPLY must include the names of all the users who are not on any channel. If all connected users are in a channel, this final RPL_NAMREPLY is omitted.
• When a single parameters is specified, that parameter is interpreted to be a channel.
• You do not need to support the ERR_TOOMANYMATCHES and ERR_NOSUCHSERVER replies.

Take into account the following:

• Channels and nicks do not need to be listed in any specific order.
• When you implement modes, nicks with channel operator privileges on a channel must have their nick prefixed by @ in the RPL_NAMREPLY reply. Similarly, nicks with “voice” privileges must have their nick prefixed by +.

## LIST¶

Implement the LIST command, as described in [RFC2812 §3.2.6], with the following exceptions:

• You only need to support LIST messages with no parameters (list all channels) or with a single parameter (list only the specified channel).
• You do not need to support the ERR_TOOMANYMATCHES and ERR_NOSUCHSERVER replies.

Take into account the following:

• Channels do not need to be listed in any specific order.
• In the RPL_LIST reply, the <# visible> refers to the total number of users on that channel (since we are not supporting invisible users, the number of visible users equals the total number of users in the channel).

## WHO¶

Implement the WHO command, as described in [RFC2812 §3.6.1], with the following exceptions:

• If a mask is specified, you only need to support the case where the mask is the name of a channel. If such channel exists, you must return a RPL_WHOREPLY for each user in that channel.
• We are not supporting invisible clients so, if no mask is specified (or if 0 or * is specified as a mask), you must return a RPL_WHOREPLY for each user in the server that doesn’t have a common channel with the requesting client.
• You do not need to support the o parameter.
• You do not need to support the ERR_NOSUCHSERVER reply.

Take into account the following:

• When a channel is not specified, the <channel> field in the RPL_WHOREPLY reply must be set to *.

• In the RPL_WHOREPLY reply, the <hopcount> should be hardcoded to 0 (zero).

• The RPL_WHOREPLY must return a series of flags, which is specified as ( "H" / "G" > ["*"] [ ( "@" / "+" ) ] without explanation (furthermore, the > is a typo, and should be a right parenthesis). The flags must be constructed thusly, in this order:

• If the user is not away, include H (“here”)
• If the user is away, include G (“gone”)
• If the user is an operator, include *
• If the user is a channel operator, include @
• If the user has the voice mode in the channel, include +

When a channel is not specified, the @ and + flags are not included (regardless of what channel modes that user may have in the users he belongs to).

## Updating commands from previous assignment¶

Update the implementation of the following commands:

• NICK: When a user sends this message, and the change of nick is successful, it must be relayed to all the channels that user is in.
• QUIT: When a user sends this message, it must be relayed to all the channels that user is in. Take into account that a QUIT results in that user leaving all the channels he is in.
• WHOIS: Add support for the RPL_WHOISOPERATOR, RPL_WHOISCHANNELS, and RPL_AWAY replies. These are only sent if the user is an IRC operator, on at least one channel, or away, respectively. The order of all the replies will be: RPL_WHOISUSER, RPL_WHOISCHANNELS, RPL_WHOISSERVER, RPL_AWAY, RPL_WHOISOPERATOR, RPL_ENDOFWHOIS.
• LUSERS: The replies need to be updated to show the correct number of IRCops and the number of channels.