Add KICK support

Downstream and upstream message handling are slightly different because
downstreams can send KICK messages with multiple channels or users,
while upstreams can only send KICK messages with one channel and one
user (according to the RFC).

downstream.go

@@ -903,6 +903,62 @@ func (dc *downstreamConn) handleMessageRegistered(msg *irc.Message) error {
 				dc.logger.Printf("failed to delete channel %q in DB: %v", upstreamName, err)
 			}
 		}
+	case "KICK":
+		var channelStr, userStr string
+		if err := parseMessageParams(msg, &channelStr, &userStr); err != nil {
+			return err
+		}
+
+		channels := strings.Split(channelStr, ",")
+		users := strings.Split(userStr, ",")
+
+		var reason string
+		if len(msg.Params) > 2 {
+			reason = msg.Params[2]
+		}
+
+		if len(channels) != 1 && len(channels) != len(users) {
+			return ircError{&irc.Message{
+				Command: irc.ERR_BADCHANMASK,
+				Params:  []string{dc.nick, channelStr, "Bad channel mask"},
+			}}
+		}
+
+		for i, user := range users {
+			var channel string
+			if len(channels) == 1 {
+				channel = channels[0]
+			} else {
+				channel = channels[i]
+			}
+
+			ucChannel, upstreamChannel, err := dc.unmarshalEntity(channel)
+			if err != nil {
+				return err
+			}
+
+			ucUser, upstreamUser, err := dc.unmarshalEntity(user)
+			if err != nil {
+				return err
+			}
+
+			if ucChannel != ucUser {
+				return ircError{&irc.Message{
+					Command: irc.ERR_USERNOTINCHANNEL,
+					Params:  []string{dc.nick, user, channel, "They aren't on that channel"},
+				}}
+			}
+			uc := ucChannel
+
+			params := []string{upstreamChannel, upstreamUser}
+			if reason != "" {
+				params = append(params, reason)
+			}
+			uc.SendMessage(&irc.Message{
+				Command: "KICK",
+				Params:  params,
+			})
+		}
 	case "MODE":
 		var name string
 		if err := parseMessageParams(msg, &name); err != nil {

upstream.go

@@ -582,6 +582,43 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 				})
 			})
 		}
+	case "KICK":
+		if msg.Prefix == nil {
+			return fmt.Errorf("expected a prefix")
+		}
+
+		var channel, user string
+		if err := parseMessageParams(msg, &channel, &user); err != nil {
+			return err
+		}
+
+		var reason string
+		if len(msg.Params) > 2 {
+			reason = msg.Params[1]
+		}
+
+		if user == uc.nick {
+			uc.logger.Printf("kicked from channel %q by %s", channel, msg.Prefix.Name)
+			delete(uc.channels, channel)
+		} else {
+			ch, err := uc.getChannel(channel)
+			if err != nil {
+				return err
+			}
+			delete(ch.Members, user)
+		}
+
+		uc.forEachDownstream(func(dc *downstreamConn) {
+			params := []string{dc.marshalChannel(uc, channel), dc.marshalNick(uc, user)}
+			if reason != "" {
+				params = append(params, reason)
+			}
+			dc.SendMessage(&irc.Message{
+				Prefix:  dc.marshalUserPrefix(uc, msg.Prefix),
+				Command: "KICK",
+				Params:  params,
+			})
+		})
 	case "QUIT":
 		if msg.Prefix == nil {
 			return fmt.Errorf("expected a prefix")