add a type for CTCP-encoded strings, and NOTICEs for error cases

irc/commands.go

 		return &TheaterActionCommand{
 			channel: NewName(args[1]),
 			asNick:  NewName(args[2]),
-			action:  NewText(args[3]),
+			action:  NewCTCPText(args[3]),
 		}, nil
 	} else {
 		return nil, ErrParseCommand

irc/reply.go

 	return NewStringReply(source, PRIVMSG, "%s :%s", target.Nick(), message)
 }
 
+func RplCTCPAction(source Identifiable, target Identifiable, action CTCPText) string {
+	return RplPrivMsg(source, target, NewText(fmt.Sprintf("\x01ACTION %s\x01", action)))
+}
+
 func RplNotice(source Identifiable, target Identifiable, message Text) string {
 	return NewStringReply(source, NOTICE, "%s :%s", target.Nick(), message)
 }

irc/strings.go

 func (text Text) String() string {
 	return string(text)
 }
+
+// CTCPText is text suitable escaped for CTCP.
+type CTCPText string
+
+var ctcpEscaper = strings.NewReplacer("\x00", "\x200", "\n", "\x20n", "\r", "\x20r")
+
+func NewCTCPText(str string) CTCPText {
+	return CTCPText(ctcpEscaper.Replace(str))
+}

irc/theater.go

 		return
 	}
 
-	if !channel.members.AnyHasMode(Theater) {
-		channel.members[client][Theater] = true
+	if channel.members.AnyHasMode(Theater) {
+		client.Reply(RplNotice(s, client, "someone else is +T in this channel"))
+		return
 	}
+
+	channel.members[client][Theater] = true
 }
 
 type TheaterPrivMsgCommand struct {
 }
 func (m *TheaterPrivMsgCommand) HandleServer(s *Server) {
 	client := m.Client()
+
 	if !m.channel.IsChannel() {
 		client.ErrNoSuchChannel(m.channel)
 		return
 		return
 	}
 
-	if channel.members.HasMode(client, Theater) {
-		for member := range channel.members {
-			member.Reply(RplPrivMsg(TheaterClient(m.asNick), channel, m.message))
-		}
+	if !channel.members.HasMode(client, Theater) {
+		client.Reply(RplNotice(s, client, "you are not +T"))
+		return
+	}
+
+	for member := range channel.members {
+		member.Reply(RplPrivMsg(TheaterClient(m.asNick), channel, m.message))
 	}
 }
 
 	BaseCommand
 	channel Name
 	asNick  Name
-	action  Text
+	action  CTCPText
 }
 
 func (cmd *TheaterActionCommand) String() string {
 
 func (m *TheaterActionCommand) HandleServer(s *Server) {
 	client := m.Client()
-	if m.channel.IsChannel() {
+
+	if !m.channel.IsChannel() {
 		client.ErrNoSuchChannel(m.channel)
 		return
 	}
 		return
 	}
 
-	if channel.members.HasMode(client, Theater) {
-		for member := range channel.members {
-			member.Reply(RplPrivMsg(TheaterClient(m.asNick), channel, NewText(fmt.Sprintf("\001ACTION %s\001", m.action))))
-		}
+	if !channel.members.HasMode(client, Theater) {
+		client.Reply(RplNotice(s, client, "you are not +T"))
+		return
+	}
+
+	for member := range channel.members {
+		member.Reply(RplCTCPAction(TheaterClient(m.asNick), channel, m.action))
 	}
 }

irc/types.go

 
 func (members MemberSet) AnyHasMode(mode ChannelMode) bool {
 	for _, modes := range members {
-		if modes[Theater] {
+		if modes[mode] {
 			return true
 		}
 	}