Fix IRC listener relay of bodies and modes, and JOIN names (closes #127)

The IRC listener relayed only the first line of a PRIVMSG or NOTICE
body; it now sends one line per body line. A MODE change reached IRC
listener members without its key, limit or mask, and "+o bob" went out
as one trailing parameter; each value is now its own parameter, in the
relay and in the echo to the IRC listener user who made the change.
CR, LF and NUL are now removed from each parameter of a line sent to an
IRC listener connection, before the leading ':' is decided, and from
the whole line, so a stored body line, key or mask cannot start a line
of its own. The channel name check moved from the HTTP handler into
service.JoinChannel, so the IRC listener's JOIN refuses the same names
with 403.

Model: opus-5-5

internal/service/service.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"log/slog"
+	"regexp"
 	"strconv"
 	"strings"
 	"sync"
@@ -35,6 +36,12 @@ const (
 // for (RFC 2812).
 const maxUserhostNicks = 5
 
+// validChannelRe matches the channel names JOIN accepts: #
+// followed by 1 to 63 letters, digits, _ or -.
+var validChannelRe = regexp.MustCompile(
+	`^#[a-zA-Z0-9_\-]{1,63}$`,
+)
+
 // Params defines the dependencies for creating a Service.
 type Params struct {
 	fx.In
@@ -473,12 +480,21 @@ func (s *Service) SendDirectMessage(
 
 // JoinChannel creates or joins a channel, making the
 // first joiner the operator. Fans out the JOIN to all
-// channel members.
+// channel members. A channel name that validChannelRe
+// does not match gets ERR_NOSUCHCHANNEL.
 func (s *Service) JoinChannel(
 	ctx context.Context,
 	sessionID int64,
 	nick, channel, suppliedKey string,
 ) (*JoinResult, error) {
+	if !validChannelRe.MatchString(channel) {
+		return nil, &IRCError{
+			irc.ErrNoSuchChannel,
+			[]string{channel},
+			msgNoSuchChannel,
+		}
+	}
+
 	chID, err := s.db.GetOrCreateChannel(ctx, channel)
 	if err != nil {
 		return nil, fmt.Errorf("get/create channel: %w", err)