Add support for stateless bridging via draft/relaymsg (irc) (#1339)

* irc: add support for stateless bridging via draft/relaymsg

As discussed at https://github.com/42wim/matterbridge/issues/667#issuecomment-634214165

* irc: handle the draft/relaymsg tag in spoofed messages too

* Apply suggestions from code review

Co-authored-by: Wim <wim@42.be>

* Run gofmt on irc.go

* Document relaymsg in matterbridge.toml.sample

Co-authored-by: Wim <wim@42.be>

bridge/irc/irc.go

@@ -205,18 +205,48 @@ func (b *Birc) doConnect() {
 	}
 }
 
+// Sanitize nicks for RELAYMSG: replace IRC characters with special meanings with "-"
+func sanitizeNick(nick string) string {
+	sanitize := func(r rune) rune {
+		if strings.ContainsRune("!+%@&#$:'\"?*,. ", r) {
+			return '-'
+		}
+		return r
+	}
+	return strings.Map(sanitize, nick)
+}
+
 func (b *Birc) doSend() {
 	rate := time.Millisecond * time.Duration(b.MessageDelay)
 	throttle := time.NewTicker(rate)
 	for msg := range b.Local {
 		<-throttle.C
 		username := msg.Username
-		if b.GetBool("Colornicks") && len(username) > 1 {
+		// Optional support for the proposed RELAYMSG extension, described at
+		// https://github.com/jlu5/ircv3-specifications/blob/master/extensions/relaymsg.md
+		// nolint:nestif
+		if (b.i.HasCapability("overdrivenetworks.com/relaymsg") || b.i.HasCapability("draft/relaymsg")) &&
+			b.GetBool("UseRelayMsg") {
+			username = sanitizeNick(username)
+			text := msg.Text
+
+			// Work around girc chomping leading commas on single word messages?
+			if strings.HasPrefix(text, ":") && !strings.ContainsRune(text, ' ') {
+				text = ":" + text
+			}
+
+			if msg.Event == config.EventUserAction {
+				b.i.Cmd.SendRawf("RELAYMSG %s %s :\x01ACTION %s\x01", msg.Channel, username, text) //nolint:errcheck
+			} else {
+				b.Log.Debugf("Sending RELAYMSG to channel %s: nick=%s", msg.Channel, username)
+				b.i.Cmd.SendRawf("RELAYMSG %s %s :%s", msg.Channel, username, text) //nolint:errcheck
+			}
+		} else {
+			if b.GetBool("Colornicks") {
 				checksum := crc32.ChecksumIEEE([]byte(msg.Username))
 				colorCode := checksum%14 + 2 // quick fix - prevent white or black color codes
 				username = fmt.Sprintf("\x03%02d%s\x0F", colorCode, msg.Username)
 			}
-
 			switch msg.Event {
 			case config.EventUserAction:
 				b.i.Cmd.Action(msg.Channel, username+msg.Text)
@@ -229,6 +259,7 @@ func (b *Birc) doSend() {
 			}
 		}
 	}
+}
 
 // validateInput validates the server/port/nick configuration. Returns a *girc.Client if successful
 func (b *Birc) getClient() (*girc.Client, error) {
@@ -275,6 +306,7 @@ func (b *Birc) getClient() (*girc.Client, error) {
 		// skip gIRC internal rate limiting, since we have our own throttling
 		AllowFlood:    true,
 		Debug:         debug,
+		SupportedCaps: map[string][]string{"overdrivenetworks.com/relaymsg": nil, "draft/relaymsg": nil},
 	})
 	return i, nil
 }
@@ -311,6 +343,15 @@ func (b *Birc) skipPrivMsg(event girc.Event) bool {
 	if event.Source.Name == b.Nick {
 		return true
 	}
+	// don't forward messages we sent via RELAYMSG
+	if relayedNick, ok := event.Tags.Get("draft/relaymsg"); ok && relayedNick == b.Nick {
+		return true
+	}
+	// This is the old name of the cap sent in spoofed messages; I've kept this in
+	// for compatibility reasons
+	if relayedNick, ok := event.Tags.Get("relaymsg"); ok && relayedNick == b.Nick {
+		return true
+	}
 	return false
 }
 

matterbridge.toml.sample

@@ -193,6 +193,19 @@ ShowTopicChange=false
 #OPTIONAL (default 0)
 JoinDelay=0
 
+#Use the optional RELAYMSG extension for username spoofing on IRC.
+#This requires an IRCd that supports the draft/relaymsg specification: currently this includes
+#Oragono 2.4.0+ and InspIRCd 3 with the m_relaymsg contrib module.
+#See https://github.com/42wim/matterbridge/issues/667#issuecomment-634214165 for more details.
+#Spoofed nicks will use the configured RemoteNickFormat, replacing reserved IRC characters
+#(!+%@&#$:'"?*,.) with a hyphen (-).
+#On most configurations, the RemoteNickFormat must include a separator character such as "/".
+#You should make sure that the settings here match your IRCd.
+#This option overrides ColorNicks.
+#OPTIONAL (default false)
+UseRelayMsg=false
+#RemoteNickFormat="{NICK}/{PROTOCOL}"
+
 ###################################################################
 #XMPP section
 ###################################################################