relaymsg: RELAYMSG + draft/relaymsg cap for bridge-style spoofed-nick channel messages

src/modules/mod.rs

@@ -47,6 +47,7 @@ pub mod profilelink;
 pub mod randquote;
 pub mod realnameban;
 pub mod recaptcha;
+pub mod relaymsg;
 pub mod reputation;
 pub mod restrictchans;
 pub mod restrictcommands;
@@ -131,5 +132,6 @@ pub fn module_commands() -> Vec<Box<dyn Command>> {
         .chain(dccallow::commands())
         .chain(geoip::commands())
         .chain(globops::commands())
+        .chain(relaymsg::commands())
         .collect()
 }

src/modules/relaymsg.rs

@@ -0,0 +1,99 @@
+//! relaymsg — `RELAYMSG <channel> <nick> <text>` (IRCv3 `draft/relaymsg`): a member
+//! whose client negotiated the capability sends a channel message under a spoofed
+//! "relay" nick (e.g. `discord/alice`), for stateless bridges. The message is
+//! tagged `@draft/relaymsg=<sender>` so clients can attribute it. The spoofed nick
+//! must contain a configured separator and must not collide with a real nick.
+//!
+//! Config: `relaymsg_separators` (default `/`), `relaymsg_ident` (default `relay`),
+//! `relaymsg_host` (default = server name). Reference: InspIRCd's `m_relaymsg`.
+//! (Local delivery; cross-server ENCAP relay is not propagated.) Original native Rust.
+
+use crate::command::{CmdResult, Command};
+use crate::numeric::{ERR_BADRELAYNICK, ERR_CANNOTSENDTOCHAN, ERR_NOPRIVILEGES, ERR_NOSUCHCHANNEL};
+use crate::server::Server;
+use crate::Uid;
+
+/// Characters never allowed in a spoofed relay nick (core IRC syntax).
+const FORBIDDEN: &str = "!+%@&#$:'\"?*,.";
+
+pub fn commands() -> Vec<Box<dyn Command>> {
+    vec![Box::new(RelayMsg)]
+}
+
+struct RelayMsg;
+impl Command for RelayMsg {
+    fn name(&self) -> &'static str {
+        "RELAYMSG"
+    }
+    fn min_params(&self) -> usize {
+        3
+    }
+    fn handle(&self, s: &mut Server, uid: Uid, params: &[String]) -> CmdResult {
+        let (chan, nick, text) = (&params[0], &params[1], &params[2]);
+        let bad = |s: &mut Server, msg: &str| {
+            s.numeric(uid, ERR_BADRELAYNICK, &format!("{nick} :{msg}"));
+            CmdResult::Fail
+        };
+
+        if !s.users.get(&uid).map(|u| u.caps.relaymsg).unwrap_or(false) {
+            s.numeric(
+                uid,
+                ERR_NOPRIVILEGES,
+                ":You must enable the draft/relaymsg capability to use RELAYMSG",
+            );
+            return CmdResult::Fail;
+        }
+        let key = chan.to_ascii_lowercase();
+        if !s.channels.contains_key(&key) {
+            s.numeric(uid, ERR_NOSUCHCHANNEL, &format!("{chan} :No such channel"));
+            return CmdResult::Fail;
+        }
+        if !s.is_member(uid, &key) {
+            s.numeric(
+                uid,
+                ERR_CANNOTSENDTOCHAN,
+                &format!("{chan} :You must be in the channel to use RELAYMSG"),
+            );
+            return CmdResult::Fail;
+        }
+        if s.find_nick(nick).is_some() {
+            return bad(s, "RELAYMSG spoofed nick is already in use");
+        }
+        if nick.chars().any(|c| FORBIDDEN.contains(c)) {
+            return bad(s, "Invalid characters in spoofed nick");
+        }
+        let seps = s
+            .conf("relaymsg_separators")
+            .filter(|v| !v.is_empty())
+            .unwrap_or("/")
+            .to_string();
+        if !nick.chars().any(|c| seps.contains(c)) {
+            return bad(
+                s,
+                &format!("Spoofed nick must include one of these separators: {seps}"),
+            );
+        }
+
+        // build the fake source and relay it to every member (sender included, so
+        // their own client sees the @draft/relaymsg echo)
+        let ident = s.conf("relaymsg_ident").filter(|v| !v.is_empty()).unwrap_or("relay").to_string();
+        let host = s
+            .conf("relaymsg_host")
+            .filter(|v| !v.is_empty())
+            .unwrap_or(s.name.as_str())
+            .to_string();
+        let sender = s.users.get(&uid).map(|u| u.nick.clone()).unwrap_or_default();
+        let body = format!(":{nick}!{ident}@{host} PRIVMSG {chan} :{text}");
+        let ctags = format!("draft/relaymsg={sender}");
+        let msgid = s.next_msgid();
+        let members: Vec<Uid> = s
+            .channels
+            .get(&key)
+            .map(|c| c.members.keys().copied().collect())
+            .unwrap_or_default();
+        for m in members {
+            s.send_tagged(m, uid, &ctags, &msgid, &body);
+        }
+        CmdResult::Ok
+    }
+}