channel-rename: implement IRCv3 draft/channel-rename — RENAME command + cap, in-place rename (RENAME for cap clients, PART/JOIN fallback for the rest), and S2S propagation

src/channels.rs

@@ -970,6 +970,110 @@ impl Server {
         self.events.push_back(Hook::Join(uid, key));
     }
 
+    /// Rename channel `oldkey` (an existing lowercase key) to display name
+    /// `newname`, preserving all state — membership, modes, topic, bans, TS. The
+    /// channel object is rekeyed in the table and every local member's channel set
+    /// is moved with it. Local members are then notified: a `RENAME` line for
+    /// draft/channel-rename clients, a PART+JOIN(+topic+names) emulation for the
+    /// rest (skipped when only the casing changed, per the spec). `src_prefix` is
+    /// the nick!user@host — or server name — shown as the RENAME source. Returns
+    /// the new lowercase key, or `None` if the move couldn't be made. Callers
+    /// validate policy first (op rank, name validity, collision).
+    pub fn rename_channel(
+        &mut self,
+        oldkey: &str,
+        newname: &str,
+        src_prefix: &str,
+        reason: &str,
+    ) -> Option<String> {
+        let newkey = newname.to_ascii_lowercase();
+        let case_only = newkey.as_str() == oldkey;
+        if !self.channels.contains_key(oldkey) {
+            return None;
+        }
+        if !case_only && self.channels.contains_key(&newkey) {
+            return None;
+        }
+        let oldname = self.channels[oldkey].name.clone();
+        let members: Vec<Uid> = self.channels[oldkey].members.keys().copied().collect();
+        if case_only {
+            if let Some(ch) = self.channels.get_mut(oldkey) {
+                ch.name = newname.to_string();
+            }
+        } else {
+            let mut ch = self.channels.remove(oldkey).unwrap();
+            ch.name = newname.to_string();
+            self.channels.insert(newkey.clone(), ch);
+            for &m in &members {
+                if let Some(u) = self.users.get_mut(&m) {
+                    u.channels.remove(oldkey);
+                    u.channels.insert(newkey.clone());
+                }
+            }
+            self.rekey_channel_state(oldkey, &newkey);
+        }
+        let renline = format!(":{src_prefix} RENAME {oldname} {newname} :{reason}");
+        for &m in &members {
+            let has_cap = self
+                .users
+                .get(&m)
+                .map(|u| u.caps.channel_rename)
+                .unwrap_or(false);
+            if has_cap {
+                self.send(m, renline.clone());
+            } else if !case_only {
+                self.emulate_rename_join(m, &oldname, newname, &newkey, reason);
+            }
+            // case-only + no cap: the spec says the PART/JOIN fallback SHOULD NOT
+            // be used, so those clients simply keep the channel under its old case.
+        }
+        Some(newkey)
+    }
+
+    /// The PART-old + JOIN-new(+topic+names) fallback shown to one member that
+    /// lacks draft/channel-rename, so their client follows the channel across a
+    /// rename. Mirrors the JOIN broadcast (extended-join aware).
+    fn emulate_rename_join(&self, m: Uid, oldname: &str, newname: &str, newkey: &str, reason: &str) {
+        let Some(u) = self.users.get(&m) else {
+            return;
+        };
+        let prefix = u.prefix();
+        let joinline = if u.caps.extended_join {
+            let acct = u.account.clone().unwrap_or_else(|| "*".to_string());
+            format!(":{prefix} JOIN {newname} {acct} :{}", u.realname)
+        } else {
+            format!(":{prefix} JOIN {newname}")
+        };
+        let partline = if reason.is_empty() {
+            format!(":{prefix} PART {oldname}")
+        } else {
+            format!(":{prefix} PART {oldname} :{reason}")
+        };
+        self.send(m, partline);
+        self.send(m, joinline);
+        if let Some(t) = self.channels.get(newkey).and_then(|c| c.topic.as_ref()) {
+            let text = t.text.clone();
+            self.numeric(m, RPL_TOPIC, &format!("{newname} :{text}"));
+        }
+        self.send_names(m, newkey);
+    }
+
+    /// Move a channel's auxiliary, name-keyed module state (recorded history,
+    /// channel metadata) from `oldkey` to `newkey` on a rename, so a CHATHISTORY
+    /// replay or a metadata read still finds it under the new name.
+    fn rekey_channel_state(&mut self, oldkey: &str, newkey: &str) {
+        if let Some(h) = self.ext.get_mut::<crate::modules::chathistory::History>() {
+            if let Some(v) = h.0.remove(oldkey) {
+                h.0.insert(newkey.to_string(), v);
+            }
+        }
+        if let Some(store) = self.ext.get_mut::<crate::modules::metadata::MetaStore>() {
+            if let Some(v) = store.0.remove(oldkey) {
+                store.0.insert(newkey.to_string(), v);
+            }
+        }
+    }
+
     /// +H chanhistory: replay a channel's recent messages to a user who just
     /// joined — the last `<lines>` (within `<secs>`, 0 = no limit) from the store,
     /// wrapped in a `chathistory` batch for batch-capable clients.

src/coremods/core_channel.rs

@@ -1,6 +1,6 @@
 //! core_channel — channel membership commands: JOIN, PART, KICK, TOPIC, NAMES.
 
-use crate::channels::{normalize_ban_mask, Ban, Topic, RANK_HALFOP};
+use crate::channels::{normalize_ban_mask, valid_chan, Ban, Topic, RANK_HALFOP, RANK_OP};
 use crate::command::{CmdResult, Command};
 use crate::module::Hook;
 use crate::numeric::*;
@@ -12,6 +12,7 @@ pub fn commands() -> Vec<Box<dyn Command>> {
     vec![
         Box::new(Join),
         Box::new(Part),
+        Box::new(Rename),
         Box::new(Kick),
         Box::new(TopicCmd),
         Box::new(Names),
@@ -479,6 +480,112 @@ impl Command for Part {
     }
 }
 
+/// RENAME `<old-channel> <new-channel> [<reason>]` — IRCv3 `draft/channel-rename`.
+/// A channel operator renames a channel in place, keeping its membership, modes
+/// and topic. Members that negotiated the cap see a `RENAME`; the rest are moved
+/// with a PART/JOIN. Registered (+r) channels are managed by services, so a
+/// client can't rename them — ChanServ does that over S2S.
+struct Rename;
+impl Command for Rename {
+    fn name(&self) -> &'static str {
+        "RENAME"
+    }
+    fn min_params(&self) -> usize {
+        2
+    }
+    fn handle(&self, s: &mut Server, uid: Uid, params: &[String]) -> CmdResult {
+        let (old, new) = (&params[0], &params[1]);
+        let reason = params.get(2).cloned().unwrap_or_default();
+        let oldkey = old.to_ascii_lowercase();
+        let newkey = new.to_ascii_lowercase();
+        let case_only = oldkey == newkey;
+        if !s.channels.contains_key(&oldkey) {
+            s.numeric(uid, ERR_NOSUCHCHANNEL, &format!("{old} :No such channel"));
+            return CmdResult::Fail;
+        }
+        if !s.is_member(uid, &oldkey) {
+            s.numeric(
+                uid,
+                ERR_NOTONCHANNEL,
+                &format!("{old} :You're not on that channel"),
+            );
+            return CmdResult::Fail;
+        }
+        let is_oper = s.is_oper(uid);
+        if s.rank(uid, &oldkey) < RANK_OP && !is_oper {
+            s.numeric(
+                uid,
+                ERR_CHANOPRIVSNEEDED,
+                &format!("{old} :You're not a channel operator"),
+            );
+            return CmdResult::Fail;
+        }
+        // A registered channel's name is owned by services; renaming it moves the
+        // registration, which only ChanServ (founder-authorised) may do.
+        if s.channels[&oldkey].modes.registered && !is_oper {
+            s.fail(
+                uid,
+                "RENAME",
+                "CANNOT_RENAME",
+                "This channel is registered — ask ChanServ to rename it.",
+            );
+            return CmdResult::Fail;
+        }
+        if !valid_chan(new, s.conf_num("maxchannel", 50usize)) {
+            s.fail(
+                uid,
+                "RENAME",
+                "CANNOT_RENAME",
+                &format!("{new} is not a valid channel name."),
+            );
+            return CmdResult::Fail;
+        }
+        // A pure prefix-type change (e.g. # -> &) isn't a rename we support.
+        if new.chars().next() != old.chars().next() {
+            s.fail(
+                uid,
+                "RENAME",
+                "CANNOT_RENAME",
+                "The channel prefix can't be changed.",
+            );
+            return CmdResult::Fail;
+        }
+        if !case_only && s.channels.contains_key(&newkey) {
+            s.fail(
+                uid,
+                "RENAME",
+                "CHANNEL_NAME_IN_USE",
+                &format!("{new} already exists."),
+            );
+            return CmdResult::Fail;
+        }
+        if !is_oper {
+            if let Some(reason) = s.matched_cban(&newkey) {
+                s.fail(
+                    uid,
+                    "RENAME",
+                    "CANNOT_RENAME",
+                    &format!("{new} is CBAN'd: {reason}"),
+                );
+                return CmdResult::Fail;
+            }
+        }
+        // Capture the identity/TS before the move, then rename + propagate.
+        let (prefix, uuid) = {
+            let u = &s.users[&uid];
+            (u.prefix(), u.uuid.clone())
+        };
+        let oldname = s.channels[&oldkey].name.clone();
+        if s.rename_channel(&oldkey, new, &prefix, &reason).is_none() {
+            s.fail(uid, "RENAME", "CANNOT_RENAME", "The channel cannot be renamed.");
+            return CmdResult::Fail;
+        }
+        s.snotice_c('a', &format!("{oldname} renamed to {new} by {prefix}"));
+        s.propagate_rename(&uuid, &oldname, new, &reason, None);
+        CmdResult::Ok
+    }
+}
+
 struct Kick;
 impl Command for Kick {
     fn name(&self) -> &'static str {

src/link.rs

@@ -178,6 +178,7 @@ impl Server {
             "TOPIC" if registered => self.link_topic_recv(uid, msg),
             "FTOPIC" if registered => self.link_ftopic_recv(uid, msg),
             "KICK" if registered => self.link_kick_recv(uid, msg),
+            "RENAME" if registered => self.link_rename_recv(uid, msg),
             "MODE" | "FMODE" if registered => self.link_mode_recv(uid, msg),
             "FJOIN" if registered => self.link_fjoin_recv(uid, msg),
             "IJOIN" if registered => self.link_ijoin_recv(uid, msg),
@@ -1525,6 +1526,27 @@ impl Server {
         }
     }
 
+    /// Tell linked servers a channel was renamed. `source` is the initiator's
+    /// uuid (a client or a services pseudoclient) or a server SID; each receiver
+    /// moves the channel and notifies its own members. `except` skips the link a
+    /// forwarded rename arrived on.
+    pub fn propagate_rename(
+        &self,
+        source: &str,
+        oldname: &str,
+        newname: &str,
+        reason: &str,
+        except: Option<Uid>,
+    ) {
+        if self.links.is_empty() {
+            return;
+        }
+        self.propagate(
+            &format!(":{source} RENAME {oldname} {newname} :{reason}"),
+            except,
+        );
+    }
+
     /// The distinct links a channel's remote members sit behind (minus `except`).
     fn channel_link_targets(&self, key: &str, except: Option<Uid>) -> Vec<Uid> {
         let mut set: HashSet<Uid> = HashSet::new();
@@ -1673,6 +1695,43 @@ impl Server {
         self.propagate(&fwd, Some(via));
     }
 
+    fn link_rename_recv(&mut self, via: Uid, msg: &Message) {
+        // :<source> RENAME <old> <new> [:reason] — a channel renamed elsewhere
+        // (by a client on another server, or by ChanServ). Apply it locally,
+        // notify our members, then forward to the rest of the mesh. A
+        // services-sourced rename is honoured unconditionally: services owns the
+        // registered name and validated the op/founder before sending this.
+        let Some(source) = msg.source.clone() else {
+            return;
+        };
+        let (Some(old), Some(new)) = (msg.params.first().cloned(), msg.params.get(1).cloned())
+        else {
+            return;
+        };
+        let reason = msg.params.get(2).cloned().unwrap_or_default();
+        let oldkey = old.to_ascii_lowercase();
+        if !self.channels.contains_key(&oldkey) {
+            return;
+        }
+        // The nick!user@host (or server name) shown to local members as the source.
+        let prefix = self
+            .remote_users
+            .get(&source)
+            .map(|r| r.prefix())
+            .or_else(|| self.servers.get(&source).map(|s| s.name.clone()))
+            .or_else(|| {
+                self.servers
+                    .get(source.get(..3).unwrap_or(source.as_str()))
+                    .map(|s| s.name.clone())
+            });
+        let Some(prefix) = prefix else {
+            return; // unknown source — don't act on a rename we can't attribute
+        };
+        if self.rename_channel(&oldkey, &new, &prefix, &reason).is_some() {
+            self.propagate_rename(&source, &old, &new, &reason, Some(via));
+        }
+    }
+
     /// Remove a remote user everywhere (channels + registries) and QUIT them to
     /// any local users who shared a channel.
     fn drop_remote_user(&mut self, uuid: &str, reason: &str) {

src/server.rs

@@ -1352,6 +1352,49 @@ mod tests {
         assert!(bob.iter().any(|l| l.contains("353") && l.contains("@ann")));
     }
 
+    #[test]
+    fn rename_moves_channel_and_notifies_by_cap() {
+        let mut s = srv();
+        let arx = add_user(&mut s, 1, "ann"); // op, cap-aware
+        let brx = add_user(&mut s, 2, "bob"); // no cap
+        s.users.get_mut(&1).unwrap().caps.channel_rename = true;
+        s.join(1, "#old", None); // ann creates -> op
+        s.join(2, "#old", None);
+        let _ = arx.try_iter().count(); // drain the join chatter
+        let _ = brx.try_iter().count();
+
+        let key = s.rename_channel("#old", "#new", "ann!u@localhost", "moving");
+        assert_eq!(key.as_deref(), Some("#new"));
+        assert!(!s.channels.contains_key("#old"), "old key gone");
+        assert!(s.channels.contains_key("#new"), "new key present");
+        assert_eq!(s.channels["#new"].members.len(), 2, "membership preserved");
+        assert!(s.users[&1].channels.contains("#new") && !s.users[&1].channels.contains("#old"));
+        assert!(s.users[&2].channels.contains("#new") && !s.users[&2].channels.contains("#old"));
+
+        // The cap holder sees a RENAME; the plain client is walked PART -> JOIN.
+        let ann: Vec<String> = arx.try_iter().collect();
+        assert!(ann.iter().any(|l| l.contains("RENAME #old #new")), "cap client got RENAME: {ann:?}");
+        assert!(!ann.iter().any(|l| l.contains("PART #old")), "cap client not PARTed");
+        let bob: Vec<String> = brx.try_iter().collect();
+        assert!(bob.iter().any(|l| l.contains("PART #old")), "plain client PARTed: {bob:?}");
+        assert!(bob.iter().any(|l| l.contains("JOIN #new")), "plain client re-JOINed");
+        assert!(!bob.iter().any(|l| l.contains("RENAME")), "plain client got no RENAME");
+    }
+
+    #[test]
+    fn rename_case_only_keeps_key_and_skips_fallback() {
+        let mut s = srv();
+        let arx = add_user(&mut s, 1, "ann");
+        s.join(1, "#chan", None);
+        let _ = arx.try_iter().count();
+        let key = s.rename_channel("#chan", "#Chan", "ann!u@localhost", "");
+        assert_eq!(key.as_deref(), Some("#chan"), "key unchanged on a case-only rename");
+        assert_eq!(s.channels["#chan"].name, "#Chan", "display casing updated");
+        // Non-cap member: the spec says no PART/JOIN fallback for a case change.
+        let ann: Vec<String> = arx.try_iter().collect();
+        assert!(!ann.iter().any(|l| l.contains("PART")), "no fallback on case-only: {ann:?}");
+    }
+
     #[test]
     fn nick_change_reindexes_and_notifies_channel() {
         let mut s = srv();

src/users.rs

@@ -132,6 +132,7 @@ pub const SUPPORTED_CAPS: &[&str] = &[
     "draft/extended-isupport",
     "reverse.im/filehost",
     "draft/relaymsg",
+    "draft/channel-rename",
     "cap-notify",
 ];
 
@@ -166,6 +167,7 @@ pub struct Caps {
     pub ext_isupport: bool,     // draft/extended-isupport — ISUPPORT command + batched 005
     pub filehost: bool,         // reverse.im/filehost — knows the file-host extension
     pub relaymsg: bool,         // draft/relaymsg — may use RELAYMSG (bridge relaying)
+    pub channel_rename: bool,   // draft/channel-rename — receives RENAME (else PART+JOIN)
     pub cap_notify: bool,
 }
 
@@ -234,6 +236,7 @@ impl Caps {
             "draft/extended-isupport" => self.ext_isupport,
             "reverse.im/filehost" => self.filehost,
             "draft/relaymsg" => self.relaymsg,
+            "draft/channel-rename" => self.channel_rename,
             "cap-notify" => self.cap_notify,
             _ => false,
         }
@@ -269,6 +272,7 @@ impl Caps {
             "draft/extended-isupport" => &mut self.ext_isupport,
             "reverse.im/filehost" => &mut self.filehost,
             "draft/relaymsg" => &mut self.relaymsg,
+            "draft/channel-rename" => &mut self.channel_rename,
             "cap-notify" => &mut self.cap_notify,
             _ => return false,
         };