Add ChanServ mode lock (MLOCK)

Founders lock channel modes with MLOCK <#channel> [modes]. The lock is a
ChannelMlock event, so it replicates and compacts like everything else;
it is applied on channel creation alongside +r and enforced by reverting
any FMODE that breaks it. Our own changes are filtered so enforcement
can't loop. Simple (paramless) modes for now.

src/engine/db.rs

@@ -40,6 +40,7 @@ pub enum Event {
     CertRemoved { account: String, fp: String },
     ChannelRegistered { name: String, founder: String, ts: u64 },
     ChannelDropped { name: String },
+    ChannelMlock { name: String, on: String, off: String },
 }
 
 // A registered channel and who owns it.
@@ -48,6 +49,57 @@ pub struct ChannelInfo {
     pub name: String,
     pub founder: String,
     pub ts: u64,
+    // Mode-lock: chars services keep set / unset (besides the implicit +r).
+    #[serde(default)]
+    pub lock_on: String,
+    #[serde(default)]
+    pub lock_off: String,
+}
+
+impl ChannelInfo {
+    /// The mode string services keep applied: +r plus the lock.
+    pub fn lock_modes(&self) -> String {
+        let mut s = format!("+r{}", self.lock_on);
+        if !self.lock_off.is_empty() {
+            s.push('-');
+            s.push_str(&self.lock_off);
+        }
+        s
+    }
+
+    /// Given a mode change, the modes to send back to restore the lock, if it was
+    /// violated. +r is always locked on. Only simple (paramless) modes are checked.
+    pub fn enforce(&self, change: &str) -> Option<String> {
+        let (mut readd, mut reremove) = (String::new(), String::new());
+        let mut adding = true;
+        for ch in change.chars() {
+            match ch {
+                '+' => adding = true,
+                '-' => adding = false,
+                m if m.is_ascii_alphabetic() => {
+                    if (m == 'r' || self.lock_on.contains(m)) && !adding && !readd.contains(m) {
+                        readd.push(m);
+                    } else if self.lock_off.contains(m) && adding && !reremove.contains(m) {
+                        reremove.push(m);
+                    }
+                }
+                _ => {}
+            }
+        }
+        if readd.is_empty() && reremove.is_empty() {
+            return None;
+        }
+        let mut s = String::new();
+        if !readd.is_empty() {
+            s.push('+');
+            s.push_str(&readd);
+        }
+        if !reremove.is_empty() {
+            s.push('-');
+            s.push_str(&reremove);
+        }
+        Some(s)
+    }
 }
 
 // A durable record: the event plus the metadata a gossip layer needs to address
@@ -288,11 +340,12 @@ impl Db {
     pub fn compact(&mut self) -> std::io::Result<()> {
         let before = self.log.len();
         let mut snapshot: Vec<Event> = self.accounts.values().cloned().map(Event::AccountRegistered).collect();
-        snapshot.extend(self.channels.values().map(|c| Event::ChannelRegistered {
-            name: c.name.clone(),
-            founder: c.founder.clone(),
-            ts: c.ts,
-        }));
+        for c in self.channels.values() {
+            snapshot.push(Event::ChannelRegistered { name: c.name.clone(), founder: c.founder.clone(), ts: c.ts });
+            if !c.lock_on.is_empty() || !c.lock_off.is_empty() {
+                snapshot.push(Event::ChannelMlock { name: c.name.clone(), on: c.lock_on.clone(), off: c.lock_off.clone() });
+            }
+        }
         self.log.compact(snapshot)?;
         tracing::info!(before, after = self.log.len(), "compacted event log");
         Ok(())
@@ -432,7 +485,7 @@ impl Db {
         self.log
             .append(Event::ChannelRegistered { name: name.to_string(), founder: founder.to_string(), ts })
             .map_err(|_| ChanError::Internal)?;
-        self.channels.insert(k, ChannelInfo { name: name.to_string(), founder: founder.to_string(), ts });
+        self.channels.insert(k, ChannelInfo { name: name.to_string(), founder: founder.to_string(), ts, lock_on: String::new(), lock_off: String::new() });
         Ok(())
     }
 
@@ -441,6 +494,21 @@ impl Db {
         self.channels.get(&key(name))
     }
 
+    /// Set the mode-lock (chars to keep set / unset) for a registered channel.
+    pub fn set_mlock(&mut self, name: &str, on: &str, off: &str) -> Result<(), ChanError> {
+        let k = key(name);
+        if !self.channels.contains_key(&k) {
+            return Err(ChanError::NoChannel);
+        }
+        self.log
+            .append(Event::ChannelMlock { name: name.to_string(), on: on.to_string(), off: off.to_string() })
+            .map_err(|_| ChanError::Internal)?;
+        let c = self.channels.get_mut(&k).unwrap();
+        c.lock_on = on.to_string();
+        c.lock_off = off.to_string();
+        Ok(())
+    }
+
     /// Unregister `name`.
     pub fn drop_channel(&mut self, name: &str) -> Result<(), ChanError> {
         let k = key(name);
@@ -473,11 +541,17 @@ fn apply(accounts: &mut HashMap<String, Account>, channels: &mut HashMap<String,
             }
         }
         Event::ChannelRegistered { name, founder, ts } => {
-            channels.insert(key(&name), ChannelInfo { name, founder, ts });
+            channels.insert(key(&name), ChannelInfo { name, founder, ts, lock_on: String::new(), lock_off: String::new() });
         }
         Event::ChannelDropped { name } => {
             channels.remove(&key(&name));
         }
+        Event::ChannelMlock { name, on, off } => {
+            if let Some(c) = channels.get_mut(&key(&name)) {
+                c.lock_on = on;
+                c.lock_off = off;
+            }
+        }
     }
 }
 
@@ -625,4 +699,24 @@ mod tests {
         assert!(db.channel("#chat").is_none());
         assert!(matches!(db.drop_channel("#chat"), Err(ChanError::NoChannel)));
     }
+
+    // Mode lock persists, renders the applied string, and detects violations.
+    #[test]
+    fn mode_lock_persists_and_enforces() {
+        let p = tmp("mlock");
+        let mut db = Db::open(&p, "local");
+        db.register_channel("#chan", "alice").unwrap();
+        db.set_mlock("#chan", "nt", "s").unwrap();
+
+        let info = db.channel("#chan").unwrap();
+        assert_eq!(info.lock_modes(), "+rnt-s");
+        assert_eq!(info.enforce("-nt"), Some("+nt".to_string())); // locked-on removed
+        assert_eq!(info.enforce("+s"), Some("-s".to_string()));   // locked-off added
+        assert_eq!(info.enforce("-r"), Some("+r".to_string()));   // +r always locked
+        assert_eq!(info.enforce("+m"), None);                     // unrelated mode ignored
+
+        drop(db);
+        let db = Db::open(&p, "local");
+        assert_eq!(db.channel("#chan").unwrap().lock_modes(), "+rnt-s", "survives reopen");
+    }
 }

src/engine/mod.rs

@@ -174,10 +174,16 @@ impl Engine {
             // creation and on the uplink burst, so registered channels regain the
             // mode after emptying, and after a services relink.
             NetEvent::ChannelCreate { channel } => {
-                if self.db.channel(&channel).is_some() {
-                    vec![NetAction::ChannelMode { channel, modes: "+r".to_string() }]
-                } else {
-                    Vec::new()
+                match self.db.channel(&channel) {
+                    Some(info) => vec![NetAction::ChannelMode { channel, modes: info.lock_modes() }],
+                    None => Vec::new(),
+                }
+            }
+            // Enforce the mode lock: revert any change that broke it.
+            NetEvent::ChannelModeChange { channel, modes } => {
+                match self.db.channel(&channel).and_then(|info| info.enforce(&modes)) {
+                    Some(revert) => vec![NetAction::ChannelMode { channel, modes: revert }],
+                    None => Vec::new(),
                 }
             }
             NetEvent::Quit { uid } => {
@@ -939,8 +945,15 @@ mod tests {
         assert!(out.iter().any(|a| matches!(a, NetAction::ChannelMode { channel, modes } if channel == "#room" && modes == "+r")), "register sets +r: {out:?}");
         assert!(notice(&to_cs(&mut e, "000AAAAAB", "INFO #room"), "alice"));
 
-        // A different, unidentified user cannot drop it.
+        // Founder sets a mode lock: it applies immediately and shows on view.
+        let out = to_cs(&mut e, "000AAAAAB", "MLOCK #room +nt-s");
+        assert!(notice(&out, "updated"));
+        assert!(out.iter().any(|a| matches!(a, NetAction::ChannelMode { channel, modes } if channel == "#room" && modes == "+rnt-s")), "mlock applied: {out:?}");
+        assert!(notice(&to_cs(&mut e, "000AAAAAB", "MLOCK #room"), "+nt-s"));
+
+        // A different, unidentified user cannot set the lock or drop it.
         e.handle(NetEvent::UserConnect { uid: "000AAAAAC".into(), nick: "bob".into() });
+        assert!(notice(&to_cs(&mut e, "000AAAAAC", "MLOCK #room +i"), "founder"));
         assert!(notice(&to_cs(&mut e, "000AAAAAC", "DROP #room"), "founder"));
 
         // The founder can, which also clears +r.
@@ -965,4 +978,27 @@ mod tests {
         let out = e.handle(NetEvent::ChannelCreate { channel: "#other".into() });
         assert!(out.is_empty(), "unregistered channel is left alone: {out:?}");
     }
+
+    // A channel's mode lock is applied on creation and enforced on violation.
+    #[test]
+    fn mode_lock_is_applied_and_enforced() {
+        let path = std::env::temp_dir().join("fedserv-mlock-engine.jsonl");
+        let _ = std::fs::remove_file(&path);
+        let mut db = Db::open(&path, "42S");
+        db.register_channel("#lk", "alice").unwrap();
+        db.set_mlock("#lk", "nt", "s").unwrap();
+        let ns = NickServ { uid: "42SAAAAAA".into(), guest_nick: "Guest".into(), guest_seq: 0 };
+        let mut e = Engine::new(vec![Box::new(ns)], db);
+
+        // Creation applies the full lock.
+        let out = e.handle(NetEvent::ChannelCreate { channel: "#lk".into() });
+        assert!(out.iter().any(|a| matches!(a, NetAction::ChannelMode { channel, modes } if channel == "#lk" && modes == "+rnt-s")), "{out:?}");
+
+        // Setting a locked-off mode is reverted.
+        let out = e.handle(NetEvent::ChannelModeChange { channel: "#lk".into(), modes: "+s".into() });
+        assert!(out.iter().any(|a| matches!(a, NetAction::ChannelMode { channel, modes } if channel == "#lk" && modes == "-s")), "{out:?}");
+
+        // An unrelated mode change is left alone.
+        assert!(e.handle(NetEvent::ChannelModeChange { channel: "#lk".into(), modes: "+m".into() }).is_empty());
+    }
 }

src/proto/inspircd.rs

@@ -95,6 +95,17 @@ impl Protocol for InspIrcd {
                 Some(chan) if !chan.is_empty() => vec![NetEvent::ChannelCreate { channel: chan.to_string() }],
                 _ => vec![],
             },
+            // :<src> FMODE <chan> <ts> <modes> [params] — a channel mode change.
+            // Skip changes we made ourselves so enforcement can't loop.
+            "FMODE" => {
+                let a: Vec<&str> = tokens.collect();
+                match (source.as_deref(), a.first(), a.get(2)) {
+                    (Some(src), Some(chan), Some(modes)) if src != self.sid && chan.starts_with('#') => {
+                        vec![NetEvent::ChannelModeChange { channel: chan.to_string(), modes: modes.to_string() }]
+                    }
+                    _ => vec![],
+                }
+            }
             "QUIT" => vec![NetEvent::Quit { uid: source.unwrap_or_default() }],
             // account-registration relay from an ircd:
             // ACCTREGISTER <reqid> <origin> <kind> <account> <p2> :<p3>
@@ -247,4 +258,16 @@ mod tests {
             "{ev:?}"
         );
     }
+
+    // A peer FMODE surfaces as a mode change; our own (sid 42S) is filtered out.
+    #[test]
+    fn parses_fmode_and_filters_own() {
+        let ev = proto().parse(":0IRAAAAAB FMODE #chan 1783845132 +m");
+        assert!(
+            matches!(ev.as_slice(), [NetEvent::ChannelModeChange { channel, modes }] if channel == "#chan" && modes == "+m"),
+            "{ev:?}"
+        );
+        let ev = proto().parse(":42S FMODE #chan 1783845132 -m");
+        assert!(!ev.iter().any(|e| matches!(e, NetEvent::ChannelModeChange { .. })), "own change filtered: {ev:?}");
+    }
 }

src/proto/mod.rs

@@ -15,6 +15,9 @@ pub enum NetEvent {
     // A channel was created or bursted (InspIRCd FJOIN). Subsequent single joins
     // arrive as IJOIN and are not surfaced.
     ChannelCreate { channel: String },
+    // A channel's modes changed (FMODE), for enforcing mode locks. Our own
+    // changes are filtered out by the protocol layer.
+    ChannelModeChange { channel: String, modes: String },
     Quit { uid: String },
     // An ircd relaying an IRCv3 account-registration request to us as the authority.
     AccountRequest { reqid: String, origin: String, kind: String, account: String, p2: String, p3: String },

src/services/chanserv.rs

@@ -1,4 +1,4 @@
-use crate::engine::db::{ChanError, Db};
+use crate::engine::db::{ChanError, ChannelInfo, Db};
 use crate::engine::service::{Sender, Service, ServiceCtx};
 
 pub struct ChanServ {
@@ -81,13 +81,91 @@ impl Service for ChanServ {
                     Err(_) => ctx.notice(me, from.uid, "Sorry, that didn't work. Please try again in a moment."),
                 }
             }
-            Some("HELP") => ctx.notice(me, from.uid, "ChanServ registers and looks after channels. Commands: \x02REGISTER\x02 <#channel>, \x02INFO\x02 <#channel>, \x02DROP\x02 <#channel>."),
+            Some("MLOCK") => {
+                let Some(&chan) = args.get(1) else {
+                    ctx.notice(me, from.uid, "Syntax: MLOCK <#channel> [modes], e.g. MLOCK #chan +nt-s");
+                    return;
+                };
+                // No modes given: show the current lock.
+                if args.len() <= 2 {
+                    match db.channel(chan) {
+                        None => ctx.notice(me, from.uid, format!("\x02{chan}\x02 isn't registered.")),
+                        Some(info) if info.lock_on.is_empty() && info.lock_off.is_empty() => {
+                            ctx.notice(me, from.uid, format!("\x02{}\x02 has no mode lock set.", info.name));
+                        }
+                        Some(info) => ctx.notice(me, from.uid, format!("Mode lock for \x02{}\x02: \x02{}\x02", info.name, show_mlock(info))),
+                    }
+                    return;
+                }
+                // Setting the lock: founder only.
+                let founder = match db.channel(chan) {
+                    Some(info) => info.founder.clone(),
+                    None => {
+                        ctx.notice(me, from.uid, format!("\x02{chan}\x02 isn't registered."));
+                        return;
+                    }
+                };
+                if from.account != Some(founder.as_str()) {
+                    ctx.notice(me, from.uid, format!("Only \x02{chan}\x02's founder can set its mode lock."));
+                    return;
+                }
+                let (on, off) = parse_mlock(&args[2..].concat());
+                match db.set_mlock(chan, &on, &off) {
+                    Ok(()) => {
+                        if let Some(info) = db.channel(chan) {
+                            ctx.channel_mode(chan, &info.lock_modes()); // apply it now
+                        }
+                        ctx.notice(me, from.uid, format!("Mode lock for \x02{chan}\x02 updated."));
+                    }
+                    Err(_) => ctx.notice(me, from.uid, "Sorry, that didn't work. Please try again in a moment."),
+                }
+            }
+            Some("HELP") => ctx.notice(me, from.uid, "ChanServ registers and looks after channels. Commands: \x02REGISTER\x02 <#channel>, \x02INFO\x02 <#channel>, \x02MLOCK\x02 <#channel> [modes], \x02DROP\x02 <#channel>."),
             Some(other) => ctx.notice(me, from.uid, format!("I don't know the command \x02{other}\x02. Try \x02HELP\x02.")),
             None => {}
         }
     }
 }
 
+// Parse a mode spec like "+nt-s" into (locked-on, locked-off) mode chars. `r` is
+// implicit for a registered channel and is ignored here.
+fn parse_mlock(spec: &str) -> (String, String) {
+    let (mut on, mut off) = (String::new(), String::new());
+    let mut adding = true;
+    for ch in spec.chars() {
+        match ch {
+            '+' => adding = true,
+            '-' => adding = false,
+            'r' => {}
+            m if m.is_ascii_alphabetic() => {
+                on.retain(|c| c != m);
+                off.retain(|c| c != m);
+                if adding {
+                    on.push(m);
+                } else {
+                    off.push(m);
+                }
+            }
+            _ => {}
+        }
+    }
+    (on, off)
+}
+
+// Render a channel's lock as "+on-off" for display.
+fn show_mlock(info: &ChannelInfo) -> String {
+    let mut s = String::new();
+    if !info.lock_on.is_empty() {
+        s.push('+');
+        s.push_str(&info.lock_on);
+    }
+    if !info.lock_off.is_empty() {
+        s.push('-');
+        s.push_str(&info.lock_off);
+    }
+    s
+}
+
 // Format a Unix timestamp (seconds) as "YYYY-MM-DD HH:MM:SS UTC", using Howard
 // Hinnant's civil-from-days algorithm so no date crate is needed.
 fn human_time(ts: u64) -> String {