perf: to_channel shares one Arc<str> across all broadcast recipients instead of cloning the line per member (server-time members share a single time-tagged variant); single-recipient sends unchanged

src/link.rs

@@ -129,7 +129,7 @@ impl Server {
                 out.send(format!(
                     "SERVER {} {} {} :{}",
                     self.name, pass, self.sid, self.server_desc
-                ));
+                ).into());
                 sent_server = true;
             }
         }
@@ -150,7 +150,7 @@ impl Server {
 
     fn link_out(&self, uid: Uid, line: String) {
         if let Some(l) = self.links.get(&uid) {
-            l.out.send(line);
+            l.out.send(line.into());
         }
     }
 

src/server.rs

@@ -22,7 +22,7 @@ use crate::link::{Link, RemoteServer, RemoteUser};
 use crate::module::Hook;
 use crate::modules::dnsbl;
 use crate::resolver;
-use crate::socketengine::OutSink;
+use crate::socketengine::{LineBuf, OutSink};
 use crate::users::{Caps, User, UserFlags};
 use crate::xline::XLine;
 use crate::Uid;
@@ -713,17 +713,17 @@ impl Server {
             } else {
                 line
             };
-            self.emit_to(uid, line);
+            self.emit_to(uid, line.into());
         }
     }
 
     /// Final hop for one line to a client: diverted into the labeled-response
     /// capture buffer when one is active for `uid`, otherwise written to the wire.
-    fn emit_to(&self, uid: Uid, line: String) {
+    fn emit_to(&self, uid: Uid, line: LineBuf) {
         if let Ok(mut cap) = self.label_capture.try_borrow_mut() {
             if let Some((cuid, buf)) = cap.as_mut() {
                 if *cuid == uid {
-                    buf.push(line);
+                    buf.push(line.into_string());
                     return;
                 }
             }
@@ -861,7 +861,7 @@ impl Server {
         } else {
             format!("@{} {base}", tags.join(";"))
         };
-        self.emit_to(uid, line);
+        self.emit_to(uid, line.into());
     }
 
     /// The escaped json-log value for `msg`, or `""` if none of `targets` want it
@@ -960,14 +960,36 @@ impl Server {
         }
     }
 
-    /// Send a line to every member of a channel, optionally skipping one uid.
+    /// Send a line to every member of a channel, optionally skipping one uid. The
+    /// line is allocated once and shared (`Arc`) across all recipients — a big
+    /// channel broadcast no longer clones the string per member. A `server-time`
+    /// member gets a time-tagged variant, itself built once and shared.
     pub fn to_channel(&self, key: &str, line: &str, except: Option<Uid>) {
-        if let Some(ch) = self.channels.get(key) {
-            for &uid in ch.members.keys() {
-                if Some(uid) != except {
-                    self.send(uid, line.to_string());
-                }
+        let Some(ch) = self.channels.get(key) else {
+            return;
+        };
+        let plain: std::sync::Arc<str> = std::sync::Arc::from(line);
+        let sourced = line.starts_with(':'); // only `:prefix …` lines carry server-time
+        let mut tagged: Option<std::sync::Arc<str>> = None;
+        for &uid in ch.members.keys() {
+            if Some(uid) == except {
+                continue;
             }
+            let want_time = sourced
+                && self
+                    .users
+                    .get(&uid)
+                    .map(|u| u.caps.server_time)
+                    .unwrap_or(false);
+            let buf = if want_time {
+                let t = tagged.get_or_insert_with(|| {
+                    std::sync::Arc::from(format!("@time={} {line}", iso_time(now())).as_str())
+                });
+                LineBuf::Shared(t.clone())
+            } else {
+                LineBuf::Shared(plain.clone())
+            };
+            self.emit_to(uid, buf);
         }
     }
 
@@ -1004,7 +1026,7 @@ impl Server {
             } else {
                 format!("@{} {body}", tags.join(";"))
             };
-            self.emit_to(uid, line);
+            self.emit_to(uid, line.into());
         }
     }
 
@@ -1396,6 +1418,30 @@ mod tests {
         assert!(!ann.iter().any(|l| l.contains("PART")), "no fallback on case-only: {ann:?}");
     }
 
+    #[test]
+    fn to_channel_shares_line_and_tags_server_time_members() {
+        let mut s = srv();
+        let arx = add_user(&mut s, 1, "ann"); // plain (no server-time)
+        let brx = add_user(&mut s, 2, "bob");
+        s.users.get_mut(&2).unwrap().caps.server_time = true;
+        s.join(1, "#c", None);
+        s.join(2, "#c", None);
+        let _ = arx.try_iter().count();
+        let _ = brx.try_iter().count();
+        s.to_channel("#c", ":x!u@h TOPIC #c :hi", None);
+        let ann: Vec<String> = arx.try_iter().collect();
+        let bob: Vec<String> = brx.try_iter().collect();
+        assert!(
+            ann.iter().any(|l| l == ":x!u@h TOPIC #c :hi"),
+            "plain member gets the untagged line: {ann:?}"
+        );
+        assert!(
+            bob.iter()
+                .any(|l| l.starts_with("@time=") && l.ends_with(":x!u@h TOPIC #c :hi")),
+            "server-time member gets the @time= variant: {bob:?}"
+        );
+    }
+
     #[test]
     fn isupport_advertises_bot_and_account_extban() {
         let s = srv();

src/socketengine.rs

@@ -57,7 +57,7 @@ fn normalize_addr(a: SocketAddr) -> SocketAddr {
 /// [`OutSink`], e.g. on quit), or a per-connection queue-limit override (from the
 /// assigned connection class).
 pub enum Out {
-    Line(usize, String),
+    Line(usize, LineBuf),
     Close(usize),
     Limits {
         token: usize,
@@ -71,6 +71,43 @@ pub enum Out {
 /// server links) get a plain channel to their writer thread; reactor connections
 /// (plaintext clients) get a token plus the shared reactor channel and its waker.
 /// Either way the core just calls [`OutSink::send`].
+/// A line queued for delivery: either uniquely owned, or an `Arc` shared by every
+/// recipient of a channel broadcast — so fanning one line out to N members allocates
+/// it once, not N times. Both forms write the identical bytes to the wire.
+pub enum LineBuf {
+    Owned(String),
+    Shared(Arc<str>),
+}
+
+impl LineBuf {
+    fn bytes(&self) -> &[u8] {
+        match self {
+            LineBuf::Owned(s) => s.as_bytes(),
+            LineBuf::Shared(a) => a.as_bytes(),
+        }
+    }
+    fn len(&self) -> usize {
+        match self {
+            LineBuf::Owned(s) => s.len(),
+            LineBuf::Shared(a) => a.len(),
+        }
+    }
+    /// Materialise an owned `String` (a move for `Owned`, one copy for `Shared`) —
+    /// for the thread-model sinks and the labeled-response capture buffer.
+    pub fn into_string(self) -> String {
+        match self {
+            LineBuf::Owned(s) => s,
+            LineBuf::Shared(a) => a.to_string(),
+        }
+    }
+}
+
+impl From<String> for LineBuf {
+    fn from(s: String) -> Self {
+        LineBuf::Owned(s)
+    }
+}
+
 pub enum OutSink {
     Thread(Sender<String>),
     Reactor {
@@ -81,11 +118,12 @@ pub enum OutSink {
 }
 
 impl OutSink {
-    /// Queue one line for delivery (the writer appends CRLF).
-    pub fn send(&self, line: String) {
+    /// Queue one line for delivery (the writer appends CRLF). The reactor sink keeps
+    /// a shared line shared (no copy); the thread sink materialises a `String`.
+    pub fn send(&self, line: LineBuf) {
         match self {
             OutSink::Thread(s) => {
-                let _ = s.send(line);
+                let _ = s.send(line.into_string());
             }
             OutSink::Reactor { token, tx, waker } => {
                 if tx.send(Out::Line(*token, line)).is_ok() {
@@ -621,7 +659,7 @@ fn reactor_loop(
                                             c.wbuf.drain(..c.wpos); // reclaim written prefix
                                             c.wpos = 0;
                                         }
-                                        c.wbuf.extend_from_slice(line.as_bytes());
+                                        c.wbuf.extend_from_slice(line.bytes());
                                         c.wbuf.extend_from_slice(b"\r\n");
                                         // softsendq: over the soft cap, stop reading
                                         // their commands until the backlog drains