extbanbanlist: matching extban b:#chan (share another channel's ban list)

src/modules/extbanbanlist.rs

@@ -0,0 +1,37 @@
+//! extbanbanlist — the matching extban `b:<#channel>`: a user is caught if they are
+//! on `#channel`'s ban list. Lets one channel share (borrow) another's bans, e.g.
+//! `+b b:#staff` bans everyone banned in #staff. Reference: InspIRCd's
+//! `m_extbanbanlist`. Original native Rust.
+//!
+//! The match is deliberately *non-recursive* — it only tests the referenced
+//! channel's plain host-mask bans (and its plain excepts), never that channel's own
+//! extbans, so two channels referencing each other can't loop.
+
+use crate::channels::glob_match;
+use crate::server::Server;
+use crate::Uid;
+
+/// A plain host-mask ban entry (not itself an extban).
+fn is_plain(mask: &str) -> bool {
+    mask.as_bytes().get(1) != Some(&b':')
+}
+
+/// True if `uid` is on `chan`'s (plain) ban list with no matching plain exception.
+pub fn matches(s: &Server, uid: Uid, chan: &str) -> bool {
+    let Some(who) = s.users.get(&uid).map(|u| u.prefix()) else {
+        return false;
+    };
+    let Some(ch) = s.channels.get(&chan.to_ascii_lowercase()) else {
+        return false;
+    };
+    if ch
+        .excepts
+        .iter()
+        .any(|e| is_plain(&e.mask) && glob_match(&e.mask, &who))
+    {
+        return false;
+    }
+    ch.bans
+        .iter()
+        .any(|b| is_plain(&b.mask) && glob_match(&b.mask, &who))
+}