conn_waitpong: optionally require a PONG cookie before registration (anti-bot)

src/modules/conn_waitpong.rs

@@ -0,0 +1,54 @@
+//! conn_waitpong — optionally hold registration until the client answers a server
+//! PING with the exact cookie we sent, filtering bots that never PONG. Config:
+//!
+//! ```text
+//! conn_waitpong = yes                  # require the pong before registering (default off)
+//! conn_waitpong_killonbadreply = yes   # disconnect on a wrong pong (default: keep waiting)
+//! ```
+//!
+//! The gate itself is the core `User.waitpong` field (checked in `try_register`,
+//! like `dns_pending`); this module just arms it at connect and clears it on the
+//! matching PONG. Behaviour reference: InspIRCd's `m_conn_waitpong`. Native Rust.
+
+use crate::server::Server;
+use crate::Uid;
+
+/// A short random cookie the client must echo back in its PONG.
+fn cookie() -> String {
+    let mut b = [0u8; 8];
+    let _ = openssl::rand::rand_bytes(&mut b);
+    b.iter().map(|x| format!("{x:02x}")).collect()
+}
+
+/// At connect: if enabled, stash a cookie on the user and PING it. `try_register`
+/// will not complete while `User.waitpong` is set.
+pub fn arm(s: &mut Server, uid: Uid) {
+    if !s.conf_bool("conn_waitpong", false) {
+        return;
+    }
+    let c = cookie();
+    if let Some(u) = s.users.get_mut(&uid) {
+        u.waitpong = Some(c.clone());
+    }
+    s.send(uid, format!(":{} PING :{c}", s.name));
+}
+
+/// On PONG: clear the gate if the cookie matches. On a wrong reply, optionally drop
+/// the client (else keep waiting — a real client will retry on the next PING).
+pub fn on_pong(s: &mut Server, uid: Uid, params: &[String]) {
+    let Some(want) = s.users.get(&uid).and_then(|u| u.waitpong.clone()) else {
+        return; // not waiting (already satisfied, or feature off)
+    };
+    let got = params.last().map(String::as_str).unwrap_or("");
+    if got == want {
+        if let Some(u) = s.users.get_mut(&uid) {
+            u.waitpong = None;
+        }
+    } else if s.conf_bool("conn_waitpong_killonbadreply", false) {
+        s.send(
+            uid,
+            "ERROR :Closing link (incorrect ping reply)".to_string(),
+        );
+        s.remove_user(uid, "Incorrect ping reply");
+    }
+}