From d1693d41aa09454bf67e033d0d10d933f82f0cd1 Mon Sep 17 00:00:00 2001
From: Denis Drakhnia <numas13@gmail.com>
Date: Mon, 23 Oct 2023 07:46:55 +0300
Subject: [PATCH] master: announce client to servers behind NAT

---
 master/src/master_server.rs | 22 +++++++++++++++++++--
 protocol/src/master.rs      | 39 +++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/master/src/master_server.rs b/master/src/master_server.rs
index bbf604b..9820b2b 100644
--- a/master/src/master_server.rs
+++ b/master/src/master_server.rs
@@ -11,7 +11,7 @@ use blake2b_simd::Params;
 use fastrand::Rng;
 use log::{error, info, trace, warn};
 use thiserror::Error;
-use xash3d_protocol::filter::{Filter, Version};
+use xash3d_protocol::filter::{Filter, FilterFlags, Version};
 use xash3d_protocol::server::Region;
 use xash3d_protocol::{admin, game, master, server, Error as ProtocolError, ServerInfo};
 
@@ -240,7 +240,12 @@ impl MasterServer {
                             .filter(|i| i.1.is_valid(now, self.timeout.server))
                             .filter(|i| i.1.matches(*i.0, p.region, &p.filter))
                             .map(|i| *i.0);
-                        self.send_server_list(from, p.filter.key, iter)?;
+
+                        self.send_server_list(from, p.filter.key, iter.clone())?;
+
+                        if p.filter.flags.contains(FilterFlags::NAT) {
+                            self.send_client_to_nat_servers(from, iter)?;
+                        }
                     }
                 }
                 game::Packet::GetServerInfo(p) => {
@@ -416,6 +421,19 @@ impl MasterServer {
         Ok(())
     }
 
+    fn send_client_to_nat_servers<I>(&self, to: SocketAddrV4, iter: I) -> Result<(), Error>
+    where
+        I: Iterator<Item = SocketAddrV4>,
+    {
+        let mut buf = [0; 64];
+        let n = master::ClientAnnounce::new(to).encode(&mut buf)?;
+        let buf = &buf[..n];
+        for i in iter {
+            self.sock.send_to(buf, i)?;
+        }
+        Ok(())
+    }
+
     #[inline]
     fn is_blocked(&self, ip: &Ipv4Addr) -> bool {
         self.blocklist.contains(ip)
diff --git a/protocol/src/master.rs b/protocol/src/master.rs
index d5bdac2..3152eaa 100644
--- a/protocol/src/master.rs
+++ b/protocol/src/master.rs
@@ -123,6 +123,37 @@ where
     }
 }
 
+#[derive(Clone, Debug, PartialEq)]
+pub struct ClientAnnounce {
+    pub addr: SocketAddrV4,
+}
+
+impl ClientAnnounce {
+    pub const HEADER: &'static [u8] = b"\xff\xff\xff\xffc ";
+
+    pub fn new(addr: SocketAddrV4) -> Self {
+        Self { addr }
+    }
+
+    pub fn decode(src: &[u8]) -> Result<Self, Error> {
+        let mut cur = Cursor::new(src);
+        cur.expect(Self::HEADER)?;
+        let addr = cur
+            .get_str(cur.remaining())?
+            .parse()
+            .map_err(|_| Error::InvalidPacket)?;
+        cur.expect_empty()?;
+        Ok(Self { addr })
+    }
+
+    pub fn encode(&self, buf: &mut [u8]) -> Result<usize, Error> {
+        Ok(CursorMut::new(buf)
+            .put_bytes(Self::HEADER)?
+            .put_as_str(self.addr)?
+            .pos())
+    }
+}
+
 #[derive(Clone, Debug, PartialEq)]
 pub struct AdminChallengeResponse {
     pub master_challenge: u32,
@@ -212,6 +243,14 @@ mod tests {
         assert_eq!(e.iter().collect::<Vec<_>>(), servers);
     }
 
+    #[test]
+    fn client_announce() {
+        let p = ClientAnnounce::new("1.2.3.4:12345".parse().unwrap());
+        let mut buf = [0; 512];
+        let n = p.encode(&mut buf).unwrap();
+        assert_eq!(ClientAnnounce::decode(&buf[..n]), Ok(p));
+    }
+
     #[test]
     fn admin_challenge_response() {
         let p = AdminChallengeResponse::new(0x12345678, 0x87654321);