feat(lib): per-member room statistics from the JoinRoom reply

The JoinRoom (code 14) reply carries, after the membership list, four
parallel vectors describing each member: status, share statistics, free
upload slots and country. The handler stopped after the usernames, so all of
it was discarded. It is now parsed and exposed as Client::room_member_stats.

Issue #48 asked for RoomStats (57) and RoomListStats (55). Those codes are
UserInterests and MyRecommendations in the Soulseek protocol; there is no
RoomStats message on the wire. Per-room user counts already arrive with
RoomList (64), which the client handles, and the per-member statistics are
part of the JoinRoom reply -- so that is where this adds them.

- join_room.rs: parse the stat vectors, each bounded by the payload so a
  hostile count cannot hang or overallocate
- types::RoomUserStats; every field looked up positionally so a server
  sending short vectors (or omitting countries) does not shift the roster
- ServerMessage/ClientOperation::RoomMemberStats and the context snapshot
  behind Client::room_member_stats, replaced on each rejoin

soulseek-rs-lib/src/message/server/join_room.rs

@@ -1,6 +1,7 @@
 use crate::{
     actor::server_actor::ServerMessage,
     message::{Message, MessageHandler},
+    types::{RoomUserStats, UserStatus},
 };
 use std::sync::mpsc::Sender;
 
@@ -12,24 +13,104 @@ impl MessageHandler<ServerMessage> for JoinRoomHandler {
     }
 
     fn handle(&self, message: &mut Message, sender: Sender<ServerMessage>) {
-        // JoinRoom (code 14): room name, then a vector of member usernames.
-        // Per-user stat vectors follow but are not needed here, so we stop
-        // after reading the names.
+        // JoinRoom (code 14): room name, the member usernames, then the
+        // parallel per-member stat vectors.
         let room = message.read_string();
-        let user_count = message.read_int32();
-        let mut users = Vec::new();
-        for _ in 0..user_count {
-            // Guard against a hostile user_count outrunning the payload; each
-            // username is a length-prefixed string (>= 4 bytes).
-            if message.get_pointer() + 4 > message.get_size() {
-                break;
-            }
-            users.push(message.read_string());
+        let users = read_strings(message);
+        let stats = parse_member_stats(message, &users);
+        let _ = sender.send(ServerMessage::RoomJoined {
+            room: room.clone(),
+            users,
+        });
+        if !stats.is_empty() {
+            let _ = sender.send(ServerMessage::RoomMemberStats { room, stats });
         }
-        let _ = sender.send(ServerMessage::RoomJoined { room, users });
     }
 }
 
+/// Read a length-prefixed vector of strings, stopping early if the count
+/// outruns the payload: a bogus (possibly hostile) count must not spin us
+/// into an OOM allocation loop. A 4-byte floor is the smallest a
+/// length-prefixed string can be.
+fn read_strings(message: &mut Message) -> Vec<String> {
+    let count = message.read_int32();
+    let mut values = Vec::new();
+    for _ in 0..count {
+        if message.get_pointer() + 4 > message.get_size() {
+            break;
+        }
+        values.push(message.read_string());
+    }
+    values
+}
+
+/// Read a length-prefixed vector of 32-bit values, bounded the same way.
+fn read_int32s(message: &mut Message) -> Vec<u32> {
+    let count = message.read_int32();
+    let mut values = Vec::new();
+    for _ in 0..count {
+        if message.get_pointer() + 4 > message.get_size() {
+            break;
+        }
+        values.push(message.read_int32());
+    }
+    values
+}
+
+/// Parse the per-member statistics that follow the membership list of a
+/// `JoinRoom` (code 14) reply: statuses, then a record of share statistics per
+/// member, then free upload slots, then country codes.
+///
+/// Each vector is independently length-prefixed and a server may send fewer
+/// entries than there are members (or, on an older server, omit the country
+/// vector entirely), so every field is looked up positionally and defaults
+/// when absent rather than shifting the whole roster.
+#[must_use]
+fn parse_member_stats(
+    message: &mut Message,
+    users: &[String],
+) -> Vec<RoomUserStats> {
+    let statuses = read_int32s(message);
+
+    let stat_count = message.read_int32();
+    let mut shares = Vec::new();
+    for _ in 0..stat_count {
+        // A share record is 20 bytes: speed, an obsolete 64-bit upload
+        // number, files and folders.
+        if message.get_pointer() + 20 > message.get_size() {
+            break;
+        }
+        let average_speed = message.read_int32();
+        let _upload_number = message.read_int64(); // obsolete
+        let shared_files = message.read_int32();
+        let shared_folders = message.read_int32();
+        shares.push((average_speed, shared_files, shared_folders));
+    }
+
+    let slots_free = read_int32s(message);
+    let countries = read_strings(message);
+
+    users
+        .iter()
+        .enumerate()
+        .map(|(i, username)| {
+            let (average_speed, shared_files, shared_folders) =
+                shares.get(i).copied().unwrap_or((0, 0, 0));
+            RoomUserStats {
+                username: username.clone(),
+                status: UserStatus::from_code(
+                    statuses.get(i).copied().unwrap_or(0),
+                ),
+                average_speed,
+                shared_files,
+                shared_folders,
+                slots_free: slots_free.get(i).copied().unwrap_or(0),
+                country: countries.get(i).cloned().filter(|c| !c.is_empty()),
+            }
+        })
+        .collect()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -53,6 +134,158 @@ mod tests {
         }
     }
 
+    /// A full JoinRoom payload: room, members, then the four parallel stat
+    /// vectors the server sends for them.
+    fn join_payload() -> Message {
+        framed(|m| {
+            m.write_string("nicotine")
+                .write_int32(2)
+                .write_string("alice")
+                .write_string("bob")
+                // statuses
+                .write_int32(2)
+                .write_int32(2)
+                .write_int32(1)
+                // share records
+                .write_int32(2)
+                .write_int32(1024)
+                .write_int64(0)
+                .write_int32(4321)
+                .write_int32(77)
+                .write_int32(50)
+                .write_int64(0)
+                .write_int32(10)
+                .write_int32(2)
+                // free slots
+                .write_int32(2)
+                .write_int32(1)
+                .write_int32(0)
+                // countries
+                .write_int32(2)
+                .write_string("NL")
+                .write_string("");
+        })
+    }
+
+    #[test]
+    fn member_stats_are_parsed_alongside_the_roster() {
+        let (tx, rx) = std::sync::mpsc::channel();
+        JoinRoomHandler.handle(&mut join_payload(), tx);
+
+        assert!(matches!(
+            rx.try_recv(),
+            Ok(ServerMessage::RoomJoined { .. })
+        ));
+        match rx.try_recv() {
+            Ok(ServerMessage::RoomMemberStats { room, stats }) => {
+                assert_eq!(room, "nicotine");
+                assert_eq!(
+                    stats,
+                    vec![
+                        RoomUserStats {
+                            username: "alice".to_string(),
+                            status: UserStatus::Online,
+                            average_speed: 1024,
+                            shared_files: 4321,
+                            shared_folders: 77,
+                            slots_free: 1,
+                            country: Some("NL".to_string()),
+                        },
+                        RoomUserStats {
+                            username: "bob".to_string(),
+                            status: UserStatus::Away,
+                            average_speed: 50,
+                            shared_files: 10,
+                            shared_folders: 2,
+                            slots_free: 0,
+                            country: None,
+                        },
+                    ]
+                );
+            }
+            other => panic!("unexpected: {other:?}"),
+        }
+    }
+
+    #[test]
+    fn a_server_that_omits_the_stat_vectors_still_yields_a_roster() {
+        // Nothing after the membership list: every stat reads as a default
+        // rather than shifting the roster or dropping members.
+        let (tx, rx) = std::sync::mpsc::channel();
+        let mut message = framed(|m| {
+            m.write_string("jazz").write_int32(1).write_string("alice");
+        });
+
+        JoinRoomHandler.handle(&mut message, tx);
+        assert!(matches!(
+            rx.try_recv(),
+            Ok(ServerMessage::RoomJoined { .. })
+        ));
+        match rx.try_recv() {
+            Ok(ServerMessage::RoomMemberStats { stats, .. }) => {
+                assert_eq!(stats.len(), 1);
+                assert_eq!(stats[0].username, "alice");
+                assert_eq!(stats[0].average_speed, 0);
+                assert_eq!(stats[0].country, None);
+            }
+            other => panic!("unexpected: {other:?}"),
+        }
+    }
+
+    #[test]
+    fn short_stat_vectors_do_not_shift_the_roster() {
+        // Stats for the first member only: the second must still be reported,
+        // with defaults, rather than inheriting the first member's figures.
+        let (tx, rx) = std::sync::mpsc::channel();
+        let mut message = framed(|m| {
+            m.write_string("jazz")
+                .write_int32(2)
+                .write_string("alice")
+                .write_string("bob")
+                .write_int32(1)
+                .write_int32(2)
+                .write_int32(1)
+                .write_int32(1024)
+                .write_int64(0)
+                .write_int32(9)
+                .write_int32(1)
+                .write_int32(0)
+                .write_int32(0);
+        });
+
+        JoinRoomHandler.handle(&mut message, tx);
+        let _ = rx.try_recv();
+        match rx.try_recv() {
+            Ok(ServerMessage::RoomMemberStats { stats, .. }) => {
+                assert_eq!(stats.len(), 2);
+                assert_eq!(stats[0].shared_files, 9);
+                assert_eq!(stats[1].username, "bob");
+                assert_eq!(stats[1].shared_files, 0);
+                assert_eq!(stats[1].status, UserStatus::Offline);
+            }
+            other => panic!("unexpected: {other:?}"),
+        }
+    }
+
+    #[test]
+    fn hostile_stat_counts_do_not_hang_or_overallocate() {
+        // Vectors claiming ~4 billion entries in a tiny frame must return
+        // promptly, bounded by the payload.
+        let (tx, rx) = std::sync::mpsc::channel();
+        let mut message = framed(|m| {
+            m.write_string("jazz")
+                .write_int32(1)
+                .write_string("alice")
+                .write_int32(u32::MAX);
+        });
+
+        JoinRoomHandler.handle(&mut message, tx);
+        assert!(matches!(
+            rx.try_recv(),
+            Ok(ServerMessage::RoomJoined { .. })
+        ));
+    }
+
     #[test]
     fn forwards_room_and_member_list() {
         let (tx, rx) = std::sync::mpsc::channel();