Derive correct UUID for offline players in lobby logic

src/lobby.rs

@@ -20,10 +20,9 @@ use tokio::net::tcp::{ReadHalf, WriteHalf};
 use tokio::net::TcpStream;
 use tokio::select;
 use tokio::time;
-use uuid::Uuid;
 
 use crate::config::*;
-use crate::mc;
+use crate::mc::{self, uuid};
 use crate::net;
 use crate::proto;
 use crate::proto::client::{Client, ClientInfo, ClientState};
@@ -198,10 +197,7 @@ async fn respond_login_success(
 ) -> Result<(), ()> {
     packet::write_packet(
         LoginSuccess {
-            uuid: Uuid::new_v3(
-                &Uuid::new_v3(&Uuid::nil(), b"OfflinePlayer"),
-                login_start.name.as_bytes(),
-            ),
+            uuid: uuid::offline_player_uuid(&login_start.name),
             username: login_start.name.clone(),
         },
         client,

src/mc/mod.rs

@@ -2,6 +2,7 @@ pub mod ban;
 #[cfg(feature = "rcon")]
 pub mod rcon;
 pub mod server_properties;
+pub mod uuid;
 
 /// Minecraft ticks per second.
 #[allow(unused)]

src/mc/uuid.rs

@@ -0,0 +1,26 @@
+use md5::{Digest, Md5};
+use uuid::Uuid;
+
+/// Offline player namespace.
+const OFFLINE_PLAYER_NAMESPACE: &str = "OfflinePlayer:";
+
+/// Get UUID for given player username.
+pub fn player_uuid(username: &str) -> Uuid {
+    Uuid::from_bytes(jdk_name_uuid_from_bytes(username.as_bytes()))
+}
+
+/// Get UUID for given offline player username.
+pub fn offline_player_uuid(username: &str) -> Uuid {
+    player_uuid(&format!("{}{}", OFFLINE_PLAYER_NAMESPACE, username))
+}
+
+/// Java's `UUID.nameUUIDFromBytes`.
+///
+/// Static factory to retrieve a type 3 (name based) `Uuid` based on the specified byte array.
+///
+/// Ported from: https://github.com/AdoptOpenJDK/openjdk-jdk8u/blob/9a91972c76ddda5c1ce28b50ca38cbd8a30b7a72/jdk/src/share/classes/java/util/UUID.java#L153-L175
+fn jdk_name_uuid_from_bytes(data: &[u8]) -> [u8; 16] {
+    let mut hasher = Md5::new();
+    hasher.update(data);
+    hasher.finalize().into()
+}