From 2fe2e8cdbc3bb520994ff0944188f2fa657c546a Mon Sep 17 00:00:00 2001
From: salmonik <salmonik@tuta.io>
Date: Sun, 1 Nov 2026 17:49:08 +0100
Subject: v4.0.0: require HELLO MAJOR.MINOR lockstep before auth

---
 src/server/core.rs | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

(limited to 'src/server/core.rs')

diff --git a/src/server/core.rs b/src/server/core.rs
index 89264f3..3cd6469 100644
--- a/src/server/core.rs
+++ b/src/server/core.rs
@@ -6,6 +6,7 @@ use std::sync::Arc;
 use crate::blackjack::BlackjackState;
 use crate::crash::CrashState;
 use crate::server::database;
+use crate::version::{download_url, hello_line, Version, VERSION};
 use crate::server::games::blackjack::{BlackjackGame, BlackjackHand};
 use crate::server::games::crash::{Clock, CrashGame, CrashRound, RealClock};
 use crate::server::games::registry::GameRegistry;
@@ -15,6 +16,7 @@ use crate::server::games::traits::{GameError, GamePhase, GameState};
 #[derive(Debug, Default)]
 pub struct ConnectionState {
     user: Option<String>,
+    greeted: bool,
 }
 
 /// Settle reservations left behind by a previous process.
@@ -32,6 +34,11 @@ impl ConnectionState {
     pub fn user(&self) -> Option<&str> {
         self.user.as_deref()
     }
+
+    /// True once the client has completed the version handshake.
+    pub fn greeted(&self) -> bool {
+        self.greeted
+    }
 }
 
 pub struct ServerCore {
@@ -91,7 +98,14 @@ impl ServerCore {
 
     pub fn handle_message(&mut self, state: &mut ConnectionState, msg: &str) -> String {
         let parts: Vec<&str> = msg.splitn(5, ' ').collect();
+
+        // Nothing but the handshake is accepted on a fresh connection.
+        if parts[0] != "HELLO" && !state.greeted {
+            return "ERROR HELLO required".to_string();
+        }
+
         match parts[0] {
+            "HELLO" => self.handle_hello(state, &parts),
             "GAME_LIST" => {
                 let mut games = self.registry.list_games();
                 games.sort();
@@ -193,6 +207,27 @@ impl ServerCore {
         }
     }
 
+    fn handle_hello(&mut self, state: &mut ConnectionState, parts: &[&str]) -> String {
+        if parts.len() != 2 {
+            return "ERROR Invalid HELLO format. Usage: HELLO <version>".to_string();
+        }
+
+        let (Some(client), Some(server)) = (Version::parse(parts[1]), Version::parse(VERSION)) else {
+            return "ERROR Invalid version".to_string();
+        };
+
+        if !client.compatible_with(server) {
+            return format!(
+                "ERROR Version mismatch: client {}, server {VERSION}. Get {VERSION} at {}",
+                parts[1],
+                download_url()
+            );
+        }
+
+        state.greeted = true;
+        hello_line(VERSION, VERSION, &download_url())
+    }
+
     fn handle_register(&mut self, username: &str, credential: &str) -> String {
         if database::get_hashed_password(&self.conn, username).is_some() {
             return "ERROR User already exists".to_string();
-- 
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