From 9c50777d53cacb96b211d1afb54f801a88dc07f5 Mon Sep 17 00:00:00 2001
From: Jomar Milan <jomarm@jomarm.com>
Date: Sun, 21 Jun 2026 22:07:14 -0700
Subject: Privatize access to internal session map

This way, RwLockReadGuard isn't being juggled anywhere, and the bounds of the session MutexGuard is limited to the FnOnce explicitly passed to with_session (less room for accidents, nice!)

This approach was inspired by the source code of RegionMap of Bamboo (https://gitlab.com/macmv/bamboo ref 8e32b54a5e7a69986339fea465d4afcc20425dd7), which uses a similar RwLock<HashMap<_, Mutex<_>>>. I like this approach because it allows me to provide access to the Session without having to clone it and allows the MutexGuard and RwLockReadGuard to be held as the user needs without allowing the user to access the RwLockReadGuard and poke around the rest of the entries in the HashMap.
---
 src/play.rs | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

(limited to 'src/play.rs')

diff --git a/src/play.rs b/src/play.rs
index 998ac29..0ec9758 100644
--- a/src/play.rs
+++ b/src/play.rs
@@ -144,16 +144,7 @@ async fn handle_play_message(
 ) -> Result<(), Error> {
     match message {
         IncomingPlayMessage::Initialize { id } => {
-            let (colors, update_rx) = {
-                let sessions = app_state.sessions.read().unwrap();
-                let session = sessions.get(&id).map(|session| session.lock().unwrap());
-                // The Option is unwrapped with let else here instead of ok_or and propagating
-                // because the error moves id which would be used later, and the compiler does not
-                // reason about propagation returning early.
-                let Some(session) = session else {
-                    return Err(Error::InvalidSession(id));
-                };
-
+            let data_opt = app_state.with_session(id.as_str(), |session| {
                 let colors: Vec<String> = session
                     .seats
                     .iter()
@@ -165,6 +156,11 @@ async fn handle_play_message(
                 let update_rx = session.update_tx.subscribe();
 
                 (colors, update_rx)
+            });
+            // let else used instead of propagating Option::ok_or_else because compiler wouldn't
+            // know about early return when moving id
+            let Some((colors, update_rx)) = data_opt else {
+                return Err(Error::InvalidSession(id));
             };
 
             let update_cancel_rx = {
@@ -194,16 +190,15 @@ async fn handle_play_message(
                 let mut state = state.lock().unwrap();
                 state.color =
                     PlayerColor::try_from(color.as_str()).map_err(|_| Error::InvalidColor)?;
+
                 let name = state
                     .session
                     .as_ref()
                     .ok_or_else(|| Error::InvalidSession(String::default()))?;
-                let sessions = app_state.sessions.read().unwrap();
-                let session = sessions
-                    .get(name)
-                    .ok_or(Error::InvalidSession(name.clone()))?;
 
-                session.lock().unwrap().seats[&state.color].clone()
+                app_state
+                    .with_session(name.as_str(), |session| session.seats[&state.color].clone())
+                    .ok_or_else(|| Error::InvalidSession(name.clone()))?
             };
 
             sender_tx
-- 
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