From baf3d0e63c0e6dd5dfaff212dd18ee52a9e1196e Mon Sep 17 00:00:00 2001
From: WarmUpTill <19472752+WarmUpTill@users.noreply.github.com>
Date: Fri, 29 May 2026 19:35:06 +0200
Subject: [PATCH] Fix race condition in Twitch event sub reconnection logic

---
 plugins/twitch/event-sub.cpp | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/plugins/twitch/event-sub.cpp b/plugins/twitch/event-sub.cpp
index a4a37f8c..e83f9f61 100644
--- a/plugins/twitch/event-sub.cpp
+++ b/plugins/twitch/event-sub.cpp
@@ -262,12 +262,21 @@ std::string EventSub::AddEventSubscription(std::shared_ptr<TwitchToken> token,
 		return "";
 	}
 
+	// Capture the session ID and release the lock before making the HTTP
+	// request. Holding the mutex during a network call would block
+	// SubscriptionIsActive() on the condition-check thread for the entire
+	// duration of the request, causing visibly slow macro evaluations.
+	const std::string sessionID = eventSub->_sessionID;
+	lock.unlock();
+
 	OBSDataAutoRelease postData = copyData(subscription.data);
-	setTransportData(postData.Get(), eventSub->_sessionID);
+	setTransportData(postData.Get(), sessionID);
 	auto result = SendPostRequest(*token, registerSubscriptionURL.data(),
 				      registerSubscriptionPath.data(), {},
 				      postData.Get());
 
+	lock.lock();
+
 	if (result.status != 202) {
 		const char *error = obs_data_get_string(result.data, "error");
 		const char *message =
@@ -280,6 +289,24 @@ std::string EventSub::AddEventSubscription(std::shared_ptr<TwitchToken> token,
 		return "";
 	}
 
+	// Verify the session has not been replaced while the HTTP request was
+	// in flight (e.g. a reconnect occurred). If it was, the subscription
+	// we just created belongs to a dead session and must be discarded so
+	// the caller will retry with the new session ID.
+	if (eventSub->_sessionID != sessionID) {
+		blog(LOG_INFO,
+		     "discarding Twitch EventSub registration - session ID "
+		     "changed during HTTP request");
+		return "";
+	}
+
+	// Another thread may have registered the same subscription while the
+	// lock was released.
+	if (isAlreadySubscribed(eventSub->_activeSubscriptions, subscription)) {
+		eventSub->LogActiveSubscriptions();
+		return eventSub->_activeSubscriptions.find(subscription)->id;
+	}
+
 	OBSDataArrayAutoRelease replyArray =
 		obs_data_get_array(result.data, "data");
 	OBSDataAutoRelease replyData = obs_data_array_item(replyArray, 0);
@@ -439,9 +466,10 @@ void EventSub::OnMessage(connection_hdl, EventSubWSClient::message_ptr message)
 
 void EventSub::HandleWelcome(obs_data_t *data)
 {
+	std::lock_guard<std::mutex> lock(_subscriptionMtx);
 	OBSDataAutoRelease session = obs_data_get_obj(data, "session");
 	_sessionID = obs_data_get_string(session, "id");
-	ClearActiveSubscriptions();
+	_activeSubscriptions.clear();
 	blog(LOG_INFO, "Twitch EventSub connected");
 	vblog(LOG_INFO, "Twitch EventSub session id: %s", _sessionID.c_str());
 }