From 90832a9610ec9e6ecb369013e6c75055c33dce55 Mon Sep 17 00:00:00 2001
From: Matej Kenda <matejken@gmail.com>
Date: Tue, 2 Dec 2025 13:20:59 +0100
Subject: [PATCH] enh(MongoDB): Add read-preference validation to replica set
 connection and pool.

---
 .../Poco/MongoDB/ReplicaSetConnection.h       |  6 ++++
 .../ReplicaSetPoolableConnectionFactory.h     |  6 ++--
 MongoDB/src/ReplicaSetConnection.cpp          | 36 +++++++++++++++++++
 3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/MongoDB/include/Poco/MongoDB/ReplicaSetConnection.h b/MongoDB/include/Poco/MongoDB/ReplicaSetConnection.h
index 3017e0e46..c6d08ba48 100644
--- a/MongoDB/include/Poco/MongoDB/ReplicaSetConnection.h
+++ b/MongoDB/include/Poco/MongoDB/ReplicaSetConnection.h
@@ -100,6 +100,12 @@ public:
 	[[nodiscard]] bool isConnected() const;
 		/// Returns true if currently connected to a server.
 
+	[[nodiscard]] bool matchesReadPreference() const;
+		/// Returns true if the currently connected server still matches the read preference.
+		/// Returns false if not connected or if the server no longer satisfies the read preference.
+		/// This is useful for connection pool validation to detect when a server role has changed
+		/// (e.g., primary became secondary).
+
 private:
 	void ensureConnection();
 		/// Ensures we have an active connection, creating one if needed.
diff --git a/MongoDB/include/Poco/MongoDB/ReplicaSetPoolableConnectionFactory.h b/MongoDB/include/Poco/MongoDB/ReplicaSetPoolableConnectionFactory.h
index 8d736538b..47ab3d8e0 100644
--- a/MongoDB/include/Poco/MongoDB/ReplicaSetPoolableConnectionFactory.h
+++ b/MongoDB/include/Poco/MongoDB/ReplicaSetPoolableConnectionFactory.h
@@ -62,8 +62,10 @@ public:
 
 	bool validateObject(MongoDB::ReplicaSetConnection::Ptr pObject)
 	{
-		// Check if the connection is still valid
-		return pObject->isConnected();
+		// Check if the connection is still valid and matches the read preference.
+		// This ensures that if a server changes role (e.g., primary becomes secondary),
+		// the cached connection is invalidated and a new one is created.
+		return pObject->isConnected() && pObject->matchesReadPreference();
 	}
 
 	void activateObject(MongoDB::ReplicaSetConnection::Ptr pObject)
diff --git a/MongoDB/src/ReplicaSetConnection.cpp b/MongoDB/src/ReplicaSetConnection.cpp
index 046e5c781..8b4c85dc6 100644
--- a/MongoDB/src/ReplicaSetConnection.cpp
+++ b/MongoDB/src/ReplicaSetConnection.cpp
@@ -116,6 +116,42 @@ bool ReplicaSetConnection::isConnected() const
 }
 
 
+bool ReplicaSetConnection::matchesReadPreference() const
+{
+	if (!isConnected())
+	{
+		return false;
+	}
+
+	// Get the current topology
+	TopologyDescription topology = _replicaSet.topology();
+
+	// Get the server description for the currently connected server
+	ServerDescription server = topology.getServer(_connection->address());
+
+	// Check if the server is Unknown or has an error
+	if (server.type() == ServerDescription::Unknown || server.hasError())
+	{
+		return false;
+	}
+
+	// Use ReadPreference::selectServers to check if our current server
+	// would be selected with the current read preference
+	std::vector<ServerDescription> eligibleServers = _readPreference.selectServers(topology);
+
+	// Check if our current server is in the list of eligible servers
+	for (const auto& eligible : eligibleServers)
+	{
+		if (eligible.address() == _connection->address())
+		{
+			return true;
+		}
+	}
+
+	return false;
+}
+
+
 void ReplicaSetConnection::ensureConnection()
 {
 	if (_connection.isNull())