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Block possibility of using a stale reference in SafeQueue #913

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merged 2 commits into from
Dec 16, 2024
Merged

Block possibility of using a stale reference in SafeQueue #913

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2849558
Fixed a possible dangling stale reference usage when using 'front' in…
AssemblyJohn Dec 13, 2024
fc129c0
Updated based on advice
AssemblyJohn Dec 16, 2024
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12 changes: 3 additions & 9 deletions include/ocpp/common/safe_queue.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,22 +13,16 @@ namespace ocpp {
/// that can be waited upon. Will take up the waiting thread on each
/// operation of push/pop/clear
template <typename T> class SafeQueue {
using safe_queue_reference = typename std::queue<T>::reference;
using safe_queue_const_reference = typename std::queue<T>::const_reference;

public:
/// \return True if the queue is empty
inline bool empty() const {
std::lock_guard lock(mutex);
return queue.empty();
}

inline safe_queue_reference front() {
std::lock_guard lock(mutex);
return queue.front();
}

inline safe_queue_const_reference front() const {
/// \brief We return a copy here, since while might be accessing the
/// reference while another thread uses pop and makes the reference stale
inline T front() {
std::lock_guard lock(mutex);
return queue.front();
}
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8 changes: 3 additions & 5 deletions lib/ocpp/common/websocket/websocket_libwebsockets.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1515,13 +1515,11 @@ void WebsocketLibwebsockets::on_conn_writable() {

// Execute while we have messages that were polled
while (true) {
WebsocketMessage* message = nullptr;

// Break if we have en empty queue
if (message_queue.empty())
break;

message = message_queue.front().get();
auto message = message_queue.front();

if (message == nullptr) {
EVLOG_AND_THROW(std::runtime_error("Null message in queue, fatal error!"));
Expand All @@ -1548,7 +1546,7 @@ void WebsocketLibwebsockets::on_conn_writable() {
// Poll a single message
EVLOG_debug << "Client writable, sending message part!";

WebsocketMessage* message = message_queue.front().get();
auto message = message_queue.front();

if (message == nullptr) {
EVLOG_AND_THROW(std::runtime_error("Null message in queue, fatal error!"));
Expand All @@ -1559,7 +1557,7 @@ void WebsocketLibwebsockets::on_conn_writable() {
}

// Continue sending message part, for a single message only
bool sent = send_internal(local_data->get_conn(), message);
bool sent = send_internal(local_data->get_conn(), message.get());

// If we failed, attempt again later
if (!sent) {
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