Subscribing to an already subscribed topic will result in crash

[shekharhimanshu]

Hello,

In one of my tests, subscribing to an already subscribed topic results in crash inside the SDK. Here is the test sequence:

1. connect
2. subscribe to a topic, TopicA
3. disconnect
4. connect
5. subscribe again to TopicA ------> CRASH!!

I found the code causing the crash to be below in Subscribe.cpp:

ResponseCode SubscribeActionAsync::PerformAction(std::shared_ptr<NetworkConnection> p_network_connection, std::shared_ptr<ActionData> p_action_data) {

....

// Read running in separate thread, Insert before sending request to avoid situations where response arrives early
            util::Vector<std::shared_ptr<Subscription>>::iterator itr = p_subscribe_packet->subscription_list_.begin();
            while (itr != p_subscribe_packet->subscription_list_.end()) {
                util::String topic_name = (*itr)->GetTopicName()->ToStdString();
                auto existing_itr = p_client_state_->subscription_map_.find(topic_name);
                if (p_client_state_->subscription_map_.end() != existing_itr) {
                    if (existing_itr->second->IsActive()) {
                        itr = p_subscribe_packet->subscription_list_.erase(itr);
                    }
                } else {
                    p_client_state_->subscription_map_.insert(std::make_pair(topic_name, (*itr)));
                }

                itr++;
            }
...

I think when subscribing to an already subscribed topic, the code is erasing an element from p_subscribe_packet->subscription_list_ vector here while iterating the same and advancing the iterator afterwards here which causes the crash.

I would be happy to submit a fix.

[vareddy-zz]

Hi @shekharhimanshu,
I'm able to reproduce it and I've added it into our backlog for the next release. If you have a fix, could you please submit a pull request? It would be good to compare all approaches to the issue.
Thanks a lot for your help!
Varun

[vareddy-zz]

Hi @shekharhimanshu,
This issue is fixed as a part of the subscription cleanup in v1.1.1.
Thanks!
Varun