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ReferenceswolfSSL - Embedded SSL Library → wolfMQTT → Shutdown required?
I am trying to track down a memory leak that occurs every time wolfSSL tries to reconnect after the socket connection with a sever was lost. I am not an expert, so I ask: Should MqttSocket_Disconnect() within mqtt_socket.c also contain a call to wolfSSL_shutdown()?
Hello @kackle123
Thanks for contacting wolfSSL Support. Calling wolfSSL_shutdown is not required, since the broker will disconnect the socket connection after the client sends the disconnect packet (MqttClient_Disconnect). The wolfSSL resources are freed using the code in MqttSocket_Disconnect:
https://github.com/wolfSSL/wolfMQTT/blo … ket.c#L465
Could there be an allocation in the application TLS setup callback? In the examples, we use mqtt_tls_cb
https://github.com/wolfSSL/wolfMQTT/blo … ple.c#L505
Thanks,
Eric @wolfSSL Support
Thank you, Eric, for your reply.
I think it's the server that is initiating the disconnect from my wolfMQTT client. Wouldn't that leave a wolfSSL socket hanging?
I did not explicitly use mqtt_tls_cb(), and after a code search, I don't see it being utilized by wolfSSL nor wolfMQTT.
The socket is closed (in the example code) by mqttexample.c::NetDisconnect, which is called from mqtt_socket.c::MqttSocket_Disconnect
https://github.com/wolfSSL/wolfMQTT/blo … ket.c#L480
There are not a lot of mallocs in the library proper, so it should be possible to use a memcheck tool to find the culprit. We sometimes use valgrind to hunt for mem leaks.
Since MqttSocket_Disconnect() is in wolfMQTT's library, wouldn't that still leave any wolfSSL socket resources allocated? Or does wolfMQTT tell wolfSSL to free its socket resources somehow? Since I can find no calls to wolfSSL_shutdown() anywhere in the wolfMQTT or wolfSSL libraries, what's the point of that function in the first place?
This is an embedded project, so I don't know how I would use Valgrind. wolfMQTT itself has only a couple of mallocs and my manual debugger tracing showed me they are handled correctly. But there are dozens within wolfSSL and it eats more memory upon every re-connection.
The socket handling is the responsibility of the application's implementation of the MqttNet structure. The example does this here:
https://github.com/wolfSSL/wolfMQTT/blo … et.c#L1048
The wolfSSL_shutdown API is used to send the FIN packet to a peer, indicating that the application will no longer listen to that socket. The wolfSSL_shutdown API is used by the client as part of a bi-directional shutdown, but otherwise is not needed at the client side. It does not clean up the socket resource.
There is built-in memory tracking in wolfSSL:
-DWOLFSSL_TRACK_MEMORYor
./configure --enable-trackmemoryAlso memory logging:
-DWOLFSSL_MEMORY_LOGor
--enable-memorylogRegarding the wolfSSL_shutdown(), I see.
About the memory flags, I am rather unfamiliar with using such flags in my embedded environment (an NXP K22 128 kB RAM, using their CodeWarrior IDE). Am I able to, or are these for full operating systems? And what do these do for me; I find no documentation.
I saw that there were memory leak fixes made in wolfSSL. I am going to try using this latest version.
wolfSSL - Embedded SSL Library → wolfMQTT → Shutdown required?
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