Comments (10)
Interesting issue. Glad that it has been raised. coap_free_context()
has been called which means that the coap_context_t
is now in an unstable state when any app call-backs are invoked.
One of the first things coap_free_context()
does is to free off all the resources - and when an 'observed' resource is freed off, the final observe notification is sent out. However, you will still get triggered by an event and so your close_session() will continue to get called.
In your case, the call to coap_resource_notify_observers()
should silently fail as the coap_context_t
is unstable.
See #1404 for a fix. Please confirm that this works as expected.
from libcoap.
It shuts down without an error now, yes. However, valgrind tells me:
==4947== Invalid read of size 1
==4947== at 0x48DFAFC: coap_resource_notify_observers (coap_resource.c:1195)
==4947== by 0x10DB3B: close_session (main.c:996)
==4947== by 0x10E0B3: coap_event_handler (main.c:1171)
==4947== by 0x48E2453: coap_free_endpoint (coap_session.c:1861)
==4947== by 0x48CEE37: coap_free_context_locked (coap_net.c:682)
==4947== by 0x48CEE37: coap_free_context_locked (coap_net.c:639)
==4947== Address 0x51db078 is 0 bytes inside a block of size 100 free'd
==4947== at 0x4867EAC: free (vg_replace_malloc.c:872)
==4947== by 0x48E0623: coap_delete_all_resources (coap_resource.c:591)
==4947== by 0x48CEDCF: coap_free_context_locked (coap_net.c:646)
==4947== by 0x48CEDCF: coap_free_context_locked (coap_net.c:639)
==4947== Block was alloc'd at
==4947== at 0x4864B70: malloc (vg_replace_malloc.c:381)
==4947== by 0x48DDC37: coap_resource_init (coap_resource.c:269)
from libcoap.
Ok, gets interesting. coap_delete_all_resources()
has been called, so any resource is no more. You are then calling coap_resource_notify_observers()
with a resource parameter pointing to a piece of de-allocated memory.
I am thinking of going in the direction of no call-back handlers are called after coap_free_context()
has been called. This does however mean that things like close_session()
will no longer be called at this point - and so some custom clean-up will not occur.
It is possible to close down server sessions before calling coap_free_context() which will then triggers the appropriate call-back handles. It is a bit messy but this does the trick. Normally server sessions are left in a pool so they can be re-used and can't just be freed off.
coap_session_set_type_client(session);
coap_session_release(session);
from libcoap.
Hm, could we just call coap_delete_all_resources() after coap_free_endpoint()?
from libcoap.
Possibly, not sure what the law of unintended consequences will also throw up!
Bottom line is any 'thing' that was associated with coap_context_t
after that 'thing' gets released is problematic.
I am going in the direction that after coap-free_context()
is called, no call-backs are invoked (which means just clearing out all the handler pointers early on in coap_free_context()
) as they inherently can be using unsafe information. I will have a play with this.
from libcoap.
Whenever coap_event_handler()
is called with COAP_EVENT_SERVER_SESSION_DEL
which invokes close_session()
in your case, the session is not associated with any observing resources. So, coap_resource_notify_observers()
makes no sense at this point and is not needed.
As a note, whenever an observe request is added to a session, the session reference count is bumped. When the observe is removed from the session, the session reference is decremented. COAP_EVENT_SERVER_SESSION_DEL can only occur when the reference count is 0. coap_free_context()
frees off all the resources (if resource is being observed, a final notify is sent out) which decrements any associated sessions.
So, coap_free_context()
should not disable any call-backs, enabling the call-backs to continue to do any custom cleanups.
from libcoap.
@anyc With the removal of the coap_resource_notify_observers()
call when handling the event COAP_EVENT_SERVER_SESSION_DEL
(as it will never do anything for the current session as the reference count is 0 - hence not observing any resource), are there any other application shutdown issues associated with COAP_EVENT_SERVER_SESSION_DEL
you are having with the latest develop branch, or can this Issue now be closed?
from libcoap.
Sorry, I am on vacation this week. I am not sure if I understand your reasoning but in my case, notify_observers() does not only notify the peer of the to-be-closed session but possibly also other peers so I cannot remove it from my event handler. To explain a little bit, a peer can acquire a mutex that protects multiple resources. The resources only accept new data if the mutex is locked by the same session and the mutex state is accessible over its own resource. If the session is closed, the lock is automatically released which shall be signaled to other sessions.
from libcoap.
Then I think the best thing to do is make all your app tracking resource pointers (the ones you are calling coap_resource_notify_observers()
with) to NULL just before you call coap_free_context()
.
Then, on (the coap_free_context()
) COAP_EVENT_SERVER_SESSION_DEL, there should not be any issues. However, coap_resource_notify_observers()
currently does not like a NULL resource pointer.
EDIT: coap_free_context()
frees off all the resources - if a resource is being observed, all subscribers will get notified.
from libcoap.
As this happens during shutdown of my server, I just check now if there is a shutdown in progress and only if not, I send notifications. The process shuts down cleanly now. Thank you!
from libcoap.
Related Issues (20)
- Request token is unexpectedly replaced with nonsense HOT 15
- Q-Block support detection fails in some cases HOT 5
- [Non-conformance] Handling CoAP Invalid Versions HOT 2
- No callback if DTLS connection with OpenSSL server and client fails due to PSK mismatch HOT 3
- Add coap_get_resource_from_uri_path() to man pages. HOT 2
- HTTP/S Support for Proxy URIs in CoAP to HTTP Proxy HOT 4
- [Non-conformance] Handling Unreapeatable Options HOT 1
- Incorrect header passed to response_handler after finishing Replay Window scenario. HOT 7
- Actively denying a new session HOT 4
- Failing to set mtu when WOLFSSL_DTLS_MTU is enabled HOT 1
- Build with wolfSSL not loading certificates on server side HOT 3
- Memory leak in LwIP function `coap_udp_recvs` HOT 1
- PDU use after free when sending an OSCORE message with OSCORE disabled at build time HOT 5
- coap-client binary PSK HOT 17
- [Question] Proxy-scheme and proxy-uri example with coap-client and coap-server applications HOT 6
- Make coap_print_wellknown customizable HOT 6
- Wrong
- Access Token option addition to libcoap HOT 1
- Clarification on cancelling a block-wise request in the middle of transaction at client's end HOT 4
Recommend Projects
-
React
A declarative, efficient, and flexible JavaScript library for building user interfaces.
-
Vue.js
🖖 Vue.js is a progressive, incrementally-adoptable JavaScript framework for building UI on the web.
-
Typescript
TypeScript is a superset of JavaScript that compiles to clean JavaScript output.
-
TensorFlow
An Open Source Machine Learning Framework for Everyone
-
Django
The Web framework for perfectionists with deadlines.
-
Laravel
A PHP framework for web artisans
-
D3
Bring data to life with SVG, Canvas and HTML. 📊📈🎉
-
Recommend Topics
-
javascript
JavaScript (JS) is a lightweight interpreted programming language with first-class functions.
-
web
Some thing interesting about web. New door for the world.
-
server
A server is a program made to process requests and deliver data to clients.
-
Machine learning
Machine learning is a way of modeling and interpreting data that allows a piece of software to respond intelligently.
-
Visualization
Some thing interesting about visualization, use data art
-
Game
Some thing interesting about game, make everyone happy.
Recommend Org
-
Facebook
We are working to build community through open source technology. NB: members must have two-factor auth.
-
Microsoft
Open source projects and samples from Microsoft.
-
Google
Google ❤️ Open Source for everyone.
-
Alibaba
Alibaba Open Source for everyone
-
D3
Data-Driven Documents codes.
-
Tencent
China tencent open source team.
from libcoap.