bbapi transfers save pointer to tdef, which can lead to a crash on resume

[adammoody]

During AXL_Create, we are saving a pointer to a transfer definition in the kvtree, which is then saved to the state file.

AXL/src/axl_async_bbapi.c

Line 276 in a799cd9

kvtree_util_set_ptr(file_list, AXL_BBAPI_KEY_TRANSFERDEF, tdef);

On resume, this pointer is extracted here, which can lead to a crash on StartTransfer:

AXL/src/axl_async_bbapi.c

Line 362 in a799cd9

kvtree_util_get_ptr(file_list, AXL_BBAPI_KEY_TRANSFERDEF, (void**) &tdef);

We need to check any/all pointers that are saved in the kvtree to make sure those values aren't referenced after a resume.

[tonyhutter]

Thanks for catching this. It's definitely a bug, but not as bad as it may seem (and it only affects BBAPI). The two most common BBAPI cases will work fine and should not trigger the bug:

1. AXL_Add() + AXL_Dispatch() + app crashes + app restarts and transfer is still going + AXL_Resume() + AXL_Wait()
2. AXL_Add() + AXL_Dispatch() + app crashes + transfer completes in background + app restarts + AXL_Resume() + AXL_Wait()

That said, I can see this being an issue if you do:

AXL_Add() + app crashes + app restarts + AXL_Resume() + AXL_Wait().