Fix SEGV in blosc2_schunk_free()

[EmilDohne]

Apologies for only getting around to it now, this should address the recent regression in 2.15.0 :)

Context:

#635 I noticed while upgrading to c-blosc2 2.15.0 that calling blosc2_schunk_free() without blosc2_init() being called first caused a SEGV as it was trying to access uninitialized memory

Changes

• Added check to blosc2_get_io_cb() that returns NULL if the library was not initialized yet so we don't try to access a nullptr function in blosc2_schunk_free()
• Added test cases for "manual" compression and decompression using blosc2_compress_ctx and blosc2_decompress_ctx. This does not in parallel but does trigger a test failure before my changes.

Considerations

@FrancescAlted I noticed that blosc2_destroy() does not actually clean up the IO callbacks (note the order of tests, if it was reversed the tests would pass even without the fix). Is this intended?

[EmilDohne]

I think the error is because clang didnt like the missing return type which I missed. I've also gone ahead and address some of the unused variable warnings. Hopefully it passes CI now!

[FrancescAlted]

I think the error is because clang didnt like the missing return type which I missed. I've also gone ahead and address some of the unused variable warnings. Hopefully it passes CI now!

Yes, your fix did it, at least on my mac laptop. I am currently traveling, but I'll come back to you later.

Regarding blosc2_destroy() not cleaning up I/O calls is probably an oversight. Can you fix this too?

[EmilDohne]

Regarding blosc2_destroy() not cleaning up I/O calls is probably an oversight. Can you fix this too?

I'll have a deeper look into this and see if it needs to be cleaned up. Enjoy your travels!

[EmilDohne]

Looks like this was also the reason for the segfaults in the aarch tests :)

[EmilDohne]

Ok so I had a look into the cleanup stuff and at least from a memory standpoint there is no concerns. One could, if wanted, set these back to be default initialized but I wouldn't personally do that

// In blosc2_init()

BLOSC2_IO_CB_DEFAULTS.id = BLOSC2_IO_FILESYSTEM;
BLOSC2_IO_CB_DEFAULTS.name = "filesystem";
BLOSC2_IO_CB_DEFAULTS.is_allocation_necessary = true;
BLOSC2_IO_CB_DEFAULTS.open = (blosc2_open_cb) blosc2_stdio_open;
BLOSC2_IO_CB_DEFAULTS.close = (blosc2_close_cb) blosc2_stdio_close;
BLOSC2_IO_CB_DEFAULTS.size = (blosc2_size_cb) blosc2_stdio_size;
BLOSC2_IO_CB_DEFAULTS.write = (blosc2_write_cb) blosc2_stdio_write;
BLOSC2_IO_CB_DEFAULTS.read = (blosc2_read_cb) blosc2_stdio_read;
BLOSC2_IO_CB_DEFAULTS.truncate = (blosc2_truncate_cb) blosc2_stdio_truncate;
BLOSC2_IO_CB_DEFAULTS.destroy = (blosc2_destroy_cb) blosc2_stdio_destroy;

BLOSC2_IO_CB_MMAP.id = BLOSC2_IO_FILESYSTEM_MMAP;
BLOSC2_IO_CB_MMAP.name = "filesystem_mmap";
BLOSC2_IO_CB_MMAP.is_allocation_necessary = false;
BLOSC2_IO_CB_MMAP.open = (blosc2_open_cb) blosc2_stdio_mmap_open;
BLOSC2_IO_CB_MMAP.close = (blosc2_close_cb) blosc2_stdio_mmap_close;
BLOSC2_IO_CB_MMAP.read = (blosc2_read_cb) blosc2_stdio_mmap_read;
BLOSC2_IO_CB_MMAP.size = (blosc2_size_cb) blosc2_stdio_mmap_size;
BLOSC2_IO_CB_MMAP.write = (blosc2_write_cb) blosc2_stdio_mmap_write;
BLOSC2_IO_CB_MMAP.truncate = (blosc2_truncate_cb) blosc2_stdio_mmap_truncate;
BLOSC2_IO_CB_MMAP.destroy = (blosc2_destroy_cb) blosc2_stdio_mmap_destroy;

From my side there is nothing else to add so feel free to merge :)

[FrancescAlted]

LGTM. Thanks @EmilDohne !