What's the recommended way of reusing one context for buffers of different size?

[v-chernyshev]

Good afternoon, I did a quick test of blosc V2 and saw that its compression ratio was much worse than what I used to get with V1. I've traced it to the btune_next_blocksize function:

c-blosc2/blosc/btune.c

Lines 53 to 56 in 50a7357

	if (user_blocksize) {
	blocksize = user_blocksize;
	goto last;
	}

Essentially what happens is that when context->blocksize is set to zero it is eventually initialised based on the very first buffer that is passed into blosc2_compress_ctx, in my case it was a very small array that caused the calculated blocksize to be set to 96. Subsequent calls to btune_next_blocksize then treat this 96 as a user-supplied block size, which leads to almost no compression of bigger buffers.

The only way I see to "fix" it while, at the same time, keeping automatic block size deduction, is to include context.h and reset blocksize to zero before calling blosc2_compress_ctx, but there is a comment in the header that says that the context is an opaque type. Is there a better way to do it? Thanks!