nanocoap/cache: Extend with option-only cache keygen

[bergzand]

Contribution description

This adds a pair of functions to the nanocoap_cache module to generate cache keys only based on the options in a request. These can be used to correlate individual requests of a blockwise tranfer with each other. For example in a larger coreconf request.

It would still be up to the user to match the peers and the coap method code in the requests involved.

Testing procedure

I've extended the unittest for the nanocoap_cache module

Issues/PRs references

Could be useful for CORECONF and such.

[bergzand]

Before I forget to mention it, this also modifies the digest a bit to include the option number in the digest.

[riot-ci]

Murdock results

✔️ PASSED

2c9bf3f unittests: Extend nanocoap_cache with option-only

Success	Failures	Total	Runtime
10011	0	10011	15m:00s

Artifacts

• Documentation preview

[benpicco]

I suppose you have a use for those functions.

[benpicco]

Suggested change

	void nanocoap_cache_key_options_generate(const coap_pkt_t *req, uint8_t *cache_key);
	void nanocoap_cache_key_options_generate(const coap_pkt_t *req, void *cache_key);

[benpicco]

Suggested change

	void nanocoap_cache_key_blockreq_options_generate(const coap_pkt_t *req, uint8_t *cache_key);
	void nanocoap_cache_key_blockreq_options_generate(const coap_pkt_t *req, void *cache_key);

[bergzand]

I suppose you have a use for those functions.

They're useful for correlating individual requests of a full CoAP blockwise transfer. Such as detecting that a client decided to restart the transfer.

[bergzand]

They're useful for correlating individual requests of a full CoAP blockwise transfer. Such as detecting that a client decided to restart the transfer.

Just to clarify (as I would otherwise just be repeating what is already in the docs and the commit message, this is supposed to be used in blockwise handlers such as the post handler in the gcoap_block_server example to detect different parallel access to the resource and prevent the whole slew of issues that could happen