nanocoap_link_format: add helper function to parse Link Format

[benpicco]

Contribution description

This moves the code to parse the link format from the ncget shell command to a common location and makes it more general.

A callback is called for each resource path in the directory.

Testing procedure

ncget still works as before for listing directories:

> ncget coap://[fe80::2454:cfff:fea7:4598]/
/fw/
/suit_manifest.signed
/suit_manifest
/payload.bin

> ncget coap://[fe80::2454:cfff:fea7:4598]/fw/
/fw/suit_update/

> ncget coap://[fe80::2454:cfff:fea7:4598]/fw/suit_update/
/fw/suit_update/same54-xpro/
/fw/suit_update/saml21-xpro/

Issues/PRs references

[maribu]

@fengelhardt may be interested in this

[maribu]

Hmm, from the text it more looks like this is an utility to obtain a CoAP Resource that is in the CoRE Link Format, rather than anything specific to Resource Directories. RDs do use the CoRE Link Format (due to the lack of decent CBOR based alternatives not yet being standardized), but it is also notably used by the default resource discovery.

Maybe it could be named better to indicate that it is useful for interaction with any server that provides a list of links in the CoRE Link Format?

Out of scope I guess, but it may be useful to also be able to add URI Query Options. E.g. querying coap://some.iot.device/.well-known/core?rt=oic.d.light would only list resources with a resource type of "oic.d.light", which (hopefully) matches smart light bulbs and similar. I guess if nanocoap_sock_url_connect() would be extended to just parse a query component from the URI given, this should just work, shouldn't it?

[benpicco]

Thank you, I was searching for what was the proper name for this.
I renamed the functions and the module accordingly.

[riot-ci]

Murdock results

✔️ PASSED

f06c763 sys/shell: ncget: make use of nanocoap_link_format_get()

Artifacts

• Documentation preview

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[maribu]

ACK. Code looks good to me. I'd say we wait the three days to hard feature freeze before merging this, but it never hurts to have an ACK :)

[benpicco]

bors merge

[kaspar030]

bors cancel
bors merge

[bors]

Canceled.

[bors]

Build succeeded:

• Murdock
• static-tests
• tools-build-success