native: add option to turn RIOT into a Linux CLI tool

[benpicco]

Contribution description

To better integrate RIOT into some automated tests, it can be useful to run commands in a one-shot fashion.
This allows to use RIOT shell commands like Linux applications and integrate them into other tooling so e.g. Linux servers that interact with RIOT can be tested using a fixed RIOT binary.

Testing procedure

First create a TAP bridge with an (optional) uplink:

sudo dist/tools/tapsetup/tapsetup -u enxf4a80d90ba50

We can ping a host from RIOT

bin/native/nanocoap_tool.elf tap0 ping riot-os.org
12 bytes from 2a01:4f9:1a:9508::1: icmp_seq=0 ttl=57 time=58.149 ms
12 bytes from 2a01:4f9:1a:9508::1: icmp_seq=1 ttl=57 time=58.647 ms
12 bytes from 2a01:4f9:1a:9508::1: icmp_seq=2 ttl=57 time=58.381 ms

--- riot-os.org PING statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 58.149/58.392/58.647 ms

We can also access CoAP servers

bin/native/nanocoap_tool.elf tap0 ncget coap://coap.me/
/test
/validate
/hello
/blåbærsyltetøy
/sink
/separate
/large
/secret
/broken
/weird33
/weird44
/weird55
/weird333
/weird3333
/weird33333
/123412341234123412341234
/location-query
/create1
/large-update
/large-create
/query
/seg1
/path
/location1
/multi-format
/3
/4
/5

Issues/PRs references

[riot-ci]

Murdock results

✔️ PASSED

51a6a84 examples/nanocoap_tool: add RIOT as a CLI tool

Success	Failures	Total	Runtime
10109	0	10109	14m:42s

Artifacts

• Documentation preview

[Teufelchen1]

Cool idea! How about making it behave like busybox? ./ncget == ./nanocoap_tool.elf ncget?

I dislike that there is a new example that does not really have value as it - add the very least add a README! I am also surprised it is nanocoap specific? While coap is a good example use case, the example itself is more "riot as cli tool" and should be presented as such.

[benpicco]

I agree that the example needs to be more fleshed out, this is a bit specific to the 'send arbitrary CoAP payloads as a RIOT node would' use case, but not sure what else I should include.