[riot-notifications] [RIOT-OS/RIOT] gcoap: don't call random_uint32_range() when COAP_ACK_VARIANCE=0 (#11784)

Martine Lenders notifications at github.com
Wed Jul 3 15:52:02 CEST 2019


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### Contribution description
`COAP_ACK_VARIANCE` is a configurable macro, so when it is 0, the [precondition for `random_uint32_range()`][1] is not held.

Background is that for some experimental setups you want to disable the randomness in retransmissions to have better comparibility, as we did e.g. for [this paper](https://conferences.sigcomm.org/acm-icn/2018/proceedings/icn18-final46.pdf).

[1]: https://doc.riot-os.org/group__sys__random.html#gab6ee09e1e56df3cc78acd1fbf97bfb24

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### Testing procedure
Compiling `examples/gcoap` with `COAP_ACK_VARIANCE=0` and the default value should still work. The randomness should be reduced with `COAP_ACK_VARIANCE` (but not completely turned of due to a race condition in `gcoap`, see [issue will follow]).
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### Issues/PRs references
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You can view, comment on, or merge this pull request online at:

  https://github.com/RIOT-OS/RIOT/pull/11784

-- Commit Summary --

  * gcoap: don't call random_uint32_range() when COAP_ACK_VARIANCE=0

-- File Changes --

    M sys/net/application_layer/gcoap/gcoap.c (4)

-- Patch Links --

https://github.com/RIOT-OS/RIOT/pull/11784.patch
https://github.com/RIOT-OS/RIOT/pull/11784.diff

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