feat: Add option to disable DNS lookups in toxcore.

[iphydf]

Allows clients to prevent leaking IP addresses through DNS lookups. This option, together with disabling Tox UDP, entirely prevents any UDP packets being sent by toxcore.

---

This change is 

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 72.22222% with 5 lines in your changes missing coverage. Please review.

Project coverage is 73.10%. Comparing base (fa20168) to head (df6d87e). Report is 5 commits behind head on master.

Files	Patch %	Lines
toxcore/network.c	55.55%	4 Missing :warning:
toxcore/DHT.c	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2694 +/- ## ========================================== + Coverage 73.03% 73.10% +0.07% ========================================== Files 149 149 Lines 30531 30537 +6 ========================================== + Hits 22298 22325 +27 + Misses 8233 8212 -21 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[emdee-is]

This should be labeled with api-break as changes it the fields in toxOptions.

[Green-Sky]

This should be labeled with api-break as changes it the fields in toxOptions.

maybe, direct usage of the options struct is deprecated.

[iphydf]

https://github.com/TokTok/c-toxcore/blob/master/toxcore/tox.h#L526-L527

The memory layout of this struct (size, alignment, and field order) is not part of the ABI.

[emdee-is]

https://github.com/TokTok/c-toxcore/blob/master/toxcore/tox.h#L526-L527

The memory layout of this struct (size, alignment, and field order) is not part of the ABI.

Adding getters and setters is a part of the ABI in semantic versionsing: https://github.com/TokTok/c-toxcore/issues/2702

[iphydf]

https://github.com/TokTok/c-toxcore/blob/master/toxcore/tox.h#L526-L527

The memory layout of this struct (size, alignment, and field order) is not part of the ABI.

Adding getters and setters is a part of the ABI in semantic versionsing: https://github.com/TokTok/c-toxcore/issues/2702

Can you quote and link to a spec of semantic versioning that confirms this?

[emdee-is]

Adding getters and setters is a part of the ABI in semantic versionsing: #2702

Can you quote and link to a spec of semantic versioning that confirms this?

I've QAed Python for 2 of the biggest companies in the world, and they have coding standards that specify this sort of thing (in one of them I wrote the first draft for Python), but I can't cite their internal documents. In brief:

• 1. MAJOR version when you make incompatible API changes,
• 2. MINOR version when you add functionality in a backwards compatible manner, and
• 3. PATCH version when you make backwards compatible bug fixes

Adding getters and setters is adding new funtionality, so must be in a new minor. I also know this is the case for the Python project from having submitted a module into the Python standard library: their developers all know the rules and follow them strictly.

You're "releasing" big aglomerations rarely (years) and features go in without notice or planning or discussion. I assume that this may be the reason the project has lost so many developers and GUIs.

[iphydf]

I understand now where the confusion is. Let me clarify: in toxcore, we've decided to use semver without patch, and shifted the version right by 1 position: 0.major.minor, and we have no patch level releases. This is documented in tox.h.

That is, until we release 1.0.0, at which point it'll be semver with patch.

[emdee-is]

You're right - I missed that comment.

[iphydf]

I approve the code changes, but why is the behavoir explained inverted. Why is dns_enabled explained by the not state?

Because it's enabled by default, and has been true forever, so I figured it would be clearer to existing client devs if we explain what happens if you disable it explicitly.

[sh3ll4rpw]

When this will be merged? I'm waiting for a long time