This is not &quot;Written in pure C, without any external library&quot; : just see skod.h it depends on socket.h<p><a href="https:&#x2F;&#x2F;github.com&#x2F;Hypsurus&#x2F;skod&#x2F;blob&#x2F;master&#x2F;src&#x2F;skod.h" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;Hypsurus&#x2F;skod&#x2F;blob&#x2F;master&#x2F;src&#x2F;skod.h</a>