I began writing a book for them in 2010 and quit when the goalposts kept being moved and had a different point of contact every week. Absolutely terrible experience.
Similar experience. In my case, they wanted a video course on a library that wasn't finalized or published, and was still in an obvious beta with frequent breaking changes. On top of that, I was in a 12hr timezone difference, and only wanted to communicate with me regularly at 11/12 at night on week days, which didn't work well. Oh, and they only wanted to use skype, an app I never use normally. I was promised promo codes and release on multiple websites, and I got a single weekend promo code, and only published on two websites. And the icing on the cake is now 100% of the people I worked with don't work at Packt any more, so I don't even have a person I can contact any more to work on promotions or updates.
If you want a cross platform network programming guide in C, Lewis Van Winkle has written an excellent reference book[1].
[1]https://www.amazon.com/Hands-Network-Programming-programming...