It has a lot of overlaps with other network frameworks such as OkHttp, AFNetworking, cronet, etc., but I think it main contributions are these two components:

Xlog: in memory mmap log for fast logging and also supports encryption. Xlog log enables them to log everything fast and "safely" even in production build to quickly identify bugs.

STN: short and long TCP connection manager, which is optimized for various networks in China.

Plus other network utilities to make development easier.

Out of curiosity, is XLog better than the app simply logging everything to STD out, then let the invoker worry about the storage?

Depends on what the invokers wants. If the invoker only wants to log things to disk and read those logs later, surely he can do it himself. What XLog provides for the invoker under the hood is essentially performance: the invoker can log lots of things and does not need to worry about IO speed, disk space, and log safety. And of course it's cross platform. A detailed performance analysis is here (in Mandarin Chinese): http://mp.weixin.qq.com/s/cnhuEodJGIbdodh0IxNeXQ

an AFNetworking/OkHttp alternative written in C++ and use socket instead of HTTP

So id could be used to avoid proxy capturing your requests?

i think it's more about performance. Wechat ha HUGE amount of users in China, an low level socket connection would get better performance than a standard HTTP request