OkHttp - HTTP & HTTP/2 client for Android and Java applications.
Using OkHttp is easy. Its request/response API is designed with fluent builders and immutability. It supports both synchronous blocking calls and async calls with callbacks.
ProGuard rules for OkHttp
Classes that aren't used at all will be removed by ProGuard shrinking phase. When obfuscating, ProGuard writes out class files named 'a.class', 'b.class', etc. You have to set up a ProGuard configuration.
-dontwarn okio.** -dontwarn javax.annotation.Nullable -dontwarn javax.annotation.ParametersAreNonnullByDefault
For more information about OkHttp please see the website.