Function sock_recv_guts

* This is the guts of the recv() and recv_into() methods, which reads into a * char buffer. If you have any inc/dec ref to do to the objects that contain * the buffer, do it in the caller. This function returns the number of bytes * successfully read. If there was an error, it returns -1. Note that it is * also possible that we return a number of bytes smaller than the request * bytes. *