s
    A socket descriptor created as the result of a call to accept()
    or connect().
 buf
    A pointer to a user-provided buffer into which received data will
    be placed.
 len
    The size of the buffer pointed to by buf.
 flags
    A bit mask that can contain one or more of the following
    flags. The mask is built by using a logical OR operation on the
    appropriate values.
    Flag                 Description
    MSG_OOB              Allows you to receive out-of-band data.
                         If out-of-band data is available, it is read
                         first. If no out-of-band data is available,
                         the MSG_OOB flag is ignored.
                         Use the send(), sendmsg(),  and sendto()
                         functions to send out-of-band data.
    MSG_PEEK             Allows you to examine data in the receive
                         buffer without removing it from the system's
                         buffers.