Receives bytes on a socket and places them into scattered
    buffers.
    Format
      #include  <types.h>
      #include  <socket.h>
      int recvmsg  ( int s, struct msghdr msg, int flags ); (BSD
                   Version 4.4)
      int recvmsg  ( int s, struct omsghdr msg, int flags ); (BSD
                   Version 4.3)

1  –  Arguments

 s
    A socket descriptor created with the socket() function.
 msg
    A pointer to a msghdr structure for receiving the data.
 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 send(),
                       sendmsg(), and sendto()  functions to send
                       out-of-band data.
    MSG_PEEK           Allows you to peek at the data that is next in
                       line to be received without actually removing
                       it from the system's buffers.

2  –  Description

    You can use this function with any socket, whether or not it
    is in a connected state. It receives data sent by a call to
    sendmsg(), send(),  or sendto(). The message is scattered into
    several user buffers if such buffers are specified.
    To receive data, the socket does not need to be connected to
    another socket.
    When the ioveciovcnt array specifies more than one buffer, the
    input data is scattered into iovcnt buffers as specified by the
    members of the iovec array:
    iov0, iov1, ..., ioviovcnt
    When a message is received, it is split among the buffers by
    filling the first buffer in the list, then the second, and so on,
    until either all of the buffers are full or there is no more data
    to be placed in the buffers.
    You can use the select() function to determine when more data
    arrives.
    Related Functions
    See also read(), send(),  and socket().

3  –  Return Values

    x                  The number of bytes returned in the msg_iov
                       buffers.
    0                  Successful completion.
    -1                 Error; errno is set to indicate the error.

4  –  Errors

    EBADF              The socket descriptor is invalid.
    ECONNRESET         A connection was forcibly closed by a peer.
    EFAULT             The message argument is not in a readable or
                       writable part of user address space.
    EINTR              This function was interrupted by a signal
                       before any data was available.
    EINVAL             The MSG_OOB flag is set, and no out-of-band
                       data is available.
                       The value of the msg_iovlen member of the
                       msghdr structure is less than or equal to zero
                       or is greater than IOV_MAX.
    ENOBUFS            The system has insufficient resources to
                       complete the call.
    ENOMEM             The system did not have sufficient memory to
                       fulfill the request.
    ENOTCONN           A receive is attempted on a connection-
                       oriented socket that is not connected.
    ENOTSOCK           The socket descriptor is invalid.
    EOPNOTSUPP         The specified flags are not supported for this
                       socket type.
    EWOULDBLOCK        The socket is marked nonblocking, and no data
                       is ready to be received.