Receives bytes from a connected socket and places them into a
    user-provided buffer.
    The $QIO equivalent is the IO$_READVBLK function.
    Format
      #include  <types.h>
      #include  <socket.h>
      int recv  ( int s, char *buf, int len, int flags );
                (_DECC_V4_SOURCE)
      size_t recv  ( int s, void *buf, ssize_t len, int flags );
                   (not_DECC_V4_SOURCE)

1  –  Arguments

 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.

2  –  Description

    This function receives data from a connected socket. To receive
    data on an unconnected socket, use the recvfrom() or recvmsg()
    functions. The received data is placed in the buffer buf.
    Data is sent by the socket's peer using the send, sendmsg(),
    sendto(), or write()  functions.
    Use the select() function to determine when more data arrives.
    If no data is available at the socket, the recv() call waits for
    data to arrive, unless the socket is nonblocking. If the socket
    is nonblocking, a -1 is returned with the external variable errno
    set to EWOULDBLOCK.
    Related Functions
    See also read(), send(),  sendmsg(), sendto(), and socket().

3  –  Return Values

    x                  The number of bytes received and placed in
                       buf.
    0                  Peer has closed its send side of the
                       connection.
    -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 data was specified to be received into a
                       nonexistent or protected part of the process
                       address space.
    EINTR              A signal interrupted the recv() function
                       before any data was available.
    EINVAL             The MSG_OOB flag is set and no out-of-band
                       data is available.
    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 or protocol.
    EWOULDBLOCK        The socket is marked nonblocking, and no data
                       is waiting to be received.