io_sendfile - send data from a file to a socket

       io_sendfile sends data from a file to a socket.  This function tries to do this in a way that allows high
       quality operating systems to do zero-copy TCP (serving the data without copying the file contents to user
       space  or  inside  kernel  space).  This function will use special operating system "sendfile" primitives
       where available and use memory mapped I/O otherwise.  It should always be faster than  using  read()  and
       write() to copy the data yourself.

       io_sendfile will return the number of bytes sent.  If an error occurred, it will return -1 for EAGAIN, or
       -3 otherwise.

       io_sendfile - send data from a file to a socket

io_wait(3), io_waituntil(3)

                                                                                                  io_sendfile(3)

#include<libowfat/io.h>

       int64 io_sendfile(int64 sock,int64 fd,uint64 off,uint64 n);