.TH io_sendfile 3
.SH NAME
io_sendfile \- send data from a file to a socket
.SH SYNTAX
.B #include <io.h>

int64 \fBio_sendfile\fP(int64 sock,int64 fd,uint64 off,uint64 n);
.SH DESCRIPTION
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.
.SH "SEE ALSO"
io_wait(3), io_waituntil(3)