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+.\" Copyright (c) 1998, David Greenman
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice unmodified, this list of conditions, and the following
+.\"    disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd November 5, 1998
+.Dt SENDFILE 2
+.Os
+.Sh NAME
+.Nm sendfile
+.Nd send a file to a socket
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/socket.h>
+.Fd #include <sys/uio.h>
+.Ft int
+.Fn sendfile "int fd" "int s" "off_t offset" "size_t nbytes" "struct sf_hdtr *hdtr" "off_t *sbytes" "int flags"
+.Sh DESCRIPTION
+.Fn Sendfile
+sends a regular file specified by descriptor
+.Fa fd
+out a stream socket specified by descriptor
+.Fa s .
+.Pp
+The
+.Fa offset
+argument specifies where to begin in the file. The
+.Fa nbytes
+argument specifies how many bytes of the file should be sent, with 0 having the special
+meaning of send until the end of file has been reached.
+.Pp
+An optional header and/or trailer can be sent before and after the file data by specifying
+a pointer to a struct sf_hdtr, which has the following structure:
+.Pp
+.Bd -literal -offset indent -compact
+struct sf_hdtr {
+	struct iovec *headers;	/* pointer to header iovecs */
+	int hdr_cnt;		/* number of header iovecs */
+	struct iovec *trailers;	/* pointer to trailer iovecs */
+	int trl_cnt;		/* number of trailer iovecs */
+};
+.Ed
+.Pp
+The
+.Fa headers
+and
+.Fa tailers
+pointers, if non-NULL, point to arrays of struct iovec structures. See the
+.Fn writev
+system call for information on the iovec structure. The number of iovecs in these
+arrays is specified by
+.Fa hdr_cnt
+and
+.Fa trl_cnt .
+.Pp
+If non-NULL, the system will write the total number of bytes sent on the socket to the
+variable pointed to by
+.Fa sbytes .
+.Pp
+The
+.Fa flags
+argument is currently undefined and should be specified as 0.
+.Pp
+When using a socket marked for non-blocking I/O,
+.Fn sendfile
+may send fewer bytes than requested. In this case, the number of bytes successfully
+written is returned in
+.Fa *sbytes
+(if specified),
+and the error
+.Er EAGAIN
+is returned.
+.Sh IMPLEMENTATION NOTES
+.Pp
+The FreeBSD implementation of
+.Fn sendfile
+is "zero-copy", meaning that it has been optimized so that copying of the file data is avoided.
+.Sh RETURN VALUES
+Upon successful completion,
+.Fn sendfile
+returns 0. Otherwise a -1 is returned and the global variable
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+.Bl -tag -width Er
+.It Bq Er EBADF
+.Fa fd
+is not a valid file descriptor.
+.It Bq Er EBADF
+.Fa s
+is not a valid socket descriptor.
+.It Bq Er ENOTSOCK
+.Fa s
+is not a socket.
+.It Bq Er EINVAL
+.Fa fd
+is not a regular file.
+.It Bq Er EINVAL
+.Fa s
+is not a SOCK_STREAM type socket.
+.It Bq Er EINVAL
+.Fa offset
+is negative or out of range.
+.It Bq Er ENOTCONN
+.Fa s
+points to an unconnected socket.
+.It Bq Er EPIPE
+The socket peer has closed the connection.
+.It Bq Er EIO
+An error occurred while reading from
+.Fa fd .
+.It Bq Er EFAULT
+An invalid address was specified for a parameter.
+.It Bq Er EAGAIN
+The socket is marked for non-blocking I/O and not all data was sent due to the socket buffer being filled.
+If specified, the number of bytes successfully sent will be returned in
+.Fa *sbytes .
+.El
+.Sh SEE ALSO
+.Xr open 2 ,
+.Xr send 2 ,
+.Xr socket 2 ,
+.Xr writev 2
+.Sh HISTORY
+.Fn sendfile
+first appeared in
+.Fx 3.0 .
+This manual page first appeared in
+.Fx 3.1 .
+.Sh AUTHORS
+.Fn sendfile
+and this manual page were written by
+.An David Greenman Aq dg@root.com .