SENDFILE(2) BSD System Calls Manual SENDFILE(2)NAMEsendfile — send a file to a socket
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>
int
sendfile(int fd, int s, off_t offset, off_t *len, struct sf_hdtr *hdtr,
int flags);
DESCRIPTION
The sendfile() system call sends a regular file specified by descriptor
fd out a stream socket specified by descriptor s.
The offset argument specifies where to begin in the file. Should offset
fall beyond the end of file, the system will return success and report 0
bytes sent as described below.
The len argument is a value-result parameter, that specifies how many
bytes of the file should be sent and/or how many bytes have been sent.
Initially the value pointed to by the len argument specifies how many
bytes should be sent with 0 having the special meaning to send until the
end of file has been reached. On return the value pointed to by the len
argument indicates how many bytes have been sent, except when a header or
trailer is specified as shown below. The len pointer may not be NULL.
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:
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 */
};
The headers and trailers pointers, if non-NULL, point to arrays of struct
iovec structures. See the writev() system call for information on the
iovec structure. The number of iovecs in these arrays is specified by
hdr_cnt and trl_cnt.
When a header or trailer is specified, the value of len argument indi‐
cates the maximum number of bytes in the header and/or file to be sent.
It does not control the trailer; if a trailer exists, all of it will be
sent. If the value of len argument is 0, all of the header and/or file
will be sent before the entire trailer is sent. On return, the len argu‐
ment specifies the total number of bytes sent.
The flags parameter is reserved for future expansion and must be set to
0. Any other value will cause sendfile() to return EINVAL.
When using a socket marked for non-blocking I/O, sendfile() may send
fewer bytes than requested. In this case, the number of bytes success‐
fully sent is returned in the via the len parameters and the error EAGAIN
is returned.
When a signal causes sendfile() to return the error EINTR, the len argu‐
ment may return 0 without necessarily meaning the end of file has been
reached as the signal may have been caught before any data was sent.
IMPLEMENTATION NOTES
The Mac OS X implementation of sendfile() uses 64 bits types for size and
offset parameters so there is no need for a 64 bits version sendfile64()
as found on some other operating systems.
RETURN VALUES
The sendfile() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
The number of bytes sent is returned via the parameter len. A value of 0
means the end of the file specified by descriptor fd has been reached or
that the value passed in offset falls beyond the end of file.
ERRORS
[EAGAIN] The socket is marked for non-blocking I/O and not all
data was sent due to the socket buffer being full. If
specified, the number of bytes successfully sent will
be returned in *len.
[EBADF] The fd argument is not a valid file descriptor.
[ENOTSUP] The fd argument does not refer to a regular file.
[EBADF] The s argument is not a valid socket descriptor.
[ENOTSOCK] The s argument does not refer stream oriented socket.
[EFAULT] An invalid address was specified for an argument.
[EINTR] A signal interrupted sendfile() before it could be
completed. If specified, the number of bytes success‐
fully sent will be returned in *len.
[EINVAL] The offset argument is negative.
[EINVAL] The len argument is NULL.
[EINVAL] The flags argument is not set to 0.
[EIO] An error occurred while reading from fd.
[ENOTCONN] The s argument points to an unconnected socket.
[ENOTSOCK] The s argument is not a socket.
[EOPNOTSUPP] The file system for descriptor fd does not support
sendfile().
[EPIPE] The socket peer has closed the connection.
SEE ALSOopen(2), send(2), socket(2), writev(2)HISTORY
The sendfile() system call first appeared in Darwin 9.0 (Mac OS X version
10.5) .
AUTHORS
This manual page is based on the FreeBSD version written by David G.
Lawrence ⟨dg@dglawrence.com⟩
Mac OS X March 31, 2006 Mac OS X
