SENDFILE(2) BSD System Calls Manual SENDFILE(2)NAMEsendfile — send a file to a socket
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>
int
sendfile(int fd, int s, off_t offset, size_t nbytes,
struct sf_hdtr *hdtr, off_t *sbytes, int flags);
DESCRIPTIONSendfile() 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. The nbytes
argument specifies how many bytes of the file should be sent, with 0 hav‐
ing the special meaning of send until the end of file has been reached.
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.
If non-NULL, the system will write the total number of bytes sent on the
socket to the variable pointed to by sbytes.
The flags argument is currently undefined and should be specified as 0.
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 written is returned in *sbytes (if specified), and the error EAGAIN
is returned.
IMPLEMENTATION NOTES
The DragonFly implementation of sendfile() is "zero-copy", meaning that
it has been optimized so that copying of the file data is avoided.
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.
ERRORS
[EBADF] fd is not a valid file descriptor.
[EBADF] s is not a valid socket descriptor.
[ENOTSOCK] s is not a socket.
[EINVAL] fd is not a regular file.
[EINVAL] s is not a SOCK_STREAM type socket.
[EINVAL] offset is negative or out of range.
[ENOTCONN] s points to an unconnected socket.
[EPIPE] The socket peer has closed the connection.
[EIO] An error occurred while reading from fd.
[EFAULT] An invalid address was specified for a parameter.
[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 *sbytes.
SEE ALSOopen(2), send(2), socket(2), writev(2)HISTORYsendfile() first appeared in FreeBSD 3.0. This manual page first
appeared in FreeBSD 3.1.
AUTHORSsendfile() and this manual page were written by David Greenman
⟨dg@root.com⟩.
BSD November 5, 1998 BSD
