path: root/usr/src/man/man3ext/sendfile.3ext

'\" te
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.TH SENDFILE 3EXT "Nov 3, 2017"
.SH NAME
sendfile \- send files over sockets or copy files to files
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR\&.\|.\|. ] \fIfile\fR\&.\|.\|. \fB-lsendfile\fR [ \fIlibrary\fR\&.\|.\|. ]
#include <sys/sendfile.h>

\fBssize_t\fR \fBsendfile\fR(\fBint\fR \fIout_fd\fR, \fBint\fR \fIin_fd\fR, \fBoff_t *\fR\fIoff\fR, \fBsize_t\fR \fIlen\fR);
.fi

.SH DESCRIPTION
.LP
The \fBsendfile()\fR function copies data from \fIin_fd\fR to \fIout_fd\fR
starting at offset \fIoff\fR and of length \fIlen\fR bytes. The \fIin_fd\fR
argument should be a file descriptor to a regular file opened for reading. See
\fBopen\fR(2). The \fIout_fd\fR argument should be a file descriptor to a
regular file opened for writing or to a connected \fBAF_INET\fR or
\fBAF_INET6\fR socket of \fBSOCK_STREAM\fR type. See \fBsocket\fR(3SOCKET). The
\fIoff\fR argument is a pointer to a variable holding the input file pointer
position from which the data will be read. After \fBsendfile()\fR has
completed, the variable will be set to the offset of the byte following the
last byte that was read. The \fBsendfile()\fR function does not modify the
current file pointer of \fIin_fd\fR, but does modify the file pointer for
\fIout_fd\fR if it is a regular file.
.sp
.LP
The \fBsendfile()\fR function can also be used to send buffers by pointing
\fIin_fd\fR to \fBSFV_FD_SELF\fR.
.SH RETURN VALUES
.LP
Upon successful completion, \fBsendfile()\fR returns the total number of bytes
written to \fIout_fd\fR and also updates the offset to point to the byte that
follows the last byte read. Otherwise, it returns \fB-1\fR, and \fBerrno\fR is
set to indicate the error.
.SH ERRORS
.LP
The \fBsendfile()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEAFNOSUPPORT\fR\fR
.ad
.RS 16n
The implementation does not support the specified address family for socket.
.RE

.sp
.ne 2
.na
\fB\fBEAGAIN\fR\fR
.ad
.RS 16n
Mandatory file or record locking is set on either the file descriptor or output
file descriptor if it points at regular files. \fBO_NDELAY\fR or
\fBO_NONBLOCK\fR is  set, and there is a blocking record lock. An attempt has
been made to write to a stream that cannot accept data with the \fBO_NDELAY\fR
or the \fBO_NONBLOCK\fR flag set.
.RE

.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 16n
The \fIout_fd\fR or \fIin_fd\fR argument is either not a valid file descriptor,
\fIout_fd\fR is not opened for writing. or \fIin_fd\fR is not opened for
reading.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 16n
The offset cannot be represented by the \fBoff_t\fR structure, or the length is
negative when cast to \fBssize_t\fR.
.RE

.sp
.ne 2
.na
\fB\fBEIO\fR\fR
.ad
.RS 16n
An I/O error occurred while accessing the file system.
.RE

.sp
.ne 2
.na
\fB\fBENOTCONN\fR\fR
.ad
.RS 16n
The socket is not connected.
.RE

.sp
.ne 2
.na
\fB\fBEOPNOTSUPP\fR\fR
.ad
.RS 16n
The socket type is not supported.
.RE

.sp
.ne 2
.na
\fB\fBEPIPE\fR\fR
.ad
.RS 16n
The \fIout_fd\fR argument is no longer connected to the peer endpoint.
The \fBSIGPIPE\fR signal is generated to the calling thread.
The process dies unless special provisions were taken to catch or ignore
the signal.
.RE

.sp
.ne 2
.na
\fB\fBEINTR\fR\fR
.ad
.RS 16n
A signal was caught during the write operation and no data was transferred.
.RE

.SH USAGE
.LP
The \fBsendfile()\fR function has a transitional interface for 64-bit file
offsets. See \fBlf64\fR(5).
.SH EXAMPLES
.LP
\fBExample 1 \fRSending a Buffer Over a Socket
.sp
.LP
The following example demonstrates how to send the buffer \fIbuf\fR over a
socket. At the end, it prints the number of bytes transferred over the socket
from the buffer. It assumes that \fIaddr\fR will be filled up appropriately,
depending upon where to send the buffer.

.sp
.in +2
.nf
int tfd;
off_t baddr;
struct sockaddr_in sin;
char buf[64 * 1024];
in_addr_t addr;
size_t len;

tfd = socket(AF_INET, SOCK_STREAM, 0);
if (tfd == -1) {
    perror("socket");
    exit(1);
}

sin.sin_family = AF_INET;
sin.sin_addr.s_addr = addr;    /* Fill in the  appropriate address. */
sin.sin_port = htons(2345);
if (connect(tfd, (struct sockaddr *)&sin, sizeof(sin))<0) {
    perror("connect");
    exit(1);
}

baddr = (off_t)buf;
len = sizeof(buf);
while (len > 0) {
    ssize_t res;
    res = sendfile(tfd, SFV_FD_SELF, &baddr, len);
    if (res == -1)
            if (errno != EINTR) {
                    perror("sendfile");
                    exit(1);
            } else continue;
    len -= res;
}
.fi
.in -2

.LP
\fBExample 2 \fRTransferring Files to Sockets
.sp
.LP
The following program demonstrates a transfer of files to sockets:

.sp
.in +2
.nf
int ffd, tfd;
off_t off;
struct sockaddr_in sin;
in_addr_t  addr;
int len;
struct stat stat_buf;
ssize_t len;

ffd = open("file", O_RDONLY);
if (ffd == -1) {
    perror("open");
    exit(1);
}

tfd = socket(AF_INET, SOCK_STREAM, 0);
if (tfd == -1) {
    perror("socket");
    exit(1);
}

sin.sin_family = AF_INET;
sin.sin_addr = addr;    /* Fill in the  appropriate address. */
sin.sin_port = htons(2345);
if (connect(tfd, (struct sockaddr *) &sin, sizeof(sin)) <0) {
    perror("connect");
    exit(1);
}

if (fstat(ffd, &stat_buf) == -1) {
    perror("fstat");
    exit(1);
}

len = stat_buf.st_size;
while (len > 0) {
    ssize_t res;
    res = sendfile(tfd, ffd, &off, len);
    if (res == -1)
            if (errno != EINTR) {
                    perror("sendfile");
                    exit(1);
            } else continue;
    len -= res;
}
.fi
.in -2

.SH ATTRIBUTES
.LP
See \fBattributes\fR(5)  for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Evolving
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.LP
\fBopen\fR(2), \fBlibsendfile\fR(3LIB), \fBsendfilev\fR(3EXT),
\fBsocket\fR(3SOCKET), \fBattributes\fR(5), \fBlf64\fR(5)