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NAME

sendfile − send files over sockets or copy files to files

SYNOPSIS

cc [flag ...] file ... -lsendfile [library ...]
#include <sys/sendfile.h>

ssize_t sendfile(int out_fd, int in_fd, off_t *off, size_t len);

DESCRIPTION

The sendfile() function copies data from out_fd to in_fd starting at offset off and of length len bytes. The in_fd argument should be a file descriptor to a regular file opened for reading. See open(2). The out_fd argument should be a file descriptor to a regular file opened for writing or to a connected AF_INET or AF_INET6 socket of SOCK_STREAM type. See socket(3SOCKET). The off argument is a pointer to a variable holding the input file pointer position from which the data will be read. After sendfile() has completed, the variable will be set to the offset of the byte following the last byte that was read. The sendfile() function does not modify the current file pointer of in_fd, but does modify the file pointer for out_fd if it is a regular file.

The sendfile() function can also be used to send buffers by pointing in_fd to SFV_FD_SELF.

RETURN VALUES

Upon successful completion, sendfile() returns the total number of bytes written to out_fd and also updates the offset to point to the byte that follows the last byte read. Otherwise, it returns -1, and errno is set to indicate an error.

ERRORS

The sendfile() function will fail if:
EAFNOSUPPORT

The implementation does not support the specified address family for socket.

EAGAIN

Mandatory file or record locking is set on either the file descriptor or output file descriptor if it points at regular files. O_NDELAY or O_NONBLOCK 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 O_NDELAY or the O_NONBLOCK flag set.

EINVAL

The offset cannot be represented by the off_t structure, or the length is negative when cast to ssize_t.

ENOTCONN

The socket is not connected.

EOPNOTSUPP

The socket type is not supported.

USAGE

The sendfile() function has a transitional interface for 64-bit file offsets. See lf64(5).

EXAMPLES

Example 1: Sending a Buffer Over a Socket

The following example demonstrates how to send the buffer buf over a socket. At the end, it prints the number of bytes transferred over the socket from the buffer. It assumes that addr will be filled up appropriately, depending upon where to send the buffer.

int tfd;
off_t baddr;
struct  sockaddr_in sin;
char buf[64 * 1024];
in_addr_t addr;

    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);
    }

    baddr = (off_t)buf;
    len = sendfile(tfd, SFV_FD_SELF, &baddr, len);

    if  (len  ==  -1)  {
        perror("sendfile");
        exit(1);
    }


    printf("Transfered %d bytes from buffer to socket0 len);

Example 2: Transferring Files to Sockets

The following program demonstrates a transfer of files to sockets:

int ffd, tfd;
off_t off;
struct sockaddr_in sin;
in_addr_t  addr;
int len;
struct stat stat_buf;

    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 = sendfile(tfd, ffd, &off, stat_buf.st_size);


    if  (len  ==  -1)  {
        perror("sendfile");
        exit(1);
    }

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

FILES

/usr/lib/libsendfile.so.1

shared object file

SEE ALSO

open(2), socket(3SOCKET), attributes(5), lf64(5)