sendfile(2)sendfile(2)NAMEsendfile() - send the contents of a file through a socket
SYNOPSISDESCRIPTION
The system call transmits the contents of a file associated with the
file descriptor fd, plus an optional header and trailer buffers across
a socket connection specified by s. can be used only when the socket
is in a connected state.
offset specifies the offset within the file at which to start the file
data transfer.
nbytes is the number of bytes to be sent from the file. If this param‐
eter is set to zero, data from the offset to the end of the file will
be sent.
hdtrl points to a two entry structure. See write(2) for a description
of the structure. The first entry is for header information. If this
pointer is non-NULL, the contents of the buffer are sent before sending
any data from the file. The second entry is for trailer information.
If this pointer is non-NULL, the contents of the buffer will be sent
after the data from the file. If both pointers are NULL, or hdtrl is a
NULL pointer, only the specified range of the file will be transferred.
At the end of the call, the socket connection will be left completely
open for both reading and writing, unless the flags parameter is set
to:
Disallow further sends and receives.
Notes
If no buffer space is available to hold the data to be transmitted,
blocks unless nonblocking mode is enabled. See send(2) for a descrip‐
tion of the nonblocking mode behavior.
See sendfile64(2) for a description of how sendfile can be used with
large file (over 2GB) with 32-bit applications.
Note that the types and are similar to and except they are defined as
64-bit values when compiled with the compile flag. See sendfile64(2).
RETURN VALUE
Upon successful completion, returns the number of bytes sent. This
includes the header, trailer, and the file contents. Otherwise, is
returned and is set to indicate the error.
ERRORS
If fails, is set to one of the following values.
[EBADF] An invalid socket descriptor s, or file descriptor
fd is specified.
[ENOTSOCK] s is a valid file descriptor, but it is not a
socket.
[EFAULT] An invalid pointer was specified in the hdtrl
parameter or the structure.
[ENOBUFS] No buffer space is available in the system to per‐
form the operation.
[EINTR] The operation was interrupted by a signal before
any data was sent. (If some data was sent, returns
the number of bytes sent before the signal, and
[EINTR] is not set).
[EINVAL] The offset or flags parameter is invalid.
The hdtrl parameter, or a length in the structure
is invalid.
[ENOTCONN] A on a socket that is not connected, or a on a
socket that has not completed the connect sequence
with its peer, or is no longer connected to its
peer.
[EPIPE] With signal. An attempt was made to send on a
socket that was connected, but the connection has
been shut down either by the remote peer or by this
side of the connection. Note that the default
action for unless the process has established a
signal handler for this signal, is to terminate the
process.
[EAGAIN] Nonblocking I/O is enabled using the flag with and
the requested operation would block.
[EWOULDBLOCK] The socket is marked non-blocking and the requested
operation would block.
[ENOMEM] No memory is available in the system to perform the
operation.
[EOPNOTSUPP] The socket is not a TCP socket.
[EOVERFLOW] An application has opened a large file (see
open(2)) and is trying to use sendfile without hav‐
ing been compiled with the and compile flags. This
operation is not allowed because the return value,
offset, and nbytes are not 64-bit values and may
overflow.
SEE ALSOconnect(2), send(2), sendfile64(2), socket(2), tcp(7P), write(2), shut‐
down(2).
sendfile(2)
