sendfile() - send the contents of a file through a socket
sbsize_t sendfile(int s, int fd, off_t offset, bsize_t nbytes,
const struct iovec *hdtrl, int flags);
The sendfile() 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. sendfile() 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
nbytes is the number of bytes to be sent from the file. If this
parameter is set to zero, data from the offset to the end of the file
will be sent.
hdtrl points to a two entry iovec structure. See write(2) for a
description of the iovec 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
SF_DISCONNECT Disallow further sends and receives.
If no buffer space is available to hold the data to be transmitted,
sendfile() blocks unless nonblocking mode is enabled. See send(2) for
a description 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 sbsize_t and bsize_t are similar to ssize_t and
size_t except they are defined as 64-bit values when compiled with the
_FILE_OFFSET_BITS=64 compile flag. See sendfile64(2).
Upon successful completion, sendfile() returns the number of bytes
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sent. This includes the header, trailer, and the file contents.
Otherwise, -1 is returned and errno is set to indicate the error.
If sendfile() fails, errno 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
[EFAULT] An invalid pointer was specified in the hdtrl
parameter or the iovec structure.
[ENOBUFS] No buffer space is available in the system to
perform the operation.
[EINTR] The operation was interrupted by a signal before
any data was sent. (If some data was sent,
sendfile() 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 iovec
structure is invalid.
[ENOTCONN] A sendfile() on a socket that is not connected, or
a sendfile() on a socket that has not completed
the connect sequence with its peer, or is no
longer connected to its peer.
[EPIPE] With SIGPIPE 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 SIGPIPE, unless the process has
established a signal handler for this signal, is
to terminate the process.
[EAGAIN] Nonblocking I/O is enabled using the O_NONBLOCK
flag with fcntl(), and the requested operation
[EWOULDBLOCK] The socket is marked non-blocking and the
requested operation would block.
[ENOMEM] No memory is available in the system to perform
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[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
having been compiled with the _FILE_OFFSET_SIZE=64
and _LARGEFILE_SOURCE/_LARGEFILE64_SOURCE compile
flags. This operation is not allowed because the
return value, offset, and nbytes are not 64-bit
values and may overflow.
connect(2), send(2), sendfile64(2), socket(2), tcp(7P), write(2),
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