241 lines
6.8 KiB
Groff
241 lines
6.8 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" From: @(#)send.2 8.2 (Berkeley) 2/21/94
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd February 15, 1995
|
|
.Dt SEND 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm send ,
|
|
.Nm sendto ,
|
|
.Nm sendmsg
|
|
.Nd send a message from a socket
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In sys/socket.h
|
|
.Ft ssize_t
|
|
.Fn send "int s" "const void *msg" "size_t len" "int flags"
|
|
.Ft ssize_t
|
|
.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen"
|
|
.Ft ssize_t
|
|
.Fn sendmsg "int s" "const struct msghdr *msg" "int flags"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn send
|
|
function,
|
|
and
|
|
.Fn sendto
|
|
and
|
|
.Fn sendmsg
|
|
system calls
|
|
are used to transmit a message to another socket.
|
|
The
|
|
.Fn send
|
|
function
|
|
may be used only when the socket is in a
|
|
.Em connected
|
|
state, while
|
|
.Fn sendto
|
|
and
|
|
.Fn sendmsg
|
|
may be used at any time.
|
|
.Pp
|
|
The address of the target is given by
|
|
.Fa to
|
|
with
|
|
.Fa tolen
|
|
specifying its size.
|
|
The length of the message is given by
|
|
.Fa len .
|
|
If the message is too long to pass atomically through the
|
|
underlying protocol, the error
|
|
.Er EMSGSIZE
|
|
is returned, and
|
|
the message is not transmitted.
|
|
.Pp
|
|
No indication of failure to deliver is implicit in a
|
|
.Fn send .
|
|
Locally detected errors are indicated by a return value of -1.
|
|
.Pp
|
|
If no messages space is available at the socket to hold
|
|
the message to be transmitted, then
|
|
.Fn send
|
|
normally blocks, unless the socket has been placed in
|
|
non-blocking I/O mode.
|
|
The
|
|
.Xr select 2
|
|
system call may be used to determine when it is possible to
|
|
send more data.
|
|
.Pp
|
|
The
|
|
.Fa flags
|
|
argument may include one or more of the following:
|
|
.Bd -literal
|
|
#define MSG_OOB 0x00001 /* process out-of-band data */
|
|
#define MSG_PEEK 0x00002 /* peek at incoming message */
|
|
#define MSG_DONTROUTE 0x00004 /* bypass routing, use direct interface */
|
|
#define MSG_EOR 0x00008 /* data completes record */
|
|
#define MSG_EOF 0x00100 /* data completes transaction */
|
|
#define MSG_NOSIGNAL 0x20000 /* do not generate SIGPIPE on EOF */
|
|
.Ed
|
|
.Pp
|
|
The flag
|
|
.Dv MSG_OOB
|
|
is used to send
|
|
.Dq out-of-band
|
|
data on sockets that support this notion (e.g.\&
|
|
.Dv SOCK_STREAM ) ;
|
|
the underlying protocol must also support
|
|
.Dq out-of-band
|
|
data.
|
|
.Dv MSG_EOR
|
|
is used to indicate a record mark for protocols which support the
|
|
concept.
|
|
.Dv MSG_EOF
|
|
requests that the sender side of a socket be shut down, and that an
|
|
appropriate indication be sent at the end of the specified data;
|
|
this flag is only implemented for
|
|
.Dv SOCK_STREAM
|
|
sockets in the
|
|
.Dv PF_INET
|
|
protocol family, and is used to implement Transaction
|
|
.Tn TCP
|
|
(see
|
|
.Xr ttcp 4 ) .
|
|
.Dv MSG_DONTROUTE
|
|
is usually used only by diagnostic or routing programs.
|
|
.Dv MSG_NOSIGNAL
|
|
is used to prevent
|
|
.Dv SIGPIPE
|
|
generation when writing a socket that
|
|
may be closed.
|
|
.Pp
|
|
See
|
|
.Xr recv 2
|
|
for a description of the
|
|
.Fa msghdr
|
|
structure.
|
|
.Sh RETURN VALUES
|
|
The call returns the number of characters sent, or -1
|
|
if an error occurred.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn send
|
|
function and
|
|
.Fn sendto
|
|
and
|
|
.Fn sendmsg
|
|
system calls
|
|
fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EBADF
|
|
An invalid descriptor was specified.
|
|
.It Bq Er EACCES
|
|
The destination address is a broadcast address, and
|
|
.Dv SO_BROADCAST
|
|
has not been set on the socket.
|
|
.It Bq Er ENOTSOCK
|
|
The argument
|
|
.Fa s
|
|
is not a socket.
|
|
.It Bq Er EFAULT
|
|
An invalid user space address was specified for an argument.
|
|
.It Bq Er EMSGSIZE
|
|
The socket requires that message be sent atomically,
|
|
and the size of the message to be sent made this impossible.
|
|
.It Bq Er EAGAIN
|
|
The socket is marked non-blocking and the requested operation
|
|
would block.
|
|
.It Bq Er ENOBUFS
|
|
The system was unable to allocate an internal buffer.
|
|
The operation may succeed when buffers become available.
|
|
.It Bq Er ENOBUFS
|
|
The output queue for a network interface was full.
|
|
This generally indicates that the interface has stopped sending,
|
|
but may be caused by transient congestion.
|
|
.It Bq Er EHOSTUNREACH
|
|
The remote host was unreachable.
|
|
.It Bq Er EISCONN
|
|
A destination address was specified and the socket is already connected.
|
|
.It Bq Er ECONNREFUSED
|
|
The socket received an ICMP destination unreachable message
|
|
from the last message sent.
|
|
This typically means that the
|
|
receiver is not listening on the remote port.
|
|
.It Bq Er EHOSTDOWN
|
|
The remote host was down.
|
|
.It Bq Er ENETDOWN
|
|
The remote network was down.
|
|
.It Bq Er EPERM
|
|
The process using a
|
|
.Dv SOCK_RAW
|
|
socket was jailed and the source
|
|
address specified in the IP header did not match the IP
|
|
address bound to the prison.
|
|
.It Bq Er EPIPE
|
|
The socket is unable to send anymore data
|
|
.Dv ( SBS_CANTSENDMORE
|
|
has been set on the socket).
|
|
This typically means that the socket
|
|
is not connected.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr fcntl 2 ,
|
|
.Xr getsockopt 2 ,
|
|
.Xr recv 2 ,
|
|
.Xr select 2 ,
|
|
.Xr socket 2 ,
|
|
.Xr write 2
|
|
.Sh HISTORY
|
|
The
|
|
.Fn send
|
|
function appeared in
|
|
.Bx 4.2 .
|
|
.Sh BUGS
|
|
Because
|
|
.Fn sendmsg
|
|
does not necessarily block until the data has been transferred, it
|
|
is possible to transfer an open file descriptor across an
|
|
.Dv AF_UNIX
|
|
domain socket
|
|
(see
|
|
.Xr recv 2 ) ,
|
|
then
|
|
.Fn close
|
|
it before it has actually been sent, the result being that the receiver
|
|
gets a closed file descriptor.
|
|
It is left to the application to
|
|
implement an acknowledgment mechanism to prevent this from happening.
|