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.\"	$NetBSD: send.2,v 1.6 1996/01/15 01:17:18 thorpej Exp $
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.\"     @(#)send.2	8.2 (Berkeley) 2/21/94
.\"
.Dd February 21, 1994
.Dt SEND 2
.Os BSD 4.2
.Sh NAME
.Nm send ,
.Nm sendmsg ,
.Nm sendto
.Nd send a message from a socket
.Sh SYNOPSIS
.Fd #include <sys/socket.h>
.Ft ssize_t
.Fo send
.Fa "int socket"
.Fa "const void *buffer"
.Fa "size_t length"
.Fa "int flags"
.Fc
.Ft ssize_t
.Fo sendmsg
.Fa "int socket"
.Fa "const struct msghdr *message"
.Fa "int flags"
.Fc
.Ft ssize_t
.Fo sendto
.Fa "int socket"
.Fa "const void *buffer"
.Fa "size_t length"
.Fa "int flags"
.Fa "const struct sockaddr *dest_addr"
.Fa "socklen_t dest_len"
.Fc
.Sh DESCRIPTION
.Fn send ,
.Fn sendto ,
and
.Fn sendmsg
are used to transmit a message to another socket.
.Fn send
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 dest_addr
with 
.Fa dest_len
specifying its size.
The length of the message is given by
.Fa length .
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
call may be used to determine when it is possible to
send more data.
.Pp
The
.Fa flags
parameter may include one or more of the following:
.Bd -literal
#define	MSG_OOB        0x1  /* process out-of-band data */
#define	MSG_DONTROUTE  0x4  /* bypass routing, use direct interface */
.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_DONTROUTE
is usually used only by diagnostic or routing programs.
.Pp
The
.Fn sendmsg
system call uses a
.Fa msghdr
structure to minimize the number of directly supplied arguments.
The 
.Fa msg_iov
and 
.Fa msg_iovlen 
fields of message specify zero or more buffers 
containing the data to be sent. 
.Fa msg_iov 
points to an array of iovec structures; 
.Fa msg_iovlen 
shall be set to the dimension of this array. 
In each iovec structure, the 
.Fa iov_base 
field specifies a storage area and 
the 
.Fa iov_len 
field gives its size in bytes. Some of these sizes can be zero. 
The data from each storage area indicated by 
.Fa msg_iov 
is sent in turn.
See 
.Xr recv 2
for a complete description of the
.Fa msghdr
structure.
.Sh RETURN VALUES
Upon successful completion,
the number of bytes which were sent is returned.
Otherwise, -1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn send ,
.Fn sendmsg ,
and
.Fn sendto
system calls will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EACCES
The SO_BROADCAST option is not set on the socket
and a broadcast address is given as the destination.
.\" ===========
.It Bq Er EAGAIN
The socket is marked non-blocking
and the requested operation would block.
.\" ===========
.It Bq Er EBADF
An invalid descriptor is specified.
.\" ===========
.It Bq Er ECONNRESET
A connection is forcibly closed by a peer.
.\" ===========
.It Bq Er EFAULT
An invalid user space address is specified for a parameter.
.\" ===========
.It Bq Er EHOSTUNREACH
The destination address specifies an unreachable host.
.\" ===========
.It Bq Er EINTR
A signal interrupts the system call
before any data is transmitted.
.\" ===========
.It Bq Er EMSGSIZE
The socket requires that message be sent atomically,
and the size of the message to be sent makes this impossible.
.Dv IOV_MAX .
.\" ===========
.It Bq Er ENETDOWN
The local network interface used to reach the destination is down.
.\" ===========
.It Bq Er ENETUNREACH
No route to the network is present.
.\" ===========
.It Bq Er ENOBUFS
The system is 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 is full.
This generally indicates that the interface has stopped sending,
but may be caused by transient congestion.
.\" ===========
.It Bq Er ENOTSOCK
The argument
.Fa socket
is not a socket.
.\" ===========
.It Bq Er EOPNOTSUPP
.Fa socket
does not support (some of) the option(s) specified in
.Fa flags . 
.\" ===========
.It Bq Er EPIPE
The socket is shut down for writing
or the socket is connection-mode and is no longer connected.
In the latter case, and if the socket is of type SOCK_STREAM,
the SIGPIPE signal is generated to the calling thread.
.\" ==========
.It Bq Er EADDRNOTAVAIL
The specified address is not available or no longer available on this machine.
.El
.Pp
The
.Fn sendmsg
and
.Fn sendto
system calls will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EAFNOSUPPORT
Addresses in the specified address family cannot be used
with this socket.
.\" ===========
.It Bq Er EDESTADDRREQ
The socket is not connection-mode and does not have its peer address set,
and no destination address is specified.
.\" ===========
.It Bq Er EISCONN
A destination address was specified and the socket is already connected.
.\" ===========
.It Bq Er ENOENT
A component of the pathname does not name an existing file
or the path name is an empty string.
.\" ===========
.It Bq Er ENOMEM
Insufficient memory is available to fulfill the request.
.\" ===========
.It Bq Er ENOTCONN
The socket is connection-mode, but is not connected.
.\" ===========
.It Bq Er ENOTDIR
A component of the path prefix of the pathname in the socket address
is not a directory.
.El
.Pp
The
.Fn send
system call will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EDESTADDRREQ
The socket is not connection-mode and no peer address is set.
.\" ===========
.It Bq Er ENOTCONN
The socket is not connected or otherwise has not had the peer pre-specified.
.El
.Pp
The
.Fn sendmsg
system call will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EINVAL
The sum of the iov_len values overflows an ssize_t.
.\" ===========
.It Bq Er EMSGSIZE
The socket requires that message be sent atomically,
and the size of the message to be sent makes this impossible, 
or the msg_iovlen member of the msghdr structure pointed to by message 
is less than or equal to 0 or is greater than 
.Dv IOV_MAX .
.El
.Sh LEGACY SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Pp
The include file
.In sys/types.h is necessary.
.Sh SEE ALSO
.Xr fcntl 2 ,
.Xr getsockopt 2 ,
.Xr recv 2 ,
.Xr select 2 ,
.Xr socket 2 ,
.Xr write 2 ,
.Xr compat 5
.Sh HISTORY
The
.Fn send
function call appeared in
.Bx 4.2 .