.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "SENDMSG" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" sendmsg 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
sendmsg \- send a message on a socket using a message structure
.SH SYNOPSIS
.LP
\fB#include <sys/socket.h>
.br
.sp
ssize_t sendmsg(int\fP \fIsocket\fP\fB, const struct msghdr *\fP\fImessage\fP\fB,
int\fP \fIflags\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIsendmsg\fP() function shall send a message through a connection-mode
or connectionless-mode socket. If the socket is
connectionless-mode, the message shall be sent to the address specified
by \fBmsghdr\fP. If the socket is connection-mode, the
destination address in \fBmsghdr\fP shall be ignored.
.LP
The \fIsendmsg\fP() function takes the following arguments:
.TP 7
\fIsocket\fP
Specifies the socket file descriptor.
.TP 7
\fImessage\fP
Points to a \fBmsghdr\fP structure, containing both the destination
address and the buffers for the outgoing message. The
length and format of the address depend on the address family of the
socket. The \fImsg_flags\fP member is ignored.
.TP 7
\fIflags\fP
Specifies the type of message transmission. The application may specify
0 or the following flag: 
.TP 7
MSG_EOR
.RS
Terminates a record (if supported by the protocol).
.RE
.TP 7
MSG_OOB
.RS
Sends out-of-band data on sockets that support out-of-bound data.
The significance and semantics of out-of-band data are
protocol-specific.
.RE
.sp
.sp
.LP
The \fImsg_iov\fP and \fImsg_iovlen\fP fields of \fImessage\fP specify
zero or more buffers containing the data to be sent.
\fImsg_iov\fP points to an array of \fBiovec\fP structures; \fImsg_iovlen\fP
shall be set to the dimension of this array. In
each \fBiovec\fP structure, the \fIiov_base\fP field specifies a storage
area and the \fIiov_len\fP field gives its size in
bytes. Some of these sizes can be zero. The data from each storage
area indicated by \fImsg_iov\fP is sent in turn.
.LP
Successful completion of a call to \fIsendmsg\fP() does not guarantee
delivery of the message. A return value of -1 indicates
only locally-detected errors.
.LP
If space is not available at the sending socket to hold the message
to be transmitted and the socket file descriptor does not
have O_NONBLOCK set, the \fIsendmsg\fP() function shall block until
space is available. If space is not available at the sending
socket to hold the message to be transmitted and the socket file descriptor
does have O_NONBLOCK set, the \fIsendmsg\fP() function
shall fail.
.LP
If the socket protocol supports broadcast and the specified address
is a broadcast address for the socket protocol,
\fIsendmsg\fP() shall fail if the SO_BROADCAST option is not set for
the socket.
.LP
The socket in use may require the process to have appropriate privileges
to use the \fIsendmsg\fP() function.
.SH RETURN VALUE
.LP
Upon successful completion, \fIsendmsg\fP() shall return the number
of bytes sent. Otherwise, -1 shall be returned and
\fIerrno\fP set to indicate the error.
.SH ERRORS
.LP
The \fIsendmsg\fP() function shall fail if:
.TP 7
.B EAGAIN \fRor\fP EWOULDBLOCK
The socket's file descriptor is marked O_NONBLOCK and the requested
operation would block.
.TP 7
.B EAFNOSUPPORT
Addresses in the specified address family cannot be used with this
socket.
.TP 7
.B EBADF
The \fIsocket\fP argument is not a valid file descriptor.
.TP 7
.B ECONNRESET
A connection was forcibly closed by a peer.
.TP 7
.B EINTR
A signal interrupted \fIsendmsg\fP() before any data was transmitted.
.TP 7
.B EINVAL
The sum of the \fIiov_len\fP values overflows an \fBssize_t\fP.
.TP 7
.B EMSGSIZE
The message is too large to be sent all at once (as the socket requires),
or the \fImsg_iovlen\fP member of the \fBmsghdr\fP
structure pointed to by \fImessage\fP is less than or equal to 0 or
is greater than {IOV_MAX}.
.TP 7
.B ENOTCONN
The socket is connection-mode but is not connected.
.TP 7
.B ENOTSOCK
The \fIsocket\fP argument does not refer to a socket.
.TP 7
.B EOPNOTSUPP
The \fIsocket\fP argument is associated with a socket that does not
support one or more of the values set in
\fIflags\fP.
.TP 7
.B 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.
.sp
.LP
If the address family of the socket is AF_UNIX, then \fIsendmsg\fP()
shall fail if:
.TP 7
.B EIO
An I/O error occurred while reading from or writing to the file system.
.TP 7
.B ELOOP
A loop exists in symbolic links encountered during resolution of the
pathname in the socket address.
.TP 7
.B ENAMETOOLONG
A component of a pathname exceeded {NAME_MAX} characters, or an entire
pathname exceeded {PATH_MAX} characters.
.TP 7
.B ENOENT
A component of the pathname does not name an existing file or the
path name is an empty string.
.TP 7
.B ENOTDIR
A component of the path prefix of the pathname in the socket address
is not a directory.
.sp
.LP
The \fIsendmsg\fP() function may fail if:
.TP 7
.B EACCES
Search permission is denied for a component of the path prefix; or
write access to the named socket is denied.
.TP 7
.B EDESTADDRREQ
The socket is not connection-mode and does not have its peer address
set, and no destination address was specified.
.TP 7
.B EHOSTUNREACH
The destination host cannot be reached (probably because the host
is down or a remote router cannot reach it).
.TP 7
.B EIO
An I/O error occurred while reading from or writing to the file system.
.TP 7
.B EISCONN
A destination address was specified and the socket is already connected.
.TP 7
.B ENETDOWN
The local network interface used to reach the destination is down.
.TP 7
.B ENETUNREACH
No route to the network is present.
.TP 7
.B ENOBUFS
Insufficient resources were available in the system to perform the
operation.
.TP 7
.B ENOMEM
Insufficient memory was available to fulfill the request.
.sp
.LP
If the address family of the socket is AF_UNIX, then \fIsendmsg\fP()
may fail if:
.TP 7
.B ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution
of the pathname in the socket address.
.TP 7
.B ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate result
whose length exceeds {PATH_MAX}.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
Done.
.SH APPLICATION USAGE
.LP
The \fIselect\fP() and \fIpoll\fP() functions can
be used to determine when it is possible to send more data.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIgetsockopt\fP(), \fIpoll\fP(), \fIrecv\fP(), \fIrecvfrom\fP(),
\fIrecvmsg\fP(), \fIselect\fP(), \fIsend\fP(), \fIsendto\fP(),
\fIsetsockopt\fP(), \fIshutdown\fP(), \fIsocket\fP(), the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<sys/socket.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .