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.TH SENDMSG 3XNET "September 10, 2018"
.SH NAME
sendmsg \- send a message on a socket using a message structure
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR ... ] \fIfile\fR ... \fB-lxnet\fR [ \fIlibrary\fR ... ]
#include <sys/socket.h>

\fBssize_t\fR \fBsendmsg\fR(\fBint\fR \fIsocket\fR, \fBconst struct msghdr *\fR\fImessage\fR, \fBint\fR \fIflags\fR);
.fi

.SH PARAMETERS
.LP
The function takes the following arguments:
.sp
.ne 2
.na
\fB\fIsocket\fR\fR
.ad
.RS 11n
Specifies the socket file descriptor.
.RE

.sp
.ne 2
.na
\fB\fImessage\fR\fR
.ad
.RS 11n
Points to a \fBmsghdr\fR 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 \fBmsg_flags\fR member is
ignored.
.RE

.sp
.ne 2
.na
\fB\fIflags\fR\fR
.ad
.RS 11n
Specifies the type of message transmission. The application may specify 0 or
the following flag:
.sp
.ne 2
.na
\fBMSG_EOR\fR
.ad
.RS 11n
Terminates a record (if supported by the protocol)
.RE

.sp
.ne 2
.na
\fBMSG_OOB\fR
.ad
.RS 11n
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
.ne 2
.na
\fB\fBMSG_NOSIGNAL\fR\fR
.ad
.RS 11n
Don't generate the \fBSIGPIPE\fR signal when a stream-oriented socket is no
longer connected.
.RE

.RE

.SH DESCRIPTION
.LP
The \fBsendmsg()\fR function sends a message through a connection-mode or
connectionless-mode socket.  If the socket is connectionless-mode, the message
will be sent to the address specified by \fImsghdr\fR.  If the socket is
connection-mode, the destination address in \fImsghdr\fR is ignored.
.sp
.LP
The  \fImsg_iov\fR and  \fImsg_iovlen\fR fields of message specify zero or more
buffers containing the data to be sent. \fImsg_iov\fR points to an array of
\fBiovec\fR structures;  \fImsg_iovlen\fR must be set to the dimension of this
array. In each  \fBiovec\fR structure, the  \fIiov_base\fR field specifies  a
storage area and the  \fIiov_len\fR field gives its size  in bytes. Some of
these sizes can be zero. The data from each storage area indicated by
\fImsg_iov\fR is sent in turn.
.sp
.LP
Successful completion of a call to \fBsendmsg()\fR does not guarantee delivery
of the message. A return value of \(mi1 indicates only locally-detected errors.
.sp
.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 \fBO_NONBLOCK\fR set,
\fBsendmsg()\fR function blocks 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 \fBO_NONBLOCK\fR set, \fBsendmsg()\fR function
will fail.
.sp
.LP
If the socket protocol supports broadcast and the specified address is a
broadcast address for the socket protocol, \fBsendmsg()\fR will fail if the
\fBSO_BROADCAST\fR option is not set for the socket.
.sp
.LP
The socket in use may require the process to have appropriate privileges to use
the \fBsendmsg()\fR function.
.SH USAGE
.LP
The \fBselect\fR(3C) and \fBpoll\fR(2) functions can be used to determine when
it is possible to send more data.
.SH RETURN VALUES
.LP
Upon successful completion, \fBsendmsg()\fR function returns the number of
bytes sent.  Otherwise, \(mi1 is returned and \fBerrno\fR is set to indicate
the error.
.SH ERRORS
.LP
In addition to the errors documented below, an asynchronous error generated by
the underlying socket protocol may be returned. For the full list of errors,
please see the corresponding socket protocol manual page. For example, for a
list of TCP errors, please see \fBtcp\fR(7P).
.sp
.LP
The \fBsendmsg()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEAGAIN\fR \fR
.ad
.br
.na
\fB\fBEWOULDBLOCK\fR\fR
.ad
.RS 16n
The socket's file descriptor is marked O_NONBLOCK and the requested operation
would block.
.RE

.sp
.ne 2
.na
\fB\fBEAFNOSUPPORT\fR\fR
.ad
.RS 16n
Addresses in the specified address family cannot be used with this socket.
.RE

.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 16n
The \fIsocket\fR argument is not a valid file descriptor.
.RE

.sp
.ne 2
.na
\fB\fBECONNRESET\fR\fR
.ad
.RS 16n
A connection was forcibly closed by a peer.
.RE

.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 16n
The  \fImessage\fR parameter, or storage pointed to by the  \fImsg_name\fR,
\fImsg_control\fR or  \fImsg_iov\fR fields of the  \fImessage\fR parameter, or
storage pointed to by the \fBiovec\fR structures pointed to by the
\fImsg_iov\fR field can not be accessed.
.RE

.sp
.ne 2
.na
\fB\fBEINTR\fR\fR
.ad
.RS 16n
A signal interrupted \fBsendmsg()\fR before any data was transmitted.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 16n
The sum of the \fBiov_len\fR values overflows an \fBssize_t\fR.
.RE

.sp
.ne 2
.na
\fB\fBEMSGSIZE\fR\fR
.ad
.RS 16n
The message is to large to be sent all at once (as the socket requires), or the
\fBmsg_iovlen\fR member of the \fBmsghdr\fR structure pointed to by
\fImessage\fR is less than or equal to 0 or is greater than \fBIOV_MAX\fR.
.RE

.sp
.ne 2
.na
\fB\fBENOTCONN\fR\fR
.ad
.RS 16n
The socket is connection-mode but is not connected.
.RE

.sp
.ne 2
.na
\fB\fBENOTSOCK\fR\fR
.ad
.RS 16n
The \fIsocket\fR argument does not refer a socket.
.RE

.sp
.ne 2
.na
\fB\fBEOPNOTSUPP\fR\fR
.ad
.RS 16n
The \fIsocket\fR argument is associated with a socket that does not support one
or more of the values set in \fIflags\fR.
.RE

.sp
.ne 2
.na
\fB\fBEPIPE\fR\fR
.ad
.RS 16n
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
\fBSOCK_STREAM\fR, the \fBSIGPIPE\fR signal is generated to the calling thread
unless the \fBMSG_NOSIGNAL\fR flag is set.
.RE

.sp
.LP
If the address family of the socket is \fBAF_UNIX\fR, then \fBsendmsg()\fR will
fail if:
.sp
.ne 2
.na
\fB\fBEIO\fR\fR
.ad
.RS 16n
An I/O error occurred while reading from or writing to the file system.
.RE

.sp
.ne 2
.na
\fB\fBELOOP\fR\fR
.ad
.RS 16n
Too many symbolic links were encountered in translating the pathname in the
socket address.
.RE

.sp
.ne 2
.na
\fB\fBENAMETOOLONG\fR\fR
.ad
.RS 16n
A component of a pathname exceeded \fINAME_MAX\fR characters, or an entire
pathname exceeded \fIPATH_MAX\fR characters.
.RE

.sp
.ne 2
.na
\fB\fBENOENT\fR\fR
.ad
.RS 16n
A component of the pathname does not name an existing file or the pathname is
an empty string.
.RE

.sp
.ne 2
.na
\fB\fBENOTDIR\fR\fR
.ad
.RS 16n
A component of the path prefix of the pathname in the socket address is not a
directory.
.RE

.sp
.LP
The \fBsendmsg()\fR function may fail if:
.sp
.ne 2
.na
\fB\fBEACCES\fR\fR
.ad
.RS 16n
Search permission is denied for a component of the path prefix; or write access
to the named socket is denied.
.RE

.sp
.ne 2
.na
\fB\fBEDESTADDRREQ\fR\fR
.ad
.RS 16n
The socket is not connection-mode and does not have its peer address set, and
no destination address was specified.
.RE

.sp
.ne 2
.na
\fB\fBEHOSTUNREACH\fR\fR
.ad
.RS 16n
The destination host cannot be reached (probably because the host is down or a
remote router cannot reach it).
.RE

.sp
.ne 2
.na
\fB\fBEIO\fR\fR
.ad
.RS 16n
An I/O error occurred while reading from or writing to the file system.
.RE

.sp
.ne 2
.na
\fB\fBEISCONN\fR\fR
.ad
.RS 16n
A destination address was specified and the socket is already connected.
.RE

.sp
.ne 2
.na
\fB\fBENETDOWN\fR\fR
.ad
.RS 16n
The local interface used to reach the destination is down.
.RE

.sp
.ne 2
.na
\fB\fBENETUNREACH\fR\fR
.ad
.RS 16n
No route to the network is present.
.RE

.sp
.ne 2
.na
\fB\fBENOBUFS\fR\fR
.ad
.RS 16n
Insufficient resources were available in the system to perform the operation.
.RE

.sp
.ne 2
.na
\fB\fBENOMEM\fR\fR
.ad
.RS 16n
Insufficient memory was available to fulfill the request.
.RE

.sp
.ne 2
.na
\fB\fBENOSR\fR\fR
.ad
.RS 16n
There were insufficient STREAMS resources available for the operation to
complete.
.RE

.sp
.LP
If the address family of the socket is \fBAF_UNIX\fR, then \fBsendmsg()\fR may
fail if:
.sp
.ne 2
.na
\fB\fBENAMETOOLONG\fR\fR
.ad
.RS 16n
Pathname resolution of a symbolic link produced an intermediate result whose
length exceeds \fIPATH_MAX\fR.
.RE

.SH ATTRIBUTES
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.LP
\fBpoll\fR(2) \fBgetsockopt\fR(3XNET), \fBrecv\fR(3XNET),
\fBrecvfrom\fR(3XNET), \fBrecvmsg\fR(3XNET), \fBselect\fR(3C),
\fBsend\fR(3XNET), \fBsendto\fR(3XNET), \fBsetsockopt\fR(3XNET),
\fBshutdown\fR(3XNET), \fBsocket\fR(3XNET), \fBattributes\fR(5),
\fBstandards\fR(5), \fBtcp\fR(7P)