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SEND(2)			  FreeBSD System Calls Manual		       SEND(2)

     send, sendto, sendmsg, sendmmsg --	send a message from a socket

     Standard C	Library	(libc, -lc)

     #include <sys/socket.h>

     send(int s, const void *msg, size_t len, int flags);

     sendto(int	s, const void *msg, size_t len,	int flags,
	 const struct sockaddr *to, socklen_t tolen);

     sendmsg(int s, const struct msghdr	*msg, int flags);

     sendmmsg(int s, struct mmsghdr *mmsg, unsigned int	vlen,
	 unsigned int flags);

     send(), sendto(), sendmsg(), and sendmmsg() are used to transmit a	mes-
     sage to another socket.  send() may be used only when the socket is in a
     connected state, while sendto(), sendmsg()	and sendmmsg() may be used at
     any time.

     The sendmmsg() call can be	used to	send multiple messages in the same
     call using	an array of mmsghdr elements with the following	form, as de-
     fined in <sys/socket.h>:

     struct mmsghdr {
	     struct msghdr   msg_hdr;	     /*	the message to be sent */
	     unsigned int    msg_len;	     /*	number of bytes	transmitted */

     The msg_len member	contains the number of bytes sent for each msg_hdr
     member.  The array	has vlen elements, which is limited to 1024.  If there
     is	an error, a number fewer than vlen may be returned, and	the error may
     be	retrieved using	getsockopt(2) with SO_ERROR.

     The address of the	target is given	by to, with tolen specifying its size.
     The length	of the message is given	by len.	 If the	message	is too long to
     pass atomically through the underlying protocol, the error	EMSGSIZE is
     returned, and the message is not transmitted.

     No	indication of failure to deliver is implicit in	a send().  Locally de-
     tected errors are indicated by a return value of -1.

     If	no messages space is available at the socket to	hold the message to be
     transmitted, then send() normally blocks, unless the socket has been
     placed in non-blocking I/O	mode.  The select(2) or	poll(2)	call may be
     used to determine when it is possible to send more	data.  Unfortunately
     this does not work	when the interface queue which is used to send the
     message is	full, and the call returns ENOBUFS.

     The flags parameter may include one or more of the	following:

     #define MSG_OOB	     0x0001 /* process out-of-band data	*/
     #define MSG_PEEK	     0x0002 /* peek at incoming	message	*/
     #define MSG_DONTROUTE   0x0004 /* bypass routing, use direct interface */
     #define MSG_EOR	     0x0008 /* data completes record */
     #define MSG_NOSIGNAL    0x0400 /* do not generate SIGPIPE on EOF */

     The flag MSG_OOB is used to send "out-of-band" data on sockets that sup-
     port this notion (e.g.  SOCK_STREAM); the underlying protocol must	also
     support "out-of-band" data.  MSG_EOR is used to indicate a	record mark
     for protocols which support the concept.  MSG_DONTROUTE is	usually	used
     only by diagnostic	or routing programs.

     See recv(2) for a description of the msghdr structure.  MSG_NOSIGNAL is
     used to prevent SIGPIPE generation	when writing a socket that may be

     The send(), sendto(), and sendmsg() calls return the number of characters
     sent, or -1 if an error occurred.	The sendmmsg() call returns the	number
     of	messages sent, or -1 if	an error occured.

     send(), sendto(), sendmsg(), and sendmmsg() fail if:

     [EACCES]		The SO_BROADCAST option	is not set on the socket, and
			a broadcast address was	given as the destination.

     [EAFNOSUPPORT]	Addresses in the specified address family cannot be
			used with this socket.

			The socket is marked non-blocking and the requested
			operation would	block.

     [EBADF]		An invalid descriptor was specified.

     [EDSTADDRREQ]	In a non-connected socket a destination	address	has
			not been specified.

     [EFAULT]		An invalid user	space address was specified for	a pa-

     [EHOSTDOWN]	The destination	is a host on the local subnet and does
			not respond to arp(4).

     [EHOSTUNREACH]	The destination	for the	message	is unreachable.

     [EINVAL]		The total length of the	I/O is more than can be	ex-
			pressed	by the ssize_t return value.

     [EMSGSIZE]		The socket requires that message be sent atomically,
			and the	size of	the message to be sent made this im-

     [ENOBUFS]		The system was unable to allocate an internal buffer.
			The operation may succeed when buffers become avail-

			An alternative reason: 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.

     [ENOTSOCK]		The argument s is not a	socket.

     [EPIPE]		In a connected socket the connection has been broken.

     sendto() will also	fail if:

     [EISCONN]		A destination address was specified and	the socket is
			already	connected.

     sendmsg() and sendmmsg() will also	fail if:

     [EMSGSIZE]		The msg_iovlen member of the msg structure is less
			than or	equal to 0 or is greater than {IOV_MAX}.

     fcntl(2), getsockopt(2), recv(2), select(2), socket(2), write(2)

     The send()	function call appeared in 4.2BSD.  The sendmmsg() function
     call appeared in Linux 3.0	and NetBSD 7.0.

FreeBSD	13.0			 June 22, 2012			  FreeBSD 13.0


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