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SEND(2)			    BSD	System Calls Manual		       SEND(2)

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

     Standard C	Library	(libc, -lc)

     #include <sys/types.h>
     #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);

     Send(), sendto(), and sendmsg() are used to transmit a message to another
     socket.  Send() may be used only when the socket is in a connected	state,
     while sendto() and	sendmsg() may be used at any time.

     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) call may be used to de-
     termine when it is	possible to send more data.

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

     #define MSG_OOB	     0x1   /* process out-of-band data */
     #define MSG_PEEK	     0x2   /* peek at incoming message */
     #define MSG_DONTROUTE   0x4   /* bypass routing, use direct interface */
     #define MSG_EOR	     0x8   /* data completes record */
     #define MSG_EOF	     0x100 /* data completes transaction */

     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_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 SOCK_STREAM sockets in	the PF_INET protocol family, and is used to
     implement Transaction TCP (see ttcp(4)).  MSG_DONTROUTE is	usually	used
     only by diagnostic	or routing programs.

     See recv(2) for a description of the msghdr structure.

     The call returns the number of characters sent, or	-1 if an error oc-

     Send(), sendto(), and sendmsg() fail if:

     [EBADF]		An invalid descriptor was specified.

     [EACCES]		The destination	address	is a broadcast address,	and
			SO_BROADCAST has not been set on the socket.

     [ENOTSOCK]		The argument s is not a	socket.

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

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

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

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

     [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	con-

     [EHOSTUNREACH]	The remote host	was unreachable.

     [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

     [EHOSTDOWN]	The remote host	was down.

     Because sendmsg() doesn't necessarily block until the data	has been
     transferred, it is	possible to transfer an	open file descriptor across an
     AF_UNIX domain socket (see	recv(2)), then close() it before it has	actu-
     ally been sent, the result	being that the receiver	gets a closed file de-
     scriptor.	It is left to the application to implement an acknowlegment
     mechanism to prevent this from happening.

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

     The send()	function call appeared in 4.2BSD.

BSD			       February	15, 1995			   BSD


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