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recv(3N)							      recv(3N)

NAME    [Toc]    [Back]

     recv, recvfrom, recvmsg - receive a message from a	socket

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>

     int recv(int s, char *buf,	int len, int flags);
     int recvfrom(int s, char *buf, int	len, int flags,	caddr_t	from,
	 int *fromlen);

     int recvmsg(int s,	struct msghdr *msg, int	flags);

DESCRIPTION    [Toc]    [Back]

     s is a socket created with	socket.	 recv, recvfrom, and recvmsg are used
     to	receive	messages from another socket.  recv may	be used	only on	a
     connected socket [see connect(3N)], while recvfrom	and recvmsg may	be
     used to receive data on a socket whether it is in a connected state or

     If	from is	not a NULL pointer, the	source address of the message is
     filled in.	 fromlen is a value-result parameter, initialized to the size
     of	the buffer associated with from, and modified on return	to indicate
     the actual	size of	the address stored there.  The length of the message
     is	returned.  If a	message	is too long to fit in the supplied buffer,
     excess bytes may be discarded depending on	the type of socket the message
     is	received from [see socket(3N)].

     If	no messages are	available at the socket, the receive call waits	for a
     message to	arrive,	unless the socket is nonblocking [see fcntl(2)]	in
     which case	-1 is returned with the	external variable errno	set to

     The select	call may be used to determine when more	data arrives.

     The flags parameter is formed by ORing one	or more	of the following:

     MSG_OOB   Read any	out-of-band data present on the	socket rather than the
	       regular in-band data.

     MSG_PEEK  Peek at the data	present	on the socket; the data	is returned,
	       but not consumed, so that a subsequent receive operation	will
	       see the same data.

     The recvmsg() call	uses a msghdr structure	to minimize the	number of
     directly supplied parameters.  This structure is defined in sys/socket.h
     and includes the following	members:

	  caddr_t      msg_name;	 /* optional address */
	  int	       msg_namelen;	 /* size of address */
	  struct iovec *msg_iov;	 /* scatter/gather array */
	  int	       msg_iovlen;	 /* # elements in msg_iov */
	  caddr_t      msg_accrights;	 /* access rights sent/received	*/
	  int	       msg_accrightslen;

									Page 1

recv(3N)							      recv(3N)

     Here msg_name and msg_namelen specify the destination address if the
     socket is unconnected; msg_name may be given as a NULL pointer if no
     names are desired or required.  The msg_iov and msg_iovlen	describe the
     scatter-gather locations, as described in read.  A	buffer to receive any
     access rights sent	along with the message is specified in msg_accrights,
     which has length msg_accrightslen.

RETURN VALUE    [Toc]    [Back]

     These calls return	the number of bytes received, or -1 if an error

ERRORS    [Toc]    [Back]

     The calls fail if:

     EBADF		 s is an invalid descriptor.

     ENOTSOCK		 s is a	descriptor for a file, not a socket.

     EINTR		 The operation was interrupted by delivery of a	signal
			 before	any data was available to be received.

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

     ENOMEM		 There was insufficient	user memory available for the
			 operation to complete.

     ENOSR		 There were insufficient STREAMS resources available
			 for the operation to complete.

SEE ALSO    [Toc]    [Back]

     fcntl(2), ioctl(2), read(2), connect(3N), getsockopt(3N), send(3N),

NOTES    [Toc]    [Back]

     The type of address structure passed to recv depends on the address
     family.  UNIX domain sockets (address family AF_UNIX) require a
     socketaddr_un structure as	defined	in sys/un.h; Internet domain sockets
     (address family AF_INET) require a	sockaddr_in structure as defined in
     netinet/in.h.  Other address families may require other structures.  Use
     the structure appropriate to the address family; cast the structure
     address to	a generic caddr_t in the call to recv and pass the size	of the
     structure in the fromlen argument.

									PPPPaaaaggggeeee 2222
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