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RECV(2)								       RECV(2)

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

SYNOPSIS
       #include <sys/types.h>
       #include <sys/socket.h>

       cc = recv(s, buf, len, flags)
       int cc, s;
       char *buf;
       int len, flags;

       cc = recvfrom(s, buf, len, flags, from, fromlen)
       int cc, s;
       char *buf;
       int len, flags;
       struct sockaddr *from;
       int *fromlen;

       cc = recvmsg(s, msg, flags)
       int cc, s;
       struct msghdr msg[];
       int flags;

DESCRIPTION
       Recv, recvfrom, and recvmsg are used to receive messages from a socket.

       The  recv  call	is  normally  used  only  on  a	 connected socket (see
       connect(2)), while recvfrom and recvmsg may be used to receive data  on
       a socket whether it is in a connected state or not.

       If  from	 is  non-zero, 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	 in  cc.   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(2)).

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

       The select(2) call may be used to determine when more data arrives.

       The flags argument to a recv call is formed by or'ing one  or  more  of
       the values,

	      #define  MSG_OOB	       0x1    /* process out-of-band data */
	      #define  MSG_PEEK	       0x2    /* peek at incoming message */

       The  recvmsg  call  uses	 a  msghdr structure to minimize the number of
       directly supplied parameters.  This structure has the  following	 form,
       as defined in <sys/socket.h>:

	      struct msghdr {
		   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;
	      };

       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(2).  A buffer to receive
       any  access  rights  sent  along	 with  the  message  is	 specified  in
       msg_accrights, which has length msg_accrightslen.   Access  rights  are
       currently limited to file descriptors, which each occupy the size of an
       int.

RETURN VALUE
       These calls return the number of bytes received,	 or  -1	 if  an	 error
       occurred.

ERRORS
       The calls fail if:

       [EBADF]		   The argument s is an invalid descriptor.

       [ENOTSOCK]	   The argument s is not a socket.

       [EWOULDBLOCK]	   The	socket	is marked non-blocking and the receive
			   operation would block.

       [EINTR]		   The receive was interrupted by delivery of a signal
			   before any data was available for the receive.

       [EFAULT]		   The	data  was specified to be received into a non-
			   existent or protected part of the  process  address
			   space.

SEE ALSO
       fcntl(2), read(2), send(2), select(2), getsockopt(2), socket(2)

4.2 Berkeley Distribution	 May 23, 1986			       RECV(2)
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