2.11BSD#431 - /usr/man/cat2/recvmsg.0

RECV(2)             UNIX Programmer's Manual		  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 non-
     blocking (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,


Printed 11/26/99	  May 23, 1986				1


RECV(2)             UNIX Programmer's Manual		  RECV(2)


	  #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 loca-
     tions, 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 avail-
			 able 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)


Printed 11/26/99	  May 23, 1986				2