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XS_RECVMSG(3)		     Crossroads	I/O Manual		 XS_RECVMSG(3)

NAME
       xs_recvmsg - receive a message part from	a socket (zero-copy)

SYNOPSIS
       int xs_recvmsg (void *socket, xs_msg_t *msg, int	flags);

DESCRIPTION
       The xs_recvmsg()	function shall receive a message part from the socket
       referenced by the socket	argument and store it in the message
       referenced by the msg argument. Any content previously stored in	msg
       shall be	properly deallocated. If there are no message parts available
       on the specified	socket the xs_recvmsg()	function shall block until the
       request can be satisfied. The flags argument is a combination of	the
       flags defined below:

       XS_DONTWAIT
	   Specifies that the operation	should be performed in non-blocking
	   mode. If there are no messages available on the specified socket,
	   the xs_recvmsg() function shall fail	with errno set to EAGAIN.

   Multi-part messages
       A Crossroads message is composed	of 1 or	more message parts. Each
       message part is an independent xs_msg_t in its own right. Crossroads
       ensures atomic delivery of messages; peers shall	receive	either all
       message parts of	a message or none at all. The total number of message
       parts is	unlimited except by available memory.

       An application that processes multipart messages	must use the
       XS_RCVMORE xs_getsockopt(3) option after	calling	xs_recvmsg() to
       determine if there are further parts to receive.

RETURN VALUE
       The xs_recvmsg()	function shall return the number of bytes in the
       received	message	if successful. Otherwise it shall return -1 and	set
       errno to	one of the values defined below.

ERRORS
       EAGAIN
	   Non-blocking	mode was requested and no messages are available at
	   the moment.

       ENOTSUP
	   The xs_recvmsg() operation is not supported by this socket type.

       EFSM
	   The xs_recvmsg() operation cannot be	performed on this socket at
	   the moment due to the socket	not being in the appropriate state.
	   This	error may occur	with socket types that switch between several
	   states, such	as XS_REP. See the messaging patterns section of
	   xs_socket(3)	for more information.

       ETERM
	   The context associated with the specified socket was	terminated.

       ENOTSOCK
	   The provided	socket was invalid.

       EINTR
	   The operation was interrupted by delivery of	a signal before	a
	   message was available.

       EFAULT
	   The message passed to the function was invalid.

       ETIMEDOUT
	   Survey has timed out. (Applicable only to XS_SURVEYOR socket.)

EXAMPLE
       Receiving a message from	a socket.

	   /* Create an	empty message */
	   xs_msg_t msg;
	   int rc = xs_msg_init	(&msg);
	   assert (rc == 0);
	   /* Block until a message is available to be received	from socket */
	   rc =	xs_recvmsg (socket, &msg, 0);
	   assert (rc != -1);
	   /* Release message */
	   xs_msg_close	(&msg);

       Receiving a multi-part message.

	   int64_t more;
	   size_t more_size = sizeof more;
	   do {
	       /* Create an empty message to hold the message part */
	       xs_msg_t	part;
	       int rc =	xs_msg_init (&part);
	       assert (rc == 0);
	       /* Block	until a	message	is available to	be received from socket	*/
	       rc = xs_recvmsg (socket,	&part, 0);
	       assert (rc != -1);
	       /* Determine if more message parts are to follow	*/
	       rc = xs_getsockopt (socket, XS_RCVMORE, &more, &more_size);
	       assert (rc == 0);
	       xs_msg_close (&part);
	   } while (more);

SEE ALSO
       Applications that do not	require	zero-copy messaging can	use the
       simpler xs_recv(3) instead of xs_recvmsg().

       xs_sendmsg(3) xs_getsockopt(3) xs_socket(7) xs(7)

AUTHORS
       This man	page was written by Martin Sustrik <sustrik@250bpm.com[1]>,
       Martin Lucina <martin@lucina.net[2]> and	Pieter Hintjens
       <ph@imatix.com[3]>.

NOTES
	1. sustrik@250bpm.com
	   mailto:sustrik@250bpm.com

	2. martin@lucina.net
	   mailto:martin@lucina.net

	3. ph@imatix.com
	   mailto:ph@imatix.com

Crossroads I/O 1.2.0		  02/28/2021			 XS_RECVMSG(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLE | SEE ALSO | AUTHORS | NOTES

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