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SCTP_RECVMSG(3)	       FreeBSD Library Functions Manual	       SCTP_RECVMSG(3)

     sctp_recvmsg -- receive a message from an SCTP socket

     Standard C	Library	(libc, -lc)

     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netinet/sctp.h>

     sctp_recvmsg(int s, void *msg, size_t len,
	 struct	sockaddr * restrict from, socklen_t * restrict fromlen,
	 struct	sctp_sndrcvinfo	*sinfo,	int *flags);

     The sctp_recvmsg()	system call is used to receive a message from another
     SCTP endpoint.  The sctp_recvmsg()	call is	used by	one-to-one
     (SOCK_STREAM) type	sockets	after a	successful connect() call or after the
     application has performed a listen() followed by a	successful accept().
     For a one-to-many (SOCK_SEQPACKET)	type socket, an	endpoint may call
     sctp_recvmsg() after having implicitly started an association via one of
     the send calls including sctp_sendmsg(), sendto() and sendmsg().  Or, an
     application may also receive a message after having called	listen() with
     a positive	backlog	to enable the reception	of new associations.

     The address of the	sender is held in the from argument with fromlen spec-
     ifying its	size.  At the completion of a successful sctp_recvmsg()	call
     from will hold the	address	of the peer and	fromlen	will hold the length
     of	that address.  Note that the address is	bounded	by the initial value
     of	fromlen	which is used as an in/out variable.

     The length	of the message msg to be received is bounded by	len.  If the
     message is	too long to fit	in the users receive buffer, then the flags
     argument will not have the	MSG_EOR	flag applied.  If the message is a
     complete message then the flags argument will have	MSG_EOR	set.  Locally
     detected errors are indicated by a	return value of	-1 with	errno set ac-
     cordingly.	 The flags argument may	also hold the value MSG_NOTIFICATION.
     When this occurs it indicates that	the message received is	not from the
     peer endpoint, but	instead	is a notification from the SCTP	stack (see
     sctp(4) for more details).	 Note that no notifications are	ever given un-
     less the user subscribes to such notifications using the SCTP_EVENTS
     socket option.

     If	no messages are	available at the socket	then sctp_recvmsg() normally
     blocks on the reception of	a message or NOTIFICATION, unless the socket
     has been placed in	non-blocking I/O mode.	The select(2) system call may
     be	used to	determine when it is possible to receive a message.

     The sinfo argument	is defined as follows.

     struct sctp_sndrcvinfo {
	     uint16_t sinfo_stream;  /*	Stream arriving	on */
	     uint16_t sinfo_ssn;     /*	Stream Sequence	Number */
	     uint16_t sinfo_flags;   /*	Flags on the incoming message */
	     uint32_t sinfo_ppid;    /*	The ppid field */
	     uint32_t sinfo_context; /*	context	field */
	     uint32_t sinfo_timetolive;	/* not used by sctp_recvmsg */
	     uint32_t sinfo_tsn;	/* The transport sequence number */
	     uint32_t sinfo_cumtsn;	/* The cumulative acknowledgment point	*/
	     sctp_assoc_t sinfo_assoc_id; /* The association id	of the peer */

     The sinfo-_sinfo_ppid field is an opaque 32 bit value that	is passed
     transparently through the stack from the peer endpoint.  Note that	the
     stack passes this value without regard to byte order.

     The sinfo-_sinfo_flags field may include the following:

     #define SCTP_UNORDERED    0x0400	     /*	Message	is un-ordered */

     The SCTP_UNORDERED	flag is	used to	specify	that the message arrived with
     no	specific order and was delivered to the	peer application as soon as
     possible.	When this flag is absent the message was delivered in order
     within the	stream it was received.

     The sinfo-_sinfo_stream field is the SCTP stream that the message was re-
     ceived on.	 Streams in SCTP are reliable (or partially reliable) flows of
     ordered messages.

     The sinfo-_sinfo_context field is used only if the	local application set
     an	association level context with the SCTP_CONTEXT	socket option.	Op-
     tionally a	user process can use this value	to index some application spe-
     cific data	structure for all data coming from a specific association.

     The sinfo-_sinfo_ssn field	will hold the stream sequence number assigned
     by	the peer endpoint if the message is not	unordered.  For	unordered mes-
     sages this	field holds an undefined value.

     The sinfo-_sinfo_tsn field	holds a	transport sequence number (TSN)	that
     was assigned to this message by the peer endpoint.	 For messages that fit
     in	or less	than the path MTU this will be the only	TSN assigned.  Note
     that for messages that span multiple TSNs this value will be one of the
     TSNs that was used	on the message.

     The sinfo-_sinfo_cumtsn field holds the current cumulative	acknowledgment
     point of the transport association.  Note that this may be	larger or
     smaller than the TSN assigned to the message itself.

     The sinfo-_sinfo_assoc_id is the unique association identification	that
     was assigned to the association.  For one-to-many (SOCK_SEQPACKET)	type
     sockets this value	can be used to send data to the	peer without the use
     of	an address field.  It is also quite useful in setting various socket
     options on	the specific association (see sctp(4)).

     The sinfo-_info_timetolive	field is not used by sctp_recvmsg().

     The call returns the number of bytes received, or -1 if an	error oc-

     The sctp_recvmsg()	system call fails if:

     [EBADF]		An invalid descriptor was specified.

     [ENOTSOCK]		The argument s is not a	socket.

     [EFAULT]		An invalid user	space address was specified for	an ar-

     [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.

     [ENOTCONN]		On a one-to-one	style socket no	association exists.

     [ECONNRESET]	An abort was received by the stack while the user was
			attempting to send data	to the peer.

     [ENOENT]		On a one to many style socket no address is specified
			so that	the association	cannot be located or the
			SCTP_ABORT flag	was specified on a non-existing	asso-

     [EPIPE]		The socket is unable to	send anymore data
			(SBS_CANTSENDMORE has been set on the socket).	This
			typically means	that the socket	is not connected and
			is a one-to-one	style socket.

     getsockopt(2), recv(2), select(2),	sendmsg(2), setsockopt(2), socket(2),
     write(2), sctp_send(3), sctp_sendmsg(3), sctp(4)

FreeBSD	13.0			April 23, 2015			  FreeBSD 13.0


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