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SCTP_RECVMSG(3)		 BSD Library Functions Manual	       SCTP_RECVMSG(3)

NAME
     sctp_recvmsg — receive a message from an SCTP socket

LIBRARY
     Standard C Library (libc, -lc)

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

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

DESCRIPTION
     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 inital 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_EOF flag applied.  If the message is a
     complete message then the flags argument will have MSG_EOF set.  Locally
     detected errors are indicated by a return value of -1 with errno set
     accordingly.  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 notifi‐
     cations are ever given unless 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
     received 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.
     Optionally a user process can use this value to index some application
     specific 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().

RETURN VALUES
     The call returns the number of bytes received, or -1 if an error
     occurred.

ERRORS
     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
			argument.

     [EMSGSIZE]		The socket requires that message be sent atomically,
			and the size of the message to be sent made this
			impossible.

     [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‐
			able.

     [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‐
			gestion.

     [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‐
			ciation.

     [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.

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

BSD				August 13, 2007				   BSD
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