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SCTP_RECVMSG(3)        FreeBSD 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
     specifying 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
     notifications 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 {
             u_int16_t sinfo_stream;  /* Stream arriving on */
             u_int16_t sinfo_ssn;     /* Stream Sequence Number */
             u_int16_t sinfo_flags;   /* Flags on the incoming message */
             u_int32_t sinfo_ppid;    /* The ppid field */
             u_int32_t sinfo_context; /* context field */
             u_int32_t sinfo_timetolive; /* not used by sctp_recvmsg */
             u_int32_t sinfo_tsn;        /* The transport sequence number */
             u_int32_t sinfo_cumtsn;     /* The cumulative acknowledgment point  */
             sctp_assoc_t sinfo_assoc_id; /* The association id of the peer */
     };

     The sinfo-_sinfo_ppid 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.

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

     The sinfo-_sinfo_tsn 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 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 characters sent, 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
                        available.

     [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
                        congestion.

     [EHOSTUNREACH]     The remote host was unreachable.

     [ENOTCON]          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
                        association.

     [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)

FreeBSD 11.0-PRERELEASE         August 13, 2007        FreeBSD 11.0-PRERELEASE

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO

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