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SCTP_SEND(3)               Library Functions Manual               SCTP_SEND(3)

     sctp_send, sctp_sendx - send a message from an SCTP socket

     Standard C Library (libc, -lc)

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

     sctp_send(int sd, const void *msg, size_t len,
         const struct sctp_sndrcvinfo *sinfo, int flags);

     sctp_sendx(int sd, const void *msg, size_t len, struct sockaddr *addrs,
         int addrcnt, const struct sctp_sndrcvinfo *sinfo, int flags);

     The sctp_send() system call is used to transmit a message to another SCTP
     endpoint.  sctp_send() may be used to send data to an existing
     association for both one-to-many (SOCK_SEQPACKET) and one-to-one
     (SOCK_STREAM) socket types.  The length of the message msg is given by
     len.  If the message is too long to pass atomically through the
     underlying protocol, errno is set to EMSGSIZE, -1 is returned, and the
     message is not transmitted.

     No indication of failure to deliver is implicit in a sctp_send().
     Locally detected errors are indicated by a return value of -1.

     If no space is available at the socket to hold the message to be
     transmitted, then sctp_send() normally blocks, 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 send more data on one-to-one type
     (SOCK_STREAM) sockets.

     The sinfo structure is used to control various SCTP features and has the
     following format:

     struct sctp_sndrcvinfo {
             uint16_t sinfo_stream;  /* Stream sending to */
             uint16_t sinfo_ssn;     /* valid for recv only */
             uint16_t sinfo_flags;   /* flags to control sending */
             uint32_t sinfo_ppid;    /* ppid field */
             uint32_t sinfo_context; /* context field */
             uint32_t sinfo_timetolive; /* timetolive for PR-SCTP */
             uint32_t sinfo_tsn;        /* valid for recv only */
             uint32_t sinfo_cumtsn;     /* valid for recv only */
             sctp_assoc_t sinfo_assoc_id; /* The association id */

     The sinfo->sinfo_ppid argument is an opaque 32 bit value that is passed
     transparently through the stack to the peer endpoint.  It will be
     available on reception of a message (see sctp_recvmsg(3)).  Note that the
     stack passes this value without regard to byte order.

     The sinfo->sinfo_flags argument may include one or more of the following:

     #define SCTP_EOF          0x0100        /* Start a shutdown procedures */
     #define SCTP_ABORT        0x0200        /* Send an ABORT to peer */
     #define SCTP_UNORDERED    0x0400        /* Message is un-ordered */
     #define SCTP_ADDR_OVER    0x0800        /* Override the primary-address */
     #define SCTP_SENDALL      0x1000        /* Send this on all associations */
                                             /* for the endpoint */
     /* The lower byte is an enumeration of PR-SCTP policies */
     #define SCTP_PR_SCTP_TTL  0x0001        /* Time based PR-SCTP */
     #define SCTP_PR_SCTP_BUF  0x0002        /* Buffer based PR-SCTP */
     #define SCTP_PR_SCTP_RTX  0x0003        /* Number of retransmissions based PR-SCTP */

     The flag SCTP_EOF is used to instruct the SCTP stack to queue this
     message and then start a graceful shutdown of the association.  All
     remaining data in queue will be sent after which the association will be
     shut down.

     SCTP_ABORT is used to immediately terminate an association.  An abort is
     sent to the peer and the local TCB is destroyed.

     SCTP_UNORDERED is used to specify that the message being sent has no
     specific order and should be delivered to the peer application as soon as
     possible.  When this flag is absent messages are delivered in order
     within the stream they are sent, but without respect to order to peer

     The flag SCTP_ADDR_OVER is used to specify that a specific address should
     be used.  Normally SCTP will use only one of a multi-homed peers
     addresses as the primary address to send to.  By default, no matter what
     the to argument is, this primary address is used to send data.  By
     specifying this flag, the user is asking the stack to ignore the primary
     address and instead use the specified address not only as a lookup
     mechanism to find the association but also as the actual address to send

     For a one-to-many type (SOCK_SEQPACKET) socket the flag SCTP_SENDALL can
     be used as a convenient way to make one send call and have all
     associations that are under the socket get a copy of the message.  Note
     that this mechanism is quite efficient and makes only one actual copy of
     the data which is shared by all the associations for sending.

     The remaining flags are used for the partial reliability extension
     (RFC3758) and will only be effective if the peer endpoint supports this
     extension.  This option specifies what local policy the local endpoint
     should use in skipping data.  If none of these options are set, then data
     is never skipped over.

     SCTP_PR_SCTP_TTL is used to indicate that a time based lifetime is being
     applied to the data.  The sinfo->sinfo_timetolive argument is then a
     number of milliseconds for which the data is attempted to be transmitted.
     If that many milliseconds elapse and the peer has not acknowledged the
     data, the data will be skipped and no longer transmitted.  Note that this
     policy does not even assure that the data will ever be sent.  In times of
     a congestion with large amounts of data being queued, the
     sinfo->sinfo_timetolive may expire before the first transmission is ever

     The SCTP_PR_SCTP_BUF based policy transforms the sinfo->sinfo_timetolive
     field into a total number of bytes allowed on the outbound send queue.
     If that number or more bytes are in queue, then other buffer-based sends
     are looked to be removed and skipped.  Note that this policy may also
     result in the data never being sent if no buffer based sends are in queue
     and the maximum specified by timetolive bytes is in queue.

     The SCTP_PR_SCTP_RTX policy transforms the sinfo->sinfo_timetolive into a
     number of retransmissions to allow.  This policy always assures that at a
     minimum one send attempt is made of the data.  After which no more than
     sinfo->sinfo_timetolive retransmissions will be made before the data is

     sinfo->sinfo_stream is the SCTP stream that you wish to send the message
     on.  Streams in SCTP are reliable (or partially reliable) flows of
     ordered messages.

     The sinfo->sinfo_assoc_id field is used to select the association to send
     to on a one-to-many socket.  For a one-to-one socket, this field is

     The sinfo->sinfo_context field is used only in the event the message
     cannot be sent.  This is an opaque value that the stack retains and will
     give to the user when a failed send is given if that notification is
     enabled (see sctp(4)).  Normally a user process can use this value to
     index some application specific data structure when a send cannot be

     The flags argument holds the same meaning and values as those found in
     sendmsg(2) but is generally ignored by SCTP.

     The fields sinfo->sinfo_ssn, sinfo->sinfo_tsn, and sinfo->sinfo_cumtsn
     are used only when receiving messages and are thus ignored by
     sctp_send().  The function sctp_sendx() has the same properties as
     sctp_send() with the additional arguments of an array of sockaddr
     structures passed in.  With the addrs argument being given as an array of
     addresses to be sent to and the addrcnt argument indicating how many
     socket addresses are in the passed in array.  Note that all of the
     addresses will only be used when an implicit association is being set up.
     This allows the user the equivalent behavior as doing a sctp_connectx()
     followed by a sctp_send() to the association.  Note that if the
     sinfo->sinfo_assoc_id field is 0, then the first address will be used to
     look up the association in place of the association id.  If both an
     address and an association id are specified, the association id has

     The call returns the number of characters sent, or -1 if an error

     The sctp_send() system call fails if:

     [EAGAIN]           The socket is marked non-blocking and the requested
                        operation would block.

     [EBADF]            An invalid descriptor was specified.

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

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

     [EHOSTUNREACH]     The remote host was unreachable.

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

     [ENOBUFS]          The system was unable to allocate an internal buffer.
                        The operation may succeed when buffers become
                        available.  This error is also returned when 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.

     [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

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

     [ENOTSOCK]         The argument s is not a socket.

     [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), socket(2), write(2),
     sctp_connectx(3), sctp_recvmsg(3), sctp_sendmsg(3), sctp(4)

     Sockets API Extensions for the Stream Control Transmission Protocol
     (SCTP), RFC, 6458, December 2011.

     These functions first appeared in NetBSD 9.0.

     Because sctp_send() may have multiple associations under one endpoint, a
     select on write will only work for a one-to-one style socket.

NetBSD 10.99                    August 1, 2018                    NetBSD 10.99