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SCTP_SEND(3) Library Functions Manual SCTP_SEND(3)
NAME
sctp_send, sctp_sendx - send 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_send(int sd, const void *msg, size_t len,
const struct sctp_sndrcvinfo *sinfo, int flags);
ssize_t
sctp_sendx(int sd, const void *msg, size_t len, struct sockaddr *addrs,
int addrcnt, const struct sctp_sndrcvinfo *sinfo, int flags);
DESCRIPTION
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
streams.
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
to.
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
made.
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
skipped.
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
ignored.
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
fulfilled.
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
priority.
RETURN VALUES
The call returns the number of characters sent, or -1 if an error
occurred.
ERRORS
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
argument.
[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
impossible.
[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
association.
[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.
SEE ALSO
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.
HISTORY
These functions first appeared in NetBSD 9.0.
BUGS
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