SCTP_SEND(3) | Library Functions Manual | SCTP_SEND(3) |
sctp_send
, sctp_sendx
—
#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);
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.
sctp_send
() system call fails if:
EAGAIN
]EBADF
]ECONNRESET
]EFAULT
]EHOSTUNREACH
]EMSGSIZE
]ENOBUFS
]ENOENT
]SCTP_ABORT
flag was specified on a non-existing association.ENOTCONN
]ENOTSOCK
]EPIPE
]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.Sockets API Extensions for the Stream Control Transmission Protocol (SCTP), RFC, 6458, December 2011.
sctp_send
() may have multiple associations under
one endpoint, a select on write will only work for a one-to-one style socket.
August 1, 2018 | NetBSD 9.2 |