9.9 sctp_sendmsg
Function
An application can control various features of
SCTP by using the sendmsg function along with ancillary
data (described in Chapter 14). However, because the
use of ancillary data may be inconvenient, many SCTP
implementations provide an auxiliary library call (possibly
implemented as a system call) that eases an application's use of
SCTP's advanced features. The call takes the following form:
|
ssize_t sctp_sendmsg(int sockfd, const void *msg, size_t msgsz, const struct sockaddr
*to, socklen_t
tolen, uint32_t
ppid, uint32_t
flags, uint16_t
stream, uint32_t
timetolive, uint32_t
context);
|
|
Returns: the number of bytes written, 鈥? on
error
|
The user of sctp_sendmsg has a greatly
simplified sending method at the cost of more arguments. The
sockfd field holds the socket
descriptor returned from a socket system call. The
msg field points to a buffer of
msgsz bytes to be sent to the peer
endpoint to. The tolen field holds the length of the address
stored in to. The ppid field holds the pay-load protocol
identifier that will be passed with the data chunk. The
flags field will be passed to the
SCTP stack to identify any SCTP options; valid values for this
field may be found in Figure 7.16.
A caller specifies an SCTP stream number by
filling in the stream. The caller
may specify the lifetime of the message in milliseconds in the
lifetime field, where 0 represents
an infinite lifetime. A user context, if any, may be specified in
context. A user context associates
a failed message transmission, received via a message notification,
with some local application-specific context. For example, to send
a message to stream number 1, with the send flags set to
MSG_PR_SCTP_TTL, the lifetime set to 1000 milliseconds, a
payload protocol identifier of 24, and a context of 52, a user
would formulate the following call:
ret = sctp_sendmsg(sockfd,
data, datasz, &dest, sizeof(dest),
24, MSG_PR_SCTP_TTL, 1, 1000, 52);
This approach is much easier than allocating the
necessary ancillary data and setting up the appropriate structures
in the msghdr structure. Note that if an implementation
maps the sctp_sendmsg to a sendmsg function call,
the flags field of the
sendmsg call is set to 0.
|
