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30 .Dd December 15, 2006
31 .Dt SCTP_SEND 3
32 .Os
33 .Sh NAME
34 .Nm sctp_send ,
35 .Nm sctp_sendx
36 .Nd send a message from an SCTP socket
37 .Sh LIBRARY
38 .Lb libc
39 .Sh SYNOPSIS
40 .In sys/types.h
41 .In sys/socket.h
42 .In netinet/sctp.h
43 .Ft ssize_t
44 .Fo sctp_send
45 .Fa "int sd" "const void *msg" "size_t len"
46 .Fa "const struct sctp_sndrcvinfo *sinfo" "int flags"
47 .Fc
48 .Ft ssize_t
49 .Fo sctp_sendx
50 .Fa "int sd" "const void *msg" "size_t len" "struct sockaddr *addrs"
51 .Fa "int addrcnt" "const struct sctp_sndrcvinfo *sinfo" "int flags"
52 .Fc
53 .Sh DESCRIPTION
54 The
55 .Fn sctp_send
56 system call
57 is used to transmit a message to another SCTP endpoint.
58 .Fn sctp_send
59 may be used to send data to an existing association for both
60 one-to-many (SOCK_SEQPACKET) and one-to-one (SOCK_STREAM) socket types.
61 The length of the message
62 .Fa msg
63 is given by
64 .Fa len .
65 If the message is too long to pass atomically through the
66 underlying protocol,
67 .Va errno
68 is set to
69 .Er EMSGSIZE ,
70 -1 is returned, and
71 the message is not transmitted.
72 .Pp
73 No indication of failure to deliver is implicit in a
74 .Fn sctp_send .
75 Locally detected errors are indicated by a return value of -1.
76 .Pp
77 If no space is available at the socket to hold
78 the message to be transmitted, then
79 .Fn sctp_send
80 normally blocks, unless the socket has been placed in
81 non-blocking I/O mode.
82 The
83 .Xr select 2
84 system call may be used to determine when it is possible to
85 send more data on one-to-one type (SOCK_STREAM) sockets.
86 .Pp
87 The
88 .Fa sinfo
89 structure is used to control various SCTP features
90 and has the following format:
91 .Bd -literal
92 struct sctp_sndrcvinfo {
93 uint16_t sinfo_stream; /* Stream sending to */
94 uint16_t sinfo_ssn; /* valid for recv only */
95 uint16_t sinfo_flags; /* flags to control sending */
96 uint32_t sinfo_ppid; /* ppid field */
97 uint32_t sinfo_context; /* context field */
98 uint32_t sinfo_timetolive; /* timetolive for PR-SCTP */
99 uint32_t sinfo_tsn; /* valid for recv only */
100 uint32_t sinfo_cumtsn; /* valid for recv only */
101 sctp_assoc_t sinfo_assoc_id; /* The association id */
102 };
103 .Ed
104 .Pp
105 The
106 .Fa sinfo->sinfo_ppid
107 argument is an opaque 32 bit value that is passed transparently
108 through the stack to the peer endpoint. It will be available on
109 reception of a message (see
110 .Xr sctp_recvmsg 3 ) .
111 Note that the stack passes this value without regard to byte
112 order.
113 .Pp
114 The
115 .Fa sinfo->sinfo_flags
116 argument may include one or more of the following:
117 .Bd -literal
118 #define SCTP_EOF 0x0100 /* Start a shutdown procedures */
119 #define SCTP_ABORT 0x0200 /* Send an ABORT to peer */
120 #define SCTP_UNORDERED 0x0400 /* Message is un-ordered */
121 #define SCTP_ADDR_OVER 0x0800 /* Override the primary-address */
122 #define SCTP_SENDALL 0x1000 /* Send this on all associations */
123 /* for the endpoint */
124 /* The lower byte is an enumeration of PR-SCTP policies */
125 #define SCTP_PR_SCTP_TTL 0x0001 /* Time based PR-SCTP */
126 #define SCTP_PR_SCTP_BUF 0x0002 /* Buffer based PR-SCTP */
127 #define SCTP_PR_SCTP_RTX 0x0003 /* Number of retransmissions based PR-SCTP */
128 .Ed
129 .Pp
130 The flag
131 .Dv SCTP_EOF
132 is used to instruct the SCTP stack to queue this message
133 and then start a graceful shutdown of the association.
134 All
135 remaining data in queue will be sent after which the association
136 will be shut down.
137 .Pp
138 .Dv SCTP_ABORT
139 is used to immediately terminate an association.
140 An abort
141 is sent to the peer and the local TCB is destroyed.
142 .Pp
143 .Dv SCTP_UNORDERED
144 is used to specify that the message being sent has no
145 specific order and should be delivered to the peer application
146 as soon as possible.
147 When this flag is absent messages
148 are delivered in order within the stream they are sent, but without
149 respect to order to peer streams.
150 .Pp
151 The flag
152 .Dv SCTP_ADDR_OVER
153 is used to specify that a specific address should be used.
154 Normally
155 SCTP will use only one of a multi-homed peers addresses as the primary
156 address to send to.
157 By default, no matter what the
158 .Fa to
159 argument is, this primary address is used to send data.
160 By specifying
161 this flag, the user is asking the stack to ignore the primary address
162 and instead use the specified address not only as a lookup mechanism
163 to find the association but also as the actual address to send to.
164 .Pp
165 For a one-to-many type (SOCK_SEQPACKET) socket the flag
166 .Dv SCTP_SENDALL
167 can be used as a convenient way to make one send call and have
168 all associations that are under the socket get a copy of the message.
169 Note that this mechanism is quite efficient and makes only one actual
170 copy of the data which is shared by all the associations for sending.
171 .Pp
172 The remaining flags are used for the partial reliability extension (RFC3758)
173 and will only be effective if the peer endpoint supports this extension.
174 This option specifies what local policy the local endpoint should use
175 in skipping data.
176 If none of these options are set, then data is
177 never skipped over.
178 .Pp
179 .Dv SCTP_PR_SCTP_TTL
180 is used to indicate that a time based lifetime is being applied
181 to the data.
182 The
183 .Fa sinfo->sinfo_timetolive
184 argument is then a number of milliseconds for which the data is
185 attempted to be transmitted.
186 If that many milliseconds elapse
187 and the peer has not acknowledged the data, the data will be
188 skipped and no longer transmitted.
189 Note that this policy does
190 not even assure that the data will ever be sent.
191 In times of a congestion
192 with large amounts of data being queued, the
193 .Fa sinfo->sinfo_timetolive
194 may expire before the first transmission is ever made.
195 .Pp
196 The
197 .Dv SCTP_PR_SCTP_BUF
198 based policy transforms the
199 .Fa sinfo->sinfo_timetolive
200 field into a total number of bytes allowed on the outbound
201 send queue.
202 If that number or more bytes are in queue, then
203 other buffer-based sends are looked to be removed and
204 skipped.
205 Note that this policy may also result in the data
206 never being sent if no buffer based sends are in queue and
207 the maximum specified by
208 .Fa timetolive
209 bytes is in queue.
210 .Pp
211 The
212 .Dv SCTP_PR_SCTP_RTX
213 policy transforms the
214 .Fa sinfo->sinfo_timetolive
215 into a number of retransmissions to allow.
216 This policy
217 always assures that at a minimum one send attempt is
218 made of the data.
219 After which no more than
220 .Fa sinfo->sinfo_timetolive
221 retransmissions will be made before the data is skipped.
222 .Pp
223 .Fa sinfo->sinfo_stream
224 is the SCTP stream that you wish to send the
225 message on.
226 Streams in SCTP are reliable (or partially reliable) flows of ordered
227 messages.
228 .Pp
229 The
230 .Fa sinfo->sinfo_assoc_id
231 field is used to
232 select the association to send to on a one-to-many socket.
233 For a one-to-one socket, this field is ignored.
234 .Pp
235 The
236 .Fa sinfo->sinfo_context
237 field is used only in the event the message cannot be sent.
238 This is an opaque
239 value that the stack retains and will give to the user when a failed send
240 is given if that notification is enabled (see
241 .Xr sctp 4 ) .
242 Normally a user process can use this value to index some application
243 specific data structure when a send cannot be fulfilled.
244 .Pp
245 The
246 .Fa flags
247 argument holds the same meaning and values as those found in
248 .Xr sendmsg 2
249 but is generally ignored by SCTP.
250 .Pp
251 The fields
252 .Fa sinfo->sinfo_ssn ,
253 .Fa sinfo->sinfo_tsn ,
254 and
255 .Fa sinfo->sinfo_cumtsn
256 are used only when receiving messages and are thus ignored by
257 .Fn sctp_send .
258 The function
259 .Fn sctp_sendx
260 has the same properties as
261 .Fn sctp_send
262 with the additional arguments of an array of sockaddr structures
263 passed in.
264 With the
265 .Fa addrs
266 argument being given as an array of addresses to be sent to and
267 the
268 .Fa addrcnt
269 argument indicating how many socket addresses are in the passed
270 in array.
271 Note that all of the addresses will only be used
272 when an implicit association is being set up.
273 This allows the
274 user the equivalent behavior as doing a
275 .Fn sctp_connectx
276 followed by a
277 .Fn sctp_send
278 to the association.
279 Note that if the
280 .Fa sinfo->sinfo_assoc_id
281 field is 0, then the first address will be used to look up
282 the association in place of the association id.
283 If both
284 an address and an association id are specified, the association
285 id has priority.
286 .Sh RETURN VALUES
287 The call returns the number of characters sent, or -1
288 if an error occurred.
289 .Sh ERRORS
290 The
291 .Fn sctp_send
292 system call
293 fails if:
294 .Bl -tag -width Er
295 .It Bq Er EBADF
296 An invalid descriptor was specified.
297 .It Bq Er ENOTSOCK
298 The argument
299 .Fa s
300 is not a socket.
301 .It Bq Er EFAULT
302 An invalid user space address was specified for an argument.
303 .It Bq Er EMSGSIZE
304 The socket requires that message be sent atomically,
305 and the size of the message to be sent made this impossible.
306 .It Bq Er EAGAIN
307 The socket is marked non-blocking and the requested operation
308 would block.
309 .It Bq Er ENOBUFS
310 The system was unable to allocate an internal buffer.
311 The operation may succeed when buffers become available.
312 .It Bq Er ENOBUFS
313 The output queue for a network interface was full.
314 This generally indicates that the interface has stopped sending,
315 but may be caused by transient congestion.
316 .It Bq Er EHOSTUNREACH
317 The remote host was unreachable.
318 .It Bq Er ENOTCONN
319 On a one-to-one style socket no association exists.
320 .It Bq Er ECONNRESET
321 An abort was received by the stack while the user was
322 attempting to send data to the peer.
323 .It Bq Er ENOENT
324 On a one-to-many style socket no address is specified
325 so that the association cannot be located or the
326 SCTP_ABORT flag was specified on a non-existing association.
327 .It Bq Er EPIPE
328 The socket is unable to send anymore data
329 .Dv ( SBS_CANTSENDMORE
330 has been set on the socket).
331 This typically means that the socket
332 is not connected and is a one-to-one style socket.
333 .El
334 .Sh SEE ALSO
335 .Xr getsockopt 2 ,
336 .Xr recv 2 ,
337 .Xr select 2 ,
338 .Xr sendmsg 2 ,
339 .Xr socket 2 ,
340 .Xr write 2 ,
341 .Xr sctp_connectx 3 ,
342 .Xr sctp_recvmsg 3 ,
343 .Xr sctp_sendmsg 3 ,
344 .Xr sctp 4
345 .Sh BUGS
346 Because
347 .Fn sctp_send
348 may have multiple associations under one endpoint, a
349 select on write will only work for a one-to-one style
350 socket.