xref: /freebsd/lib/libc/net/sctp_send.3 (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
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34.Dd December 15, 2006
35.Dt SCTP_SEND 3
36.Os
37.Sh NAME
38.Nm sctp_send ,
39.Nm sctp_sendx
40.Nd send a message from an SCTP socket
41.Sh LIBRARY
42.Lb libc
43.Sh SYNOPSIS
44.In sys/types.h
45.In sys/socket.h
46.In netinet/sctp.h
47.Ft ssize_t
48.Fo sctp_send
49.Fa "int sd" "const void *msg" "size_t len"
50.Fa "const struct sctp_sndrcvinfo *sinfo" "int flags"
51.Fc
52.Ft ssize_t
53.Fo sctp_sendx
54.Fa "int sd" "const void *msg" "size_t len" "struct sockaddr *addrs"
55.Fa "int addrcnt" "const struct sctp_sndrcvinfo *sinfo" "int flags"
56.Fc
57.Sh DESCRIPTION
58The
59.Fn sctp_send
60system call
61is used to transmit a message to another SCTP endpoint.
62.Fn sctp_send
63may be used to send data to an existing association for both
64one-to-many (SOCK_SEQPACKET) and one-to-one (SOCK_STREAM) socket types.
65The length of the message
66.Fa msg
67is given by
68.Fa len .
69If the message is too long to pass atomically through the
70underlying protocol,
71.Va errno
72is set to
73.Er EMSGSIZE ,
74-1 is returned, and
75the message is not transmitted.
76.Pp
77No indication of failure to deliver is implicit in a
78.Fn sctp_send .
79Locally detected errors are indicated by a return value of -1.
80.Pp
81If no space is available at the socket to hold
82the message to be transmitted, then
83.Fn sctp_send
84normally blocks, unless the socket has been placed in
85non-blocking I/O mode.
86The
87.Xr select 2
88system call may be used to determine when it is possible to
89send more data on one-to-one type (SOCK_STREAM) sockets.
90.Pp
91The
92.Fa sinfo
93structure is used to control various SCTP features
94and has the following format:
95.Bd -literal
96struct sctp_sndrcvinfo {
97	u_int16_t sinfo_stream;  /* Stream sending to */
98	u_int16_t sinfo_ssn;     /* valid for recv only */
99	u_int16_t sinfo_flags;   /* flags to control sending */
100	u_int32_t sinfo_ppid;    /* ppid field */
101	u_int32_t sinfo_context; /* context field */
102	u_int32_t sinfo_timetolive; /* timetolive for PR-SCTP */
103	u_int32_t sinfo_tsn;        /* valid for recv only */
104	u_int32_t sinfo_cumtsn;     /* valid for recv only */
105	sctp_assoc_t sinfo_assoc_id; /* The association id */
106};
107.Ed
108.Pp
109The
110.Fa sinfo->sinfo_ppid
111argument is an opaque 32 bit value that is passed transparently
112through the stack to the peer endpoint. It will be available on
113reception of a message (see
114.Xr sctp_recvmsg 2 ) .
115Note that the stack passes this value without regard to byte
116order.
117.Pp
118The
119.Fa sinfo->sinfo_flags
120argument may include one or more of the following:
121.Bd -literal
122#define SCTP_EOF 	  0x0100	/* Start a shutdown procedures */
123#define SCTP_ABORT	  0x0200	/* Send an ABORT to peer */
124#define SCTP_UNORDERED 	  0x0400	/* Message is un-ordered */
125#define SCTP_ADDR_OVER	  0x0800	/* Override the primary-address */
126#define SCTP_SENDALL      0x1000	/* Send this on all associations */
127					/* for the endpoint */
128/* The lower byte is an enumeration of PR-SCTP policies */
129#define SCTP_PR_SCTP_TTL  0x0001	/* Time based PR-SCTP */
130#define SCTP_PR_SCTP_BUF  0x0002	/* Buffer based PR-SCTP */
131#define SCTP_PR_SCTP_RTX  0x0003	/* Number of retransmissions based PR-SCTP */
132.Ed
133.Pp
134The flag
135.Dv SCTP_EOF
136is used to instruct the SCTP stack to queue this message
137and then start a graceful shutdown of the association.
138All
139remaining data in queue will be sent after which the association
140will be shut down.
141.Pp
142.Dv SCTP_ABORT
143is used to immediately terminate an association.
144An abort
145is sent to the peer and the local TCB is destroyed.
146.Pp
147.Dv SCTP_UNORDERED
148is used to specify that the message being sent has no
149specific order and should be delivered to the peer application
150as soon as possible.
151When this flag is absent messages
152are delivered in order within the stream they are sent, but without
153respect to order to peer streams.
154.Pp
155The flag
156.Dv SCTP_ADDR_OVER
157is used to specify that a specific address should be used.
158Normally
159SCTP will use only one of a multi-homed peers addresses as the primary
160address to send to.
161By default, no matter what the
162.Fa to
163argument is, this primary address is used to send data.
164By specifying
165this flag, the user is asking the stack to ignore the primary address
166and instead use the specified address not only as a lookup mechanism
167to find the association but also as the actual address to send to.
168.Pp
169For a one-to-many type (SOCK_SEQPACKET) socket the flag
170.Dv SCTP_SENDALL
171can be used as a convenient way to make one send call and have
172all associations that are under the socket get a copy of the message.
173Note that this mechanism is quite efficent and makes only one actual
174copy of the data which is shared by all the associations for sending.
175.Pp
176The remaining flags are used for the partial reliability extension (RFC3758)
177and will only be effective if the peer endpoint supports this extension.
178This option specifies what local policy the local endpoint should use
179in skipping data.
180If none of these options are set, then data is
181never skipped over.
182.Pp
183.Dv SCTP_PR_SCTP_TTL
184is used to indicate that a time based lifetime is being applied
185to the data.
186The
187.Fa sinfo->sinfo_timetolive
188argument is then a number of milliseconds for which the data is
189attempted to be transmitted.
190If that many milliseconds ellapse
191and the peer has not acknowledged the data, the data will be
192skipped and no longer transmitted.
193Note that this policy does
194not even assure that the data will ever be sent.
195In times of a congestion
196with large amounts of data being queued, the
197.Fa sinfo->sinfo_timetolive
198may expire before the first transmission is ever made.
199.Pp
200The
201.Dv SCTP_PR_SCTP_BUF
202based policy transforms the
203.Fa sinfo->sinfo_timetolive
204field into a total number of bytes allowed on the outbound
205send queue.
206If that number or more bytes are in queue, then
207other buffer-based sends are looked to be removed and
208skipped.
209Note that this policy may also result in the data
210never being sent if no buffer based sends are in queue and
211the maximum specified by
212.Fa timetolive
213bytes is in queue.
214.Pp
215The
216.Dv SCTP_PR_SCTP_RTX
217policy transforms the
218.Fa sinfo->sinfo_timetolive
219into a number of retransmissions to allow.
220This policy
221always assures that at a minimum one send attempt is
222made of the data.
223After which no more than
224.Fa sinfo->sinfo_timetolive
225retransmissions will be made before the data is skipped.
226.Pp
227.Fa sinfo->sinfo_stream
228is the SCTP stream that you wish to send the
229message on.
230Streams in SCTP are reliable (or partially reliable) flows of ordered
231messages.
232.Pp
233The
234.Fa sinfo->sinfo_assoc_id
235field is used to
236select the association to send to on a one-to-many socket.
237For a one-to-one socket, this field is ignored.
238.Pp
239The
240.Fa sinfo->sinfo_context
241field is used only in the event the message cannot be sent.
242This is an opaque
243value that the stack retains and will give to the user when a failed send
244is given if that notification is enabled (see
245.Xr sctp 4 ) .
246Normally a user process can use this value to index some application
247specific data structure when a send cannot be fulfilled.
248.Pp
249The
250.Fa flags
251argument holds the same meaning and values as those found in
252.Xr sendmsg 2
253but is generally ignored by SCTP.
254.Pp
255The fields
256.Fa sinfo->sinfo_ssn ,
257.Fa sinfo->sinfo_tsn ,
258and
259.Fa sinfo->sinfo_cumtsn
260are used only when receiving messages and are thus ignored by
261.Fn sctp_send .
262The function
263.Fn sctp_sendx
264has the same properties as
265.Fn sctp_send
266with the additional arguments of an array of sockaddr structures
267passed in.
268With the
269.Fa addrs
270argument being given as an array of addresses to be sent to and
271the
272.Fa addrcnt
273argument indicating how many socket addresses are in the passed
274in array.
275Note that all of the addresses will only be used
276when an implicit association is being set up.
277This allows the
278user the equivalent behavior as doing a
279.Fn sctp_connectx
280followed by a
281.Fn sctp_send
282to the association.
283Note that if the
284.Fa sinfo->sinfo_assoc_id
285field is 0, then the first address will be used to look up
286the association in place of the association id.
287If both
288an address and an association id are specified, the association
289id has priority.
290.Sh RETURN VALUES
291The call returns the number of characters sent, or -1
292if an error occurred.
293.Sh ERRORS
294The
295.Fn sctp_send
296system call
297fail if:
298.Bl -tag -width Er
299.It Bq Er EBADF
300An invalid descriptor was specified.
301.It Bq Er ENOTSOCK
302The argument
303.Fa s
304is not a socket.
305.It Bq Er EFAULT
306An invalid user space address was specified for an argument.
307.It Bq Er EMSGSIZE
308The socket requires that message be sent atomically,
309and the size of the message to be sent made this impossible.
310.It Bq Er EAGAIN
311The socket is marked non-blocking and the requested operation
312would block.
313.It Bq Er ENOBUFS
314The system was unable to allocate an internal buffer.
315The operation may succeed when buffers become available.
316.It Bq Er ENOBUFS
317The output queue for a network interface was full.
318This generally indicates that the interface has stopped sending,
319but may be caused by transient congestion.
320.It Bq Er EHOSTUNREACH
321The remote host was unreachable.
322.It Bq Er ENOTCON
323On a one-to-one style socket no association exists.
324.It Bq Er ECONNRESET
325An abort was received by the stack while the user was
326attempting to send data to the peer.
327.It Bq Er ENOENT
328On a one-to-many style socket no address is specified
329so that the association cannot be located or the
330SCTP_ABORT flag was specified on a non-existing association.
331.It Bq Er EPIPE
332The socket is unable to send anymore data
333.Dv ( SBS_CANTSENDMORE
334has been set on the socket).
335This typically means that the socket
336is not connected and is a one-to-one style socket.
337.El
338.Sh SEE ALSO
339.Xr getsockopt 2 ,
340.Xr recv 2 ,
341.Xr select 2 ,
342.Xr sendmsg 2 ,
343.Xr socket 2 ,
344.Xr write 2
345.Xr sctp_connectx 3 ,
346.Xr sctp_recvmsg 3 ,
347.Xr sctp_sendmsg 3 ,
348.Xr sctp 4
349.Sh BUGS
350Because
351.Fn sctp_send
352may have multiple associations under one endpoint, a
353select on write will only work for a one-to-one style
354socket.
355