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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)send.2 8.2 (Berkeley) 2/21/94 33.\" $FreeBSD$ 34.\" 35.Dd December 15, 2006 36.Dt SCTP_SENDMSG 3 37.Os 38.Sh NAME 39.Nm sctp_sendmsg , 40.Nm sctp_sendmsgx 41.Nd send a message from an SCTP socket 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In sys/types.h 46.In sys/socket.h 47.In netinet/sctp.h 48.Ft ssize_t 49.Fo sctp_sendmsg 50.Fa "int s" "const void *msg" "size_t len" "const struct sockaddr *to" 51.Fa "socklen_t tolen" "uint32_t ppid" "uint32_t flags" "uint16_t stream_no" 52.Fa "uint32_t timetolive" "uint32_t context" 53.Fc 54.Ft ssize_t 55.Fo sctp_sendmsgx 56.Fa "int s" "const void *msg" "size_t len" "const struct sockaddr *to" 57.Fa "int addrcnt" "uint32_t ppid" "uint32_t flags" "uint16_t stream_no" 58.Fa "uint32_t timetolive" "uint32_t context" 59.Fc 60.Sh DESCRIPTION 61The 62.Fn sctp_sendmsg 63system call 64is used to transmit a message to another SCTP endpoint. 65The 66.Fn sctp_sendmsg 67may be used at any time. 68If the socket is a one-to-many type (SOCK_SEQPACKET) 69socket then an attempt to send to an address that no association exists to will 70implicitly create a new association. 71Data sent in such an instance will result in 72the data being sent on the third leg of the SCTP four-way handshake. 73Note that if 74the socket is a one-to-one type (SOCK_STREAM) socket then an association must 75be in existence (by use of the 76.Xr connect 2 77system call). 78Calling 79.Fn sctp_sendmsg 80or 81.Fn sctp_sendmsgx 82on a non-connected one-to-one socket will result in 83.Va errno 84being set to 85.Er ENOTCONN , 86-1 being returned, and the message not being transmitted. 87.Pp 88The address of the target is given by 89.Fa to 90with 91.Fa tolen 92specifying its size. 93The length of the message 94.Fa msg 95is given by 96.Fa len . 97If the message is too long to pass atomically through the 98underlying protocol, 99.Va errno 100is set to 101.Er EMSGSIZE , 102-1 is returned, and 103the message is not transmitted. 104.Pp 105No indication of failure to deliver is implicit in a 106.Xr sctp_sendmsg 3 107call. 108Locally detected errors are indicated by a return value of -1. 109.Pp 110If no space is available at the socket to hold 111the message to be transmitted, then 112.Xr sctp_sendmsg 3 113normally blocks, unless the socket has been placed in 114non-blocking I/O mode. 115The 116.Xr select 2 117system call may be used to determine when it is possible to 118send more data on one-to-one type (SOCK_STREAM) sockets. 119.Pp 120The 121.Fa ppid 122argument is an opaque 32 bit value that is passed transparently 123through the stack to the peer endpoint. 124It will be available on 125reception of a message (see 126.Xr sctp_recvmsg 3 ) . 127Note that the stack passes this value without regard to byte 128order. 129.Pp 130The 131.Fa flags 132argument may include one or more of the following: 133.Bd -literal 134#define SCTP_EOF 0x0100 /* Start a shutdown procedures */ 135#define SCTP_ABORT 0x0200 /* Send an ABORT to peer */ 136#define SCTP_UNORDERED 0x0400 /* Message is un-ordered */ 137#define SCTP_ADDR_OVER 0x0800 /* Override the primary-address */ 138#define SCTP_SENDALL 0x1000 /* Send this on all associations */ 139 /* for the endpoint */ 140/* The lower byte is an enumeration of PR-SCTP policies */ 141#define SCTP_PR_SCTP_TTL 0x0001 /* Time based PR-SCTP */ 142#define SCTP_PR_SCTP_BUF 0x0002 /* Buffer based PR-SCTP */ 143#define SCTP_PR_SCTP_RTX 0x0003 /* Number of retransmissions based PR-SCTP */ 144.Ed 145.Pp 146The flag 147.Dv SCTP_EOF 148is used to instruct the SCTP stack to queue this message 149and then start a graceful shutdown of the association. 150All 151remaining data in queue will be sent after which the association 152will be shut down. 153.Pp 154.Dv SCTP_ABORT 155is used to immediately terminate an association. 156An abort 157is sent to the peer and the local TCB is destroyed. 158.Pp 159.Dv SCTP_UNORDERED 160is used to specify that the message being sent has no 161specific order and should be delivered to the peer application 162as soon as possible. 163When this flag is absent messages 164are delivered in order within the stream they are sent, but without 165respect to order to peer streams. 166.Pp 167The flag 168.Dv SCTP_ADDR_OVER 169is used to specify that an specific address should be used. 170Normally 171SCTP will use only one of a multi-homed peers addresses as the primary 172address to send to. 173By default, no matter what the 174.Fa to 175argument is, this primary address is used to send data. 176By specifying 177this flag, the user is asking the stack to ignore the primary address 178and instead use the specified address not only as a lookup mechanism 179to find the association but also as the actual address to send to. 180.Pp 181For a one-to-many type (SOCK_SEQPACKET) socket the flag 182.Dv SCTP_SENDALL 183can be used as a convenient way to make one send call and have 184all associations that are under the socket get a copy of the message. 185Note that this mechanism is quite efficient and makes only one actual 186copy of the data which is shared by all the associations for sending. 187.Pp 188The remaining flags are used for the partial reliability extension (RFC3758) 189and will only be effective if the peer endpoint supports this extension. 190This option specifies what local policy the local endpoint should use 191in skipping data. 192If none of these options are set, then data is 193never skipped over. 194.Pp 195.Dv SCTP_PR_SCTP_TTL 196is used to indicate that a time based lifetime is being applied 197to the data. 198The 199.Fa timetolive 200argument is then a number of milliseconds for which the data is 201attempted to be transmitted. 202If that many milliseconds elapse 203and the peer has not acknowledged the data, the data will be 204skipped and no longer transmitted. 205Note that this policy does 206not even assure that the data will ever be sent. 207In times of a congestion 208with large amounts of data being queued, the 209.Fa timetolive 210may expire before the first transmission is ever made. 211.Pp 212The 213.Dv SCTP_PR_SCTP_BUF 214based policy transforms the 215.Fa timetolive 216field into a total number of bytes allowed on the outbound 217send queue. 218If that number or more bytes are in queue, then 219other buffer based sends are looked to be removed and 220skipped. 221Note that this policy may also result in the data 222never being sent if no buffer based sends are in queue and 223the maximum specified by 224.Fa timetolive 225bytes is in queue. 226.Pp 227The 228.Dv SCTP_PR_SCTP_RTX 229policy transforms the 230.Fa timetolive 231into a number of retransmissions to allow. 232This policy 233always assures that at a minimum one send attempt is 234made of the data. 235After which no more than 236.Fa timetolive 237retransmissions will be made before the data is skipped. 238.Pp 239.Fa stream_no 240is the SCTP stream that you wish to send the 241message on. 242Streams in SCTP are reliable (or partially reliable) flows of ordered 243messages. 244The 245.Fa context 246field is used only in the event the message cannot be sent. 247This is an opaque 248value that the stack retains and will give to the user when a failed send 249is given if that notification is enabled (see 250.Xr sctp 4 ) . 251Normally a user process can use this value to index some application 252specific data structure when a send cannot be fulfilled. 253.Fn sctp_sendmsgx 254is identical to 255.Fn sctp_sendmsg 256with the exception that it takes an array of sockaddr structures in the 257argument 258.Fa to 259and adds the additional argument 260.Fa addrcnt 261which specifies how many addresses are in the array. 262This allows a 263caller to implicitly set up an association passing multiple addresses 264as if 265.Fn sctp_connectx 266had been called to set up the association. 267.Sh RETURN VALUES 268The call returns the number of characters sent, or -1 269if an error occurred. 270.Sh ERRORS 271The 272.Fn sctp_sendmsg 273system call 274fails if: 275.Bl -tag -width Er 276.It Bq Er EBADF 277An invalid descriptor was specified. 278.It Bq Er ENOTSOCK 279The argument 280.Fa s 281is not a socket. 282.It Bq Er EFAULT 283An invalid user space address was specified for an argument. 284.It Bq Er EMSGSIZE 285The socket requires that message be sent atomically, 286and the size of the message to be sent made this impossible. 287.It Bq Er EAGAIN 288The socket is marked non-blocking and the requested operation 289would block. 290.It Bq Er ENOBUFS 291The system was unable to allocate an internal buffer. 292The operation may succeed when buffers become available. 293.It Bq Er ENOBUFS 294The output queue for a network interface was full. 295This generally indicates that the interface has stopped sending, 296but may be caused by transient congestion. 297.It Bq Er EHOSTUNREACH 298The remote host was unreachable. 299.It Bq Er ENOTCONN 300On a one-to-one style socket no association exists. 301.It Bq Er ECONNRESET 302An abort was received by the stack while the user was 303attempting to send data to the peer. 304.It Bq Er ENOENT 305On a one-to-many style socket no address is specified 306so that the association cannot be located or the 307.Dv SCTP_ABORT 308flag was specified on a non-existing association. 309.It Bq Er EPIPE 310The socket is unable to send anymore data 311.Dv ( SBS_CANTSENDMORE 312has been set on the socket). 313This typically means that the socket 314is not connected and is a one-to-one style socket. 315.El 316.Sh SEE ALSO 317.Xr connect 2 , 318.Xr getsockopt 2 , 319.Xr recv 2 , 320.Xr select 2 , 321.Xr socket 2 , 322.Xr write 2 , 323.Xr sctp_connectx 3 , 324.Xr sendmsg 3 , 325.Xr sctp 4 326.Sh BUGS 327Because in the one-to-many style socket 328.Fn sctp_sendmsg 329or 330.Fn sctp_sendmsgx 331may have multiple associations under one endpoint, a 332select on write will only work for a one-to-one style 333socket. 334