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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd December 15, 2006 29.Dt SCTP_SENDMSG 3 30.Os 31.Sh NAME 32.Nm sctp_sendmsg , 33.Nm sctp_sendmsgx 34.Nd send a message from an SCTP socket 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In sys/types.h 39.In sys/socket.h 40.In netinet/sctp.h 41.Ft ssize_t 42.Fo sctp_sendmsg 43.Fa "int s" "const void *msg" "size_t len" "const struct sockaddr *to" 44.Fa "socklen_t tolen" "uint32_t ppid" "uint32_t flags" "uint16_t stream_no" 45.Fa "uint32_t timetolive" "uint32_t context" 46.Fc 47.Ft ssize_t 48.Fo sctp_sendmsgx 49.Fa "int s" "const void *msg" "size_t len" "const struct sockaddr *to" 50.Fa "int addrcnt" "uint32_t ppid" "uint32_t flags" "uint16_t stream_no" 51.Fa "uint32_t timetolive" "uint32_t context" 52.Fc 53.Sh DESCRIPTION 54The 55.Fn sctp_sendmsg 56system call 57is used to transmit a message to another SCTP endpoint. 58The 59.Fn sctp_sendmsg 60may be used at any time. 61If the socket is a one-to-many type (SOCK_SEQPACKET) 62socket then an attempt to send to an address that no association exists to will 63implicitly create a new association. 64Data sent in such an instance will result in 65the data being sent on the third leg of the SCTP four-way handshake. 66Note that if 67the socket is a one-to-one type (SOCK_STREAM) socket then an association must 68be in existence (by use of the 69.Xr connect 2 70system call). 71Calling 72.Fn sctp_sendmsg 73or 74.Fn sctp_sendmsgx 75on a non-connected one-to-one socket will result in 76.Va errno 77being set to 78.Er ENOTCONN , 79-1 being returned, and the message not being transmitted. 80.Pp 81The address of the target is given by 82.Fa to 83with 84.Fa tolen 85specifying its size. 86The length of the message 87.Fa msg 88is given by 89.Fa len . 90If the message is too long to pass atomically through the 91underlying protocol, 92.Va errno 93is set to 94.Er EMSGSIZE , 95-1 is returned, and 96the message is not transmitted. 97.Pp 98No indication of failure to deliver is implicit in a 99.Xr sctp_sendmsg 3 100call. 101Locally detected errors are indicated by a return value of -1. 102.Pp 103If no space is available at the socket to hold 104the message to be transmitted, then 105.Xr sctp_sendmsg 3 106normally blocks, unless the socket has been placed in 107non-blocking I/O mode. 108The 109.Xr select 2 110system call may be used to determine when it is possible to 111send more data on one-to-one type (SOCK_STREAM) sockets. 112.Pp 113The 114.Fa ppid 115argument is an opaque 32 bit value that is passed transparently 116through the stack to the peer endpoint. 117It will be available on 118reception of a message (see 119.Xr sctp_recvmsg 3 ) . 120Note that the stack passes this value without regard to byte 121order. 122.Pp 123The 124.Fa flags 125argument may include one or more of the following: 126.Bd -literal 127#define SCTP_EOF 0x0100 /* Start a shutdown procedures */ 128#define SCTP_ABORT 0x0200 /* Send an ABORT to peer */ 129#define SCTP_UNORDERED 0x0400 /* Message is un-ordered */ 130#define SCTP_ADDR_OVER 0x0800 /* Override the primary-address */ 131#define SCTP_SENDALL 0x1000 /* Send this on all associations */ 132 /* for the endpoint */ 133/* The lower byte is an enumeration of PR-SCTP policies */ 134#define SCTP_PR_SCTP_TTL 0x0001 /* Time based PR-SCTP */ 135#define SCTP_PR_SCTP_BUF 0x0002 /* Buffer based PR-SCTP */ 136#define SCTP_PR_SCTP_RTX 0x0003 /* Number of retransmissions based PR-SCTP */ 137.Ed 138.Pp 139The flag 140.Dv SCTP_EOF 141is used to instruct the SCTP stack to queue this message 142and then start a graceful shutdown of the association. 143All 144remaining data in queue will be sent after which the association 145will be shut down. 146.Pp 147.Dv SCTP_ABORT 148is used to immediately terminate an association. 149An abort 150is sent to the peer and the local TCB is destroyed. 151.Pp 152.Dv SCTP_UNORDERED 153is used to specify that the message being sent has no 154specific order and should be delivered to the peer application 155as soon as possible. 156When this flag is absent messages 157are delivered in order within the stream they are sent, but without 158respect to order to peer streams. 159.Pp 160The flag 161.Dv SCTP_ADDR_OVER 162is used to specify that an specific address should be used. 163Normally 164SCTP will use only one of a multi-homed peers addresses as the primary 165address to send to. 166By default, no matter what the 167.Fa to 168argument is, this primary address is used to send data. 169By specifying 170this flag, the user is asking the stack to ignore the primary address 171and instead use the specified address not only as a lookup mechanism 172to find the association but also as the actual address to send to. 173.Pp 174For a one-to-many type (SOCK_SEQPACKET) socket the flag 175.Dv SCTP_SENDALL 176can be used as a convenient way to make one send call and have 177all associations that are under the socket get a copy of the message. 178Note that this mechanism is quite efficient and makes only one actual 179copy of the data which is shared by all the associations for sending. 180.Pp 181The remaining flags are used for the partial reliability extension (RFC3758) 182and will only be effective if the peer endpoint supports this extension. 183This option specifies what local policy the local endpoint should use 184in skipping data. 185If none of these options are set, then data is 186never skipped over. 187.Pp 188.Dv SCTP_PR_SCTP_TTL 189is used to indicate that a time based lifetime is being applied 190to the data. 191The 192.Fa timetolive 193argument is then a number of milliseconds for which the data is 194attempted to be transmitted. 195If that many milliseconds elapse 196and the peer has not acknowledged the data, the data will be 197skipped and no longer transmitted. 198Note that this policy does 199not even assure that the data will ever be sent. 200In times of a congestion 201with large amounts of data being queued, the 202.Fa timetolive 203may expire before the first transmission is ever made. 204.Pp 205The 206.Dv SCTP_PR_SCTP_BUF 207based policy transforms the 208.Fa timetolive 209field into a total number of bytes allowed on the outbound 210send queue. 211If that number or more bytes are in queue, then 212other buffer based sends are looked to be removed and 213skipped. 214Note that this policy may also result in the data 215never being sent if no buffer based sends are in queue and 216the maximum specified by 217.Fa timetolive 218bytes is in queue. 219.Pp 220The 221.Dv SCTP_PR_SCTP_RTX 222policy transforms the 223.Fa timetolive 224into a number of retransmissions to allow. 225This policy 226always assures that at a minimum one send attempt is 227made of the data. 228After which no more than 229.Fa timetolive 230retransmissions will be made before the data is skipped. 231.Pp 232.Fa stream_no 233is the SCTP stream that you wish to send the 234message on. 235Streams in SCTP are reliable (or partially reliable) flows of ordered 236messages. 237The 238.Fa context 239field is used only in the event the message cannot be sent. 240This is an opaque 241value that the stack retains and will give to the user when a failed send 242is given if that notification is enabled (see 243.Xr sctp 4 ) . 244Normally a user process can use this value to index some application 245specific data structure when a send cannot be fulfilled. 246.Fn sctp_sendmsgx 247is identical to 248.Fn sctp_sendmsg 249with the exception that it takes an array of sockaddr structures in the 250argument 251.Fa to 252and adds the additional argument 253.Fa addrcnt 254which specifies how many addresses are in the array. 255This allows a 256caller to implicitly set up an association passing multiple addresses 257as if 258.Fn sctp_connectx 259had been called to set up the association. 260.Sh RETURN VALUES 261The call returns the number of characters sent, or -1 262if an error occurred. 263.Sh ERRORS 264The 265.Fn sctp_sendmsg 266system call 267fails if: 268.Bl -tag -width Er 269.It Bq Er EBADF 270An invalid descriptor was specified. 271.It Bq Er ENOTSOCK 272The argument 273.Fa s 274is not a socket. 275.It Bq Er EFAULT 276An invalid user space address was specified for an argument. 277.It Bq Er EMSGSIZE 278The socket requires that message be sent atomically, 279and the size of the message to be sent made this impossible. 280.It Bq Er EAGAIN 281The socket is marked non-blocking and the requested operation 282would block. 283.It Bq Er ENOBUFS 284The system was unable to allocate an internal buffer. 285The operation may succeed when buffers become available. 286.It Bq Er ENOBUFS 287The output queue for a network interface was full. 288This generally indicates that the interface has stopped sending, 289but may be caused by transient congestion. 290.It Bq Er EHOSTUNREACH 291The remote host was unreachable. 292.It Bq Er ENOTCONN 293On a one-to-one style socket no association exists. 294.It Bq Er ECONNRESET 295An abort was received by the stack while the user was 296attempting to send data to the peer. 297.It Bq Er ENOENT 298On a one-to-many style socket no address is specified 299so that the association cannot be located or the 300.Dv SCTP_ABORT 301flag was specified on a non-existing association. 302.It Bq Er EPIPE 303The socket is unable to send anymore data 304.Dv ( SBS_CANTSENDMORE 305has been set on the socket). 306This typically means that the socket 307is not connected and is a one-to-one style socket. 308.El 309.Sh SEE ALSO 310.Xr connect 2 , 311.Xr getsockopt 2 , 312.Xr recv 2 , 313.Xr select 2 , 314.Xr sendmsg 2 , 315.Xr socket 2 , 316.Xr write 2 , 317.Xr sctp_connectx 3 , 318.Xr sctp 4 319.Sh BUGS 320Because in the one-to-many style socket 321.Fn sctp_sendmsg 322or 323.Fn sctp_sendmsgx 324may have multiple associations under one endpoint, a 325select on write will only work for a one-to-one style 326socket. 327