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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.\" $FreeBSD$ 33.\" 34.Dd December 15, 2006 35.Dt SCTP_RECVMSG 3 36.Os 37.Sh NAME 38.Nm sctp_recvmsg 39.Nd send a message from an SCTP socket 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In sys/types.h 44.In sys/socket.h 45.In netinet/sctp.h 46.Ft ssize_t 47.Ft ssize_t 48.Fn sctp_recvmsg "int s" "void *msg" "size_t len" "struct sockaddr * restrict from" "socklen_t * restrict fromlen" "struct sctp_sndrcvinfo *sinfo" "int *flags" 49.Sh DESCRIPTION 50The 51.Fn sctp_recvmsg 52system calls 53is used to receive a message from another SCTP endpoint. 54The 55.Fn sctp_recvmsg 56call is used by one-to-one (SOCK_STREAM) type sockets after a 57sucessful 58.Fn connect 2 59call or after the application has performed a 60.Fn listen 61followed by a sucessful 62.Fn accept 2 63For a one-to-many (SOCK_SEQPACKET)type socket, an endpoint may call 64.Fn sctp_recvmsg 65after having implicitly started an association via one 66of the send calls including 67.Fn sctp_sendmsg 2 68.Fn sendto 2 69and 70.Fn sendmsg 2 71Or, an application may also receive a message after having 72called 73.Fn listen 2 74with a postive backlog to enable the reception of new associations. 75.Pp 76.Pp 77The address of the sender is held in the 78.Fa from 79argument with 80.Fa fromlen 81specifying its size. At the completion of a sucessful 82.Fn sctp_recvmsg 83call 84.Fa from 85will hold the address of the peer and 86.Fa fromlen 87will hold the length of that address. Note that 88the address is bounded by the inital value of 89.Fa fromlen 90which is used as an in/out variable. 91.Pp 92The length of the message 93.Fa msg 94to be received is bounded by 95.Fa len . 96If the message is to long to fit in the users 97receive buffer, then the 98.Fa flags 99argument will NOT have the MSG_EOF flag 100applied. If the message is a complete message then 101the 102.Fa flags 103argument will have MSG_EOF set. Locally detected errors are 104indicated by a return value of -1 with errno set accordingly. 105The 106.Fa flags 107argument may also hold the value MSG_NOTIFICATION. When this 108occurs this indicates that the message received is NOT from 109the peer endpoint, but instead is a notification from the 110SCTP stack (see 111.Fn sctp 4 112for more details). Note that no notifications are ever 113given unless the user subscribes to such notifications using 114the SCTP_EVENTS socket option. 115.Pp 116If no messages is available at the socket then 117.Fn sctp_recvmsg 118normally blocks on the reception of a message or NOTIFICATION, unless the socket has been placed in 119non-blocking I/O mode. 120The 121.Xr select 2 122system call may be used to determine when it is possible to 123receive a message. 124.Pp 125 126The 127.Fa sinfo 128argument is defined as follows. 129.Bd -literal 130struct sctp_sndrcvinfo { 131 u_int16_t sinfo_stream; /* Stream arriving on */ 132 u_int16_t sinfo_ssn; /* Stream Sequence Number */ 133 u_int16_t sinfo_flags; /* Flags on the incoming message */ 134 u_int32_t sinfo_ppid; /* The ppid field */ 135 u_int32_t sinfo_context; /* context field */ 136 u_int32_t sinfo_timetolive; /* not used by sctp_recvmsg */ 137 u_int32_t sinfo_tsn; /* The transport sequence number */ 138 u_int32_t sinfo_cumtsn; /* The cumulative acknowledgment point */ 139 sctp_assoc_t sinfo_assoc_id; /* The association id of the peer */ 140}; 141.Ed 142 143The 144.Fa sinfo->sinfo_ppid 145is an opaque 32 bit value that is passed transparently 146through the stack from the peer endpoint. 147Note that the stack passes this value without regard to byte 148order. 149.Pp 150The 151.Fa sinfo->sinfo_flags 152field may include the following: 153.Bd -literal 154#define SCTP_UNORDERED 0x0400 /* Message is un-ordered */ 155.Ed 156.Pp 157The 158.Dv SCTP_UNORDERED 159flag is used to specify that the message arrived with no 160specific order and was delivered to the peer application 161as soon as possible. When this flag is absent the message 162was delivered in order within the stream it was received. 163.Pp 164.Fa sinfo->sinfo_stream 165is the SCTP stream that the message was received on. 166Streams in SCTP are reliable (or partially reliable) flows of ordered 167messages. 168.Pp 169 The 170.Fa sinfo->sinfo_context 171field is used only if the local application set a association level 172context with the SCTP_CONTEXT socket option. 173Optionally a user process can use this value to index some application 174specific data structure for all data coming from a specific 175association. 176.Pp 177The 178.Fa sinfo->sinfo_ssn 179will hold the stream sequence number assigned 180by the peer endpoint if the message is NOT unordered. 181For unordered messages this field holds an undefined value. 182.Pp 183The 184.Fa sinfo->sinfo_tsn 185holds a transport sequence number (TSN) that was assigned 186to this message by the peer endpoint. For messages that fit in or less 187than the path MTU this will be the only TSN assigned. 188Note that for messages that span multiple TSN's this 189value will be one of the TSN's that was used on the 190message. 191.Pp 192The 193.Fa sinfo->sinfo_cumtsn 194holds the current cumulative acknowledgment point of 195the transport association. Note that this may be larger 196or smaller than the TSN assigned to the message itself. 197.Pp 198The 199sinfo->sinfo_assoc_id 200is the unique association identification that was assigned 201to the association. For one-to-many (SOCK_SEQPACKET) type 202sockets this value can be used to send data to the peer without 203the use of an address field. It is also quite useful in 204setting various socket options on the specific association 205(see 206.Fn sctp 4 207). 208.Pp 209The 210sinfo->info_timetolive 211field is not used by 212.Fa sctp_recvmsg . 213.Sh RETURN VALUES 214The call returns the number of characters sent, or -1 215if an error occurred. 216.Sh ERRORS 217The 218.Fn sctp_recvmsg 219system call 220fail if: 221.Bl -tag -width Er 222.It Bq Er EBADF 223An invalid descriptor was specified. 224.It Bq Er ENOTSOCK 225The argument 226.Fa s 227is not a socket. 228.It Bq Er EFAULT 229An invalid user space address was specified for an argument. 230.It Bq Er EMSGSIZE 231The socket requires that message be sent atomically, 232and the size of the message to be sent made this impossible. 233.It Bq Er EAGAIN 234The socket is marked non-blocking and the requested operation 235would block. 236.It Bq Er ENOBUFS 237The system was unable to allocate an internal buffer. 238The operation may succeed when buffers become available. 239.It Bq Er ENOBUFS 240The output queue for a network interface was full. 241This generally indicates that the interface has stopped sending, 242but may be caused by transient congestion. 243.It Bq Er EHOSTUNREACH 244The remote host was unreachable. 245.It Bq Er ENOTCON 246On a one to one style socket no association exists. 247.It Bq Er ECONNRESET 248An abort was received by the stack while the user was 249attempting to send data to the peer. 250.It Bq Er ENOENT 251On a one to many style socket no address is specified 252so that the association cannot be located or the 253SCTP_ABORT flag was specified on a non-existing association. 254.It Bq Er EPIPE 255The socket is unable to send anymore data 256.Dv ( SBS_CANTSENDMORE 257has been set on the socket). 258This typically means that the socket 259is not connected and is a one-to-one style socket. 260.El 261.Sh SEE ALSO 262.Xr sctp 4 , 263.Xr sendmsg 3 , 264.Xr sctp_sendmsg 3 , 265.Xr sctp_send 3 , 266.Xr getsockopt 2 , 267.Xr setsockopt 2 , 268.Xr recv 2 , 269.Xr select 2 , 270.Xr socket 2 , 271.Xr write 2 272 273