1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. 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.Fo sctp_recvmsg 48.Fa "int s" "void *msg" "size_t len" "struct sockaddr * restrict from" 49.Fa "socklen_t * restrict fromlen" "struct sctp_sndrcvinfo *sinfo" "int *flags" 50.Fc 51.Sh DESCRIPTION 52The 53.Fn sctp_recvmsg 54system call 55is used to receive a message from another SCTP endpoint. 56The 57.Fn sctp_recvmsg 58call is used by one-to-one (SOCK_STREAM) type sockets after a 59successful 60.Fn connect 61call or after the application has performed a 62.Fn listen 63followed by a sucessful 64.Fn accept 65For a one-to-many (SOCK_SEQPACKET) type socket, an endpoint may call 66.Fn sctp_recvmsg 67after having implicitly started an association via one 68of the send calls including 69.Fn sctp_sendmsg 70.Fn sendto 71and 72.Fn sendmsg . 73Or, an application may also receive a message after having 74called 75.Fn listen 76with a postive backlog to enable the reception of new associations. 77.Pp 78The address of the sender is held in the 79.Fa from 80argument with 81.Fa fromlen 82specifying its size. 83At the completion of a successful 84.Fn sctp_recvmsg 85call 86.Fa from 87will hold the address of the peer and 88.Fa fromlen 89will hold the length of that address. 90Note that 91the address is bounded by the inital value of 92.Fa fromlen 93which is used as an in/out variable. 94.Pp 95The length of the message 96.Fa msg 97to be received is bounded by 98.Fa len . 99If the message is too long to fit in the users 100receive buffer, then the 101.Fa flags 102argument will NOT have the 103.Dv MSG_EOF 104flag applied. 105If the message is a complete message then 106the 107.Fa flags 108argument will have 109.Dv MSG_EOF 110set. 111Locally detected errors are 112indicated by a return value of -1 with 113.Va errno 114set accordingly. 115The 116.Fa flags 117argument may also hold the value 118.Dv MSG_NOTIFICATION . 119When this 120occurs this indicates that the message received is NOT from 121the peer endpoint, but instead is a notification from the 122SCTP stack (see 123.Xr sctp 4 124for more details). 125Note that no notifications are ever 126given unless the user subscribes to such notifications using 127the 128.Dv SCTP_EVENTS 129socket option. 130.Pp 131If no messages are available at the socket then 132.Fn sctp_recvmsg 133normally blocks on the reception of a message or NOTIFICATION, unless the 134socket has been placed in non-blocking I/O mode. 135The 136.Xr select 2 137system call may be used to determine when it is possible to 138receive a message. 139.Pp 140The 141.Fa sinfo 142argument is defined as follows. 143.Bd -literal 144struct sctp_sndrcvinfo { 145 u_int16_t sinfo_stream; /* Stream arriving on */ 146 u_int16_t sinfo_ssn; /* Stream Sequence Number */ 147 u_int16_t sinfo_flags; /* Flags on the incoming message */ 148 u_int32_t sinfo_ppid; /* The ppid field */ 149 u_int32_t sinfo_context; /* context field */ 150 u_int32_t sinfo_timetolive; /* not used by sctp_recvmsg */ 151 u_int32_t sinfo_tsn; /* The transport sequence number */ 152 u_int32_t sinfo_cumtsn; /* The cumulative acknowledgment point */ 153 sctp_assoc_t sinfo_assoc_id; /* The association id of the peer */ 154}; 155.Ed 156.Pp 157The 158.Fa sinfo->sinfo_ppid 159is an opaque 32 bit value that is passed transparently 160through the stack from the peer endpoint. 161Note that the stack passes this value without regard to byte 162order. 163.Pp 164The 165.Fa sinfo->sinfo_flags 166field may include the following: 167.Bd -literal 168#define SCTP_UNORDERED 0x0400 /* Message is un-ordered */ 169.Ed 170.Pp 171The 172.Dv SCTP_UNORDERED 173flag is used to specify that the message arrived with no 174specific order and was delivered to the peer application 175as soon as possible. 176When this flag is absent the message 177was delivered in order within the stream it was received. 178.Pp 179.Fa sinfo->sinfo_stream 180is the SCTP stream that the message was received on. 181Streams in SCTP are reliable (or partially reliable) flows of ordered 182messages. 183.Pp 184The 185.Fa sinfo->sinfo_context 186field is used only if the local application set an association level 187context with the 188.Dv SCTP_CONTEXT 189socket option. 190Optionally a user process can use this value to index some application 191specific data structure for all data coming from a specific 192association. 193.Pp 194The 195.Fa sinfo->sinfo_ssn 196will hold the stream sequence number assigned 197by the peer endpoint if the message is NOT unordered. 198For unordered messages this field holds an undefined value. 199.Pp 200The 201.Fa sinfo->sinfo_tsn 202holds a transport sequence number (TSN) that was assigned 203to this message by the peer endpoint. 204For messages that fit in or less 205than the path MTU this will be the only TSN assigned. 206Note that for messages that span multiple TSN's this 207value will be one of the TSN's that was used on the 208message. 209.Pp 210The 211.Fa sinfo->sinfo_cumtsn 212holds the current cumulative acknowledgment point of 213the transport association. 214Note that this may be larger 215or smaller than the TSN assigned to the message itself. 216.Pp 217The 218.Fa sinfo->sinfo_assoc_id 219is the unique association identification that was assigned 220to the association. 221For one-to-many (SOCK_SEQPACKET) type 222sockets this value can be used to send data to the peer without 223the use of an address field. 224It is also quite useful in 225setting various socket options on the specific association 226(see 227.Xr sctp 4 228). 229.Pp 230The 231.Fa sinfo->info_timetolive 232field is not used by 233.Fa sctp_recvmsg . 234.Sh RETURN VALUES 235The call returns the number of characters sent, or -1 236if an error occurred. 237.Sh ERRORS 238The 239.Fn sctp_recvmsg 240system call 241fails if: 242.Bl -tag -width Er 243.It Bq Er EBADF 244An invalid descriptor was specified. 245.It Bq Er ENOTSOCK 246The argument 247.Fa s 248is not a socket. 249.It Bq Er EFAULT 250An invalid user space address was specified for an argument. 251.It Bq Er EMSGSIZE 252The socket requires that message be sent atomically, 253and the size of the message to be sent made this impossible. 254.It Bq Er EAGAIN 255The socket is marked non-blocking and the requested operation 256would block. 257.It Bq Er ENOBUFS 258The system was unable to allocate an internal buffer. 259The operation may succeed when buffers become available. 260.It Bq Er ENOBUFS 261The output queue for a network interface was full. 262This generally indicates that the interface has stopped sending, 263but may be caused by transient congestion. 264.It Bq Er EHOSTUNREACH 265The remote host was unreachable. 266.It Bq Er ENOTCON 267On a one-to-one style socket no association exists. 268.It Bq Er ECONNRESET 269An abort was received by the stack while the user was 270attempting to send data to the peer. 271.It Bq Er ENOENT 272On a one to many style socket no address is specified 273so that the association cannot be located or the 274SCTP_ABORT flag was specified on a non-existing association. 275.It Bq Er EPIPE 276The socket is unable to send anymore data 277.Dv ( SBS_CANTSENDMORE 278has been set on the socket). 279This typically means that the socket 280is not connected and is a one-to-one style socket. 281.El 282.Sh SEE ALSO 283.Xr recv 2 , 284.Xr select 2 , 285.Xr socket 2 , 286.Xr write 2 , 287.Xr getsockopt 2 , 288.Xr setsockopt 2 , 289.Xr sctp_send 3 , 290.Xr sctp_sendmsg 3 , 291.Xr sendmsg 3 , 292.Xr sctp 4 293