1.\" $OpenBSD: send.2,v 1.30 2014/04/07 10:04:17 mpi Exp $ 2.\" $NetBSD: send.2,v 1.6 1996/01/15 01:17:18 thorpej Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)send.2 8.2 (Berkeley) 2/21/94 32.\" 33.Dd $Mdocdate: April 7 2014 $ 34.Dt SEND 2 35.Os 36.Sh NAME 37.Nm send , 38.Nm sendto , 39.Nm sendmsg 40.Nd send a message from a socket 41.Sh SYNOPSIS 42.Fd #include <sys/types.h> 43.Fd #include <sys/socket.h> 44.Ft ssize_t 45.Fn send "int s" "const void *msg" "size_t len" "int flags" 46.Ft ssize_t 47.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen" 48.Ft ssize_t 49.Fn sendmsg "int s" "const struct msghdr *msg" "int flags" 50.Sh DESCRIPTION 51.Fn send , 52.Fn sendto , 53and 54.Fn sendmsg 55are used to transmit a message to another socket. 56.Fn send 57may be used only when the socket is in a 58.Em connected 59state, while 60.Fn sendto 61and 62.Fn sendmsg 63may be used at any time. 64.Pp 65The address of the target is given by 66.Fa to 67with 68.Fa tolen 69specifying its size. 70The length of the message is given by 71.Fa len . 72If the message is too long to pass atomically through the 73underlying protocol, the error 74.Er EMSGSIZE 75is returned, and 76the message is not transmitted. 77.Pp 78No indication of failure to deliver is implicit in a 79.Fn send . 80Locally detected errors are indicated by a return value of \-1. 81.Pp 82If no messages space is available at the socket to hold 83the message to be transmitted, then 84.Fn send 85normally blocks, unless the socket has been placed in 86non-blocking I/O mode. 87The 88.Xr select 2 89or 90.Xr poll 2 91system calls may be used to determine when it is possible to 92send more data. 93.Pp 94The 95.Fa flags 96parameter may include one or more of the following: 97.Pp 98.Bl -tag -width "MSG_DONTROUTEXX" -offset indent -compact 99.It Dv MSG_OOB 100process out-of-band data 101.It Dv MSG_DONTROUTE 102bypass routing tables, silently ignored 103.It Dv MSG_NOSIGNAL 104don't send 105.Dv SIGPIPE 106.It Dv MSG_DONTWAIT 107don't block 108.El 109.Pp 110The flag 111.Dv MSG_OOB 112is used to send 113.Dq out-of-band 114data on sockets that support this notion (e.g., 115.Dv SOCK_STREAM ) ; 116the underlying protocol must also support 117.Dq out-of-band 118data. 119.Dv MSG_NOSIGNAL 120is used to request not to send the 121.Dv SIGPIPE 122signal if an attempt to send is made on a socket that is shut down for 123writing or no longer connected. 124.Pp 125See 126.Xr recv 2 127for a description of the 128.Fa msghdr 129structure. 130.Sh RETURN VALUES 131The call returns the number of characters sent, or \-1 132if an error occurred. 133.Sh ERRORS 134.Fn send , 135.Fn sendto , 136and 137.Fn sendmsg 138fail if: 139.Bl -tag -width Er 140.It Bq Er EBADF 141An invalid descriptor was specified. 142.It Bq Er ENOTSOCK 143The argument 144.Fa s 145is not a socket. 146.It Bq Er EFAULT 147An invalid user space address was specified for a parameter. 148.It Bq Er EMSGSIZE 149The socket requires that message be sent atomically, 150and the size of the message to be sent made this impossible. 151.It Bq Er EAGAIN 152The socket is marked non-blocking and the requested operation 153would block. 154.It Bq Er ENOBUFS 155The system was unable to allocate an internal buffer. 156The operation may succeed when buffers become available. 157.It Bq Er ENOBUFS 158The output queue for a network interface was full. 159This generally indicates that the interface has stopped sending, 160but may be caused by transient congestion. 161.It Bq Er EACCES 162The 163.Dv SO_BROADCAST 164option is not set on the socket, and a broadcast address 165was given as the destination. 166.It Bq Er EHOSTUNREACH 167The destination address specified an unreachable host. 168.It Bq Er EINVAL 169The 170.Fa flags 171parameter is invalid. 172.It Bq Er EHOSTDOWN 173The destination address specified a host that is down. 174.It Bq Er ENETDOWN 175The destination address specified a network that is down. 176.It Bq Er ECONNREFUSED 177The destination host rejected the message (or a previous one). 178This error can only be returned by connected sockets. 179.It Bq Er ENOPROTOOPT 180There was a problem sending the message. 181This error can only be returned by connected sockets. 182.It Bq Er EDESTADDRREQ 183The socket is not connected, and no destination address was specified. 184.It Bq Er EISCONN 185The socket is already connected, and a destination address was specified. 186.It Bq Er EPIPE 187The socket is shut down for writing or not longer connected and the 188.Dv MSG_NOSIGNAL 189flag is set. 190.El 191.Pp 192In addition, 193.Fn send 194and 195.Fn sendto 196may return the following error: 197.Bl -tag -width Er 198.It Bq Er EINVAL 199.Fa len 200was larger than 201.Dv SSIZE_MAX . 202.El 203.Pp 204Also, 205.Fn sendmsg 206may return the following errors: 207.Bl -tag -width Er 208.It Bq Er EINVAL 209The sum of the 210.Fa iov_len 211values in the 212.Fa msg_iov 213array overflowed an 214.Em ssize_t . 215.It Bq Er EMSGSIZE 216The 217.Fa msg_iovlen 218member of 219.Fa msg 220was less than 0 or larger than 221.Dv IOV_MAX . 222.It Bq Er EAFNOSUPPORT 223Addresses in the specified address family cannot be used with this socket. 224.It Bq Er EMFILE 225The message contains control information utilizing 226.Xr CMSG_DATA 3 227to pass file descriptors, but too many file descriptors 228are already in-flight. 229.El 230.Sh SEE ALSO 231.Xr fcntl 2 , 232.Xr getsockopt 2 , 233.Xr poll 2 , 234.Xr recv 2 , 235.Xr select 2 , 236.Xr socket 2 , 237.Xr write 2 , 238.Xr CMSG_DATA 3 239.Sh HISTORY 240The 241.Fn send 242function call appeared in 243.Bx 4.2 . 244